SS-OCT Base Unit
Swept Source OCT Systems:
VEGA series
User Manual
Original User Manual – not translated
Table of Contents
Chapter 1 Introduction ............................................................................................................... 1
1.1. Safety ..................................................................................................................... 2
1.2. Care and Maintenance .......................................................................................... 3
Optical Cleaning .......................................................................................................... 4
Fiber Cleaning Techniques Using the FBC1 ............................................................... 4
Service ........................................................................................................................ 5
Accessories and Customization .................................................................................. 5
Chapter 2 Setup .......................................................................................................................... 6
2.1. Unpacking ............................................................................................................. 6
2.2. System Connections ............................................................................................ 6
Base Unit Connections ................................................................................................ 6
Internal Electrical Connections.................................................................................... 7
Electrical Interfaces to Probe ...................................................................................... 7
2.3. Optical Interface to Probe .................................................................................... 7
2.4. System Installation ............................................................................................... 8
Chapter 3 Description .............................................................................................................. 15
3.1. Tutorial ................................................................................................................ 15
Theory ....................................................................................................................... 16
Thorlabs SS-OCT System Technology ..................................................................... 17
Nomenclature in OCT imaging .................................................................................. 19
3.2. SS-OCT Base Unit Components ........................................................................ 21
Base Unit ................................................................................................................... 21
PC with Graphical User Interface .............................................................................. 21
SDK ........................................................................................................................... 21
Imaging Scanner (Accessory) ................................................................................... 23
OCT-Stand (Accessory) ............................................................................................ 25
Chapter 4 System Operation ................................................................................................... 27
4.1. Starting the System ............................................................................................ 27
Turning ON the Imaging Module ............................................................................... 27
Turning ON the Laser Module ................................................................................... 27
Starting the Software ................................................................................................. 28
4.2. Basic Adjustments ............................................................................................. 28
Adjusting the Focus ................................................................................................... 28
Adjusting the Reference Length ................................................................................ 29
Adjusting the Polarization .......................................................................................... 30
4.3. Advanced Adjustments ...................................................................................... 31
Focus and Choice of Objective Lens ........................................................................ 31
Imaging through Refractive Media ............................................................................ 32
Reflecting Surfaces and Interfaces ........................................................................... 33
Rough Surfaces ........................................................................................................ 33
4.4. Shutting Down the System ................................................................................ 33
4.5. Example Images.................................................................................................. 34
Chapter 5 Imaging Artifacts ..................................................................................................... 36
5.1. Saturation and Non-Linearity ............................................................................. 36
5.2. Multiple Scattering .............................................................................................. 37
5.3. Phase Wrapping and Fringe Washout ............................................................... 39
5.4. Flipped Image ..................................................................................................... 40
5.5. Shadowing .......................................................................................................... 41
5.6. Image Distortion by Refractive Media ............................................................... 42
The Group Refraction Index ...................................................................................... 43
Measurement Depth in OCT Systems ...................................................................... 44
Distortions in the Image ............................................................................................ 45
Chapter 6 Troubleshooting ...................................................................................................... 47
6.1. Changing the Input Fuses .................................................................................. 48
Chapter 7 Certifications and Compliance .............................................................................. 49
7.1. Declaration of Conformity Vega Series Base Units .......................................... 49
Chapter 8 Warranty ................................................................................................................... 51
8.1. Lasers and Imaging Systems............................................................................. 51
8.2. Non-Warranty Repairs ........................................................................................ 51
8.3. Warranty Exclusions .......................................................................................... 51
Chapter 9 Specifications .......................................................................................................... 52
Chapter 10 Mechanical Drawings ............................................................................................. 53
Chapter 11 Regulatory ............................................................................................................... 54
11.1. Waste Treatment is Your Own Responsibility .................................................. 54
11.2. Ecological Background ...................................................................................... 54
Chapter 12 Thorlabs Worldwide Contacts ............................................................................... 55
SD-OCT Base Unit Chapter 1: Introduction
Rev A, March 3, 2017 Page 1
Chapter 1 Introduction
ATTENTION
Please read the instruction manual carefully before operating the SS-OCT system. All
statements regarding safety and technical specifications will only apply when the unit is
operated correctly.
This equipment is intended for laboratory use only and is not certified for medical applications,
including but not limited to life support situations.
Refer to this manual whenever the following symbols are encountered on the SS-OCT system:
Attention symbol indicates that additional information is given in this manual.
Laser Safety symbol indicates that laser radiation is present.
ATTENTION
Check the supply voltage of the system before plugging in the computer. Make sure the
included power cords for the base unit, computer, and monitor are connected to a properly
grounded outlet (100 – 240 VAC; 50 – 60 Hz).
Transportation and delivery may cause the SS-OCT system to be warm or cool upon receipt.
Please wait for the system to reach room temperature before attempting to operate.
Operate this system on a flat, dry, and stable surface only.
WARRANTY WARNING
Do not open the base unit, imaging scanner or PC. There are no user serviceable parts in this
product. Opening the device will void your warranty. Any modification or servicing of this
system by unqualified personnel renders Thorlabs free of any liability. This device can only be
returned when packed into the complete original packaging, including all foam packing inserts.
If necessary, ask for replacement packaging.
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1.1. Safety
SHOCK WARNING – HIGH VOLTAGE
Before applying power to the system, make sure that the protective conductor of the three-
conductor mains power cord is correctly connected to the protective earth contact of the socket
outlet. Improper grounding can cause electrical shock resulting in severe injury or even death.
Make sure that the line voltage rating agrees with your local supply and that the appropriate
fuses are installed. Fuses should only be changed by qualified service personnel. Contact
Thorlabs for assistance. Do not operate without cover installed. Refer servicing to qualified
personnel.
ATTENTION
Do not obstruct the air-ventilation slots in the computer housing. Do not obstruct air-ventilation
into the bottom of the base unit or out of the exhaust fan on the rear of the unit.
Mobile telephones, cellular phones, or other radio transmitters are not to be used within the
range of three meters of this unit, since the electromagnetic field intensity may exceed the
maximum allowed disturbance values according to IEC 61000-6-1:2005.
The safety of any system incorporating the equipment is the responsibility of the assembler of
the system.
If equipment is used in a manner not specified by the manufacturer, the protection provided by
the equipment may be impaired.
LASER RADIATION WARNING
Laser emission may be emitted
a) from the scan lens of a scanner (intended use)
b) from the back of the base unit when the fiber cap is removed and the fiber disconnected
c) from the output of the fiber when the fiber is not connected to a scanner
Do not look into the optical output when the device is operating. The laser radiation is not
visible to the human eye and can cause serious damage to your eyesight.
The laser class information is also stated on the laser safety labels on the back of the housing.
Example given for class 1M LASER product:
INVISIBLE LASER RADIATION
DO NOT STARE INTO BEAM OR VIEW
DIRECTLY WITH OPTICAL INSTRUMENTS
CLASS 1M LASER PRODUCT
CLASSIFIED ACCORDING TO DIN EN 60825-1:2014
SD-OCT Base Unit Chapter 1: Introduction
Rev A, March 3, 2017 Page 3
1.2. Care and Maintenance
Handle the system with care during transportation and unpacking. Banging or dropping the system can damage
the unit or lower system performance. If the system is mishandled during shipment, the optical components
may become misaligned, which could lead to a decrease in image quality. If this occurs, the system will need
to be realigned by qualified personnel. Please contact Thorlabs technical support for more information.
Do not store or operate in a damp, closed environment.
Do not store or operate on surfaces that are susceptible to vibrations.
Do not expose to direct sunlight.
Do not use solvents on or near the equipment.
Keep away from dust, dirt, and air-borne pollutants (including cigarette smoke). The system is not
designed for outdoor use. Protect the equipment from rain, snow, and humidity.
Do not expose to mechanical and thermal extremes. Protect the equipment from rapid variation in
temperature.
Handle all connectors, both electrical and optical, with care. Do not use unnecessary force, as this may
damage the connectors.
Handle the optical fiber with care. Mechanical stress can decrease performance and potentially destroy
the fiber. Continual bending of the optical fiber can cause damage. It is important, therefore, to keep
the optical fiber patch cable as straight as possible to minimize bending.
Note: The most common cause of low signal intensity is contamination of the fiber due to airborne pollutants.
To minimize exposure, avoid unnecessarily disconnecting the optical fiber patch cable. In addition, it is
advisable to check the fiber before making other adjustments to the optical system, such as changing the focus
or optical path length. Be sure to check the patch cord for a loose connection, and make sure that the fiber is
kept as straight as possible.
All lasers, especially lasers with resonator cavities that are defined by mechanical tolerances, are delicate
precision instruments and must be handled accordingly. The SS-OCT system is designed to withstand normal
transportation and operating conditions. Do not move the system while it is connected and in operation.
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Optical Cleaning
Good performance and image quality of the OCT imaging system relies on clean optical connections. Whenever
using the Thorlabs OCT system, the following guidelines for optical fiber connection should be followed:
1) Always make sure that the light source is switched off when you clean the fiber.
2) Always inspect and clean the fiber end before plugging it into a receptacle.
3) Always cover the fiber end that is not in use with a fiber cap or dust protection cover.
The cleaning procedure sucess could be visualized using a fiber inspection scope
Figure 1 Fiber Inspection Scope FS201
Fiber Cleaning Techniques Using the FBC1
This section details how to clean fiber bulkheads and fiber connectors using the FBC1 one-step cleaner.
Using Extended Mode
Figure 2 FBC1 Extended Mode
To use extended mode, pull the tip outward while simultaneously pushing down on the lock button. Extended
mode is useful for panels with multiple bulkhead connectors or other tight spaces.
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Rev A, March 3, 2017 Page 5
Cleaning Fiber Bulkheads
Figure 3 Cleaning Fiber Bulkheads
Remove the guide cap completely from the device, and insert the tip of the cleaner into the bulkhead connector.
Push the case to start the cleaning process; a click indicates that the cleaning is complete.
Cleaning Fiber Connectors
Figure 4 Cleaning Fiber Connectors
Open the cover on the guide cap, and insert the fiber connector over the guide cap. Push the case to start the
cleaning process; a click indicates that the cleaning is complete.
Service
Only trained and approved Thorlabs personnel are allowed to service the system. Please contact Thorlabs
technical support for more information.
Accessories and Customization
The OCT base unit can easily be adapted for custom interfaces. To achieve the listed specifications however
this system should only be used with the accessories that Thorlabs provides. Any modification or maintenance
by unqualified personnel will render the warranty null and void, leaving Thorlabs free of liability. Please contact
Thorlabs technical support for questions on customization.
SD-OCT Base Unit Chapter 2: Setup
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Chapter 2 Setup
2.1. Unpacking
Carefully unpack the components from the transport boxes. Make sure that all components are delivered
according to the packing list included in the transport box. After unpacking, store the packing cartons and
inserts. You may need them in case of a service or upgrade of your OCT system.
2.2. System Connections
Base Unit Connections
All of the base unit connections are located in the rear (see Figure 5)
Figure 5 Rear View of Base Unit
A. Power Plugs (Laser and Imaging Module)
B. VHDCI Data Port to connect to the NI PCIe-6351
C. Auxiliary Connection Port (LEMO, 14 Pin)
D. Probe Connection Port (LEMO, 19 Pin)
E. SMA Connector for SYNC TRIGGER to Connect to Alazar Tech. ATS9350
F. SMA Connector for OCT SIGNAL to Connect to Alazar Tech. ATS9350
G. Probe Fiber Receptacle (FC/APC)
H. Laser Input Fiber Receptacle (FC/APC)
I. USB Data Port to Connect PC (USB 2.0 Type B Interface)
J. Laser Output Fiber Receptacle (FC/APC)
K. SMA Connector for DAQ k-CLOCK to Connect to Alazar Tech. ATS9350
L. SMA Connectzor for DAQ SWEEP TRIGGER to Connect to Alazar Tech. 9350
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Internal Electrical Connections
The USB connection to the PC is used for the control communication between the Software and Base Unit
(Imaging Module). The acquisition and synchronization of the spectral information is using the SYNC TRIGGER
connection.
Electrical Interfaces to Probe
For the connection to a scanner application there are two different interfaces available:
The probe connection port is intended to be used together with dedicated Thorlabs imaging scanners
OCTG and OCTP.
The auxiliary connection port is intended to be used together with dedicated Thorlabs imaging scanner
OCTH and furthermore allows the use of a custom scanner. It hosts two analogue signals for driving
separate actuators (e.g. Galvanometer scanner), communication lines and supply voltages.
Electrical Probe Connection Interfaces
Probe Connection Port
Lemo ECG.2B.319.CLL
Auxiliary Connection Port
Lemo ECA.1B.314.CLL
Table 1 Electrical Probe Connection Interface
Please contact Thorlabs’ tech support for information regarding the pin configuration.
2.3. Optical Interface to Probe
The base unit incorporates one FC/APC fiber interface depending on the internal fiber architecture. If not
different due to customization the single mode fiber used in the base units is given in Table 2:
Optical Probe Connection Interface
Base Unit Series
Fiber Plug / Receptacle
Single Mode Fiber
Vega
FC/APC
Corning SMF28e+
Table 2 Optical Probe Connection Interface
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2.4. System Installation
ATTENTION
Make sure the included power cords for the base unit, computer and monitor are connected to a
properly grounded outlet (100 – 240 VAC; 50 – 60 Hz).
Transportation and delivery may cause the SD-OCT system to be warm or cool upon receipt.
Please wait for the system to reach room temperature before attempting to operate.
Operate this system on a flat, dry, and stable surface only.
1) Install the PC, monitor, mouse and keyboard according to the documentation provided by the PC
manufacturer.
2) If applicable, assemble the OCT-Stand as described in the documents provided in the OCT-Stand
box.
3) If applicable, mount the scanner in the OCT-Stand by sliding the dove tail at the back of the scanner
into the dove tail slide of the OCT-Stand.
Figure 6 Mounting the Scanner into the Dove Tail Slide of the OCT-Stand
4) Connect the CameraLink cable between the base unit and the PC
5) Attach the USB cable to the base unit and to the PC.
6) Connect the power supply plug to the socket of the base unit and connect the other end to a wall
plug.
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7) Attach the electric connection cable to the imaging scanner.
Align the red dot of the plug to the alignment mark of the electric connection port of the scanner
(e.g.: OCTG).
Figure 7 Plugging the Electric Connector into the Scanner
Push the connector into the plug until you hear a “click” sound.
Figure 8 Electric Connector plugged into the Scanner
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8) Fiber connection to the imaging scanner
ATTENTION
When installing the fiber, make sure that the fiber tip does not get contaminated by dust.
Do not touch the fiber tip!
Remove the dust caps from one fiber end and from the FC/APC fiber connection at the imaging
scanner. Store these with the system packaging.
Figure 9 Fiber Connection to the Imaging Scanner
A) Slide the fiber tip into the center bore of the fiber connection.
B and C) The fiber needs to be oriented in rotation, so that the alignment nose slides into the mating
part of the probe connector as show in Figure 9 C.
NOTE: If the nose slide is not properly aligned, you will still be able to secure the fiber but
there will be significant light losses produced by this incorrect connection.
D) Secure the fiber connection by turning the lock cap clockwise. No force is needed for this
operation.
A
D
C
B
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9) Attach the electric connection cable to the base unit
Align the red dot upwards, facing the alignment mark in the base unit.
Figure 10 Installing the Electric Connection Cable at the Base Unit
Push the connector into the plug until a “click” sound is heard.
10) Fiber connection to the base unit.
ATTENTION
When installing the fiber, make sure that the fiber tip does not get contaminated by dust.
Do not touch the fiber tip!
Remove the dust caps from the fiber end and from the FC/APC fiber connection at the base unit. The
fiber should be installed in a similar fashion as at the scanner. Follow the steps indicated in Figure 9
and pay attention not to touch the fiber tip.
ATTENTION
The fiber is slightly longer than the interconnection cable to avoid stress to it. Please be careful
not to pull the loop of the fiber at the back of the base unit!
Figure 11 Fiber Connection to the Base Unit
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11) USB, Signal and Trigger connections at the Imaging Module (see Figure 12):
Attach the SMA cable labeled “OCT SIGNAL” to the respective SMA port at the Imaging Module
and make sure the connection is tight.
Attach the VHDCI cable to the respective port which is labeled “CONTROL”. Make sure both
fastening screws which are attached to the connector are bolted tightly.
Attach the SMA cable labeled “SYNC TRIGGER” to the respective SMA port at the Imaging
Module and make sure the connection is tight.
Connect the USB cable to the USB port and make sure the connection is tight.
Figure 12 Installation of the Electrical Connections at the Imaging Module
12) k-CLOCK and Trigger connections at the Laser Module (see Figure 13):
Attach the SMA cable labeled “DAQ SWEEP TRIGGER” to the respective SMA port at the Laser
Module and make sure the connection is tight.
Attach the SMA cable labeled “DAQ k-CLOCK” to the respective SMA port at the Laser Module
and again make sure that the connection is secured tightly.
Any other SMA ports at the Laser Module are not to be used. These are meant for monitoring
purposes only and should not be connected. These ports are capped when delivered. Similarly,
the USB port at the Laser Module is for service purposes only and must not be connected.
Figure 13 Installation of the Electrical Connections at the Laser Module
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13) Connections at the DAQ cards (see Figure 14):
Identify both the Alazar ATS9350 DAQ card and the NI PCIe-6351 DAQ card at the back of the
PC (see Figure 14).
Connect the VHDCI cable to the NI PCIe-6351 DAQ card. Make sure both fastening screws which
are attached to the connector are bolted tightly.
Attach the k-CLOCK cable to the only available SMA port at the Alazar ATS9350 DAQ card. This
port and the respective cable are labeled “ECLK”. Make sure the connection is secured tightly.
Attach the BNC end of the cable labeled “DAQ SWEEP TRIGGER” / “TRIG IN” to the second
BNC port from the left marked as “TRIG IN”. Make sure the connection is secured tightly.
Attach the BNC end of the cable labeled “SYNC TRIGGER” / “AUX I/O” to the first BNC port from
the left marked as “AUX I/O”. Make sure the connection is secured tightly.
Attach the BNC end of the cable labeled “OCT SIGNAL” / “CH B” to the third BNC port of the
Alazar ATS9350 DAQ from the left marked as “CH B”. Again make sure the connection is secured
tightly.
The BNC port marked as CH A is not used!
Figure 14 Connections of the Alazar and NI DAQ Cards
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14) Fiber connection between the Laser and Imaging Module:
Connect one end of the 1m long fiber to the Laser Module at the fiber port labeled “LASER APERTURE”
and the other end to the Imaging Module at the fiber port labeled “LASER IN” as indicated in Figure
15. When attaching the fiber, make sure the orientation is correct, otherwise there will be a
substantial loss in optical power transferred from the Laser into the Imaging Module!
Figure 15 Fiber Connection between the Laser and the Imaging Module
15) Removing the protective cap off the scan objective
Pull the protective cap off the scan objective. Do not rotate the protective cap, as this might loosen the
fit of the illumination tube. Do not touch the optical surface of the lens.
Figure 16 Protective Cap Removal
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Chapter 3 Description
3.1. Tutorial
Fourier Domain Optical Coherence Tomography (FD-OCT) is based on low-coherence interferometry, which
utilizes the coherent properties of a light source to measure optical path length delays in a sample.
To obtain cross-sectional images with micron-level resolution using OCT, an interferometer is set up to measure
optical path length differences between light reflected from the sample and reference arms.
There are two types of FD-OCT systems, each characterized by its light source and detection schemes:
Spatially encoded Frequency Domain OCT (SeFD-OCT) and time encoded Frequency Domain OCT (TeFDOCT), also named Swept Source OCT (SS-OCT). In both types of systems, light is divided by a fiber coupler
into the sample and reference arms of an interferometer setup.
Back reflected light, attributed to variations in the index of refraction within a sample, recouples into the sample
arm fiber and then combines with the light that has traveled a fixed optical path length along the reference arm.
The resulting interferogram is measured by either a spectrometer (SeFD-OCT) or balanced photodetectors
(SS-OCT).
The frequency of the interferogram measured by the sensor is related to the depth location of the reflector in
the sample. As a result, a depth reflectivity profile (A-scan) is produced by taking a Fourier transform of the
detected interferogram. 2D cross-sectional images (B-scans) are produced by scanning the OCT sample beam
across the sample; by doing so, a series of A-scans are collected to create the 2D image. Similarly, when the
OCT beam is scanned in a second direction, a series of 2D images is collected to produce a 3D volume dataset.
Figure 17 FD-OCT Signal Processing
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Theory
The interference equation for the cross correlated interference term is
With the phase difference being a function of the optical path length difference and the wavenumber
This optical amplification of a small sample intensity with a strong reference intensity allows the detection of
single photons from the sample and is the key to the outstanding sensitivity of OCT.
Due to the reflective character of the measurement modality the optical path length difference is twice the
distances in the image. The maximum imaging depth, and so twice optical path length difference, is defined by
the wavenumber spacing of the acquisition .
In Full-Range OCT setups the image depth could be doubled
The signal width has two limits,
One limit for the signal width is given by the spectral distribution of the light source. For a fully used
light source being Gaussian shaped in the equation is:
with:
The other limitation for the signal width is given by the sampling. For a rectangular spectrum the FFT
results in a sinc function
with:
A light source is not shaped in a way that the autocorrelation function is clean normally. Therefore the shape
should be apodized to get a clean point spread function. A good compromise between resolution and side lobe
suppression could be a Hanning window showing a signal width of:
In real mesurements the signal width is furthermore limited by noise, dispersion mismatch between sampleand reference arm of the interferometer, and optical path length distribution of the imaging caused by
aberration.
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Thorlabs SS-OCT System Technology
Swept Source Optical Coherence Tomography (SS-OCT) technology uses a rapidly tuned narrowband source
to illuminate the interferometer and records the information with a balanced detector. SS-OCT technology
measures the magnitude and time delay of reflected light in order to construct depth profiles (A-scans) of the
sample being imaged. Adjacent A-scans are then synthesized to create an image.
Advanced data acquisition and digital signal processing techniques are employed in the SS-OCT system to
enable real-time video rate OCT imaging. The 2D OCT images are analogous to ultrasound images and show
the cross-sectional structure view of the sample. The transverse and axial resolutions of the images are limited
by the focusing optics and spectral bandwidth of the light source respectively. The actual imaging depth into
the sample is highly dependent on the sample scattering properties at the measurement wavelength. The OCT
system also enables the generation of images similar to confocal microscopy by summing signals in the axial
direction. High-speed 3D OCT imaging provides comprehensive data that combines the advantages of surface
microscopy and structural OCT imaging in a single system.
At the heart of the SS-OCT system is a swept laser source that tunes the lasing wavelength over a broad
wavelength range, at hundreds of kilohertz repetition rate. Sample depth profile measurements are performed
at the high sweeping rate of the laser. The interference signals from the sample are collected using a highefficiency balanced detection scheme. Each sweep of the laser wavelength provides a depth scan at a sample
surface point that yields a depth dependent reflectivity profile along the direction of the laser illumination path.
The MEMS-VCSEL SS-OCT system utilizes the latest MEMS-VCSEL swept laser as the light source to perform
Fourier domain OCT measurements. The very short cavity length (on the level of a few micrometers) of the
MEMS-VCSEL cavity enables very long coherence length (≥100 mm) of the source when sweeping at very
high speed (a few hundreds of kHz). The very long coherence length of the MEMS-VCSEL swept laser supports
the large depth measurement range in OCT experiments, as its distinctive advantage compared to conventional
short external cavity (on the level of a few millimeters) based swept sources. The MEMS-VCSEL SS-OCT
system is capable of providing highly detailed, 2D cross-sectional imaging of a sample’s internal structure, as
well as computer generated 3D reconstruction of a volume near the sample surface. The internal structure of
a sample can be accurately mapped via computer generated tomographic images.
The VEG110 Swept Source OCT Base Unit combined with a Thorlabs Scanner provides simultaneous multiple
imaging channels for microscopic viewing of the sample. The en-face images, similar to those obtained from a
conventional microscope, can be acquired from the video camera channel while the cross-sectional images
that show the sample's internal structure are acquired from the OCT channel. Due to the novel data acquisition
and signal processing methods employed, real-time video-rate imaging speed has been achieved on both
channels.
The system includes a high-speed MEMS-VCSEL swept laser with -10 dB spectral bandwidth larger than 100
nm, and an average output power greater than 20 mW, sweeping at ≥ 100000 A-scans per second. The swept
laser provides an A-scan trigger signal to be connected to the trigger input of the data acquisition device. The
laser also has a built-in monitoring interferometer that provides the real-time clock signals to be connected to
the external clock input of the data acquisition device. The main output of the laser is coupled into a fiber-based
Mach-Zehnder interferometer located inside the imaging module. The light is split into the sample and reference
arms using a broadband 90/10 coupler.
In the reference arm of the interferometer, the light is reflected back into the fiber by a stationary mirror. In the
sample arm, the light is fiber coupled into the handheld probe, collimated, and then directed by the XY
galvanometric scanning mirrors towards the sample. The axial scans (A-scans) in the depth direction are
performed at the sweeping frequency of the laser. The transverse scan (B-scan) is controlled by the
galvanometric scanning mirrors and determines the frame rate of the OCT system. The light exits the handheld
probe is focused onto the sample surface by an objective. A dichroic mirror is inserted into the beam path to
reflect the visible light from the sample onto a CCD camera that records the conventional microscope images
of the sample.
The schematic setup of the SS-OCT system is shown in Figure 18.
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Figure 18 Schematic Diagram of a SS-OCT System
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Nomenclature in OCT imaging
Figure 19 A-Scan Data Set
As described before, the FD-OCT engine creates a depth profile from the interference of photons sent into the
sample and received back with photons reflected in the reference arm. This depth profile is referred to as Ascan. Figure 19 shows a tomato’s A-scan data. The ordinate of this graph represents the modulation amplitude
based on the number of measured electrons per camera pixel.Other scales do not change the measurement.
The imaging application could make use of up to two scanning directions. When scanning one direction while
collecting multiple A-scans, a 2-dimensional image is created. This is referred to as a B-scan. Here, the depth
information is typically displayed from top to bottom, while the scan axis is from left to right. Figure 20 shows a
B-scan data set.
Figure 20 B-Scan Data Set
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When scanning both galvanometer mirrors, a volume can be acquired. This can be imaged by movable sections
through the volume or by 3D rendering. Please refer to the SD-OCT Software Manual for all features available.
Figure 21 Rendered Volumetric Data Set
Figure 22 En-Face View or C-Scan
When displaying a plane with both scan directions as axes, an en-face image is created. Here, the viewing
plane is parallel to the image plane of the color camera in the scanner. This plane is referred to as C-scan.
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3.2. SS-OCT Base Unit Components
The base unit is delivered together with a pre-installed PC.
A scanner as well as the OCT-Stand are not included in the base unit and must be ordered separately.
When ordered together with a scanner, the System will be pre-assembled at Thorlabs and the PC settings will
already be calibrated and optimized for the usage of the delivered OCT-scanner.
Base Unit
The base unit is the main component of the SS-OCT system. This unit sends light to the application,
communicates with the PC through a USB connection, and delivers the measurement data to the PC. The base
unit contains a MEMS-VCSEL Swept Source Laser which is directed through a fiber from the Imaging Module
at the backside of the device. The back-scattered and reflected light from the application is returned through
the fiber optical coupler, which directs the light to an interferometer (as described in Figure 18). Other
components in the base unit include a balanced detector, analog and digital timing circuitry, analog control
signals for the application, and data acquisition hardware.
Figure 23 Base Unit (VEG1x0)
The central wavelength of the MEMS-VCSEL in the SS-OCT Base Unit depends on the type. The use of nearIR broad sweeping bandwidth sources balances the desire for low scattering losses with the need to operate
within the wavelength range that will provide higher penetration depth into the sample. Near-IR broadband
sources are a perfect compromise between sufficient transparency and a significantly reduced scattering
coefficient.
PC with Graphical User Interface
This SS-OCT system is delivered with application software made for the imaging scanners provided by
Thorlabs. All required data analysis as well as 2D and 3D display can be performed within the software
package. The data can be saved, analyzed and exported for further use.
Detailed operating instructions for the SS-OCT software are provided in the SS-OCT Software User’s Manual.
SDK
A software development kit (SDK) is provided with the system. The SDK gives access to all software routines
used to control the units and to process the acquired data. It allows a quick start for application specific software
development. The SDK is implemented in two programming languages, C and LabVIEW. For professional and
advanced users the C interface guarantees a seamless integration into their own object oriented software.
SD-OCT Base Unit Chapter 3: Description
Page 22 MTN008437-D02
For easy access to the functionality we also provide a LabVIEW Interface. The LabVIEW interface has the
same functionality as the C interface and maintains the same high processing speed achieved with the C
interface.
Hardware control through the SDK ranges from low level functions such as setting the galvo scanners to a
desired position, to very powerful functions such as initiating full 3D measurements. The programmer can:
• define either a standard scanner provided by Thorlabs or create a software representation of a custom-
built device.
• Define simple or complex scan patterns.
• Acquire simple A-Scans, B-Scans or complete volumetric measurements.
Processing of acquired OCT data ranges from simple A-Scan processing to advanced routines for Doppler
speed measurements. The programmer can:
• Take the standard processing steps necessary to convert a spectrum measurement into an A-Scan
• Set the color scheme, brightness and contrast of images
• Calculate the speed of particles in the sample via Doppler OCT
• Import and export the different file formats data types
The function library also contains the source code for the LabVIEW software applications supplied with the
instrument and other example programs. Often these can be used as a starting point for software development
projects.
The SDK can be installed from the DVD which ships with the system.
A complete documentation of the SDK with a description of all functions can be found in PDF format in the
SpectralRadar SDK program group after installation of the SDK.
SD-OCT Base Unit Chapter 3: Description
Rev A, March 3, 2017 Page 23
Imaging Scanner (Accessory)
Thorlabs SS-OCT systems use a dual path OCT setup in which the interferometer and the reference path are
located in the Imaging Module. The imaging scanners presented below are “no-reference” (NR) versions.
Various Lens Kits are available for these scanners.
For further detail please refer to the specific manual of the scanner.
Figure 24 OCTG-NR Rigid Scanner
Figure 25 OCTP-NR Adjustable Cage-Compatible Scanner
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Page 24 MTN008437-D02
Figure 26 OCTH-NR Handheld Scanner
SD-OCT Base Unit Chapter 3: Description
Rev A, March 3, 2017 Page 25
OCT-Stand (Accessory)
The Thorlab´s OCTG and OCTP scanners could be adapted to an OCT-STAND. For this OCT-STAND the
rotation- and translation stage OCT-XYR1 is available.
Figure 27 OCT-STAND with OCT-XYR1
Figure 28 OCT-STAND Adjuster
SD-OCT Base Unit Chapter 3: Description
Page 26 MTN008437-D02
Figure 29 OCT-XYR1 Sample Rotation Stage
For further details on the OCT-STAND and the OCT-XYR1 please refer to their manual.
SD-OCT Base Unit Chapter 4: System Operation
Rev A, March 3, 2017 Page 27
Chapter 4 System Operation
4.1. Starting the System
Follow the steps described in the next three subchapters for proper initialization of the system. Your PC system
should already be running.
Turning ON the Imaging Module
Start the imaging module by placing the POWER switch to the “|” Position. Verify that the “POWER ON”
indicator turns green. Wait for 30 seconds until the PC has recognized the hardware. Furthermore, the ringlight illumination should be turned on.
Turning ON the Laser Module
The following turn ON procedure is required for proper operation of the laser.
1) Start the swept source laser by switching on the power switch to the ON position. All the green LEDs
on the front panel turn green for a few seconds while the system performs a self-test as show in Figure
30.
Figure 30 Swept Source Laser turn ON Step 1: Power Switch
The TEMP indicator will remain green until the temperature of the system is stable as indicated in Figure 31.
Note that this can take longer than 60 seconds if the system starts up from a very cold state.
Figure 31 Swept Source Laser warming up
2) Wait until the SYS OK indicator turns green, the TEMP indicator should turn off as shown in Figure
32.
Figure 32 Swept Source Laser ready to be enab
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3) Press the LASER ENABLE button. The LASER ON indicator will blink for about 15 seconds and then
become steady and illuminated as shown in Figure 33. If the blinking time of the LASER ON indicator
is longer than 25 seconds, please turn off the laser and call your local Thorlabs Technical Support for
assistance.
Figure 33 Swept Source Laser enabled
Starting the Software
4) Start the ThorImage OCT software (see Software User’s Manual for details). The system will be
switched on via remote control from the computer.
4.2. Basic Adjustments
When receiving the SS-OCT system from Thorlabs, the reference length is adjusted, so that OCT imaging in
air is possible simply by adjusting the focus to the region of interest. Once the scanner is significantly
misadjusted, the following procedure will aid you to a good basic adjustment. For OCT imaging through
refractive media, e.g. water or glass, please refer to chapter 4.3.2.
Adjusting the Focus
For a coarse adjustment of the focus, place a suitable sample, e.g. the IR viewing card delivered with the
system, underneath the scanner. Using the OCT software, a fraction of the card can be seen in the sample
monitor. Now adjust the height of the imaging scanner with respect to the card by adjusting the focus block of
the OCT-Stand (see Figure 34) to obtain a sharp image.
Figure 34 Basic Focus Adjustment
off focus
in focus
SD-OCT Base Unit Chapter 4: System Operation
Rev A, March 3, 2017 Page 29
Adjusting the Reference Length
The VEGA Swept Source OCT System is preset so that the “zero-delay” line is set to a depth position of 0 mm,
meaning that when the surface of the sample under test is placed in the focus of the objective in use, it will be
shown at 0 mm. However, in case of any misalignment due to shipping, etc., corrections can be made by
adjusting the length of the reference arm. Also, when using a different objective, the reference arm length will
have to be changed accordingly. The reference arm in the VEGA OCT system is motorized and is controlled
through the GUI (ThorImage OCT). For further information please refer to the respective software manual.
Adjustment of the reference length may be done in combination with focus height adjustment (using the OCT
stand), so that the focus position in the OCT data is shifted. Also, this adjustment is necessary when imaging
in a refractive material.
The following steps will guide you to a basic adjustment of the reference length:
- Start B-scan acquisition. When significantly misadjusted, you will get an incorrect OCT image or no
image of your sample, irrespective of the focus position.
- Using the jog buttons or the input field in the reference stage control to move the reference stage in
both directions so that you can see how the image position is shifted.
- Find a value for the reference stage control so that the image is not “flipped” (upside -down). Use a
sample where you know for sure what the top surface looks like.
- Hit the auto-adjust button (see Software Manual) to adjust the dynamic range of your B-scan.
- When using the IR card for adjustment, your B-scan image should look as shown in Figure 35.
Figure 35 B-Scan of an IR Viewing Card
After basic alignment, you need to adjust the focus position inside your sample by use of the fine focus adjuster
(see Figure 27) of the OCT-Stand. Then, the final position of the OCT image in the B-scan or volume scan can
be set using the reference stage control again. Vary the value to move the image up and down until you achieve
the desired location. Next time the system is restarted the reference length will be set according to the last
modifications made.
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Figure 36 B-Scan of a Fingertip Out of Focus and In Focus
In Figure 36 two images of a fingertip are shown, the left is out of focus and the right is in focus.
The focus can usually be identified by one of more of the following features:
Sharp (thin) features in lateral direction
Autocorrelation terms (see Chapter 5 Imaging Artifacts)
Higher contrast (i.e. a strong signal). Note, that the focus does not always have to be on the top surface
of your sample, but needs to be adjusted to the layer of interest in your sample.
Adjusting the Polarization
If necessary, polarization in the reference arm can be modified with the reference polarization adjuster, as
indicated in Figure 37.
Figure 37 Polarization Adjustment in the Reference Path
In order to adjust polarization in the reference arm, use the 2mm hex key (shipped with the system) to turn the
adjuster. The polarization adjuster is connected to an inline fiber polarization controller (PLC-900). By moving
the adjuster a section of the fiber is twisted, thus changing the state of polarization. Once the desired state of
polarization is achieved the position can be secured via a headless set screw as indicated in Figure 38.
Figure 38 Set Screw for Securing the State of Polarization
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Rev A, March 3, 2017 Page 31
4.3. Advanced Adjustments
Focus and Choice of Objective Lens
In OCT, an objective lens is used to focus the light beam on and into the sample and also to collect the
backscattered light. The focused nature of the beam means that the lateral extension of the beam is different
along the depth axis. Since OCT records signals along this depth axis, the collected signal corresponds to
different lateral extensions of the beam and therefore the resolution is different along the depth axis. The best
resolution can be obtained from the axial focus plane; the further away from the focal plane the light is
backscattered from, the more blurred out the signal will appear.
The length of the axial focus depends on the optics of the OCT system, especially on the choice of the objective
lens. For samples with a small axial focus length, an objective lens with a high numerical aperture can be
chosen. This will grant a small lateral and axial focus, hence allowing a more in-depth analysis of the sample
but also restricting the axial depth that can be investigated. For samples with a deep region of interest it is
helpful to choose an objective with a low numerical aperture, thus being able to collect signals from a large
focus band. However, low numerical aperture objective lenses will decrease the lateral resolution of the image.
Figure 39 OCT B-Scans of scattering particles taken with LSM02, LSM03, and LSM
Thorlabs offers three objective lenses for different purposes. Figure 39 shows the difference in lateral resolution
and depth of focus for the LSM02 (high resolution imaging), LSM03 (general purpose), and LSM04 (high depth
of focus). Note the change in signal strength and lateral resolution over depth caused by an increasing focus
band.
Please contact Thorlabs for more information on how to incorporate different objective lenses in your OCT
system.
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Imaging through Refractive Media
To acquire OCT images, the optical path lengths of the sample arm and reference arm have to be matched.
When imaging through refractive media
The optical path length of the sample arm is increased which has to be compensated in the reference
arm (for more details see chapter 5.6).
The amount of dispersion changes, this can be compensated using the ThorImage OCT software.
Every time the amount of refractive media is changed, this procedure has to be repeated in order to achieve
a good image quality.
Figure 40 Step by Step Adjustments when Imaging through Refractive Media
Instead of adjusting focus and reference arm length at the same time, it is often helpful to first find the focus
and then adjust the reference arm length. Figure 40 shows this procedure step by step, starting with a sample
that is out of focus and with a misaligned reference arm, so that no sample can be seen in the B-scan (Figure
40 A). After finding the focus, autocorrelation terms will appear in the upper part of the image even without any
reflecting surface in the field of view of the B-scan. When these artifact signals are the strongest stop focusing
and adjust the reference arm length so that the image appears in the top half of the window.
Furthermore, the refractive media will introduce dispersion effects, i.e. washing out due to a dependence of the
phase velocity on the wavelength. This can be compensated using the ThorImage OCT software (for more
details see the software manual). Note that the amount of dispersion depends on the thickness of the refractive
media, hence, the dispersion compensation has to be changed every time the thickness of the refractive media
was changed.
Note: If you are able to identify autocorrelation signals but are not able to move the OCT image into the
observable window, the optical path length of the sample arm is likely increased to an extent that cannot be
adjusted by the reference arm anymore. Thorlabs offers a special reference arm adapter to further increase
the reference arm length, please contact Thorlabs for more information.
Autocorrelation
Signals
B
C
D
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Rev A, March 3, 2017 Page 33
Reflecting Surfaces and Interfaces
Reflecting surfaces and interfaces might lead to a saturation of the detector and in turn lead to artifacts
described in more detail in chapter 5.1. The influence of the artifacts can be decreased by tilting the probe or
the sample. By doing that the reflections from the sample are directed back at a different angle than the incident
beam and are not collected by the objective lens.
Rough Surfaces
Rough interfaces between two layers with different refractive indices will lead to reduced sensitivity. The reason
is that the sample light is scattered at the interface and directed into various directions. Here it is often helpful
to use an immersion gel and a flat surface (e.g. a glass slide) to reduce scattering.
Thorlabs offers sample z-spacers that provide a glass plate at a fixed distance to reduce scattering effects and
to keep the sample in focus, please contact Thorlabs for more information.
Figure 41 Plastic with Matte Surface, Partially Covered with Clear Adhesive Tape
Figure 41 shows a B-scan of a plastic substrate with a matte surface. The right part of the surface was covered
with a strip of adhesive tape to make the rough surface smoother. Due to this smooth surface the OCT image
is much more consistent and the contrast in deeper layers is much better compared to the plain matte surface
that is shown on the left. This is the same effect that can be seen when looking through a transparent material
with a matte surface. As an example, frosted glass becomes more transparent with water.
4.4. Shutting Down the System
The following steps should be followed when shutting down the system:
1) Save any important data.
2) Stop imaging by clicking on the “Stop OCT” button in the ThorImage User Interface Toolbar. Close the
ThorImage OCT software.
3) Press the LASER ENABLE button to disable the laser output. The LASER ON indicator will blink for a
few seconds and then become steady OFF.
4) Turn the power switch to OFF to completely turn off the Laser Module.
5) Turn the power switch to OFF to completely turn off the Imaging Module.
6) Shut down the PC.
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Page 34 MTN008437-D02
4.5. Example Images
Spectral Domain OCT can be used for a wide range of real-time monitoring applications in biological and clinical
fields as well as in manufacturing and materials science. This technology is ideal for in-line industrial imaging
applications ranging from laminated packaging films to 3D visualization of mechanical parts.
Skin Imaging
SS-OCT provides real-time high resolution surface and sub-surface imaging of human skin, making this system
ideal for many dermal and sub-dermal applications, including burn-depth monitoring, wound healing, and
cancer detection.
Figure 42 B-Scan of a Nailfold
Figure 43 B-Scan of a Fingertip
SD-OCT Base Unit Chapter 4: System Operation
Rev A, March 3, 2017 Page 35
Material Imaging
SS-OCT can also be used for non-biological material science applications. SS-OCT is ideal for monitoring
surface topography and layered structures.
Figure 44 B-Scan of a Semi-Transparent Molded Plastic Cap
Figure 45 B-Scan of a Laminated IR Card
Biological Imaging
Figure 46 B-Scan of a Section of a Grape
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Page 36 MTN008437-D02
Chapter 5 Imaging Artifacts
5.1. Saturation and Non-Linearity
The OCT A-scan data is created by frequency analysis of the spectral data generated by the spectrometer.
Intense reflection from the sample can saturate the sensor of the spectrometer or illuminate very close to
saturation. This effect broadens the signal and leads to a nonlinear response. For example, a sinusoidal optical
signal is interpreted as partially rectangular. Consequently, additional harmonic frequencies of the root signal
appear.
Figure 47 High Surface Reflection Causing Saturation and Nonlinear Response of the Spectrometer
A typical example of this effect is shown in Figure 47. Saturation can be reduced or avoided by:
- Changing focus position
- Tilting the sample with respect to the A-scan axis
- Introduction of a wedge into the optical path (first reflex reflecting outside of NA) and immersion (see
Figure 48)
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Rev A, March 3, 2017 Page 37
Figure 48 Avoiding Strong Surface Reflection by Use of an Immersed Wedge
When operating with a wedge, the image will be tilted in the direction of the wedge angle. When scanning in
the orthogonal direction, no tilt occurs.
5.2. Multiple Scattering
When imaging highly scattering material, a large portion of the photons returned to the detection system have
been scattered multiple times from travelling into the sample until exiting. Since OCT visualizes the relative
travelled path lengths of photons, signals from multiple scattered photons are shown deeper in the image than
physically present.
Figure 49 Schematic of a Setup to Show the Influence of Multiple Scattering
Multiple scattering is intense in paper. For illustration of this artifact, a setup as depicted in Figure 49 is imaged.
Here, a piece of paper is placed over a glass substrate.
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Page 38 MTN008437-D02
Figure 50 OCT Image Showing Multiple Scattering
In the OCT image (see Figure 50), one can clearly see that the paper appears to be very thick. This apparent
thickness is induced by the relatively long travel of photons that are scattered multiple times before finding their
way back into the detecting aperture.
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Rev A, March 3, 2017 Page 39
5.3. Phase Wrapping and Fringe Washout
The A-scan data created by the SD-OCT system is produced from spectral information of an optical
interference. Depending on the system setting, a certain integration time is applied for acquisition of each Ascan. Certain movement of the sample or parts of it can well be detected by comparing the phase information
of adjacent A-scans. This Doppler Imaging mode is provided by the SD-OCT Software (please refer to the SD-
OCT Software Manual for details). Sample movements of more than ¼ of the detected wavelength (from Ascan to A-scan) lead to misleading results. The maximum detectable speed (in direction of the A-scan axis) is
4
max
fv
For an A-scan rate of f = 1.25 kHz at 930nm, the maximum detectable speed v (in the direction of the A-scan
axis) is 290µm/s. When the direction of the movement occurs at an angle with respect to the A-scan axis, larger
speeds can be imaged.
For larger movements within the integration time of the detector, a complete washout of the interference will
occur.
Figure 51 Sample Image Showing Fringe Washout and Phase Wrapping
To illustrate these effects, a sample has been moved quickly while slowly acquiring a B-scan. Figure 51 shows
the result. The intensity data is shown in black and white, while the Doppler information is displayed red to blue.
When the movement starts, the Doppler information is displayed red which means that the sample moves
down. Now at increasing speed, the Doppler information turns blue. This means that the phases of the signal
have wrapped and an inverse speed is shown. In the middle of the movement where the speed is at its
maximum almost no OCT data is displayed (fringe washout).
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Page 40 MTN008437-D02
5.4. Flipped Image
Without the introduction of additional techniques not provided by the standard SD-OCT system, there is no
distinguishing between photons that traveled a distance d shorter or longer from the beam splitter to the
sample compared to the reference arm length. When adjusting the reference length to be too long, the image
appears flipped.
Figure 52 Right Orientation Up Reference Length Adjustment for Imaging of an IR Viewing Card
Figure 53 Upside Down Reference Length Adjustment Showing a Flipped Image
Figure 52 and Figure 53 show the different adjustments of the reference length when imaging the IR viewing
card provided with the system.
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Rev A, March 3, 2017 Page 41
5.5. Shadowing
Since the SS-OCT imaging uses light for detection of depth information, one can only see information from
regions in the sample, where photons are transmitted to and allowed back into the sampling aperture.
Reflections, strong scattering and absorption lead to shadows in the depth distribution of the data acquired.
Figure 54 Rendered Volume of a Screw on an IR Viewing Card Displaying the Shadowing Effect
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5.6. Image Distortion by Refractive Media
OCT images display path length differences in between reference arm length and sample arm length (distance
from the beam splitter to the scattering or reflecting object). These path lengths are optical path lengths,
calculated from the physical path length multiplied by the group refractive index of the sample.
Figure 55 Schematic of a Setup to Show Distorsion from Refracting Media
Figure 56 Height Shift of OCT Image Through Refractive Media
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Rev A, March 3, 2017 Page 43
The Group Refraction Index
The principle of optical coherence tomography is the detection of optical path length differences between the
two arms of an interferometer. The optical paths within these arms are defined by the mechanical path lengths
and the refractive indices of the materials.
When talking about the refractive index of an optical material most of the time it refers to the phase velocity
index. As the name indicates this is a factor for the velocity of the phase when travelling through the material
in relation to the vacuum speed of light. The standard abbreviation of the Phase refractive index is n.
The group velocity of a wave is the velocity with which the overall shape of the wave's amplitudes - known as
the modulation or envelope of the wave - propagates through space. This velocity usually is different from the
speed of the phases of the single wavelengths. This velocity is calculated by using the group refractive index
g
n
of a material.
The relation of these two values is:
0
0
d
dn
nn
g
In OCT systems the group refractive index defines the optical path lengths.
In the table below some materials and their phase refractive indices
p
n
as well as their group refractive indices
g
n
are given.
Material
= 900nm
= 1050nm
= 1310nm
np
ng
np
ng
np
ng
Water 24°C
1.327
1.340
1.324
1.340
1.320
1.343
Water 37.6°C
1.324
1.341
1.321
1.339
1.316
1.339
Quartz
1.452
1.465
1.450
1.463
1.447
1.462
N-BK7
1.510
1.523
1.507
1.521
1.504
1.519
N-LAK22
1.640
1.659
1.638
1.655
1.634
1.651
N-SF11
1.760
1.798
1.754
1.786
1.748
1.775
N-SF57
1.818
1.861
1.812
1.847
1.805
1.834
In vacuum the values for
p
n
as well as for
g
n
are 1 for all wavelengths. The difference for the performance in
air is negligible for most instances.
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Page 44 MTN008437-D02
Measurement Depth in OCT Systems
The spectral resolution of a frequency domain OCT system defines its possible measurement depth. This depth
is the maximum detectable optical path length difference limited by the Nyquist criteria. In real materials the
measurement depth of OCT systems as well as the axial resolution is reduced. The reduction of the resolution
depends on the material properties between the two measured interface signals used. The reduction of the
imaging depth is a result of the materials in the sample image as visualized in the graphic below:
Figure 57 Measurement Depth With Refractive Media
In the image the incoming beam from above is scanned over a structure made of two different materials named
one (d1, ng1) and two (d2, ng2) stacked on a flat surface (red line). The imaging range is displayed as a light
grey area. Vertical structures are barely visible.
The materials are displayed in the OCT image with an axial dimension corresponding to the optical path lengths.
In most cases the sample is not well known. The measurement depth in air (vacuum) is known and the optical
path lengths of the materials are obtained – only with the knowledge of the material properties it is possible to
determine the real physical thickness.
The loss of imaging depth depends on the thickness and the group refractive indices of the materials displayed
within the image. It is calculated as follows:
i
igi
dnloss )1(
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Rev A, March 3, 2017 Page 45
Distortions in the Image
In complex structures distortions occur in the OCT image which require a close look to be understood.
Figure 58 Different Materials in One Measurement
The loss of imaging depth depends on the amount of material through which the beam passes. As a result the
measured depth in the sample changes throughout the scan.
In the setup shown in Figure 58 one can determine the properties of the materials assuming the underlying
surface to be flat and horizontal in the image. In the OCT image on the right the physical thicknesses
i
d
, optical
path lengths
igi
dn
as well as the resulting shifts of underlying structures
igi
dn )1(
can be determined directly.
The real imaging areas are displayed in the graphic for real sample dimensions on the left.
When the physical structure becomes more complex the resulting OCT image becomes more difficult to
interpret.
Especially when the surface is not horizontal or curved, effects like shadowing, diffraction on interfaces and
possible multiple measured structures may occur in addition to the changes in optical path length.
SD-OCT Base Unit Chapter 5: Imaging Artifacts
Page 46 MTN008437-D02
As an example a material with wedge is analyzed:
Figure 59 Complex Structure in Image
The block shows “standard” behavior on the right side where the surface is perpendicular to the incoming beam.
In the chamfered area there is diffraction and the beam travels under an angle through the block. The real
angled physical path is enlarged a little (
a
d
and
b
d
), and
s
d
is not in-line with
a
d
.
These paths are displayed strictly vertical in the OCT image showing the expected optical path lengths
igi
dn
.
The beam is displayed without rotation.
This difference between the real diffracted optical path and the displayed OCT image makes it difficult to
perform an inverse ray tracing because all the diffractive interfaces need to be determined in 3D.
Even this determination needs to be undertaken step after step since the first interface affects the OCT image
of the second interface and so on.
The most challenging part is the light grey area in the sample marking the imaged field. In the left edge of the
chamfered block there is an area which is not reached by OCT light and therefore cannot be visualized at all.
On the other hand there are structures that are measured twice because of the two different optical paths
leading to these structures.
In very complex structures these effects become more and more difficult to handle – Just assume spherical or
curved interfaces, bubbles, inhomogeneous materials, possible imaging aberrations in the sample etc.
SD-OCT Base Unit Chapter 6: Troubleshooting
Rev A, March 3, 2017 Page 47
Chapter 6 Troubleshooting
Symptom
Possible Cause
Solution
System Does Not Start
No power is supplied to the unit
Connect the power supply
Power cord is broken
Change power cord
Other reason
Call Thorlabs1
System Does Not Make
Measurements
PC crashed
Restart PC
Poor connection of USB cable
Check USB connection
Data acquisition cables not inserted
Connect data acquisition
cables
Optical path length not matched
Adjust optical path length
Beam is blocked
clean fiber tip
Other reason
Call Thorlabs1
No Signal in Image
Fiber not connected
Connect fiber patch cable
Fiber tip is dirty
Clean fiber tip
Scanner not connected
Connect Scanner
Focus is out of imaging area
Adjust reference length,
readjust focus
Other reason
Call Thorlabs1
Bad Image Quality
Mirrored image shown
Observe the OCT image
while adjusting the
distance of the scanner to
the sample
Distance to the sample is too short
When decreasing the
distance, the image
needs to move towards
the top of the OCT image
Other reason
Call Thorlabs1
Flipped Image
Reference length set incorrectly
Adjust reference length
Table 3 Troubleshooting
1
Please refer to Chapter 12 for Thorlabs contact information.
SD-OCT Base Unit Chapter 6: Troubleshooting
Page 48 MTN008437-D02
6.1. Changing the Input Fuses
If for some reason you need to replace an open fuse in the base unit, you must perform the following procedure:
Remove the AC input cable that may be connected to the unit.
Slide open the cover of the fuse holder located at the rear panel of the either the Laser Module or the
Imaging Module. Remove the existing fuse and install the appropriate replacement fuse for the
respective unit.
1. Use only IS 500mA 250VAC Type 250 style fuses (IEC 60127-2/III, low breaking capacity, slow
blow) for the Laser Module.
2. Use only IS 1A 250VAC Type T 5x20mm style fuses (IEC 60127-2/III, low breaking capacity,
slow blow) for the Imaging Module.
Slide the fuse cover closed.
Figure 60 Fuse Cover on Rear Panel (Laser Module)
Figure 61 Fuse Cover on Rear Panel (Imaging Module)
If for some reason you need to replace the mains lead, the power connection is made using the IEC 60320
C14 plug. When choosing the cord, ensure to choose a cord following local applicable standards. The cord
must be specified for 10A 250V.
To avoid electrical shock the power cord protective ground conductor must be connected to ground.
SD-OCT Base Unit Chapter 7: Certifications and Compliance
Rev A, March 3, 2017 Page 49
Chapter 7 Certifications and Compliance
7.1. Declaration of Conformity Vega Series Base Units
SD-OCT Base Unit Chapter 7: Certifications and Compliance
Page 50 MTN008437-D02
SD-OCT Base Unit Chapter 8: Warranty
Rev A, March 3, 2017 Page 51
Chapter 8 Warranty
8.1. Lasers and Imaging Systems
Thorlabs offers a one year warranty on all lasers and imaging systems, with the exceptions of laser diodes.
8.2. Non-Warranty Repairs
Products returned for repair that are not covered under warranty will incur a standard repair charge in addition
to all shipping expenses. This repair charge will be quoted to the customer before the work is performed.
8.3. Warranty Exclusions
The stated warranty does not apply to products which are (a) specials, modifications, or customized items
(including custom patch cables) meeting the specifications you provide; (b) ESD sensitive items whose static
protection packaging has been opened; (c) items repaired, modified, or altered by any party other than
Thorlabs; (d) items used in conjunction with equipment not provided by or acknowledged as compatible by
Thorlabs; (e) subjected to unusual physical, thermal, or electrical stress; (f) damaged due to improper
installation, misuse, abuse, or storage; (g) damaged due to accident or negligence in use, storage,
transportation, or handling.
SD-OCT Base Unit Chapter 9: Specifications
Page 52 MTN008437-D02
Chapter 9 Specifications
General Performance Specifications – SS-OCT Base Unit
Supply Voltage for base unit*
100 V – 240 V / AC
Maximum Power Consumption
150 W
Weight base unit (Laser + Imaging Module)
< 18 kg
Storage/Operating Temperature
10 °C to 35 °C
Dimensions of OCT-Stand (L x W x H)
206 mm x 305 mm x 248 mm
Dimensions of base unit (L x W x H)
320 mm x 320 mm x 215 mm
Airborne Noise Emission
< 70 dBA
Table 4 General Specifications
*
base (MEMS VCSEL Swept Source Laser + Imaging Module) has universal AC input
Optical Performance Specifications – Vega Series Base Unit
Base Unit
VEG110
Central Wavelength
1300 nm
Axial Scan Rate
100 kHz
Maximum Imaging Depth
Air/Water (typical)
12 mm / 9.0 mm
Axial Resolution Air/Water (typical)
16 µm / 12 µm
Lateral Resolution at Focus with OCT Scan
Lens Kit
20 µm (OCT-LK4)
Table 5 Vega Specifications
Some specifications depend on the actual type of accessory used. (Selection Preferred Systems)
SD-OCT Base Unit Chapter 10: Mechanical Drawings
Rev A, March 3, 2017 Page 53
Chapter 10 Mechanical Drawings
Figure 62 Base Unit Dimensions
SD-OCT Base Unit Chapter 11: Regulatory
Page 54 MTN008437-D02
Chapter 11 Regulatory
As required by the WEEE (Waste Electrical and Electronic Equipment Directive) of the European Community
and the corresponding national laws, Thorlabs offers all end users in the EC the possibility to return “end of
life” units without incurring disposal charges.
This offer is valid for Thorlabs electrical and electronic equipment:
Sold after August 13, 2005
Marked correspondingly with the crossed out “wheelie bin” logo (see right)
Sold to a company or institute within the EC
Currently owned by a company or institute within the EC
Still complete, not disassembled and not contaminated
As the WEEE directive applies to self-contained operational electrical and electronic products, this end of life
take back service does not refer to other Thorlabs products, such as:
Pure OEM products, that means assemblies to be built into a unit by the user (e. g. OEM laser driver
cards)
Components
Mechanics and optics
Left over parts of units disassembled by the user (PCB’s, housings etc.).
If you wish to return a Thorlabs unit for waste recovery, please contact Thorlabs or your nearest dealer for
further information.
11.1. Waste Treatment is Your Own Responsibility
If you do not return an “end of life” unit to Thorlabs, you must hand it to a company specialized in waste recovery.
Do not dispose of the unit in a litter bin or at a public waste disposal site.
11.2. Ecological Background
It is well known that WEEE pollutes the environment by releasing toxic products during decomposition. The
aim of the European RoHS directive is to reduce the content of toxic substances in electronic products in the
future.
The intent of the WEEE directive is to enforce the recycling of WEEE. A controlled recycling of end of life
products will thereby avoid negative impacts on the environment.
Wheelie Bin Logo
Rev A, March 3, 2017 Page 55
Chapter 10 Thorlabs Worldwide Contacts
USA, Canada, and South America
Thorlabs, Inc.
56 Sparta Avenue
Newton, NJ 07860
USA
Tel: 973-300-3000
Fax: 973-300-3600
www.thorlabs.com
www.thorlabs.us (West Coast)
Email: sales@thorlabs.com
Support: techsupport@thorlabs.com
UK and Ireland
Thorlabs Ltd.
1 Saint Thomas Place
Ely CB7 4EX
Great Britain
Tel: +44 (0) 1353-654440
Fax: +44 (0) 1353-654444
www.thorlabs.com
Email: sales.uk@thorlabs.com
Support: techsupport.uk@thorlabs.com
Europe
Thorlabs GmbH
Hans-Böckler-Str. 6
85221 Dachau / Munich
Germany
Tel: +49-(0) 8131-5956-0
Fax: +49-(0) 8131-5956-99
www.thorlabs.de
Email: europe@thorlabs.com
Scandinavia
Thorlabs Sweden AB
Bergfotsgatan 7
431 35 Mölndal
Sweden
Tel: +46-31-733-30-00
Fax: +46-31-703-40-45
www.thorlabs.com
Email: scandinavia@thorlabs.com
France
Thorlabs SAS
109, rue des Côtes
78600 Maisons-Laffitte
France
Tel: +33 (0) 970 444 844
Fax: +33 (0) 825 744 800
www.thorlabs.com
Email: sales.fr@thorlabs.com
Brazil
Thorlabs Vendas de Fotônicos Ltda.
Rua Riachuelo, 171
São Carlos, SP 13560-110
Brazil
Tel: +55-16-3413 7062
Fax: +55-16-3413 7064
www.thorlabs.com
Email: brasil@thorlabs.com
Japan
Thorlabs Japan, Inc.
3-6-3 Kitamachi,
Nerima-ku, Tokyo 179-0081
Japan
Tel: +81-3-6915-7701
Fax: +81-3-6915-7716
www.thorlabs.co.jp
Email: sales@thorlabs.jp
China
Thorlabs China
Room A101, No. 100, Lane 2891,
South Qilianshan Road
Putuo District
Shanghai 200331
China
Tel: +86 (0) 21-60561122
Fax: +86 (0) 21-32513480
www.thorlabschina.cn
Email: chinasales@thorlabs.com
SD-OCT Base Unit Chapter 12: Thorlabs Worldwide Contacts
M0009-510-531-A
www.thorlabs.com
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