Olson Technology OTPN-3850-SA User Manual

Table of Contents

Model OTPN-3850-SA

3.85GHz Wideband FTTH PON Receiver

Instruction Manual

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025-000641 REV X5 06 Sep 2012 Page 1

Table of Contents

INTRODUCTION

THEORY OF OPERATION

BLOCK DIAGRAM

INSTALLATION / ENVIRONMENTAL CONSIDERATIONS

OPTICAL CONNECTORS AND CLEANING

INTERNAL CONTROLS

EXTERNAL INDICATORS AND CONNECTORS

SETUP AND OPERATION

ACCESSORIES AND SYSTEM APPLICATIONS

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025-000641 REV X5 Olson Technology, Inc. Page 2

INTRODUCTION

The Olson Technology, Inc. Model OTPN-3850-SA provides 50-3,850MHz bandwidth,
allowing it to carry CATV signals from 50-870MHz along with two stacked 950-2,150MHz
groups of L-Band signals. The L-Band signals are at a level at least 10dB below the CATV
signals.

The optical input contains downstream forward path CATV and L-Band signals at 1550nm,
downstream Ethernet data at 1490nm and upstream Ethernet data at 1310nm. The optical
output passes the 1310nm and 1490 signals. The 1550nm wavelength goes to a photodiode
and is amplified. The optical input level is sensed to trigger an optical alarm when the input
light level is less than -10dBm. The input optical level is also used to control a PIN diode
attenuator to maintain constant RF level as the optical input level varies from 0dBm to -6dBm.
The signal is then amplified and output to a single “F” connector output.

The OTPN-3850-SA Integrated PON Receiver dimensions are 1.05" H x 3.15" W x 4.75" L.
Optical connections are via two SC/APC connectors, one for the optical input carrying
1310nm, 1490nm & 1550nm, the second for the optical output carrying the 1310nm and
1490nm optical signals. The unit is powered from +12 to +16 Volts DC at 0.2A maximum. A
Green Power LED is lit whenever valid supply voltage is applied. A Red LED is lit only when the
1550nm optical power drops below -10dBm, the minimum usable optical input level. The right
side of the unit has a single “F” connector providing a 50-3,850MHz signal.

The OTPN-3850 is designed to give optimum performance at a received CATV optical power
(1550nm) of -4dBm although it will give good performance over the full rated optical input
range of 0dBm to -6dBm.

THEORY OF OPERATION

Refer to the Block Diagram for the following discussion. The Optical In to the receiver, actually
carries three wavelengths. The 1550nm ±10nm wavelength carries the downstream CATV
and L-Band signals. This wavelength passes through the FWDM (Filter Wavelength Division
Multiplexer) to the optical detector. The 1310nm and 1490nm wavelengths usually carry the
Ethernet signals in a Fiber-to-the-Home (FTTH) PON application. They pass through the
FWDM to the Optical Out port. The 1490nm wavelength usually carries the downstream
Ethernet signals and the 1310nm wavelength carries the upstream Ethernet signals.

The 1550nm light that reaches the photodiode (PD) is processed by two different circuits. The
first circuit measures the DC average current to determine what optical light level is hitting the
photodiode. This is converted to a logarithmic value with a scale factor of 1 Volt per decade. An
input level of -10dBm yields -1.0 Volts, 20dBm yields -2.0 Volts, etc. See Figure 3 for details of
this output. The photodiode RF output also goes to a low-noise, wide-bandwidth RF amplifier.
The output of the first amplifier goes to a wide bandwidth PIN diode attenuator which is con­trolled by the Optical Level signal to keep the RF output constant. For each 1dB drop in the
input optical level, the RF attenuation of the PIN diode attenuator is decreased by 2dB, match­ing the optical-to-RF conversion characteristics of the optical detector. This circuit is optimized
to operate over the optical input range from -6dBm to 0dBm. Note that these power levels

ONLY refer to the 1550nm energy in the fiber. Since there are multiple wavelengths
on the fiber, a simple optical power meter may be fooled by the 1310nm or 1490nm
power that may also be contained in the fiber. The easiest way to measure only the

1550nm power is to use the optical level function that is built into the OTPN-3850. See Figure
3 for the exact transfer function. The optical level function is calibrated at the factory and
rivals the accuracy of most field optical power meters.

025-000641 REV X5 Page 3Olson Technology, Inc.