Data Sheet
September 1999
1241/1243/1245-Type Uncooled Laser Transmitter
Offering multiple output power options and SONET/SDH compatibility, the 1241/1243-Type Uncooled Laser Transmitter is manufactured in a 20-pin, plastic DIP with a single-mode fiber pigtail.
Features
■Backward compatible with 1227/1229/1238-Type Laser Transmitters
■Space-saving, self-contained, 20-pin DIP
■Uses field-proven, reliable InGaAsP MQW laser
■Requires single 5 V power supply
■SONET/SDH compatible
■Uncooled laser with automatic optical power control for constant output power over case temperature range
■No thermoelectric cooler required; reduces size and power consumption
■Uses low-power dissipation CMOS technology
■Qualified to meet the intent of Bellcore reliability practices
■Operates over data rates to 1062.5 Mbits/s (NRZ)
■Operation at 1.3 µm or 1.55 µm wavelength
■Typical average output power options of –11 dBm, –8 dBm, –5 dBm, –2 dBm, and 0 dBm
■ECL compatible, differential inputs
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Operating temperature range of –40 °C to +85 °C
Transmitter-disable option
Applications
■Telecommunications
—Interand intraoffice SONET/ITU-T SDH
—Subscriber loop
—Metropolitan area networks
■High-speed data communications
—Fibre channel (FC-0)
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Data Sheet |
1241/1243/1245-Type Uncooled Laser Transmitter |
September 1999 |
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Description
The 1241/1243/1245-type Laser Transmitters are designed for use in transmission systems and highspeed data communication applications. Used in intraoffice and intermediate-reach applications, the transmitters are configured to operate at SONET rates up to OC-12, as well as at ITU-T synchronous digital hierarchy (SDH) rates up to STM-4. Specific versions are also capable of operating up to 1062.5 Mbits/s.
The transmitter meets all present Bellcore GR-253- CORE requirements, ANSI T1.117-1991 SONET sin- gle-mode, and the ITU-T G.957 and G.958 recommendations. (See Table 5 to select transmitters for the various SONET/SDH segments.)
The transmitter requires a single power supply (+5 V or –5 V) and operates over data rates of 1 Mbits/s to 622 Mbits/s (NRZ). Automatic power control circuitry
provides constant optical output power over the operating case temperature range. The automatic power control circuitry also compensates for laser aging. The optical wavelength tolerance at 25 °C is 1310 nm. The temperature coefficient of wavelength for 1.3 µm FabryPerot transmitters (1241-Type) is approximately
0.4 nm/°C. The temperature coefficient of wavelength for 1.3 µm and 1.55 µm distribut ed-feedback (DFB) transmitters (1243/1245-Type) is approximately
0.1 nm/°C.
Transmitters are available for operation over several different temperature ranges from –40 °C to +85 °C. Manufactured in a 20-pin DIP, the transmitter consists of a hermetic, InGaAs laser and a single CMOS driver IC. The low-power consumption circuit provides modulation, automatic optical output power control, and data reference. The module can be driven by either acor dc-coupled data in single-ended or differential configuration. (See Recommended User Interfaces section for typical connection schemes.) The laser bias and backfacet monitor currents are electrically accessible for transmitter performance monitoring. The transmitter optical output may be disabled by a logic-level input.
Functional Overview
Transmitter Circuit Description and
Operation
Figure 1 shows a simplified schematic of the transmitter; pin information is listed in Table 1. The laser within the transmitter is driven by a single CMOS integrated circuit, which provides the input data signal reference level with automatic, temperature-compensated laser bias, and modulation-current control. A back-facet pho-
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todetector diode within the laser module provides an indication of the laser's average optical output power. The back-facet diode current is accessible as a voltage proportional to photocurrent through pins 17 and 19 on the transmitter. The back-facet diode also forms part of the feedback control circuit, which helps maintain constant output power.
The laser bias current is accessible as a dc-voltage by measuring the voltage developed across pins 2 and 4 of the transmitter. Dividing this voltage by 10 Ω will yield the value of the laser bias current. This value will change up or down in response to operating temperature, power supply voltage, data pattern, and laser aging characteristics.
Table 1. Pin Descriptions
Pin Number |
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1 |
No user connection* |
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2 |
Laser bias monitor (+)† |
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3 |
No user connection* |
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4 |
Laser bias monitor (–)† |
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5 |
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VEE |
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6 |
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VCC |
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7 |
Transmitter disable |
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8 |
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VCC |
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9 |
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VCC |
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10 |
No user connection† |
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11 |
Case ground (RF ground) |
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12 |
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VCC |
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13 |
Case ground (RF ground) |
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14 |
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VEE |
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15 |
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DATA |
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16 |
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DATA |
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17 |
Laser back-facet monitor (–)* |
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18 |
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VCC |
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19 |
Laser back-facet monitor (+)* |
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20 |
No user connection† |
*Pins designated as no user connection should not be tied to ground or any other circuit potential.
†Laser back-facet and bias monitor functions are customer-use options that are not required for normal operations of the transmitter. They are normally used during manufacture and for diagnostics.
Agere Systems Inc.
Data Sheet |
1241/1243/1245-Type Uncooled Laser |
September 1999 |
Functional Overview (continued)
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VCC |
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BACK-FACET |
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LASER |
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DETECTOR |
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15 k• |
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FIBER PIGTAIL |
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(2) |
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(+) |
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LASER BIAS MONITOR VOLTAGE |
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(4) |
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(–) |
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15 k• |
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(19) |
15 k• |
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(+) |
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LASER BACK-FACET MONITOR VOLTAGE |
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(–) |
(17) |
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15 k• |
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BAND GAP |
AUTOMATIC POWER |
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IBF |
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10 • |
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REFERENCE |
CONTROL CIRCUITRY |
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(16) |
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TEMPERATURE |
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DATA |
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SENSOR |
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INPUT DATA |
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COMPARATOR |
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30 k• |
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VCC – 1.3 V |
MODULATION |
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IBIAS |
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CIRCUITRY |
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IMOD |
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30 k•
(15)
DATA
(7)
TRANSMITTER DISABLE
1-868(C).h
Figure 1. Simplified Transmitter Schematic Input Data
Input Data
Data enters the transmitter through a comparator. These inputs have internal pull-down resistors to a voltage reference that is 1.3 V below VCC. This configuration allows the transmitter to be driven from either a single-ended or a differential input signal. Since the input is a comparator instead of a gate, the absolute input signal levels are not important when the inputs are driven differentially. When driven single-ended, however, the input signal voltage should be centered around VCC – 1.3 V to eliminate pulse-width distortion. With a single-ended input, either input can be used and the unused input can be left as an open circuit due to the internal reference shown in Figure 1. The optical output signal will be in the same sense as the input data—an input logic high turns the laser diode on and an input logic low turns the laser diode off. However, if the negative input is used with a single-ended data
input signal, the optical signal will be the complement of the data input signal.
The differental inputs of the 1241 Gbit versions are ter- minated internally with 100 Ω between the DATA and DATA inputs.
Minimum Data Rate
Because the modulation and bias control circuitry are influenced by the input data pattern, the standard transmitter cannot be used in burst-mode type applications. For burst-mode applications, please contact your Agere Account Manager. The minimum data rate (pseudorandom data, 50% average duty cycle) for the 1241/1243/1245-Type Transmitters is approximately
1 Mbit/s.
Agere Systems Inc. |
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Data Sheet |
1241/1243/1245-Type Uncooled Laser Transmitter |
September 1999 |
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Functional Overview (continued)
Since most applications operate at very high data rates, high-frequency design techniques need to be used to ensure optimum performance from the transmitter and interfacing circuitry. Input signal paths should be kept as short and as straight as possible; differential signal lines should be equal in length, and controlled-impedance stripline or microstrip construction should always be used when laying out the printedwiring board traces for the data lines. The Recommended User Interfaces section of this data sheet shows several methods of interfacing to the transmitter.
Power Supplies
The transmitter is configured for operation from either a single +5 V power supply or a single –5 V power supply. For positive power supply operation, connect Vcc to the +5 V power supply and connect VEE to ground or circuit common. For operation from a –5 V power supply, connect VCC to ground and connect VEE to the –5 V power supply. Whichever option is chosen, the VCC or VEE connection to the transmitter should be well filtered to prevent power supply noise from interfering with transmitter operation.
Transmitter Specifications
Optical Output Power
During manufacture, the optical output power of every transmitter is tuned to the typical value specified in the data sheet for that particular transmitter code. The tuning is performed at room ambient and a power supply voltage of 5 V. The minimum and maximum values listed in the data sheet for each code group reflect the worst-case limits that the transmitter is expected to operate within over its lifetime and over the allowed power supply and the operating temperature range.
Every transmitter shipped receives a final test, which includes a SONET eye-mask test at either the OC-3 (STM-1) data rate of 155.52 Mbits/s, the OC-12 (STM4) data rate of 622.08 Mbits/s, or the fibre channel FC-0 data rate of 1062.5 Mbits/s. The eye-mask test is meant to examine the performance of the transmitter's output optical waveform relative to a minimum data pattern eye opening.
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Connector Options
The standard optical fiber pigtail is 8 µm core singlemode fiber having a 0.036 in. (914 µm) diameter tightbuffered outer-jacket. The standard length is 39 in. ± 4 in. (1 m ± 10 cm) and can be terminated with either an SC or FC-PC optical connector. Other connector
options may be available on special order. Contact your Agere Account Manager for ordering information.
Handling Precautions
CAUTION: This device is susceptible to damage as a result of electrostatic discharge (ESD). Take proper precautions during both handling and testing. Follow guidelines such as JEDEC Publication No. 108-A (Dec. 1988).
Although protection circuitry is designed into the device, take proper precautions to avoid exposure to ESD. Agere employs a human-body model (HBM) for ESD-susceptibility testing and protection-design evaluation. ESD voltage thresholds are dependent on the critical parameters used to define the model. A standard HBM (resistance = 1.5 kΩ , capacitance = 100 pF) is widely used and, therefore, can be used for comparison purposes. The HBM ESD withstand voltage established for the 1241-/1243-Type Transmitter is ±1000V.
Transmitter Processing
The transmitter can withstand normal wave-soldering processes. The complete transmitter module is not hermetically sealed; therefore, it should not be immersed in or sprayed with any cleaning solution or solvents. The process cap and fiber pigtail jacket deformation temperature is 85 °C. Transmitter pins can be wavesoldered at maximum temperature of 250 °C for
10 seconds.
Installation Considerations
Although the transmitter features a robust design, care should be used during handling. The optical connector should be kept free from dust, and the process cap should be kept in place as a dust cover when the device is not connected to a cable. If contamination is present on the optical connector, canned air with an extension tube can be used to remove any debris. Other cleaning procedures are identified in the technical note, Cleaning Fiber-Optic Assemblies (TN95010LWP).
Agere Systems Inc.