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 1.55 �m wavelength Typical average output power options of �11 dBm, �8 dBm, �5 dBm, �2 dBm, and 0 dBm ECL compatible, differential inputs Operating temperature range +85 �C Transmitter-disable option
Offering multiple output power options and SONET/SDH compatibility, the 1241/1243-Type Uncooled Laser Transmitter is manufactured a 20-pin, plastic DIP with a single-mode fiber pigtail.Applications
Telecommunications Inter- and intraoffice SONET/ITU-T SDH Subscriber loop Metropolitan area networks High-speed data communications Fibre channel (FC-0)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 OC-12, as well as at ITU-T synchronous digital hierarchy (SDH) rates to STM-4. Specific versions are also capable of operating to 1062.5 Mbits/s. The transmitter meets all present Bellcore GR-253CORE requirements, ANSI T1.117-1991 SONET single-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) 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 is 1310 nm. The temperature coefficient of wavelength for 1.3 �m FabryPerot transmitters (1241-Type) is approximately 0.4 nm/�C. The temperature coefficient of wavelength for 1.3 �m and 1.55 �m distributed-feedback (DFB) transmitters (1243/1245-Type) is approximately 0.1 nm/�C. Transmitters are available for operation over several different temperature ranges from to +85 �C. Manufactured 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 ac- or 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.
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 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 Name No user connection* Laser bias monitor No user connection* Laser bias monitor VEE VCC Transmitter disable VCC No user connection Case ground (RF ground) VCC Case ground (RF ground) VEE DATA Laser back-facet monitor * VCC Laser back-facet monitor No user connection
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 pho2
* 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.LASER BACK-FACET DETECTOR (2) LASER BIAS MONITOR VOLTAGE 15 k FIBER PIGTAIL
Figure 1. Simplified Transmitter Schematic Input Data Input Data enters the transmitter through a comparator. These inputs have internal pull-down resistors to a voltage reference that 1.3 V below V CC. 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 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 Agere Systems Inc. input signal, the optical signal will be the complement of the data input signal. The differental inputs of the 1241 Gbit versions are terminated internally with 100 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.