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1241FBLC Datasheet(PDF) 2 Page - Agere Systems |
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1241FBLC Datasheet(HTML) 2 Page - Agere Systems |
2 / 12 page 2 Agere Systems Inc. Data Sheet 1241/1243/1245-Type Uncooled Laser Transmitter September 1999 Description The 1241/1243/1245-type Laser Transmitters are designed for use in transmission systems and high- speed 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 recommen- dations. (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 operat- ing case temperature range. The automatic power con- trol 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 Fabry- Perot transmitters (1241-Type) is approximately 0.4 nm/°C. The temperature coefficient of wavelength for 1.3 µm and 1.55 µm distributed-feedback (DFB) transmitters (1243/1245-Type) is approximately 0.1 nm/°C. Transmitters are available for operation over several dif- ferent temperature ranges from –40 °C to +85 °C. Man- ufactured 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 modula- tion, 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 configu- ration. (See Recommended User Interfaces section for typical connection schemes.) The laser bias and back- facet 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 transmit- ter; 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- 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 con- stant 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 tempera- ture, power supply voltage, data pattern, and laser aging characteristics. Table 1. Pin Descriptions * 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 trans- mitter. They are normally used during manufacture and for diagnostics. Pin Number Name 1 No user connection* 2 Laser bias monitor (+)† 3 No user connection* 4 Laser bias monitor (–)† 5VEE 6VCC 7 Transmitter disable 8VCC 9VCC 10 No user connection† 11 Case ground (RF ground) 12 VCC 13 Case ground (RF ground) 14 VEE 15 DATA 16 DATA 17 Laser back-facet monitor (–)* 18 VCC 19 Laser back-facet monitor (+)* 20 No user connection† |
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