Data Sheet
1241/1243/1245-Type Uncooled Laser Transmitter
September 1999
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.
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 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.
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.)
Table 1. Pin Descriptions
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 µmFabry-
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.
Pin Number
Name
No user connection*
Laser bias monitor (+)†
No user connection*
1
2
3
4
Laser bias monitor (–)†
5
VEE
6
VCC
7
Transmitter disable
8
VCC
9
VCC
No user connection†
Case ground (RF ground)
VCC
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.
10
11
12
13
14
15
16
17
18
19
20
Case ground (RF ground)
VEE
DATA
DATA
Laser back-facet monitor (–)*
VCC
Laser back-facet monitor (+)*
No user connection†
Functional Overview
* 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.
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-
2
Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
