Data Sheet

September 1999

Agere Systems Inc.

3

1241/1243/1245-Type Uncooled Laser

1-868(C).h

Figure 1. Simplified Transmitter Schematic Input Data

LASER BACK-FACET MONITOR VOLTAGE

15 k•

(2)

(4)

(+)

(–)

15 k•

LASER BIAS MONITOR VOLTAGE

15 k•

(19)

(17)

(+)

(–)

15 k•

BAND GAP

REFERENCE

AUTOMATIC POWER

CONTROL CIRCUITRY

INPUT DATA

COMPARATOR

MODULATION

CIRCUITRY

TEMPERATURE

SENSOR

t

LASER

BACK-FACET

DETECTOR

FIBER PIGTAIL

10 •

DATA

(16)

(7)

(15)

TRANSMITTER

DISABLE

30 k•

30 k•

DATA

Input Data

Data enters the transmitter through a comparator.

These inputs have internal pull-down resistors to a volt-

tion 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

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 applica-

tions. 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.