Model 2510-AT
autotuning TEC
SourceMeter
Model 2602B
dual channel
SourceMeter
Regulate module
temperature
LD
module
Light
output Model 2500INT
integrating
sphere
Source I,
Measure V
Measure I
GPIB cable
September 2013 www.laserfocusworld.com Laser Focus World 50
LASER DIODE AND VCSEL TEST continued
lowers throughput. In this scenario, a
large percentage of this test sequence is
consumed by communicating information to and from the PC. However, recent advances in SMU architecture are
beginning to eliminate these communications delays.
The latest generation of SMUs,
like Keithley’s Series 2600B System
SourceMeter SMU instruments, can in-
crease the throughput of complicated
test sequences dramatically by decreasing
the amount of traffic
over the communica-
tions bus. The majori-
ty of the test sequence
is embedded in the instrument itself. The
Test Script Processor (TSP) is a full-fea-
tured test sequence engine that allows con-
trol of the test sequence, with internal pass/
fail criteria, math, calculations, and con-
trol of digital I/O. The TSP can store a us-
er-defined test sequence in memory and
execute it on command. This limits the set-
up and configuration time for each step in
the test sequence and increases throughput
by lessening the amount of communica-
tions to and from the instrument and PC.
Recent advances in SMU architecture
can speed and simplify the module testing
process; for more information, download
the application note “High Throughput
DC Production Testing of Laser Diode
Modules and VCSELs” at http://keithley.
com/data?asset=50303.
ACKNOWLEDGEMENT
Series 2600B System SourceMeter SMU
instruments are a registered trademark of
Keithley Instruments.
Dale Cigoy is a lead applications engineer for
Keithley Instruments, Inc., a part of the Tek-tronix test and measurement group, Cleveland, OH; e-mail: dcigoy@keithley.com; www.
keithley.com.
FIGURE 4. In a typical LIV test setup for an LD module, a Keithley Model 2602B
characterizes the module and monitors the light output while a Model 2510-AT controls the
LD module’s thermoelectric cooler (TEC) element and maintains stable module temperature.
Proportional, integral, and derivative (P, I, and D) values for closed-loop temperature
control are determined by the instrument using a modified Zeigler-Nichols algorithm, which
eliminates the need to determine the optimal values for these coefficients experimentally.
The PC programs the meters via the general-purpose interface bus (GPIB), coordinates the
execution of the test, and then collects and analyzes the measurement results.
