Keithley 5187 pulse laser free download

File name 5187_pulse_laser.pdf

Pulse Testing Of Laser Diodes By: Paul Meyer Keithley Instruments, Inc. Thermal management is critical during the testing of laser diodes at the semiconductor wafer, bar, and chip-on-carrier (submount) production stages. This has led to pulse testing of laser diodes to minimize power dissipation. Still, pulse mode testing requires careful selection and configuration of test equipment to avoid measurement errors and achieve the most cost-effective results. L-I-V Testing Basic Light intensity-Current-Voltage (L-I-V) testing is an I-V test with the addition of optical power measurements. This test is primarily used to sort laser diodes or weed out bad devices before they become part of an assembly. The device under test (DUT) is subjected to a current sweep while the forward voltage drop is recorded for each step in the sweep. Simultaneously, instrumentation is used to monitor the optical power output of the laser's front facet and rear facet. The resulting data is then analyzed to determine laser characteristics, including lasing threshold current, quantum efficiency, and "kink" detection (localized negative slope in the first derivative optical power output vs. injection current curve). L-I-V characteristics are a function of laser temperature, which must be tightly controlled during the test, just as in normal operation. The principal reasons for performing low duty cycle pulsed L-I-V testing are thermal management, thermal response, and transient response. Typically, these issues arise because of the need to perform DC testing of laser diodes prior to mounting on a thermal management device, such as a heat sink or TEC (thermoelectric cooler - also called a Peltier device). Vertical cavity surface emitting lasers (VCSELs) can be tested at the wafer stage prior to dicing because they radiate optical power perpendicular to the wafer plane. Although many VCSELs can be tested in non-pulse mode due to their high efficiency, higher power devices require pulse testing in the early stages of production. This avoids high thermal gradients that would induce mechanical stresses if non-pulse DC testing were performed. The first opportunity to test an edge emitting laser diode is at the bar stage, where a linear array of diodes is cut from the wafer to expose the sides where light exits. After the wafer has been cut into bars, the edges of the bar are polished to form a suitable optical interface. The individual diodes on the bar then undergo L-I-V testing before further processing. The data from these tests are used to correlate optical performance characteristics, electrical characteristics, and semiconductor process information. After a laser diode has passed the bar stage tests, it is diced into chips, which are mounted on sub-carriers. These are small metallic or ceramic mounts designed to ease handling of tiny laser chips during final assembly of the laser diode modules (LDMs) in whi