Protect Laser Diodes from Overheating During Characterization Tests

摘要

Laser diode temperature must be tightly controlled during characterization tests. How you do that depends on the laser's physical configuration. Laser diodes such as those used in fiber-optic communications systems and data storage devices require extensive testing during development and production. The high value of the end product and intense pricing pressure mandate the use of only those lasers known to have acceptable characteristics. To get the highest possible yield, it is important to protect the laser diodes from damage during these tests. The two principal types of laser diodes are the edge-emitting laser and the vertical-cavity surface-emitting laser (VCSEL), both of which are produced with semiconductor wafer processing techniques. These diodes do not require optical pumping but rather emit light when their current reaches a lasing threshold. The first opportunity to test an edge-emitting laser is after a group of diodes is cut from the wafer in the form of a bar that exposes the sides where light exits. After the edges are coated with a reflective film, individual diodes are probed and subjected to current sweeps to determine their light-current-voltage (L-I-V) characteristics. The same measurements are made on VCSELs, but they can be individually tested in the uncut state since their emissions are perpendicular to the wafer plane.