Wafer probing of surface-emitting laser diodes

Contacts:

David Larsson, DTU Fotonik, 4525-5763 (davla@fotonik.dtu.dk)

Kresten Yvind, DTU Fotonik, 4525-6366 (kryv@fotonik.dtu.dk)

Il-Sug Chung, DTU Fotonik, 4525-6383 (ilch@fotonik.dtu.dk)

Schematic of VCSEL emitting light from the surface.

2D VCSEL array.

A) Schematic of an optical wafer probing system. B) Close-up of commercial wafer probing.

Vertical-cavity surface-emitting lasers or VCSELs are among the most widely used lasers today. They are for example used in optical mice as part of the movement sensor, and in short range (1-300 m) optical communications connecting equipment in local area networks (LANs), for example in a car or an office network. VCSELs have many advantages over the older edge emitting laser diodes both in performance and in cost and manufacturability: they have low power consumption and high wall-plug efficiency, they have very good beam shapes and they can be put into 2D-arrays. Furthermore the surface emission makes testing easy since the lasers can be tested directly on the wafer.

The aim of this project is to make a wafer testing system for VCSELs that we make at DTU’s cleanroom “Danchip”. These VCSELs are e.g. used as part of gas sensing systems (nanonoses) or as part of medical imaging systems (optical coherence tomography). The actual project will include some theoretical understanding of the lasers and of the optical and electrical quantities that we want to measure, e.g. optical power emitted from the laser and electrical resistance. However, the main challenges are practical and lie in designing a wafer probing system and some of the mechanical parts, e.g. probe holders for photodetectors and fibres. The mechanical parts will be realised by professionals at our mechanical workshop. All required measurement equipment is available in the laboratory. Data acquisition, data handling, data presentation and data interpretation (understanding) should also be performed by using computer controlled programming of the equipment (LabView) and data handling programs such as Origin or Matlab.