VCSEL are now used as singlemode and multimode laser sources in many application fields. Many users are not laser expert and may discover VCSEL unstability late in a development …VCSEL Unstability can be related to two mains parameters : drive current and temperature. The following videos can help feeling how sensitive VCSEL unstability can be for a specific application.
Here is a video of the spectrum of VCSEL when changing its current from 90 mA to 140 mA. From a rather singlemode behavior it then goes to a highly multimode behavior.
This VCSEL has a multimode behavior at 140 mA. And this behavior is highly unstable when temperature is not very stable as you can see in the video below.
In conclusion, it is often very useful to check carefully the spectrum of VCSEL you intend to use in a system, without to be too much confident in a datasheet providing single-mode characterisctics, FWHM or wavelength. For demanding applications, this behaviour will not be reproductible enough and a quality check of each unit may be required.
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