Is the output a single spatial transverse mode?
Yes, but it depends on the operating point of the VCSEL. Firecomms’ visible VCSEL operates in a single-mode fashion in those circumstances where the VCSEL remains Class 1 eye-safe, i.e. an output power of <390μW at the lowest operating temperature of 0°C, at room temperature. This translates to a maximum single mode power of ~0.3mW. In single mode operation, the VCSEL produces a circular, Gaussian far field beam profile with a FWHM of ~8 degrees. The side mode suppression ratio is always >10dB.
