Sulasailor, sorry to disappoint you, but the POET detector has nothing to do with the Luxmux deal. POET delivers superluminescent diodes (SLED) to Luxmux, not detectors. An SLED is a light source, not a light detector.

An SLED sends out light at many different wavelengths ("colors") at the same time, illuminating the object to be probed. The characteristics of the reflected light (at these multiple wavelengths) allows for determining characteristics of the probed material. Yes, this requires a detector resp. many detectors at different wavelengths.

However, the POET detector is not part of the deal. Look at the Luxmux BeST-SLED brochure, and you get an idea why: Their spectrometers operate in the 1200 – 1800 nm range, while the POET detector operates at 850 nm. The wavelengths don't match. Additionally, you need to detect a multitude of wavelengths.

As a rule-of-thumb, GaAs is suitable for the shorter wavelengths while you'd use InP for the longer wavelengths.