Unknown chip on diode

[Exerd]

I was examining an 808nm diode from a very old laser tonight, and I noticed a small chip onboard which I had not seen before on a diode. I thought that it might be a capacitor, or maybe even a photocell for feedback. Hoping for someone to confirm. :yh:

 

[HIMNL9]

It's a photodiode.

It takes the light from the back of the chip, and is normally used in "feedback regulated drivers" for read the output power and regulate the current.