Agilent / HP / Keysight 81519A

This is an Optical Receiver (optical to electrical converter) with a frequency response from DC to 400MHz.

It contains a PIN photodiode with a spectral response from 550 to 950nm and a response graph attached to the top of the instrument.

The 50ohms impedance electrical output is -1volt per mW of optical input and has an impulse response (transition) time of 1.1ns.

This unit is designed to be a general purpose optical front end for a wide variety of test and measurement instruments.

It powers up fine and responds to a flashlight beam shone into the input connector.