Three laser two-tone setup for measurement of photodiode intercept points.

The third-order intermodulation product intercept (IP3) has become an important figure of interest for photodiodes in high-performance, externally modulated, analog links. With the desire for highly linear photodiodes comes the need to be able to accurately measure the device without additional variables. The purpose of this work is to redesign the current IP3 setup to accurately measure the third order intermodulation distortions of the photodiode and to also be able to measure the second order intercept point (IP2) using the same setup. The new setup will isolate equipment contributed nonlinearities by maintaining a small RF drive voltage amplitude on the modulators and by optically changing the photodiode input modulation depth while maintaining a constant input optical power to the photodiode. The goal is to measure a specific knee point where different slopes will indicate the change to photodiode dominated nonlinearity.