Time-Domain Characterization of High-Speed Mid-Infrared Photodetectors Using a Laser-Based Non-Linear Vector Network Analyzer System

We describe a new system for broadband characterization of mid-infrared (MIR) photodetectors, manufactured by the VIGO System and encapsulated in TO-8 can. The system comprises a high repetition rate pulsed laser source, stimulating a detector in a special test fixture that is connected to ports of a vector network analyzer (VNA) with a pair of cables. After calibrating the VNA at the cable ends using the thru-reflect match (TRM) method supplemented with power and phase calibration, it operates in mode of nonlinear VNA, i.e. it is capable of measuring magnitude and phase spectra of harmonic signals both corrected for effects of systematic errors. In order to recover the differential signal at the detector reference plane on the can header, we utilize the transfer matrix of the test fixture, which counts 16 nonzero entries due to signal crosstalk in the fixture. This matrix is determined with another calibration procedure, based on measuring special built-inhouse standards, mounted inside TO-8 housing. With the matrix determined, we transfer the measured spectra to the TO-8 reference plane and then convert them with IFFT to the time-domain. This approach enables recovering sub-nanosecond differential pulses of amplitudes below 1 mV and speed up performance evaluation of MIR detectors tested.