Ultrastable Fiber-Based Time-Domain Balanced Homodyne Detector for Quantum Communication

We present an ultrastable fiber-based time-domain balanced homodyne detector which can be used for precise characterization of pulsed quantum light fields. A variable optical attenuator based on bending the fiber is utilized to compensate for the different quantum efficiencies of the photodiodes precisely, and a common mode rejection ratio of above 76 dB is achieved. The detector has a gain of 3.2 μV per photon and a signal-to-noise ratio above 20 dB. Optical pulses with repetition rates up to 2 MHz can be measured with a detection efficiency of 66%. The stability of the detector is analyzed via an Allan variance measurement and the detector exhibits superior stability which enables a 100-s window for measurement without calibration.