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 3.2μV 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.