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.
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.
We present a high-speed time-domain shot-noise-limited balanced homodyne detector that is suitable for the detection of the quantum states of nanosecond pulsed optical fields. The detector can detect the quantum noise of individual nanosecond optical pulses at a repetition rate of 40 MHz and achieve a signal-to-noise ratio of above 14.5 dB at a local oscillator power of 9.9×107 photons per pulse. The stability of the detector is characterized via an Allan variance measurement, and superior stability is observed. The detector is especially applicable in the fields of quantum optics and quantum information, where high-speed time-domain detection of nanosecond pulsed optical field quadratures is required.
We design and experimentally characterize a balanced homodyne detector optimized for high-repetition-rate (100 MHz) pulsed optical sources. Unlike conventional transimpedance-amplifier architectures, which suffer from nonlinearities and dynamic instabilities with ultrashort pulses, our approach allows to directly amplify the photocurrent extracted at the common photodiode node without feedback loops. A theoretical model describing the detector response, noise, and pulse-to-pulse correlations is developed, providing quantitative predictions for the signal variance, signal-to-noise ratio (SNR), and inter-pulse correlations. Implemented with two matched InGaAs photodiodes illuminated by a 1030 nm mode-locked laser at 100 MHz, the detector exhibits excellent linearity and shot-noise-limited scaling of the signal variance with optical power. Optimizing the temporal integration window yields a maximum SNR of about 14 dB, while correlation measurements confirm negligible inter-pulse correlations. These results demonstrate that the proposed architecture offers a robust and simple solution for high-speed pulsed homodyne detection, suitable for quantum optics and continuous-variable quantum information applications.
Low-noise, efficient, phase-sensitive time-domain optical detection is essential for foundational tests of quantum physics based on optical quantum states and the realization of numerous applications ranging from quantum key distribution to coherent classical telecommunications. Stability, bandwidth, efficiency, and signal-to-noise ratio are crucial performance parameters for effective detector operation. Here we present a high-bandwidth, low-noise, ultra-stable time-domain coherent measurement scheme based on balanced homodyne detection ideally suited to characterization of quantum and classical light fields in well-defined ultrashort optical pulse modes.
Quantum key distributions, which could make legitimate communication parties Alice and Bob achieve the same random key with unconditional security, will have broad applications in defense, commerce, and communication. The protocol of the continuous variable quantum key distribution (CVQKD) has many advantages, such as easy preparation of the light source, high detector efficiency, and good compatibility with the classic fiber-optic communication systems. In recent years, great progress in the research of CVQKD has been made both theoretically and experimentally. In the protocol, the quadratures of the optical field with Gaussian or Non-Gaussian modulation are employed as the carriers of the key.The quadratures of the pulsed optical quantum states in CVQKD can be detected with a time-domain pulsed homodyne detector. The performance of the detector has great influences on the excess noises and the safe key rate of the quantum communication system. The measurement accuracy, which depends crucially on the common mode rejection ratio and the long-term stability, is the key performance of the detector. In order to improve the accuracy of measurement and avoid saturating the detector, we propose and demonstrate a technique to balance the two output beams of a 50/50 fiber coupler of the homodyne detector automatically. The auto-balance technique, which improves the long-term stability and high common mode rejection ratio, is described in the following.Firstly, the relation between the balance degree and the measurement accuracy is theoretically analyzed in detail. The result shows that a balance degree larger than 10-4 should be reached to ensure a high precision measurement when the intensity of the local oscillator pulse is 108 photons per pulse. Secondly, a fiber-based variable attenuator based on computer-controlled linear stepper motor is designed. The linear stepper motor that is used to drive the fiber coils has a small dimension of 20 cm20 cm28 cm and a minimum step size of 78 nm, and is controlled through the I/O port of a multifunction data acquisition card connected to a computer. The attenuations of the fiber coils of different radii are detected. The precision of attenuation is estimated to be on the order of 10-6 per 100 nm.The principle of the feedback control is described. A method of changing step-size which depends on the balance degree is proposed to fulfill a fast auto-balance process. Using the auto-feedback-control system, a balance degree of about 1.5610-6 can be achieved. The procedure of auto-balance takes about 1 s, and the evolution curves that represent the transformation process from various unbalanced states to the balanced state are presented.The auto-balance apparatus can ensure that the time-domain pulsed homodyne detector run stably in a longterm with a high common mode rejection ratio. The nonlinear and saturation effects due to the drift of the balance point are eliminated. The presented auto-balance time-domain pulsed homodyne detector can be well integrated into the continuous variable quantum key distribution system, and is expected to play an important role in improving the measurement accuracy and reducing the excess noises of the system. We believe that it could also be found to have potential applications in other areas.
This thesis reports the realization and applications of a versatile wideband balanced homodyne detector operating in the time domain and intended for Quantum Optical Tomography. The detector can work with high repetition rate lasers used for the production and measurement of the electric field quadratures of quantum states of light. Full characterization of the detector by shot-noise measurements and by verifying its capability to reconstruct the density matrix and Wigner function of various states of interest is given. By overcoming photodiodes response mismatch, high frequency electronics issues and by choosing an appropriate optical set-up, a high level of common mode suppression (52.4dB) and a low electronic noise gave a shot-to-electronic noise ratio of I3dB for a Local Oscillator with 6.2 x 108 photons-per-pulse on a ~ 100MHz bandwidth. Results for the characterization of a single-photon Fock state are presented. An average efficiency of 56% was obtained for the generation/detection of the state.
A balanced homodyne detector, with a maximum common mode rejection ratio and clearance of 75.2 dB and 37 dB, is experimentally obtained with two arbitrary photodiodes of the same model. On the basis of self-subtraction photodetector scheme, we divide the influence of photodiodes on the common mode rejection ratio into two parts, including magnitude and phase of output signal. The discrepancy of quantum efficiency and dark current affects magnitude of output signal of photodiodes, which is compensated by adjusting the splitter ratio. The difference of the equivalent capacitance and resistance affects the phase of output signal of photodiodes, which is compensated by the differential fine tuning circuit and adjustable bias voltage circuit. With these designs, the developed homodyne detector can be used for measuring accurately the squeezed state.