We present a high-speed balanced homodyne detector whose bandwidth is above 900 MHz and quantum to classical noise ratio reaches 12 dB respectively, which could be applied to the high-speed continuous variable quantum information.
In Gaussian-modulated coherent-state quantum key distribution, the measurement of quadratures of coherent states is performed by using a homodyne detector. However, conventional detectors usually suffer from narrow bands. We present a method to design a high-speed shot-noise-limited balanced homodyne detector. A 300-MHz bandwidth detector is experimentally tested and the level of shot noise is 14 dB higher than the electronic noise. The results show that a detector with this method is potential to design a GHz bandwidth detector for continuous variable quantum key distribution at a low level of ratio of shot noise to electronic noise.
Balanced homodyne detector (BHD) that can measure the field quadratures of coherent states has been widely used in a range of quantum information technologies. Generally, the BHD tends to suffer from narrow bands and an expanding bandwidth behavior usually traps into a compromise with the gain, electronic noise, and quantum to classical noise ratio, etc. In this paper, we design and construct a wideband BHD based on radio frequency and integrated circuit technology. Our BHD shows bandwidth behavior up to 1.2 GHz and its quantum to classical noise ratio is around 18 dB. Simultaneously, the BHD has a linear performance with a gain of 4.86 k and its common mode rejection ratio has also been tested as 57.9 dB. With this BHD, the secret key rate of continuous-variable quantum key distribution system has a potential to achieve 66.55 Mb/s and 2.87 Mb/s, respectively, at the transmission distance of 10 and 45 km. Besides, with this BHD, the generation rate of quantum random number generator could reach up to 6.53 Gb/s.
We study a relatively excellent BHD(Balanced Homodyne Detector)with large bandwidth and low noise pre-amplification, which is different from the specific BHD implementation scheme and can better adapt to the subsequent cascade scheme, thereby achieving the implementation of BHD with specific needs. Specifically, we optimize our BHD performance by compromising various parameters of BHD, focusing on optimizing and increasing BHD bandwidth, and choosing a more reasonable BHD implementation solution. Judging from the test results, the produced BHD has good performance in extracting effective signals. The bandwidth reaches about 2GHz, which meets the requirements of detection applications. It has a high signal-to-noise ratio of 10 dB and a common-mode rejection ratio (CMRR) of 20 dB near the 2 GHz frequency point.
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.