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Review of Scientific Instruments

1.55 GHz balanced homodyne detector with high gain flatness based on low noise amplifier

Shaofeng Wang, Xuyin Niu, Guangqian Wu, Ruifang Dong

Published Feb 1, 2025• 7 citations
Publisher

Abstract

In this paper, a model for simulating the shot noise power and the electronic noise power of a balanced homodyne detector (BHD) using cascaded low noise amplifiers (LNAs) is presented. Moreover, the factors influencing the enhancement of BHD gain flatness are analyzed. Based on these theories, a BHD with a large clearance between shot noise and electronic noise, along with a flat broadband frequency response, is designed using LNAs and an optimized printed circuit board design. According to the experimental measurements, the bandwidth for 1 dB flatness reaches 1.4 GHz with the -3 dB bandwidth extending up to 1.55 GHz. With a 4 mW optical signal input, a signal-to-noise ratio of 12 dB is obtained at 1 GHz. The BHD exhibits excellent linearity for shot noise output up to an 8 mW optical signal input and a tested common mode rejection ratio of 63 dB. This developed BHD is well-suited for applications in high-speed continuous variable quantum key distribution and quantum random number generation.

DOI
10.1063/5.0239073

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In this paper, a model for simulating the shot noise power and the electronic noise power of a balanced homodyne detector (BHD) using cascaded low noise amplifiers (LNAs) is presented. Moreover, the factors influencing the enhancement of BHD gain flatness are analyzed. Based on these theories, a BHD with a large clearance between shot noise and electronic noise, along with a flat broadband frequency response, is designed using LNAs and an optimized printed circuit board design. According to the experimental measurements, the bandwidth for 1 dB flatness reaches 1.4 GHz with the -3 dB bandwidth extending up to 1.55 GHz. With a 4 mW optical signal input, a signal-to-noise ratio of 12 dB is obtained at 1 GHz. The BHD exhibits excellent linearity for shot noise output up to an 8 mW optical signal input and a tested common mode rejection ratio of 63 dB. This developed BHD is well-suited for applications in high-speed continuous variable quantum key distribution and quantum random number generation.
We present a high-performance, fully discrete balanced homodyne detector (BHD) with a 2.5 GHz bandwidth, exceptional gain flatness, and superior common-mode rejection ratio. The design leverages a Rogers 4350B-based printed circuit board, a broadband multi-section RF choke bias network, and inter-stage π-section attenuators, complemented by precise photodiode matching and phase-magnitude compensation to ensure signal integrity and suppress common-mode noise. Experimental results show a -3 dB bandwidth of 2.5 GHz and 1 dB gain flatness up to 2.4 GHz-significantly exceeding our prior 1.55 GHz/1.4 GHz implementation and representing state-of-the-art performance among discrete BHDs. At 16 mW optical input, the detector delivers a 16.5 dB signal-to-noise ratio at 2 GHz while maintaining excellent linearity, and achieves a 66 dB common-mode rejection ratio at the same frequency. This cost-effective and flexible BHD is ideally suited for high-speed continuous-variable quantum key distribution and quantum random number generation.
The rapid development of continuous-variable quantum communication has driven an increasing demand for high-performance quantum signal processing modules. Among these, the balanced homodyne detector (BHD) has emerged as a leading solution for practical quantum state measurement due to its capability to provide complete quantum mechanical characterization. However, its performance is often constrained by limited bandwidth and high noise levels, primarily due to the reliance on bulk optical components and discrete receiver electronics. The dominant noise source in these systems typically stems from electronic noise, while imbalances in the optical path further degrade the signal-to-noise ratio (SNR) of the BHD. In this work, we present an adjustable integrated optical path to enhance the balance within the BHD system, along with a low-noise transimpedance amplifier (TIA) by employing optoelectronic co-design. Our design achieves a bandwidth of 2.5 GHz, an input-referred noise current of only 2 pA/√Hz in 180 nm CMOS technology, and a measured quantum shot noise clearance of 15 dB generated from a 700 μA photocurrent. This is the maximum quantum shot noise clearance at the same BHD photocurrent reported to date above the GHz bandwidth.
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.
The research of quantum noise in the interaction of laser and atoms plays a critical role in quantum optical experiments. The measurement of quantum noise is mainly based on the balanced homodyne detection method. Here, we reported a balanced homodyne detector with low noise, high gain, and high common-mode rejection ratio (CMRR) at the wavelength of 795 nm. By optimizing the selection of components and printed circuit board (PCB) layout, a minimum electronic noise of −96.7 dBm is obtained. Over the range of 1 MHz to 5 MHz, we get a flat CMRR above 59 dB and a linear gain regime, which can enable a shot noise measurement with the laser power of100 μw100~\mu \text{w}100 μw. The developed detector can be used in quantum coherent experiments with a weak probe laser of power down to tens of microwatts.
True random numbers are extracted through measurements of vacuum fluctuations in quantum state components. We propose an improved scheme utilizing an optimization-based simulation methodology to enhance the temporal resolution of quantum state detection and processing efficiency of vacuum fluctuation signals in continuous-variable quantum random number generators (CV-QRNGs), while simultaneously maximizing the entropy content of quantum noise sources. This work presents the first application of optimization simulation methodology to balanced homodyne detector (BHD) circuit design, with particular emphasis on improving high-frequency transmission characteristics. The design framework prioritizes system stability and S-parameter sensitivity to optimize both circuit architecture and critical component parameters. The AC amplifier circuit was implemented through ADS high-frequency simulations using two ABA-52563 RF amplifiers in a cascaded configuration, with circuit modeling performed on Rogers 4350 substrate optimized for high-frequency applications. This approach enabled the development of a switched-configuration BHD featuring: 1) 1.9 GHz bandwidth, 2) 41.5 dB signal-to-noise ratio at 1.75 GHz, 3) 30 dB common-mode rejection ratio at 100 MHz, and 4) frequency response flatness within 1.5 dB across 1.3-1.7 GHz. Additionally, the Husimi function is employed for entropy analysis to reconstruct vacuum state phase-space distributions, validating the detector's quantum measurement fidelity. The implemented system demonstrates a collective generation rate of 20.0504 Gbps across four parallel channels, with all output streams successfully passing NIST SP 800-22 statistical testing requirements.