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Chinese Physics B

A low-noise, high-SNR balanced homodyne detector for the bright squeezed state measurement in 1–100 kHz range*

JinRong Wang, Qing-Wei Wang, Long Tian, Jing Su, Yaohui Zheng

Published Jan 7, 2020• 14 citations
Publisher

Abstract

We report a low-noise, high-signal-to-noise-ratio (SNR) balanced homodyne detector based on the standard transimpedance amplifier circuit and the inductance and capacitance combination for the measurement of the bright squeezed state in the range from 1 kHz to 100 kHz. A capacitance is mounted at the input end of the AC branch to prevent the DC photocurrent from entering the AC branch and avoid AC branch saturation. By adding a switch at the DC branch, the DC branch can be flexibly turned on and off on different occasions. When the switch is on, the DC output provides a monitor signal for laser beam alignment. When the switch is off, the electronic noise of the AC branch is greatly reduced at audio-frequency band due to immunity to the impedance of the DC branch, hence the SNR of the AC branch is significantly improved. As a result, the electronic noise of the AC branch is close to −125 dBm, and the maximum SNR of the AC branch is 48 dB with the incident power of 8 mW in the range from 1 kHz to 100 kHz. The developed photodetector paves a path for measuring the bright squeezed state at audio-frequency band.

DOI
10.1088/1674-1056/ab683b

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We report a low-noise, high-signal-to-noise-ratio (SNR) balanced homodyne detector based on the standard transimpedance amplifier circuit and the inductance and capacitance combination for the measurement of the bright squeezed state in the range from 1 kHz to 100 kHz. A capacitance is mounted at the input end of the AC branch to prevent the DC photocurrent from entering the AC branch and avoid AC branch saturation. By adding a switch at the DC branch, the DC branch can be flexibly turned on and off on different occasions. When the switch is on, the DC output provides a monitor signal for laser beam alignment. When the switch is off, the electronic noise of the AC branch is greatly reduced at audio-frequency band due to immunity to the impedance of the DC branch, hence the SNR of the AC branch is significantly improved. As a result, the electronic noise of the AC branch is close to −125 dBm, and the maximum SNR of the AC branch is 48 dB with the incident power of 8 mW in the range from 1 kHz to 100 kHz. The developed photodetector paves a path for measuring the bright squeezed state at audio-frequency band.
Squeezing-based quantum metrology has been extensively applied in the field of precision measurement. Performance characteristics of squeezed light are obtained by a balanced homodyne detector. Here, we report a large dynamic range balanced homodyne detector with low-noise and high-signal-to-noise-ratio (SNR) for broadband squeezed light measurement. We perform a comprehensive theoretical analysis of the SNR in a wide bandwidth and experimentally analyze the important printed circuit board (PCB) layout and electronic components. Consequently, in the 100 MHz frequency band, the SNR and common mode rejection ratio (CMRR) rise over 12.6 dB and 55 dB, respectively, and the electronic noise is suppressed below -90 dB. The directly observed squeezing level at 1550 nm with the specified detector is 11.8 dB at 2 MHz and 3.1 dB at 100 MHz.
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.
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.
The pulsed squeezed state plays a pivotal role in quantum information processing and precision measurement. In the detection of the pulsed squeezed state, the high noise power at its repetition rate prevents the achievement of a high signal-to-noise ratio (SNR). Therefore, a high-SNR detector that can suppress the high noise power of the repetition rate of pulsed light is very crucial. In this paper, we present a high-SNR resonant balanced photodetector that filters out the noise power of the repetition rate by introducing an LC series notch filter. A 24.37 dB attenuation is obtained at the 80 MHz repetition rate by finely adjusting the capacitance of the LC series notch filter. Consequently, the photodetector's maximum SNR is improved to 19.60 dB, which is 5 dB higher than previous studies. Our work provides a key detection tool for the measurement of the pulsed squeezed state.
A low-noise, high-speed balanced homodyne detector is demonstrated, combining a capacitive-feedback transimpedance amplifier implemented in 28 nm CMOS with a custom photonic integrated circuit fabricated in imec's iSiPP200 silicon photonics platform. The receiver achieves a 3-dB bandwidth of 7.6 GHz, a maximum shot noise clearance of 27 dB, a shot noise-limited bandwidth of 13.7 GHz and a common-mode rejection ratio up to 54.8 dB. These results demonstrate the suitability of CMOS capacitive-feedback transimpedance amplifiers for demanding quantum and coherent sensing optical applications, including continuous-variable quantum key distribution, quantum random number generation, and optical coherence tomography.
A high-performance resonant balanced homodyne detector is a key element for the measurement of picosecond pulsed squeezed light, which is an important quantum resource in quantum-enhanced microscopic imaging. In this paper, we design and demonstrate a resonant photodetector for homodyne measurement with a maximum signal-to-noise ratio of 22.42 dB at resonant frequency of 20 MHz. Using this detector to pulsed regime, a maximum signal-to-noise ratio at resonant frequency is 10.02 dB, where a 40 dB subtraction capability at 80 MHz repetition rate of pulsed laser is obtained. With this design, the quantum noise of picosecond pulsed squeezed light is measured and the best squeezing level −1.7 dB below the shot noise level is clearly observed at 20 MHz.