Design Of Broadband Balanced Homodyne Detector

Characterizing optical quantum states demands efficient and trustworthy methodologies given the rapid development of quantum information technology.Due to its high sensitivity to the amplitude and phase of the incident light,the balanced homodyne detector(BHD)can reliably extract the noise fluctuation of the quadrature component of the quantum state in applications of non-classical light,amplify the fluctuation to macro level,and suppress the classical common mode noise.It is commonly utilized in research on quantum random number generators(QRNG)and continuous variable quantum key distribution(CVQKD).The benefits of CVQKD include efficient information transmission,high secure key rate,and secure and simple creation of quantum signals.However,the repetition frequency of the CVQKD is lower when compared to discrete variable quantum key distribution.The primary factor influencing CVQKD repetition frequency is the BHD bandwidth.The balanced homodyne detector’s bandwidth needs to be improved asap in order to achieve high speed CVQKD.The QRNG based on vacuum state measurement,however,has the benefit of a simple optical setup,insensitive detection efficiency,and multiple bits per sample,but its random number generation rate is likewise constrained by detector bandwidth.High speed CVQKD and QRNG are progressively emerging as research hotspots as a result of the rapid growth of quantum communication.Also,the advancement of broadband BHD has emerged as a significant study area.The internal circuit layout determines the BHD’s bandwidth.There aren’t many commercial wideband BHDs on the market right now,and those that do have worse signal to noise ratios,lower common mode rejection ratios,and performance that degrades quickly at low analysis frequencies.This research focuses on the investigation of broadband BHD.To increase the detector’s bandwidth,we construct a circuit layout based on two types of amplifiers:transimpedance amplifiers and radio frequency(RF)amplifiers.The specific tasks are completed as follows: First,the main parameters and operating theory of transimpedance amplifier and the RF amplifier are investigated.The amplifier with the best performance is chosen to design the circuit structure of the detector in accordance with the findings of the analysis.The detector circuit is next examined using simulation tools or a noise equivalent circuit model.Then,after realizing that the physical thing is finished,we design the printed circuit board of the detectors and the detector shielding box for packaging.Finally,the performance parameters of the two types of BHD were finally tested and analyzed using an experimental test device.In this paper,two types of broadband BHD are ultimately realized.One uses an R-C coupling structure,which reduces electronic noise at the analysis frequency of k Hz considerably when compared to an L-C coupling structure,and is a wideband BHD based on a transimpedance amplifier.The detector satisfies the criteria for quantum detection in terms of signal-to-noise ratio and linearity,and has low electronic noise in the working frequency ranges of low frequency(0～30 k Hz)and high frequency(30 k Hz～200 MHz).The signal to noise ratio at 5 k Hz is 12 d B and the common mode rejection ratio approaches 70 d B when the laser incident at 8 m W@1550 nm.At 100 MHz,the common mode rejection ratio hits 66 d B and the signal to noise ratio is 20 d B.The detector’s gain uniformity is 0.5 d B.The second type of broadband BHD uses RF amplifiers and has transmission bandwidths that range from low frequency to 6 MHz and high frequency to1.8 GHz.The signal-to-noise ratio at 10 MHz and 200 MHz is 10 d B when a laser incident at 2 m W@1550 nm.The detector’s gain level is 1 d B for bands from 6 MHz to 100 MHz and 1.5 d B for bands from 100 MHz to 1.8 GHz.The two detectors have good performance indices and are appropriate for signal detection in various wide band ranges.For high-rate continuous variable quantum key distribution and high-rate quantum random number generator,they can offer high performance detection tools.