A low-noise photodetector is a basic tool for the research of quantum information processing. We present a specially designed low-noise photoelectric detector with a bandwidth of 130 MHz, using a transimpedance amplification circuit. Based on the detailed calculation of the dependence on each parameter of the detector, a useful method of how to design a low-noise and broadband photodetector is provided. When the optical power is between 1.0 and 16 mW, the photodetector has a good linear response to the injected light. Its electronics noise power is below −77 dBm, which is within the whole bandwidth. When the incident light power is 2 mW, the output noise powers are 10.0, 8.0, and 6.0 dB higher than the corresponding electronics noise within the bandwidth of 1-50, 50-90, and 90-130 MHz, respectively, which is in good agreement with the theoretical prediction. Thus, this photoelectric detector could have good application prospects in quantum communication and an optical cavity locking system.
The dependence of the quantum correlation of twin beams generated from a non-degenerate optical parametric oscillator on the analysis frequency was theoretically studied with semi-classical method. It was pointed out that the quantum entanglement is higher at lower analysis frequency. By means of a pair of unbalanced fiber Mach-Zehnder interferometers,the correlation noise spectrum of the intensity-difference and the phase-sum of twin beams with non-degenerate frequencies and total power of 20mW were experimentally measured,which were 3.1 and 1.3dB below the corresponding shot noise limit at 2MHz,respectively. The experimental results are in agreement with the theoretical predictions.
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