Resonant photodetector for cavity- and phase-locking of squeezed state generation

Abstract

Based on the requirement of squeezed state generation, we build the phase relationship between two electronic local oscillators for the cavity- and phase-locking branches, and a 2-way 90° power splitter is adopted to satisfy the phase relationship simultaneously, which greatly simplifies the experimental setup and adjusting process. A LC parallel resonant circuit, which is composed by the inherent capacitance of a photodiode and an extra inductor, is adopted in the resonant photodetector to improve the gain factor at the expected frequency. The gain of the resonant photodetector is about 30 dB higher than that of the broadband photodetector at the resonant frequency. The peak-to-peak value of the error signal for cavity-locking (phase-locking) with the resonant photodetector is 240 (260) times of that with the broadband photodetector, which can improve the locking performance on the premise of not affecting the squeezing degree.

Low-noise, transformer-coupled resonant photodetector for squeezed state generation

“…The network analyzer performs a normalized measurement by calculating the ratio between the photodetector output and the internal reference signal. 22 We measured the transfer function of the transformer-coupled photodetector and the results are shown in Fig. 5.…”

“…[19][20][21] In our former studies, a high gain resonant photodetector has been obtained for cavity locking and phase locking by utilizing a LC circuit to couple the photodiode to the load directly. 22 A quality factor Q more than 90 at the resonance frequency 58.6 MHz is experimentally observed. While we adjust the resonance frequency to other bands away from 58.6 MHz by changing the inductance, the quality factor decreases, which may come from the inductance variation, loss increase, and so on.…”

“…Referring to the article, 22 the Q value of the LC-coupled resonant circuit can be expressed as Q LC = R L X , where the R L is the load resistance and the X is the impedance of the C d or L at the resonance frequency. Compared with the LC-coupled, if we ignore the influence of the resistances R 0 , R s , and suppose β = 1, the load resistance of the transformer-coupled resonant circuit can be simplified as N 2 R L ; therefore, the quality factor Q tr -coupled of the transformer-coupled resonance circuit is N 2 times as large as Q LC in principle.…”

“…By adjusting the parameters of the transformer, the quality factor Q of the resonant circuit is close to 100 over a frequency range of more than 100 MHz, which meets the requirement for weak power detection in the application of squeezed state generation. Compared with our previous work, 22 we analyze the noise feature of transformer-coupled resonant photodetectors, employ a multiple strands winding transformer, and obtain the resonant photodetector with a wide frequency range on the premises of keeping the quality factor Q.…”

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“…M10, L4, and M11 are finetuned to match the pattern of the seed laser and the slave cavity. If the patterns matches well, the DC terminal of the resonant photo-detector (RPD) will output a periodic, smooth resonance signal [25] . Secondly, RF signals are applied with the same frequency but different phases to the EOM and the mixer, one of which is used to modulate the seed light, and the other is used to demodulate the detuned signal obtained by the AC terminal of the RPD, that is, the error signal.…”