Servo-control And Detection Systems For Squeezed Light Generation

Squeezed states of light were first experimentally obtained in 1985.It is a non-classical light field that breaks the quantum noise limit and has broad application prospects in high-precision measurement,such as gravitational wave detection,quantum imaging,quantum radar,etc.All these applications are dependent on the improvement of the squeezing level.A typical method to generate a squeezed state is to use a sub-threshold optical parametric oscillator(OPO).The squeezing level is proportional to the escape efficiency and the detection efficiency of the balanced homodyne photodetection.High escape efficiency requires the loss of cavity caused by detuning as small as possible.What’s more,the relative phase between the pump and seed beams,and between the local and seed beams should be locked for keeping the optical parametric process with high conversion efficiency and the balanced homodyne detection system with high detection efficiency.All of these put forward high requirements on the sensitivity and stability of the locking system.And the squeezed light generator requires multiple locking loops,which further increases the difficulty of locking.In this thesis,we optimized the locking system and the detection system of the squeezed light generator for obtaining stabilized strongly squeezed states.The main innovation points of this thesis are as follows:1.The Pound-Drever-Hall(PDH)technique is described in detail and the theory of locking the OPA cavity length and relative phase between the pump and seed beams simultaneously is put forward.2.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.Furthermore,a unique transformer-coupled LC resonant amplifier is proposed to improve the quality factor and reduce the electronic noise of the resonant photodetector.The quality factor Q of the resonant circuit closing to 100 in the frequency range of more than 100 MHz is achieved.3.A kind of series PID servo control system is given,which increases the low-frequency gain effectively and improves the stability of the control system.The adoption of the notch filters reduces the effect of mechanical resonance on the control system.4.By measuring the transfer function of the resonance cavity,the optimal PID parameter is calculated by Mathmatica program and the optimized locking of the cavity is realized.5.A broadband high voltage amplifier is designed by adopting the high voltage power operational amplifier PA98.The bandwidth of the high voltage amplifier is 420 kHz.6.Considering the gain,bandwidth,electronic noise,dynamic range,common mode rejection ratio and so on,we present three balanced homodyne detectors for measuring squeezed state at different frequencies.We optimized the locking system and the detection system of the squeezed light generator,improving the stability and the detection efficiency.A 12.6dB@1064nm bright squeezed state and a 13.2dB squeezed vacuum state were measured.The phase fluctuation of the system is about 3.1mrad and Long-term working stability is more than 3 hours.All of the locking control system and the detection system are self-made,which need the smaller volume and lower cost.It has contributed to the miniaturization and commercialization of squeezed light generator.