We investigate the effects of cavity detuning on squeezing in the generation of the squeezed light at 1064 nm with a degenerate optical parametric amplifier (OPA) based on a periodically poled KTiOPO4 crystal. We theoretically analyze several effects that lead to cavity detuning, including the displacement and tilt of the incident laser light and the cavity length fluctuations of the OPA. To reduce the influence of the cavity detuning and increase the degree of generated quantum noise reduction, a side-of-fringe locking technique is applied to achieve the resonance between the OPA cavity and the injected laser beam. The experimental results show that the transmitted power through the locked cavity is increased and the cavity detuning is greatly suppressed. After locking of the cavity, we could expect to get a value for the control loop with an accuracy of 10−9 and the locking time is not less than 2 h, which paves the way for the preparation of the squeezed light.
We demonstrate the methods for increasing the observed squeezing level in the generation of squeezed states of light at
1064 nm with periodically poled KTiOPO4 (PPKTP) crystal. We analyze the technical limits to the reduction of noise in
the squeezed quadrature theoretically, including the intra-cavity loss of the optical parametric amplifier (OPA) cavity, the
normalized amplitude, the detection frequency, and the mode matching on the balanced homodyning stage. To observe a
high degree of squeezing, we improve the quality of mode matching into the OPA cavity and the mode cleaning (MC)
cavity experimentally. By optimizing mode matching of the light into cavities, the finesse of the cavities would be higher
in practice and the desirable spatial mode can be realized. As the intensity noise of the laser light reach the shot noise
limit above the frequency of 1 MHz, which is sufficient for our experiment, so the MC cavity is incorporated to filter
higher-order transverse modes of the local oscillator (LO) beam for the balanced homodyne detection. The experimental
and theoretical results show that it is essential to optimize the mode matching efficiency to generate and detect high
degree of squeezing otherwise an inefficiency mode matching will throw away the squeezing and transform the squeezed
field into a vacuum field.
We analyze the balanced homodyne detection technique in the detection of squeezed light, which is controlled by dither
locking scheme. We discuss how the balanced homodyne detection efficiency influences the detected degree of
squeezing. Also, fluctuation in the relative phase between the local beam and the squeezed light is discussed, since a little
phase fluctuation would decrease the detected degree of squeezing greatly. Then, the dither locking technique is studied
in detail, which is used to lock the relative phase between the local beam and the squeezed light. The simulation
experiments and theoretically results show that the balanced homodyne detection technique and the dither locking
scheme are efficient methods to get more accurate degree of squeezing in the preparation of the squeezed states of light.
The effect of mode matching on the preparation of the squeezed light at 1064 nm with periodically poled KTiOPO 4 (PPKTP) crystal is reported. We can derive the desired mode by improving the spatial mode matching into optical cavities, including the beam from the laser mode matched to the optical parametric amplifier cavity and mode cleaning cavity; also it is useful for the stability of the locking systems. By increasing the fringe visibility between the squeezed light and the local oscillator beam, a squeezing level of −8.75 dB or even higher could be observed, even with the same experimental parameters as described elsewhere.
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