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Optical Engineering

Experimental study on mode matching for preparation of squeezed light at 1064 nm

Fei Feng, Tongyi Zhang, Wenyan Qu, Jiazheng Song

Published Aug 1, 2013• 4 citations
Publisher

Abstract

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.

DOI
10.1117/1.oe.52.8.086102

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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.
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.
Optical parametric oscillation is the critical part in the preparation of squeezed states of light. The mode-matching and fringe locking technique should be employed to improve the stability of the optical parametric oscillator cavity. How the mode-matching efficiency influence the squeezing degree of the squeezed light and the locking accuracy of the fringe locking technique were analyzed theoretically. Then the fringe locking technique was employed to stabilize the optical parametric oscillator cavity after the mode-matching between the laser mode and the fundamental mode of the cavity. The theoretical and experimental results show that a perfect mode-matching would improve the squeezing degree and the locking accuracy of the fringe locking technique, when the mode-matching is optimized, the length variance of the cavity is 7.35 nm and the locking time is no less than 2 h, which is sufficient for the detection of the squeezed states of light. ©, 2015, Editorial Board of Journal of Infrared and Laser Engineering. All right reserved.
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 report the experimental demonstration of directly produced polarization squeezing at 1064 nm from a type I optical parametric amplifier (OPA) based on a periodically poled KTP crystal (PPKTP). The orthogonal polarization modes of the polarization squeezed state are both defined by the OPA cavity mode, and the birefringence induced by the PPKTP crystal is compensated by a second, but inactive, PPKTP crystal. Stokes parameter squeezing of 3.6 dB and anti squeezing of 9.4 dB is observed. (c) 2007 Optical Society of America.
We generate squeezed state of light at 860 nm with a monolithic optical parametric oscillator. The optical parametric oscillator consists of a periodically poled KTiOPO(4) crystal, both ends of which are spherically polished and mirror-coated. We achieve both phase matching and cavity resonance by controlling only the temperature of the crystal. We observe up to -8.0±0.2 dB of squeezing with the bandwidth of 142 MHz. Our technique makes it possible to drive many monolithic cavities simultaneously by a single laser. Hence our monolithic optical parametric oscillator is quite suitable to continuous-variable quantum information experiments where we need a large number of highly squeezed light beams.