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Europhysics Letters (EPL)

Observation of squeezing using cascaded nonlinearity

K. Kasai, Jiangrui Gao, Claude Fabre

Published Oct 1, 1997• 45 citations
Publisher

Abstract

We have observed that the pump beam reflected by a triply resonant optical parametric oscillator, after a cascaded second-order nonlinear interaction in the crystal, is significantly squeezed. The maximum measured squeezing in our device is 30% (output beam squeezing inferred: 48%). The direction of the noise ellipse depends on the cavity detuning and can be adjusted from intensity squeezing to phase squeezing.

DOI
10.1209/epl/i1997-00418-8

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Generation of bright squeezed light at 1.06 μmμmμm using cascaded non-linearities in a triply resonant c.w. PPLN OPO
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We have used an ultralow threshold continuous-wave optical parametric oscillator (OPO) to reduce the quantum fluctuations of the reflected pump beam below the shot noise limit. The OPO consisted of a triply resonant cavity containing a periodically poled lithium niobate crystal pumped by a Nd:YAG (yttrium aluminum garnets) laser and giving signal and idler wavelengths close to $2.12\ensuremath{\mu}\mathrm{m}$ and a threshold as low as $300\ensuremath{\mu}\mathrm{W}.$ We detected the quantum fluctuations of the pump beam reflected by the OPO using a slightly modified homodyne detection technique. The measured noise reduction was 3030%30 (inferred noise reduction at the output of the OPO 3838%).38
Optical parametric amplifiers (OPA's) and optical parametric oscillators (OPO's) can exhibit squeezed amplification when an injected signal beam is used to elicit small-signal gain saturation. This paper extends previous work on OPA/OPO noise behavior under signal injection. Doubly resonant and triply resonant, single-ended cavities are considered in the good-cavity limit. Owing to the nonlinear coupling between the signal and idler beams within the cavity, both are sensitive to the detuning of each beam from its respective resonance. Signal and idler output noise spectra are found by linearizing the quantum coupled-mode equations about the classical mean-field solutions. Cavity detunings lead to frequency dependent phase shifts between the low-noise and high-noise quadratures of both the signal and idler beams. Moreover, the phase of the low-noise quadrature need not coincide with that of the corresponding mean field. The resulting large-signal, signal-to-noise ratio improvement afforded by squeezed amplification is therefore sensitive to the cavity detunings. The effects of classical excess noise on the pump beam and the injected signal beam are also considered.
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