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Journal of the Optical Society of America B

Squeezed singly resonant second-harmonic generation in periodically poled lithium niobate

M. J. Lawrence, Robert L. Byer, M. M. Fejer, Warwick P. Bowen, Ping Koy Lam, Hans‐A. Bachor

Published Jul 1, 2002• 19 citations
Publisher

Abstract

We determine the theoretical singly resonant second-harmonic generation squeezing performance of several cavity designs and nonlinear materials. We show that, for the doubling of the 1064-nm output of Nd:YAG lasers, monolithic cavities made from periodically poled LiNbO3 (PPLN) will produce the largest amount of squeezing. We also present experimental results for a free-space cavity with a PPLN sample that yielded slightly less than 0.6 dB of measured squeezing. The cavity performance as a function of input power agrees with our theoretical predictions and shows the superior performance of periodically poled materials for the production of bright squeezed light.

DOI
10.1364/josab.19.001592

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We determine the theoretical singly resonant second-harmonic generation squeezing performance of several cavity designs and nonlinear materials. We show that, for the doubling of the 1064-nm output of Nd:YAG lasers, monolithic cavities made from periodically poled LiNbO3 (PPLN) will produce the largest amount of squeezing. We also present experimental results for a free-space cavity with a PPLN sample that yielded slightly less than 0.6 dB of measured squeezing. The cavity performance as a function of input power agrees with our theoretical predictions and shows the superior performance of periodically poled materials for the production of bright squeezed light.
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Abstract Quantum noise limits the sensitivity of optical measurements, but squeezed states of light enable quantum-enhanced metrology, sensing, and information processing. Most on-chip squeezed-light sources rely on Kerr (χ(3)) nonlinearities, remain limited by pump power and excess loss constraints. Quadratic (χ(2)) platforms instead provide stronger parametric interactions, lower pump power requirements, and greater spectral engineering flexibility. Here, we demonstrate strong, broadband squeezed-light generation on a thin-film lithium niobate (TFLN) photonic chip using a dual-resonant optical parametric amplifier implemented in a single periodically poled LN (PPLN) microresonator. Near-full-depth domain inversion is achieved simultaneously with highly over-coupled resonances, exhibiting escape efficiencies exceeding 90% and intrinsic quality factors above 2.5 million in a 0.6mm2 X-cut TF-PPLN resonator, enabling efficient squeezing at 1587nm when pumped at 793.5 nm. Operating in the continuous-wave regime, we directly measure −0.81 dB of squeezing below the shot-noise limit with a pump power of 27mW, together with +4.29 dB of anti-squeezing. From these measurements, we infer an on-chip squeezing level of −7.52 dB±0.22 dB (95% confidence interval: [−7.96,−7.10] dB), and an on-chip anti-squeezing level of +9.62 dB±0.25 dB . We demonstrate single-mode squeezing at degeneracy with a squeezed-light spectrum exceeding 10.3 THz. This work reports the highest squeezing ratio among integrated χ(2) cavity platforms and the first quasi-phase matched, fully resonant χ(2) cavity squeezer on chip, establishing a scalable route to fully integrated power-efficient squeezed-light sources for quantum-enhanced sensing and metrology.
We discuss different approaches to the generation of bright amplitude-squeezed light using second-order nonlinear effects in optical cavities. A 0.2 mW beam at 1064 nm exhibiting 4 dB squeezing has been generated using a phase-sensitive type-I parametric amplifier pumped by a frequency-doubled Nd:YAG laser. In applying frequency-doubling processes to the generation of amplitude-squeezed light, the appearance of parasitic parametric oscillation must be considered. This effect has been observed in a singly-resonant frequency doubler. We also describe recent developments in optical cavity design for doubly-resonant frequency-doubling. Finally, we show theoretically that phase-mismatched second-harmonic generation in an optical cavity can be employed to generate a strong effective Kerr nonlinearity. This system appears promising for achieving optical bistability and for generating squeezed light of high power. Keywords: Non-classical light, squeezed light, amplitude squeezing, nonlinear op...
We have generated squeezed states of light by the process of second harmonic conversion within an optical cavity resonant at both fundamental and harmonic frequencies. The experiment consists of a standing-wave cavity containing a crystal of lithium niobate doped with magnesium oxide and driven by the field from a frequency-stabilized Nd:YAG laser (incident power, ~10 mW). The total field reflected from the cavity illuminates a pair of high quantum efficiency photodiodes, whose individual photocurrents are summed. Observations of squeezing are made by analyzing the spectral density of fluctuations for this sum photo-current while the cavity detuning is scanned through resonance. An intensity regulator holds the reflected light intensity constant during the scan by control of the incident light level. Reductions in photocurrent fluctuations of 12% relative to the vacuum-state or shot-noise level are achieved for frequency offsets near 4 MHz. Since significantly higher degrees of squeezing are predicted by our theoretical analysis, we discuss those processes that currently limit the observed noise reduction, including phase noise produced by the intracavity crystal in the absence of nonlinear conversion.
Squeezed vacuum pulses up to $\ensuremath{-}1.7\text{ }\text{dB}$ at telecom-band $(\ensuremath{\sim}1550\text{ }\text{nm})$ is generated with femtosecond laser pulses using cascaded ${\ensuremath{\chi}}^{(2)}$ optical nonlinearity in a periodically poled lithium niobate crystal placed in a Sagnac interferometer. In spite of group velocity mismatch at short laser pulse pumping, sufficient cascaded nonlinear wave mixing is obtainable at the wavelength shifted from the phase matching wavelength for second harmonic generation. The theoretical model prediction agrees well with the experimental results.