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Journal of the Optical Society of America B

Enhanced sensitivity of fiber-optic rotation sensors with squeezed light

Monika A. M. Marte, Daniel F. Walls

Published Nov 1, 1987• 6 citations
Publisher

Abstract

A new technique is proposed by which optical squeezing may be applied to reduce the quantum noise in a fiber-optic rotation sensor below the standard quantum limit. The gain of sensitivity is achieved by making use of the nonlinearity of the glass fiber in a passive Sagnac rotation sensor to produce squeezed light with reduced phase fluctuations.

DOI
10.1364/josab.4.001849

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A new technique is proposed by which optical squeezing may be applied to reduce the quantum noise in a fiber-optic rotation sensor below the standard quantum limit. The gain of sensitivity is achieved by making use of the nonlinearity of the glass fiber in a passive Sagnac rotation sensor to produce squeezed light with reduced phase fluctuations.
The fiber optic Sagnac interferometer can measure the rotation rate of a system with a high sensitivity. However, they require a large sensor area, which leads to a huge footprint and size compared with their micro-electromechanical systems (MEMS) counterpart. Consequently, the performance decreases when using chip-integrated Sagnac interferometers with small sensor areas. In this letter, we address this issue and present a method to improve the sensitivity at a small scale. Therefore, we utilize two-mode squeezed light that can be generated in a ring resonator via four-wave mixing, which can have a very low noise. We show that the combination of classical coherent light and squeezed light can improve the sensor performance compared with a classical fiber optic Sagnac interferometer. For this purpose, we discuss two different configurations that are suited for various applications. The first one makes use of the low noise of squeezed light and is suited for small- and low-loss systems using intensity difference measurements, while the second one measures the variance of squeezed light via product detection and is suited for larger and lossy systems.
The injection of squeezed light can be used to improve the sensitivity of an interferometer beyond the limit imposed by the zero-point fluctuation of the electromagnetic field. Here, we report on the realization of such a quantum-enhanced interferometer with a fiber-based Sagnac topology. Continuous wave squeezed states at 1550 nm with a noise reduction of 6.4 dB below shot noise were produced by type I optical parametric amplification and subsequently injected into the dark port of the interferometer. A reduction of the interferometer shot noise by 4.5 dB was observed, and the enhancement of the signal-to-noise ratio for a phase modulation signal generated within the interferometer could be demonstrated. We achieved a 95% fiber transmission for the squeezed states, which suggests that corresponding fiber-based quantum metrology and communication systems are feasible.
We present a simple and robust design for a squeezing-enhanced Sagnac interferometer that significantly surpasses the the shot-noise limit of sensitivity in rotational sensing. By strategically placing an optical parametric amplifier (OPA) inside the Sagnac loop, light is automatically squeezed in both forward and backward directions of the loop, which enhances the detectability of a small phase. For measuring the squeezed quadrature, we explore two approaches: parametric homodyne and direct detection. In direct detection, the intensity of the output dark port is measured directly, which is very simple, but necessitates photo-detectors of near-unit efficiency. With parametric homodyne, an additional OPA is placed at the Sagnac output to amplify the quadrature of interest above the classical noise limit, eliminating the need for near-ideal photo-detectors. Our analysis demonstrates super-classical sensitivity under most realistic conditions of loss and detector inefficiency, thereby leveraging leveraging the resources of squeezing and the principles of SU(1,1) interference, while maintaining compatibility with standard Sagnac configurations.
Optical fibers offer considerable advantages over bulk nonlinear media for the generation of squeezed states. This thesis reports on experimental investigations of reducing quantum noise by means of squeezing in nonlinear fiber optic interferometers. Fibers have low insertion loss which allows for long interaction lengths. High field intensities are easily achieved in the small cores of single mode fibers. Additionally, the nonlinear process employed is self phase modulation or the Kerr effect, whose broad band nature requires no phase matching and can be exploited with ultra-short pulses of high peak intensity. All these advantageous features of fibers result in easily obtained large nonlinear phase shifts and subsequently large squeezing parameters. By the self phase modulation process a correlation is produced between the phase and amplitude fluctuations of the optical field. The attenuated or squeezed quadrature has a lower noise level than the initial level associated with the coherent state field before propagation. The resulting reduced quantum noise quadrature can be utilized to improve the sensitivity of a phase measuring instrument such as an interferometer.
High-Q optical microresonators combine low losses and high optical energy concentration in a small effective mode volume, making them an attractive platform for optical sensors. While light is confined in the microresonator by total internal reflection, a portion of the optical field, known as the evanescent field, extends outside. This makes the mode's resonant frequency sensitive to changes in the surrounding environment. In this work, we explore the quantum sensitivity limits of this type of sensors. We show that using the intracavity squeezing of the light in the microresonator, it is possible to suppress the influence of the optical losses and cancel the undesirable self phase modulation effect, originating from the cubic non-linearity of the microresonators media. As a result, the sensitivity surpassing the shot noise limit can be achieved. An additional sensitivity gain can be obtained by preparing the input light in a squeezed quantum state.
The greater confinement of light that is possible in photonic crystal fibers (PCFs) leads to greater effective nonlinearity, which promises to yield greater quantum squeezing than is possible in standard optical fiber. However, experimental work to date has not achieved improvements over standard fiber. We present a comprehensive numerical investigation of polarization squeezing in PCF in a Sagnac configuration. By including loss, a noninstantaneous Raman response, excess phase-noise, second- and third-order dispersion, and self-steepening, the simulations are able to identify the physical factors that limit current PCF squeezing experiments.