Rotation-induced Asymmetry of Far-field Emission from Optical Microcavities

Abstract

We study rotation-induced asymmetry of far-field emission from optical microcavities, based on which a new scheme of rotation detection may be developed. It is free from the "dead zone" caused by the frequency splitting of standing-wave resonances at rest, in contrast to the Sagnac effect. A coupled-mode theory is employed to provide a quantitative explanation and guidance on the optimization of the far-field sensitivity to rotation. We estimate that a 10 4 enhancement of the minimal detectable rotation speed can be achieved by measuring the far-field asymmetry, instead of the Sagnac effect, in microcavities 5 microns in radius and with distinct emission directions for clockwise and counterclockwise waves.Optical microcavities have found a wide range of applications from coherent light sources in integrated photonic circuits to cavity quantum electrodynamics, single-photon emitters, and biochemical sensors [1,2]. Recently they have also been proposed as a platform for rotation detection [3][4][5], replacing their tabletop counterparts in optical gyroscopes for reduced system size and weight [6][7][8][9][10][11][12][13]. An optical gyroscope utilizes the Sagnac effect [14][15][16][17][18], which manifests as a rotation-induced phase shift in a non-resonant structure or frequency splitting in a resonant cavity, between two counter-propagating waves. It has several advantages over its mechanical counterparts, including the absence of moving parts and system simplicity, with a high resolution typically less than 1 deg/h.The Sagnac effect is proportional to the size of the cavity, which puts optical microcavities at a serious disadvantage when compared with macroscopic cavities. Thus a new detection scheme is needed to make optical microcavities a viable option for rotation sensing. Previous studies [5,19] indicate that the quality (Q) factors of two counter-propagation modes also display a rotationinduced splitting, and its relative change can be much higher than that of the resonant frequencies. This enhancement however is still not large enough to compensate for the small size of microcavities, with a sensitivity still far below the Sagnac effect in macroscopic cavities.In this Letter we propose to use the asymmetry of the far-field emission pattern of deformed microcavity lasers as a measurable signature of rotation, which shows surprisingly high sensitivity. In a perfectly circular cavity, the output directionality of a resonance remains isotropic with rotation (see Appendix A). Therefore, we need to employ asymmetric resonant cavities (ARCs) [20][21][22] to obtain directional emission so that we can detect the change in output directionality by rotation. As the rotation speed increases, either the CW or CCW wave in a resonance gradually become the dominant component, * Electronic address: li.ge@csi.cuny.edu † Electronic address: hui.cao@yale.edu and consequently the far-field intensity pattern changes appreciably if the CW and CCW waves have very different output directionality. One well-studied non-rotating AR...