Controlling multimode coupling by boundary-wave scattering

Li, Ge; Song, Qinghai; Redding, Brandon; Eberspächer, Alexander; Wiersig, Jan; Cao, Hui

doi:10.1103/physreva.88.043801

Cited by 23 publications

(20 citation statements)

References 43 publications

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“…When the system is perturbed, the eigenmodes of the original, unperturbed system become coupled. In optics, for example, the coupling can be introduced by matter-mediated interaction in cavity quantum electrodynamics [1,2], by nonlinearity in multimode lasers [3], and by linear scattering from a local defect or a gradual boundary deformation in optical waveguides [4] and microcavities [5][6][7][8]. In addition, rotation causes a minute change of the refractive index [9], which leads to the mixing of standing-wave resonances in optical microcavities [10,11].…”

Section: Introductionmentioning

confidence: 99%

Rotation-induced mode coupling in open wavelength-scale microcavities

Sarma

Cao

2014

Phys. Rev. A

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We study the interplay between rotation and openness for mode coupling in wavelength-scale microcavities. In cavities deformed from a circular disk, the decay rates of a quasi-degenerate pair of resonances may cross or anti-cross with increasing rotation speed. The standing-wave resonances evolve to traveling-wave resonances at high rotation speed, however, both the clockwise (CW) and counter-clockwise (CCW) traveling-wave resonances can have a lower cavity decay rate, in contrary to the intuitive expectation from rotation-dependent effective index. With increasing rotation speed, a phase locking between the CW and CCW wave components in a resonance takes place. These phenomena result from the rotation-induced mode coupling, which is strongly influenced by the openness of the microcavity. The possibility of a non-monotonic Sagnac effect is also discussed.

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Section: Introductionmentioning

confidence: 99%

Rotation-induced mode coupling in open wavelength-scale microcavities

Sarma

Cao

2014

Phys. Rev. A

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“…It applies both in and beyond the "dead zone" and takes into account the phase of the coupling constant. Since ψ + and ψ − are quasi-degenerate, their mutual coupling is much stronger than that with any resonance farther away in frequency [27,28]. Therefore, it is a good approximation to write their wave function as ψ(Ω) ≈ a + (Ω)ψ + + a − (Ω)ψ − when discussing how they evolve towards the CW and CCW resonances with rotation.…”

Section: Arxiv:14045289v1 [Physicsoptics] 21 Apr 2014mentioning

confidence: 99%

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

Sarma

Cao

2014

Frontiers in Optics 2014

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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...

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“…For example, scattering from m 0 to m 0 − ν is enhanced when the frequencies of the WG modes with m 0 and m 0 − ν are well aligned. The spectral overlap can make higher-order scattering processes significant and even comparable to the lower-order ones [27].…”

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confidence: 99%

“…Hence, introducing harmonic perturbations to the cavity boundary shape may be used as a "knob" to tune the far-field emission pattern. In previous studies [26,27], we showed theoretically that the emission patterns of deformed microcavities can be varied significantly with the first-order or the second-order perturbations; however, many of these numerical examples required a fine-tuning of the cavity shape, which is difficult to realize experimentally. In this Letter, we use higher-order scattering, which is more tolerant to the limited accuracy of experimental fabrication than lower-order scattering (see the Supplemental Material [28]).…”

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confidence: 99%

Manipulation of High-Order Scattering Processes in Ultrasmall Optical Resonators to Control Far-Field Emission

Redding

Song

et al. 2014

Phys. Rev. Lett.

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By imposing a set of harmonic perturbations to a microcavity boundary, we induce conversion and mixing of orbital angular momentum of light via surface scattering. Multiple scattering paths are available due to high-order scattering, which can be greatly enhanced by quasidegenerate resonances. By manipulating the relative strengths of these scattering processes, we theoretically synthesize the angular momentum spectra of individual modes so as to control their far-field patterns. We demonstrate experimentally that in wavelength-scale cavities of a fixed shape, the neighboring modes can have dramatically different emission directionality. This phenomenon is robust against slight shape deviation and surface roughness, and provides a general mechanism to control the emission direction of ultrasmall resonators.

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Controlling multimode coupling by boundary-wave scattering

Cited by 23 publications

References 43 publications

Rotation-induced mode coupling in open wavelength-scale microcavities

Rotation-induced mode coupling in open wavelength-scale microcavities

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

Manipulation of High-Order Scattering Processes in Ultrasmall Optical Resonators to Control Far-Field Emission

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