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Journal of the Optical Society of America B

Harnessing coupler-induced localized backscattering for enhanced fast and slow light performances in a traveling wave microresonator

Thomas Y. L. Ang, Nam Quoc Ngo

Published Nov 9, 2010• 4 citations
Publisher

Abstract

We present an analytical study on the effects of coupler-induced localized backscattering (CILB) on the nature of superluminal and subliminal propagations in a traveling wave microresonator (TWMR). It is found that in the weak CILB regime, the flexibility to control the light propagation velocity is improved, and fast and slow light with high output power can be generated for a TWMR with a small net optical gain.

DOI
10.1364/josab.27.002639

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We present an analytical study on the effects of coupler-induced localized backscattering (CILB) on the nature of superluminal and subliminal propagations in a traveling wave microresonator (TWMR). It is found that in the weak CILB regime, the flexibility to control the light propagation velocity is improved, and fast and slow light with high output power can be generated for a TWMR with a small net optical gain.
We look into the use of the intracavity backscattering in twin-coupled traveling wave microresonators (TWMRs) to generate enhanced coupled-resonator-induced transparency (CRIT) and optical Fano resonance (OFR). Intracavity backscattering makes it possible to either generate a single CRIT peak or a pair of CRIT peaks within one free spectral range in the transmission spectrum. The distance between the twin-CRIT peaks can be tuned by controlling the intracavity backscattering strength. Also, the use of intracavity backscattering allows the simultaneous production of both fast and slow light effects. In addition, it is found that the symmetric CRIT peaks can be reshaped into asymmetric OFR line shapes either by using TWMRs with different intracavity backscattering strengths when one input is launched into the circuit or by modulating the phase/amplitude difference between the dual contrapropagating inputs, which are launched into the circuit in the presence of intracavity backscattering. These allow switching between CRIT and OFR to be realized in the absence of gain or phase tuning elements in the cavities, unlike conventional twin-coupled TWMR systems.
We predict the propagation of slow and fast light in two co-resonant coupled optical resonators. In coupled resonators, slow light can propagate without attenuation by a cancellation of absorption as a result of mode splitting and destructive interference, whereas transparent fast light propagation can be achieved by the assistance of gain and splitting of the intracavity resonances, which consequently change the dispersion from normal to anomalous. The effective steady-state response of coupled-resonators is derived using the temporal coupled-mode formalism, and the absorptive and dispersive responses are described. Specifically, the occurrence of slow light via coupled-resonator-induced transparency and gain-assisted fast light are discussed.
We utilize the contra-propagating cavity modes that arise from the evanescent coupling of both the resonators to the bus waveguide in a twin coupled traveling-wave microresonators (MRs) system to generate flat-band slow light (SL). The contra-propagating cavity modes will generate multipeaks in the resonance spectra. Flat-band SL can be generated if such multipeaks become undistinguishable and merge into one single broadened peak that is maximally flat when the inter-resonator coupling strength is optimized relative to the resonators-to-bus-waveguide coupling strengths. The bandwidth and the group delay can be tuned by adjusting the coupling strengths. It is shown that the delay-bandwidth products of the output light at the through (reflection) port are 3- to 12-fold (6- to 24-fold) higher than that of conventional MR-based SL systems. Fabrication tolerance and cavity losses analyses have also revealed that the proposed scheme is rather robust to the fabrication errors and limitations of current state-of-the-art semiconductor processing technology.
Light propagating in an optical waveguide can gain or lose power through interaction with a travelling acoustic wave or radio-frequency modulation of permittivity. Here, we model this propagation by considering an optical wave interacting with a weak travelling-wave permittivity perturbation whose frequency is much smaller than the optical frequency and whose amplitude decays exponentially along the propagation direction. Four modulation cases are analyzed: instantaneous modulation, synchronous modulation, and the Stokes and anti-Stokes resonances. For these cases, simple expressions are obtained for the carrier and sideband transmission and reflection powers as well as for the total gain and loss powers. Although the achievable total gain remains small for realistic modulation and waveguide parameters, the anti-Stokes resonance is identified as the most promising condition for observing modulation-induced light amplification.