Abstract
We propose and experimentally demonstrate the enhancement in the filtering quality (Q) factor of an integrated micro-ring resonator (MRR) by embedding it in an integrated Fabry-Perot (FP) cavity formed by cascaded Sagnac loop reflectors. By utilizing coherent interference within the FP cavity to reshape the transmission spectrum of the MRR, both the Q factor and the extinction ratio (ER) can be significantly improved. The device is theoretically analyzed and practically fabricated on a silicon-on-insulator wafer. Experimental results show that up to 11-times improvement in the Q factor, together with an 8-dB increase in the ER, can be achieved via our proposed method. The impact of varying structural parameters on the device performance is also investigated and verified by the measured spectra of the fabricated devices with different structural parameters.
Highlights
Along with the development of micro/nano-fabrication technologies, integrated resonators with compact footprints, mass-producibility, high scalability, and versatile applications have come of age and become key building blocks for photonic integrated circuits.[1,2] The quality (Q) factor, defined as the ratio of resonance wavelength to full width at half maximum (FWHM),[1] is one of the fundamental parameters for integrated resonators
When N continues to increase until the free spectral range (FSR) of the Sagnac loop reflectors (SLRs)-FP cavity approaches the linewidth of the micro-ring resonator (MRR), filtering shapes with multiple transmission peaks begin to appear
Since we have demonstrated in Ref. 30 that dynamic tuning of ts can be realized by using interferometric couplers to replace the directional couplers and tuning them in a differential mode, tuning the Q factor of the proposed FP-cavity-assisted MRR (FP-MRR) filter can be achieved in the same way
Summary
Along with the development of micro/nano-fabrication technologies, integrated resonators with compact footprints, mass-producibility, high scalability, and versatile applications have come of age and become key building blocks for photonic integrated circuits.[1,2] The quality (Q) factor, defined as the ratio of resonance wavelength to full width at half maximum (FWHM),[1] is one of the fundamental parameters for integrated resonators. The Fano resonance based methods come at the expense of yielding sharp asymmetric filtering spectra for high Q factors, which have undesired distortions on the filtered signal and limit the applications of these filters. The EIT analog based methods can achieve high-Q transmission peaks within the resonance notches, but the stopbands are usually limited by the linewidths of the resonance notches. We propose and experimentally demonstrate a novel scheme to improve the Q factor of integrated resonators based on a novel device configuration employing an integrated Fabry-Perot (FP) cavity. The bandwidths of the stopbands are no longer limited by the resonance linewidths as those in EIT analog based approaches.[19,20,21] Our operation principle is universal, which can apply to enhancing Q factors of other types of integrated resonators. The comparison between the measured spectra of different fabricated devices verifies the impact of varying structural parameters on the device performance
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