Selective excitation of axial modes in a high-Q microcylindrical resonator for controlled and robust coupling

Simulation and Optimization of SNAP-Taper Coupling System in Displacement Sensing

Sensing applications based on whispering gallery mode (WGM) microcavities have attracted extensive attention recently, especially in displacement sensing applications. However, the traditional displacement sensing scheme based on shift in a single resonance wavelength, has a lot of drawbacks. Herein, a novel displacement sensing scheme based on the surface nanoscale axial photonics (SNAP) is proposed to achieve a wide range and high-resolution displacement sensor through analyzing the transmittance of multiple axial modes. By analyzing the surface plot of the resonance spectrum with different coupling positions, the ideal coupling parameters and ERV for displacement sensing are obtained. In the following, displacement sensing with high sensitivity and a wide range is theoretically realized through adjusting the sensitivity threshold and the number of modes. Finally, we present our views on the current challenges and the future development of the displacement sensing based on an SNAP resonator. We believe that a comprehensive understanding on this sensing scheme would significantly contribute to the advancement of the SNAP resonator for a broad range of applications.

Ultranarrow filter based on Fano resonance in a single cylindrical microresonator for single-longitudinal-mode fiber lasers

A novel single-longitudinal-mode (SLM) fiber laser with a single cylindrical microresonator (CMR) as the filter is proposed. The CMR has a nanoscale variation in radius, in which high-Q localized modes interfere with continuum radiative modes, generating a peak-like transmission spectrum based on the Fano resonance effect. The peak linewidth is sufficiently small to select only one SLM oscillation in a fiber cavity. In an Er-doped fiber laser coupled with the CMR, we achieve a stable SLM laser operation by optimizing the coupling location of the tapered fiber. Stable lasing at 1568 nm with a 3-dB linewidth of ∼15 kHz is obtained. The laser slope efficiency reduction introduced by the CMR for SLM lasing is limited to 1.4%. This scheme can be a competitive approach for the development of compact, highly efficient, and cost-effective SLM fiber lasers.

High spectral purity electromagnetically induced transparency-based microwave optoelectronic oscillator with a quasi-cylindrical microcavity

High spectral purity microwave oscillators are widely exploited in science and military areas including communication, radar, and navigation. Here, we theoretically analyze and experimentally observe the application of tunable electromagnetically induced transparency (EIT) effect generated within a single quasi-cylindrical microresonator (QCMR) to a high spectral purity microwave optoelectronic oscillator (OEO). Stable single-frequency microwave oscillation with phase noise of -123 dBc/Hz at 10 kHz offset from ~5 GHz carrier and -135 dBc/Hz at 100 kHz offset is demonstrated without using any narrow-band RF filters. Moreover, we evaluate the impact of laser-mode locking state, quality factor as well as spectral lineshapes of the EIT resonance, laser coupling efficiency, and three configurations of optical energy storage elements on the spectral purity of the oscillator, so as to improve its phase noise and stability performances. Extending the concept of EIT to a microwave generator opens a promising avenue towards compact low-phase-noise oscillator systems for emerging mass applications.

Stable controlling of electromagnetically induced transparency-like in a single quasi-cylindrical microresonator

We experimentally and theoretically demonstrate electromagnetically induced transparency (EIT)-like and Fano resonance in a single quasi-cylindrical microresonator (QCMR). Stable controlling of the EIT and Fano resonance lineshapes can be achieved by vertically moving the resonator along its axis while in touch with the tapered fiber. Moreover, by horizontally scanning the coupling point along the tapered fiber, asymmetric Fano resonances of the transmission spectra are observed and can be engineered to vary periodically. Interestingly, the two different kinds of mechanisms that induce the Fano or EIT resonances can work on the same mode simultaneously. Our device offers a stable platform for controlling the EIT and Fano resonances and holds unique potential in all-optical switching, quantum information processing and sensitivity-enhanced sensing applications.