Showing papers by "Leilei Shi published in 2021"

A Fiber-Attached Coupler for Transmission Bandpass Whispering Gallery Mode Resonator

Abstract: A fiber attached coupler for transmission bandpass whispering gallery mode (WGM) resonator is proposed and experimentally demonstrated. The coupler fabricated by femtosecond laser ablation consists of a pair of curved waveguides with a curvature radius of 50 μm, by which the WGM field is excited and collected through evanescent field coupling, respectively. As a proof of concept, a polymer microsphere functioning as the WGM cavity is embedded into a femtosecond laser ablated hole between the two curved waveguides. A passband with a full width of 0.15 nm at half maximum is observed when the microsphere is surrounded by air, verifying the feasibility of the proposed coupler for constructing a WGM cavity-based transmission narrow bandpass optical fiber filter. Benefitting from the relatively high thermo-optical coefficient, the passband of a packaged transmission bandpass WGM resonator can be thermo-optically tuned with a sensitivity of 446.6 pm/°C.

In-Fiber Butt-Coupled Spherical Microcavity With Whispering Gallery Mode and Fabry-Perot Resonances

Abstract: An integrated in-fiber coupling configuration for simultaneously exciting whispering gallery mode (WGM) and Fabry-Perot (FP) resonances in one cavity is proposed and demonstrated experimentally. The WGMs traveling circularly in both clockwise and counter-clockwise directions are simultaneously excited by perpendicularly injecting the light from the single-mode-fiber (SMF) core into a polymeric microsphere embedded in the femtosecond laser micromachined coupling structure. While the standing wave between the two axial interfaces of the microsphere and its external media results in a spherical FP resonator, meaning that the WGM and the FP resonances coexist in the same spherical cavity. The superposition of WGM and FP resonances results in asymmetric Fano-like lineshape, which is of high importance for optical fiber sensors, filters, and switches due to its sharp slope around the resonant wavelength. Experimental results show that asymmetric spectral lineshape can be achieved even as the spatial coupling gap is larger than the wavelength, indicating that the proposed coupler has higher fabrication tolerance than the evanescent field-based coupling configuration. Such an integrated coupling configuration provides an effective method for the coupling between the optical fiber and WGM cavities made of any functional material by liberating them from the phase-matching condition and enriching the functionality by importing other resonance into the same cavity.

Simultaneous self-injection locking of two VCSELs to a single whispering-gallery-mode microcavity.

Abstract: Simultaneous self-injection locking of two vertical-cavity surface-emitting lasers (VCSELs) to a single whispering-gallery-mode (WGM) microcavity is experimentally demonstrated. The linewidths of the two VCSELs are compressed from 3.5 MHz and 5 MHz to 20.9 kHz and 24.1 kHz, which is on the same order of magnitude as that of locking each VCSEL to the microcavity separately. Moreover, the frequency noises of the two simultaneously locked VCSELs are suppressed by more than 60 dB below the offset frequency of 100 kHz compared to that of the free-running VCSELs. The method demonstrated here might be used in the multi-wavelength laser array with low phase and frequency noises, especially the VCSELs with the unique architecture of a two-dimensional array.

Narrow Linewidth VCSEL based on Resonant Optical Feedback from an On-chip Microring Add-Drop Filter

Abstract: We demonstrate a narrow linewidth vertical-cavity surface-emitting laser (VCSEL) by injecting resonant optical feedback into the lasing cavity. A single longitudinal mode VCSEL with a Lorentzian linewidth of 32.6 kHz and a purified optical spectrum is experimentally achieved by an on-chip microring add-drop filter with a quality factor of 1.36 million, where the feedback level is ${-}{47.77}\;{\rm{dB}}$. The frequency noise spectrum of the VCSEL demonstrates that the thermo-optic effect in the microring resonator can also stabilize the lasing frequency. A VCSEL with narrow linewidth and stable frequency provides a high-performance light source for a single VCSEL or VCSEL array-based application.