Abstract
We propose and demonstrate, by simply inserting an air-hole in the waveguide side-coupling with a microring resonator (MRR), that the transmission spectrum presents Fano lineshapes at all of the resonant modes. Measured from the fabricated devices, Fano lineshapes with slope rates over 400 dB/nm and extinction ratios over 20 dB are obtained. We ascribe it to the air-hole-induced phase-shift between the discrete resonant modes of the MRR and the continuum propagating mode of the bus-waveguide, which modifies their interference lineshapes from symmetric Lorentzian to asymmetric Fano. From devices with varied locations and diameters of the air-hole, different Fano asymmetric parameters are extracted, verifying the air-hole-induced phase-shifts. This air-hole-assisted waveguide-MRR structure for achieving Fano resonance lineshapes has the advantage of simple design, compact footprint, and large tolerance of fabrication errors, as well as broadband operation range. It has great potential to expand and improve the performances of on-chip MRR-based devices, including sensors, switches, and filters.
Highlights
Microring resonators (MRRs) play crucial roles in on-chip interconnect, signal processing, and nonlinear optics.1–4 Fano resonance lineshapes of microring resonator (MRR) have recently attracted much interest for improving these chip-integration functions.5–8 As opposed to the usual symmetric Lorentzian resonance lineshapes, they have asymmetric and sharp slopes around the resonant wavelengths
By inserting an air-hole in the waveguide side-coupling with a microring resonator (MRR), that the transmission spectrum presents Fano lineshapes at all of the resonant modes
We have demonstrated that Fano resonance lineshapes could be realized reliably in a waveguide-MRR structure by inserting an air-hole in the side-coupled waveguide
Summary
Microring resonators (MRRs) play crucial roles in on-chip interconnect, signal processing, and nonlinear optics. Fano resonance lineshapes of MRRs have recently attracted much interest for improving these chip-integration functions. As opposed to the usual symmetric Lorentzian resonance lineshapes, they have asymmetric and sharp slopes around the resonant wavelengths. By considering resonant modes in MRRs as the discrete state, Fano resonances were realized by coupling MRRs with other photonic structures, including Mach-Zehnder interferometers and Fabry-Perot (FP) cavities, which provide a quasicontinuum mode. These integrated structures sacrifice the compact footprint of MRRs, and it is challenging to achieve precise structure designs and device fabrications for overlapping MMR’s discrete modes with the quasicontinuum modes. This inserted air-hole functions as a phase-shifter between the discrete resonant mode in MRR and the continuum propagating mode in the bus-waveguide, which is experimentally verified by the transmission spectra of the fabricated devices with different air-hole locations and diameters. The obtained slope rate (SR) and extinction ratio (ER) of the Fano resonance lineshapes exceed 20 dB and 400 dB/nm, respectively
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