A compact structure for realizing Lorentzian, Fano, and electromagnetically induced transparency resonance lineshapes in a microring resonator

Linpeng Gu,Xuetao Gan,Liang Fang,Juntao Li,Soo Jin Chua,Jianlin Zhao,Hanlin Fang

doi:10.1515/nanoph-2018-0229

Abstract

Abstract Microring resonators, as a fundamental building block of photonic integrated circuits, are well developed into numerous functional devices, whose performances are strongly determined by microring’s resonance lineshapes. We propose a compact structure to reliably realize Lorentzian, Fano, and electromagnetically induced transparency (EIT) resonance lineshapes in a microring. By simply inserting two air-holes in the side-coupled waveguide of a microring, a Fabry-Perot (FP) resonance is involved to couple with microring’s resonant modes, showing Lorentzian, Fano, and EIT lineshapes over one free spectral range of the FP resonance. The quality factors, extinction ratios (ERs), and slope rates (SRs) in different lineshapes are discussed. At microring’s specific resonant wavelength, the lineshape could be tuned among these three types by controlling the FP cavity’s length. Experiment results verify the theoretical analysis well and represent Fano lineshapes with ERs of about 20 dB and SRs over 280 dB/nm. The reliably and flexibly tunable lineshapes in the compact structure have potentials to improve microring-based devices and expand their application scopes.

Highlights

Microring resonators (MRRs) are widely employed for on-chip optical interconnects, nonlinear optics, and sensings relying on their compact size, high quality (Q) factor, and compatibility with the integration of other passive and active photonic devices [1,2,3,4,5,6]
By inserting two air-holes in the side-coupled waveguide of a microring, a Fabry-Perot (FP) resonance is involved to couple with microring’s resonant modes, showing Lorentzian, Fano, and electromagnetically induced transparency (EIT) lineshapes over one free spectral range of the FP resonance
We demonstrate that, by coupling an MRR with a bus-WG inserted with two air-holes, as shown schematically in Figure 1A, all of the above mentioned resonance lineshapes could be realized

Summary

Introduction

Microring resonators (MRRs) are widely employed for on-chip optical interconnects, nonlinear optics, and sensings relying on their compact size, high quality (Q) factor, and compatibility with the integration of other passive and active photonic devices [1,2,3,4,5,6]. Gu et al.: A compact structure for realizing Lorentzian, Fano, and EIT resonance lineshapes. It is possible to alter the MRR’s resonance into an electromagnetically induced transparency (EIT) lineshape, showing a narrow transparency peak residing in a broad transmission valley It has potentials in ultra-dense on-chip wavelength division multiplexer [15] as well as enhancing the cavity’s finesse [16]. The EIT resonances originate from coherent interferences between coupled resonant modes They are realized in structures consisting of two or more MRRs coupled with a bus-WG or a MZI [15, 17,18,19], which have large device footprint and require rigorous considerations of the resonant modes’ overlap. L. Gu et al.: A compact structure for realizing Lorentzian, Fano, and EIT resonance lineshapes 843 modes.

Model and theory

Experimental results

Conclusions