Accurate frequency alignment in fabrication of high-order microring-resonator filters

Jie Sun,Henry I Smith,Jeffrey T Hastings,Marcus Dahlem,Charles W Holzwarth

doi:10.1364/oe.16.015958

Jie Sun, Henry I Smith + Show 3 more

Open Access

https://doi.org/10.1364/oe.16.015958

Copy DOI

Journal: Optics Express	Publication Date: Sep 23, 2008
Citations: 4	License type: cc-by

Affiliation: Massachusetts Institute of Technology

Abstract

Frequency mismatch in high-order microring-resonator filters is investigated. We demonstrate that this frequency mismatch is caused mainly by the intrafield distortion of scanning-electron-beam-lithography (SEBL) used in fabrication. The intrafield distortion of an SEBL system is measured, and a simple method is also proposed to correct this distortion. By applying this correction method, the average frequency mismatch in second-order microring-resonator filters was reduced from -8.6 GHz to 0.28 GHz.

Highlights

Microring-resonator filters have attracted much attention for their promising applications as optical add-drop filters in wavelength-division-multiplexing (WDM) networks [1,2], and in optical interconnections
The small device size, high index contrast, and multi-ring configuration present a number of fabrication challengers, as the optical response of such filters is extremely sensitive to nanoscale dimensional deviations [7]
We demonstrate that the frequency mismatch is caused primarily by the intrafield distortion in Scanning-Electron-Beam-Lithography (SEBL)

Summary

Introduction

Microring-resonator filters have attracted much attention for their promising applications as optical add-drop filters in wavelength-division-multiplexing (WDM) networks [1,2], and in optical interconnections. High-performance add-drop filters require a wide free-spectral-range (FSR), low loss, high in-band extinction, and a fast roll-off. One of the crucial issues in high-order microring filters is the resonant-frequency mismatch between rings, which markedly reduces the filter performance [8,9,10,11,12]. In a second-order microring filter designed to achieve maximally flat response, the flatness and symmetry of the through-port response, the in-band extinction and the filter roll-off are degraded due to the mismatch of resonant frequencies of the two rings. The intrafield distortion of an SEBL system (Raith 150) was measured, and the resulting frequency mismatch simulated for second-order microring filters. A simple method is proposed to correct the intrafielddistortion-induced frequency mismatch By applying this correction, the average frequency mismatch was reduced from -8.6GHz to 0.28GHz in second-order microring filters

Intrafield distortion in SEBL and its impact on frequency mismatch

Experimental demonstration

Correction of intrafield distortion

Conclusion