A General Variable Bandwidth Microring Filter for Lossless Bandwidth Tuning

We propose a general variable bandwidth filter of arbitrary even order based on the sum-difference microring filter architecture. The filter bandwidth can be varied by tuning only the resonant frequencies of the microrings and thus do not require additional controls other than those used to tune the filter center frequency. In addition, we show that there exists a bandwidth tuning range over which the filter exhibits no extra insertion loss and no degradation in the filter shape. We demonstrated a 4^th-order variable bandwidth filter in Silicon-on-Insulator, achieving a bandwidth tuning range from 0.3 nm to 1.35 nm with a maximum in-band ripple of 3 dB. The proposed variable bandwidth filter could serve as a key element in elastic optical networks which can support variable data bandwidth allocation on demand.

I. Introduction

To Meet the increasing growth in internet data traffic, elastic optical networks (EONs) have recently emerged as a viable solution that can adapt in real time to data transmission dynamics and thus more efficiently manage network resources [1], [2]. One of the key enabling elements of EONs is the variable bandwidth filter (VBF), which allows both the center wavelength and bandwidth to be reconfigured on demand. The ability to vary the bandwidth allows for real-time accommodation of different data modulation formats, such as ON-OFF keying [3], [4], DPSK, PAM-4 [5], [6] and high-order QAMs [7], [8], each with different spectral efficiency and bandwidth requirements. This has motivated recent research and development of VBFs, especially those that can be implemented on an integrated photonics platform.