Abstract
A chip-scale tunable optical filter is indispensable to meeting the demand for reconfigurability in wavelength division multiplexing systems, channel routing, and switching, etc. Here, we propose a new scheme of bandwidth tunable band-pass filters based on a parity-time (PT) symmetric coupled microresonator system. Large bandwidth tunability is realized on the basis of the tuning of the relative resonant frequency between coupled rings and by making use of the concept of the exception point (EP) in the PT symmetric systems. Theoretical investigations show that the bandwidth tuning range depends on the intrinsic loss of the microresonators, as well as on the loss contrast between the two cavities. Our proof-of-concept device confirms the tunability and shows a bandwidth tuning range from 21 GHz to 49 GHz, with an extinction ratio larger than 15 dB. The discrepancy between theory and experiment is due to the non-optimized design of the coupling coefficients, as well as to fabrication errors. Our design based on PT symmetry shows a distinct route towards the realization of tunable band-pass filters, providing new ways to explore non-Hermitian light manipulation in conventional integrated devices.
Highlights
Driven by the great need for low-cost, scalable, and low-power-consumption integrated optical systems, functional devices based on silicon photonics have been extensively explored in recent years to host system-level integration for various functionalities, including modulators, filters, isolators, and transceivers [1]
A 3 μm-thick silica layer is deposited on the top by plasma-enhanced chemical vapor deposition (PECVD)
The conversion between the gap numbers and the coupling coefficients are determined by the coupled mode theory [16], with the optical fields extracted from finite-difference time-domain (FDTD) software (FDTD solutions)
Summary
Driven by the great need for low-cost, scalable, and low-power-consumption integrated optical systems, functional devices based on silicon photonics have been extensively explored in recent years to host system-level integration for various functionalities, including modulators, filters, isolators, and transceivers [1]. Proposed a structure composed of MZI with coupled rings and realized a ~113-GHz tuning range [3]. An optical filter based on cascaded rings was proposed by Ong et al [5], reaching a tuning range of 113 GHz using the broadened nature of the synthetic spectra of multiple coupled resonant modes. We propose a simple design for a tunable bandwidth band-pass filter based on a PT symmetric coupled dual-ring system. A clear physical picture behind the coupled microresonators in terms of the PT symmetry is explicitly derived, providing a new guideline for the design of bandwidthtunable filter This bandwidth tuning concept is confirmed by theoretical modeling, as well as by experimental measurements of the proof-of-concept devices that have been fabricated on the silicon-on-insulator (SOI) platform
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