Abstract
A new reconfigurable, tunable on-chip optical filter bank is proposed and analyzed for the silicon-on-insulator platform at the ~1550 nm wavelength. The waveguided bank is a cascade connection of 2 x 2 Mach-Zehnder interferometer (MZI) filters. An identical standing-wave resonator is situated in each MZI "arm." Using the thermo-optic (TO) effect to perturb this waveguide's index, the TO heater stripes provide continuous tuning of the filter by shifting the resonance smoothly along the wavelength axis. To reconfigure and program the cascade array, a broadband 2 x 2 MZI-related switch is inserted between adjacent filters. The novel TO switch, described here, can provide either single or double interconnection of 2 x 2 filters. The filter resonator is a new in-guide array of N closely coupled phase-shifted Bragg-grating resonators that provide one resonant spectral profile with 5 to 100 GHz bandwidth. The length of each grating cavity in the N group is chosen according to the Butterworth filter technique, and this gives high peak transmission for the composite. The predicted spectral profiles of a three-stage cascade show two-or-three peaks, or two-or-three notches with movable wavelength-locations as well as tunable wavelength-separations between those features. A tunable notch within a wider movable passband is also feasible. Potential applications include microwave photonics, wavelength-selective systems, optical spectroscopy and optical sensing.
Highlights
This theoretical modeling-and-simulation paper deals with a new kind of waveguided on-chip integrated-photonic network called the “reconfigurable cascaded-filter array”(RCFA)which is a type of optical filter bank
At the output ports of the bank, complex optical spectral profiles are available, and those profile shapes are readily tuned by means of thermo-optical (TO) heater strips deployed upon individual Mach-Zehnder interferometer (MZI) filters located within the bank
The RCFA is constructed from 2 x 2 building-block filters and in this paper we have focused on a new type of building block which is an MZI in which each of two identical waveguided “arms” consists of several Bragg-grating resonantors that are closely coupled to each other within a strip channel to form one effective resonator
Summary
This theoretical modeling-and-simulation paper deals with a new kind of waveguided on-chip integrated-photonic network called the “reconfigurable cascaded-filter array”(RCFA)which is a type of optical filter bank. The RCFA is constructed from 2 x 2 building-block filters and in this paper we have focused on a new type of building block which is an MZI in which each of two identical waveguided “arms” consists of several Bragg-grating resonantors that are closely coupled to each other within a strip channel to form one effective resonator. As discussed below, this allows Bragg engineering of “rectanglelike” filter profiles having very steep side walls (fast roll off) as desired for high performance optical-microwave applications.
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