Widely bandwidth-tunable silicon filter with an unlimited free-spectral range

Abstract

Next-generation high-capacity optical networks require flexible allocation of spectrum resources, for which low-cost optical filters with an ultra-wide bandwidth tunability beyond 100 GHz are desired. We demonstrate an integrated band-pass filter with the bandwidth continuously tuned across 670 GHz (117-788 GHz) which, to the best of our knowledge, is the widest tuning span ever demonstrated on a silicon chip. The filter also features simultaneous wavelength tuning and an unlimited free spectral range. We measured an out-of-band contrast of up to 55 dB, low in-band ripples of less than 0.3 dB, and in-band group delay variation of less than 8 ps. This result was achieved using cascaded Bragg-grating-assisted contra-directional couplers and micro-heaters on the 220 nm silicon-on-insulator platform with a very compact footprint of less than 7000 μm2. Another design with the bandwidth continuously tunable from 50 GHz to 1 THz is also presented.

Coherency‐Broken Bragg Filters: Overcoming On‐Chip Rejection Limitations

“…In the case of cascaded multistage filters, relative phase errors may result in destructive interferences or relative wavelength shifts that offset the benefits of cascading. These interference effects have been minimized in optical fibers and Si chips by cascading grating sections with different Bragg resonance wavelengths. Although effective for dispersion compensation or tuning of the filter bandwidth, this strategy does not overcome rejection depth limitations as each grating section reflects in a different wavelength range.…”

Subwavelength-grating contradirectional couplers for large stopband filters

“…Various kinds of devices have been proposed to realize filtering on the 220-nm-thick SOI platform such as Bragg gratings [1], microring resonators [2], Mach-Zehnder interferometers [3], contra-directional couplers [4] and many others. While most of these demonstrations are narrow band, there is an interest to develop broader filter designs, from hundreds of GHz to a few THz, for applications such as bandwidth-tunable filtering [5] and dispersion engineering [6]. Few designs have been demonstrated to allow wide band filtering so far.…”

“…Those values are then used as inputs for the transfer matrix method (TMM) to calculate the spectral responses of the device. The TMM also allows to consider linear chirp, random phase noise, phase-shift and loss to adjust the simulation to fabrication variability [5]. However, coupling-coefficient calculation using the coupled-mode theory for gratings structure tends to overestimate the coupling coefficient due to the innate approximation of strong corrugations.…”

Hybrid multimode resonators based on grating-assisted counter-directional couplers

“…GACDC operate as four-port Bragg reflectors that produce a spectral stop band in the throughport, a transmission window at the drop-port, and negligible add-port transmission when the phase-matching condition is met [22]. They consist of closely spaced waveguides with periodic sidewall perturbations (grating) that act as counter-directional mirrors on either side of a cavity created by an unperturbed waveguide section, as depicted in Fig.…”