Deep-learning-based model for the inverse design of a reconfigurable multi-tap optical filter.

Reconfigurable optical filter can satisfy diverse filtering requirements in different application scenarios and shorten development cycle. However, it is still challenging to achieve multi-functional filtering richness with high performance. Here, based on a tunable optical coupler cascaded with a coupled resonator optical waveguide (CROW), a highly flexible and reconfigurable integrated optical filter is proposed and demonstrated on the low-loss silicon nitride platform. Both single injection and double injection configurations can be deployed to obtain rich spectral responses. For the single injection configuration, flat-top bandpass filter was experimentally achieved, whose shape factor could be as low as 1.648 and extinction ratio (ER) can be 37.5 dB with a bandwidth tuning range from 2.12 to 4.01 GHz. For the double injection configuration, Lorentz, triangular, sinusoidal, square, tangent-like, and interleaver spectral responses have been reconfigured by controlling seven phase shifters. Moreover, both single and double free spectral ranges (FSR) can be obtained for a fixed ring perimeter in the double injection configuration. The measured ER for the notch filter of Lorentz responses with double FSR is 36.8 dB. We believe that the proposed device has great potential for reconfigurable photonic filtering and microwave photonic signal processing.

In general, to fit various application scenarios, different types of optical filters are needed and designed individually, which leads to high cost and long development times. Here we proposed a reconfigurable multi-functional optical filter based on self-coupled microring assisted MZI structure, which can be reconfigured into five different kinds of devices, including the optical switch, asymmetric MZI filter, ring assisted MZI filter, double injection microring resonator and self-coupled micro-ring assisted MZI filter. An analytical model was established based on the transfer matrix method to investigate the function reconfigurations, which were then verified experimentally by simply controlling the six thermo-optical phase shifters in the structure. Furthermore, our proposed reconfigurable multi-functional optical filter provides performances that are comparable to the individual devices or even better, which has the potential to be applied in the integrated optical signal processing and microwave photonics systems.

Fully reconfigurable optical filters are indispensable building blocks to realize reconfigurable photonic networks/systems. This paper proposes a reconfigurable and dual-polarization optical filter based on a subwavelength grating waveguide operating in the Bragg reflection mechanism and combined with a low-loss phase change material Ge2Sb2Se4Te1. Numerical simulations indicate that, for TE(TM) polarization, the presented Bragg grating filter offers up to 20 nm (17 nm) redshift with amplitude modulation of 6 dB (0.15 dB) at 1550 nm. Using the effective medium theory, we obtained the six-level crystallization performance of the optical filter. The proposed optical filter has potential applications in wavelength-division-multiplexing systems, optical signal processing, and optical communications.

Reconfigurable optical filters with tailorable performances are highly demanded in multi-purpose adaptive signal processing applications. We demonstrate infinite impulse response (IIR) silicon optical filters with a variable filter order by switching the optical path in a 16 × 16 Benes switch chip. The basic unit of the optical filter is a dual-ring assisted Mach-Zehnder interferometer. TiN microheaters are integrated in both ring resonators for resonance control, allowing for continuous tuning of the filter center wavelength and the bandwidth. Multiple high-order optical filters from the 2nd order up to the 14th order are obtained. The filter bandwidth tuning range is from 0.19 nm (23.75 GHz) to 1.06 nm (132.5 GHz) with a 1-dB in-band ripple. The out-of-band rejection ratio exceeds 30 dB for the 8th and 10th-order filters, limited by the inter-path optical crosstalk in the Benes architecture. The results point to new ways of reutilizing an existing switch matrix to flexibly construct wavelength-filtering devices.

We present a silicon microring resonator-based reconfigurable optical lattice filter for on-chip signal processing. The device design employs a novel infinite impulse response (IIR) structure with high flexibility for rapid reconfiguration. Preliminary measurement results show high-quality filter response.

Over the past ten years, DARPA has made significant investments toward advancing the field of microwave photonics. This paper reviews DARPA-funded progress in this subject over the past decade. DARPA-funded research has advanced the state-of-the-art for microwave-photonic components, including low noise laser diodes, electrooptic modulators and high power photodiodes, as well as microwave photonic link configurations, including photonic downconversion, reconfigurable optical filters and optical phase-locked loops. These investments have yielded dramatic improvements in spurious-free dynamic range (SFDR). Measured performance includes SFDRs exceeding 115 dB · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> at 16 GHz using broadband externally modulated links; exceeding 120 dB · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> at 10 GHz using sub-octave electrooptic modulators; near 135 dB · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> at 100 MHz using optical phased-locked loops as linear phase demodulators; and exceeding 125 dB · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> at 5 GHz using optical filtering, downconversion and predistortion compensation.

We report our recent progress on reconfigurable self-coupled optical waveguide (SCOW) resonators as optical filters. The SCOW resonators exhibit high-order optical filtering features with less strict requirement on device fabrication as required in regular coupled microring filters.

In this paper, a silicon photonic crystal waveguide-based 1×4 and 2×4 reconfigurable optical switch and tunable bandpass filter are designed with low insertion loss, fast response time, and a high-quality factor for an ultrafast optical network. This device comprises three directional couplers and four waveguides arranged on a hexagonal lattice platform. The proposed nanophotonic device operating wavelength range is calculated by the plane wave expansion method, and performance parameters are numerically analyzed by the finite-difference-time-domain method. An all-optical mechanism with different operating wavelengths is used to realize the reconfigurable switch. The thermo-optic effect is used to design the tunable optical filter. The proposed silicon photonic structure is designed with an ultrafast response of 0.91 ps, a minimum insertion loss of 0.00021 dB, and an ultra-compact size of 346.56µm2. Hence, this nanophotonic platform is appropriate for photonic integrated circuits, optical signal processing systems, and quantum computing.

Most of the present communication applications have switched onto the photonic filtering as it gives numerous advances over its counterparts. Reconfigurable filter design is gaining popularity for applications having complex hardware circuitry. The paper discusses about a reconfigurable optical filter by Wavelength Selective Switching using Liquid Crystal on Silicon technology for filtering of Radio and Microwave frequency signals. The main aim of the work is to explore the feasibility of usage of photonic filters along with fiber links in radar signal distribution networks.

We experimentally demonstrate reconfigurable ultra-narrowband optical filters realized by localized dynamic Brillouin gratings in a polarization maintaining fiber. The filters are characterized in terms of bandwidth, optical signal-to-noise ratio and peak to sidelobe ratio.

Optical notch filters with tunable central wavelength and reconfigurable free spectral range on SOI platform

We present a reconfigurable optical filter with multiple passband channels based on the combination of a diffraction grating and an array of digital micromirrors. The filter allows for adjustment of the central frequency of its individual passband channels to match standard wavelength grids with precision better than 0.033 nm. The number of channels, the channel passband width, and the channel peak profile can be dynamically reconfigured by changing the periodic pattern imposed to the digital micromirror array. Experimental results are in excellent agreement with basic design relations describing the spectral characteristics of the filter.

We present a novel reconfigurable optical add-drop filter based on phase-sensitive amplifiers (PSAs). By manipulating the relative phase among an optical pump, signals, and idlers, spectral selectivity can be achieved along with low noise amplification. The use of backward Raman amplification enhances the phase-sensitive operation of the parametric process, enabling higher stopband isolation and lower intra-band crosstalk. A Raman-assisted phase-sensitive amplifier (RA-PSA) is characterized in detail, showing a 7.8-dB combined gain extinction ratio enhancement and 10.85-dB gain improvement. For the first time, we demonstrate an RA-PSA enabled optical add-drop filter with less than 0.4-dB penalty using three-channel QPSK signals. The novel scheme provides a simple way to enhance the extinction ratio of the PSA enabled add-drop filter, which can be an essential subsystem in optical links based on phase-sensitive amplification.

With increasing packet-based traffic in metro networks, fast reconfigurability is becoming a requirement for optical networks. Since manual reconfiguration could take weeks, carriers are upgrading their SONET/SDH infrastructures with reconfigurable optical add-drop multiplexers (ROADMs) and tunable optical filters. This paper looks at the issue of the impact of reconfigurability on a network's performance.

Thin film optical bandpass filters are widely used in Aditya Tokamak for the diagnosis of $\mathrm{H}\alpha$ and Carbon emission. In recent years, Fabry Perot based filters, polarization based filter and Bragg’s mirror based filters are cited in literatures for plasma diagnosis. Performance of these filters can be improved through optimization techniques like Particle Swarm optimization, Genetic Algorithm etc. However the major challenge lies in developing thin film optical bandpass filters for the desired Central WaveLength (CWL) and expected Full Width Half Maximum (FWHM). In this paper, a detailed literature survey is performed on the physics behind the design of optical band pass filters, optimization techniques and plasma diagnostics using optical filters.