Silicon Photonic Filter Research Articles

Narrow-bandwidth silicon photonic CROW filter for carrier-extracted self-coherent (CESC) detection.

In this Letter, we report a second-order silicon photonic (SiP) coupled resonator optical waveguide (CROW) filter with an ultra-narrow 10-dB bandwidth of 1.75 GHz and a high extinction ratio (ER) of ∼50 dB. By utilizing this CROW filter, we demonstrated an innovative self-coherent detection, called carrier-extracted self-coherent (CESC) detection. By effectively suppressing signal components with the narrow-bandwidth CROW, full-field recovery can be achieved without expensive coherent lasers and sophisticated iteration algorithms. The performance of the CROW filter-based CESC system was further experimentally verified by retrieving 100 Gb/s QPSK signals.

On-Chip Reconstructive Spectrometer Based on Parallel Cascaded Micro-Ring Resonators

In contrast to cumbersome benchtop spectrometers, integrated on-chip spectrometers are well-suited for portable applications in health monitoring and environmental sensing. In this paper, we have developed an on-chip spectrometer with a programmable silicon photonic filter by simply using parallel cascaded micro-ring resonators (MRs). By altering the transmission spectrum of the filter, multiple and diverse sampling of the input spectrum is achieved. Then, combined with an artificial neural network (ANN) model, the incident spectrum is reconstructed from the sampled signals. Each MR is coupled to adjacent ones, and the phase shifts within each MR can be independently tuned. Through dynamic programming of the phases of these MRs, sampling functions featuring diverse characteristics are obtained based on a single programmable filter with an adjustable number of sampling channels. This eliminates the need for a filter array, significantly reducing the area of the on-chip reconstructive spectrometer. The simulation results demonstrate that the proposed design can achieve the reconstruction of continuous and sparse spectra within the wavelength range of 1450 nm to 1650 nm, with a tunable resolution ranging from 2 nm to 0.2 nm, depending on the number of sampling states employed. This benefit arises from the programmable nature of the device. The device holds tremendous potential for applications in wearable optical sensing, portable spectrometry, and other related scenarios.

Silicon Photonic Filters: A Pathway from Basics to Applications

Silicon photonics has found a profound place among emerging technologies in the past few decades due to several advantages. Due to a series of breakthroughs and increased funding from private and government sectors, the development of silicon photonics has accelerated especially starting from the two years 2004–2005 with a persisting and ever‐growing momentum. Among various components, the silicon photonic filters that selectively pass or block particular wavelengths with a finite bandwidth have found particular interest as they are useful in signal processing in different fields ranging from optical communication to microwave photonics and quantum photonics. Herein, a comprehensive review of silicon photonic filters focusing on the four most commonly used architectures, such as microring resonators, waveguide Bragg grating, Mach–Zehnder interferometers, and arrayed waveguide grating, encapsulating basics, and guidelines, in terms of simulating tools and topologies, of realizing reconfigurable and high‐performing filters for several applications, is provided. The novelty of this review relies on the fact that it summarizes these filter architectures covering a broad range of applications concisely and constructively and includes the basics, growth, and future trends, providing a clear understanding and importance of silicon photonic filters from research to commercialization perspective.

Computational reconstruction on-chip spectrometer based on reconfigurable silicon photonic filters

<sec>Spectroscopic analysis technique is an indispensable tool in many disciplines such as biomedical research, materials science, and remote sensing. Traditional benchtop spectrometers have several drawbacks; bulky, complex, and expensive, making them ineffective for emerging applications such as wearable health monitoring and Lab-on-Chip systems. Compared with bulky desktop spectrometers, integrated chip-level spectrometers find many applications in portable health monitoring, environmental sensing, and other scenarios. We design an on-chip spectrometer based on a silicon photonics platform. The device consists of a silicon photonic filter with a reconfigurable transmission spectrum.</sec><sec>By changing the transmission spectrum of the filter, the multiple and diverse sampling of the input spectrum can be obtained. Using an artificial neural network algorithm, the incident spectrum is reconstructed from the sampled signals. The reconfigurable silicon photonic filter is composed of intercoupled Mach-Zehnder interferometer and micro-ring resonator. The introduction of thermal-optic phase shifter facilitates the reconstruction of the transmission spectrum of filter. Through this approach, a response function encompassing diverse features of broad and narrow spectra can be obtained from a single reconfigurable filter, eliminating the need for a filter array and significantly reducing the footprint of the spectrometer.</sec><sec> Simulation results demonstrate that the designed device can achieve continuous and sparse spectrum reconstruction in a wavelength range of 1500–1600 nm, with a resolution of approximately 0.2 nm. On a test set composed of synthetic spectra, the calculated average RMSE for the reconstructed spectra is 0.0075, with an average relative error of 0.0174. Owing to the reconfigurable nature of the silicon photonic filter, this device exhibits the ability to flexibly adjust the number of sampling channels, thus enabling users to configure the chip according to specific application scenarios. This device possesses significant potential applications such as in wearable optical sensors and portable spectrometers.</sec>

High‐Performance Silicon Photonic Filter Using Subwavelength‐Structure Multimode Waveguide Gratings

AbstractOn‐chip photonic filters are one of the most important elements for spectrum manipulation in various optical systems, including wavelength‐division multiplexing and spectrum analysis. Currently, it is still very challenging to achieve scalable photonic filters with flexibly‐designed bandwidths, low excess losses, flat tops, and ultra‐wide free‐spectral ranges (FSRs). Here an unprecedented silicon photonic filter is proposed and demonstrated with high performances by using apodised antisymmetric multimode subwavelength gratings (MSWGs) structures. For the present silicon photonic filter, the MSWGs enable the index engineering in the Bragg lattice, which easily manipulates the coupling coefficient, the local effective index, and the mode profile flexibly. As a result, the strong side lobes of the grating filter are efficiently suppressed, while the bandwidth can be designed flexibly and the FSR is free. The fabricated silicon photonic filter is FSR‐free and shows a low excess loss of <1 dB and a high sidelobe suppression ratio of 20–40 dB.

Self-configuring programmable silicon photonic filter for integrated microwave photonic processors

Reconfigurable photonic filters show great promise as a potential solution to meet the evolving needs of future microwave communication systems. By integrating high-performance filters into programmable microwave photonic processors, they can provide significant benefits for signal processing applications. The development of an algorithm that can automatically characterize and reconfigure the filter using a single optical input and output port is essential for this purpose. This paper presents an optimization technique for a fully tunable ring-assisted Mach–Zehnder interferometer filter. The proposed filter design eliminates the need for monitoring components and employs a novel algorithm that operates independently in each ring by switching between the two arms of the filter. In addition, the filter can be configured to implement different filter architectures, allowing for flexible filtering requirements. Measurements were performed using the device as an interleaver, implementing different types of infinite impulse response filters in the optical and radio frequency domains. Side-coupled integrated spaced sequence of resonator filters were also implemented by reconfiguring the same device. These results demonstrate the exceptional reconfigurability of the filter design proposed herein in terms of bandwidth and central frequency.

Ultra-Broadband Integrated Optical Filters Based on Adiabatic Optimization of Coupled Waveguides

Broadband spectral filters are highly sought-after in many integrated photonics applications such as ultra-broadband wavelength division multiplexing, multi-band spectroscopy, and broadband sensing. In this study, we present the design, simulation, and experimental demonstration of compact and ultra-broadband silicon photonic filters with adiabatic waveguides. We first develop an optimization algorithm for coupled adiabatic waveguide structures, and use it to design individual, single-cutoff spectral filters. These single-cutoff filters are 1×2 port devices that optimally separate a broadband signal into short-pass and long-pass outputs, within a specified device length. We control the power roll-off and extinction ratio in these filters using the adiabaticity parameter. Both outputs of the filters operate in transmission, making it possible to cascade multiple filters in different configurations. Taking advantage of this flexibility, we cascade two filters with different cutoff wavelengths on-chip, and experimentally demonstrate band-pass operation. The independent and flexible design of these band edges enables filters with bandwidths well over 100 nm. Experimentally, we demonstrate band-pass filters with passbands ranging from 6.4 nm up to 96.6 nm. Our devices achieve flat-band transmission in all three of the short-pass, band-pass, and long-pass outputs with less than 1.5 dB insertion loss and extinction ratios of over 15 dB. These ultra-broadband filters can enable new capabilities for multi-band integrated photonics in communications, spectroscopy, and sensing applications.

Reconfigurable optical filter based on microring resonator assisted by tunable Sagnac reflector

To meet the demands for various applications in optical filtering and microwave signal processing, integrated silicon photonic filters are required to be multifunctional, reconfigurable and tunable. In this work, an integrated multi-functional optical filter is proposed, which is designed based on a tunable Sagnac loop reflector and a microring resonator. The through port and drop port of an add-drop microring resonator are connected with the two ports of a tunable reflector. By controlling the thermal phase shifters in different scenarios, the device can be reconfigured into a reflective-type asymmetric Mach-Zehnder interferometer filter, a reflective-type all-pass microring resonator filter and self-interference microring resonator filters. An analytical model is established based on the transfer matrix. The simulation results show that the device can achieve the following functions: sinusoidal spectral filtering with four different free spectral ranges, Lorentzian spectral filtering toggling between band pass and band stop, and spectral reconfigurations of Fano resonance, electromagnetically induced transparency, and electromagnetically induced absorption. Each spectrum mentioned above can be tuned fast and widely. Reflection provides a new degree of freedom in design, breaks through the inherent footprint limit, and achieves a wide range of free spectral ranges. Our proposed tunable Sagnac loop reflector assisted microring resonator provides a new scheme for realizing flexible, tunable and multi-functional reconfigurable integrated photonic filters, and has broad applications in the integrated photonic analog signal processing and microwave photonics.

Ultraflat bandpass, high extinction, and tunable silicon photonic filters.

We report on the design and the demonstration of silicon photonic ultraflat bandpass filters with low insertion loss and high out-of-band rejection for an operation near the 1550 nm wavelength band. These filters are based on cascading low (2nd) order Ring-Assisted Mach-Zehnder Interferometer (RAMZI) filter stages. The cascade design enables high out-of-band rejection while keeping the unit cells of each stage low order to be more tolerant to fabrication imperfections. The characterization of filters shows an insertion loss of ∼1 dB, an in-band ripple of <0.1 dB, an out-of-band rejection of >50 dB for a filter 3-dB bandwidth of ∼1.1 nm, and tunable up to ∼6 nm. We also investigate the filter's spur-free dynamic range at high input optical powers, which is important for RF photonics applications, and quantify a dynamic range of >60 dB for a laser power as high as ∼11.6 mW sent to the filter. Such integrated filters are promising for applications in pump wavelength rejection in four-wave mixing photon pair generation, and in RF antenna remoting where multiple RF signals are carried on different coarse wavelengths to be separated.

Surface acoustic wave photonic filters with a single narrow radio-frequency passband in standard silicon on insulator

Integrated microwave photonic filters are becoming increasingly important for signal processing within advanced wireless and cellular networks. Filters with narrow transmission passbands mandate long time delays, which are difficult to accommodate within photonic circuits. Long delays may be obtained through slow moving acoustic waves instead. Input radio-frequency information can be converted from one optical carrier to another via surface acoustic waves and filtered in the process. However, the transfer functions of previously reported devices consisted of multiple periodic passbands, and the selection of a single transmission band was not possible. In this work, we demonstrate surface acoustic wave, silicon-photonic filters of microwave frequency with a single transmission passband. The filter response consists of up to 32 tap coefficients, and the transmission bandwidth is only 7 MHz. The results extend the capabilities of integrated microwave photonics in the standard silicon-on-insulator platform.

CMOS compatible athermal silicon photonic filters based on hydrogenated amorphous silicon.

We report for the first time, wavelength filters with reduced thermal sensitivity, based on a combination of crystalline silicon and hydrogenated amorphous silicon (a-Si:H) waveguides, integrated on the same silicon on an insulator wafer through a Complementary Metal Oxide Semiconductor (CMOS) compatible process flow. To demonstrate the concept, we design and fabricate Mach Zehnder Interferometers (MZIs) and Arrayed Waveguide Gratings (AWGs) based on this approach, and we measure thermal drift <1[pm/°K] in MZIs and <10 [pm/°K] in AWGs at C band.

High-performance silicon photonic filters based on all-passive tenth-order adiabatic elliptical-microrings

Ultra-compact silicon photonic filters with box-like responses and high extinction ratios are proposed and demonstrated by introducing tenth-order adiabatic elliptical-microrings (AEMs) with bent directional couplers. For the AEMs, the waveguides in the non-coupling regions are wide and have a minimal bending radius, while the waveguides in the coupling regions are narrowed and have a maximal bending radius. The present silicon photonic filters based on tenth-order AEMs show a free spectral range as large as 37 nm for the first time. Even fabricated with commercial complementary metal–oxide–semiconductor-compatible 248 nm deep-ultraviolet lithography processes, the present devices show high performances with excess losses as low as ∼1 dB and extinction ratios as high as &amp;gt;60 dB. More importantly, the present silicon photonic filters work very well all-passively without any thermal control for calibration.

Dynamic mitigation of nonlinear effects in a silicon photonic add-drop filter.

Nonlinear effects limit the maximum amount of optical power that can be handled by silicon photonic integrated circuits (PICs). This limitation is particularly tight in resonant devices such as microring resonator (MRR) filters, suffering from a power-dependent resonance spread due to intracavity power enhancement. In this Letter, we present an automatic control system that can dynamically mitigate the nonlinear spectral distortion of silicon MRR filters by thermally controlling each MRR. The benefit of the proposed scheme is demonstrated on the spectral response of a polarization-transparent coupled-MRR filter operating on a 200 Gbit/s signal. The proposed technique, which does not require a priori information on the PIC topology and functionality, is scalable to more complex architectures and can be employed to compensate for generic nonlinear effects in different photonic platforms.

High-Order Adiabatic Elliptical-Microring Filter with an Ultra-Large Free-Spectral-Range

A silicon photonic filter with an ultra-large free spectral range (FSR) is proposed and demonstrated by introducing high-order adiabatic elliptical-microrings (AEMs) with bent directional couplers (DCs). For the AEMs, the waveguides in the non-coupling regions are wide and have a minimal bending radius, while the waveguides in the coupling regions are relatively narrow and have a maximal bending radius. Both the radius and width of AEMs have varied adiabatically. Furthermore, bent DCs are used to realize a sufficient coupling between the access waveguide and the microring waveguide and suppress the higher-order mode excitation. The fabricated filters based on the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order, 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order, and 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order AEMs have box-like spectral responses with an ultra-large FSR of ∼37 nm, which is a record for high-order microring filters to the best of our knowledge. Finally, an eight-channel silicon photonic filter with a channel-spacing of ∼3.2 nm and high extinction ratios of >30 dB is demonstrated.

Polarization-transparent silicon photonic add-drop multiplexer with wideband hitless tuneability

Flexible optical networks require reconfigurable devices with operation on a wavelength range of several tens of nanometers, hitless tuneability (i.e. transparency to other channels during reconfiguration), and polarization independence. All these requirements have not been achieved yet in a single photonic integrated device and this is the reason why the potential of integrated photonics is still largely unexploited in the nodes of optical communication networks. Here we report on a fully-reconfigurable add-drop silicon photonic filter, which can be tuned well beyond the extended C-band (almost 100 nm) in a complete hitless (>35 dB channel isolation) and polarization transparent (1.2 dB polarization dependent loss) way. This achievement is the result of blended strategies applied to the design, calibration, tuning and control of the device. Transmission quality assessment on dual polarization 100 Gbit/s (QPSK) and 200 Gbit/s (16-QAM) signals demonstrates the suitability for dynamic bandwidth allocation in core networks, backhaul networks, intra- and inter-datacenter interconnects.

Silicon photonic filters

AbstractPhotonic filters are playing a very important role in many applications, including optical interconnects as well as optical sensing. As silicon photonics has provided a very attractive platform to realize the high integrated intensity and low cost, various silicon‐based on‐chip photonic filters have been proposed and demonstrated in the past decade. In this paper, we give a review of recent progresses of silicon photonic filters based on different structures, including Mach‐Zehnder interferometers, microring resonators, waveguide Bragg grating, and arrayed‐waveguide gratings.

Thermally-Reconfigurable Silicon Photonic Devices and Circuits

Reconfigurable photonic integrated devices and circuits are very important for many applications. Among various mechanisms for realizing reconfigurability, thermo-optic effect is popular because of the availability for many materials, the design simplicity and the fabrication ease. In particular, silicon has a large thermo-optic coefficient as well as a high heat conductivity, and thus it is promising to realize efficient thermally-reconfigurable silicon photonic integrated devices and circuits. Recent progress is reviewed in this paper. First, thermally-tunable silicon photonic filters based on different structures are summarized, including microring resonators (MRRs) and MRRs-assisted Mach-Zehnder interferometers (MZIs). Second, silicon photonic switches based on MZIs and MRRs are reviewed. Finally, a review is given for thermally-reconfigurable silicon photonic integrated circuits developed for the applications in quantum photonics, microwave photonics, and optical interconnects.

Silicon photonic add-drop filter for quantum emitters.

Integration of single-photon sources and detectors to silicon-based photonics opens the possibility of complex circuits for quantum information processing. In this work, we demonstrate integration of quantum dots with a silicon photonic add-drop filter for on-chip filtering and routing of telecom photons. A silicon microdisk resonator acts as a narrow filter that transfers the quantum dot emission and filters the background over a wide wavelength range. Moreover, by tuning the quantum dot emission wavelength over the resonance of the microdisk, we can control the transmission of the quantum dot emission to the drop and through channels of the add-drop filter. This result is a step toward the on-chip control of single photons using silicon photonics for applications in quantum information processing, such as linear optical quantum computation and boson sampling.

Silicon photonic add-drop filter based on a grating-assisted co-directionally coupled vertical hybrid structure.

Add-drop filters (ADFs) are an essential component in optical interconnection using dense wavelength-division multiplexing. Silicon photonic ADFs based on contra-directional coupling have been well developed, but those based on grating-assisted co-directional coupling (GACC) have never been studied. This paper reports an ADF based on GACC in a vertical hybrid structure (VHS). which consists of two width-modulated silicon strip waveguides with a large lateral gap and a wide silicon nitride strip waveguide above them. The VHS makes it possible for the ADF to have a narrow 3-dB bandwidth as well as a short grating length. An efficient analysis method for design is explained, and the ADF is designed. Theoretical investigation of the ADF demonstrates that the ADF has a 3-dB bandwidth of 1.16 nm and a grating length of 1.13 mm, which are similar to those of ADFs based on contra-directional coupling. As an application, the ADF is used for a nonvolatile switchable ADF by adding an optical phase change material strip above the silicon nitride waveguide. The nonvolatile switchable ADF is shown to have an extinction ratio larger than 30 dB. The investigated ADF requires neither waveguides in close proximity nor grating teeth with dimensions close to the resolution of deep UV lithography. In this regard, it has the advantage of ease of fabrication as compared to ADFs based on contra-directional coupling. Therefore, the ADF is expected to play a key role in optical interconnection using dense wavelength-division multiplexing, prevailing over ADFs based on contra-directional coupling.

Wideband adaptive microwave frequency identification using an integrated silicon photonic scanning filter

Photonic-assisted microwave frequency identification with distinct features, including wide frequency coverage and fast tunability, has been conceived as a key technique for applications such as cognitive radio and dynamic spectrum access. The implementations based on compact integrated photonic chips have exhibited distinct advantages in footprint miniaturization, light weight, and low power consumption, in stark contrast with discrete optical-fiber-based realization. However, reported chip-based instantaneous frequency measurements can only operate at a single-tone input, which stringently limits their practical applications that require wideband identification capability in modern RF and microwave applications. In this article, we demonstrate, for the first time, a wideband, adaptive microwave frequency identification solution based on a silicon photonic integrated chip, enabling the identification of different types of microwave signals from 1 to 30 GHz, including single-frequency, multiple-frequency, chirped-frequency, and frequency-hopping microwave signals, and even their combinations. The key component is a high Q-factor scanning filter based on a silicon microring resonator, which is used to implement frequency-to-time mapping. This demonstration opens the door to a monolithic silicon platform that makes possible a wideband, adaptive, and high-speed signal identification subsystem with a high resolution and a low size, weight, and power (SWaP) for mobile and avionic applications.