Wavelength Selective Optical Switch Research Articles

Flexible waveband routing node architecture for spatial-division and multi-band optical networks [Invited

We propose a network architecture named flexible waveband routing (FWR) that adopts flexible path bundling and bundled path routing. This two-stage routing scheme can be implemented by a combination of small degree wavelength selective switches (WSSs) and optical matrix switches. As the optical-cross-connect (OXC) scale depends on just that of the matrix switches adopted, large-scale OXC nodes are realized by introducing recently developed high-port-count switches. FWR supports spatial division multiplexing efficiently through its introduction of spatially joint switching at WSSs. Multi-band transmission can also be supported by the use of WSSs handling different frequency bands. Numerical simulations and transmission experiments confirm its validity.

Flexible channel selection method based on optical combs for broadband signals receiving.

A flexible channel selection method based on optical combs is proposed for reconfigurable optical channels in this paper. Optical-frequency combs with a large frequency interval are used to modulate broadband radio frequency (RF) signals, and an on-chip reconfigurable optical filter [Proc. of SPIE, 11763, 1176370 (2021).10.1117/12.2587403] is used to perform periodic carrier separation of wideband and narrowband signals and channel selection. In addition, flexible channel selection is achieved by presetting the parameters of a fast-response programmable wavelength-selective optical switch and filter device. Channel selection only relies on the combs through the Vernier effect of the combs and the passbands for different periods and does not require the use an additional switch matrix. Finally, flexible switching between and selection of specific channels for 13 GHz and 19 GHz broadband RF signals are experimentally verified.

RF Frequency Selective Switch by Multiple PMIM Conversions

Nowadays, broadband and multi-channel radio frequency (RF) processing has been widely used in communication, radar, countermeasure, and other applications. At present, multiple-input and multiple-output (MIMO)-oriented microwave photonic signal processing technology is relatively scarce, so this paper proposes an RF frequency selective switch (FSS) based on multiple phase modulation to intensity modulation (PMIM) conversions. PMIM conversion has been used in narrowband microwave photonic filtering in the past. We extend it to a wideband and arbitrarily reconfigurable RF spectrum processing unit through an optical frequency comb and periodic optical filter. Although we use the incoherent combination of a multi-wavelength light source, we can obtain any frequency response including rectangles only by using all positive tap coefficients. Using an optical wavelength selective switch (WSS), we obtain RF FSS, and the spectral resolution of RF FSS is much better than that of optical WSS, which is improved by more than two orders of magnitude. The above principles, including single-channel reconfigurable filtering and multi-channel RF FSS, are verified by experiments. Our technology provides a stable solution for future RF MIMO signal processing.

Dual-band polarized optical switch with opposite thermochromic properties to vanadium dioxide

A dual-band polarized wavelength-selective optical switch whose thermochromic transmission property is opposite to VO2 itself is proposed. The switch shows a low and high transmittance during phase transition from insulating VO2 to metallic VO2, respectively. The multi-mode coupled circuit model is employed to calculate and tailor the operating frequency of the switch in xz sections for TM waves and yz sections for TE waves. The switch exhibits a transmittance difference of more than one order of magnitude between “on” and “off” modes when the structure is same in the x and y directions under circularly polarized light incidence. For the condition that the structure is not same in the x and y directions, thermochromic transmittance becomes polarization-dependent. By superimposing two polarization states, a dual-band as well as broadband thermochromic transmission property is obtained. The mechanisms of suppressed and enhanced transmission lie in the excitation of MPC and MPV2, respectively. This study may have theoretical guiding significance for design and tailoring of metamaterials with wavelength-selective broadband thermochromic transmission property and potentially apply in active filters and architectural energy-efficient glass.

Tunable Infrared Optical Switch Based on Vanadium Dioxide.

A tunable infrared optical switch based on a plasmonic structure consisting of aluminum nanoarrays with a thin film of vanadium dioxide is proposed. This optical switch can realize arbitrary wavelength-selective optical switching in the mid-infrared region by altering the radii of the aluminum nanoarrays. Furthermore, since vanadium dioxide transforms from its low-temperature insulator phase to a high-temperature metallic phase when heated or applied voltage, the optical switch can achieve two-way switching of its “ON” and “OFF” modes. Finite-difference time-domain software is used to simulate the performance of the proposed infrared optical switch. Simulation results show that the switch offers excellent optical performances, that the modulation depth can reach up to 99.4%, and that the extinction ratio exceeds −22.16 dB. In addition, the phase transition time of vanadium dioxide is on the femtosecond scale, which means that this optical switch based on a vanadium dioxide thin film can be used for ultrafast switching.

A 1×20 MEMS mirror array with large scan angle and low driving voltage for optical wavelength-selective switches

Wavelength-selective switches (WSSs) are the core devices for reconfigurable optical add-drop multiplexers (ROADMs) that are essential in all-optical networks. WSSs based on microelectromechanical (MEMS) mirror arrays exhibit high potential due to their high switching speed and large port counts, but there still exist challenges to achieve large optical scanning angle at low voltage. This paper presents a 1×20 MEMS mirror array (MMA) design that can scan over 10° in both axes at less than 5 V. The MMA is based on an unique electrothermal bimorph actuator design that can perform 2D scanning and its fill factor reaches 96 %. The 1×20 MMA design has been successfully fabricated using a combined bulk- and surface- micromachining process. The size of each mirror plate is 240 μm by 500 μm. The measured maximum optical scan angles in the x-axis and y-axis are 29.3° and 11.8°, respectively, at 3 V. The measured response time is about 3.7 ms. The thermal crosstalks between adjacent electrothermal actuators are about 10 %. Long-term stability tests show that the angular drifts of the individual mirrors are about 0.002°/h.

Compensation of fiber dispersion induced-power fading in reconfigurable millimeter-wave optical networks

Radio-over-fiber (RoF) systems can be incorporated into a wavelength division multiplexing (WDM) and distributed antenna system (DAS) to vastly increase the data throughput. In this paper, a reconfigurable WDM system at millimeter (mm-wave) frequencies is theoretically proposed and experimentally demonstrated based on an optical frequency comb (OFC) and wavelength selective switch (WSS). The photonic carrier generation using OFC spectra is affected by chromatic dispersion which results in power fading and optical noise. Therefore, the tolerance of the mm-wave heterodyne carrier to fiber propagation is discussed and considered in the proposed architecture. Furthermore, this paper examines how the WSS can pre-compensate the fiber dispersion in terms of power fading on the beating carrier. Experimental measurements show that by variable adjustment of the amount of dispersion compensation applied, power fading of 15 dB can be mitigated and error vector magnitude (EVM) is reduced by 10%. By utilizing the well-known periodic behavior between carrier power penalty and chromatic dispersion, the WSS can also overcome the deep power fading over long fiber lengths (>25 km).

Thermal driven wavelength-selective optical switch based on magnetic polaritons coupling

A wavelength-selective optical switch by thermally controlling which has higher transmittance at metallic phase of Vanadium dioxide (VO2) and lower transmittance at insulating phase is presented. By skillfully designing the structure, magnetic polaritons (MPs) are excited to enhance transmission to 0.79 indicating “on” mode with VO2 at metallic phase. The coupling between two magnetic polariton modes is excited at the same frequency to suppress the transmittance peak to 0.045 indicating “off” mode with VO2 at insulating phase, demonstrating tunability by over an order of magnitude during phase transition. Magnetic polariton coupling mode is proposed to explain the phenomenon of surpressed transmission and the electromagnetic field distributions confirm it. The proposed optical switch still works well at a large oblique incidence and the resonant frequency does not change with the incident angle. Our study may benefit the microelectronics and infrared active filtering applications.

Hitless Wavelength-Selective Switch Using a Single Microring Resonator Assisted With a Symmetric MZI

We demonstrate an optical hitless wavelength-selective switch using a single microring resonator assisted with a symmetric Mach-Zehnder interferometer (MZI). A part of the ring waveguide and its symmetrical waveguide are designed to be an equally armed MZI as an on-off switch for the resonant state of the microring. The symmetric MZI is insensitive to the spectrum and it avoids free spectral range (FSR) matching or alignment in use. The FSR of the structure is 2.18 nm and the insertion loss (IL) at the drop-port is 1.8 dB. Our experimental results reveal that the fabricated device permits on-chip hitless rerouting of multi-wavelength signals, which means the intermediate wavelength remains unaffected during wavelength switching.

High-Resolution Tunable Filter With Flexible Bandwidth and Power Attenuation Based on an LCoS Processor

High-resolution optical filters and wavelength selective switches are the essential components in the current and next-generation dynamic optical networks. A high-resolution programmable filter for telecom application is proposed and experimentally demonstrated based on a 4 k phase-only liquid crystal on silicon (LCoS) spatial light modulator. The tuning resolution, bandwidth, and power attenuation for each wavelength channel can be modulated independently by remote software control. For each channel, the center wavelength is tuned in the step of 7.5 $ \pm$ 1 pm and the 3 dB bandwidth achieves from 10 GHz to 3 THz. Furthermore, by multi-casting hologram design techniques for an LCoS, the power attenuation is adjusted from 0 dB to 30 dB with the step of 0.1 dB. The insertion loss is less than 6 dB across the entire C -band and 1.8 dB of it can be further improved by adopting an LCoS chip with smaller reflection loss.

Integrated Reconfigurable Silicon Photonics Switch Matrix in IRIS Project: Technological Achievements and Experimental Results

This paper reports the performances of a silicon photonics optical switch matrix fabricated by using large-scale three-dimensional (3-D) integration. The wavelength selective optical switch consists of a photonic integrated circuit (PIC), with 1398 circuit elements, interconnected in a 3-D stack with its control electronic integrated circuit (EIC). Each PIC element can be trimmed or reconfigured by using metallic heaters. The EIC is designed to drive the heaters and to read the signal of monitor photodiodes integrated into the PIC. Small footprint and high energy efficiency are achieved in the PIC and the EIC. Automatic wavelength alignment of the optical circuits in the PIC to the ITU grid and fine temperature tuning of each photonic element to optimize the switch insertion losses are obtained by an optimization routine. A fully packaged switch with input/output fibers is tested both for optical and electrical characteristics as well as for the system performances. Fiber-to-fiber insertion losses of about 20 dB and channel isolation of −35 dB are achieved. Bit error rate characteristics at 25 Gb/s are evaluated. Perspective applications of the optical switch in optical transport and intra-data center networks are discussed.

De-multiplexing the required spectrum in a traffic demand into multiple non-adjacent granular spectrums for dynamic traffic grooming in EON

An elastic light-trail, the advanced version of a traditional light-trail, is one of the most recent dynamic traffic grooming technologies in an elastic optical network. In such networks, Orthogonal Frequency Division Multiplexing (OFDM) is a promising technology to execute the RSA (routing and spectrum assignment) algorithm and implement an elastic light-trail as a result. However, the reconfigurable optical add-drop multiplexers (ROADMs) and bandwidth variable Wavelength Selective Switches (WSSs) are required to implement an optically switched and spectrum varying elastic lightpath. In addition to the hardware equipment mentioned above, Add Drop Couplers (ADC) and optical ON/OFF switches (OS) are required to facilitate elastic light-trail in an elastic optical network. Hereafter, deployment of Add Drop Couplers (ADC) and optical ON/OFF switches incurs a significant network cost to facilitate elastic light-trail implementation. Toward the approach for eliminating this costly hardware setup, we have highlighted the fragmentation problem that occurs in spectrum domain in an optical fiber link. In this problem, the entire spectrum range in an elastic optical link is fragmented into several non-contiguous free spectrum slots at an instance during a data transportation session. In this regard, we have proposed “Multiple multi-hop non-contiguous elastic lightpath - MMNCEL” algorithm, where the required spectrum B of a traffic demand r(s, d, B, T) is sliced into n distinct granular spectrums {b1, b2, … bn} according to the current availability and status of fragmented spectrum slots in an elastic optical link. Moreover, to setup an elastic lightpath, the algorithm allocates the same range of spectrum from every optical link in a route to preserve Spectrum Continuity Constraint (SCC), whereas, at each hop in a multi-hop elastic lightpath the algorithm performs opto-electrical conversion. In this paper, our objective is to achieve maximum network throughput in an elastic optical network without deploying ADC and optical ON/OFF switches. However, in this work, we have investigated optical spectrum utilization efficiency for the proposed MMNCEL, existing elastic light-trail (Multi-hop Elastic Light-trail algorithm - MELT) and elastic lightpath (Multi-hop elastic Lightpath algorithm - MEL), and performed comparison measurements preciously.

Cross-cascaded AWG-based wavelength selective switching integrated module using polymer optical waveguide circuits

100-GHz cross-cascaded arrayed waveguide gratings (AWGs)-based wavelength selective optical switching optical cross-connects (OXCs) modules with Mach-Zehnder interferometer (MZI) thermo-optic (TO) variable optical attenuator (VOA) arrays and optical true-time-delay (TTD) line arrays is successfully designed and fabricated using polymer photonic lightwave circuit. Highly fluorinated photopolymer and grafting modified organic-inorganic hybrid material were synthesized as the waveguide core and cladding, respectively. The one-chip transmission loss is ~6 dB and the crosstalk is less than ~30 dB for the transverse-magnetic (TM) mode. The actual maximum modulation depths of different thermo-optic switches are similar, ~15.5 dB with 1.9 V bias. The maximum power consumption of a single switch is less than 10mW. The delay time basic increments are measured from 140 to 20 ps. Proposed novel module is flexible and scalable for the dense wavelength division multiplexing network.

Design and Implementation of Hybrid Light and Microwave Switches Based on Wavelength Selective Switch for Future Satellite Networks

A hybrid switching node structure with light and microwave links is proposed, which is applicable to the future data relay satellite systems, aiming at the development trend of coexistence of light- link and microwave-link in the future. An experimental system for the light and microwave hybrid switching node based on wavelength selective optical switches (WSS) and optical transceiver modules, is established. It is shown by our experiment that this hybrid switching node can realize the dynamic bandwidth allocation and wavelength routing while the bit error rate of light link is less than 10?12, which provides a method for solving the hybrid switching problem of light-link and microwave-link on the future data relay satellite systems.

Architecture to Integrate a Large-Scale DOPC-Based Optical Switching System on a Chip

In this paper, we propose a four-level architecture to integrate an entire N × M × K optical switching system on a chip using wavelength selective optical switches based on digital optical phase conjugation (DOPC), where N is the number of input fibers, M the number of output fibers and K the number of wavelengths carried within each input and output fiber. We show that a strictly non-blocking 128 × 128 × 48 system might be built on a 131 mm × 67 mm chip. With a 0.8 nm channel space, such optical switching systems might be widely used for dense wavelength division multiplexing networks.

Simultaneous beam steering of multiple signals based on optical wavelength-selective switch

A novel, photonics-based scheme for the independent and simultaneous beam steering of multiple radio frequency signals at a wideband phased-array antenna is presented. As a proof of concept, a wavelength-selective switch (WSS) is employed both as a wavelength router to feed multiple antenna elements and as a tunable phase shifter to independently control the phase of each signal at any antenna element. In the experiment, two signals at 12.5 and 37.5 GHz are simultaneously fed to the four output ports of the WSS with independent and tunable phase shifts, emulating the independent steering of two signals in a four-element phased-array antenna. The results confirm the precision and flexibility of the proposed scheme, which can be realized both with bulk components or resorting to photonic integrated circuits, especially for wide-band applications. The architecture for a possible integrated implementation of the proposed solution is presented, employing a structure based on micro-ring resonator. Starting from these results, the feasibility of an integrated version of the presented architecture is also considered. The proposed photonic integrated circuit realizing the beam-forming network might be based on tunable true-time delay, as well as on phase shift through micro-ring resonators, and could be conveniently implemented with CMOS-compatible silicon technology.

Enhancing tilt range of electrostatic torsional micromirrors using robust adaptive critic-based neurofuzzy control

Electrostatic torsional micromirrors, as instances of Micro Electro Mechanical Systems (MEMS), have many optical network applications; such as optical wavelength-selective switches, optical cross-connects, etc. For all these applications, the micromirror needs to have minimal overshoot and settling time in order to minimize the time between two successive switching operations. Moreover, the controllability and stability of a torsional micromirror are major challenges due to high nonlinearities in its dynamic characteristics.In this paper, a robust adaptive critic-based neurofuzzy controller is proposed for electrostatic torsional micromirrors, which can improve the performance of the mirror tilting and enhance the robustness of the system to any stochastic perturbations. Furthermore, utilizing this adaptive neurofuzzy controller, which is based on a proportional and derivative (PD) critic, the micromirror “pull-in” phenomenon is crucially eliminated. Thus, the mirror tilting range is significantly expanded. Moreover, the stability of the closed-loop system is guaranteed via the Lyapunov theorem.The robust adaptive critic-based neurofuzzy controller is simulated for a 1-DOF electrostatic torsional micromirror and the results show the effectiveness of this approach for various tilt ranges and conditions. In addition, the robustness of this controller is examined in the presence of input noises and parameter uncertainties.

Control for Suppression of Channel Power Excursions in ROADM-Based WDM Chain Networks

This paper addresses the problem of reducing power excursions in amplified wavelength division multiplexed networks with reconfigurable optical add-drop multiplexers (ROADM) and wavelength selective switches (WSS). In dynamic network loading scenarios, conventional WSS control leads to transient power excursions across the chain. Two WSS control strategies are considered: an integral-control and a modified integral-coordinated control for tracking. For both algorithms, convergence at an isolated node is shown to depend on the optical amplifier nonlinear gain coupling quantified by its Lipschitz constant. In a chain network with independently controlled ROADM nodes, the modified WSS control effectively decouples the nodes and reduces WSS transient power excursions across the chain. The bounds on these reductions are quantified analytically with respect to the L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> norm, by applying Lyapunov analysis techniques for the interconnected chain system. Numerical results that verify and compare the two WSS control strategies are provided by implementation on a Transparent Optical Mesh (ATOM) platform for two realistic dynamic network loading scenarios.

Compact wavelength-selective optical switch based on digital optical phase conjugation

In this Letter, we show that digital optical phase conjugation might be utilized to construct a new kind of wavelength-selective switches. When incorporated with a multimode interferometer, these switches have wide bandwidth, high tolerance for fabrication error, and low polarization dependency. They might help to build large-scale multiwavelength nonblocking switching systems, or even to fabricate an optical cross-connecting or routing system on a chip.

High-performance optical wavelength-selective switches based on double ring resonators

In order to improve the performance of optical wavelength-selective switches based on double micro-ring resonators, an asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQWs) structure is utilized as the active light guiding medium. The AICD-SQW active layer has advantages, such as large change range in absorption coefficient, high extinction ratio, large Stark shift and very low insertion. For predicting the switching characteristics of double ring resonators structure, the absorption coefficient and real refractive index changes of the AICD-SQW active layer are calculated for different applied electric fields for TE input light polarization. Simulation results show that switching characteristics strongly depend on changes in absorption coefficient and real refractive index of active layer. In addition, isolations of 37.44 dB and 26.84 dB are realized between drop and through ports, when drop and through ports are ON and OFF, respectively, and vice versa.