Series Coupled Microring Resonator Research Articles

Photonic time-delayed reservoir computing based on series-coupled microring resonators with high memory capacity.

On-chip microring resonators (MRRs) have been proposed to construct time-delayed reservoir computing (RC) systems, which offer promising configurations available for computation with high scalability, high-density computing, and easy fabrication. A single MRR, however, is inadequate to provide enough memory for the computation task with diverse memory requirements. Large memory requirements are satisfied by the RC system based on the MRR with optical feedback, but at the expense of its ultralong feedback waveguide. In this paper, a time-delayed RC is proposed by utilizing a silicon-based nonlinear MRR in conjunction with an array of linear MRRs. These linear MRRs possess a high quality factor, providing enough memory capacity for the RC system. We quantitatively analyze and assess the proposed RC structure's performance on three classical tasks with diverse memory requirements, i.e., the Narma 10, Mackey-Glass, and Santa Fe chaotic timeseries prediction tasks. The proposed system exhibits comparable performance to the system based on the MRR with optical feedback, when it comes to handling the Narma 10 task, which requires a significant memory capacity. Nevertheless, the dimension of the former is at least 350 times smaller than the latter. The proposed system lays a good foundation for the scalability and seamless integration of photonic RC.

Design of high-order series-coupled microring resonator wavelength filter with differential evolution method

A design method for higher-order series-coupled microring resonator (MRR) wavelength filters is proposed and discussed. The differential evolution method is one of the machine learning methods, and it is a type of evolutionary algorithm that can be applied to a variety of optimization problems, including non-linear, partially impossible, and multi-modal problems. We design an evaluation function that satisfies multiple requirements by weighting each evaluation item, and optimize the design parameters using the differential evolution method. The weighting values of the evaluation function are adjusted by supervised learning Support Vector Machine to produce a more accurate evaluation function. The designs of high-order MRR filters with target parameters, such as a 3 dB passband, a free spectral range, ripples, and crosstalk, are successfully demonstrated, which shows that the differential evolution method is one of the most effective methods for designing high-order MRR filters.

Design of a series-coupled microring resonator wavelength filter using the digital filter design method

We propose a digital filter design method for high-order series-coupled microring resonator (MRR) filters considering coupling loss in coupling areas. This method makes it possible to design high-order MRR filters with desired parameters such as a 3 dB wavelength bandwidth, free spectral range (FSR), and center wavelength, which have been difficult to design so far. It is possible to apply the proposed design method to design MRR filters based on the Vernier effect with an expanded FSR. We demonstrate fourth-order Butterworth and Chebyshev silicon-based MRR filters designed with the proposed method. The 3 dB wavelength bandwidth, FSR, and center wavelength of the designed MRR filter are almost identical with the target values.

Terahertz plasmonic SWAP and Fredkin gates utilizing graphene nano-ribbon waveguides

In this paper, terahertz plasmonic SWAP and Fredkin gates using the Si–SiO2 -air–graphene–air structure deposited on the SiO2/Si substrate are presented and numerically studied. The presented terahertz plasmonic SWAP gate is composed of a symmetric Y-junction, two all-pass microring resonators, and a double series-coupled microring resonator, and the proposed terahertz plasmonic Fredkin gate comprises a three-arm Y-junction, three all-pass microring resonators, and a double series-coupled microring resonator. By flexibly adjusting graphene’s chemical potential in rings, microring resonators’ resonant states produce the change, then logic operations of SWAP and Fredkin gates can be correctly executed. Simulation results show that our designed terahertz plasmonic SWAP and Fredkin gates exhibit excellent extinction ratio and crosstalk. For the designed terahertz plasmonic SWAP gate, the extinction ratio can be greater than 20.92 dB and the crosstalk can be less than −21.38 dB. With input logic states of ‘000’, ‘001’, ‘010’, ‘011’, ‘100’, ‘101’, ‘110’, and ‘111’, the designed terahertz plasmonic Fredkin gate has a minimum extinction ratio of 21.65 dB and a maximum crosstalk of −21.15 dB.

Design of full-bandwidth ROADM based on MMI and MRRs

In this paper, we propose a full-bandwidth reconfigurable optical add/drop multiplexer (ROADM) equipped with multiplexer/demultiplexer (MUX/DEMUX) and switch array. Based on the pairwise multimode interference (MMI) and side-ported MMI, the full-bandwidth MUX/DEMUX is achieved. The switch array based on microring resonators (MRRs) can achieve the function of the wavelength selective switches. By designing the second-order series-coupled MRR structure, using thermo-optic effect, the switch is able to get a switching ratio above 16 dB. The proposed ROADM system shows good performance for application in dynamic optical networks.

A novel pressure sensor based on series-coupled double microring resonators with a simple beam

ABSTRACTWe propose and analyse a novel optical pressure sensor based on series-coupled double microring resonators (SDMRRs) on a simple beam. The pressure applied on the sensor is measured through the change of the optical transmission spectrum at the output port. The optical transmission performances of the SDMRRs have been analysed and compared with the single and paralleled-coupled structures by the method of finite element analysis and numerical simulation. The simulation results showed that the stress sensitivity is 0.0225 kPa–1 and linear measurement range of the sensor is 30 kPa. Furthermore, the influence of the amplitude transmission coefficient, half round phase shift and microring radius on the sensitivity have been investigated to optimize the sensor performance. This proposed sensor can be used for the smaller pressure detection in automotive, aerospace, oil/logging equipment and other harsh environmental application.

Bandwidth-tunable optical passband filter based on graphene–silicon waveguide

A bandwidth-tunable optical passband filter based on graphene–silicon waveguide is proposed. The device is designed by utilizing a structure with four triple series-coupled microring resonators. By changing the Fermi level of graphene to lead to the variation of the modal effective index, the transmission spectra of triple series-coupled microring resonators can be coherently combined to provide the adjustable bandwidth as desired. A detailed analysis of the designed device is presented. Numerical simulations show that the effective bandwidth tuning range from 2.70 to 6.30 nm can be obtained when each microring resonator is independently controlled. With the maximum bandwidth tunability, the designed tunable filter has a minimum extinction ratio larger than 92.35 dB.

Crosstalk in SOI Microring Resonator-Based Filters

We experimentally investigate the interchannel and intrachannel crosstalk of first- and second-order microring resonator (MRR) filters fabricated on a silicon-on-insulator platform. We find that there is an MRR radius that maximizes the wavelength division multiplexing channel count given a waveguide geometry, a maximum tolerable insertion loss, and a minimum permissible adjacent channel isolation. The measured power penalties due to interchannel crosstalk of two-channel demultiplexers based on first-order and series-coupled MRR filters are presented as functions of channel spacing and adjacent channel isolation. Next, we compare the intrachannel crosstalk of first-order, cascaded, and series-coupled MRR add-drop filters. Our results show that first-order MRR devices are unsuitable for simultaneous add-drop operation at high data rates and small channel spacings. Intrachannel crosstalk of cascaded and series-coupled designs are measured as functions of the data rate and the level of detuning between the MRRs. Low intrachannel crosstalk power penalties are demonstrated for cascaded and series-coupled MRR filters for data rates up to 20 Gb/s. Based on the measured results, we present requirements for the input-to-through response of add-drop filters that will ensure low intrachannel crosstalk.

Wavelength tuning and stabilization of microring-based filters using silicon in-resonator photoconductive heaters.

We demonstrate that n-doped resistive heaters in silicon waveguides show photoconductive effects with high responsivities. These photoconductive heaters, integrated into microring resonator (MRR)-based filters, were used to automatically tune and stabilize the filter's resonance wavelength to the input laser's wavelength. This is achieved without requiring dedicated defect implantations, additional material depositions, dedicated photodetectors, or optical power tap-outs. Automatic wavelength stabilization of first-order MRR and second-order series-coupled MRR filters is experimentally demonstrated. Open eye diagrams were obtained for data transmission at 12.5 Gb/s while the temperature was varied by 5 °C at a rate of 0.28 °C/s. We theoretically show that series-coupled MRR-based filters of any order can be automatically tuned by using photoconductive heaters to monitor the light intensity in each MRR, and sequentially aligning the resonance of each MRR to the laser's wavelength.

Hitless wavelength-selective switch with quadruple series-coupled microring resonators using multiple-quantum-well waveguides

We demonstrate a hitless wavelength-selective switch (WSS) based on InGaAs/InAlAs five-layer asymmetric coupled quantum well (FACQW) quadruple series-coupled microring resonators. The WSS is driven by the electric-field-induced change in refractive index in the FACQW core layer caused by the quantum-confined Stark effect (QCSE) for high-speed operation. The WSS with high-mesa waveguides is fabricated on a molecular beam epitaxy-grown wafer by dry etching. The fabricated WSS consists of four microrings, each with a round-trip length of 350 μm and five directional couplers with shallow grooves. A boxlike spectral response and hitless switching with higher extinction ratios than a double series-coupled microring resonator are successfully demonstrated. In addition, we propose the improvement of switching characteristics by controlling the coupling efficiencies at the directional couplers.

Hitless wavelength-selective switch based on quantum well second-order series-coupled microring resonators

A hitless wavelength-selective switch (WSS) based on InGaAs/InAlAs multiple quantum well (MQW) second-order series-coupled microring resonators is proposed and fabricated. In the core layer, a five-layer asymmetric coupled quantum well (FACQW) structure is employed. The WSS is driven by the electrorefractive index change in the FACQW core layer caused by the quantum-confined Stark effect (QCSE). The wafer for the WSS is grown by molecular beam epitaxy and waveguide structures are formed by dry etching. Boxlike spectrum responses and hitless switching characteristics of the WSS are successfully demonstrated for the first time. The change in coupling efficiency at a coupler between a ring and a busline and between rings and its effect on the switching characteristics are also discussed.

All-optical clock recovery from 40 Gbit/s RZ signal based on microring resonators

A scheme for high-speed clock recovery from return-to-zero (RZ) signal with microring resonators is presented. By using a silicon microring resonator (MRR) for clock extraction and a 3-order nonlinear series-coupled microring resonator (SCMR) for amplitude equalization, clock pulses with amplitude modulation less than 1 dB can be obtained. The proposed scheme is also designed and numerically studied by 3D full vectorial film mode matching method (FMM) and coupled mode theory (CMT). Simulation results show that clock can be recovered at 40 Gbit/s with short rise- and fall- times.

Demonstration of OCDM Coder and Variable Bandwidth Filter Using Parallel Topology of Quadruple Series Coupled Microring Resonators

The quadruple series coupled microring resonator (MRR) can realize a boxlike spectral response and lower adjacent channel crosstalk. Utilizing these features, we demonstrated the element of Optical Code Division Multiplexing (OCDM) coding circuit using two wavelength selective switches (WSSs) consisting of quadruple series coupled MRRs laid out in parallel topology and a phase shifter incorporated in the one arm between them. In addition, a digitally variable bandwidth filter was successfully demonstrated using the same circuit as the OCDM coder.

Numerical Solution of the Dynamics of Microring Resonator Modulators

A numerical solution of the dynamics of microring resonator modulators is proposed in which the transmission process is discretized in the time domain. This solution is effective and provides theoretical rigor, and is compatible with computer programming applications. A numerical example demonstrates that the dynamic process should be taken into account at high modulation frequencies that are comparable to the free-spectral range frequency. The bandwidth of the index modulation series-coupled microring resonators is limited by the resonator linewidth.

Analysis of electro-optic switches with series-coupled multiple microring resonators

In terms of the coupled mode theory, microring resonance and electro-optic modulation princeple, a reasonable project is proposed for designing an electro-optic switch with the series-coupled multiple microring resonators. The simulation and optimization are performed at the resonant wavelength of 1550 nm. The results are as follows: the core size of the microring is 1.6 μm×1.6 μm, the confined layer between the core and the electrode is 1.6 μm, the thickness of the electrode is 0.15 μm, the radius of the microring is 15.2 μm, the coupling gap between the microring and the channel is 0.14 μm, and the one between the microring and the microring is 0.6 μm, microring number M is 4, the switching voltage is 4 V, the insertion loss is 5.4 dB, and the crosstalk is −20 dB. The output spectrum is much flatter and much steeper than that of the single microring.

Optimal Detuning Combination of Hitless Wavelength Selective Switch using Quadruple Series Coupled Microring Resonator

This paper presents an analytic discussion of the optimal detuning combination of a hitless wavelength selective switch using individual thermo-optic tuning of a quadruple series coupled microring resonator. We found analytically that asymmetrically detuning the resonant wavelengths of two ring resonators closest to the input busline waveguide can reduce the extinction ratio and switching crosstalk compared with other combinations. The intuitive insight on the optimal combination to realize a low crosstalk OFF-state is derivable through a metaphor of the Vernier effect, i.e., it is equivalent to the optimal arrangement of series-coupled microring resonators with different ring radii to reduce the crosstalk. Large extinction ratio of 24.9 dB and small switching crosstalk of -28.6 dB were experimentally demonstrated.

Optical cross-connect circuit using hitless wavelength selective switch

We have proposed and demonstrated the basic elements of a full matrix optical switching circuit (cross-connect circuit) using a hitless wavelength selective switch (WSS). The cross-connect circuits are made of a multi-wavelength channel selective switch consisting of cascaded hitless WSSs, and a multi-port switch. These switching elements are realized through the individual Thermo-Optic (TO) tuning of a series-coupled microring resonator, and can switch arbitrary wavelength channels without blocking other wavelength channels during tuning. We demonstrate a four wavelength selective switch using a parallel topology of double series coupled microring resonators and a three wavelength selective switch using a parallel topology of quadruple series coupled microring resonators. Since the spectrum shape of quadruple series coupled microring is much more box-like than the double series, a high extinction ratio of 39.0-46.6 dB and low switching cross talk of 19.3-24.5 dB were achieved.

串联微环谐振器的光学特性

串联微环谐振器的光学特性

Multiwavelength and Multiport Hitless Wavelength-Selective Switch Using Series-Coupled Microring Resonators

We demonstrate the basic elements of a full matrix optical switching circuit using a hitless wavelength-selective switch (WSS). It is a multiwavelength channel-selective switch consisting of cascaded hitless WSS, and a multiport switch. These switching elements are based on the individual thermooptic tuning of double series-coupled microring resonators, and can switch arbitrary wavelength channels without blocking other wavelength channels during tuning. The fundamental switching operations, such as four switching states from a three-wavelength selection to a zero-wavelength selection and multiport switching characteristics, are successfully demonstrated

Reversal of UV Sensitivity and Loss Reduction of SiON Microring Resonator by Thermal Annealing

To investigate the origin of the large UV sensitivity of SiON film, we measureed the Fourier transform infrared (FT-IR) spectrum of SiON films before and after UV exposure, and also before and after thermal annealing. As a result, we discovered the reversal of the UV sensitivity of SiON film treated by thermal annealing at 1160 °C. Next, the origin of the reversal of UV sensitivity induced by thermal annealing was studied by positron annihilation lifetime spectroscopy (PALS) measurement. The redshift trimming of a microring resonator with a SiON core and the improvement of a double series coupled microring resonator by selective UV trimming were successfully demonstrated using this phenomenon.