Research On Resonant Silicon Photonic Switch And Filter Based On Wavelength Locking

In the past few decades,silicon photonic devices and integrated circuits have been extensively studied and found wide applicaions.With compact device footprint,ultra-high bandwidth,low power consumption,and high integration desentiy,silicon photonics is highly desired for many communication systems and networks including telecommunication networks,interconnects in data centers,signal processing,and so on.Therefore,silicon photonics has received much attention from both the academia and the industry and developed rapidly.Among the various silicon photonic devices,resonant devices possess wavelength selectivity and are advantageous in footprints and power consumption.Therefore,resonant devices are desired to be used as optical filters,optical switches,lasers,modulators,photodetectors,etc.Despite their wide applications in optical commnunication systems and networks,the resonance wavelengths of these devices are highly susceptible to fabrication errors and chip teamperture changes,which is caused by the high thermo-optic coefficient of silicon and the wavelength selectivity.For a silicon micro-resoantor,the wavelength misalignment between the resonance wavelength and the signal wavelength(i.e.,the wavelength of the input signal light)would significantly degrade the device performances such as insertion loss,crosstalk,and extinction ratio.Hence wavelength control of silicon resonant devices is required in practical applications to solve the problem of wavelength misalignments.However,most researches regarding silicon resonant devices focus on device design or fabrication,while the corresponding wavelength control schemes are rarely demonstrated.In this thesis,we present our research on resonant silicon photonic switch and filter based on wavelength locking.We first introduce several basic device structures of silicon microring resonator based devices and the basic principles of wavelength locking.In the following sections,we mainly present resonant silicon photonic switches and a microring-based filter based on three new wavelength locking methods.The main achievements of this research are summarized as follows:1.Dual-ring silicon photonic switches based on a saddle-point searching(SPS)locking methodHigh-port-count optical switches are the key building blocks for achieving optical interconnects in data centers.An N × N optical switch is typically composed of 2 × 2switching elements,indicating that the switching elements may work with two optical inputs.To realize the wavelength locking of resonant silicon photonic switches in the presence of dual inputs,we propose an SPS wavelength locking method and experimental demonstrate four dual-ring silicon photonic switches based on this control method:1)4 × 4 silicon thermo-optic dual-ring switch based on an SPS locking method: We experimentally demonstrate a 4 × 4 silicon thermo-optic dual-ring switch employing Benes architecture.An SPS locking method is proposed to eliminate the wavelength misalignment of a dual-ring switching element with either a single optical input or dual inputs,then this method is extended to mitigate the wavelength misalignments of the 4 × 4switch.By properly designing the device structure and the structural paprameters of a dual-ring resonantor,a monitoring light is obtained,and its power versus the round-trip phase shifts of the two rings is always subject to a saddle shape for either the single-input state or the dual-input state.Moreover,the wavelength misalignments of the two rings are0 at the saddle point,therefore the wavelength locking of such a device can be realized by locating the saddle point.In the experiments,the wavelength misalignments of ?0.3 free spectral range(FSR)can be mitigated.The crosstalk and operation bandwidth of the 4 × 4switch are ?-13.6 d B and ?46 GHz,respectively.2)2 × 2 silicon electro-optic dual-ring switch based on an improved SPS locking method: We experimentally demonstrate a 2 × 2 silicon electro-optic dual-ring switch and propose an improved SPS locking method that exhibits insensitivity to the thermal crosstalk between the two rings.By overcoming the thermal challenges,the dual-ring switch can operate over a full FSR of 6 nm.High-speed switching is also relized after wavelength locking.3)4 × 4 silicon electro-optic dual-ring switch based on an improved SPS locking method: Here we experimentally demonstrate a 4 × 4 silicon electro-optic dual-ring switch employing Benes architecture based on our previously proposed improved SPS locking method.The 4 × 4 switch works after the multi-stage wavelength locking,and high-speed switch is demonstrated.4)16 × 16 silicon electro-optic dual-ring switch based on an improved SPS locking method: Based on the demonstrated 4 × 4 silicon electro-optic dual-ring switch,we realize a 16 × 16 silicon electro-optic dual-ring switch and the corresponding multi-channel control subsystem based on improved SPS locking.2.Silicon microring and dual-ring switches based on an artificial neural network(ANN)locking methodFor a reconfigurable resonant silicon photonic switch,the reconfiguration time of the whole switch mainly depends on the reconfiguration time of each switching element.Therefore,fast wavelength control is important for flexible and reconfigurable optical communication networks.To achieve this goal,we propose a noval ANN-based wavelength locking method,and demonstrate two silicon photonic switches based on this method:1)1 × 2 silicon electro-optic microring switch based on an ANN locking method: We propose and experimentally demonstrate a wavelength locking method based on a two-layer ANN for a silicon microring switch.To the best of our knowledge,a record-high wavelength locking speed of 20 nm/ms for a resonator-based switch is achieved by the ANN locking method.The silicon microring is integrated with a power monitoring port.With a learning capability and prior knowledge,a neural network knows the relation between a monitored signal and its wavelength misalignment,so it can predict the proper thermal tuning power loaded onto the resonator according to the monitored signal.In the experiment,any wavelength misalignments within one FSR can be eliminated,and the duration of the locking process is only 290 ?s.High-speed switching is also realized after the wavelength locking.2)1 × 2 silicon electro-optic dual-ring switch based on an improved ANN locking method: Here,we propose a multi-dimentional implementation of our previously proposed ANN locking method,therefore resonant devices containing multiple resonantors(e.g.,cascaded microrings)can be controlled.Note that the multi-dimentional ANN locking method offers two important benefits:(a)a high locking speed;(b)thermal crosstalk insensitivity.Here,we design a two-dimentional ANN-based wavelength locking algorithm,and then verify its fesibility in simulation.The results show that effective wavelength locking can be achieved.The demonstrated wavelength locking range is up to one FSR.For any wavelength misalignment within this range,the average predicted errors for the required heating powers are less than 1 m W,and the corresponding average wavelength locking errors would be less than 0.05 nm.3.Silicon microring filter based on a self-homodyne locking(SHL)methodOptical filters are the key building blocks in wavelength devision multiplexing(WDM)networks.In practical applications,the optical power budget is usually related to various factors,leading to unpredictable input optical powers of filters.To realize power-variation insensitive optical filtering,we propose and experimental demonstrate a silicon microring filter based on a SHL method.In this work,we employ a new device structure based on self-homodyne detection and a corresponding control subsystem to lock the silicon microing filter in the presence of input optical power variation.In the experiment,the central wavelength of the filter is automatically aligned to the signal wavelength with a power variation of 8.7 d B.The wavelength locking range is up to one FSR,and the locking errors are ?0.015 nm.