Silicon Microring Resonator Research Articles

Silicon microring resonator waveguide-based graphene photodetector

Here we study and analyze the performance of a graphene-based photodetector integrated onto a silicon-on-insulator microring using optical and electrical simulations. The electrical simulation reveals the role of material interface losses and allows one to extract key behavioral parameters such as dark current, responsivity and bandwidth.

Manipulation of extinction features in frequency combs through the usage of graphene

Lately, the integration of two-dimensional materials into semiconductor devices has allowed the modification of their effective index by simply applying a modest voltage (between 0 and 3 volts). In this work, we present a device composed of two evanescently coupled silicon microring resonators where both rings have a graphene layer on top. This design is aimed to produce frequency combs with transmission characteristics controlled upon voltage application to the graphene layer. We numerically analyze the device response as a function of the incident wavelength and applied voltage. The results showed a low input intensity (0.6 GW/cm2) needed and a rapid response time (0.1 μs), in comparison to devices controlled by heat injection.

Frequency-Hopping Microwave Generation With a Large Time-Bandwidth Product

We propose and demonstrate an approach to generating large time-bandwidth product (TBWP) frequency-hopping (FH) microwave waveforms by using an ultra-high-quality factor (Q) silicon microring resonator (MRR) with thermal tuning. An ultra-high-Q MRR (Q ∼ 106) is used to filter out an expected frequency component from an optical frequency comb. Heterodyne beating between the filtered frequency and another seed frequency light detected by a photodetector will generate an FH microwave waveform. In addition, the FH microwave signal can be flexibly and independently tuned in terms of the central frequency, bandwidth, frequency order, and time sequence length, just altering the driving voltage on the MRR. The proof-of-concept experiments show that the TBWP of the stepped linear, stepped arbitrary, and Costas sequence microwave signal can be over 4.5 × 107. Our paper offers an integrated FH microwave generation approach to support the optics communications and the next-generation photonic radar systems.

Silicon-Micro-Ring Resonator-Based Erbium Fiber Laser With Single-Longitudinal-Mode Oscillation

In this paper, we propose and experimentally illustrate a wavelength-switchable erbium-doped fiber (EDF) dual-ring (DR) laser with stable single-longitudinal-mode (SLM) oscillation. In the experiment, a silicon-micro-ring-resonator (SiMRR) is applied in the proposed DR cavity for tuning different output wavelengths, when the birefringence loss is adjusted correctly. To compress the densely multilongitudinal-mode oscillations, the DR scheme together with a 2-m unpumped EDF-based saturable absorber is acted as the mode filter. The DR also can produce self-injection loop for an SLM operation. The wavelength tunability is between 1532.61 to 1557.98 nm and the measured 3-dB output linewidth is ∼22.5 kHz. Moreover, the output stabilizations of the proposed SiMRR-based EDF DR laser are also analyzed and discussed.

Flexible-Grid Wavelength-Selective Switch Based on Silicon Microring Resonators With Interferometric Couplers

In this paper, a kind of integrated flexible-grid wavelength-selective switch composed of reconfigurable add-drop silicon microring resonators with interferometric couplers is described in detail. Owing to tunable interferometric couplers, the proposed device is capable of realizing an increase in adjustable channel spacing for a given field coupling coefficient. By carefully controlling the path phase differences and tunable interferometric couplers, the transmission spectra of adjacent channels can be selectively combined to form adjustable bandwidths as desired. As an example, an integrated flexible-grid 1 × 2 wavelength-selective switch is designed and theoretically analyzed. The channel spacing can increase from 0.1 to 0.8 nm. When the channel spacing is selected to be 0.8 nm, the bandwidth varies from 0.36 to 2.91 nm and a minimum extinction ratio of 14.8 dB is obtained.

Design and modeling of mode-conversion in ring resonator and its application in all-optical switching

The present paper describes the mode conversion of the optical signal using single waveguide coupled silicon micro-ring resonator (MRR). The mode conversion occurs between quasi-TM and the quasi-TE mode at the through port output with the application of the suitable optical pump power. The modeling of mode-conversion using ring resonator is performed through MATLAB as well as by finite-difference-time-domain (FDTD) simulation and further used to perform the all-optical switch. The refractive index contrast, height to width ratio of the waveguide and the choice of suitable wavelength and power for optical pumping and source are responsible for mode-conversion in the ring resonator. The application of mode-conversion to design all-optical switch in MRR is also included in the paper. Mode-conversion in terms of electric field intensity at a resonant wavelength of around 1.53 μm occurs and is utilized to design all-optical switch. The results obtained from both MATLAB and FDTD justify each other and validate the proposed concept. Some ‘Figure of merits’ and ‘Spectral parameters’ are calculated in the report to analyze the performance of the design.

GST-on-silicon hybrid nanophotonic integrated circuits: a non-volatile quasi-continuously reprogrammable platform

Reconfiguration of silicon photonic integrated circuits relying on the weak, volatile thermo-optic or electro-optic effect of silicon usually suffers from a large footprint and energy consumption. Here, integrating a phase-change material, Ge2Sb2Te5 (GST) with silicon microring resonators, we demonstrate an energy-efficient, compact, non-volatile, reprogrammable platform. By adjusting the energy and number of free-space laser pulses applied to the GST, we characterize the strong broadband attenuation and optical phase modulation effects of the platform, and perform quasi-continuous tuning enabled by thermo-optically-induced phase changes. As a result, a non-volatile optical switch with a high extinction ratio, as large as 33 dB, is demonstrated.

Photonic Delay Lines Based on Silicon Coupled Resonator Optical Waveguide Structures

We propose a Coupled Resonator Optical Waveguide Structure based on silicon microring resonators. The proposed structure is designed on Silicon on Insulator platform so as to scale down the device dimensions as silicon on insulator platform provides the advantage of large index contrast, miniaturization of device dimensions. Tunability is incorporated on the structure in the simulation environment by placing thermal heaters on the top of the rings which change the refractive indices of the rings thereby changing the resonance wavelength. Finite difference time domain method is used to simulate the structure. Variable delays are achieved by tuning the necessary number of ring structures to their resonant wavelengths. This structure can be helpful in realizing optical delay lines for on chip optical interconnects.

Silicon microring resonators

Silicon microring resonators (MRRs) are very popular for many applications because of the advantages of footprint compactness, easy scalability, and functional versatility. Ultra-compact silicon MRRs with box-like spectral responses are realized with a very large free-spectral range (FSR) by introducing bent directional couplers. The measured box-like spectral response has an FSR of >30 nm. The permanent wavelength-alignment techniques for MRRs are also presented, including the laser-induced local-oxidation technique as well as the local-etching technique. With these techniques, one can control finely the permanent wavelength shift, which is also large enough to compensate the random wavelength variation due to the random fabrication errors.

A Continuously Tunable Sub-Gigahertz Microwave Photonic Bandpass Filter Based on an Ultra-High-Q Silicon Microring Resonator

Microwave photonic filter (MPF) is one of the key fundamental subsystems in microwave photonics, and it shows great potentiality in numbers of applications such as optoelectronic oscillator, microwave frequency measurement, and so forth. A narrowband bandpass MPF is highly desirable with its high selectivity in microwave photonic applications. However, a resonator with a high quality factor (>106) is very difficult to fabricate on the mature silicon photonics platform without optimization, thus restraining the applications of the MPF. In this paper, we propose and experimentally demonstrate a tunable sub-gigahertz bandwidth MPF based on an ultrahigh quality factor silicon microring resonator. Most performance aspects of the MPF are well-balanced. A full width at half-maximum bandwidth of 170 MHz is achieved thanks to the ultrahigh total quality factor as 1.14 × 106 of the microring resonator, and the average waveguide loss and the intrinsic Q factor of the microring resonator are calculated as 0.25 dB/cm and 2.67 × 106, respectively. The corresponding rejection ratio of the bandpass filter is 26.5 dB. Besides, the central frequency of the filter could be continuously tuned from 2.0 to 18.4 GHz with a microheater fabricated upon the microring, and a 16.4 GHz tuning range is achieved with the maximum power consumption of 14.4 mW. The device area is ∼0.05 mm2.

Photonic Multiple Microwave Frequency Measurement Based on Frequency-to-Time Mapping

A photonic multiple microwave frequency measurement system is presented and demonstrated based on a swept frequency silicon microring resonator (MRR). The drop-port of a high-Q MRR is employed as a periodic narrowband scanning filter driven by a sawtooth voltage signal. The unknown frequency can be mapped to time interval between pulse appearances when scanning the modulated signal and the frequency-to-time mapping is established. In the experiments, we obtain a measurement range of 25 GHz with an error of ±510 MHz. Meanwhile, the measurement resolution for multi-frequency measurement is about 5 GHz. Our scheme offers a simple structure, low-cost solution, capability of multiple frequency measurement, and potential of chip-integration.

Design Space Exploration of Microring Resonators in Silicon Photonic Interconnects: Impact of the Ring Curvature

A detailed analysis of fundamental tradeoffs between ring radius and coupling gap size is presented to draw realistic borders of the possible design space for microring resonators (MRRs). The coupling coefficient for the ring-waveguide structure is estimated based on an integration of the nonuniform gap between the ring and the waveguide. Combined with the supermode analysis of two coupled waveguides, this approach is further expanded into a closed-form equation that describes the coupling strength. This equation permits to evaluate how the distance separating a waveguide from a ring resonator, and the ring radius, affect coupling. The effect of ring radius on the bending loss of the ring is furthermore modeled based on the measurements for silicon MRRs with different radii. These compact models for coupling and loss are subsequently used to derive the main optical properties of MRRs, such as 3-dB optical bandwidth, extinction ratio of resonance, and insertion loss, hence identifying the design space. Our results indicate that the design space for add-drop filters in a wavelength division multiplexed link is currently limited to 5–10 $\mu$ m in radius and gap sizes ranging from 120 to 210 nm. The good agreement between the results from the proposed compact model for coupling and the numerical FDTD and experimental measurements indicate the application of our approach in realizing fast and efficient design space exploration of MRRs in silicon photonic interconnects.

Design and demonstration of ultra-high-Q silicon microring resonator based on a multi-mode ridge waveguide

We present the design and experimental demonstration of the ultra-high-Q-factor silicon microring resonator based on a multi-mode ridge waveguide. The multi-mode ridge waveguide is designed to decrease the propagation loss and to improve the Q factor. The ultra-high Q factor of 1.1×106 is experimentally demonstrated, with the free spectrum range of 0.208nm. The single-mode ridge waveguide is used in the coupling region to reduce the dimension of the microring resonator, and the bend radius is only 20μm. To precisely control the resonance wavelength, a small heater is implemented on the silicon microring resonator with the tuning efficiency of 7.1 pm/mW. The degenerate four-wave mixing of the silicon microring resonator is investigated, and the conversion efficiency is measured to be -15.5 dB without optimizing the dispersion of the microring resonator and carriers extraction.

Demonstration of an optical directed half-subtracter using integrated silicon photonic circuits.

An integrated silicon photonic circuit consisting of two silicon microring resonators (MRRs) is proposed and experimentally demonstrated for the purpose of half-subtraction operation. The thermo-optic modulation scheme is employed to modulate the MRRs due to its relatively simple fabrication process. The high and low levels of the electrical pulse signal are utilized to define logic 1 and 0 in the electrical domain, respectively, and the high and low levels of the optical power represent logic 1 and 0 in the optical domain, respectively. Two electrical pulse sequences regarded as the operands are applied to the corresponding micro-heaters fabricated on the top of the MRRs to achieve their dynamic modulations. The final operation results of bit-wise borrow and difference are obtained at their corresponding output ports in the form of light. At last, the subtraction operation of two bits with the operation speed of 10 kbps is demonstrated successfully.

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

Employment of silicon-micro-ring resonator and compound-ring architecture for stable and tunable single-longitudinal-mode fiber laser

In this work, a wavelength-switchable erbium-doped fiber (EDF) glasses-type compound-ring (GTCR) laser with stable single-longitudinal-mode (SLM) oscillation is proposed and presented. In the experiment, to accomplish wavelength-tunable operation, a silicon-micro-ring-resonator (SiMRR) is utilized inside the ring cavity, when the birefringent loss of EDF laser is adjusted properly. Moreover, the GTCR configuration is proposed to as the mode-filter for suppressing the multi-longitudinal-mode (MLM) to achieve the SLM oscillation. Here, the measured linewidth of output wavelength is ∼61 kHz. The output stabilities of the proposed SiMRR EDF compound-ring laser are also discussed experimentally.

Compact high-efficiency vortex beam emitter based on a silicon photonics micro-ring.

Photonic integrated devices that emit vortex beam carrying orbital angular momentum are becoming key components for multiple applications. Here we propose and demonstrate a high-efficiency vortex beam emitter based on a silicon micro-ring resonator integrated with a metal mirror. Such a compact emitter is capable of generating vortex beams with a high efficiency and small divergence angle. Vector vortex beams of various topological charges are selectively generated by the emitter at different wavelengths with an emission efficiency of up to 37%.

Photonic D-type flip flop based on micro-ring resonator

This paper demonstrates the novel design of a photonic D-Type flip flop based on silicon micro-ring resonator as its core component. The design incorporates the carrier-injection forward-biased PIN waveguide resonance response for its logical operation. This work also provides the working principle of the designed D flip-flop. This work proceeds with the demonstration and analysis of the operation with the D input information injected at 1 Gbps, and the clocking rate of 5 GHz. The performance of the proposed D flip-flop is verified by clear output timing as well as eye diagrams.

Fast and slow light generated by surface plasmon wave and gold grating coupling effects

We present here the results of a simulation of the effect of gold and graphene coatings on silicon micro-ring resonators. We studied the effect of different radii of graphene on the time delay, from which one an interesting aspect of light pulse behaviors, such as fast light, was numerically investigated. The obtained results indicate that the time delay can be varied, which is in good agreement with theoretical predictions. Fast and slow light pulse trains can be obtained by modifying the throughput port, which forms the gold grating length. The temporal gaps between the fast and slow light in the used graphene and gold are 140 and 168 fs, respectively, which can be tuned by varying the radius or grating length. The obtained results show that such a device may be useful in applications requiring fast and slow light pulse train pairs, such as optical switching, sensors, communications, and security applications.

Design of a Flexible-Grid 1 × 2 Wavelength-Selective Switch Using Silicon Microring Resonators

In this paper, a compact integrated flexible-grid 1 × 2 wavelength-selective switch is proposed. The device is designed by utilizing a structure with nine reconfigurable add-drop silicon microring resonators. Using thermal tuning, the transmission spectra of silicon microring resonators are coherently combined to provide adjustable bandwidths as desired. The operation principle and detailed analysis of the designed device are presented. Calculation results show the bandwidth tuning for the spectrum with the large bandwidth varies from 0.56 to 4.09 nm and the bandwidth tuning for the spectrum with the moderate bandwidth ranges from 0.38 to 2.64 nm. The integrated flexible-grid 1 × 2 wavelength-selective switch with the maximum bandwidth tunability has a maximum crosstalk of −11.5 dB.