Side-coupled Ring Resonator Research Articles

Tunable acoustic resonances: From weak to strong coupling regime

Tunable interaction strength between a side-coupled ring resonator and an acoustic waveguide structure is demonstrated. Fano resonances in the weak coupling regime are observed from the interference between a discrete state of the ring resonator and a continuum state of the waveguide. As the distance between the two structures is decreased, a transition from weak to strong coupling regime is obtained, where we observe splitting in the transmission spectrum and Rabi oscillations in the temporal behavior for smaller values. The findings of the finite-element method simulations are supported with the results obtained from a simple theoretical model in which one can explain the dynamics of the hybrid modes. The results can contribute to device applications in acoustic sensors, switches, and surface acoustic wave integrated circuits.

Cooperative Spontaneous Four-wave Mixing in Single-channel and Dualchannel Sequences of Side-coupled Ring Resonators

Cooperative photon pair generation by Spontaneous Four-Wave Mixing (SFWM) process in singlechannel and dual-channel side-coupled ring resonator sequences is investigated. Our analysis shows that superlinear growth of generation rate with respect to the number of rings is possible even in presence of loss. Experimental evidence of super-SFWM is provided by comparing individual and collective generation rates obtained from a dual-channel ring resonator sequence. The results are in good agreement with theory and suggest that high photon pair generation rates can be achieved from integrated silicon ring resonator sequences without initiating nonlinear absorption processes.

High-Sensitive Multi-Gas Detection Based on MDM Waveguide With Symmetric Dual Side-Coupled Ring-Resonators

A high-sensitive multi-parameter gas sensor composed of symmetric dual side-coupled ring resonators in a metallic-dielectric-metallic (MDM) structure is investigated by the finite difference time domain (FDTD) method. The dual side-coupled resonators have lower transmission dip and faster response due to the superposition of the outgoing fields’ amplitude of the symmetric dual resonators, which is very beneficial for detection. Two independently tunable transmission dips are achieved by expanding the ring resonator in ${x}$ -direction, making it possible for dual-parameter sensing. The electric and magnetic distribution characteristics at the two resonant wavelengths are analyzed. Another plasmonic structure expanded along both sides in a central resonator-straight waveguide way is also investigated, and the former structure expanded in ${x}$ -direction works better in detection difficulty and structural utilization. After optimizing the radius and position of ring resonators, the refractive index sensitivities of cavity A and B can reach 2427 nm/RIU and 2431.9 nm/RIU, respectively. The methane and hydrogen sensitivities are −9.213 nm/% and −1.65 nm/% with an extremely high linearity, after coating the methane and hydrogen gas-sensitive film in cavity A and B respectively. This investigation provides an effective way for the design of multi-parameter high-sensitive independently tunable sensors.

Temperature tunable Fano resonance based on ring resonator side coupled with a MIM waveguide

The temperature control of Fano resonance via a resonator waveguide system which is composed of a side coupled ring cavity and a metal nanowall is presented. The ring resonator is filled with sealed ethanol which can tune the Fano resonance by the temperature. Two dimensional finite difference time domain method is used to calculate the transmission and field distribution. The Fano resonance is originated from the coupling between the discrete state and the continua state. The discrete state and continua state is from the side coupled ring resonator and the metal nanowall, respectively. The asymmetrical Fano linestyle can be tuned by changing the temperature of the sealed ethanol or the geometric parameters. Multiple Fano resonance can be obtained by introducing another ring resonator and can be tuned by temperature or size independently. The proposed plasmonic structure may have application in slow light device, nanoscale filter, all optical switch and refractive index sensor.

Refractive Index Sensor Based on Fano Resonances in Plasmonic Waveguide With Dual Side-Coupled Ring Resonators

A refractive index sensor based on Fano resonances in metal-insulator-metal (MIM) waveguides coupled with rectangular and dual side rings resonators is proposed. The sensing properties are numerically simulated by the finite element method (FEM). For the interaction of the narrow-band spectral response and the broadband spectral response caused by the side-coupled resonators and the rectangular resonator, respectively, the transmission spectra exhibit a sharp and asymmetric profile. Results are analyzed using the coupled-mode theory based on the transmission line theory. The coupled mode theory is employed to explain the Fano resonance effect. The results show that with an increase in the refractive index of the fill dielectric material in the slot of the system, the Fano resonance peak exhibits a remarkable red shift. Through the optimization of structural parameters, we achieve a theoretical value of the refractive index sensitivity (S) as high as 1160 nm/RIU, and the corresponding sensing resolution is 8.62 × 10–5 RIU. In addition, the coupled MIM waveguide structure can be easily extended to other similar compact structures to realize the sensing task and integrated with other photonic devices at the chip scale. This work paves the way toward the sensitive nanometer scale refractive index sensor for design and application.

Method proposing a slow light ring resonator structure coupled with a metal-dielectric-metal waveguide system based on plasmonic induced transparency.

We demonstrate the analogue of electromagnetically induced transparency (EIT) in a metal-dielectric-metal (MDM) plasmonic waveguide. Plasmonic induced transparency is a method similar to EIT. In this paper, a plasmonic MDM waveguide is proposed by using an ellipse shaped side-coupled ring resonator and simulated by finite difference time domain. Plasmonics as a new field of chip-scale technology is an interesting substrate, which is used to propose and numerically investigate a novel MDM structure. The aforementioned framework is a 2×2 plasmonic ring resonator, employing gold as a metal and polymethyl methacrylate as a dielectric. Simulations show that a transparent window is located at 1550 nm and signal wavelength is assumed to be 860 nm, which is the phenomenon of plasmonic induced transparency. The velocity of the plasmonic mode can be considerably slowed while propagating along the MDM bends. Our proposed configuration may thus be applied to storing and stopping light in plasmonic waveguide bends. This plasmonic waveguide system may find important applications for multichannel plasmonic filters, nano-scale optical switching, delay time devices, and slow-light devices in highly integrated optical circuits and networks. In comparison with our previous theoretical work based on circular shaped ring resonators, it is shown that ellipse shaped ring resonators demonstrate better specifications with a slow down factor estimated to be more than 30.

Pole–Zero Dynamics of High-Order Ring Resonator Filters

We present a pole-zero analysis, based on the transfer matrix method, for ring resonator (RR)-based filters of Type I and Type II, consisting of mutually coupled and side-coupled RRs. The pole-zero plot determines the filter spectral characteristics and is determined primarily by the coupling coefficient between the resonators. The pole-zero dynamics (or root locus) shows how the poles and zeros move in the complex frequency plane as we vary the coupling coefficient. We show that the pole-zero dynamics for the two types of filter are complementary and, furthermore, that the pole-zero plots are related to the conditions of critical coupling and oscillation in the presence of loss or gain. We also show a pole-zero analysis for the apodization of these filters based on an actively tunable Mach-Zehnder-type coupler, where it is shown that apodization corresponds to designing pole-zero pairs with wide separations, whereas the required bandwidth determines the specific values of the coupling coefficient.

Pole-Zero Dynamics of High-Order Ring Resonator Filters

We present a pole-zero analysis, based on the transfer matrix method, for ring resonator (RR)-based filters of Type I and Type II, consisting of mutually coupled and side-coupled RRs. The pole-zero plot determines the filter spectral characteristics and is determined primarily by the coupling coefficient between the resonators. The pole-zero dynamics (or root locus) shows how the poles and zeros move in the complex frequency plane as we vary the coupling coefficient. We show that the pole-zero dynamics for the two types of filter are complementary and, furthermore, that the pole-zero plots are related to the conditions of critical coupling and oscillation in the presence of loss or gain. We also show a pole-zero analysis for the apodization of these filters based on an actively tunable Mach-Zehnder-type coupler, where it is shown that apodization corresponds to designing pole-zero pairs with wide separations, whereas the required bandwidth determines the specific values of the coupling coefficient.

Loss-less pulse intensity repetition-rate multiplication using optical all-pass filtering

Schemes based on an optical all-pass filtering techniques for multiplying the intensity repetition-rate of an optical pulse train are examined. These methods are in principle without energy loss and the multiplication factor can be any given integer. Practical implementation using cascaded side-coupled ring resonators or multireflection filters is proposed and analyzed for the first time.

Ultra-compact Si-SiO2 microring resonator optical channel dropping filters

Compact optical channel dropping filters incorporating side-coupled ring resonators as small as 3 μm in radius are realized in silicon technology. Quality factors up to 250, and a free-spectral range (FSR) as large as 24 nm are measured. Such structures can be used as fundamental building blocks in more sophisticated optical signal processing devices.