Coupled Ring Resonators Research Articles

Electrically tunable vertically coupled ring resonator based on Si–ITO heterojunction

Electrically tunable vertically coupled ring resonator based on Si–ITO heterojunction

Non‐Hermitian Broadside Coupled Split Ring Resonators with Directional Sensitivity (Advanced Optical Materials 17/2024)

Non‐Hermitian Broadside Coupled Split Ring Resonators with Directional Sensitivity (Advanced Optical Materials 17/2024)

Polarization-resolved near-field characterization of coupling between a bus waveguide and a ring resonator

Light propagation in Photonic integrated circuits (PICs), which can nowadays involve complex systems of light-guiding structures, is measured with different approaches(Nuzhdin et al., 2020, Lončar et al., 2002, Hopman et al., 2007, Morichetti et al., 2014, Sapienza et al., 2012, Vesseur et al., 2007). An interferometric polarization-sensitive measurement of the evanescent fields of these structures provides insight in the performance of the circuit detects possible malfunction with sub-wavelength precision(Engelen et al., 2007, Gersen et al., 2005, Barwick et al., 2009). We demonstrate a Near-field scanning optical microscopy (NSOM) measurement on coupled ring resonators that shows how the guided modes evolve as they propagate across the optical chip. Analysis of the measurements provides information about intensity distribution of the two polarization components (TE and TM) and their spatial confinement. The data validates our methodology and opens new possibilities for analysis of signal propagation in prototyping and optimization of integrated optical systems. Direct observation of polarization state of the guided modes allows for clear understanding of mode conversion in coupling systems.

Non‐Hermitian Broadside Coupled Split Ring Resonators with Directional Sensitivity

AbstractDirectional radiofrequency (RF) sensing, also known as radio direction finding, is essential in various applications that involve localizing RF sources. However, existing RF sensing technologies face challenges due to their large antenna sizes and complex RF signal processing circuits, which hinder the realization of miniaturized subwavelength direction sensors. In this article, a non‐Hermitian broadside coupled split ring resonators (BC‐SRRs) are presented, which can identify the direction of an incident RF signal with angles ranging from 0° to 180°. The non‐Hermitian Hamiltonian of the system, which can be interpreted by the temporal coupled mode theory, gives rise to asymmetric resonant modes of the BC‐SRRs. The asymmetry allows the direct measurement of RF wave incident angle by probing the resonant strength of the two BC‐SRRs. For the proof of concept, a one‐stage Dickson voltage multiplier is employed to rectify the RF signals and demonstrate angle sensing ability by relating the rectified voltage to the incident angle. The results showcase the potential of the proposed technique using non‐Hermitian BC‐SRRs as a pathway toward subwavelength antenna‐based radio direction finding.

Hyperbolic photonic topological insulators

Topological photonics provides a new degree of freedom to robustly control electromagnetic fields. To date, most of established topological states in photonics have been employed in Euclidean space. Motivated by unique properties of hyperbolic lattices, which are regular tessellations in non-Euclidean space with a constant negative curvature, the boundary-dominated hyperbolic topological states have been proposed. However, limited by highly crowded boundary resonators and complicated site couplings, the hyperbolic topological insulator has only been experimentally constructed in electric circuits. How to achieve hyperbolic photonic topological insulators is still an open question. Here, we report the experimental realization of hyperbolic photonic topological insulators using coupled ring resonators on silicon chips. Boundary-dominated one-way edge states with pseudospin-dependent propagation directions have been observed. Furthermore, the robustness of edge states in hyperbolic photonic topological insulators is also verified. Our findings have potential applications in the field of designing high-efficient topological photonic devices with enhanced boundary responses.

High-Sensitivity RFID Tag Sensor with Coupled Ring Resonators for Multi-Position Crack Monitoring

High-Sensitivity RFID Tag Sensor with Coupled Ring Resonators for Multi-Position Crack Monitoring

Stacked ring resonators for optical vortices

In this paper, we study transmission of higher-order modes, optical vortices (OVs) included, through a bus fiber coupled to a vertical stack of ring resonators—stack multi-ring resonator (SMR). We show that transmission curves for OVs feature a characteristic gap-like structure, whose presence we explain as a manifestation of the band structure of an infinite stack of coupled ring resonators. We show a principal possibility to use SMRs as elements of delay lines for fiber optics communications on orbital angular momentum (OAM) states. We emphasize the advantages of such systems as delay lines for communications that use as signal carriers odd and even Laguerre–Gaussian (LG) modes. We also show that SMRs are able to exert super-efficient parametric control over the OAM of the transmitted optical field, as well as to generate OAM beams from odd and even LG modes.

Refractive index sensing near exceptional point of a system of triple microcavity

Degeneracies of non-Hermitian Hamiltonian i.e., exceptional points (EPs) of parity-time (PT)-symmetric systems have received considerable research attention due to their various possible applications in optical devices. At EPs, at least two eigenvalues as well as their eigenvector coalesce. Recently, the effect of the eigenfrequency splitting on transfer function near EP was studied for an optical system consisting of two micro ring resonators, which led to complex splitting in PT‐symmetric and real splitting in anti‐PT‐symmetric sensors. In present work, we propose a simple system of three coupled ring resonators to show real splitting in both PT-symmetric and anti-PT-symmetric parameter domains by exploiting higher-order EPs. We indirectly couple two rings with equal amount of gain and loss via an intermediate neutral ring. This system is then tested for refractive index (RI) sensing by modulating the cladding index and we numerically show a huge enhancement in sensitivity as compared to those reported in previous studies of micro ring resonators. Importantly, the enhancement is found to be of the order of 108. Further, we have found that the order of EP can be tuned by perturbating the cladding. The outcomes of this study may set up a wide range of applications in non-Hermitian triplet cavity systems.

All optical modulation in vertically coupled indium tin oxide ring resonator employing epsilon near zero state

We present an innovative approach to achieve all-optical modulation within an ITO-based vertically coupled ring resonator. This method leverages the material's enhanced nonlinear response in the near-infrared wavelengths, particularly within the epsilon-near-zero (ENZ) state. To enhance the interaction between light and the material while minimizing scattering losses, our approach employs an ITO-based vertically connected ring resonator. The vertical arrangement eliminates the need for etching fine gaps to separate the ring and bus waveguide. The novel waveguide design addresses the necessity of high sensitivity, non-linear effects and compact size opening the possibilities for all-optical signal processing. This unique resonator structure effectively facilitates the coupling of a high-intensity pump wavelength into the ITO-based micro-ring resonator. Consequently, this optical pumping induces electron heating within the ITO material, leading to a significant increase in its nonlinear optical properties. This, in turn, results in a noteworthy alteration of ITO's refractive index, specifically in the unity order, thereby modifying the complex effective index of the optical beam propagating at 1550 nm. Our experimental findings demonstrate an impressive extinction ratio of 18 dB for a 30 µm long device, which highlights the efficiency of our approach in achieving all-optical modulation through the optical pumping of an ITO-based vertically coupled ring resonator. The proposed all-optical modulator has outperformed as compared to conventional waveguide-based modulators in terms of extinction ratio and footprint. This novel technique holds immense potential for advancing high-speed data communication systems in the future. As the demand for advanced processing capabilities, such as artificial intelligence, continues to grow, all-optical modulation emerges as a groundbreaking technology poised to revolutionize the next generation of computing and communication systems.

Enhanced Q-factor and effective length silicon photonics filter utilizing nested ring resonators

In this study, we investigate a novel design of an on-chip nested coupled ring resonator to enhance the quality factor and the effective length of the resonator. The configuration consists of an open ring and racetrack resonator, with lengths of 340 μm and 184.4 μm, respectively, with a coupling ratio of 97/3. In this regard, the proposed nested cavity has been experimentally characterized and compared with a single cavity ring resonator. Our results show a significant improvement in the quality factor by a factor of four. This improvement in performance opens up exciting new possibilities for state-of-the-art applications, such as compact optical sensors and delay lines. Our proposed design represents a significant advancement in the field of integrated optics, and we believe that it has the potential to enable a broad range of applications in the future.

Topological Microlaser with a Non-Hermitian Topological Bulk.

Bulk-edge correspondence, with quantized bulk topology leading to protected edge states, is a hallmark of topological states of matter and has been experimentally observed in electronic, atomic, photonic, and many other systems. While bulk-edge correspondence has been extensively studied in Hermitian systems, a non-Hermitian bulk could drastically modify the Hermitian topological band theory due to the interplay between non-Hermiticity and topology, and its effect on bulk-edge correspondence is still an ongoing pursuit. Importantly, including non-Hermicity can significantly expand the horizon of topological states of matter and lead to a plethora of unique properties and device applications, an example of which is a topological laser. However, the bulk topology, and thereby the bulk-edge correspondence, in existing topological edge-mode lasers is not well defined. Here, we propose and experimentally probe topological edge-mode lasing with a well-defined non-Hermitian bulk topology in a one-dimensional (1D) array of coupled ring resonators. By modeling the Hamiltonian with an additional degree of freedom (referred to as synthetic dimension), our 1D structure is equivalent to a 2D non-Hermitian Chern insulator with precise mapping. Our Letter may open a new pathway for probing non-Hermitian topological effects and exploring non-Hermitian topological device applications.

Engineered zero-dispersion microcombs using CMOS-ready photonics

Normal group velocity dispersion (GVD) microcombs offer high comb line power and high pumping efficiency compared to bright pulse microcombs. The recent demonstration of normal GVD microcombs using CMOS foundry-produced microresonators is an important step toward scalable production. However, the chromatic dispersion of CMOS devices is large and impairs the generation of broadband microcombs. Here, we report the development of a microresonator in which GVD is reduced due to a coupled-ring resonator configuration. Operating in the turnkey self-injection locking mode, the resonator is integrated in a hybrid manner with a semiconductor laser pump to produce high-power efficiency combs spanning a bandwidth of 9.9 nm (1.22 THz) centered at 1560 nm, corresponding to 62 comb lines. Fast, linear optical sampling of the comb waveform is used to observe the rich set of near-zero GVD comb behaviors, including soliton molecules, switching waves (platicons), and their hybrids. Tuning of the 20 GHz repetition rate by electrical actuation enables servo locking to a microwave reference, which simultaneously stabilizes the comb repetition rate, offset frequency, and temporal waveform. This integrated hybrid system could be used in coherent communications or for ultrastable microwave signal generation by two-point optical frequency division.

Observation of the transition from inverted coupled-resonator-induced transparency to inverted Autler-Townes splitting

Inverted coupled-resonator-induced transparency eliminates amplification as a result of destructive interference between two competing excitation pathways and induces a ``nonamplifying'' transparency window in an otherwise strongly amplifying spectral region. Using coupled ring resonators as a model system, we systematically examined the transition from inverted induced transparency to Autler-Townes splitting (ATS) by controlling the coupling strength between two resonators. The inverted induced transparency spectrum transitioned into different ATS spectra depending on the parameters of the resonators. We also examined the transition that occurs when the second resonator has gain. In this case, the system showed enhanced transparency, in which the intensity of the induced window was much greater than the incident laser level.

Antihelical edge states in two-dimensional photonic topological metals

Topological edge states are the core of topological photonics. Here we introduce the antihelical edge states of time-reversal symmetric topological metals and propose a photonic realization in an anisotropic square lattice of coupled ring resonators, where the clockwise and counterclockwise modes play the role of pseudospins. The antihelical edge states robustly propagate across the corners toward the diagonal of the square lattice: The same (opposite) pseudospins copropagate in the same (opposite) direction on the parallel lattice boundaries; the different pseudospins separate and converge at the opposite corners. The antihelical edge states in the topological metallic phase alter to the helical edge states in the topological insulating phase under a metal-insulator phase transition. The antihelical edge states provide a unique manner of topologically-protected robust light transport applicable for topological purification. Our findings create new opportunities for topological photonics and metamaterials.

Development, Characterization, and Circuit Modeling of Inkjet-Printed Coupled Ring Resonators for Application in Biological Samples

Development, Characterization, and Circuit Modeling of Inkjet-Printed Coupled Ring Resonators for Application in Biological Samples

Design and Simulation Study of an Optical Mode-Localized MEMS Accelerometer.

In this paper, we demonstrate a novel photonic integrated accelerometer based on the optical mode localization sensing mechanism, which is designed on an SOI wafer with a device layer thickness of 220 nm. High sensitivity and large measurement range can be achieved by integrating coupled ring resonators with a suspended directional coupler on a proof mass. With the help of FEA simulation and numerical analysis, the proposed optical mode-localized sensor presents a sensitivity of 10/g (modal power ratio/acceleration) and an inertial displacement of from -8 to 10 microns corresponding to a range from -23.5 to 29.4 g. The free spectral range is 4.05 nm around 1.55 microns. The acceleration resolution limited by thermomechanical noise is 4.874 μg. The comprehensive performance of this design is competitive with existing MEMS mode localized accelerometers. It demonstrates the potential of the optical mode-localized inertial sensors as candidates for state-of-the-art sensors in the future.

Generating Loss Dependent Bifid Dips of Optical Carrier Based Microwave With Self-Feedback Anti-Symmetric Coupled Fiber Ring Resonator

A self-feedback anti-symmetric coupled fiber ring resonator (SACFRR) is proposed and demonstrated to generate the distinctive loss dependent bifid dips. The universal derivation of the ring resonators in both lightwave and optical carrier based microwave domains considering different conditions including attenuation, coupling and self-feedback is systematically elaborated, which is applicable to diverse ring resonator configurations. The lightwave and optical carrier based microwave experience different phase evolution during the cross-coupling procedure, thereby causing very different output. The anti-symmetric coupling strategy is creatively introduced into the ring resonator, which dominates the splitting of the original resonance dip for the optical carrier based microwave interferometry (OCMI). And OCMI shows the noticeable bifid dips within the lower envelope which receives less attention before. By performing the measurement of temperature and bend-induced loss, the bifid dips based demodulation of OCMI is employed to present the property of SACFRR and compared with the conventional upper envelope based demodulation, contributing to the utilization of lower envelope information. The temperature sensitivity is 521.4 kHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> C at 3.05 GHz and the bend-induced loss sensitivity is 24.845 MHz/turn (diameter of 2.30 cm) at 10 turns where is adjacent to the critical point of bifid dips merging. The proposed scheme provides an extraordinary design avenue which can be extended to diverse ring resonators in both photonic integrated circuits and fiber links for exploring compelling functions.

Anomalous Floquet non-Hermitian skin effect in a ring resonator lattice

We present a one-dimensional coupled ring resonator lattice exhibiting a variant of the non- Hermitian skin effect (NHSE) that we call the anomalous Floquet NHSE. Unlike existing approaches to achieving the NHSE by engineering gain and loss on different ring segments, our design uses fixed on-site gain or loss in each ring. The anomalous Floquet NHSE is marked by the existence of skin modes at every value of the Floquet quasienergy, allowing for broadband asymmetric transmission. Varying the gain/loss induces a non-Hermitian topological phase transition, reversing the localization direction of the skin modes. An experimental implementation in an acoustic lattice yields good agreement with theoretical predictions, with a very broad relative bandwidth of around 40%.

Single-photon nonlinearities and blockade from a strongly driven photonic molecule.

Achieving the regime of single-photon nonlinearities in photonic devices by just exploiting the intrinsic high-order susceptibilities of conventional materials would open the door to practical semiconductor-based quantum photonic technologies. Here we show that this regime can be achieved in a triply resonant integrated photonic device made of two coupled ring resonators, in a material platform displaying an intrinsic third-order nonlinearity. By strongly driving one of the three resonances of the system, a weak coherent probe at one of the others results in a strongly suppressed two-photon probability at the output, evidenced by an antibunched second-order correlation function at zero-time delay under continuous wave driving.

Sensitivity Enhancement of Thermal Piezoresistive Resonant MEMS Sensors Using Mechanical Coupling and DC Tuning

In this work, we present a Silicon on Insulator (SOI) mechanically coupled MEMS device composed of three rotating ring resonators for enhancing its sensitivity. It shows the exploration of Thermal Piezoresistive (TPR) transduction in mechanically coupled ring resonators for mass sensing applications. Mass sensing experiments are performed by dropping the silver nano drops on the surface of the resonator. It includes the first-time investigation of a three degree of freedom (3-DOF) differential ring-shaped TPR (DR-TPR) MEMS coupled-resonator and involves the selection of the best configuration of the differential drive and sense scheme that enhances the signal-to-noise ratio (SNR) using feedthrough cancellation. Amplitude change and amplitude ratio offer an enhancement in normalized sensitivity by 92 and 131 times respectively along with the common-mode rejection in comparison to their frequency shift counterparts. This coupled-resonator can show a quality factor of more than 1300 in ambient conditions, facilitating the resolution and DC tunability improvement. This work paves the way to realize various sensors for ambient environment applications. [2022-0045]