Photonic Microring Resonators Research Articles

Photonic crystal-connected bidirectional micro-ring resonator array for duplex mode and wavelength channel (de)multiplexing

The progress of on-chip optical communication relies on integrated multi-dimensional mode (de)multiplexers to enhance communication capacity and establish comprehensive networks. However, existing multi-dimensional (de)multiplexers, involving modes and wavelengths, face limitations due to their reliance on single-directional total internal reflection and multi-level mode conversion based on directional coupling principles. These constraints restrict their potential for full-duplex functionality and highly integrated communication. We solve these problems by introducing a photonic-like crystal-connected bidirectional micro-ring resonator array (PBMRA) and apply it to duplex mode-wavelength multiplexing communication. The directional independence of total internal reflection and the cumulative effect of the subwavelength-scale pillar within the single-level photonic crystal enable bidirectional mode and wavelength multiplexed signals to transmit among multi-pair nodes without interference, improving on-chip integration in single-level mode conversion. As a proof of concept, we fabricated a nine-channel bidirectional multi-dimensional (de)multiplexer, featuring three wavelengths and three TE modes, compactly housed within a footprint of 80 μm×80 μm, which efficiently transmits QPSK-OFDM signals at a rate of 216 Gbit/s, achieving a bit error rate lower than 10−4. Leveraging the co-ring transmission characteristic and the orthogonality of the mode-wavelength channel, this (de)multiplexer also enables a doubling of communication capacity using two physical transmission channels.

On-chip silicon photonic micro-ring processor lights up optical image encryption.

Optical image encryption has long been an important concept in the fields of photonic network processing and communication. Here, we propose a convolution-like operation-based optical image encryption algorithm exploiting a silicon photonic multiplexing architecture to achieve content security. Particularly, the encryption process is completed in a 3 × 3 cross-shaped photonic micro-ring resonator (MRR) array on chip. For the first time, to the best of our knowledge, this algorithm encodes information in an integrated intensity modulation, effectively reducing the encoding difficulty. Moreover, the high reliability and scalability of optical encryption are ensured using both linear and nonlinear operations on photonic chips according to characteristics of MRRs. As the encryption and decryption experiments show, the image restoration accuracy of our optical encryption algorithm exceeds 99% under real system noise at the pixel level, indicating its noise-robust property. Meanwhile, the peak signal-to-noise ratios of the restored and encrypted images are >60 and <15 dB, respectively, revealing both the high accuracy of the restored image and the small correlation between the encrypted and original images. This work adds to the rapidly expanding field of optical image encryption on photonic chips.

Sensitive, accurate, and high spatiotemporal resolution photonic thermometry

Real-time temperature monitoring with high accuracy and spatiotemporal resolution is critical for many biological applications, including disease diagnosis, drug delivery, and biomedical research. However, traditional methods for measuring temperature in biological systems present difficulties for a variety of reasons, such as slow response time, limited spatial resolution, low amplitude, and susceptibility to electromagnetic interference. Most importantly, in many cases, the thermal mass of temperature probes limits the accuracy and speed of measurement significantly. Here, we show that photonic microring resonators (MRRs) can be used for sensitive, precise, and high spatiotemporal resolution measurement of temperature in the biological milieu. The high refractive index of Si MRR and negligible thermal mass enable sensitive, ultrafast, and accurate temperature transients. By using a double resonator circuit, we demonstrate that MRR sensors can measure temperature with a 1 mm spatial resolution. We then show that MRR yields more accurate results than fiber optic probes for measuring temperature transients. Finally, we demonstrate the localized temperature measurement capability of MRRs in mouse brain tissue heated by superparamagnetic nanoparticles in an alternating magnetic field. This compact, lab-on-chip photonic temperature sensing platform holds great promise for continuous monitoring of temperature in critical biological and biomedical applications.

High-resolution photonic-assisted microwave frequency identification based on an ultrahigh-Q hybrid optical filter

Photonic-assisted microwave frequency identification has been extensively studied in civil and defense applications due to its distinct features including wide frequency coverage, large instantaneous bandwidth, high frequency resolution, and immunity to electromagnetic interference. In this paper, we propose and experimentally demonstrate an approach for high-resolution frequency identification of wideband microwave signals by linearly mapping the microwave frequencies to the time delays of the optical pulses. In the proposed system, an ultrahigh-Q hybrid optical filter is a key component, which consists of a fiber ring resonator (FRR) and a silicon photonic racetrack micro-ring resonator (MRR). The FRR has an ultra-narrow bandwidth of 7.6 MHz and a small free spectral range (FSR) of 292.5 MHz, while the MRR has a bandwidth of 167.5 MHz and a large FSR of 73.8 GHz. By precisely matching the resonance wavelengths of the FRR and the MRR, a hybrid optical filter with an ultrahigh Q-factor and a large FSR is realized, which is much preferred to realizing a high resolution and a wide measurement range for microwave frequency identification. An experiment is performed and different types of microwave signals are identified. A frequency measurement range as broad as 33 GHz from 2 to 35 GHz, a frequency resolution as high as 15 MHz and a measurement accuracy as high as 5.6 MHz are experimentally demonstrated. The proposed frequency identification system holds great advantages including high frequency resolution, high measurement accuracy, and wide frequency coverage, which can find extensive applications in next-generation electronic warfare and cognitive radio systems.

B-036 Multi-Biomarker Approach to Latent Tuberculosis Diagnosis Using Microring Resonator Sensors

Abstract Background Tuberculosis (TB) is an infectious disease that induces a complex response from the host immune system. Most carriers of the bacteria experience the asymptomatic, non-infectious phase, latent tuberculosis infection (LTBI), but have the potential to reactivate to active, contagious TB infection. Current diagnostics for TB are not sufficient for LTBI and are focused on using one biomarker, interferon-gamma (IFN-g). To build better diagnostics for the complex disease, multi-biomarker approaches to profile the immune system, coupled with machine learning algorithms, are necessary to diagnose LTBI and determine patients' risks of reactivation to active TB. We aim to use a multiplexed silicon photonic microring resonator sensing platform to profile thirteen biomarkers in patients with LTBI infection and use machine learning data analysis to identify biomarkers relevant for diagnosing LTBI and predicting reactivation risk. Methods We employed microring resonators coupled with a sandwich-style detection format to simultaneously detect thirteen cytokines and chemokines in plasma in under 40 minutes. Chip-integrated silicon photonic microrings are small in size and easily multiplexed with up to sixteen different capture agents. Biomolecular binding events are measured by monitoring the resonant wavelength within the sensing cavity, which shifts as binding events occur. Quantitation of each biomarker is possible with calibration curves that correlate standard protein concentrations to wavelength shifts. The multiplexed assay has been optimized for each individual biomarker, tested for cross-reactivity, and calibrated in the plasma matrix of interest. The LODs vary, depending on biomarker and matrix dilution, but range from 4.9 pg/mL to 691 pg/mL. The patient plasma samples are left over from the TB screening IFN-g release assay, QuantiFERON-TB Gold Plus (QFT), putting this method within the current clinical workflow. We use precision normalization approaches from the four QFT stimulations to account for immunologic differences among the subjects. The biomarker concentrations are evaluated using a random forest machine learning model to identify which biomarkers are important for identifying patients with LTBI and predicting their reactivation risk. Results We used this sensor method to profile 42 patients, 24 LTBI negative controls and 18 LTBI positive controls, with 13 being considered at high risk of reactivation. Using a precision normalization approach, a combination of nine normalized conditions using five of the thirteen biomarkers (CCL4, CCL8, IP-10, IL-2, IL-17) discriminated between LTBI positive and negative subjects with a ROC AUC of 0.90. Additionally, eight normalized conditions using four of the same biomarkers discriminated between high and low-risk subjects with an AUC of 0.83. Currently, we have expanded the sample cohort to include an additional 72 subjects, 25 LTBI positive and 47 LTBI negative. Preliminary analysis shows CCL8, IL-2, and IP-10 alone are able to distinguish between LTBI status (P values &amp;lt;0.01) using raw target concentrations prior to precision normalization. Conclusion Overall, we show the importance of multi-biomarker approaches to develop diagnostic and prognostic tools for a complex disease, such as TB. Further work to use the initial machine learning algorithm with the expanded cohort to validate biomarker importance is underway.

Fourier synthesis dispersion engineering of photonic crystal microrings for broadband frequency combs

Dispersion engineering of microring resonators is crucial for optical frequency comb applications, to achieve targeted bandwidths and powers of individual comb teeth. However, conventional microrings only present two geometric degrees of freedom – width and thickness – which limits the degree to which dispersion can be controlled. We present a technique where we tune individual resonance frequencies for arbitrary dispersion tailoring. Using a photonic crystal microring resonator that induces coupling to both directions of propagation within the ring, we investigate an intuitive design based on Fourier synthesis. Here, the desired photonic crystal spatial profile is obtained through a Fourier relationship with the targeted modal frequency shifts, where each modal shift is determined based on the corresponding effective index modulation of the ring. Experimentally, we demonstrate several distinct dispersion profiles over dozens of modes in transverse magnetic polarization. In contrast, we find that the transverse electric polarization requires a more advanced model that accounts for the discontinuity of the field at the modulated interface. Finally, we present simulations showing arbitrary frequency comb spectral envelope tailoring using our Fourier synthesis approach.

Low Noise Ultra-Flexible SiP Switching Platform for mmWave OCDM &amp; Multi-Band OFDM ARoF Fronthaul

A highly flexible wavelength and space switched analog radio-over-fiber (ARoF) fronthaul transmission of a millimeter-wave (mmWave) emerging 6G waveform over a centralized/ cloud radio access network (C-RAN) is experimentally demonstrated in this work. A spread spectrum multiplexing technique — orthogonal chirp division multiplexing (OCDM) — which is highly resilient to inter-channel interference and enables enhanced channel estimation is utilized in the fronthaul transmission demonstration. The flexible properties of a low noise silicon photonic (SiP) microring resonator (MRR) based tunable laser and a low cross-talk 4×4 SiP optical wavelength/space switch are combined to form a reconfigurable 10 km fronthaul system enabling 64-QAM OCDM transmission at 24 GHz with consistent performances ~5% EVM across all test wavelengths/ports. A signal constituting Wi-Fi and 5G NR standard compatible 64-QAM orthogonal frequency division multiplexing (OFDM) bands, at 10 GHz and 24 GHz respectively, are also transmitted and evaluated in the proposed system with EVM performances below 64-QAM EVM limit (8%) achieved, thus demonstrating the system’s potential in a future converged multi-service environment.

CMOS-compatible electro-optical SRAM cavity device based on negative differential resistance

The impending collapse of Moore-like growth of computational power has spurred the development of alternative computing architectures, such as optical or electro-optical computing. However, many of the current demonstrations in literature are not compatible with the dominant complementary metal-oxide semiconductor (CMOS) technology used in large-scale manufacturing today. Here, inspired by the famous Esaki diode demonstrating negative differential resistance (NDR), we show a fully CMOS-compatible electro-optical memory device, based on a new type of NDR diode. This new diode is based on a horizontal PN junction in silicon with a unique layout providing the NDR feature, and we show how it can easily be implemented into a photonic micro-ring resonator to enable a bistable device with a fully optical readout in the telecom regime. Our result is an important stepping stone on the way to new nonlinear electro-optic and neuromorphic computing structures based on this new NDR diode.

Biosensing with Silicon Nitride Microring Resonators Integrated with an On-Chip Filter Bank Spectrometer.

Wearable, mobile, and point-of-care (POC) sensors comprise a rapidly expanding field of devices aimed at improving human health by relaying real-time biometric data such as heart rate and glucose levels. The current scope of what these devices can offer healthcare is limited by their inability to measure biomarkers associated with inflammation, well-being, and disease. Photonic biosensors that integrate sensing elements directly with spectrometers, lasers, and detectors are an attractive approach to enabling POC sensors, with distinct advantages in terms of size, weight, power consumption, and cost. Here, we have demonstrated for the first time the integration of photonic microring resonator biosensors with an on-chip microring filter bank spectrometer for the controlled detection of inflammatory biomarker C-reactive protein (CRP) in serum. We demonstrate that sensor and spectrometer performance is tolerant of temperature variation, as temperature dependence moves in parallel. Finally, we assess the impact of manufacturing variability on the 300 mm wafer scale on the performance of the spectrometer. Taken together, these results suggest that integration of on-chip ring filter bank spectrometers with ring resonator-based biosensors constitutes an attractive approach toward cost-effective integrated sensor development.

Photonic Reconfigurable Accelerators for Efficient Inference of CNNs With Mixed-Sized Tensors

Photonic microring resonator (MRR)-based hardware accelerators have been shown to provide disruptive speedup and energy-efficiency improvements for processing deep convolutional neural networks (CNNs). However, previous MRR-based CNN accelerators fail to provide efficient adaptability for CNNs with mixed-sized tensors. One example of such CNNs is depthwise separable CNNs. Performing inferences of CNNs with mixed-sized tensors on such inflexible accelerators often leads to low hardware utilization, which diminishes the achievable performance and energy efficiency from the accelerators. In this article, we present a novel way of introducing reconfigurability in the MRR-based CNN accelerators, to enable dynamic maximization of the size compatibility between the accelerator hardware components and the CNN tensors that are processed using the hardware components. We classify the state-of-the-art MRR-based CNN accelerators from prior works into two categories, based on the layout and relative placements of the utilized hardware components in the accelerators. We then use our method to introduce reconfigurability in accelerators from these two classes, to consequently improve their parallelism, the flexibility of efficiently mapping tensors of different sizes, speed, and overall energy efficiency. We evaluate our reconfigurable accelerators against three prior works for the area proportionate outlook (equal hardware area for all accelerators). Our evaluation for the inference of four modern CNNs indicates that our designed reconfigurable CNN accelerators provide improvements of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.8\times $ </tex-math></inline-formula> in frames-per-second (FPS) and up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.5\times $ </tex-math></inline-formula> in FPS/W, compared to an MRR-based accelerator from prior work.

Nanoporous Silica–Alumina Films Fabricated on Silicon Photonic Chips for Selective Ammonia Sensing

Surface-modified nanoporous silica films offer attractive features for analyte-specific gas detection applications. Here we demonstrate the integration of highly porous silica–alumina films on silicon nanophotonic chips and their performance in selective NH3 detection. Prototype sensors with microporous as well as mesoporous silica films were assembled. The incorporation of aluminum in trace amount needed to generate acid sites was achieved during film deposition or using postsynthesis atomic layer deposition. Silicon photonic micro-ring resonators functionalized with both techniques demonstrated a selective response to NH3 relative to CO2. Furthermore, the response was rapid and reversible. The role of preadsorbed water vapor on the reversible nature of the sensor is also investigated. Experimental observations indicate that water vapor preadsorbed on the films leads to fast sensor recovery while maintaining selectivity toward NH3. This could be attributed to the relatively less strong and still selective binding of NH3 on protonated water molecules preadsorbed on the surface acid sites. The potential of modified nanoporous films for portable and low-cost NH3 sensing on optical chips demonstrated here can be exploited in health care as well as industrial applications.

Silicon Photonic Microring Resonators: A Comprehensive Design-Space Exploration and Optimization Under Fabrication-Process Variations

Silicon photonic microring resonators (MRRs) offer many advantages (e.g., compactness) and are often considered as the fundamental building block in optical interconnects and emerging photonic nanoprocessors and accelerators. Such devices are, however, sensitive to inevitable fabrication-process variations (FPVs) stemming from optical lithography imperfections. Consequently, silicon photonic integrated circuits (PICs) integrating MRRs often suffer from high power overhead required to compensate for the impact of FPVs on MRRs and, hence, realizing a reliable operation. On the other hand, the design space of MRRs is complex, including several correlated design parameters, thereby further exacerbating the design optimization of MRRs under FPVs. In this article, we present, for the first time, a comprehensive design-space exploration in passive and active MRRs under FPVs. In addition, we present design optimization in MRRs under FPVs while considering different performance metrics, such as tolerance to FPVs, quality factor, and 3-dB bandwidth in MRRs. Simulation and fabrication results obtained by measuring multiple fabricated MRRs designed using our design-space exploration demonstrate a significant 70% improvement on average in the MRRs’ tolerance to different FPVs. Furthermore, we apply the proposed design optimization to a case study of a wavelength-selective MRR-based demultiplexer, where we show considerable channel-spacing accuracy within 0.5 nm even when the MRRs are placed 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> apart on a chip. Such improvements indicate the efficiency of the proposed design-space exploration and optimization to enable power-efficient and variation-resilient PICs and optical interconnects integrating MRRs.

High sensitivity and enhanced measurement range biosensing based on defective photonic crystal microring resonators

In this paper, we propose a defective photonic crystal microring resonator (DPhCMRR) by introducing a point defect into a conventional photonic crystal microring resonator (PhCMRR). The defective resonant wavelength within the photonic mode gap and the location of the defect mode distribution can be readily controlled. Unlike conventional PhCMRR, where the free spectral range (FSR) is limited by the dispersive band structure, our DPhCMRR can take advantage of the tunability of the defect mode within the photonic mode gap, leading to a significant increase of the measurement range. Moreover, the bulk refractive index sensitivity can reach 200 nm/RIU (refractive index unit) and the local refractive index sensitivity is about 5 to 10 times larger than that of the conventional PhCMRR. For sensing applications, our DPhCMRR can possess high sensitivity and wide measurement range simultaneously. As proof of principle, it is demonstrated that our proposed DPhCMRR can perform as a sensitive virus biosensor, which can detect a single virus and a concentration of viruses quantitatively. Therefore, our DPhCMRRs can provide a new platform for achieving high sensitivity and wide measurement range biosensing.

On-chip simultaneous measurement of humidity and temperature using cascaded photonic crystal microring resonators with error correction.

We present the design, fabrication, and characterization of cascaded silicon-on-insulator photonic crystal microring resonators (PhCMRRs) for dual-parameter sensing based on a multiple resonances multiple modes (MRMM) technique. Benefitting from the slow-light effect, the engineered PhCMRRs exhibit unique optical field distributions with different sensitivities via the excitation of dielectric and air modes. The multiple resonances of two distinct modes offer new possibilities for enriching the sensing receptors with additional information about environmental changes while preserving all essential properties of traditional microring resonator based sensors. As a proof of concept, we demonstrate the feasibility of extracting humidity and temperature responses simultaneously with a single spectrum measurement by employing polymethyl methacrylate as the hydrophilic coating, obtaining a relative humidity (RH) sensitivity of 3.36 pm/%RH, 5.57 pm/%RH and a temperature sensitivity of 85.9 pm/°C, 67.1 pm/°C for selected dielectric mode and air mode, respectively. Moreover, the MRMM enriched data further forges the capability to perform mutual cancellation of the measurement error, which improves the sensing performance reflected by the coefficient of determination (R2-value), calculated as 0.97 and 0.99 for RH and temperature sensing results, respectively.

Real-Time In Vivo Sensing of Nitric Oxide Using Photonic Microring Resonators.

Real-time in vivo detection of biomarkers, particularly nitric oxide (NO), is of utmost importance for critical healthcare monitoring, therapeutic dosing, and fundamental understanding of NO's role in regulating many physiological processes. However, detection of NO in a biological medium is challenging due to its short lifetime and low concentration. Here, we demonstrate for the first time that photonic microring resonators (MRRs) can provide real-time, direct, and in vivo detection of NO in a mouse wound model. The MRR encodes the NO concentration information into its transfer function in the form of a resonance wavelength shift. We show that these functionalized MRRs, fabricated using complementary metal oxide semiconductor (CMOS) compatible processes, can achieve sensitive detection of NO (sub-μM) with excellent specificity and no apparent performance degradation for more than 24 h of operation in biological medium. With alternative functionalizations, this compact lab-on-chip optical sensing platform could support real-time in vivo detection of myriad of biochemical species.

Use of transmission and reflection complex time delays to reveal scattering matrix poles and zeros: Example of the ring graph.

We identify the poles and zeros of the scattering matrix of a simple quantum graph by means of systematic measurement and analysis of Wigner, transmission, and reflection complex time delays. We examine the ring graph because it displays both shape and Feshbach resonances, the latter of which arises from an embedded eigenstate on the real frequency axis. Our analysis provides a unified understanding of the so-called shape, Feshbach, electromagnetically induced transparency, and Fano resonances on the basis of the distribution of poles and zeros of the scattering matrix in the complex frequency plane. It also provides a first-principles understanding of sharp resonant scattering features and associated large time delay in a variety of practical devices, including photonic microring resonators, microwave ring resonators, and mesoscopic ring-shaped conductor devices. Our analysis involves use of the reflection time difference, as well as a comprehensive use of complex time delay, to analyze experimental scattering data.

Broadband single-mode planar waveguides in monolithic 4H-SiC

Color-center defects in silicon carbide promise opto-electronic quantum applications in several fields, such as computing, sensing, and communication. In order to scale down and combine these functionalities with the existing silicon device platforms, it is crucial to consider SiC integrated optics. In recent years, many examples of SiC photonic platforms have been shown, like photonic crystal cavities, film-on-insulator waveguides, and micro-ring resonators. However, all these examples rely on separating thin films of SiC from substrate wafers. This introduces significant surface roughness, strain, and defects in the material, which greatly affects the homogeneity of the optical properties of color centers. Here, we present and test a method for fabricating monolithic single-crystal integrated-photonic devices in SiC: tuning optical properties via charge carrier concentration. We fabricated monolithic SiC n-i-n and p-i-n junctions where the intrinsic layer acts as waveguide core, and demonstrate the waveguide functionality for these samples. The propagation losses are below 14 dB/cm. These waveguide types allow for addressing color centers over a broad wavelength range with low strain-induced inhomogeneity of the optical-transition frequencies. Furthermore, we expect that our findings open the road to fabricating waveguides and devices based on p-i-n junctions, which will allow for integrated electrostatic and radio frequency control together with high-intensity optical control of defects in silicon carbide.

Design and simulation of an electro-optic even parity bit error detection system

In the present day, optical communication technology is proving to be one of the potential replacements to the current electronic-based systems due to its much higher data transmission rate with low loss and electromagnetic interference. This paper designed and simulated our proposed circuit of a digital photonic even parity bit error detection system that is widely employed for the long-range digital signal transmission. Silicon photonic micro-ring resonators are used as their core component. Each of the rings is configured to operate as a digital logic XOR mode by taking advantage of the silicon waveguide's resonance shifting properties. Dynamic response characterization was carried out by simulating the proposed circuits at the data rate of 1-Gbps, with the data sampling rate of 1.6-THz. A clear timing waveform was generated to confirm that the proposed circuit operates as the parity bit error detection system.

2D Materials Enabled Next-Generation Integrated Optoelectronics: from Fabrication to Applications.

2D materials, such as graphene, black phosphorous and transition metal dichalcogenides, have gained persistent attention in the past few years thanks to their unique properties for optoelectronics. More importantly, introducing 2D materials into silicon photonic devices will greatly promote the performance of optoelectronic devices, including improvement of response speed, reduction of energy consumption, and simplification of fabrication process. Moreover, 2D materials meet the requirements of complementary metal‐oxide‐semiconductor compatible silicon photonic manufacturing. A comprehensive overview and evaluation of state‐of‐the‐art 2D photonic integrated devices for telecommunication applications is provided, including light sources, optical modulators, and photodetectors. Optimized by unique structures such as photonic crystal waveguide, slot waveguide, and microring resonator, these 2D material‐based photonic devices can be further improved in light‐matter interactions, providing a powerful design for silicon photonic integrated circuits.

Optimization of Nanodisc Array Generation on Silicon Photonic Microring Resonators for Lipid-Protein and Membrane Protein-Protein Interaction Characterization

Optimization of Nanodisc Array Generation on Silicon Photonic Microring Resonators for Lipid-Protein and Membrane Protein-Protein Interaction Characterization