Silicon Photonic Microring Resonators Research Articles

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 <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.

Low Noise Ultra-Flexible SiP Switching Platform for mmWave OCDM & 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.

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.

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.

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

New Interfaces to Silicon Photonic Microring Resonator Arrays for Chemical Separations

New Interfaces to Silicon Photonic Microring Resonator Arrays for Chemical Separations

Real-Time Measurement of Polymer Brush Dynamics Using Silicon Photonic Microring Resonators: Analyte Partitioning and Interior Brush Kinetics.

Polymer brushes are found in biomedical and industrial technologies, where they exhibit functionalities considerably dependent on polymer brush-solvent-analyte interactions. It remains a difficult challenge to quickly analyze solvent-swollen polymer brushes, both at the solvent-polymer brush interface and in the brush interior, as well as to monitor the kinetics of interaction of solvent-swollen brushes with key analytes. Here, we demonstrate the novel use of silicon photonic microring resonators to characterize in situ swollen polymer brush-analyte interactions. By monitoring resonant wavelength shifts, we find that brush-solvent-analyte interaction parameters can be extracted from a single set of data or from successive analyte introductions using a single brush-coated sensor. The partition coefficient of three industrially relevant plasticizers into hydrophobic and hydrophilic brushes was determined and found to be in agreement with known solubility trends. We found that the diffusion coefficient of the plasticizer into the brush decreases as brush thickness increases, supporting a model of a dense inner brush layer and diffuse outer layer. pKa's of pH-sensitive brushes were determined on the microring resonator platform; upon increasing the dry brush thickness, the pKa for poly(2-dimethylamino ethyl methacrylate) decreased from 8.5 to approach the bulk material pKa of 7.3 and showed dependence on the presence and concentration of salt. These proof-of-concept experiments show how the surface-sensitive nature of the microring resonator detection platform provides valuable information about the interaction of the polymer brushes with the solvents and analytes, not easily accessed by other techniques.

Thermo-Optic Multistability and Relaxation in Silicon Microring Resonators with Lateral Diodes

We demonstrate voltage-tunable thermo-optic bi- and tri-stability in silicon photonic microring resonators with lateral p-i-n junctions and present a technique for characterizing the thermo-optic transient response of integrated optical resonators. Our method for thermo-optic transient response measurement is applicable to any integrated photonics platform and uses standard equipment. Thermo-optic relaxation in encapsulated waveguides is found to be approximately logarithmic in time, consistent with the analytic solution for 2D heat diffusion. We develop a model for thermo-optic microring multi-stability and dynamics which agrees with experiment data over a wide range of operating conditions. Our work highlights the fundamental connection in semiconductor waveguides between active free-carrier removal and thermo-optic heating, a result of particular relevance to Kerr soliton state stability and on-chip frequency comb generation. The devices studied here were fabricated in a CMOS foundry process and as a result our model is useful for design of silicon photonic waveguide devices.

Digital photonics parity bit error detection system

The optical communication medium is emerging to be one of the potential replacements to the current electronic systems widely used today. This is due to its much higher data transmission with extremely low loss properties, not to mention that it is almost invulnerable to electromagnetic interference. In this paper we demonstrated our proposed design of a digital photonic parity bit error detection system, one of the fundamental digital electronic circuits used during long-range digital signal transmission. Silicon photonic micro-ring resonators are used as its core component, where each of the rings operates as a digital logic XOR mode, by taking advantage of the resonance shifting properties of the silicon waveguide. Dynamic response characterization has been carried out by simulating the proposed circuits at the data rate of 1Gbps, with the data sampling rate of 1.6THz, and clear timing waveform was generated to show that the proposed circuit operates as the parity bit error detection system.

A linear mass concentration detector for solvent gradient polymer separations

Characterization of copolymers requires the measurement of two distributions-molecular weight (MW) and chemical composition (CC). Molecular weight distributions (MWD) are traditionally determined using size exclusion chromatography (SEC) run under isocratic solvent conditions. Chemical composition distributions (CCD) are often determined using liquid adsorption chromatography (LC) with solvent gradients. The use of solvent gradients, however, often limits options of compatible detectors. A gradient compatible, universal linear mass concentration detector is a longstanding unmet need. Many industrially-relevant polymers lack chromophores or other discriminating moieties requiring detectors with a universal response. Differential refractive index (dRI) is incompatible with gradient elution due to its small dynamic range. Charged aerosol detectors (CAD) and evaporative light scattering detectors (ELSD) are probably the most promising options for gradient elution detection, but both suffer from a nonlinear mass concentration response. Silicon photonic microring resonators are optical sensors that are responsive to changes in the local refractive index (RI). The substantial dynamic range of this technology makes it attractive for refractive index-based detection during solvent gradient elution. Previously, the microring resonator platform was used as a SEC detector to characterize the MWD of broadly dispersed polystyrene (PS) standards. In this study, we demonstrate the gradient compatibility of the microring resonator platform for polymer detection by quantifying the CCD of polymer blend components. Control experiments were run with UV and ELSD detection, highlighting the uniqueness of the platform as a linear mass concentration detector with a universal detector response.

Addressing Common HPLC Detector Challenges Using Silicon Photonic Microring Resonators with Applications for Polymer Separations and More

Addressing Common HPLC Detector Challenges Using Silicon Photonic Microring Resonators with Applications for Polymer Separations and More

Silicon Photonic Microring Resonator Arrays as a Universal Detector for Capillary Electrophoresis.

Electrophoretic separations conventionally rely on chromogenic, fluorogenic, or redox properties for analyte detection that, in many instances, involve chemical modification of samples prior to analysis. For analytes natively lacking chemical signatures, refractive index-based measurements are appealing as a method to detect these molecules without pretreatment. Microring resonators are a type of whispering gallery mode sensor capable of detecting bulk changes in refractive index. Here, we demonstrate the use of silicon photonic microring resonator arrays as a postcolumn detector for capillary electrophoresis. In this approach, we establish the universal detection capabilities of microrings through calibration with analytes lacking unique spectral signatures. Separations of small molecule mixtures are demonstrated using capillary zone electrophoresis. For these separations, the microring resonators maintain a linear response over several orders of magnitude in concentration for three candidate small molecules. Successful separation of three sugars with direct detection is also demonstrated. We further present the successful separation and detection of three model proteins, exemplifying the promise of microring resonators arrays as a biocompatible detector for capillary electrophoresis. Additionally, the spatially offset, array-based nature of the sensing platform enables real-time analysis of analyte mobility and performance characterization-a combination that is not typically provided using single-point detectors.

Silicon photonic switch-based optical equalization for mitigating pulsewidth distortion.

Optical transmitters typically require electrical pre-amplification using driver amplifiers to optimize the optical modulation depth. To enhance the detection sensitivity and optimize the overall link budget, equalization is required to compensate for undesired signal distortion induced by the transmitter. In this paper, we propose and demonstrate a novel optical equalization scheme using a silicon photonic micro-ring resonator (MRR)-based switching circuit for mitigating driver-amplifier-induced pulsewidth distortion. The switching circuit simultaneously functions as a spatial optical switch as well as a two-stage optical bandpass filter for optical equalization. The experimental results indicate a 4.5-dB detection sensitivity enhancement at a data rate of 12.5 Gbits/s. The proposed approach is robust to different levels of pulsewidth distortion without additional signal processing, and has possibilities to support higher data rates by adjusting the MRR parameters.

Silicon Photonic Microring Resonator Arrays for Mass Concentration Detection of Polymers in Isocratic Separations.

Molecular weight distribution (MWD) is often the most informative analytical parameter in polymer analysis, with gel permeation chromatography (GPC) being the most common approach for determining the MWD for polymer samples. Many industrially relevant polymers lack chromogenic or fluorogenic signatures, precluding use of spectroscopy-based detection. Universal detectors, such as evaporative light scattering and charged aerosol detectors, are nonlinear, limiting quantitative polymer analysis. Differential refractive index (dRI) detectors show linear mass concentration sensitivity but are limited for some analyses given that they are incompatible with gradient-based separations, have a limited dynamic range, and require extended thermal equilibration times. In this study, we investigated the utility of silicon photonic microring resonator arrays as a quantitative mass concentration detector for industrial polymer analysis. Microring resonators have optical properties that are sensitive to changes in refractive index, offer an extended dynamic range, have a broad solvent compatibility, and have a linear mass concentration detection for a range of molecular weights. Linear mass concentration detection for microrings was demonstrated through a series of isocratic GPC separations using narrow MWD polystyrene (PS) standards. This detection technology was then utilized in conjunction with conventional GPC detectors to analyze a series of broad MWD PS standards, with results in good agreement with dRI and UV/visible. These results demonstrate the potential of the microring resonator platform as a detector for industrial polymer analysis.

Bloch mode selection in silicon photonic crystal microring resonators

A novel method of selecting a subset of Bloch modes in silicon-based photonic crystal microring resonators (PhCR)s is demonstrated. Bloch modes in the PhCR are calculated, and their intensity beating patterns are analyzed. Based on the different spatial intensity distribution for each resonance, a subset of resonances is out-coupled using an output coupler waveguide (CWG) which is positioned at an angle θ=90° with respect to the input CWG. As shown in theory and experiment, resonances with an even mode number are selected, while resonances with an odd mode number are rejected. The highest contrast between mode selection and mode rejection is ∼9 dB in the experiments. This approach opens another design freedom for ring resonator-based devices and could potentially reduce the footprint of microring resonator-based multiplexers and add-drop filters.

Combining asymmetric PCR-based enzymatic amplification with silicon photonic microring resonators for the detection of lncRNAs from low input human RNA samples.

A method for quantifying biologically relevant long-non-coding RNAs by combining nucleic acid amplification via asymmetric polymerase chain reaction (PCR) with label-free PCR product detection using silicon photonic microring resonator arrays is described. This approach eliminates the need for fluorophores, which presents a limit for spectral multiplexing in conventional qPCR methods, and rather offers potential for much higher levels of plexity by spatially arraying capture probes. Here, we demonstrate the potential of this technique to detect two differentially expressed lncRNA transcripts and an internal control mRNA transcript in different commercial human tissue specimens, as well as in a glioblastoma cell line using only nanogram input amounts of total RNA. The obtained results were validated using single-plex RT-qPCR and found to be in good agreement, demonstrating the potential of this technique for lncRNA quantification applications.

Multiplexed silicon photonic sensor arrays enable facile characterization of coagulation protein binding to nanodiscs with variable lipid content

Interactions of soluble proteins with the cell membrane are critical within the blood coagulation cascade. Of particular interest are the interactions of γ-carboxyglutamic acid-rich domain-containing clotting proteins with lipids. Variability among conventional analytical methods presents challenges for comparing clotting protein-lipid interactions. Most previous studies have investigated only a single clotting protein and lipid composition and have yielded widely different binding constants. Herein, we demonstrate that a combination of lipid bilayer nanodiscs and a multiplexed silicon photonic analysis technology enables high-throughput probing of many protein-lipid interactions among blood-clotting proteins. This approach allowed direct comparison of the binding constants of prothrombin, factor X, activated factor VII, and activated protein C to seven different binary lipid compositions. In a single experiment, the binding constants of one protein interacting with all lipid compositions were simultaneously determined. A simple surface regeneration then facilitated similar binding measurements for three other coagulation proteins. As expected, our results indicated that all proteins exhibit tighter binding (lower Kd ) as the proportion of anionic lipid increases. Interestingly, at high proportions of phosphatidylserine, the Kd values of all four proteins began to converge. We also found that although koff values for all four proteins followed trends similar to those observed for the Kd values, the variation among the proteins was much lower, indicating that much of the variation came from the kinetic binding (kon) of the proteins. These findings indicate that the combination of silicon photonic microring resonator arrays and nanodiscs enables rapid interrogation of biomolecular binding interactions at model cell membrane interfaces.

Polymer Brush‐Modified Microring Resonators for Partition‐Enhanced Small Molecule Chemical Detection

AbstractSilicon photonic microring resonators have emerged as a promising technology for the sensitive detection of biological macromolecules, including proteins and nucleic acids. However, not all species of interest are large biologics that can be targeted by highly specific capture agents. For smaller organic chemicals, including many toxic and regulated species, a general approach to improving sensitivity would be desirable. By functionalizing the surface of silicon photonic microring resonators with polymer brushes, small molecules can selectively partition into the surface‐confined sensing region of the optical resonators. This in turn leads to response enhancements in excess of 1000% percent, relative to non‐functionalized sensors, for representative targets including 4‐methylumbelliferyl phosphate, a simulant for highly toxic organophosphates, Bisphenol A, an industrial pollutant, as well as other small organic analytes of interest. There are many polymer brush chemistries compatible with silicon resonators, making this a general strategy towards tuning sensor selectivity and specificity by optimizing interactions between the agent(s) of interest and the polymer construct.