Microring Sensor Research Articles

Wide Range Si3N4 Optical Sensor Using Cascaded Mach-Zehnder Interferometer Coupled Ring Resonator

Abstract A cascaded MZI-coupled ring resonator (CMCR) optical sensor based on silicon nitride waveguide is proposed. The sensor is composed of a large size microring and a bus waveguide coupled with the microring for four times. The three-segment bus and the microring waveguide between the four coupling regions form three MZI of the same size, forming a three-stage cascaded MZI. The resonant effect of the cascaded MZI transforms the smooth comb spectrum of the microring into a V-shaped comb spectrum, expands the effective free spectral range of the ring resonator, and realizes the cascaded MZI-coupled microring sensor with a large measurement range. For the cascade MZI-coupled microring with a radius of 100μm, the effective free spectrum range is 53.7nm, which is more than 24 times larger than that of the all-pass microring of the same size. The refractive index sensitivity is 339.49 nm RIU/and the detection limit is 2.95 × 10−5 RIU. these excellent properties prove the feasibility of cascaded MZI-coupled microring structure for large measurement range sensing, and are expected to be used in large refractive index range sensing applications in the future.

Parallel interrogation of the chalcogenide-based micro-ring sensor array for photoacoustic tomography

Photoacoustic tomography (PAT), also known as optoacoustic tomography, is an attractive imaging modality that provides optical contrast with acoustic resolutions. Recent progress in the applications of PAT largely relies on the development and employment of ultrasound sensor arrays with many elements. Although on-chip optical ultrasound sensors have been demonstrated with high sensitivity, large bandwidth, and small size, PAT with on-chip optical ultrasound sensor arrays is rarely reported. In this work, we demonstrate PAT with a chalcogenide-based micro-ring sensor array containing 15 elements, while each element supports a bandwidth of 175 MHz (−6 dB) and a noise-equivalent pressure of 2.2 mPaHz−1/2. Moreover, by synthesizing a digital optical frequency comb (DOFC), we further develop an effective means of parallel interrogation to this sensor array. As a proof of concept, parallel interrogation with only one light source and one photoreceiver is demonstrated for PAT with this sensor array, providing images of fast-moving objects, leaf veins, and live zebrafish. The superior performance of the chalcogenide-based micro-ring sensor array and the effectiveness of the DOFC-enabled parallel interrogation offer great prospects for advancing applications in PAT.

Design of Suspended Slot Racetrack Microring Refractive Index Sensor Based on Polymer Nanocomposite.

Recently, polymer nanocomposites have attracted great interest due to their remarkable characteristics of high performance and enabling production of low-cost devices. This article explores the reflective index sensing application of the polymer nanocomposite IOC-133, which is a TiOx/polymer nanocomposite with a reflective index between 1.8 and 1.9. Considering the material properties of high reflective index, low absorption loss, and compatibility with nanoimprint lithography, a microring-based reflective index sensor with a suspended slot waveguide structure is proposed. We combined the sensing mechanism of slot waveguides with high reflective index polymer nanocomposites and designed the suspended structure to address the problem of decreasing sensitivity caused by residual layers. The sensing device was adopted as a microring resonator, which is conducive to large-scale integration. The finite-difference time-domain (FDTD) method was employed to analyze the effects of several key parameters. The results showed that the racetrack microring sensor we propose can achieve a high sensitivity of 436 nm/RIU (Refractive Index Units), about six times higher than the microring sensor with a ridge waveguide. The Q factor of the microring reaches 1.42 × 104, and the detection limit is 1.38 × 10-4 RIU. The proposed suspended slot microring sensor has potential value in the field of nanoprinted photonic integrated circuits.

Optical Waveguide Refractive Index Sensor for Biochemical Sensing

This study describes the basic principles of optical waveguide refractive index sensing and the various design structures of refractive index sensors. These waveguides generate different optical resonances, which cause changes in the sensing refractive index and temperature and are subsequently used to detect the concentration in the analyses. First, the structural characteristics and performance indices of the microring sensor and interferometer are studied based on the refractive index of the optical waveguide. Second, the principle and sensing detection mechanism of the two types of refractive index sensing employed in these sensors are analyzed. Then, the two sensors are classified and discussed from the perspective of the waveguide materials and structures, as well as the substances to be measured. Simultaneously, performance indicators such as sensitivity and detection range are compared and summarized. The comparison results show that there is a compromise between the sensitivity and quality factor of the optical waveguide refractive index sensor. Finally, applications of refractive index sensing in the biochemical field for material detection are discussed, showing that the optical waveguide refractive index sensor has significant advantages over other types of biochemical optical sensors.

High-sensitivity polarization-independent terahertz Taichi-like micro-ring sensors based on toroidal dipole resonance for concentration detection of Aβ protein

Abstract Terahertz (THz) metamaterial sensor is a newly-developing interdisciplinary technology, which combines the essential characteristics of THz spectroscopy and metamaterials, to obtain better sensitivity for trace detection of the different target analytes. Toroidal dipole resonances show great sensing potential due to their suppression of the radiative loss channel. Here, we found a high-quality planar toroidal dipole resonance in the breaking Chinese Taichi-like ring and then designed a novel polarization-independent terahertz toroidal sensor by combining four Taichi-like rings into a cycle unit. The sensor shows high-sensitivity sensing characteristics for the ultrathin analyte and refractive index. The optimized sensitivity of pure analytes under 4 μm coating thickness can numerically reach 258 GHz/RIU in the corresponding ∼1.345 THz frequency domain, which is much higher than that of previously reported sensors. We further fabricated experimentally the sensor and demonstrated its fascinating polarization-independent characteristics. Finally, it was successfully applied to the low-concentration detection (ranging from 0.0001 mg/mL to 10 mg/mL) of Aβ protein associated with Alzheimer’s disease. Our high-sensitivity polarization-independent THz toroidal dipole sensor would give access to rich applications in label-free biosensing.

High extinction ratio optical pulse characterization method via single-photon counting

We present the characterization of high extinction ratio (ε) square optical pulses using a photon counting technique, as other techniques only offer a limited range of measurement up to 60 dB. High-ε pulses are generated by applying a square pulse modulation on sinusoidally modulated optical signals, then inducing self-phase modulation (SPM) using the nonlinear Kerr effect and extracting an SPM-generated sideband. We measured a 10 ns Kerr-generated optical pulse exhibiting a 120.1 dB extinction ratio, originating from a conventional electro-optic modulator delivering a pulse with a 20-dB extinction ratio, by counting the number of photons at the peak and the pedestal of the generated pulse. These proven high-ε pulses allow for long-range distributed vibration sensing in optical time-domain reflectometry systems and open new horizons in high-Q microring sensors.

Portable Automatic Microring Resonator System Using a Subwavelength Grating Metamaterial Waveguide for High-Sensitivity Real-Time Optical-Biosensing Applications

The slow light sensor techniques have been applied to bio-related detection in the past decades. However, similar testing-systems are too large to carry to a remote area for diagnosis or point-of-care testing. This study demonstrated a fully automatic portable biosensing system based on the microring resonator. An optical-fiber array mounted on a controller based micro-positioning system, which can be interfaced with MATLAB to locate a tentative position for light source and waveguide coupling alignment. Chip adapter and microfluidic channel could be packaged as a product such that it is cheap to be manufactured and can be disposed of after every test conducted. Thus, the platform can be more easily operated via an ordinary user without expertise in photonics. It is designed based on conventional optical communication wavelength range. The C-band superluminescent-light-emitting-diode light source couples in/out the microring sensor to obtain quasi-TE mode by grating coupler techniques. For keeping a stable chemical binding reaction, the cost-effective microfluidic pump was developed to offer a specific flow rate of 20 μL/min by using a servo-motor, an Arduino board, and a motor driver. The subwavelength grating metamaterial ring resonator shows highly sensitive sensing performance via surface index changes due to biomarker adhered on the sensor. The real-time peak-shift monitoring shows 10μg/mL streptavidin detection of limit based on the biotin-streptavidin binding reaction. Through the different specific receptors immobilized on the sensor surface, the system can be utilized on the open applications such as heavy metal detection, gas sensing, virus examination, and cancer marker diagnosis.

Microring Distributed Sensors Using Space-Time Function Control

Distributed microring sensors using space-time function control is proposed for artificial microfacial sensors. The system consists of 6 different node locations, corresponding to the form of the human microfacial structure. Two space-time function input sources are fed into the system simultaneously. The distributed stereo network sensors are investigated. Each sensor node is embedded by a different gold grating period, in which the coupling between the photon and grating generates different plasmonic Bragg wavelengths outputs, which can be used to identify the node positions. The changes introduced to the sensor nodes via the space-time function relationship, such as the polariton (phonon), wavelength, frequency, and temporal change of the Bragg wavelength, can be measured. By using the whispering gallery mode output, the dipole oscillation of each node can be obtained, which can be used for a distributed facial sensor network. The distributed network is connected by the microring coupling in the system. By using the stereo sensor and space-time function sources, a balance of the two-channel sensing signals, known as a stereo sensor, can enable a self-calibration of the sensor, which is achieved. Moreover, exchange between the polariton and electron can be achieved, and electro-optic conversion is obtained. Moreover, the electro-optic conversion obtained by exchanging the polariton and electron energies means that both wireless and cable transmission modes can be employed.

A slot microring sensor with feedback spiral waveguide for trace gas CH4 sensing in mid-infrared region

In this paper, a slot microring resonator with a piece of spiral feedback waveguide for CH4 sensing application is proposed. This sensor is based on silicon-on-insulator (SOI) substrate and with the operation wavelength in mid-infrared region. To reach high sensitivity and good selectivity, slot cross section and spiral feedback waveguide are carefully tailored. The sensor shows ppb-scale trace gas sensing potential and is easy to be packaged in integrated photonics circuits. Calculation results show that the sensitivity reaches 1.4×10-2 dB/ppm and the detection limit achieves 700 ppb in the case of Lspiral=100Lr.

Vernier effect of cascaded dual microring sensor

We demonstrate a Vernier microring sensor consisting of a traditional cascaded dual microring resonator and an additional measurement range unit. The sensor’s performance is simulated for different concentrations of aqueous solutions of ethylene glycol ( $$\hbox {C}_2 \hbox {H}_6 \hbox {O}_2 )$$ . The theoretical sensitivity of our system is as high as 7386 nm / RIU, an order of magnitude much larger than that of the traditional cascaded dual microring sensor (562 nm / RIU), 13.1 times more than the traditional cascaded dual microring sensor. At the same time, the measurement range can reach as high as $$\hbox {2.49}\times 10 ^{- 2}$$ RIU.

Real-time compensation of errors in refractive index shift measurements of microring sensors using thermo-optic coefficients.

We report a method for compensation of errors caused by temperature fluctuations in refractive index measurements using Silicon photonic microring sensors. The method involves determination of resonance wavelength shifts caused by thermal fluctuations using real-time measurement of on-chip temperature variations and thermo-optic coefficient (TOC) of analyte liquids. Resistive metal lines patterned around Silicon microrings are used to track temperature variations and TOC of analyte is calculated by measuring wavelength shifts caused by controlled increments in device temperature. The TOC of de-ionized water is determined to be -1.12 × 10-4/°C, with an accuracy of ±8.26 × 10-6/°C. In our system, chip-surface temperature variations were measured with an instrument limited precision of 0.004 °C yielding a factor of 16 enhancement in tracking accuracy compared to conventional, bottom-of-chip temperature measurement. We show that refractive index detection limit of the microring sensor is also improved by the same factor.

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

LeTrungThanh Optical Biosensors Based on Multimode Interference and Microring Resonator Structures

Label-free, real-time and multiplex detection of Mycobacterium tuberculosis based on silicon photonic microring sensors and asymmetric isothermal amplification technique (SPMS-AIA)

Rapid diagnosis of Mycobacterium tuberculosis complex (MTBC) is crucial for the control and treatment of tuberculosis. Currently available diagnostic tools are unable to meet clinical needs, especially in resource limited settings, as they suffer from being time-consuming, costly, insensitive, or dependant on sophisticated instruments and well trained personnel. An optical diagnostic platform (SPMS-AIA) consisting of the silicon photonic microring sensor and the asymmetric isothermal amplification technique was developed to detect MTBC in a rapid (one hour), isothermal, label-free and real-time manner. The performance of the SPMS-AIA platform was assessed by detecting two MTBC specific biomarkers, IS6110 and IS1081. Detection limits were as low as 3.2 copies for IS6110 and 12 copies for IS1081 respectively when tested with Mycobacterium tuberculosis H37Rv genomic DNA. An evaluation for detection of IS6110 in clinical sputa showed that the SPMS-AIA platform performed as well as the established market leader GeneXpert MTB/RIF platform. Of 26 MTBC culture-positive and smear-positive specimens, 23 were found positive by the SPMS-AIA platform (89% sensitivity). Of 47 MTBC culture-positive and smear-negative specimens, 34 were positive by the SPMS-AIA platform (72% sensitivity): this is similar to the sensitivity of 70% by the GeneXpert MTB/RIF platform. The versatility of the SPMS-AIA platform was demonstrated by multiplex detection of IS6110 and IS1081 in 10 clinical specimens. The SPMS-AIA platform shows great potential for development into a point-of-care (POC) diagnostic tool for use in resource limited settings.

Improving the detection limit for on-chip photonic sensors based on subwavelength grating racetrack resonators.

Compared to the conventional strip waveguide microring resonators, subwavelength grating (SWG) waveguide microring resonators have better sensitivity and lower detection limit due to the enhanced photon-analyte interaction. As sensors, especially biosensors, are usually used in absorptive ambient environment, it is very challenging to further improve the detection limit of the SWG ring resonator by simply increasing the sensitivity. The high sensitivity resulted from larger mode-analyte overlap also brings significant absorption loss, which deteriorates the quality factor of the resonator. To explore the potential of the SWG ring resonator, we theoretically and experimentally optimize an ultrasensitive transverse magnetic mode SWG racetrack resonator to obtain maximum quality factor and thus lowest detection limit. A quality factor of 9800 around 1550 nm and sensitivity of 429.7 ± 0.4nm/RIU in water environment are achieved. It corresponds to a detection limit (λ/S·Q) of 3.71 × 10-4 RIU, which marks a reduction of 32.5% compared to the best value reported for SWG microring sensors.

Photonic crystal microring resonator for label-free biosensing.

A label-free optical biosensor based on a one-dimensional photonic crystal microring resonator with enhanced light-matter interaction is demonstrated. More than a 2-fold improvement in volumetric and surface sensing sensitivity is achieved compared to conventional microring sensors. The experimental bulk detection sensitivity is ~248nm/RIU and label-free detection of DNA and proteins is reported at the nanomolar scale. With a minimum feature size greater than 100nm, the photonic crystal microring resonator biosensor can be fabricated with the same standard lithographic techniques used to mass fabricate conventional microring resonators.

Nested microring resonator with a doubled free spectral range for sensing application

The microring resonator has received increasing attention in the optical sensing application because of its micro-size, optical property, and high sensitivity. An additional waveguide is commonly used to change the output spectra in the early research on microring resonators. In this study, we proposed a nested microring resonator that doubles the free spectral range (FSR) compared with the conventional single microring. This structure improved the sensing property as the FSR in the filter output spectra could be considered as a measurement range in the microring sensor. Moreover, the parameters including the coupling coefficient of the three coupling sections, length of the U-bend waveguide, and effective index of a waveguide were tested and carefully selected to optimize the sensing properties. The relationship between these parameters and the output spectra was demonstrated. With linear sensitivity, the structure has a good potential in sensing application.

Full-Range Detection in Cascaded Microring Sensors Using Thermooptical Tuning

We present detailed analysis and experimental demonstration of full-range detection in cascaded microring sensors by using thermooptical tuning. A cascaded microring sensor translates spectrum shifts into intensity changes eliminating the need for expensive spectral analysis equipment for sensing applications. Without tuning capability, this configuration provides high sensitivity, but a small detection range since the intensity output decays toward zero for low overlap between spectra of individual microrings. We overcome this limitation by using thermooptic tuning in one of the microrings for extending the detection range to span an entire free spectral range of the probing microring. Additionally, we analyze the impact of resonance linewidths and differences in free spectral ranges (FSRs) of microrings on the widths of output intensity peaks. With full FSR thermooptical tuning, we demonstrate a total detection range of 0.0241 refractive index units (RIU) and a limit of detection of 4.6 × 10 $^{-5}$ RIU for microrings with 100-μm radii. Photodetector-based signal readout combined with CMOS compatible manufacturability makes this device design attractive as a silicon-based optical sensing platform.

Design of a lithium niobate-on-insulator-based optical microring resonator for biosensing applications

A label-free optical microring resonator biosensor based on lithium niobate-on-insulator (LNOI) technology is designed and simulated for biosensing applications. Although silicon-on-insulator technology is quite mature over LNOI for fabricating more compact microring resonators, the latter is attractive for its excellent electro-optic, ferroelectric, piezoelectric, photoelastic, and nonlinear optic properties, which can offer a wide range of tuning facilities for sensing. To satisfy the requirement of high sensitivity in biosensing, the dual-microring resonator model is applied to design the proposed sensor. The transmission spectrum obtained from two-dimensional simulations based on finite-difference time-domain method demonstrates that the designed LNOI microring sensor consisting of a 10- μ m outer ring and a 5- μ m inner ring offers a sensitivity of ∼68 nm/refractive index unit (RIU) and a minimum detection limit of 10 −2 RIU. Finally, the sensor’s performance is simulated for glucose sensing, a biosensing application.

A Microring Temperature Sensor Based on the Surface Plasmon Wave

A structure of microring sensor suitable for temperature measurement based on the surface plasmon wave is put forward in this paper. The sensor uses surface plasmon multilayer waveguiding structure in the vertical direction and U-shaped microring structure in the horizontal direction and utilizes SOI as the thermal material. The transfer function derivation of the structure of surface plasmon microring sensor is according to the transfer matrix method. While the change of refractive index of Si is caused by the change of ambient temperature, the effective refractive index of the multilayer waveguiding structure is changed, resulting in the drifting of the sensor output spectrum. This paper focuses on the transmission characteristics of multilayer waveguide structure and the impact on the output spectrum caused by refractive index changes in temperature parts. According to the calculation and simulation, the transmission performance of the structure is stable and the sensitivity is good. The resonance wavelength shift can reach 0.007 μm when the temperature is increased by 100 k and FSR can reach about 60 nm. This structure achieves a high sensitivity in the temperature sense taking into account a wide range of filter frequency selections, providing a theoretical basis for the preparation of microoptics.

Serologic and Phenotypic Analysis of Blood Types Via Silicon Nanophotonics

Tens of millions of donor and patient samples are tested yearly to establish blood type compatibility between donor and recipient and to protect recipients from blood-borne infectious diseases. Blood type testing, particularly donor testing, is traditionally based in centralized clinical laboratories. However, current blood typing methods are encumbered by reagent availability, cost, technical training requirements, and time, placing a costly burden on the medical system. To address practical needs in blood typing, we have developed a multiplexed blood analysis platform using a low-cost and scalable silicon photonic biochip. This study investigates the use of silicon microring sensors to capture, detect, and quantify specific red blood cell (RBC) membrane antigens and anti-blood type antibodies from blood.To validate ABO blood phenotyping, microring resonators were streptavidin coated and functionalized with biotinylated anti-A IgM or biotinylated anti-B IgM antibodies. First, the response of anti-A/B functionalized microring resonators to characterized RBC membranes (RBC ghosts, 108 cells/ml) were measured in real-time (Figure 1). The biosensor arrays also exhibited minimal non-specific adsorption of RBC membrane fragments to the sensor surface. Microring resonators were shown to be suitable for identifying RBC ABO phenotype from donor blood samples.For ABO serologic analysis, silicon chips were functionalized with synthetic multivalent polymeric blood group antigens to serve as capture elements for circulating anti-ABO antibodies. Each chip also had sensors functionalized with biotinylated Protein A (btn-ProtA) and a biotinylated polyacrylamide polymer scaffold (btn-paa) to serve as on-chip positive and negative controls, respectively. The multiplexed biosensor chips were exposed to 100mL of plasma, followed by an anti-human-IgM antibody to enhance detection and quantification of antibodies bound to the surface. The resonance shift in each microring resonator was monitored over time, and the sensor response of the polymeric A and B blood group antigens was normalized to the control sensors. Figure 2 illustrates the levels of bound anti-A and anti-B for a panel of donor blood samples with varying ABO blood type, expressed as a relative shift in sensor resonance wavelength. These results demonstrate the detection of the 'naturally occurring’ anti-A/B IgM antibodies for each respective ABO blood type.We have demonstrated that microring resonator biosensor arrays can quantitatively determine the donor ABO phenotypic and serologic status while incorporating on-chip controls for process standardization. Our work serves as proof-of-concept that a multiplexed silicon nanophotonics platform can rapidly detect both RBC antigens and anti-RBC antibodies in biological samples. This method has the potential for broad applicability in hematology and transfusion medicine for blood typing, quantitative monitoring of specific antibodies, and pathogen screening. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.