Multi-component gas sensing based on slotted photonic crystal waveguide with liquid infiltration

To realize a high sensitivity gas sensor, a large wideband, temperature stabilized and large light confinement slow light structure in slotted photonic crystal waveguide (SPCW) is designed. The simulation results indicate that with a proper optimization of the SPCW structure, a very high group index of 105 can be achieved and the electric field enhancement factor would reach to 12. Combined with the correlation spectroscopy for signal processing, the detection limit of 10 ppm is achieved.

A comprehensive analysis of Raman mediated solitonic compression of pulses inside a silicon nanocrystal embedded slotted photonic crystal waveguide (SPCW) is presented. The ultrahigh Raman gain coefficient of the silicon nanocrystal material, being fortified further by the intense optical confinement inside the SPCW, essentially outweighs the contribution of the Kerr in the self-phase modulation phenomenon that is responsible for the solitonic propagation of a pulse. This work particularly emphasizes the contribution of Raman nonlinearity in the soliton dynamics, which however has been neglected conventionally, leading to an unprecedented miniaturization in both the operating power and footprint. Spatiotemporal evolution of pulses inside the SPCW has been calculated using the nonlinear Schrödinger equation considering the slow-light regime. A compression factor as high as 44.3 is obtained using a 30 µm long SPCW with a peak input power of 8 mW at 1550 nm.

A transverse-electric (TE)-pass polarization filter based on a slotted photonic crystal waveguide structure is proposed for application in photonic integrated circuits. The silicon-slab-based structure is fabrication-compatible with the standard silicon-on-insulator process technologies. Different structural parameters, such as the r/a ratio of the photonic crystal sections, slab height, slot width, and slot length, are optimized for improved performance. Moreover, the conversion efficiency of a mode of a W1 waveguide to that of a slot waveguide is analyzed for different starting positions of the slot in order to achieve a high extinction ratio of the TE wave over the transverse-magnetic wave. A 3D finite difference time domain simulation methodology, which has been verified against an earlier experimental study made by researchers on another structure, is adopted to evaluate the transmittance of the structure. It shows that the polarization filter, with a footprint of merely 6.28 μm×4.35 μm, offers an extinction ratio in the order of 22 dB; this corresponds to an effective extinction ratio of 3.5 dB μm−1 considering the total length (or 6.5 dB μm−1 considering only the slot length). TE transmittance of the device is calculated as ≈−3 dB at a wavelength of 1550 nm.

Mid infrared silicon photonic integrated components, namely grating couplers, strip and slot waveguides, slotted and un-slotted photonic crystal waveguides, photonic crystal microcavities are experimentally demonstrated in silicon-on-sapphire. Application in trace gas sensing is experimentally demonstrated. Progress towards monolithic integration of lasers and detectors are discussed.

A new procedure of designing slotted photonic crystal waveguides is proposed to achieve slow light with improved normalized delay-bandwidth product and low group velocity dispersion that is suitable for both the W1 defect mode and the slot mode. The lateral symmetry of the waveguide in our study is broken by shifting the air holes periodically along the slot axis. The conversion of the "flat band" from band-up slow light to band-down slow light is achieved for the W1 defect mode. The group index curves of the W1 mode change from U-like to step-like and the group indices of 47, 67 and 130 are obtained with the bandwidth over 7.2, 4.8, and 2.3nm around 1550nm, respectively. We also obtain the group indices of 42, 55, and 108 for the slot mode with the bandwidth over 6.2, 5.6, and 2.2nm, respectively. Then the low dispersion slow light propagation is numerically demonstrated by the finite-difference time-domain method.

In this paper, the sensitivity of slotted photonic crystal waveguides (SPCW) with triangular lattice pattern of ring-shaped holes is analyzed in order to realize highly refractive index (RI) sensor devices at mid-infrared wavelengths. The sensing principle is based on the shift of the transmission spectrum edge of these specific ring hole SPCW waveguides giving rise to reinforced light–matter interaction. The 3D simulation results applied to silicon waveguides on membrane show that this guide geometry leads to a very high sensitivity to variations in the ambient environment index, with very dependent trends on the opto-geometric factors of the waveguides. As a matter of example, a $$720 \,\mathrm{nm}$$ wavelength position band edge shift is predicted, corresponding to a sensitivity of more than $$1450 \,\mathrm{nm}$$ per refractive index unit with a device insertion loss level of $$-\,3 \,\mathrm{dB}$$ .

A completely new design for an all‐silicon all‐optical pass switch has been proposed based on the stimulated Raman scattering (SRS) in silicon nanocrystal embedded slotted photonic crystal waveguide (SPCW). Substantial miniaturisation in the device footprint and operating power has been attained by merging the benefits of the giant SRS gain and the ultra‐high optical confinement of the SPCW. The proposed switch offers a tremendously high contrast ratio of between the logic levels and an extraordinary bit rate of 125 Gbps.

In an on-chip silicon-organic hybrid electro-optic (EO) modulator, the mode overlap with EO materials, in-device effective r33, and propagation loss are among the most critical factors that determine the performance of the modulator. Various waveguide structures have been proposed to optimize these factors, yet there is a lack of comprehensive consideration on all of them. In this Letter, a one-dimensional (1D) photonic crystal (PC) slot waveguide structure is proposed that takes all these factors into consideration. The proposed structure takes advantage of the strong mode confinement within a low-index region in a conventional slot waveguide and the slow-light enhancement from the 1D PC structure. Its simple geometry makes it robust to resist fabrication imperfections and helps reduce the propagation loss. Using it as a phase shifter in a Mach-Zehnder interferometer structure, an integrated silicon-organic hybrid EO modulator was experimentally demonstrated. The observed effective EO coefficient is as high as 490 pm/V. The measured half-wave voltage and length product is less than 1 V·cm and can be further improved. A potential bandwidth of 61 GHz can be achieved and further improved by tailoring the doping profile. The proposed structure offers a competitive novel phase-shifter design, which is simple, highly efficient, and with low optical loss, for on-chip silicon-organic hybrid EO modulators.

Total internal reflection (TIR) is a ubiquitous phenomenon used in photonic devices ranging from waveguides and resonators to lasers and optical sensors. Controlling this phenomenon and light confinement are keys to the future integration of nanoelectronics and nanophotonics on the same silicon platform. We introduced the concept of relaxed total internal reflection in 2014 to control evanescent waves generated during TIR. These unchecked evanescent waves are the fundamental reason photonic devices are inevitably diffraction-limited and cannot be miniaturized. Our key design concept is the engineered anisotropy of the medium into which the evanescent wave extends thus allowing for skin depth engineering without any metallic components. In this article, we give an overview of our approach and compare it to key classes of photonic devices such as plasmonic waveguides, photonic crystal waveguides and slot waveguides. We show how our work can overcome a long standing issue in photonics nanoscale light confinement with fully transparent dielectric media.

A comprehensive overview on signal processing and artificial intelligence techniques applications in classification of power quality disturbances

In the recent years, there has been an unpredicted increase in data transmission. To cope with this increase, a reliable technology is required. The next-generation passive optical network 2 (NG-PON2) was used in integration with future technology that works on radio over fiber (RoF). However, the optical communication system is subject to the following nonlinear effects: Self-phased modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM), stimulated Brillouin scattering (SBS), and stimulated Raman scattering (SRS). These effects are dominant, and they risk the performance of the optical fiber system. Therefore, digital signal processing (DSP) technique is used in this study to minimize and offset the nonlinear effects. In this study, three digital filters working on (DSP) are compared for the same data transmission rate at different distances from the transmitter without using compensation techniques. The results were compared by bit error rate (BER) and the error vector magnitude (EVM). Thus, the error vector magnitude (EVM) was noticed to be ~19.58% without using DSP. Nonlinear effects were mitigated by filters of Gaussian, Bessel and DSP-64QAM raised cosine to ~9.09%, ~14.22% and ~17.54%, respectively. Hence, the bit error rate (BER) of the best technique after comparison was minimized to DSP-64QAM raised cosine. It occurred after minimizing the nonlinear effects as 1.11E−14 at a distance of 40 km and 100 km. The BER value was 3.43E−10, which is within the acceptable values of performance for the proposed optical communication system with nonlinear effects. The system was simulated using the optical simulator optisystem 15.

Cardiac auscultation is a basic means of initial diagnosis of congenital heart disease (CHD). It is significant to analyze Phonocardiogram (PCG) by using signal processing and machine learning techniques for the purpose of machine-assisted diagnosis of CHD. A novel method of machine-assisted diagnosis of CHD was proposed in this paper. First, the duration of the hidden Markov model (DHMM) was applied to locate and segment PCG into each cardiac cycle. Then, the envelope of the PCG was extracted by using Viola integral. After that, the variant logic theory was applied to extract the features and convert the envelope data of the heart sound signal into visual analysis measurement data. Finally, the classifier of the support vector machine (SVM) was used to classify the normal and abnormal heart sounds. There were 1000 cases used in this study. It was divided into a training set of 600 cases, a test set of 200 cases, and validation set of 200 cases. An accuracy of 0.965, a specificity of 0.898, and a sensitivity of 0.937 were achieved using the novel signal processing techniques. The results showed that DHMM and variant logic theory models were suitable for heart sound classification.

Advances in millimeter wave solid-state power amplifier technology over the past decade have led to the development of a new generation of compact, lightweight cloud and precipitation radars. Solid-state power amplifiers (SSPAs) have lower peak power than traditional vacuum tube transmitters, but generally are capable of operating at much higher duty cycle. Taking advantage of the high duty cycle of SSPAs usually requires some signal processing and/or pulse compression technique to achieve similar sensitivity at comparable range resolution. FMCW (frequency modulated continuous wave) radars take full advantage of SSPAs capable of CW (continuous wave) operation, but the usual requirement for separate transmit and receive antennas is often impractical. Radars that combine a pulse compression waveform with a short pulse offset in frequency are now commonly used to operate at duty cycles as high as 10–20%. This paper reviews the latest solid-state millimeter wave radar designs, benefits, and limitations and describes operating modes and signal processing techniques that are especially well suited for single antenna operation. High PRF (pulse repetition frequency) operation using coherent power (single lag covariance) provides automatic noise cancellation without requiring explicit noise sampling. A novel phase coding technique employing Chu-codes with quadratically-increasing phase can be used to separate ambiguous signals when running at MHz-level PRFs. Weather data measured using the quadratic phase coding (QPC) technique with a solid-state Ka-band radar running at 3.1 MHz PRF is presented. This data was gathered at a transmitter duty cycle of approximately 50 percent and exhibits a 20 dB sensitivity improvement when compared to conventional short pulse data gathered at the same range resolution.

Recently, data-driven models for Structural Health Monitoring (SHM) have been of great interest among many researchers. In data-driven models, the sensed data are processed to determine the structural performance and evaluate the damages of an instrumented structure without necessitating the mathematical modeling of the structure. A framework of data-driven models for online assessment of the condition of a structure has been developed here. The developed framework is intended for automated evaluation of the monitoring data and structural performance by the Internet technology and resources. The main challenges in developing such framework include: (a) utilizing the sensor measurements to estimate and localize the induced damage in a structure by means of signal processing and data mining techniques, and (b) optimizing the computing and storage resources with the aid of cloud services. The main focus in this paper is to demonstrate the efficiency of the proposed framework for real-time damage detection of a multi-story shear-building structure in two damage scenarios (change in mass and stiffness) in various locations. Several features are extracted from the sensed data by signal processing techniques and statistical methods. Machine learning algorithms are deployed to select damage-sensitive features as well as classifying the data to trace the anomaly in the response of the structure. Here, the cloud computing resources from Amazon Web Services (AWS) have been used to implement the proposed framework.

We present all-fiber resonating Fabry-Perot gas cells made with a piece of hollow-core photonic bandgap fiber (HC-PBF) sandwiched by two single mode fibers with mirrored ends. A HC-PBF cavity made of 6.75-cm-long HC-1550-06 fiber achieved a cavity finesse of 128, corresponding to an effective optical path length of 5.5 m. Such HC-PBF cavities can be used as absorption cells for high sensitivity gas detection with fast response. Preliminary experiment with a 9.4-cm-long resonating gas cell with a finesse of 68 demonstrated a detection limit better than 7.5 p.p.m. acetylene.