Search Results (105)

In this paper, we report a novel self-smoothed gradient index cladding waveguide for low-loss, high-density photonic integrated circuits (PICs). In conventional PIC waveguides, there is a fundamental trade-off between propagation loss and bending loss. High-index-contrast waveguides can provide strong mode confinement and small bending radius, but they are highly sensitive to sidewall roughness and therefore exhibit increased scattering loss. In contrast, low-index-contrast waveguides can reduce propagation loss, but they require a much larger bending radius and are not suitable for dense photonic integration. To overcome this limitation, we propose a self-smoothed double-cladding waveguide architecture composed of a high-index core, a gradient index first cladding layer, and a low-index second cladding layer. The first cladding layer can be formed by advanced conformal coating processes, such as non-uniformly cycled atomic layer deposition and gradient index dip coating, which provide both a gradual refractive index transition and a self-smoothing effect on the rough sidewall. We perform quantitative analyses of the propagation loss, bending loss, and mode field distribution of the proposed structure. The numerical results confirm that the propagation loss can be reduced by approximately two orders of magnitude while maintaining low bending loss and mode confinement comparable to that of a conventional rib-shaped waveguide. We also experimentally verify the self-smoothing effect by using atomic layer deposition (ALD)-grown non-uniformly cycled nanolaminates and coating a rough sapphire bar with a high-refractive-index polymer, which significantly reduces the measured surface roughness and improves optical transparency. These results confirm that the proposed self-smoothed gradient index cladding waveguide can be an effective platform for realizing low-loss, high-density PICs. Full article

Fiber optic gyroscopes (FOGs) are core sensors in inertial navigation systems, and their miniaturization and integration are currently hot research topics. This work presents an FOG system driven by a silicon photonics integrated circuit (PIC). The PIC, based on a 90 nm silicon-on-insulator (SOI) process, integrates core components such as polarizers, 3 dB couplers, and phase modulators within a compact footprint of 3 × 0.45 mm². These components exhibit excellent performance over a wide spectral range and play a crucial role in high-performance FOG systems. Experimental results show that the proposed FOG system can definitively measure the small angular velocity of the Earth’s rotation (±7.5 °/h). Further Allan variance analysis reveals that the FOG system has an angular random walk (ARW) of 0.00358 °/h^1/2 and a bias instability (BIS) of 0.1185 °/h. These results demonstrate the application potential of silicon photonics-based FOG systems. Full article

Smart manufacturing, Industry 4.0, and cyber-physical systems (CPSs) require sensing architectures capable of resolving both spatially distributed asset behavior and highly localized process states. This review examines optical fiber sensors (OFSs) and integrated photonic sensors for industrial monitoring through a deployment-oriented, multi-scale perspective. The discussion covers five major application regimes: continuous infrastructure surveillance, structural health monitoring (SHM) of load-bearing composites, dynamic condition monitoring of machinery, in situ observability in advanced manufacturing, and localized chemical or gas sensing. Extended fiber-optic networks, including distributed fiber-optic sensing (DFOS) based on Rayleigh, Raman, and Brillouin scattering, together with multiplexed fiber Bragg grating (FBG) sensors, provide passive, embeddable, and remotely interrogated monitoring for large-scale assets and harsh environments. Photonic integrated circuits (PICs) shift transduction to compact node-level devices for localized thermal, mechanical, refractive-index, absorption, vibration, and inertial measurements, while plasmonic and dielectric nanophotonic sensors extend optical monitoring toward surface-selective and chemically specific detection. Across these platforms, digital signal processing (DSP), machine learning (ML), sensor fusion, and digital-twin (DT) coupling are treated as artificial-intelligence-enabled (AI-enabled) layers for signal recovery, inverse mapping, uncertainty reduction, and predictive maintenance. The review argues that scalable industrial adoption is less limited by sensing physics than by the complete deployment chain: packaging, fiber–chip interfacing, calibration stability, interrogation robustness, and AI-enabled data interpretation. This manuscript is structured as a deployment-oriented narrative review of optical fiber and integrated photonic sensors for industrial monitoring and smart manufacturing. Full article

As silicon photonics technology advances toward high-density integration scenarios—such as large-scale matrices, optical phased arrays, and optical neural networks—single-layer waveguide routing encounters severe topological challenges, rendering waveguide crossings indispensable fundamental components for constructing complex on-chip interconnect networks. As photonic hubs bridging distinct functional regions, the insertion loss, crosstalk, and bandwidth of these crossings directly dictate the signal integrity and transmission capacity of optical links. This paper systematically reviews recent research progress and key technologies concerning silicon-based waveguide crossings. Initially, the mechanism of scattering loss in direct crossings is elucidated, followed by a detailed examination of three mainstream design paradigms for loss mitigation: multimode interference (MMI) structures based on the self-imaging principle, adiabatic transformation structures relying on mode evolution, and medium engineering structures utilizing sub-wavelength gratings and metamaterials. Furthermore, the application of algorithm-driven inverse design in overcoming the constraints of traditional physical configurations is discussed. Crucially, addressing the urgent demand for ultra-high transmission capacity in the post-Moore era, this review highlights functional crossings capable of polarization division multiplexing (PDM) and mode division multiplexing (MDM), analyzing the design challenges and breakthroughs associated with multi-dimensional light field manipulation. Finally, this paper presents prospects for the future development trends of the waveguide crossing junction. Full article

Fiber Bragg Grating (FBG) sensors are widely used for strain and temperature monitoring due to their high sensitivity, compact size, electromagnetic immunity, and multiplexing capability. While conventional FBG interrogators remain bulky and costly, Photonic Integrated Circuit (PIC) platforms provide a promising route toward compact, scalable, and low-power FBG interrogation. However, the choice of architecture strongly determines the achievable resolution, bandwidth, multiplexing capacity, and robustness. This review compares on-chip demodulation architectures, evaluating their performance in resolution, bandwidth, and interrogation speed. We show that the optimal architecture depends strongly on the application: AWG-based schemes excel in compact, multi-FBG readout; ring-resonator systems are highly effective for tunable filtering; and interferometric phase-domain schemes offer the highest sensitivity for dynamic strain sensing. Despite these architectural advances, practical deployment remains constrained by system-level bottlenecks. These challenges primarily include source/detector integration, fiber–chip coupling, packaging robustness, and thermal drift. Overcoming these barriers requires a shift in future development from isolated photonic-device optimization toward comprehensive, system-level co-design. Full article

Wafer-level testing of Photonic Integrated Circuits (PICs) represents a critical throughput bottleneck in silicon photonics manufacturing, particularly as co-packaged optics demand testing of thousands of optical I/O per wafer. This work introduces optimized alignment algorithms for the Technoprobe Eclipse Dynamic probe card system, which integrates electrical probes and a piezoelectrically actuated fiber array unit within a single probe head, eliminating external positioning equipment. We systematically evaluate seven alignment algorithms: Reference Coarse Scan, Reference Coarse+Fine Scan, Cross Scan, Local and Global Bayesian Optimization, Variable and Fixed Gradient Ascent. The evaluation is made across 72 simulated test cases derived from eight experimental datasets through systematic spatial windowing, combined with experimental validation. Performance is assessed under four operating regimes—high-speed (HS) and low-speed (LS) operation, each with or without hysteresis compensation (H/NH). Experimental validation across eight die positions confirms 100% success rate for both Local Bayesian (98.24% accuracy in 99.87 arbitrary units (a.u.)) and Fixed Gradient (99.18% accuracy in 154.01 a.u.) baseline algorithms. Comprehensive simulation results with improved algorithms across all four scenarios reveal distinct performance characteristics. Fixed Gradient achieves the highest reliability (95.8%) with 99.4% average accuracy across all operating conditions. Variable Gradient provides the fastest alignment (1.18 a.u. in HS-NH) with 90.3% reliability. Local Bayesian demonstrates 94.4% reliability with intermediate performance. Global Bayesian Optimization achieves the best sample efficiency (average 24 steps) but exhibits scenario-dependent reliability ranging from 88.9% (HS-H, LS-H) to 93.1% (LS-NH). For the ideal production scenario, high speed with effective hysteresis compensation (HS-NH), Fixed Gradient emerges as the optimal choice, delivering 95.8% reliability with 1.44 a.u. alignment time, resulting in the best success rate while being nearly as fast as the fastest method. Variable Gradient achieves the absolute fastest alignment (1.18 a.u.) but with 5.5% lower reliability (90.3%), making it suitable only for applications tolerating higher failure rates. Under realistic production conditions with uncompensated hysteresis (HS-H), Fixed Gradient maintains its advantage (95.8% reliability, 3.32 a.u.), while Global Bayesian degrades significantly (88.9% reliability, 4.29 a.u.). Statistical analysis using data profiles validates these methods for high-volume PIC manufacturing, with the Eclipse Dynamic system demonstrating per-die optical alignments in sub-second timescales using open-loop control hardware. Full article

We introduce a novel cross-coupled self-coupled optical waveguide (CC-SCOW) architecture that leverages coupled-resonator-induced transparency (CRIT) via a cross-coupling mechanism. This design addresses key limitations of conventional self-coupled optical waveguides (SCOWs), particularly their restricted spectral tunability and fixed interference characteristics arising from direct coupling. For the first time, we demonstrate and analyze the CRIT behavior of the CC-SCOW structure, showing that it offers enhanced design flexibility, compactness, and improved spectral performance. Through analytical modeling and finite-difference time-domain (FDTD) simulations, we show that CC-SCOWs enable tunable, narrowband filtering with improved free spectral range (FSR) and phase response. These features make the CC-SCOW architecture highly suitable for advanced photonic integrated circuits requiring high selectivity, tunability, and miniaturization. Full article

The 100 GHz-class ultrafast photonic integrated circuit (PIC) positions itself as a promising technology in the post-Moore era, when the bandwidth limit of metallic interconnections constrains current electronic integrated circuits. Nevertheless, the lack of an effective on-chip, CMOS-compatible laser source challenges the ongoing development of PIC. Germanium straintronics facilitate bandgap transformation from indirect to direct, thereby enabling effective band-to-band radiative recombination. Some parameters, such as nanowire diameters or crystalline orientation and strain direction, have a profound effect on the bandgap transformation of Ge nanowires. In this review, we will discuss changes in the fundamental physical properties of Ge nanowires under strain, including mechanical, electronic, optical, and thermal properties. Subsequently, we summarize common methods for strain engineering, as well as novel approaches that have emerged in recent years. Some notable application cases reported in the last few decades will be discussed in detail. This review may fill knowledge gaps and provide a solid background for forthcoming investigations of on-chip strained Ge lasers. Full article

Metal–organic chemical vapor deposition (MOCVD) is a crystal growth technique used to achieve high-purity thin films, especially III–V materials, for fabricating semiconductor devices. It allows for thickness tunability, controlled doping, and composition of epilayers. This review focuses on the principle of MOCVD, its historical background, and its applications in III–V semiconductor devices such as solar cells, high electron mobility transistors (HEMTs), light-emitting diodes (LEDs), laser diodes (LDs), and photonic integrated circuits (PICs). This review highlights the recent developments in MOCVD aimed at improving its efficiency, performance, and sustainability. Finally, we emphasize emerging trends and challenges in MOCVD process innovation, reactor design, and material integration that are poised to drive the development of next-generation optoelectronic, photonic, and quantum technologies. Together, these findings underscore MOCVD’s pivotal role in enabling high-performance devices and sustaining leadership in post-Moore semiconductor technologies. Full article

Silicon photonic integrated circuit (Si-PIC) components/devices based on silicon-on-insulator (SOI) waveguides have become critical components in modern optoelectronic information systems. This investigation systematically examines optical propagation losses (OPLs) induced by the sidewall roughness (SWR) of a waveguide through comparative analysis of two scattering-loss theoretical frameworks: the SWR-improved Payne–Lacey (P-L) three-dimensional (3-D) formalism and Hörmann’s 3-D perturbation model. Crucially, our computational results identify SWR = 10 nm as the convergence threshold where both models exhibit consistent OPL predictions across waveguide architectures. Single-mode SOI rib waveguides with 0.5 µm high ribs on 2.0 µm silicon film and a 2.0 μm BOX layer were designed and fabricated using the classic ICP-RIE technique. Furthermore, SWRs of 28 nm were obtained with confocal laser scanning microscopy for SOI waveguides, leading to OPLs of 2.66 and 2.67 dB/cm for TE and TM modes, respectively, from the 2-D SWR-enhanced P-L model, and 1.7 and 1.9 dB/cm, respectively, from the Hörmann 3-D model. Finally, the average experimental result of OPL for the same waveguide was 2.61 dB/cm, showing a strong agreement with the numerical values of the SWR-improved P-L 3-D formalism, providing a robust framework for optimizing industrial-grade SOI waveguide-based PIC devices/components. Full article

The growing need for real-time, accurate monitoring of hazardous gases in environmental, industrial, and healthcare settings has highlighted the limitations of traditional sensing methods. Photonic Integrated Circuits (PICs) have become a revolutionary platform due to their high sensitivity, accurate selectivity, compact size and cost-effectiveness. We present in this work a comprehensive overview of the best-reported PIC-based gas sensors. We discuss the basic concepts behind resonance-based and absorption-based sensing. A detailed overview of the various material platforms, from well-known silicon and silicon nitride to new polymers, chalcogenide glasses, and 2D materials, is presented. A comparison of key device topologies, such as waveguides, microring resonators, Mach–Zehnder interferometers, and metasurfaces, is conducted, with performance benchmarks indicating the limit of detection (LoD). The main limitations of PIC sensors are discussed in this review. We also discuss promising technologies, especially the game-changing potential of artificial intelligence to create fully autonomous devices. Full article

The silicon nitride (SiN) platform offers a low-loss solution for photonic integrated circuits (PICs). The bent waveguide represents one of the primary sources of propagation loss in such integrated systems. In this work, we present a comprehensive review of recent advances in SiN bent waveguide technologies. We propose a low-loss SiN bent waveguide design integrated with modified Hermite curves. We adopt a waveguide geometry of 800 nm × 300 nm in the simulations, with the material refractive index derived from the LPCVD process. Simulations conducted at a wavelength of 1311 nm reveal that the proposed bends exhibit bending losses of 0.076 dB, 0.021 dB, 0.0055 dB, and 0.0012 dB per 90° bend, corresponding to bending radii of 15 μm, 20 μm, 25 μm, and 30 μm, respectively. Furthermore, the fabrication tolerance and wavelength dependence of the proposed design are systematically investigated to verify its practical applicability. Full article

Infrared (IR) photodetectors are indispensable to modern optoelectronic systems, ranging from night vision imaging, surveillance, and industrial process control to environmental monitoring and medical diagnostics. However, traditional detectors based on bulk semiconductors are constrained by prohibitive fabrication costs and the stringent requirement for bulky cryogenic cooling, which severely hinders their widespread deployment in Size, Weight, and Power (SWaP)-sensitive scenarios. Silicon-based on-chip integration, leveraging compatibility with mature CMOS processes, has emerged as a transformative paradigm. It enables the realization of fully functional photonic integrated circuits (PICs) capable of on-chip sensing and high-speed data transmission, offering a pathway toward miniaturized and cost-effective architectures. This article provides a review of recent progress in silicon-based infrared photodetectors across three core material systems: Group IV (Ge/GeSn), III–V compounds, and two-dimensional (2D) materials. In the end, we offer an outlook on the development trends of next-generation intelligent sensing systems driven by optoelectronic convergence. Full article

The development of photonic-integrated circuits (PICs) for data communication, sensing, and quantum computing is hindered by the high complexity and cost of traditional fabrication methods, which rely on expensive equipment, limiting accessibility for research and prototyping. This study introduces a Direct Laser Writing (DLW) system designed as a low-cost alternative, utilizing an XY platform for precise substrate movement and an optical system comprising a collimator and lens to focus the laser beam. Operating on a single layer, the system employs SU-8 photoresist to fabricate polymer-based structures on substrates such as ITO-covered glass. Preparation involves thorough cleaning, spin coating with photoresist, and pre- and post-baking to ensure material stability. This approach reduces dependence on costly infrastructure, making it suitable for academic settings and enabling rapid prototyping. A user interface and custom slicer process standard .dxf files into executable commands, enhancing operational flexibility. Experimental results demonstrate a resolution of 10 µm, with successful patterning of structures, including diffraction grids, waveguides, and multimode interference devices. This system aims to transform PIC prototype fabrication into a cost-effective, accessible process. Full article

Silicon–nitride (SiN) waveguides have emerged as fundamental building blocks in silicon photonic integrated circuits (Si-PICs), offering advantages that compensate for the intrinsic limitations of silicon-on-insulator (SOI) and silica-on-silicon (SOS) platforms. In this work, two sizes of single-mode SiN strip waveguides are investigated: (i) 600 nm wide strip waveguide cores on a 400 nm thick Si₃N₄ film and (ii) 1.0 µm wide strip waveguide cores on a 1.0 µm thick Si₃N₄ film. First, we design two AWG architectures and develop a generalized theoretical model for one of the key specifications—polarization mode dispersion (PMD)—by considering a pair of orthogonal polarization states in these two waveguides. Then, as the two-size SiN waveguides are generally fabricated via multiple operating processes of coating, photolithography, and etching, we investigate the dependences of PMD performances on the device errors of the two AWG architectures caused by the coating/manufacturing qualities and accuracies, and the dependences of PMD performance on the refractive index errors of the waveguide core. As a consequence, the softwaretool simulations for the two AWG architectures of 40-channel 0.8 nm channelspacing show that the average PMDs of the above two waveguide sizes are <0.50 ps and <0.35 ps, respectively, and the PMD responses to the ±10% fabrication error are < ±0.20 ps and ±10% fluctuation, respectively, but the ±2.5% variations have no obvious impacts upon the PMD performance. Therefore, it turns out that the PMD performance of a smaller waveguide has a relatively strong error sensitivity to the AWG architecture, while the larger waveguide size has a relatively weak error sensitivity to the AWG architecture. Full article