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Transition-edge sensors (TESs) have the potential to perform electron spectroscopic measurements with far greater measurement rates and efficiencies than can be achieved using existing electron spectrometers. Existing spectrometers filter electrons by energy before detecting a narrow energy band at a time, discarding the vast majority of electrons available for measurement. In contrast, TESs have intrinsic energy sensitivity and so do not require prior filtering to perform energy-resolved measurements. Despite this fundamental advantage, TES electron spectroscopy has not, to our knowledge, previously been reported in the literature. We present the results of a set of proof-of-principle experiments demonstrating TES electron spectroscopy experiments using Mo/Au TESs repurposed for electron calorimetry. Using these detectors, we successfully measured the electron spectrum generated by an electron beam striking a graphite target with energies between 750 and 2000 eV, at a noise-limited energy resolution of 4 eV. Based on the findings of these experiments, we suggest improvements that could be made to TES design to enhance their electron detection capabilities through the use of a dedicated electron absorber in the device with integrated electron optics. [ABSTRACT FROM AUTHOR]

High‐speed data movement in data center communications and telecommunications is the cornerstone of society's connectivity. It serves as a critical driver of economic activity, social networks, and education. Complementary metal‐oxide semiconductor compatible silicon‐based photonic integrated circuits have proliferated transceiver technology, owing to their ease of integration with application‐specific integrated circuits and mass manufacturability. Fiber impairments in the transmission of high‐speed data stem from both optical attenuation and optical dispersion. As data rates scale and modulation formats advance, the impact of fiber dispersion even at shorter reaches becomes more important to address. In this review article, recent advancements made in integrated, chip‐scale dispersion compensation solutions are covered. The focus on chip‐scale devices stems from their ability to be easily integrated within the transmitter or receiver chip of transceivers. Future perspectives on how these devices may become commonplace within transceivers and their potential impact are discussed. [ABSTRACT FROM AUTHOR]

Optical encoders are widely used circuits in digital systems. One of the most critical features of an optical encoder is the power values in two logic states; low and high. The difference between these two values is expressed with the contrast ratio (CR) parameter. This research has designed and simulated an optical encoder based on a two-dimensional (2D) photonic crystal with four inputs and two outputs. The results show that the proposed structure has low power in low mode and high intensity in high mode. This difference in two logical modes has caused the proposed encoder to have CR = 19.8 dB, which is improved compared to previous works. Also, the proposed structure is very compact and its footprint is as small as 96.88 µm2. The data speed for the designed encoder is B R = 2 Tb/s . This encoder can be used in high-speed optical integrated circuits with low error according to the obtained values. [ABSTRACT FROM AUTHOR]

Optical pulse shaping stands as a formidable technique in ultrafast optics, radio-frequency photonics, and quantum communications. While existing systems rely on bulk optics or integrated platforms with planar waveguide sections for spatial dispersion, they face limitations in achieving finer (few- or sub-GHz) spectrum control. These methods either demand considerable space or suffer from pronounced phase errors and optical losses when assembled to achieve fine resolution. Addressing these challenges, we present a foundry-fabricated six-channel silicon photonic shaper using microresonator filter banks with inline phase control and high spectral resolution. Leveraging existing comb-based spectroscopic techniques, we devise a system to mitigate thermal crosstalk and enable the versatile use of our on-chip shaper. Our results demonstrate the shaper's ability to phase-compensate six comb lines at tunable channel spacings of 3, 4, and 5 GHz. Specifically, at a 3 GHz channel spacing, we showcase the generation of arbitrary waveforms in the time domain. This scalable design and control scheme holds promise in meeting future demands for high-precision spectral shaping capabilities. High-resolution pulse shaping is highly sought after, but existing systems are impractical outside of laboratory settings. Here, the authors introduce a chip-scale spectral shaper that uses high-Q microresonator filter banks and inline phase control to manipulate lines at GHz-level spacing. [ABSTRACT FROM AUTHOR]

Emerging miniaturized optically pumped magnetometers (OPMs) are becoming one of the most desirable approaches for biomagnetic imaging, especially for OPM with elliptically polarized light, which promises single‐light optical pumping and detection with high sensitivity. However, conventional schemes of this kind require a set of bulk polarization optics and tedious adjustment procedures, which compromise the system's compactness and practicality. In this paper, a novel chip‐scale OPM scheme that leverages the monolithic elliptical meta‐polarizer is presented and experimentally demonstrated. The meta‐polarizer with a side length of 3 mm is laid out on a 2 × 2 cm2 glass wafer. It offers the capability to convert arbitrary incident polarization into the desired elliptical polarization and exhibits a tailorable elliptical dichroism (ED) of ≈0.77 at the wavelength of 795 nm. A 4 × 4 × 4 mm3 vapor cell containing 87Rb and N2 is combined with this elliptical meta‐polarizer to construct a miniaturized OPM. The sensitivity of this sensor reaches approximately 13 fT/Hz1/2 in a four‐layer magnetic shield with a dynamic range near zero magnetic field ≈ ±0.55 nT. By exploiting the advantages of planar integrated optics, reduced footprints and scalability are promised. And this work paves the way for the integration of emerging quantum sensors on a chip. [ABSTRACT FROM AUTHOR]

Significance: Light-sheet fluorescence microscopy is widely used for high-speed, high-contrast, volumetric imaging. Application of this technique to in vivo brain imaging in non-transparent organisms has been limited by the geometric constraints of conventional light-sheet microscopes, which require orthogonal fluorescence excitation and collection objectives. We have recently demonstrated implantable photonic neural probes that emit addressable light sheets at depth in brain tissue, miniaturizing the excitation optics. Here, we propose a microendoscope consisting of a light-sheet neural probe packaged together with miniaturized fluorescence collection optics based on an image fiber bundle for lensless, light-field, computational fluorescence imaging. Aim: Foundry-fabricated, silicon-based, light-sheet neural probes can be packaged together with commercially available image fiber bundles to form microendoscopes for light-sheet light-field fluorescence imaging at depth in brain tissue. Approach: Prototype microendoscopes were developed using light-sheet neural probes with five addressable sheets and image fiber bundles. Fluorescence imaging with the microendoscopes was tested with fluorescent beads suspended in agarose and fixed mouse brain tissue. Results: Volumetric light-sheet light-field fluorescence imaging was demonstrated using the microendoscopes. Increased imaging depth and enhanced reconstruction accuracy were observed relative to epi-illumination light-field imaging using only a fiber bundle. Conclusions: Our work offers a solution toward volumetric fluorescence imaging of brain tissue with a compact size and high contrast. The proof-of-concept demonstrations herein illustrate the operating principles and methods of the imaging approach, providing a foundation for future investigations of photonic neural probe enabled microendoscopes for deep-brain fluorescence imaging in vivo. [ABSTRACT FROM AUTHOR]

This paper investigates the integration of optical fibers into an on-chip Fabry–Pérot (FP) resonator to achieve high-quality (Q) factors, which is favorable in sensing applications. Initially designed for high-speed data transmission, optical fibers are now utilized in sensing applications because of their flexibility and sensitivity to optical phenomena. This article focuses on the role of single-mode fibers (SMF) and the geometry of different structures in enhancing light confinement within FP resonators. Two distinct on-chip designs utilizing SMFs are demonstrated, modeled, and experimentally evaluated. One achieves a Q-factor higher than 5200, demonstrating significant improvement in light confinement, while the other maximizes the spectral range between the resonant modes' peaks, maximizing the sensing range through the wavelength shift. This is supported by visualized simulation and coupling efficiencies calculations for fundamental and higher-order modes for comprehensive analysis. Comparison with existing literature is also made, underscoring the advancements achieved by the presented approaches. The findings contribute to the development of microscale refractive index sensing applications, highlighting the vital role of optical fiber integration for high-performance sensing. [ABSTRACT FROM AUTHOR]

SU-8 is an emerging polymer material for integrated optical circuits that has demonstrated good structural properties in a cryogenic environment. In this article, we investigate the thermo-optical properties of SU-8 for a wavelength λ = 850   n m , from room temperature to cryogenic temperature down to 14 K. To measure the material properties, we designed and fabricated SU-8 racetrack resonators via electron beam lithography. While cooling the device in a closed-cycle cryostat, we measured the resonance spectrum as a function of the temperature from which we determined the temperature-induced variations of the group and effective indices of the waveguide. With the aid of waveguide eigenmode simulations, we used these data to derive the temperature dependence of the SU-8 refractive index n S U − 8 T . At room temperature (T~295 K), the thermo-optic coefficient d n S U − 8 / d T = − 5.3 ± 0.2 × 10 − 5   K − 1 . At low temperature (T~14 K), d n S U − 8 / d T = − 1.27 ± 0.05 × 10 − 4   K − 1 . Our research shows the potential of SU-8 photonics in a cryogenic environment, suitable for the integration with quantum light sources emitting in the near infrared (NIR). [ABSTRACT FROM AUTHOR]

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Developing a miniatured laser vibrometer becomes important for many engineering areas, such as experimental and operational modal analyses, model validation, and structural health monitoring. Due to its compact size and light weight, a miniatured laser vibrometer can be attached to various mobilized platforms, such as an unmanned aerial vehicle and a robotic arm whose payloads can usually not be large, to achieve a flexible vibration measurement capability. However, integrating optics into a miniaturized laser vibrometer presents several challenges. These include signal interference from ghost reflectance signals generated by the sub-components of integrated photonics, polarization effects caused by waveguide structures, wavelength drifting due to the semiconductor laser, and the poorer noise characteristics of an integrated laser chip compared to a non-integrated circuit. This work proposes a novel chip-based high-precision laser vibrometer by incorporating two or more sets of quadrature demodulation networks into its design. An additional set of quadrature demodulation networks with a distinct reference arm delay line length can be used to conduct real-time compensation to mitigate linear interference caused by temperature and environmental variations. A series of vibration measurements with frequencies ranging from 0.1 Hz to 1 MHz were conducted using the proposed laser vibrometer to show its repeatability and accuracy in vibration and ultrasonic vibration measurements, and its robustness to test surface conditions. The proposed laser vibrometer has the advantage of directly measuring the displacement response of a vibrating structure rather than integrating its velocity response to yield the measured displacement with a conventional laser Doppler vibrometer. [ABSTRACT FROM AUTHOR]

An optical waveguide that transmits the electromagnetic waves is a critical component for various optoelectrical applications including integrated optical circuits and optical communications. Among many, the 1D tubular optical waveguide structure enables efficient distant energy transfer via mode selection within the optical microcavity. However, its application is limited due to the complicated fabrication process. Herein, hexagonal tris(8‐hydroxyquinoline) aluminum (Alq3) microtubes with an average longitudinal length of ≈15 µm are self‐assembled within few minutes by utilizing 1‐butyl‐3‐methylimidazolium tetrafluoroborate (BMIMBF4) ionic liquids. The swift fabrication is enabled by the high electron affinity of BMIMBF4 that forms hexagonal microrods. Also, BMIMBF4 ionic liquid etches the central region of micorods during its growth, forming microtubes with a wall thickness of ≈650 nm. The fabricated Alq3 microtubes show significantly improved waveguide characteristics with reduced optical loss coefficient (0.054 µm−1) compared to that of microrods (0.271 µm−1). The demonstrated method to fabricate Alq3 microtubes with ionic liquid is an efficient approach to utilize organic microstructures as an optoelectrical components for advanced optical communications. [ABSTRACT FROM AUTHOR]

Optical logic devices are essential functional devices for achieving optical signal processing. In this study, we design an ultra-compact (4.92 × 2.52 μm2) reconfigurable optical logic gate by using inverse design method with DBS algorithm based on Sb2Se3-SOI integrated platform. By selecting different amorphous/crystalline distributions of Sb2Se3 via programmable electrical triggers, the designed structure can switch between OR, XOR, NOT or AND logic gate. This structure works well for all four logic functions in the wavelength range of 1540–1560 nm. Especially at the wavelength of 1550 nm, the Contrast Ratios for XOR, NOT and AND logic gate are 13.77 dB, 11.69 dB and 3.01 dB, respectively, indicating good logical judgment ability of the device. Our design is robust to a certain range of fabrication imperfections. Even if performance weakens due to deviations, improvements can be obtained by rearranging the configurations of Sb2Se3 without reproducing the whole device. [ABSTRACT FROM AUTHOR]

Integrated tunable optical filters are essential components in photonic signal processors, telecom systems, sensors, and quantum optical devices. Two of the most important features of a tunable filter are its dimensions and power consumption. Herein, the design and experimental validation of an on‐chip optical filter composed of a 1D topological photonic crystal cavity based on a hybrid integrated lithium tantalite‐silicon platform is presented. The strong optical confinement of the boundary state allows the fabrication of a tunable filter with an ultra‐compact size of 1.14 × 75 µm2 is demonstrated. Moreover, lithium tantalite has excellent electro‐optic properties and enables ultra‐low‐power wavelength tuning of the topological boundary state. The measured power consumption and tuning efficiency of the device are 0.0218 nW pm−1 and 6.64 pm V−1, respectively. The anisotropy of thin‐film lithium tantalite is verified by evaluating its tuning efficiency at different optical angles. The device can compensate for thermally induced refractive index changes ≈20 °C, exhibiting operational robustness. High‐speed transmission experiments confirm the stability of the developed tunable filter. This optical filter implements a topological structure with a compact size and can potentially be applied in on‐chip quantum optics, nonlinear optics, and optical sensing. [ABSTRACT FROM AUTHOR]

Ultrashort pulse laser provides an efficient way to fabricate integrated photonic devices by modulating the refractive index of optical materials with nonlinear absorption to form three-dimensional optical waveguides. Er3+-doped phosphate glass, due to its excellent characteristics and emission spectrum in the communication band near 1.55 μm, has become a research hotspot in integrated optical active gain materials. In the experiment, the Ti: sapphire femtosecond laser amplification system with the output pulse laser parameters of repetition frequency of 1 kHz, center wavelength of 800 nm and pulse width of 120 fs was used as the inscribed light source. The impact of processing parameters on waveguide formation, waveguide morphology and optical properties were systematically studied. The experimental results show that under the transverse writing condition with slit shaping assisted short focus microscope objective, with a fixed pulse energy of 1.8 μJ, the optical waveguide can be formed in the scan speed range of 10 μm/s-160 μm/s. With a fixed scan speed of 40 μm/s, the writing pulse energy window of the optical waveguide is 1.6 μJ-2.0 μJ. The waveguide cross-section is symmetrical and the refractive index is obviously modified, within the depth range of 125 μm-200 μm from the surface. The near-field intensity measurement results show that the near-field intensity distribution of the prepared waveguide is symmetrical, and the light guiding characteristics are maintained well. The refractive index modification distribution in the waveguide region is simulated based on the finite difference method, and the results show that the maximum refractive index modification value is Δn=6.6×10-4. The results of cut-back measurement show that the lowest waveguide propagation loss is only 0.91 dB/cm. [ABSTRACT FROM AUTHOR]

In order to meet the demand for multi-stopband filters and high filtering efficiency in optical nanodevices, a surface plasmon band-stop filter coupled with a straight waveguide and an arch-type resonator is proposed in this paper. Simulation analysis of visible and near-infrared spectra and field distribution using the finite element method shows that the transmittance spectrum of this structure has five stop bands in the 800 nm band range with a minimum transmittance of 9.10%; when the key parameters such as the bottom size of the resonant cavity are changed, the transmission curves are red-shifted and the performance of some of the stop bands is significantly enhanced; the sensitivity, quality factor and figure of merit can reach 1780 nm/RIU, 108.86 and 102.49 RIU−1, respectively. Finally, two optimized structures are proposed to further enhance the filter performance, allowing a minimum transmittance as low as 0.41%. The filter has a wide application prospect in optical integrated circuits. [ABSTRACT FROM AUTHOR]

Micro-electromechanical systems (MEMS) have the potential to provide low-power phase shifting in silicon photonics, but techniques for designing low-loss devices are necessary for adoption of the technology. Based on coupled mode theory (CMT), we derive analytical expressions relating the loss and, in particular, the phase-dependent loss, to the geometry of the MEMS phase shifters. The analytical model explains the loss mechanisms of MEMS phase shifters and enables simple optimization procedures. Based on that insight, we propose phase shifter geometries that minimize coupling power out of the waveguide. Minimization of the loss is based on mode orthogonality of a waveguide and phase shifter modes. We numerically model such geometries for a silicon nitride MEMS phase shifter over a silicon nitride waveguide, predicting less than −1.08 dB loss over a 2π range and −0.026 dB loss when optimized for a π range. We demonstrate this design framework with a custom silicon nitride process and achieve −0.48 dB insertion loss and less than 0.05 dB transmission variation over a π phase shift. Our work demonstrates the strength of the coupled mode approach for the design and optimization of MEMS phase shifters.

The novel ternary 2D material Bi2O2Se exhibits numerous unique properties in the optical discipline due to its distinctive structure, rendering it of significant research importance and application potential in the domains of new‐generation microelectronics, optoelectronic sensors, and multidimensional optical recognition. However, the optical anisotropy and multidimensional angular resolution of Bi2O2Se have yet to be investigated under the condition of 3D spatial variation of incidence angle. Herein, the spatial optical sensing of the few‐layer Bi2O2Se is investigated under 3D spatially varying incidence conditions using a combination of polarized Raman spectroscopy and multidimensional angle‐resolved spectroscopy. By manipulating the incident angle conditions and adjusting the sample placement angle, a comprehensive optical characterization of materials from diverse spatial orientations is conducted. It is observed that few‐layer Bi2O2Se exhibits a systematically transformed multidimensional spatial photoresponse within visible and near‐infrared wavelengths. This demonstrates the capability of Bi2O2Se as photosensitive semiconductors for 3D stereo optical detection. Furthermore, finite difference time domain simulations reveal that the spatial optical anisotropy of few‐layer Bi2O2Se can be manifested under 3D variable‐angle incidence conditions. The work serves as a crucial guide for the future of Bi2O2Se in anisotropic integrated optics applications, based on polarization‐based chiral recognition. [ABSTRACT FROM AUTHOR]

The growing interests have been witnessed in the evolution and improvement of artificial compound eyes (CE) inspired by arthropods. However, the existing CE cameras are suffering from a defocusing problem due to the incompatibility with commercial CMOS cameras. Inspired by the CEs of South American Shrimps, we report a compact biologically inspired camera that enables wide-field-of-view (FOV), high-resolution imaging and sensitive 3D moving trajectory reconstruction. To overcome the defocusing problem, a deep learning architecture with distance regulation is proposed to achieve wide-range-clear imaging, without any hardware or complex front-end design, which greatly reduces system complexity and size. The architecture is composed of a variant of Unet and Pyramid-multi-scale attention, with designed short, middle and long distance regulation. Compared to the current competitive well-known models, our method is at least 2 dB ahead. Here we describe the high-resolution computational-CE camera with 271 ommatidia, with a weight of 5.4 g an area of 3 × 3 cm2 and 5-mm thickness, which achieves compatibility and integration of CE with commercial CMOS. The experimental result illustrates this computational-CE camera has competitive advantages in enhanced resolution and sensitive 3D live moving trajectory reconstruction. The compact camera has promising applications in nano-optics fields such as medical endoscopy, panoramic imaging and vision robotics. [ABSTRACT FROM AUTHOR]

In this study, an adiabatic mode circulator based on the adiabatic mode evolution mechanism with thickness of 220 nm for the cyclic transfer of TE1 modes is presented, which has two adiabatic mode converters suitable for mode conversion between TE1 and TM0 modes, and four adiabatic taper waveguides suitable for the transfer of either TE1 or TM0 modes. Due to the symmetry of the structure, only the first half needs to be considered: the first adiabatic taper waveguide evolves the TE1 mode at width W1 = 1.5 μm to the TE1 mode at width W2 = 0.7 μm. The first adiabatic mode converter evolves the TE1 mode at width W2 = 0.7 μm to the TM0 mode at width W3 = 0.62 μm. The second adiabatic taper waveguide evolves the TM0 mode at width W3 = 0.7 μm to the TM0 mode at width W4 = 0.4 μm. The design results show that the adiabatic mode circulator designed in this study can achieve the same power transfer efficiency with an ultra-compact device size compared with other design methods (such as the design approach in Ref. (Dai et al. Opt Exp 20(12):13425-13439, 2012). The device length of the proposed adiabatic mode circulator has been reduced by a factor of 80 compared to the design approach in Ref. (Dai et al. Opt Exp 20(12):13425-13439, 2012). As a result, the device size of the proposed adiabatic mode circulator is drastically reduced, enabling the design of ultra-compact adiabatic mode circulators. [ABSTRACT FROM AUTHOR]

The construction of a large-scale quantum internet requires quantum repeaters containing multiple entangled photon sources with identical wavelengths. Semiconductor quantum dots can generate entangled photon pairs deterministically with high fidelity. However, realizing wavelength-matched quantum-dot entangled photon sources faces two difficulties: the non-uniformity of emission wavelength and exciton fine-structure splitting induced fidelity reduction. Typically, these two factors are not independently tunable, making it challenging to achieve simultaneous improvement. In this work, we demonstrate wavelength-tunable entangled photon sources based on droplet-etched GaAs quantum dots through the combined use of AC and quantum-confined Stark effects. The emission wavelength can be tuned by ~1 meV while preserving an entanglement fidelity f exceeding 0.955(1) in the entire tuning range. Based on this hybrid tuning scheme, we finally demonstrate multiple wavelength-matched entangled photon sources with f > 0.919(3), paving the way towards robust and scalable on-demand entangled photon sources for quantum internet and integrated quantum optical circuits. Realising scalable entangled photon sources with quantum dots requires compensating for both wavelength mismatches and exciton fine-structure splitting (FSS). So far, multiple QDs with the same emission wavelength and near-zero FSS have not been demonstrated. Here, the authors fill this gap, reaching high entanglement fidelity for multiple QDs tuned into resonance with each other or with Rb atoms. [ABSTRACT FROM AUTHOR]

Photonic-integrated circuits based on erbium-doped thin film lithium niobate on insulator has attracted broad interests with insofar various waveguide amplifiers and microlasers demonstrated. Wideband operation facilitated by the broadband absorption and emission of erbium ions necessitates the functional integration of wavelength filter and multiplexer on the same chip. Here, a low-loss wavelength division multiplexer at the resonant pumping and emission wavelengths (∼1480 nm and 1530–1560 nm) of erbium ions based on angled multimode interferometer is realized in the erbium-doped thin film lithium niobate on insulator fabricated by the photolithography assisted chemomechanical etching technique. The minimum on-chip insertion losses of the fabricated device are <0.7 dB for both wavelength ranges, and a 3-dB bandwidth of >20 nm is measured at the telecom C-band. Besides, direct visualization of the multimode interference pattern by the visible upconversion fluorescence of erbium ions compares well with the simulated light propagation in the multimode interferometer. Spectral tuning of the wavelength division multiplexer by structural design is also demonstrated and discussed. [ABSTRACT FROM AUTHOR]

Multimode interference (MMI) couplers based on silicon slot-waveguide structures have received widespread attention in recent years. The key issues that need to be addressed are the size and loss of such devices. This study introduces a 1 × 3 silicon-based slot-waveguide multimode interference power splitter. The device uses a gallium-nitride slot-waveguide structure to reduce the length of the coupling region and decrease additional losses. To reduce the width of the coupling region, the multimode interference coupling area is designed with a parabolic-shaped structure. The introduction of a tapered structure between the input/output waveguides and the coupling region improves additional losses and non-uniformity. Furthermore, we conducted an analysis of the fabrication tolerances of the coupling region. In this paper, we use mode solution to simulate the design of the device in the 1550 nm optical wavelength range. The eigenmode expansion method is used to simulate and optimize the parameters of the device. The device is simulated using the eigenmode expansion solver. The simulation results show that the total length of the coupling region for the device is only 4 μm. The normalized transmission of the device is 0.992, and its excess loss and imbalance are 0.036 dB and 0.003 dB, respectively. The proposed power splitter can be applied to integrated optical circuit design, optical sensing, and optical power measurement. [ABSTRACT FROM AUTHOR]

Recently there has been growing interest in using photonics to perform the linear algebra operations of neuromorphic and quantum computing applications, aiming at harnessing silicon photonics' (SiPho) high-speed and energy-efficiency credentials. Accurately mapping, however, a matrix into optics remains challenging, since state-of-the-art optical architectures are sensitive to fabrication imperfections. This leads to reduced fidelity that degrades as the insertion losses of the optical matrix nodes or the matrix dimensions increase. In this work, we present the experimental deployment of a 4 × 4 coherent crossbar (Xbar) as a silicon chip and validate experimentally its theoretically predicted fidelity restoration credentials. We demonstrate the experimental implementation of 10,000 arbitrary linear transformations achieving a record-high fidelity of 99.997% ± 0.002, limited mainly by the measurement equipment. Our work represents an integrated optical circuit providing almost unity and loss-independent fidelity in the realization of arbitrary matrices, highlighting light's credentials in resolving complex computations. The Authors demonstrate a fidelity-restorable universal integrated linear optical circuit that relies on a novel 4 × 4 silicon photonic crossbar architecture. Its experimental characterization yields a fidelity of 99.93 ± 0.06%, calculated over 10,000 matrices. [ABSTRACT FROM AUTHOR]

Convolutional neural networks (CNNs) have shown great performance in computer vision tasks, from image classification to pattern recognition. However, CNNs′${\rm CNNs}^{\prime }$ superior performance arises at the expense of high computational costs, which restricts their employment in real‐time decision‐making applications. Computationally intensive convolutions can be offloaded to optical metasurfaces, enabling sub‐picosecond latency and nearly zero energy consumption, but the currently reported approaches require additional bulk optics and can only process polarized light, which limits their practical usages in integrated lightweight systems. To solve these challenges, a novel design of the metasurface‐based optical convolutional accelerator is experimentally demonstrated, offering an ultra‐compact volume of 0.016 mm3${\rm mm}^{3}$, a low cross‐talk of ‐20 dB, polarization insensitivity, and is capable of implementing multiple convolution operations and extracting simultaneously various features from light‐encoded images. The ultra‐compact metasurface‐based optical accelerator can be compactly integrated with a digital imaging system to constitute an optical‐electronic hybrid CNN, which experimentally achieves a consistent accuracy of 96 % in arbitrarily polarized MNIST digits classification. The proposed ultra‐compact metasurface‐based optical convolutional accelerator paves the way for power‐efficient edge‐computing platforms for a range of machine vision applications. [ABSTRACT FROM AUTHOR]

Definition: Integrated Fabry–Perot cavities (IFPCs), often referred to as nanobeams due to their form factor and size, have profoundly modified the landscape of integrated photonics as a new building block for classical and quantum engineering. In this entry, the main properties of IFPCs will be summarized from the classical and quantum point of view. The classical will provide some of the main results obtained in the last decade, whereas the quantum point of view will explore cavity quantum electrodynamics (CQED), which promises to revolutionize the future "quantum internet". [ABSTRACT FROM AUTHOR]

Silicon is essential to the production of integrated circuits and optical components. Grinding is a commonly used method of silicon surface machining, but it often leads to surface and subsurface damage. These damages need to be removed by subsequent processes, typically through polishing. The surface quality generated by grinding directly impacts the cost of polishing. To enhance the quality of the grinding surface and reduce the time and cost of polishing, a grind-polishing wheel with a different structure from the conventional diamond wheel was developed. This wheel utilized ultrafine zirconia with grit size of 200 nm as abrasives and nonwoven as substrate to support the abrasives. Furthermore, to optimize the wheel and achieve better grinding performance, various wheels with different abrasive mass fractions and elastic moduli were fabricated and grinding experiments were conducted. The surface integrity of processed silicon and the material removal rate (MRR) were used to compare the grinding performance of the various wheels. After optimization, the MRR of the grind-polishing wheel reaches its peak at 0.81 μm/min. The silicon wafer ground with the grind-polishing wheel exhibited a surface roughness S a of 0.51 nm and a subsurface damage depth of 74 nm, which is close to the effect of chemical mechanical polishing processing. Compared to conventional diamond grinding wheel (mesh size of #5000), the optimized grind-polishing wheel is better suited for semi-fine finishing and can significantly reduce the cost and time of polishing. [Display omitted] • Grind-polishing wheel with ultrafine abrasives and nonwoven structure is developed. • The newly developed wheel produces silicon wafer with high surface integrity. • Relationship between wheel characteristics and grinding performance is revealed. • High MRR is obtained by optimizing the characteristics of grind-polishing wheel. [ABSTRACT FROM AUTHOR]

In this paper, we explore new optical solitons for the coupled nonlinear Schrödinger equation with generalized anti-cubic nonlinearity, which governs the propagation of electromagnetic waves in magneto-optic waveguides. These components play a crucial role in optical transmission lines and lasers, being utilized in integrated optical circuits as modulators, circulators, and isolators. To retrieve optical soliton solutions, we have implemented, for the first time, two powerful schemes for the model equation, namely the modified Sardar sub-equation method and the new Φ6-model expansion method. As a result, we obtained a wide variety of new soliton solutions, including bright, dark, gray, dark bell-type, kink, anti-kink, singular, mixed bright-singular, and dark-singular solitons. Additionally, various other solution forms emerged, such as Jacobi elliptic functions, periodic, and rational solutions. Finally, by extracting parametric conditions for the existence of soliton solutions, we discovered that physical parameters, including inter-modal dispersions, self-steepening effect, nonlinear dispersion, and the magneto-optic effect, play a crucial role in both the existence and shaping of the extracted solitons. [ABSTRACT FROM AUTHOR]

The integrated interferometric imaging system has pointed out a highly promising direction for the development of high-resolution, small-volume, and lightweight optical imaging systems in orbit. However, the current integrated interferometric imaging system has the problem of a low signal-to-noise ratio (SNR) in orbit, which seriously restricts the practical application and development of the system. To solve this problem, a design method for a multi-waveguide merged multi-frame integration (MWMMFI) system is proposed in this paper. This method proposes a novel non-uniform sampling time axis, which achieves accurate extraction of multi-frame integration signals between interferometric arms, overcoming the limitations of traditional time delay integration (TDI) techniques that are not applicable to tilted optical waveguide arrays. Consequently, it extends the integration time and increases the accumulation of effective optical signals. Additionally, noise is suppressed through an accumulate first and then differentiate algorithm. Ultimately, this achieves an enhancement of the system's SNR and optimizes the quality of the reconstructed images, all without increasing motion degradation. Simulation experiments indicate that compared to traditional systems, the MWMMFI design can increase the peak signal-to-noise ratio (PSNR) up to 4 times when the merging number is two, and up to 6.58 times when the merging number is three. This provides both technical insights and theoretical guidance for addressing the issue of enhancing the SNR of integrated interferometric imaging systems in orbit. [ABSTRACT FROM AUTHOR]

A variable optical attenuator (VOA) is a crucial component for optical communication, especially for a variable multiplexer (VMUX) and reconfigurable optical add-drop multiplexer (ROADM). With the capacity increasing dramatically, a large-port-count and low-power-consumption VOA array is urgent for an on-chip system. In this paper, we experimentally demonstrate a 16-channel VOA array based on a polymer/silica hybrid waveguide. The proposed array is able to work over C and L bands. The VOA array shows an average attenuation larger than 14.38 dB with a low power consumption of 15.53 mW. The low power consumption makes it possible to integrate silica-based passive devices with a large port count on-chip. [ABSTRACT FROM AUTHOR]

A Silicon Photonics modulator is a high-speed photonic integrated circuit for optical data transmission in high-capacity optical networks. Silicon Photonics modulators in the configuration of a Mach–Zehnder interferometer, in which a PN-junction rib-waveguide phase shifter is inserted in each arm of the interferometer, are studied in this paper because of their superior performance of high-quality optical data generation in a wide range of spectral bands and their simplicity in fabrication processes suitable to production in foundries. Design, fabrication, and fundamental characteristics of Silicon Photonics Mach–Zehnder modulators are reviewed as an introduction to these high-speed PICs on the Silicon Photonics platform. Modulation speed, or modulation bandwidth, is a key performance item, as well as optical loss, in the application to high-speed optical transmitters. Limiting factors on modulation speed are addressed in equations. Electrical resistance–capacitance coupling, which causes optical modulation bandwidth–optical loss trade-off, is the most challenging limiting factor that limits high-speed modulation. Expansion of modulation bandwidth is not possible without increasing optical loss in the conventional approaches. A new idea including quantum-mechanical effect in the design of Silicon Photonics modulators is proposed and proved in computational analysis to resolve the bandwidth loss trade-off. By adding high-mobility quantum-well overlayers to the side slab wings of the rib-waveguide phase shifter, the modulation bandwidth is doubled without increasing optical loss to achieve a 200 Gbaud modulation rate. [ABSTRACT FROM AUTHOR]

We report the design, fabrication, and characterization of hollow-core anti-resonant reflecting optical waveguides (ARROWs) fabricated in a membrane-covered trench. These structures are built on silicon wafers using standard microfabrication techniques, including plasma etching, to form trenches. Four waveguide designs are demonstrated, which have different numbers of thin-film reflecting layers. We demonstrate that optical loss decreases with additional reflecting layers, with measured loss coefficients as low as 1 cm−1. [ABSTRACT FROM AUTHOR]

Optical fiber gratings can be appropriately packaged and integrated for the real-time monitoring of the structural health of buildings or composite-material films. In this work, a tilted fiber Bragg grating at the micron scale was proposed, designed, and optimized via simulation model analysis using OptiFDTD software. The effects of the grating inclination, grating period, and grating length on the transmission spectrum of the tilted microfiber Bragg grating (TMFBG) were studied. The transmission spectrum's responses to different refractive indices were simulated and compared. A TFBG was uniformly etched with hydrofluoric acid based on the chemical etching method, and several TMFBGs with different diameters were prepared. The refractive index-sensing characteristics of the TMFBGs with different structures were studied. It was found that the sensitivity of the etched TFBG was greatly improved from 0.964 nm/RIU to 6.368 nm/RIU for the higher-order cladding mode, and from 0.294 nm/RIU to 2.353 nm/RIU for the lower-order cladding mode, being approximately six times and eight times higher, respectively. [ABSTRACT FROM AUTHOR]

Micro-electromechanical systems (MEMS) have the potential to provide low-power phase shifting in silicon photonics, but techniques for designing low-loss devices are necessary for adoption of the technology. Based on coupled mode theory (CMT), we derive analytical expressions relating the loss and, in particular, the phase-dependent loss, to the geometry of the MEMS phase shifters. The analytical model explains the loss mechanisms of MEMS phase shifters and enables simple optimization procedures. Based on that insight, we propose phase shifter geometries that minimize coupling power out of the waveguide. Minimization of the loss is based on mode orthogonality of a waveguide and phase shifter modes. We numerically model such geometries for a silicon nitride MEMS phase shifter over a silicon nitride waveguide, predicting less than −0.08 dB loss over a 2 π range and −0.026 dB loss when optimized for a π range. We demonstrate this design framework with a custom silicon nitride process and achieve −0.48 dB insertion loss and less than 0.05 dB transmission variation over a π phase shift. Our work demonstrates the strength of the coupled mode approach for the design and optimization of MEMS phase shifters. [ABSTRACT FROM AUTHOR]

The ability to encode different operations into a single miniaturized optical device is required to reduce the complexity and size of optical paths for light manipulation, which usually employs dynamic optical components, interferometric setups, and/or multiple bulky elements in cascade. A very efficient solution is provided by metalenses, which are flat optical elements able to generate and manipulate structured light beams in a compact and efficient way, offering a powerful and attractive tool in many fields, such as life science and telecommunications. In this work, we present the design and test of transmission dielectric bi-functional metalenses that exploit both the dynamic and the geometric phases, to enable the spin-controlled manipulation of different focused orbital angular momentum (OAM) beams, depending on the circularly polarized state in input. In detail, we provide numerical algorithms for the design and simulation of the meta-optics in the telecom infrared, the fabrication processes, and the optical characterization under different impinging polarized optical vortices. This solution provides new integrated flat optics for applications in imaging, optical tweezing and trapping, optical computation, and high-capacity telecommunication and encryption. [ABSTRACT FROM AUTHOR]

This study extensively explores the Biswas–Milovic equation (BME) with Kerr and power law nonlinearity to extract the unique characteristics of optical soliton solutions. These optical soliton solutions have different applications in the field of precision in optical switching, applications in waveguide design, exploration of nonlinear optical effects, imaging precision, reduced intensity fluctuations, suitability for optical signal processing in optical physics, etc. Through the powerful ( G ′ / G , 1 / G )-expansion analytical method, a variety of soliton solutions are expressed in three distinct forms: trigonometric, hyperbolic, and rational expressions. Rigorous validation using Mathematica software ensures precision, while dynamic visual representations vividly portray various soliton patterns such as kink, anti-kink, singular soliton, hyperbolic, dark soliton, and periodic bright soliton solutions. Indeed, a sensitivity analysis was conducted to assess how changes in parameters affect the exact solutions, aiding in the understanding of system behavior and informing decision-making, especially in accurately designing or analyzing real-world optical phenomena. This investigation reveals the significant influence of parameters λ , τ , c , B , and Κ on the precise solutions in Kerr and power law nonlinearities within the BME. Notably, parameter λ exhibits consistently high sensitivity across all scenarios, while parameters τ and c demonstrate pronounced sensitivity in scenario III. The outcomes derived from this method are distinctive and carry significant implications for the dynamics of optical fibers and wave phenomena across various optical systems. [ABSTRACT FROM AUTHOR]

In this work, nanophotonic circuits with directional couplers are studied, which, along with phase shifters, are one of the main elements for creating circuits of a linear optical quantum computer. Directional couplers are two closely spaced waveguides, were made of silicon nitride. The subject of the study was the splitting ratio of directional couplers at a wavelength of 914 nm at room (300 K) and helium (3 K) temperatures. On the basis of experimental data, the coupling length at which all the power from one waveguide passes into another was extracted, and the refractive indices of silicon nitride at room (300 K) and helium temperatures (3 K) were found. The results of the work are of great importance in the design and manufacture of fully integrated quantum optical microcircuits with superconducting detectors operating at helium temperatures. [ABSTRACT FROM AUTHOR]

Multidimensional multiplexing technologies have been proven to be a promising scheme to meet the demands of high‐capacity optical interconnects and optical processing networks. However, challenges remain to realize multidimensional hybrid multiplexing data transmission and signal processing between few‐mode fiber transmission links and on‐chip optical processing networks, since the optical coupling between fiber and chip is almost exclusively in the single‐mode regime. Here, a multidimensional fiber‐to‐chip optical processing system is proposed and demonstrated for hybrid wavelength‐, mode‐, and polarization‐division multiplexing signals, where multidimensional coupling between few‐mode fiber transmission link and on‐chip multi‐mode processing network is realized by using a 3D photonic integrated (de)multiplexers on a glass chip as well as 2D photonic integrated (de)multiplexers on a silicon chip, and the on‐chip multidimensional optical processing network composed by parallel cascaded micro‐ring resonator array performs a function of reconfigurable optical add/drop multiplexer. By operating wavelength‐division multiplexing in conjunction with mode‐division multiplexing and polarization‐division multiplexing, the communication bandwidth of fiber‐to‐chip optical processing systems can be further scaled. [ABSTRACT FROM AUTHOR]

In this paper, the implementation of an integrated system of half adder and half subtractor based on 2D Si-air photonic crystal is proposed. The structure includes two input ports, one control port, and two output ports. When light is absent in the control port, the structure operates as a half adder and when light is present in the control port, it functions as a half subtractor. The operation of the structure is based on the phenomenon of constructive and destructive interference of light waves. The novelty of the proposed structure is that using a single control signal, both half adder and half subtractor operations can be realized. Since no nonlinear material has been used to design the structure, the power consumption of the structure is very low. Another advantage of the structure is that same materials have been used for all the rods which makes the fabrication process easier. The structure has been simulated by utilizing PWE and FDTD methods. Different performance parameters such as contrast ratio, rise time, delay time, fall time, response time, and bit rate for the designed structure have been obtained as 14.78 dB, 0.25 ps, 0.3 ps, 0.11 ps, 0.44 ps, and 2.27 Tb/s respectively. Due to its high contrast ratio, fast response time, high bit rate, and smaller dimension, the designed structure can be a promising candidate for realizing high speed optical integrated circuits. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive numerical analysis is conducted on a hybrid plasmonic waveguide (HPWG)-based racetrack ring resonator (RTRR) structure, tailored specifically for refractive index sensing applications. The sensor design optimization yields remarkable results, achieving a sensitivity of 275.7 nm/RIU. Subsequently, the boundaries of sensor performance are pushed even further by integrating a subwavelength grating (SWG) structure into the racetrack configuration, thereby augmenting the light–matter interaction. Of particular note is the pivotal role played by the length of the SWG segment in enhancing device sensitivity. It is observed that a significant sensitivity enhancement can be obtained, with values escalating from 377.1 nm/RIU to 477.7 nm/RIU as the SWG segment length increases from 5 µm to 10 µm, respectively. This investigation underscores the immense potential of HPWG in tandem with SWG for notably enhancing the sensitivity of photonic sensors. These findings not only advance the understanding of these structures but also pave the way for the development of highly efficient sensing devices with unprecedented performance capabilities. [ABSTRACT FROM AUTHOR]

Integrated Fabry–Perot cavities (IFPCs), often referred to as nanobeams due to their form factor and size, have profoundly modified the landscape of integrated photonics as a new building block for classical and quantum engineering. In this entry, the main properties of IFPCs will be summarized from the classical and quantum point of view. The classical will provide some of the main results obtained in the last decade, whereas the quantum point of view will explore cavity quantum electrodynamics (CQED), which promises to revolutionize the future “quantum internet”.

Abstract The optical losses and the refractive index change of optical planar waveguides formed by MeV ion implantation were correlated with the experimental ion implantation parameters. Direct ion implantation was performed by means of carbon, silicon and copper ion beams impinging on the substrate surface at normal incidence. The ions were accelerated at energies ranging from 3 to 12 MeV with fluences varying from 1 × 1012 to 2 × 1016 ion/cm2, according to the type of implanted ion. The modification of the substrate refractive index due to the ion irradiation‐induced damage was evaluated using the prism coupler method, and the refractive index profiles were determined by means of a reconstruction method using a multilayer structure approximation. The guiding properties of the waveguides were analysed using the fibre‐coupling technique to determine both the optical transmission and transversal modes at 635 nm. The main practical relevance of our research is the obtention of high‐quality waveguides at low current density MeV ion implantation (≤80 nA/cm2) without post‐implantation annealing.

Silicon carbide, a wide bandgap semiconductor material platform, has emerged as an exceptional material for nonlinear integrated photonics. Among the different poly-structures, 4H-silicon carbide-on-insulator stacks show promising results to their low loss, which are crucial for commercial applications like communication, metrology, and spectroscopy. High Q-values and low-loss microring resonators are imperative for miniaturization and photonic integration in these applications. This Perspective emphasizes recent advancements in enhancing the quality factor of microresonators based on 4H-silicon carbide, as well as the strides made in experimental results of third-order nonlinearities. Furthermore, this Letter addresses and outlines the prospects of integrating 4H-silicon carbide microring resonators into frequency comb technologies and potential applications. [ABSTRACT FROM AUTHOR]

The microcavity is a promising sensor platform, but any perturbation will disturb its linewidth, cause resonance shift or splitting. However, such sensing resolution is limited by the cavity's optical quality factor and mode volume. Here, an on‐chip integrated microcavity system is proposed and demonstrated that the resolution of a self‐referenced sensor can be enhanced with multi‐mode coupling. In experiments, inter‐mode coupling strength is carefully optimized with a pulley waveguide and observed a resolution improvement of nearly 3 times in the frequency domain. While experiencing small refractive index change tuned by temperature, mode‐coupled system shows a 7.2 times sensitivity enhancement that is than the uncoupled system on the same chip and a very significant lineshape contrast ratio change as great reference for minor frequency shifts. This approach will help design microcavity sensors to improve detection sensitivity and resolution under limited manufacture precision. [ABSTRACT FROM AUTHOR]

In this study, Γ-shaped rectangular resonators, which are created in a metal insulator metal (MIM) structure, have been studied analytically and numerically. The metal is silver and rectangular resonators are filled by Si and the peak of transparency profile is tuned in the communication band with proper geometrical parameters. By employing 2-D finite difference time domain method (FDTD), simulations show a plasmonic induced transparency (PIT) window in the transmission diagram. The PIT is created by instructive and destructive interference between bright and dark resonator modes. The presented structure demonstrates tunable transparency window by variation of symmetry parameter, s. The maximum group velocity is obtained 0.1 ps in communication band corresponded to 30 μm traveling of light in the vacuum which is comparable to previous articles. The proposed structure may have potential applications in optical memory and delay blocks in designing integrated optical circuits. [ABSTRACT FROM AUTHOR]

In this paper, plasmonic band-pass and band-stop filters employing ring resonators within the framework of the Wilkinson power divider structure are presented. It is shown that the resonance wavelengths can be effectively manipulated by adjusting the inner and outer radii of the ring resonators. Furthermore, by precisely controlling the gap size between the ring resonators and the waveguides, we have successfully designed efficient band-pass and band-stop filters. This study encompasses a thorough investigation into the propagating modes of surface plasmon polaritons (SPPs) within these filters. The transmission characteristics of the proposed filters are meticulously examined and analyzed using the finite-difference time-domain (FDTD) method. The proposed plasmonic filters exhibit a compact size, thus holding promising potential for integrated optics applications. Moreover, they possess the inherent capability to eliminate higher-order modes, enhancing their utility in practical implementations which require a single mode response. The proposed design has the possibility of manipulating the filtering wavelength by adjusting the stubs and ring parameters. This capability opens up exciting avenues for tuning the filter's response and tailoring it to the desired application requirements. [ABSTRACT FROM AUTHOR]

A Janus layered metamaterial (JLM) operating in the terahertz (THz) region is proposed, which increases the direction dimension to manipulate the propagation of electromagnetic waves (EWs) through the introduction of nonlinear Kerr media. It achieves multi-scale multitasking with different logic gates and mode-switching biosensing, making a breakthrough on traditional single-function and single-scale THz devices. Due to the electro-optical effect, the liquid crystal (LC) is adjusted by the electric field, and the sharp transmission peak generated by the located defect mode resonance can be used to realize the forward scale logic product gate and the backward scale exclusive NOR gate. In addition, by locking the sharp transmission peak, the biosensing can have different detection ranges under the LC modulation. Therefore, when EWs propagate forward and backward, the mode switching of different biosensing categories with a glucose concentration of 300–550 g/l, creatinine concentration of 80.9–85.28 μmol/l, and the blood component in refractive index of 1.33–1.38 can be realized. The JLM proposed provides a possibility for the design of the chip-level compact optical integrated circuit and offers a new idea for multi-purpose biomedical detection, owning certain research value. [ABSTRACT FROM AUTHOR]

Marcatili's analytical solution for the guided modes of rectangular optical waveguides (ROWGs) depends on (1) using the separation of variables (SOV) and (2) applying the paraxial approximation. It results in two classes of modes: the TE-like and the TM-like modes which are supported by these waveguides. These modes are uncoupled under low-index-contrast conditions. In the case of silicon-on-insulator (SOI) waveguides, the coupling between them can no longer be neglected. This paper extends using the SOV to find analytical modal solutions of SOI-ROWGs. It expands these solutions in quadruples of plane waves and develops a novel non-paraxial scattering model to account for the polarization coupling between these waves under high-index-contrast conditions. This model yields approximate analytical expressions of the field components of the guided modes which are the sum of major and minor Marcatili's TE-like and TM-like modal fields. Numerical examples show excellent agreement with the field components of full-vectorial mode solvers. [ABSTRACT FROM AUTHOR]

Methods of laser micro- and nano-modification of the structure of transparent dielectrics offer much for the creation of a new type of glass-crystalline materials and new applications. In the present work, after a brief excursion into the history of glass-ceramics, transparent aluminosilicate sitalls [glass-ceramics] are discussed, mainly for the example of the Li2O–Al2O3–SiO2 system, and the areas of their new applications. The recently discovered possibilities of laser micro-modification of the structure of sitalls and the writing of elements of photonics and integrated optics in their interior volume are considered. Special attention is given to transparent glass-ceramics with thermal expansion coefficient close to zero. [ABSTRACT FROM AUTHOR]

Photonic devices based on silicon waveguides are essential to versatile high‐performance and low‐cost photonic integrated systems. Extremely complex silicon photonic devices with hundreds or even thousands of degrees of freedom (DOF) are successfully designed and manufactured based on recent advances in data science and nanofabrication technology. At this level, conventional forward‐reasoning may no longer be suitable for designing high‐performance silicon photonic devices with novel functionalities since the light‐matter interaction is complex and non‐intuitive. Therefore, the timely development of sub‐wavelength silicon photonic devices that can precisely mold the flow of light is a critical and urgent issue requiring joint engineering and scientific efforts. In this paper, an inverse design strategy based on heuristic and gradient descendant algorithms, enabling the realization of large‐scale integrated devices is first introduced. Subsequently, the burgeoning deep learning technology, which offers a promising direction for the automation design of silicon photonics with a data‐driven approach, is discussed. Finally, the obstacles and prospects in this emerging research direction are revealed. Detail discussions from multiple perspectives are provided. This review aims to provide general guidance and a comprehensive reference for scientists developing photonic integrated systems. [ABSTRACT FROM AUTHOR]