Waveguide Chip Research Articles

Linear and nonlinear optical properties of femtosecond laser inscribed waveguides into GLS glass

Gallium lanthanum sulfide (GLS) glass is a promising material for mid-infrared photonics due to its wide transmission window and its high nonlinear refractive index that is almost three orders of magnitude higher than that of fused silica. In this paper, we present the results of a detailed study into the linear and nonlinear optical properties of waveguides fabricated in GLS glass via ultrafast laser direct-inscription using three different techniques: cumulative heating in the thermal regime as well as multi-scan and half-scan in the athermal regime. Using quadriwave lateral shearing interferometry, we fully characterized the refractive index profiles of such inscribed waveguides and found no difference between half-scan and multi-scan writing which indicates the absence of laser-induced stress in this soft glass in stark contrast to fused silica. In terms of nonlinearity, we utilized self-phase modulation (SPM)-induced spectral broadening experiments at mid-IR wavelengths to demonstrate that waveguides fabricated in the athermal regime preserve the high intrinsic nonlinearity of the GLS bulk material, outperforming those written in the thermal regime based. These findings pave the way for the fabrication of fiber-coupled optical waveguide chips for nonlinear mid-infrared photonics.

Broadband Waveguide Chip Design with Phase Measurement Function for Enhancing Optical Interferometric Imaging

The waveguide chip with a phase measurement function has garnered significant attention in the field of imaging optics, emerging as a crucial component in optical interferometric imaging systems. Enhancing the working bandwidth of these waveguide chips is essential for improving the imaging quality of interferometric systems. However, most existing designs primarily focus on narrow bands, with no reported research on broadband designs. This paper introduces a novel broadband waveguide chip design that incorporates a phase measurement function. We explore the fundamental structure and working principle of this innovative design. Fabricated on a silicon substrate, the chip features a silicon dioxide cladding layer and a germanium-doped silicon dioxide core layer, strategically optimized for performance. Utilizing the Beam Propagation Method (BPM), we conduct detailed simulations to determine the optimal device parameters. The simulation results demonstrate the effectiveness of our design, showing a phase measurement deviation of approximately 5° at a center wavelength of 1550 nm across a 300 nm wavelength range. The loss of the device is approximately 0.8 dB. These findings provide a solid foundation for future experimental implementations and fabrications, offering both a theoretical framework and technical reference for advancing the practical use of broadband waveguide chips with phase measurement functions in optical interferometric imaging.

All optical third order tunable ordinary differential equation solutions based on double Sagnac rings coupled MZI on silicon waveguide chips

All optical third order tunable ordinary differential equation solutions based on double Sagnac rings coupled MZI on silicon waveguide chips

Polaronic Nonlinear Optical Response and All-Optical Switching Based on an Ionic Metal Oxide.

It has been well-established that light-matter interactions, as manifested by diverse linear and nonlinear optical (NLO) processes, are mediated by real and virtual particles, such as electrons, phonons, and excitons. Polarons, often regarded as electrons dressed by phonons, are known to contribute to exotic behaviors of solids, from superconductivity to photocatalysis, while their role in materials' NLO response remains largely unexplored. Here, the NLO response mediated by polarons supported by a model ionic metal oxide, TiO2, is examined. It is observed that the formation of polaronic states within the bandgap results in a dramatic enhancement of NLO absorption coefficient by over 130 times for photon energies in the sub-bandgap regions, characterized by a 100fs scale ultrafast response that is typical for thermalized electrons in metals. The ultrafast polaronic NLO response is then exploited for the development of all-optical switches for ultrafast pulse generation in near-infrared (NIR) fiber lasers and modulation of optical signal in the telecommunication band based on evanescent interaction on a planar waveguide chip. These results suggest that the polarons supported by dielectric ionic oxides can fill the gaps left by dielectric and metallic materials and serve as a novel platform for nonlinear photonic applications.

3-Port beam splitter of arbitrary power ratio enabled by deep learning on a multimode waveguide

A 3-port beam splitter with arbitrary power ratio is developed on a multimode waveguide by effectively manipulating the multimode interference through 4 locally placed microheaters. For matched interference, different light powers are coupled to the three output waveguides but the sum does not undergo extra loss, whereas the splitter integrates also the variable attenuation function, from zero to maximum, to any of the outputs. Different from the conventional design approach using extensive simulations, an equivalent neural network is established to represent such a multimode waveguide system based on experimental data only. From this neural network, an optimization program is developed to inverse the output and input. For a target power splitting ratio, the required heater currents can be readily calculated on a computer and then loaded onto the waveguide chip. The experimental results match well with the targets. This work demonstrates that the nonlinear activation is inherently integrated in the thermally controlled multimode waveguide though the optical material itself is linear. This feature can be used to construct complex deep learning networks. It may lead to the development of advanced integrated optical switches and computing networks.

Optical leaky fin waveguide for long-range optical antennas on high-index contrast photonic circuit platforms

Long-distance light detection and ranging (LiDAR) applications require an aperture size in the order of 30 mm to project 200–300 m. To generate such collimated Gaussian beams from the surface of a chip, this work presents a novel waveguide antenna concept, which we call an “optical leaky fin antenna,” consisting of a tapered waveguide with a narrow vertical “fin” on top. The proposed structure (operating around λ=1.55 μm) overcomes fundamental fabrication challenges encountered in weak apodized gratings, the conventional method to create an off-chip wide Gaussian beam from a waveguide chip. We explore the design space of the antenna by scanning the relevant cross section parameters in a mode solver, and their sensitivity is examined. We also investigate the dispersion of the emission pattern and angle with the wavelength. The simulated design space is then used to construct and simulate an optical antenna to emit a collimated target intensity profile. Results show inherent robustness to crucial design parameters and indicate good scalability of the design. Possibilities and challenges to fabricate this device concept are also discussed. This novel antenna concept illustrates the possibility to integrate long optical antennas required for long-range solid-state LiDAR systems on a high-index contrast platform with a scalable fabrication method.

Dual-layer optical encryption fluorescent polymer waveguide chip based on optical pulse-code modulation technique

Information encryption technique has broad applications in individual privacy, military confidentiality, and national security, but traditional electronic encryption approaches are increasingly unable to satisfy the demands of strong safety and large bandwidth of high-speed data transmission over network. Optical encryption technology could be more flexible and effective in parallel programming and multiple degree-of-freedom data transmitting application. Here, we show a dual-layer optical encryption fluorescent polymer waveguide chip based on optical pulse-code modulation technique. Fluorescent oligomers were doped into epoxy cross-linking SU-8 polymer as a gain medium. Through modifying both the external pumping wavelength and operating frequency of the pulse-code modulation, the sender could ensure the transmission of vital information is secure. If the plaintext transmission is eavesdropped, the external pumping light will be switched, and the receiver will get warning commands of ciphertext information in the standby network. This technique is suitable for high-integration and high-scalability optical information encryption communications.

Triple-layered optical interconnecting integrated waveguide chip based on epoxy cross-linking fluorinated polymer photonic platform.

In this study, a triple-layered optical interconnecting integrated waveguide chip was designed and fabricated using an epoxy cross-linking polymer photonic platform. Fluorinated photopolymers FSU-8 and AF-Z-PC EP were self-synthesized as waveguide cores and cladding materials, respectively. The triple-layered optical interconnecting waveguide device comprised 4 × 4 arrayed waveguide grating (AWG) -based wavelength-selective switching (WSS) arrays, 4 × 4 multi-mode interference (MMI) -cascaded channel-selective switching (CSS) arrays, and 3 × 3 direct-coupling (DC) interlayered switching arrays. The overall optical polymer waveguide module was fabricated by direct UV writing. For the multilayered WSS arrays, the wavelength-shifting sensitivity was ∼0.48 nm/°C. For the multilayered CSS arrays, the average switching time was ∼280 µs, and the maximum power consumption was <30 mW. For interlayered switching arrays, the extinction ratio approximated 15.2 dB. The transmission loss for the triple-layered optical waveguide chip was measured as 10.0-12.1 dB. The flexible multilayered photonic integrated circuits (PIC) can be used in high-density integrated optical interconnecting systems with a large-volume optical information transmission capacity.

Machine learning at the edge for AI-enabled multiplexed pathogen detection

Multiplexed detection of biomarkers in real-time is crucial for sensitive and accurate diagnosis at the point of use. This scenario poses tremendous challenges for detection and identification of signals of varying shape and quality at the edge of the signal-to-noise limit. Here, we demonstrate a robust target identification scheme that utilizes a Deep Neural Network (DNN) for multiplex detection of single particles and molecular biomarkers. The model combines fast wavelet particle detection with Short-Time Fourier Transform analysis, followed by DNN identification on an AI-specific edge device (Google Coral Dev board). The approach is validated using multi-spot optical excitation of Klebsiella Pneumoniae bacterial nucleic acids flowing through an optofluidic waveguide chip that produces fluorescence signals of varying amplitude, duration, and quality. Amplification-free 3× multiplexing in real-time is demonstrated with excellent specificity, sensitivity, and a classification accuracy of 99.8%. These results show that a minimalistic DNN design optimized for mobile devices provides a robust framework for accurate pathogen detection using compact, low-cost diagnostic devices.

Integrated fluorescence excitation, collection, and filtering on a GaN waveguide chip

Integrated fluorescence excitation, collection, and filtering on a GaN waveguide chip

A photonic integrated continuous-travelling-wave parametric amplifier.

The ability to amplify optical signals is of pivotal importance across science and technology typically using rare-earth-doped fibres or gain media based on III-V semiconductors. A different physical process to amplify optical signals is to use the Kerr nonlinearity of optical fibres through parametric interactions1,2. Pioneering work demonstrated continuous-wave net-gain travelling-wave parametric amplification in fibres3, enabling, for example, phase-sensitive (that is, noiseless) amplification4, link span increase5, signal regeneration and nonlinear phase noise mitigation6. Despite great progress7-15, allphotonic integrated circuit-based demonstrations of net parametric gain have necessitated pulsed lasers, limiting their practical use. Until now, only bulk micromachined periodically poled lithium niobate (PPLN) waveguide chips have achieved continuous-wave gain16,17, yet their integration with silicon-wafer-based photonic circuits has not been shown. Here we demonstrate a photonic-integrated-circuit-based travelling-wave optical parametric amplifier with net signal gain in the continuous-wave regime. Using ultralow-loss, dispersion-engineered, metre-long, Si3N4 photonic integrated circuits18 on a silicon chip of dimensions 5 × 5 mm2, we achieve a continuous parametric gain of 12 dB that exceeds both the on-chip optical propagation loss and fibre-chip-fibre coupling losses in the telecommunication C band. Our work demonstrates the potential of photonic-integrated-circuit-based parametric amplifiers that have lithographically controlled gain spectrum, compact footprint, resilience to optical feedback and quantum-limited performance, and can operate in the wavelength ranges from visible to mid-infrared and outside conventional rare-earth amplification bands.

Micro Light Flow Controller on a Programmable Waveguide Engine.

A light flow controller that can regulate the three-port optical power in both lossless and lossy modus is realized on a programmable multimode waveguide engine. The microheaters on the waveguide chip mimic the tunable "pixels" that can continuously adjust the local refractive index. Compared to the conventional method where the tuning takes place only on single-mode waveguides, the proposed structure is more compact and requires less electrodes. The local index changes in a multimode waveguide can alter the mode numbers, field distribution, and propagation constants of each individual mode, all of which can alter the multimode interference pattern significantly. However, these changes are mostly complex and not governed by analytical equations as in the single-mode case. Though numerical simulations can be performed to predict the device response, the thermal and electromagnetic computing involved is mostly time-consuming. Here, a multi-level search program is developed based on experiments only. It can reach a target output in real time by adjusting the microheaters collectively and iteratively. It can also jump over local optima and further improve the cost function on a global level. With only a simple waveguide structure and four microheaters, light can be routed freely into any of the three output ports with arbitrary power ratios, with and without extra attenuation. This work may trigger new ideas in developing compact and efficient photonic integrated devices for applications in optical communication and computing.

Photonic integration of lithium niobate micro-ring resonators onto silicon nitride waveguide chips by transfer-printing

The heterogeneous integration of pre-fabricated lithium niobate photonic waveguide devices onto a silicon nitride waveguide platform via a transfer-printing approach has been demonstrated for the first time. A fabrication process was developed to make free-standing lithium niobate membrane devices compatible with back-end integration onto photonic integrated circuits. Micro-ring resonators in membrane format were lithographically defined by using laser direct writing and plasma dry etching. The lithium niobate micro-ring resonators were then transferred from their host substrate and released onto a silicon nitride waveguide chip. An all-pass ring resonator transmission spectrum was obtained in the 1.5 µm to 1.6 µm wavelength range, with a measured loaded Q-factor larger than 3.2 × 104.

An Optical Parametric Amplifier via $ \chi ^{(2)}$ in AlGaAs Waveguides

We report parametric gain by utilizing $ \chi^{(2)} $ non-linearities in a semiconductor Bragg Reflection Waveguide (BRW) waveguide chip. Under the two-mode degenerate type II phase matching, it can be shown that more than 18 dBs of parametric gain for both TE and TM modes is tenable in 100s of micrometers of device length. Polarization insensitive parametric gain can be attained within the 1550 nm region of the spectrum. These AlGaAs BRW waveguides exhibit sub-photon per pulse sensitivity. This is in sharp contrast to other types of parametric gain devices which utilize $ \chi^{(3)} $, where the pump wavelength is in the vicinity of the signal wavelength. This sensitivity, which reached 0.1~photon/pulse, can usher a new era for on-chip quantum information processing using compact, micrometer-scale devices.

Fiber spectrum analyzer based on planar waveguide array aligned to a camera without lens

We propose and experimentally demonstrate a fiber spectrum analyzer based on a planar waveguide chip butt-coupled with an input fiber and aligned to a standard camera without any free-space optical elements. The chip consists of a single-mode waveguide to connect with the fiber, a beam broadening area, and a waveguide array in which the lengths of the waveguides are designed for both wavelength separation and beam focusing. The facet of the chip is diced open so that the outputs of the array form a near-field emitter. The far field are calculated by the Rayleigh-Sommerfeld diffraction integral. We show that the chip can provide a focal depth on the millimeter scale, allowing relaxed alignment to the camera without any fine-positioning stage. Two devices with 120 and 220 waveguides are fabricated on the polymer waveguide platform. The measured spectral width are 0.63 nm and 0.42 nm, respectively. This simple and practical approach may lead to the development of a spectrum analyzer for fiber that is easily mountable to any commercial camera, thereby avoiding the complication for customized detectors as well as electronic circuits afterwards.

SmartPrint Single-Mode Flexible Polymer Optical Interconnect for High Density Integrated Photonics

This paper reports on the demonstration of a single-mode flexible polymer optical interconnect for efficiently and conveniently connecting integrated photonics chips to one another (chip-to-chip) and to optical printed circuit boards (chip-to-board). The interconnect uses a low-loss partially fluorinated refractive index contrast (RIC) polymer, referred to as poly(F-SBOC), that provides for direct patterning of the desired refractive index profiles into a slab waveguide consisting of poly(F-SBOC) and a flexible fluoropolymer film (Tefzel). Using a maskless lithography system, interconnects consisting of s-bends and tapers can be printed in situ into the poly(F-SBOC) material with no need for mechanical alignment. We demonstrate the efficacy of this approach by connecting two separate ion-exchange (IOX) glass waveguide chips, achieving fiber-to-fiber total insertion losses below 6dB in some cases, through the use of grayscale tapers that are written directly into the poly(F-SBOC) material.

Metal-printing tunable interlayer waveguide coupler using low-loss fluorinated polycarbonate.

Tunable three-dimensional (3D) integrated optical waveguide chips with optical interconnection function are beneficial to expand the application of optical devices in a 3D integrated photonic module. Here, we propose a thermo-optic (TO) tunable interlayer waveguide coupler based on the metal-printing technique. Low-loss fluorinated polycarbonate (AF-Ali-PC MA) and poly (methyl methacrylate-glycidyl methacrylate) [P(MMA-co-GMA)] are synthesized as waveguide core and cladding layer, respectively. The thermal stability and optical adsorption characteristics of AF-Ali-PC MA are analyzed. Optical signal transmission features of the interlayer coupling waveguides are simulated. The optical response properties and fabrication process flows of a dynamic multilayer waveguide chip can be greatly improved by the metal-printing technique. The on-off time of the TO interlayer coupling chip is obtained as 250 µs, and the electrical power consumption is measured as 7.6 mW. To the best of our knowledge, this is the first time that a TO tunable interlayer waveguide coupler is achieved by an efficient metal-printing method, which is suitable for large-scale photonic integrated circuit (PIC) systems and multilayer optical interconnection (OXC) networks.

Interlayer directional coupling thermo-optic waveguide switches based on functionalized epoxy-crosslinking polymers

In this study, interlayer directional coupling (DC) thermo-optic (TO) waveguide switches were designed and fabricated using functionalized epoxy-crosslinking polymers. Fluorinated SU-8 (FSU-8) with a photo-initiating epoxy-crosslinking network was self-synthesized as a waveguide core material. A copolymer of methyl methacrylate and glycidyl methacrylate P(MMA-co-GMA) with a thermo-initiating epoxy crosslinking structure was self-synthesized as a waveguide cladding material. Compared with commercial pure SU-8 and PMMA, FSU-8 exhibited a lower absorption loss and P(MMA-co-GMA) exhibited a higher thermal stability. Using epoxy-crosslinking functionalized polymers, the structure of the waveguides and electrode heaters were optimized, and the performance parameters of the interlayer DC TO switches were simulated. At a signal wavelength of 1550 nm, the insertion loss, extinction ratio, and power consumption of the actual interlayer devices were measured as 6.7 dB, 15.6 dB, and 9 mW, respectively. The rising and falling response times of the TO switches were obtained as 631.6 µs and 362 µs, respectively. The self-leveling ability and solvent resistance characteristic of the epoxy-crosslinking network for FSU-8 and P(MMA-co-GMA) may guarantee the realization of interlayer DC TO waveguide switches. The proposed technique will be suitable for photonic integrated waveguide chips with multilayer stacking dynamic optical information interactions.

90°-bent graded-index core polymer waveguide for a high-bandwidth-density VCSEL-based optical engine.

In this paper, we present a low-loss optical assembly utilizing a 90°-bent graded-index (GI) core polymer optical waveguide on vertical cavity surface emitting laser (VCSEL) based optical transceivers. The proposed assembly can replace conventional components such as mirrors and lenses for realizing subminiature optical engines applicable to on-board integration. To minimize the total insertion loss of the waveguide when connected to a high-speed VCSEL and a GI-core multimode fiber (MMF) at each end, the characteristics of the beam emitted from VCSELs are measured and taken into consideration for the waveguide design. In order to confirm the effect of insertion loss reduction by the waveguide numerical aperture control, 90°-bent GI-core polymer waveguides are fabricated applying the Mosquito method. The fabricated waveguide exhibits a total insertion loss as low as about 2 dB at 850-nm wavelength, which includes the coupling losses at both ends, bending, and propagation losses. We also investigate a way to reduce the insertion loss when a gap exists between the waveguide and VCSEL chip. We theoretically and experimentally confirm that filling the gap with a high index resin can reduce the coupling loss by 5 dB.

High precision integrated photonic thermometry enabled by a transfer printed diamond resonator on GaN waveguide chip.

We demonstrate a dual-material integrated photonic thermometer, fabricated by high accuracy micro-transfer printing. A freestanding diamond micro-disk resonator is printed in close proximity to a gallium nitride on a sapphire racetrack resonator, and respective loaded Q factors of 9.1 × 104 and 2.9 × 104 are measured. We show that by using two independent wide-bandgap materials, tracking the thermally induced shifts in multiple resonances, and using optimized curve fitting tools the measurement error can be reduced to 9.2 mK. Finally, for the GaN, in a continuous acquisition measurement we record an improvement in minimum Allan variance, occurring at an averaging time four times greater than a comparative silicon device, indicating better performance over longer time scales.