This PDF file contains the front matter associated with SPIE Proceedings Volume 12424, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

We present a low propagation loss aluminium oxide integrated photonics platform enabling applications with operation down to the UV wavelength range (i.e., <250 nm). Single mode fully etched waveguides were fabricated with losses below 2 dB/cm at 405 nm. The influence of waveguide dimensions on the propagation losses are presented, indicating that losses are sidewall roughness limited. Lower losses can be achieved by further optimization of the cross-section of the waveguides. In this presentation, the aluminium oxide platform will be introduced together with the characterization of the waveguides at near-UV wavelengths.

Photonic integrated circuits (PICs) have experienced an exponential growth in a number of applications, including telecom/datacom, LiDAR, optical sensing/metrology and quantum technology. Most materials and platforms commonly used in integrated photonics, such as silicon-on-insulator (SOI), silicon nitride (Si₃N₄) and indium phosphide (InP) do not show transmission below ~400 nm, hindering the development of PICs operating in the ultraviolet wavelength range. Furthermore, devices in this wavelength range also require fast modulation and switching in order to enable complex emerging applications. Aluminum nitride (AlN) is a material with a band gap of 6.2 eV, exhibiting a wide transparency window, from the ultraviolet to the mid-infrared. AlN has the capacity to achieve high electro-optic[1], non-linear[2] and piezo-electric[3,4] coefficients, which makes AlN an interesting material for PICs with operation down to the ultraviolet wavelength range. However, high losses have prevented PICs from benefiting from its excellent optical properties. In this work, we present our work on the sputter deposition of low-loss AlN slab waveguides. The optical performance of AlN sputtered slab waveguides after annealing at different temperatures and their relation with the film morphology will be discussed. Preliminary slab propagation losses as low as 1.5 dB/cm at 633 nm of wavelength have been demonstrated.

We describe a prototyping process for silicon nitride photonic integrated circuits, targeting applications in the visible and near-infrared wavelength ranges. The platform is based on direct-write electron beam lithography technology and provides a route toward the rapid fabrication of passive and thermo-optic active photonic devices. The fabrication turnaround time is on the order of several weeks, and critical feature sizes are demonstrated down to 100 nm which enables the fabrication of subwavelength metastructures. Two waveguiding material thicknesses have been demonstrated, 150 nm for visible light applications and 400 nm for infrared.

Integrated optomechanical cavities allow precise control of optical and mechanical modes and enable strong photonphonon interactions in micron-scale volume, key for the implementation of microwave-photonic oscillators and quantum transducers. Silicon photonics provides low production cost and compatibility with the state-of-art optoelectronic circuitry. Thus, it is particularly interesting for the implementation of on-chip optomechanics. However, silicon has higher stiffness and acoustic velocity than the silica cladding, hampering phonon confinement in silicon-on-insulator (SOI) waveguides. Here, we present our most recent results on SOI optomechanical systems coupling mechanical and guided optical modes. The cavities use silicon pillars with subwavelength period. Strong radiation pressure is exploited to drive the optomechanical coupling. Based on this concept, we experimentally demonstrate the optomechanical coupling between photons and high-quality factor phonons in non-suspended cavities, with a great potential for applications in quantum and classical photonics.

We present advanced photonic architectures based on a state-of-the-art silica-on-silicon planar lightwave circuit (PLC) platform. The industry-leading performance characteristics of the platform with respect to fiber coupling, propagation losses, and polarization control have led to its mass deployments in telecom and datacom applications. Recently, a broad range of architectures has emerged that take advantage of the unmatched phase control in silica-on-silicon PLCs for demanding applications. We review some exceptional capabilities of our PLC platform and discuss how ultra-low propagation loss of <0.009 dB/cm is achieved concurrently with polarization-insensitive operation with relatively high confinement that allows loss-free waveguide bends with a 1 mm radius of curvature. Combined with fiber-matched mode converters and temperature-stable operation (< 10 pm/°C), consistent performance is achieved across entire optical communication bands. End-to-end optimizations allow us to reach high performance in advanced optical building blocks such as cascaded lattice filters, polarization-beam splitters, arrayed waveguide gratings (AWGs), and coherent systems. The robustness and versatility of the platform are demonstrated by a survey of mature designs that encompass multiple classes of applications. We discuss multi-channel (de-)multiplexer designs that address the challenging requirements of today’s datacom and telecom deployments, the realization of 10+ meter long delay lines and K-clocks, the utilization of the platform in optical coherence tomography (OCT) systems, and PLC-based solutions for automotive manufacturers of LiDAR systems. Finally, we discuss how our design, manufacturing, and testing processes are controlled with machine learning, allowing in-situ monitoring of wafer fabrication, real-time process adjustments, and wafer-level predictions of device performance across a wide range of performance metrics.

Silicon photonic (SiPho) platforms hold vast potential for providing multi-functional processing capabilities, such as filtering, mode-handling, modulation, etc. Structures for polarization manipulation have become essential elements to enhance channel capacity and to facilitate polarization multiplexing functions. Therefore, 1x2 polarization beam splitters (PBS) are introduced as polarization-division key building blocks based on a silicon-on-insulator (SOI) platform for separating/combining the fundamental modes. By cascading three bent directional couplers (DC), high-performance coupling characteristics can be obtained similar to those of asymmetric ones. A first-ever integration of this kind of PBS has been achieved utilizing Tower Semiconductor's PH18MA silicon photonics platform, which offers 180 nm SOI process technology. In this work, both output ports of the proposed PBS are being tested for polarization filtering across a polarization sweep. The advanced features of this integration process pave the way for next-generation coherent transceivers and aim to meet future optical interconnecting requirements. Furthermore, Synopsys OptoCompiler and the Photonic IC Design Flow, featured in Tower’s process design kit (PDK), were used to design the devices.

The power-sensitive photo-thermal tuning (PTT) of two-dimensional (2D) graphene oxide (GO) integrated on the top surface of silicon nitride (SiN) waveguides is experimentally investigated. For SiN waveguide coating with monolayer GO, the light power thresholds for reversible and permanent GO reduction are measured. There are three reduction stages identified based on the presence of reversible versus permanent reduction. We also compared the PTT induced by a continuous-wave laser and a pulsed laser with the same average power, confirming that the PTT is primarily determined by the average input power.

We demonstrate a novel spectrometer based on a hybrid guided wave and free-space optical system, consisting of a silicon nitride optical phased array (OPA), free-space grating couplers, and Fourier-space imaging to an image sensor. Each wavelength dispersed by the photonic integrated circuit corresponds to a unique position in the Fourier plane. We demonstrate the reconstruction of a spectrum in the near-infrared from the position and the intensity in this plane. From preliminary measurements on a small-sized OPA (0.1 mm²), we report a spectral range of 100 nm and a resolution of around 0.5 nm.

In this paper, we present the development of a miniaturized Laser Doppler Vibrometer (LDV) system, based on the 3D hybrid integration of the Si3N4 platform of LioniX (TriPleX) and the polymer platform of FhG-HHI (PolyBoard). The photonic integrated circuit (PIC) supports all the functionalities of an LDV system including the splitting of the input light to the measurement and the reference beam, the introduction of an optical frequency shift up to 100 kHz, polarization handling and detection of the reflected measurement beam, using a heterodyne detection technique. The optical frequency shift is accommodated in the TriPleX section of the PIC based on a simple serrodyne scheme, where a phase modulator is driven with a sawtooth signal with the desired frequency. The modulation of the optical field is based on the stress-optic effect utilizing thin-films of PZT deposited on top of the waveguide structures of the TriPleX platform, capable of supporting modulation frequencies up to several MHz. The PolyBoard part enables polarization handling and heterodyne detection of the reflected beam using micro-optic elements on chip, including a polarization beam splitter (PBS), a half wave plate (HWP), and a pair of balanced detectors with four photodiodes that are flip chip bonded on the top. The TriPleX and the PolyBoard platform were brought together based on the 3D hybrid integration, using mode size converters and vertical directional couplers with coupling losses lower than 15 dB. On-chip beating, using the integrated photodiodes is experimentally demonstrated.

Photonic Integrated Circuits (PIC) are best known for their important role in the telecommunication sector, e.g. high speed communication devices in data centers. However, PIC also hold the promise for innovation in sectors like life science, medicine, sensing, automotive etc. The past two decades have seen efforts of utilizing PIC to enhance the performance of instrumentation for astronomical telescopes, perhaps the most spectacular example being the integrated optics beam combiner for the interferometer GRAVITY at the ESO Very Large Telescope. This instrument has enabled observations of the supermassive black hole in the center of the Milky Way at unprecedented angular resolution, eventually leading to the Nobel Price for Physics in 2020. Several groups worldwide are actively engaged in the emerging field of astrophotonics research, amongst them the innoFSPEC Center in Potsdam, Germany. We present results for a number of applications developed at innoFSPEC, notably PIC for integrated photonic spectrographs on the basis of arrayed waveguide gratings and the PAWS demonstrator (Potsdam Arrayed Waveguide Spectrograph), PIC-based ring resonators in astronomical frequency combs for precision wavelength calibration, discrete beam combiners (DBC) for large astronomical interferometers, as well as aperiodic fiber Bragg gratings for complex astronomical filters and their possible derivatives in PIC.

Recent developments in computational inverse design offer the promise of significantly reducing the footprint and allowing complex optical functionality in silicon photonic components as compared to existing conventional building blocks. However, reliable fabrication of such components is one of the major bottlenecks in its widespread adoption. A common characteristic of such designs is the presence of small features that have meaningful impact on the optical performance. Current approaches to tackle this problem consider designing for robustness, such as by co-optimizing for over- and under-etched geometries at the design stage. This is often followed with a design-for-manufacturing optimization step to meet specifications of a foundry such as minimum feature size and curvature radii. Those approaches often incur additional significant computational costs as well as a reduction in peak optical performance. In this work, we highlight our recent progress to bridge the gap between inverse design methods and their ability to deliver reliable and manufacturable designs. We observe that the so-called parameterized shape optimization methods are more likely to produce robust designs for certain classes of components, as showcased in integrated mode converter designs. For components that benefit from topological inverse design such as wavelength demultiplexers, we propose a new optimization penalty that naturally leads the optimizer towards more robust designs. In a new research direction, we also consider improving fabrication reliability by the development and use of data-driven predictive models for fabrication. Leveraging deep learning tools, we present prediction and correction models that improve fabrication outcomes for a variety of components made at an e-beam prototyping foundry.

In this work we explain the methodology and techniques for building an end-to-end design enablement (DE) platform from component design to process design kit (PDK) release for silicon photonics-based photonic integrated circuit (PIC) design. Elements of the DE include: component design, layout and test site development, measurement infrastructure and PDK development. Our methodology builds on the best practices followed in CMOS and RF foundries but adds unique features specific to silicon photonics. The DE flow is developed on the American Institute for Manufacturing Integrated Photonics’ (AIM Photonics) 300 mm silicon photonic technologies manufactured in a limited-volume foundry at the Albany Nanotech Complex, in Albany, NY. For component development, the AIM Photonics PDK offers a process stack file supported in Lumerical platform that applies linewidth corrections and doping information to imported layouts increasing the efficiency and accuracy of the design. For test sites, an automated layout and connectivity framework is explained that allows users to generate a layout from spreadsheet inputs that is also compatible with automated waferscale measurements. AIM Photonics PDKs include layout, models and design-rule-check (DRC) tools that are offered across multiple platforms. The DRC decks are offered in commercial tools such as Cadence and Synopsys, as well as KLayout. We present features of layouts and communication with schematics. In addition, we also explain techniques for processing and analyzing measured statistical data and extracting platform specific compact models. Presenting this methodology to the wider community is integral to the mission of AIM Photonics and will be of immense benefit particularly to small organizations engaged in prototype development.

We demonstrate integrated distributed Bragg reflector lasers on a hybrid platform composed of silicon nitride waveguides coated with erbium-doped tellurium dioxide. The asymmetrical laser cavities are enclosed by gratings patterned on the 2.2-cm-long waveguide walls. Cavities with varying grating strengths are studied, yielding laser efficiencies up to 0.36%, a minimum lasing threshold of 13 mW, and emission wavelengths between 1530 and 1565 nm.

Terahertz applications have been extensively studied during the last decade since they allow not only increasing the bandwidth of telecom systems but also the detection of many organic molecules in solid and liquid phase, including hazardous materials such as explosives. In this contribution, we present a device that allows generating frequencies in the Terahertz domain through the heterodyning of signals emitted by two distributed feedback lasers made by ion exchange on a erbium-ytterbium co-doped glass. Thanks to the intrinsic thermal stability of the glass substrate, the slow dynamic of the amplifier medium and since the laser pairs are integrated on a single chip and identically pumped by the same sources, stable frequencies have been generated in the millimeter and sub-Terahertz frequency range, without any thermal or electrical control loop being implemented.

We have developed a compact PIC external cavity laser consisting of a hybrid integrated InP gain section and SiN tunable mirror, with a superior combination of characteristics. The laser has shown a narrow linewidth < 5 kHz, broad tuning range of 140 nm over the S-, C- and L- band, from 1473 nm to 1612 nm, and high single mode output power of 60 mW. The laser frequency can be modulated at frequencies < 10 MHz having a wavelength modulation depth of < 20 MHz.

Optical frequency combs based on broadband-gain bulk lasers, due to the low intrinsic linewidth and sub-GHz repetition rates, have gained tremendous interest for applications such as high-resolution spectroscopy, dual-comb spectroscopy or LIDAR. However, susceptibility to mechanical and acoustic perturbations, the complexity of optical pumping and the larger physical size of these lasers has motivated research toward chip-based integrated extended cavity diode lasers with low-loss Si₃N₄ waveguide feedback circuits for low repetition rates. In diode lasers, mode-locking via saturable absorbers is generally used for generating frequency combs, however, the short upper-state carrier lifetime results in repetition rates of at least a few GHz. Here, we demonstrate absorber-free, passive mode-locking as well as hybrid mode-locking at sub-GHz repetition rates using a long Si₃N₄ feedback circuit with three highly frequency-selective microring resonators for extending the cavity roundtrip length to more than 0.6 m. This enables frequency-domain mode-locking in the form of a continuous wave, with a line spacing of around 500 MHz. Hybrid mode-locking, in addition to passive mode-locking, is demonstrated by adding a weak AC drive current with a frequency close to 500 MHz. This stabilizes the repetition rate and reduces the Gaussian component of the laser’s RF linewidth attaining a negligible Lorentzian component. Our numerical simulations predict that further lowering of the repetition rate and line spacings might be achievable with further cavity length extension.

Atomic ions controlled by laser light are among the leading candidates for large scale quantum computing. However operational systems today require vast scaling to reach levels capable of useful computational tasks. The integration of light delivery will be an essential component of this for the trapped-ion approach. I will describe results in which the use of photonics integrated into ion trap chips has allowed us to perform high fidelity two-qubit gates, which are an essential building block for quantum computers. These systems have now been extended to the operation of multiple trap zones, and the creation of novel optical fields for ion trap control while a new generation of chips allowing integration of all required wavelengths as well as optimised light delivery offers further enhancements in performance and scaling.

Quantum technologies and optical sensors with ultimate sensitivity require efficient counting of single photons. Superconducting nanowire single-photon detectors have set leading performance benchmarks in this regard but evolving from stand-alone fiber-coupled detectors to highly integrated receivers with large numbers of photonic channels and configurable optical functionalities has remained a challenge. Here we show how large numbers of superconducting nanowire single-photon detectors with high detection efficiency and low timing jitter can be integrated with nanophotonic circuits. The latter allow for combining photon counting capabilities of superconducting nanowires with active and passive optical control functionalities, such as switching, phase shifting and photon number resolution, which we demonstrate for leading photonic integrated circuit platforms. Broadband optical interconnects produced in 3D direct laser writing enable competitive system detection efficiency, which we can reproduce in a receiver unit that integrates 64 individually addressable superconducting nanowire single-photon detectors. We show that the system is well-suited for massively parallelized quantum key distribution, achieving secret key generation rates beyond 10 Mbit/sec in a field test. Integrating large numbers of superconducting nanowire single photon detectors with optical waveguides on configurable nanophotonic chips offers a wide range of applications in quantum communication, information processing and sensing.

Artificial neural networks have been a major driving force in a wide variety of technologies from pattern recognition and natural language reprocessing to medical diagnosis. Neural networks can be trained to perform a certain set of tasks and are typically formed by the interconnection of multiple layers of neurons to perform linear and nonlinear computations. Highly reconfigurable clock-based digital signal processors have been the main hardware platform to implement such networks. However, clock frequency and memory access time are two main contributors in limiting the processing speed. Integrated photonics benefits from the large available bandwidth at optical frequencies and low-loss interconnects, and has proved to be a promising candidate to address the challenges of electronic systems. Most of the demonstrated photonic neural networks have been either using bench-top setups, or the partial integration of some of the linear and/or nonlinear computation blocks. A scalable solution that can integrate all computation blocks has been an open problem. Here, we demonstrate the first end-to-end photonic deep neural network (PDNN) for direct image classification. On-chip image formation of the target object using a 2D array of grating couplers and direct processing of the received optical signals through linear (optical) and nonlinear (opto-electronic) computation, enable an end-to-end classification time of 570 ps. Using a uniformly distributed supply light enables scaling the PDNN to networks with more layers of neurons. The PDNN chip is used to demonstrate classification of 2- and 4-class datasets of handwritten letters and the system achieves accuracies higher than 93.8% and 89.8%, respectively.

Convolution Neural Networks have raised as the key technology for most of the novel applications that appear in the last years. Convolution, the main operation that CNN has to perform, has a high computational cost, raising power consumption and latency, especially for large matrices. Optics and photonics can perform the same operation at virtual O(1) cost and speed-of-light latency, thanks to the properties of Fourier optics. In this paper, we will show the implementation of the main components and the modeling for non-idealities that might occur.

Integrated optics has shown itself very convenient for exploiting nonlinear processes as it results in high confinement factor, freedom of dispersion engineering and compactness. However, the choice of materials is crucial for the development of nonlinear systems. Ideally, one looks for a platform that offers high second and/or third order nonlinearities, low loss and ease of fabrication. Silicon nitride (Si3N4) is now proven to be a good platform for frequency conversion based on third order nonlinearity. Supercontinuum generation (SCG) was obtained in the near-IR and mid-IR regions by pumping waveguides with common fiber lasers. It resulted in broadband coherent combs extending in the mid-IR thanks to dispersive wave generation. Yet, Si₃N₄ does not exhibit any second order nonlinearity desirable for comb self-referencing via second-harmonic generation (SHG). On the other hand, lithium niobate (LiNbO3) is widely used in integrated photonics for second order nonlinear processes. In our work, we exploit a hybrid Si₃N₄-LiNbO₃ photonic integrated platform that combines maturity and dispersion engineering capabilities of Si₃N₄ integrated photonics with second-order nonlinear properties of LiNbO₃ bypassing challenging lithium niobate etching. We study numerically and experimentally the potential of SCG and SHG for frequency comb self-referencing on this platform when pumping with a fiber laser operating at 2 μm for mid-IR operation, a window useful for sensing as it contains many molecular signatures.

The interest in integrated photonic processors is growing rapidly, with the perspective of the realization of devices capable to provide single photon qubits for efficient and scalable quantum computation. While the on-chip single photon manipulation is well developed in quantum photonics circuits, the integration of photon generation and photon detection stages on the same chip is currently far from being established. In this work we present a potentially scalable, integrated source of near-infrared photon pairs based on ring resonators, realized with dispersion-engineered silicon oxynitride waveguides. The use of high-index silicon oxynitride as core material gives the possibility to engineer the optical properties of waveguides by adapting the ratio between oxygen and nitrogen gases in the deposition chamber and allows the realization of films with thicknesses over 500nm without the formation of cracks. An efficient photon generation process via nonlinear Four-Wave-Mixing (FWM) in a ring resonator requires a zero group-velocity-dispersion in order to have energy equidistant resonances. Here we show that, while it is almost impossible to achieve such a condition with oxide-cladded SiON waveguides, the zero-dispersion-point in the red and near-infrared wavelengths can be engineered if the waveguides are in direct contact with air. This can be achieved through a selective removal of the top oxide cladding from the ring resonators by the means of wet chemical etching and a silicon nitride etch-stop layer. We show that the realized devices are characterized by a constant Free Spectral Range at the engineered wavelengths and are thus feasible devices for nonlinear photon generation via FWM.

Self-phase modulation (SPM) is an important third-order nonlinear optical process that has been widely used in many applications, such as broadband optical sources, optical diodes, optical spectroscopy, pulse compression, and many others. The ability to realize SPM based on-chip integrated photonic devices will reap attractive benefits of compact footprint, high stability, high scalability, and low-cost mass production. Here, we experimentally investigate enhanced SPM in silicon nitride (Si3N4) waveguides by integrating with 2D graphene oxide (GO) films. The on-chip integration of GO films is achieved on Si3N4 waveguides through a solution-based, transfer-free, layer-by-layer coating method with precise control of the film thickness. We use both picosecond and femtosecond optical pulses to perform detailed SPM measurements. Owing to the high Kerr nonlinearity of GO, the GO-coated waveguides show significantly improved spectral broadening for both the picosecond and femtosecond optical pulses compared to the uncoated waveguide, achieving a broadening factor of up to ~3.4 for a device with 2 layers of GO. Based on the experimental results which show good agreement with theory, we obtain an improvement in the waveguide nonlinear parameter by a factor of up to 18.4 and a Kerr coefficient (n2) of GO that is about 5 orders of magnitude higher than Si3N4. These results reveal the effectiveness of 2D GO films to improve the nonlinear performance of Si3N4 waveguides.

Photonic integrated circuits (PIC) have been established for miniaturized, on-chip optical systems. Current approaches for producing PICs mostly rely on semiconductor processing technologies, which are complex and costintensive. A promising alternative with the potential to revolutionize PIC fabrication is additive manufacturing (AM), which offers the opportunity to develop tailored and customized waveguide designs for functionalities needed in fast-evolving modern applications like the Internet of Things. Here, an AM technology called laser glass deposition (LGD) is presented for the production of on-chip core-cladding waveguides based on fused silica. Commercially available glass fibers with a diameter of 125 μm are fused onto a quartz glass substrate using a CO2-laser in a 2.5D-printing process. Test series are performed to determine the process window to reach a stable connection between fiber and substrate while maintaining the fiber´s optical functionality. To enable efficient light coupling into the waveguide, the fiber end facets are laser cleaved after the deposition within the same process environment. Again, parameter studies are performed to reach a high surface quality. Both the waveguides and the cleaved surfaces are characterized using different imaging techniques. In addition, the optical properties of the generated waveguides are analyzed.

Photonic wire bonding is a disruptive technology that solves the problem of efficiently coupling light between best-inbreed integrated photonic chips, providing insertion losses unattainable with other hybrid integration techniques. Enabled by advances in machine vision technology, photonic wire bonding uses two-photon polymerization to print a waveguide with arbitrary 3D geometry for connecting dissimilar integrated waveguides. Unlike butt-coupling hybrid integration approaches, specialized waveguide edge couplers and precise alignment between chips are not required since the photonic wire bond (PWB) is customized to a given pair of waveguides. The machine vision system detects the onchip waveguide facet locations and orientations for accurate placement of the PWB. Mode converters in the PWB efficiently transition light between the dissimilar optical spatial modes. Other hybrid integration approaches, including butt-coupling, flip-chip bonding, direct wafer bonding, and heteroepitaxy cannot achieve comparable insertion losses and are limited in their applicability and throughput. Freedom Photonics (a Luminar company) has demonstrated worldclass coupling losses between best-in-breed photonic platforms using a photonic wire bonding tool from Vanguard Automation. In this paper, we present photonic wire bond results between high performance semiconductor lasers and silicon nitride and lithium niobate waveguides as well as opportunities for prototyping of next generation, highly integrated photonic sub-assemblies.

High performance photonic gyroscope microchips need ring resonators with high quality factors and low loss waveguides for enhanced accuracy. The industry trend is toward thin ring resonators with thick cladding layers above and below the waveguides. Thick cladding layers are typically required to ensure that the guided light’s fields extending out from the waveguide are negligible before reaching any lossy material beyond the cladding layers. Otherwise, a significant portion of the field would be attenuated by the lossy material, thereby increasing the waveguide’s overall propagation losses. However, thick cladding layers are undesirable from a process cost standpoint. We show that cavities etched below waveguides facilitate much thinner bottom cladding without increasing waveguide propagation losses. Commercial software computed the light within 100 nm thick and 40 nm thick waveguide designs as a function of their bottom cladding thickness. These simulations show that, with the underlying cavities, a 2 μm thick bottom cladding layer sufficiently confines the 100 nm thick waveguide’s light. In the case of the 40 nm thick waveguide, this minimum cladding thickness was 3 μm. With these cavities, conventional bottom cladding thicknesses, normally 8 μm and 15 μm, respectively, are no longer necessary. 100 nm thick Si₃N₄ waveguides with 3 μm thick SiO₂ bottom cladding layers were then fabricated, with and without cavities, alongside horizontally coupled coplanar ring resonators. Characterization of the fabricated structures show that the cavities reduce waveguide loss and improve ring resonator quality factor by a factor of three.

It is well known that interferometers make great sensors. This is because phase is a magnitude that can be measured with very accurate precision and with a great dynamic range at the same time. Integrating these devices on a chip is very appealing because it can make the device much smaller, lighter, and affordable. However, this technology also poses some challenges, which can degrade performance with respect to free-space or fiber-based devices. In this work we overview these challenges and possible strategies to tackle them.

Integrated photonics on glass offers advantages for sensing applications because of its relative low cost and its detection sensitivity. In this paper we discuss the design, fabrication and characterization of a micro device for sorting and sensing dielectric microparticles. The target application is the analysis of bacteria used as sentinel for water pollution. The sorting function, that does not include any functionalization layer, is done by means of dielectrophoretic forces. They are induced by castellated electrodes fed by a low frequency electric signal. The sensing function is obtained by a surface waveguide that is perturbed by the particles collected on top of it by dielectrophoresis. We first discuss the co-integration of the castellated electrodes with an optical waveguide. An efficient interaction of polystyrene beads with the guided light (up to 50% of intensity modulation) is then simulated and observed experimentally. We also showed that this multiphysics device can be used as a sensor, presenting curves of the intensity modulation depending on the concentration of beads. The attenuation in the optical signal varies between 2 and 5 dB with particle concentrations ranging from 136 to 455 beads per μL in the analyte.

In this work, we demonstrate a cascaded ring resonator based wide stop-band filter. The filter consists of four cascaded rings and a bus waveguide. The first ring has a radius of 7μm, the second, third and the fourth rings have radius of 7.01 μm, 7.02 μm, and 7.03 μm, respectively. The radius varion is designed for a small shift of resonant wavelength so that the combined resonance effect of four ring resonators exhibits a wide stop-band filter function compare to a single ring resonator. Both the bus and ring waveguides have a width of 480 nm. The thickness of the waveguides were 220 nm which is a standard silicon-on-insulator (SOI) wafer available in the market. A 100-nm gap is designed between the ring and the bus waveguide to provide optimum filtering. The device is fabricated using the American Institute for Manufacturing integrated Photonics (AIM Photonics) 300mm Multi-Project Wafer (MPW) service. It is tested using the AIM Photonics inline vertical grating coupled automated measurement tool with a tunable light source that has wavelengths ranging from 1485 nm to 1590 nm and a wavelength resolution of 60 pm. The fabricated cascaded ring filter exhibits a 3-dB stop-band about 6 nm wide with an extinction ratio of ~30 dB in across the S, C and L-bands. It is noted that the desired width of the stop-band is achievable by cascading required number of rings with slight radius variation.

Self-written waveguides (SWWs) are established as interconnection between different optical elements. They enable a rigid and easy-to-manufacture low-loss optical connection, which can be employed in many optical configurations. For the writing process, a UV-curable monomer is applied in between the two optical elements which need to be connected. If UV- or near-UV light is applied through on of the elements (i.e. fiber), the monomer starts to polymerize and increases the refractive index locally leading to a self-trapping of the beam. Subsequently, the surrounding resin can be cured with UV-flood exposure to create a rigid connection between the two components. In recent works we demonstrated that SWWs can also be used as sensing elements. Hereby, the behavior of the SWW during the heating process itself was used for measuring of changes of the temperature. Another approach is the combination of SWWs with Fe(II)triazol-complexes to detect different physical parameters such as electric and magnetic fields or temperature and humidity changes, respectively. We also investigated the implementation of thin-film filters for splitting of an SWW in multiple beams, enabling us to create a reference and sensing arm for versatily measurement applications.

Surface gratings are key devices on photonic chips to enable a free-space light coupling or chip interfacing with optical fibers. These elements can be employed in a variety of applications, ranging from optical interconnects and sensing, to light detection and ranging (LIDARs) and free-space communications. For LIDARs and free-space communications, dualpolarization gratings are important in modern optical phased arrays. However, surface gratings in silicon photonics are intrinsically polarization-sensitive due to the strong geometrical birefringence of the waveguides. In this work, we present a design of polarization-insensitive photonic nano-antennas in the silicon-on-insulator (SOI) platform. The proposed antennas have a L-shaped radiating profile with sub-wavelength metamaterials to simultaneously provide polarization independence and high radiation efficiency. The optical antennas are designed on a 300 nm thick SOI with a 3 μm thick buried oxide layer. The antenna has a compact footprint of 6.5 μm x 3.18 μm and critical dimensions larger than 50 nm, which are feasible for public silicon-foundry processing and fabrication. At the nominal wavelength of 1.55 μm, the antennas have a radiation efficiency of 50% and 21% for the TE and TM polarized light, with emission angles of -17° and -21°, respectively. Polarization-independent nano-antennas in mature SOI platform offer great potential for multi-element photonic circuits required by LIDARs and free-space communications.

Silicon photonics offers platforms to build mass-producible optical circuits. Extremely small optical components are required for this purpose, so fiber coupled systems are an order of magnitude too large. In order to successfully integrate laser source to the circuits, output beam properties have to be controlled and desired for the purpose. When fabricating single-mode ridge waveguide (RWG) laser diodes, ridge width has to be narrow enough for ensuring single-mode operation. When designing RWG device, one must take also electrical properties and catastrophic optical damage into account – narrow ridges tend to have higher series resistance values and are more prone to COD in low output powers than wide ridges. However, having too wide ridge for a wavelength, RWG starts to support multiple modes. In this work, we have experimentally found a way to utilize 2-step etching to alter the output beam horizontal far-field values of originally nominally identical ridge width devices. By being able to alter the output beam shape, coupling of the laser beams to different photonic integrated circuits can be done based on the circuit, not the laser. Correlation between ridge sidewall angle and horizontal beam width is presented with experimental data. By altering the angle, the ridge can become effectively wider than it physically is, meaning advantages such as low series resistance can be achieved as well as higher COD levels. We present implementing the method for 6XX nm region laser diode source.

Based on commonly used dielectric materials in Si processing platforms, multiple-layer anti-reflection stacks were designed and fabricated, with the main goal of highly efficient light coupling for Si waveguides over a wide wavelength range. Initial characterization results indicate that a <-20dB light reflection was successfully achieved over 1310-1550 nm wavelength range over the whole 150mm wafer. The fluctuation of reflection spectra over the whole wafer was observed to be only 1-2 dB, which guarantees the high yield and mass production capabilities for further applications.

We report experimental measurements of optical loss and n₂ nonlinearity in two possible InP-based mid-IR waveguiding platforms with waveguide cores made of In_0.53Ga_0.47As and GaAs_0.51Sb_0.49, both lattice-matched and grown on InP. We report the first broadband (5-11 μm) characterization and optimization of optical losses within InP/InGaAs and InP/GaAsSb based waveguides with losses as low as 0.5 dB/cm at shorter wavelengths and 4-5 dB/cm at longer wavelengths of this wavelength range. In addition, we measure the values of Kerr nonlinearity in these waveguides to be approximately an order of magnitude higher than that reported for Si- and SiGe-based waveguides in mid-IR.

3D printed rib waveguides were demonstrated with dimensions from 11 to 30 μm wide, 5 to 31 μm tall and had ribs between <500 nm and 11 μm tall. The structures were made using a custom stereolithography 3D printer and a formulated hydrogel resin with UV light exposures of one second. The waveguides were characterized using the cutback method and showed losses of 1.0 to 1.6 cm^-1 and coupling coefficients of <0.9. This demonstrates a very quick and inexpensive method to fabricate planar rib waveguides without the need for a cleanroom and promising for more complex integrated devices.

Molecules have ‘fingerprint’ absorptions in the mid-infrared, enabling their identification via infrared spectroscopy. For applications beyond the lab, such as medical diagnosis, fully integrated mid-infrared spectroscopy on chip would be ideal. Germanium offers low absorption in the mid-IR, making it an ideal candidate for waveguides for mid-IR spectroscopy via the evanescent field. Amorphous germanium could offer a low-cost fabrication route; our work compares methods to deposit amorphous germanium films via RF sputtering, e-beam evaporation and plasma-enhanced chemical vapour deposition (PECVD). In addition to standard germanium waveguides produced by etching a germanium film, an alternative manufacturing method is proposed, where silicon is etched to form pedestals, followed by deposition of amorphous germanium to produce waveguides. Pedestal waveguides offer potential for single-mode operation across a broad wavelength range, making them a strong candidate for spectroscopy applications.

The benefits of photonics over electronics in the application of optical transceivers and both classical and quantum computing have been demonstrated over the past decades, especially in the ability to achieve high bandwidth, high interconnectivity, and low latency. Due to the high maturity of silicon photonics foundries, research on photonics devices such as silicon micro ring resonators (MRRs), Mach-Zehnder modulators (MZM), and photonic crystal (PC) resonators has attracted plenty of attention. Among these photonic devices, silicon MRRs using carrier depletion effects in p-n junctions represent optical switches manufacturable in the most compact magnitude at high volume with demonstrated switching energies ~5.2fJ/bit. In matrix multiplication demonstrated with integrated photonics, one approach is to couple one bus straight waveguide to several MRRs with different resonant wavelengths to transport signals in different channels, corresponding to a matrix row or column. However, such architectures are potentially limited to ~30 MRRs in series, by the limited free-spectral range (FSR) of an individual MRR. We show that PC switches with sub-micron optical mode confinements can have a FSR <300nm, which can potentially enable energy efficient computing with larger matrices of ~200 resonators by multiplexing. In this paper, we present designs for an oxide-clad bus-coupled PC switch with 1dB insertion loss, 5dB extinction, and ~260aJ/bit switching energy by careful control of the cavity geometry as well as p-n junction doping. We also demonstrate that air-clad bus-coupled PC switches can operate with 1dB insertion loss, 3dB extinction, and ~80aJ/bit switching energy.

Exceptional points (EPs) in whispering-gallery-mode microresonators systems have attracted substantial attention due to their intriguing and anomalous optical characteristics. Recently, EPs have been experimentally observed in silicon microrings with coupling manipulation elements, such as an S-shaped waveguide and notch. In this paper, the observation of EP in a nanocylinder-loaded silicon microring is experimentally demonstrated. The device consists of a 5- μm microring with two nanocylinders placed close to the outer edge of the microring. By tailoring the size and position of the two nanocylinders, the fully asymmetric coupling between the clockwise- and counterclockwise-propagating modes occurs, leading to the implementation of EP. Experimentally, the spectral response is investigated by single-side excitation from clockwise and counter-clockwise directions. The reciprocal transmission and nonreciprocal reflection spectra are observed, which confirms the proposed device works in the vicinity of EP. The construction of EP in silicon microring paves the way to basic science and applied technology in non-Hermitian physics.

Germanium-on-Silicon (Ge-on-Si) platform has been demonstrated as an excellent candidate for mid-infrared photonics applications, including on-chip mid-infrared spectroscopy and biochemical sensing. However, this platform is often saddled by high propagation loss due to a combination of threading dislocation defects at the Ge/Si interface, absorption in the silicon for λ < 8 μm, and surface scattering due to sidewall roughness. This work investigates the effects on loss reduction through different annealing techniques on Ge-on-Si waveguides fabricated using CMOS-compatible processes. We explore the use of local laser annealing at waveguide sidewalls, whereby the fluence was varied. A non-local annealing technique in hydrogen ambient was also employed as comparison. The propagation losses for wavelengths, ranging from λ = 5 μm to λ = 11 μm, were systematically characterized by fabricating waveguide and grating coupler structures on the same chip. Cutback measurements were performed by varying the waveguide length (of the same width) from L = 1 mm to L = 4 mm. Both hydrogen and laser annealing experiments show marked reduction in the propagation loss, by up to 27% and 46% respectively. This finding paves the way for post-processing techniques to reduce propagation loss in Ge-on-Si platform, which will enable various on-chip mid-IR applications in the future.

We introduce an integrated Whispering Gallery Mode (WGM) resonator in reflection mode for sensing. The design includes a Deep Seated Negative Axicon (DSNA) embedded with WGM resonator. DSNA is fabricated in photosensitive optical fiber (GF4-A) by chemical etching. The reflected signal indicating Q factor ~6x10³ is achieved. The developed WGM resonator is used to sense Toluene with sensitivity of 1.73nm/RIU.

We demonstrate a sensing platform for composite manufacturing (RTM-6) process based on silicon photonics, being controlled by novel Process Monitoring Optimization Control (PMOC) system. The photonic multi-sensor is based on bragg grating components, allowing measurements of temperature, pressure and refractive index, and is packaged employing a ball lens fiber-to-chip interface. We present results of the packaged temperature photonic sensor regarding bandwidth, linearity and thermo-optic efficiency, being controlled by our PMOC system. We experimentally achieve 0.074 nm/C with R^2 = 0.995 linearity for temperature up to 180°C (RTM-6 compatible) with 1 kHz data acquisition and 0.2°C accuracy.

3D shape sensors find important applications in industries, e.g. structural health monitoring and medical technology. (Fiber-)Optical shape sensors possess various advantages such as miniature size, high sensitivity and low costs. Current challenges are the necessary increase of stability and reproducibility and the lack of application cases. We present a 3D shape sensor based on an ultra-thin glass (100 um) approach which allows both a stable and reproducible measurement. The 3D shape sensor presented here is part of the development of a novel and flexible X-ray detector, which serves as a practical application. Femtosecond laser pulses are used for the optical integration of both light waveguides and Bragg gratings into the ultra-thin glass. Bragg gratings serve as strain and ultimately curvature sensors (0 to 20/m) as they are integrated parallel to the neutral bending axis (20-30 um). The Bragg gratings are organized in a bi-directional network at known positions as all Bragg gratings can be integrated in a single step. The 3D shape sensor has to be calibrated only a single time as it can be mounted on and removed from surfaces without the need of a direct adhesion, resulting in easier integration and higher reproducibility as the neutral bending axis is not moved. A 3D reconstruction algorithm provides a 3D point cloud, which allows the calculation of the shape of the surface (here the detector surface). As the positions of Bragg gratings are well known, a more precise 3D shape recalculation is possible compared to fiber Bragg gratings.

In this work, we investigated the possibilities and limitations of using the arrayed waveguide grating structure in biosensing applications where the arrayed arms region of the structure has been used as a sensing region to maximize the sensitivity and selectivity of the biosensor. The biosensor design is generic and not specific to certain analyte/gas for sensing but rather based on justifying the principle of operation of the biosensor. Here, the concept of sensing is based on the slight change in the effective index of the sensing arms of the arrayed waveguides that happens due to the direct influence of the presence of analyte/gas on the evanescent field of the sensing optical element. The design of the arrayed waveguide grating is done based on silicon nitride (Si3N4) technology due to its transparency in the very near infrared domain which facilitates the operation of the biosensor in the very near-infrared domain where negligible water (in the case of using water as an analyte) absorption values are achievable. The arrayed waveguides region is designed to allow an upper enclosure containing the analyte flow in a chamber made of polydimethylsiloxane over all arms while preserving the additive phase on each arm. The presence of the analyte with an induced refractive indices leads to altering the output wavelength output ports order in the output free propagation region. The shift of the exit wavelengths from different ports is significant to the change in the effective refractive index and consequently to the change in the analyte contents and concentration.

In recent years, there has been a spurring research interest growing on photonics integrated circuits as the way to scale up quantum communications. In particular, building a reliable integrated source of entangled photons is one of the main challenges remaining for commercial exploitation in quantum sensing and metrology. Therefore, advances in design of integrated sources of entangled photons is a necessary and crucial task to be performed for miniaturization and cost-effectiveness. Microring resonators are one of the most promising candidates to generate entangled photons via nonlinear interactions, especially Spontaneous Four-Wave Mixing (SFWM). But fabrication limitations in reproducibility of high-quality resonators mandate the use of active devices. Here we present the results of preparing the excitation pulse with different spectral, intensity and dispersion parameters to optimize the quantum efficiency in passive devices after fabrication. Different numerical methods such as Finite Difference Time Domain (FDTD) and Split-Step Fourier Method (SSFM) are used to reproduce the nonlinear propagation, interplay with dispersion and losses. Exploiting the degree of freedom of the excitation pulse can bring more energy efficient and passive devices as quantum entangled pair sources in an integrated chip. Considerations on different degrees of entanglement are also discussed for applications in quantum sensing and quantum metrology.

In modern communications networks, data is transmitted over long distances using optical fibers. At nodes in the network, the data is converted to an electrical signal to be processed, and then converted back into an optical signal to be sent over fiber optics. This process results in higher power consumption and adds to transmission time. However, by processing the data optically, we can begin to alleviate these issues and surpass systems which rely on electronics. One promising approach for this is plasmonic devices. Plasmonic waveguide devices have smaller footprints than silicon photonics for more compact photonic integrated circuits, although they suffer from typically having higher loss than silicon photonic devices. Inverse design software can be used to optimize the plasmonic device topology to maximize the device throughput, mitigating the inherent loss of plasmonics. Additionally, inverse design tools can help us make plasmonic devices with an even smaller footprint and higher efficiency than conventionally designed plasmonic devices. Recently, commercial inverse design tools have become available for popular photonic simulation software suites. Using these commercial inverse design tools with a compatible plasmonic architecture, we create compact, efficient, and manufacturable devices such as XOR gates, grating couplers, y-splitters, and waveguide crossings. We compare the inverse-designed devices to conventional devices to characterize the performance of the commercial inverse design tool.

Diverse chip-based sensors utilizing integrated silicon photonics have been demonstrated in resonator and phase shifter/interferometer configurations. Till date, interferometric techniques with the Mach-Zehnder Interferometer (MZI) and Young’s interferometer have shown the lowest mass detection limits (in pg/mm²). Slow light in photonic crystal waveguides integrated with MZIs enables compact geometries due to enhanced optical path lengths as light propagates with high group index. In a typical MZI, light propagating in the signal arm overlaps with analytes and undergo a relative phase change with respect to the light in the reference arm which leads to measured output intensity changes. In this paper, using integrated photonic methods, we demonstrate a slow light enhanced Michelson interferometer (MI) biosensor, wherein the reference and signal arms are traversed twice by the propagating optical mode. As a result, the analyte interaction length is effectively doubled since the propagating optical mode undergoes twice the phase shift as would be observed in a MZI. In an asymmetric MI configuration, the resultant doubling of the phase shift is observed as a doubling of the resonance wavelength shift for a fixed change in the analyte concentration. The device sensitivity is thus doubled with respect to a conventional MZI while also effectively halving the geometric length compared to the MZI sensor.

Metalenses have shown great promise in performing high-efficiency subwavelength focusing with wavelength-scale flat optical components. The majority of metalenses designed for telecommunication wavelengths, particularly at 1550 nm, utilize relatively tall amorphous silicon posts to form an array of scattering elements with phase control spanning the 0 to 2π range. In this work, we present the design of a binary phase Fresnel zone plate metalens in a silicon-on-insulator platform. The proposed metalens uses trapezoidally segmented subwavelength grating to form concentric rings to spatially vary the effective index across the device. Only one single etch step is required to achieve desired performance.

We demonstrate a large-scale two dimensional silicon-based optical phased array (OPA) composed of nanoantennas with circular gratings that are balanced in power and aligned in phase, required for producing desired radiation patterns in the far-field. The OPAs are numerically optimized to have an upward efficiency of up to 90%, targeting radiation concentration mainly in the field of view. We envision that our OPAs have the ability of generating complex holographic images, rendering them an attractive candidate for a wide range of applications like LiDAR sensors, optical trapping, optogenetic stimulation and augmented-reality displays.

We demonstrate the numerical and experimental realization of optimized optical traveling-wave antennas made of low-loss dielectric materials. These antennas exhibit highly directive radiation patterns and our studies reveal that this nature comes from two dominant guided TE modes excited in the waveguide-like director of the antenna, in addition to the leaky modes. The optimized antennas possess a broadband nature and have a nearunity radiation efficiency at an operational wavelength of 780 nm. Compared to the previously studied plasmonic antennas for photon emission, our all-dielectric approach demonstrates a new class of highly directional, low-loss, and broadband optical antennas.

Performance of multimode interference couplers is constrained by the phase errors caused by the deviations of the modes propagation constants from the required quadratic dependence upon mode number. In this work, we show that by creating a rectangular grating on the top surface of the coupler with a spatial frequency matching the intensity distribution of the i-th order mode, it is possible to control the phase errors of all spatial modes up to the i-th order. The effect of the grating on the propagation constants of higher-order modes is studied using perturbation-based and strict vector calculus. The efficacy of the method was demonstrated using numerical examples of an MMI-based two-mode (TE₀ and TE₁) coupler in the 1.31 μm wavelength region and the singlemode (TE₀) 1.31/1.55 μm wavelength splitter, both made of medium index contrast material (TiO₂:SiO₂).

The Artificial Bee Colony (ABC) algorithm was applied to solve an inverse design problem of integrated photonics. The ABC algorithm was applied to optimize large photonic bandgaps (PBGs) in 2D-dimensional PhCs composed of silicon carbide (SiC) and air, in a triangular lattice, for transverse magnetic polarization. The band diagram was calculated using the finite element method for the frequency domain. The ABC algorithm reached PhC structures with PBGs as large as 33.94%.

In this work, an integrated platform based on silicon nitride strip waveguides is used as a reference platform to investigate some waveguiding characteristics in metamaterial cladding. The novel platform is composed of an alldielectric anisotropic metamaterial cladding positioned at the bottom of a silicon nitride waveguide core. The fundamental TM mode showed a bend loss reduction of about 1.8 dB/180˚ in comparison to a standard platform.

Whispering Gallery Mode (WGM) sensors provide high sensitivity, high resolution, small footprint, and resistance to electromagnetic interference, making them a great option for displacement sensing. An efficient method of coupling light into and out of WGM resonators is through the use of tapered tapers, but their instability can be a limitation in practical applications. Conventional packaging methods for WGM resonators use UV-curable polymers with low refractive indices to improve robustness, but their rigidity can make them less suitable for displacement sensing. Additionally, their high cost, potential toxicity and the interference from ambient moisture pose a critical issue. In this study, we demonstrate an alternative method of packaging WGM devices using non-toxic polydimethylsiloxane (PDMS). The Q-factor of 10⁷ is achieved at the 780 nm band. The PDMS packaging technique not only improves the robustness and compactness of the WGM device, but also enhances humidity resistance significantly. By take advantages of the unique flexibility of PDMS, we demonstrate displacement detection with a high sensitivity of ~0.1 pm/μm and a detection limit of 600 nm.

We have assessed and reduced the particle count in coatings from a magnetron sputter coater used for production of optical coatings for applications in photonics and semiconductor industry. Results for particle levels in single layers from Al₂O₃, SiO₂, Nb₂O₅, Ta₂O₅, and TiO₂ showed semiconductor grade particle levels for the upgraded deposition system. Moreover, particle levels were also investigated for optical filter stacks deposited on bare Si, glass substrates and actual CMOS device wafers, which were used for the manufacturing of hyperspectral imaging (HSI) sensors. In all cases, low particle counts were detected in the optical filters as expected from the results obtained for the single layer. It could be shown that the coating on the device wafers had no negative impact on the production yield of the HSI sensors.

We present a hybrid-integrated extended cavity diode laser tunable around 637 mn, with a total tuning range of 8 nm, allowing to address the zero-phonon line of nitrogen vacancy centers. The laser provides wide mode-hop free tuning over 43.6 GHz and a narrow intrinsic linewidth below 10 kHz. The maximum output power is 2.5 mW in a single-mode fiber, corresponding to an on-chip power of 4.0 mW. The laser is assembled in a standard laser housing and fiber-pigtailed.

A new light responsive arylazopyrazole (AAP) containing polymer matrix thin film is fabricated by spincoating of different concentrations of the AAP azo dye into the polydimethylsiloxane (PDMS) polymer at 150°C. The new AAP molecular switch was also used to fabricate a solid-state PDMS-AAP waveguide by contact lithography and soft replica modeling methods in the micrometer scale. The refractive index of the spin-coated photoswitchable material can be modulated via the reversible trans-to-cis photoisomerization behavior of the AAP unit using different concentrations. When 0.01 M solution of the AAP unit was used, the refractive of the composite was 2.32 in the trans state and dropped to 1.85 in the cis state in the operating wavelength of 340 nm. At higher concentrations of 0.020 and 0.03 M, a wide refractive index tuning is achieved under the same wavelength. In 0.030 M the refractive index was 2.65 for the trans state and 2.0 for the cis state. The results suggest that the increase in refractive index tuning is related to the concentration of the AAP unit of the composite film. Theoretically, the spectral properties of the composite film are also simulated with two methods: 1) the Maxwell Equations; and 2) the frequency dependent finite element, showing excellent agreement for the different propagation modes of the proposed waveguide for regulated signals of 365/525 nm wavelengths. Furthermore, the photoisomerization of the PDMS-AAP thin film is analyzed with UV-vis spectroscopy to demonstrate the isomerization responses of the AAP moiety in the solid state. Additionally, preliminary photomechanical actuation properties of the composite film have been investigated. The PDMS-AAP waveguide described in this study provides a new approach for optically tunable photonics applications in the Visible-IR region.

The authors report the detailed characterisation of a widely tunable laser and module that offers the elusive combination of very fast (nanosecond) tuning and narrow linewidth. The laser is fabricated on an active-passive InP-based platform and packaged into a 14-pin butterfly module. Electro-optic tuning is used with reversevoltage bias of tuning sections allowing mA-order dark currents and facilitating nanosecond switching speeds with low power dissipation. The device is suitable for integration into fiber coupled modules such as the nanoiTLA or can be monolithically integrated with other components in a III-V PIC. It is a promising new laser for applications that require fast and wide tuning with low linewidth, such as FMCW (Frequency-Modulated Continuous-Wave) LiDAR and coherent optical packet or burst switching.

Group-IV photonics has gained a lot of interest in recent years due to its CMOS compatibility. Silicon on Insulator (SOI) has dominated the optical and optoelectronics field for past decades. On the other hand Germanium based platform, GeOI is another promising candidate for the above mentioned field.¹ It has wide application in Mid Infrared Sensing due to it’s abundance, transparency and high index contrast (Δn = 2.6 at 3 μm) with reference to silicon on insulator. In order to take the advantage of wide transparency of Germanium in the Mid Infrared applications like chemical sensing, where most hazardous chemical molecules have their fingerprints, we have designed a compact adiabatic tapered waveguide2-4 sensor based on evanescent wave coupling which will be able to sense more than six analytes (Carbon dioxide (CO₂), Nitrous oxide (N₂O), Nitrogen dioxide (NO₂), Nitric oxide (NO), Ammonia (NH₃), Ethylene (C₂H₄), Acetylene (C₂H₂), Hydrogen Cyanide (HCN) and Methane (CH₄)) having absorption peaks in between 2.5 to 3.5 μm. The proposed device provide a suitable method for label-free detection of target molecules and can be integrated on-chip for industrial and environmental monitoring , health analysis and food processing which can be leveraged over hefty conventional spectrometer like Fourier Transform Infrared Spectroscopy (FTIR). We have also studied and found an optimum tapered length of 40 μm for the proposed geometry, having more than 80 % transmission for both fundamental Transverse Electric (TE) and Transverse Magnetic (TM) mode making it polarisation insensitive.

We investigate the reconfigurable resonator based on five times self-coupled photonic waveguide for versatile functionalities. These include a high-performance notch filter, bandpass filters of Bessel and Chebyshev types with improved shape factors, extinction ratio (ER) of more than 40 dB, high Q-factors, tunable ultra-high sharp Fano resonances with slope rates exceeding 1000 dB/nm and high ERs, the optical analog of multi-band electromagnetically induced transparencies, and tunable true-time delay lines with a considerable delay range.

An ultra-compact, polarization-independent, dual-channel wavelength demultiplexer is designed by the inverse method with a footprint of 2.5μm × 2.5μm. The topology optimization-based inverse design method is used for designing the device. It is designed on the CMOS-compatible silicon on Insulator (SOI) platform. The peak transmission obtained for quasi-TE polarization at 1310nm and 1550nm is approx -1.0 dB and -1.7 dB respectively and for quasi-TM polarization at 1310 nm and 1550 nm is approx -1.0 dB and -1.9 dB respectively.

Steric acid is used to fabricate cladding and core layers on z-cut lithium niobate (LiNbO3) substrate by maintaining the solution melt at 280°C for 4 and 2 hours, respectively. After completing the two-step proton exchange (PE), the refractive indices of the core and cladding layers are ascertained by using the prism coupling technique, and with this information at hand, the grating period Λ of 50 μm is deduced by solving a system of transcendental waveguide equations with MATLAB. There are three methods adopted to fabricate the gratings. The first one is to utilize the proton-exchange method by directly diffusing ions into LiNbO₃ to realize phase grating while keeping the solution melt at 280°C for 0.5 hours. The second one relies on using a Shipley S1813 photoresist as the corrugation grating via standard lithography. The third approach is to deposit and subsequently pattern silver metal as corrugation grating. A series of measurements would show that the maximum dip contrast of the phase grating could reach up to 31.188 dB, and the corresponding full width at half maximum (FWHM) is about 0.77 nm. In comparison, the maximum dip contrast of the photoresist corrugation grating attains up to 28.44 dB with an FWHM of approximately 1.18 nm. On the other hand, the maximum dip contrast ratio of the silver corrugation grating is determined to be around 8.15 dB with an FWHM of about 0.6 nm. The thermal dependency of the phase grating is also probed by increasing the temperature from 40 to 60°C and the corresponding dips have appeared to be blue-shifted. All of these devices have managed to demonstrate the multiple rejection bands, which is believably due to the multimode interference (MMI) phenomenon.