Photonic Components Research Articles

Towards facile fabrication of photonics components from inorganic and hybrid sol-gel films. Preparation and optical properties characterization

New trends towards development of integrated optics and miniaturization of photonic devices require fabrication of miniaturized photonic components. Fabrication of waveguiding films with designed optical properties is a fundamental process for production of planar integrated devices.We report here preparation of thin layers based on TiO2 precursor (TET – titanium(IV) ethoxide) and SiO2 precursors, namely inorganic (TEOS – tetraethyl orthosilicate) or organically modified (GLYMO − 3-glycidoxypropyltrimethoxysilane) as candidates for potential application in the planar integrated circuits.The thin layers were deposited on soda-lime glass substrates using the sol-gel method and dip-coating technique and processed at relatively low temperature (up to 300 °C). Several parameters e.g. a) the type of SiO2 precursor, b) the presence of complexing agent for TET and c) heat treatment temperature were tested for their influence on thickness and refractive index of the obtained films.Furthermore, a few series of sol-gel films activated with luminescent dye (Rhodamine B) was fabricated. The influence of the above-listed parameters on luminescent properties of the films was characterized because of lack of systematic study in the literature in this aspect. Moreover, a spectrum of the light at the output of a chosen luminescent dye-doped waveguiding film excited by laser source was investigated.In addition, the subject of our investigations were films prepared at 200 °C with various amounts of TET and organically modified SiO2 precursor in concentration range not presented before. Their optical properties such as homogeneity and values of optical band gap of TiO2 clusters were explored. For selected samples the waveguide properties including the optical losses were evaluated. For the first time, hybrid films with presented composition and refractive index in range of 1.59–1.71 were used for patterning by nanoimprint technique allowing for reproduction of periodic structures, which may serve for example as grating couplers or DFB (distributed feedback) resonators.

An integrated photonic device for on-chip magneto-optical memory reading

AbstractThis study presents the design, fabrication and experimental demonstration of a magneto-photonic device that delivers non-volatile photonic memory functionality. The aim is to overcome the energy and speed bottleneck of back-and-forth signal conversion between the electronic and optical domains when retrieving information from non-volatile memory. The device combines integrated photonic components based on the InP membrane on silicon (IMOS) platform and a non-volatile, built-in memory element (ferromagnetic thin-film multilayers) realized as a top-cladding on the photonic waveguides (a post-processing step). We present a design where the phase of the guided light is engineered via two mechanisms: the polar magneto-optical Kerr effect (MOKE) and the propagation in an asymmetrical cross-section (triangular) waveguide. Thanks to its design, the device yields different mode-specific transmissions depending on the memory state it encodes. We demonstrate the recording of the magnetic hysteresis using the transmitted optical signal, providing direct proof for all optical magnetic memory reading using an integrated photonic chip. Using mathematical model and optical simulations, we support the experimental observations and quantitatively reproduce the Kerr signal amplitudes on-chip. A 1% transmitted power contrast from devices is promising indicating that in a shot noise limited scenario the theoretical bandwidth of memory read-out exceeds 50 Gbits/s.

Subwavelength Grating Waveguide Structures Proposed on the Low-Cost Silica-Titania Platform for Optical Filtering and Refractive Index Sensing Applications.

The sol–gel dip-coating method is a cost-efficient way for the realization of thin films on a planar substrate. In this work, high-quality, low-loss, and low-surface roughness silica–titania thin films are deposited on a glass substrate with the sol–gel dip-coating method. This platform works in the visible to near-IR wavelength ranges and can be useful for several eye-catching photonic components. The paper is comprised of two parts: the first part deals with the development of a low-cost silica–titania waveguide system, whereas the second part provides detail on the numerical modeling of the SWG waveguide filter and SWG waveguide FP-sensor design. The SWG waveguide NIR-stopband filter can achieve an ER of >40 dB and 3-dB bandwidth of 110 nm designed at optimized parameters. The SWG waveguide-FP structure proposed in this work act as a refractive index sensor where the sensitivity is ~120 nm/RIU by reducing the width of the waveguide. This sensitivity can be further enhanced by reducing the waveguide height. We believe that this work is quite important for the realization of low-cost integrated photonic devices based on the silica–titania platform developed via the sol–gel dip-coating method.

Inverse Design of Photonic Devices with Strict Foundry Fabrication Constraints

We introduce a new method for inverse design of nanophotonic devices which guarantees that resulting designs satisfy strict length scale constraints - including minimum width and spacing constraints required by commercial semiconductor foundries. The method adopts several concepts from machine learning to transform the problem of topology optimization with strict length scale constraints to an unconstrained stochastic gradient optimization problem. Specifically, we introduce a conditional generator for feasible designs and adopt a straight-through estimator for backpropagation of gradients to a latent design. We demonstrate the performance and reliability of our method by designing several common integrated photonic components.

Additive manufacturing for the development of optical/photonic systems and components

The ambition of this review is to provide an up-to-date synopsis of the state of 3D printing technology for optical and photonic components, to gauge technological advances, and to discuss future opportunities. While a range of approaches have been developed and some have been commercialized, no single approach can yet simultaneously achieve small detail and low roughness at large print volumes and speed using multiple materials. Instead, each approach occupies a niche where the components/structures that can be created fit within a relatively narrow range of geometries with limited material choices. For instance, the common Fused Deposition Modeling (FDM) approach is capable of large print volumes at relatively high speeds but lacks the resolution needed for small detail ( > 100 µ m ) with low roughness ( > 9 µ m ). At the other end of the spectrum, two-photon polymerization can achieve roughness ( < 15 n m ) and detail ( < 140 n m ) comparable to commercial molded and polished optics. However, the practical achievable print volume and speed are orders of magnitude smaller and slower than the FDM approach. Herein, we discuss the current state-of-the-art 3D printing approaches, noting the capability of each approach and prognosticate on future innovations that could close the gaps in performance.

Are phase change materials ideal for programmable photonics?: opinion

The objective of this Opinion is to stimulate new research into materials that can meet the needs of tomorrow’s programmable photonics components. Herein, we argue that the inherent property portfolios of the common telluride phase change materials, which have been successfully applied in data storage technologies, are unsuitable for most emerging programmable photonics applications. We believe that newer PCMs with wider bandgaps, such as Sb2S3, Sb2Se3, and Ge2Sb2Se4Te (GSST), can be optimized to meet the demands of holographic displays, optical neural network memories, and beam steering devices.

Proximity-effect-related reduction of the minimum element size in thermochemical laser writing

This study is intended to identify patterns in reducing the minimum size of writable elements in a structure as a function of the distance between elements when they are produced successively by direct thermochemical recording on a thin metal film using direct laser thermochemical writing, as a result of natural thermo-optical effects. Subject of study. The change in writable-element size (the proximity effect) studied here occurs because reduced absorption at the periphery of the beam as it passes through films on which elements have previously been written results in containment of the energy. Methods. This effect was studied by obtaining a solution to the quasi-steady-state heat conduction equation in closed form while taking into account the time-dependent, nonuniform spatial distribution of optical properties within the sample, using titanium films oxidized by exposure to laser light in air as an example. The model results are compared against available experimental studies of the optical and geometric properties of structures written on a 10 nm titanium film by a focused near-infrared cw laser beam. Main results. This research led to a means of predicting the widths of successively written tracks as a function of track separation. The upper threshold track separation values where the effect begins and the lower threshold values below which the new track no longer appears were determined. Both the theoretical and experimental results reveal that the resolution of thermochemical laser writing on thin metal films that form optically transparent oxides can be increased. Practical significance. The theoretical model proposed in this paper can be used to determine the laser exposure parameters required to produce various high-resolution photonic components, such as diffractive optical elements, half-tone photomasks, etc.

An Ultra-Broadband Polarization Beam Splitter Based on the Digital Meta-Structure at the 2 µm Waveband

The 2 μm waveband is considered to have great potential in optical communications. Driven by the demands on high-performance functional devices in this spectral band, various integrated photonic components have been demonstrated. In this work, an analog and digital topology optimization method is proposed to design an ultra-broadband polarization beam splitter at the 2 μm waveband. Within an optical bandwidth of 213 nm, the excess losses of TE and TM modes are <0.53 dB and 0.3 dB, respectively. The corresponding polarization extinction ratios are >16.5 dB and 18.1 dB. The device has a very compact footprint of only 2.52 µm × 5.4 µm. According to our best knowledge, this is a benchmark demonstration of an ultra-broadband and ultra-compact polarization beam splitter enabled by the proposed optimization method.

Spectrally tunable liquid resonator based on electrowetting.

We present a tunable on-chip liquid resonator in conjunction with a tapered fiber coupling scheme. The resonator consists of a glycerol droplet submerged within an immiscible liquid bath, which mitigates the effects of environmental fluctuations. The platform is fabricated using standard semiconductor techniques, which enable the future integration of photonic components for an on-chip liquid resonator device. The liquid resonator maintains its high Q-factor on chip (105) due to surface tension forming an atomically smooth liquid-liquid interface. Higher Q-factor resonance modes experienced linewidth broadening due to the random excitation of thermal capillary vibrations. Spectral tuning is demonstrated using the electrowetting effect, increasing the surface's wettability and an expansion in the droplet diameter. A maximum spectral tuning of 1.44 nm ± 5 pm is observed by applying 35 V. The tuning range is twice the free spectral range (FSR) of 0.679 nm measured at a pumping wavelength range of 770-775 nm. A 2D axisymmetric finite-element simulation shows resonance modes in good agreement with experimentally measured spectra and with predicted tuning speeds of 20 nm/s.

Advancement in Silicon Integrated Photonics Technologies for Sensing Applications in Near-Infrared and Mid-Infrared Region: A Review

Exploration and implementation of silicon (Si) photonics has surged in recent years since both photonic component performance and photonic integration complexity have considerably improved. It supports a wide range of datacom and telecom applications, as well as sensors, including light detection and ranging, gyroscopes, biosensors, and spectrometers. The advantages of low-loss Si WGs with compact size and excellent uniformity, resulting from the high quality and maturity of the Si complementary metal oxide semiconductor (CMOS) environment, are major drivers for using Si in photonics. Moreover, it has a high refractive index and a reasonably large mid-infrared (MIR) transparency window, up to roughly 7 μm wavelength, making it beneficial as a passive mid-IR optical material. Several gases and compounds with high absorption properties in the MIR spectral region are of prodigious curiosity for industrial, medicinal, and environmental applications. In comparison to current bulky systems, the implementation of Si photonics devices in this wavelength range might allow inexpensive and small optical sensing devices with greater sensitivity (S), power usage, and mobility. In this review, recent advances in Si integrated photonic sensors working in both near-infrared (NIR) and MIR wavelength ranges are discussed. We believe that this paper will be valuable for the scientific community working on Si photonic sensing devices.

Thermal Control of Plasmonic Surface Lattice Resonances.

Plasmonic metasurfaces exhibiting collective responses known as surface lattice resonances (SLRs) show potential for realizing flat photonic components for wavelength-selective processes, including lasing and optical nonlinearities. However, postfabrication tuning of SLRs remains challenging, limiting the applicability of SLR-based components. Here, we demonstrate how the properties of high quality factor SLRs are easily modified by breaking the symmetry of the nanoparticle surroundings. We break the symmetry by changing the refractive index of the overlying immersion oil by controlling the ambient temperature of the device. We show that a modest temperature change of 10 °C can increase the quality factor of the SLR from 400 to 750. Our results demonstrate accurate and reversible modification of the properties of the investigated SLRs, paving the way toward tunable SLR-based photonic devices. More generally, we show how symmetry breaking of the environment can be utilized for efficient and potentially ultrafast modification of the SLR properties.

Enhancing the efficiency of the topological phase transitions in spin–orbit photonics

A light beam reflected and refracted at a sharp interface can acquire a momentum-dependent Pancharatnam–Berry (PB) phase, which produces a topological phase transition from one kind of spin–orbit interaction (e.g., spin-controlled vortex generation) to another (e.g., photonic spin-Hall effect). However, this process is extremely inefficient and difficult to observe directly in experiments, which also hinders its applications. Here, we propose to enhance significantly the topological phase transitions by c-cut uniaxial crystals. We first give a full-wave theory to describe the spin–orbit interactions of a beam passing through a c-cut uniaxial crystal and experimentally observe the topological phase transition process of the transmitted beam when the angle between the beam propagation direction and the optical axis direction changes. It is found that the efficiency of the spin–orbit interactions caused by the momentum-dependent PB phase can be increased as high as 50%, which is much larger than that at isotropic sharp interfaces. Our findings provide an alternative approach for manipulating the spin and orbital angular momenta of light and exhibit potential applications in the future spin–orbit photonic components.

Fully Integrated FMCW LiDAR Optical Engine on a Single Silicon Chip

We present the demonstration of two novel chip-scale FMCW LiDAR optical engines in which all photonic components, including the laser sources, were integrated on single silicon chips. Using the first LiDAR chip design, with an integrated distributed Bragg reflector laser and grating couplers as input/output ports for the receive/transmit light, we demonstrated a maximum range of 28 m limited by transmit light output power of 2 mW. We further demonstrated a maximum range of 75 m using a second LiDAR chip architecture having an on-chip sampled grating distributed Bragg reflector master laser with integrated power amplifier in which the local oscillator light was obtained from the laser back facet. This maximum range can be further increased by improving the laser linewidth. The measured range dependence of the FMCW signal level for both LiDAR chips agreed well with theory. The chip-scale FMCW LiDAR optical engines can be used in conjunction with a variety of off-chip two dimensional beam scanners to realize a chip-scale scanning LiDAR solution. To the best of our knowledge, this is the first published demonstration of fully integrated FMCW LiDAR optical engines on a single silicon chip.

Piezo-optomechanical cantilever modulators for VLSI visible photonics

Visible-wavelength very large-scale integration photonic circuits have a potential to play important roles in quantum information and sensing technologies. The realization of scalable, high-speed, and low-loss photonic mesh circuits depends on reliable and well-engineered visible photonic components. Here, we report a low-voltage optical phase shifter based on piezo-actuated mechanical cantilevers, fabricated on a CMOS compatible, 200 mm wafer-based visible photonics platform. We show linear phase and amplitude modulation with 6 Vπ cm in differential operation, −1.5 to −2 dB insertion loss, and up to 40 dB contrast in the 700–780 nm range. By adjusting selected cantilever parameters, we demonstrate a low-displacement and a high-displacement device, both exhibiting a nearly flat frequency response from DC to a peak mechanical resonance at 23 and 6.8 MHz respectively, which, through resonant enhancement of Q ∼ 40, further decreases the operating voltage down to 0.15 Vπ cm.

Integrated Tunable Sideband Suppressor for Optical Carrier Reuse in Millimeter-Wave Radio-Over-Fiber Transmission

An integrated Si photonic tunable sideband suppressor is presented for application of remote optical carrier reuse. This tunable sideband suppressor is constructed by a two-rings-coupled Mach Zehnder interferometer with a tuning function to synthesize a box-like, narrow band-pass filter through dual Fano resonance interference. By varying the resonant wavelengths of the ring resonators, we can tune the suppression band adapted to the working millimeter wave (mmWave) frequency. We demonstrate a suppression ratio more than 25 dB on both 28 and 39 GHz downlink mmWave radio-over-fiber (RoF) signals. By applying this component in a bi-directional mmWave RoF system, we observe the quality of the uplink signal modulated on the recycled optical carrier is almost the same as that modulated on a clean laser source without extra power penalty. Since the sideband suppressor is made by Si photonic circuits, it potentially can be integrated with other high-speed Si photonic components to implement an on-chip mmWave radio-over-fiber transceiver.

High-Performance Silicon Photonics Using Heterogeneous Integration

The performance of silicon photonic components and integrated circuits has improved dramatically in recent years. As a key enabler, heterogeneous integration not only provides the optical gain which is absent from native Si substrates and enables complete photonic functionalities on chip, but also lays the foundation of versatile integrated photonic device performance engineering. This paper reviews recent progress of high-performance silicon photonics using heterogeneous integration, with emphasis on ultra-low-loss waveguides, single-wavelength lasers, comb lasers, and photonic integrated circuits including optical phased arrays for LiDAR and optical transceivers for datacenter interconnects.

Soliton frequency comb generation in CMOS-compatible silicon nitride microresonators

The monolithic integration of soliton microcomb devices with active photonic components and high-frequency electronics is highly desirable for practical applications. Among many materials, silicon nitride ( SiN x ) waveguide layers prepared by low-pressure chemical vapor deposition (LPCVD) have been the main platform for on-chip optical frequency comb generation. However, the high temperatures involved in LPCVD render it incompatible as a back-end process with complementary metal oxide semiconductor (CMOS) or active III-V compound semiconductor fabrication flows. We report the generation of coherent soliton frequency combs in micro-ring resonators fabricated in deuterated silicon nitride ( SiN x : D ) waveguides with a loss of 0.09 dB/cm. Deposited at 270°C by an inductance-coupled plasma chemical vapor deposition (ICP-CVD) process, the material preparation and fabrication flow are fully CMOS-compatible. These results enable the integration of silicon-nitride-based optical combs and photonic integrated circuits (PICs) on prefabricated CMOS and/or III-V substrates, therefore marking a major step forward in SiN x photonic technologies.

Graphene microheater for phase change chalcogenides based integrated photonic components [Invited

In order to effectively control the state of an active integrated photonic component based on chalcogenide phase change materials, an efficient microheater operating at low voltage is required. Here, we report on the design of a graphene based microheater. The proposed system contains two separate graphene layers between which the phase change material cell of Ge2Sb2Te5 is placed. Three distinct switching possibilities are explored, using only the bottom layer, only the top layer or both graphene layers. A detailed investigation of the heater parameters is performed to optimise switching performance. A self-consistent multiphysics simulation of the crystallization process in the phase change material cell is conducted demonstrating the switching capabilities of the proposed design.

Silicon Carbide Photonics Bridging Quantum Technology

In the last two decades, bulk, homoepitaxial, and heteroepitaxial growth of silicon carbide (SiC) has witnessed many advances, giving rise to electronic devices widely used in high-power and high-frequency applications. Recent research has revealed that SiC also exhibits unique optical properties that can be utilized for novel photonic devices. SiC is a transparent material from the UV to the infrared, possess nonlinear optical properties from the visible to the mid-infrared and it is a meta-material in the mid-infrared range. SiC fluorescence due to color centers can be associated with single photon emitters and can be used as spin qubits for quantum computation and communication networks and quantum sensing. This unique combination of excellent electronic, photonic and spintronic properties has prompted research to develop novel devices and sensors in the quantum technology domain. In this perspective, we highlight progress, current trends and prospects of SiC science and technology underpinning the development of classical and quantum photonic devices. Specifically, we lay out the main steps recently undertaken to achieve high quality photonic components, and outline some of the current challenges SiC faces to establish its relevance as a viable photonic technology. We will also focus on its unique potential to bridge the gap between classical and quantum photonics, and to technologically advance quantum sensing applications. We will finally provide an outlook on possible alternative applications where photonics, electronics, and spintronics could merge.

Optical and geometric parameter extraction for photonic integrated circuits.

We describe an in-situ technique to characterize the material refractive indices and waveguide geometry for photonic integrated circuits over hundreds of nanometers of optical bandwidth. By combining white light spectroscopy with unbalanced Mach-Zehnder interferometers, we can simultaneously and accurately extract the core thickness, core width, core refractive index, and cladding refractive index. This information is important for the technological maturation of photonic integrated circuit foundry fabrication. Capturing the inter-wafer and intra-wafer variation of these parameters is necessary to predict the yield of photonic components and for overall process quality control. Refractive indices are found with a 1-σ error of between 0.1% and 0.5%, and geometric parameters are found with an error of between 3 nm and 7 nm. Our analysis and validation are implemented and verified using the same waveguide layers as are used in the standard photonic wafer build, without any external techniques such as ellipsometry or microscopy.