This PDF file contains the front matter associated with SPIE Proceedings Volume 11284, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

The identification of neuromorphic computing as a highly promising alternative computing system has been emerged from its potential to increase rapidly the computational efficiency that is currently restricted by Moore’s law end. First electronic neuromorphic chips like IBM’s TrueNorth and Intel’s Loihi revealed a tremendous performance improvement in terms of computational speed and density; however, they are still operating in MHz rates. To this end, neuromorphic photonic integrated circuits can further increase the computational speed and density, having a large portfolio of components with GHz-bandwidth and low-energy. Herein, we present an all-optical sigmoid activation function as well as a single-λ linear neuron. The all-optical sigmoid activation function comprises a Semiconductor Optical Amplifier-Mach-Zehnder Interferometer (SOA-MZI) configured in differentially-biased scheme followed by an SOA. Its thresholding capabilities have been experimentally demonstrated with 100psec optical pulses. Then, we introduce an all-optical phase-encoded weighting scheme and we experimentally demonstrate its linear algebra operational credentials by the means of a typical IQ modulator operated at 10Gbaud/s.

The design and implementation of engineered photonic structures, conventionally, relies on the expertise of a skilled scientist to guide a progression of electromagnetic simulations that iteratively solve Maxwell’s equations until an optimized solution can be achieved. However, the intricate mechanisms and the large degrees of freedom in photonic systems often impede an effective strategy for the design and optimization process. We circumvent this conventional procedure by means of a hybrid artificial intelligence architecture. When fed an input set of customer-defined optical responses, the constructed network generates candidate structures that match the on-demand properties with high fidelity in a systematic manner.

Here we discuss two different approaches to realize optical neural networks (NN). Part ‘A’ focuses on integrated-photonics solution to realize a perceptron using (i) optoelectronic components to perform the MAC operation and (ii) a more novel concept of an all-optical nonlinearity for thresholding and thermo-optical memory for zero-power synaptic weighting. The latter is unique since the processor’s delay simply depends on the time-of-flight of the photon through the NN, which can be in the picosecond range enabling applications in real-time signal processing. Part ‘B’ discusses our recent process of 4f-based Fourier-optical filtering towards convolution neural networks (CNN); this approach uses massive parallelism (10^6 channels) of digital-mirror-display (DMD) technology. Here the computational expensive convolution is simple realized as a multiplication in the Fourier domain via a lens. Our generation (Gen) 1 system shows 250 TMAC/s process capability at 8-bit resolution.

We show that optical waves passing through a nanophotonic medium can perform artificial neural computing. Complex information, such as an image, is encoded in the wave front of in-put light. The medium continuously transforms the wave front to realize highly sophisticated computing tasks such as image recognition. At the output, optical energy is concentrated to well defined locations, which for example can be interpreted as the identity of the object in the image. These computing media can be as small as tens of wavelengths in size and thus offer extremely high computing density. They exploit sub-wavelength linear and nonlinear scatterers to realize sophisticated input-output mapping far beyond traditional nanophotonic devices. To enable these complex neural computing, we draw inspiration from artificial neural network and use stochastic gradient decent to optimize nonlinear nanophotonic structures with structural gradient computed from adjoint state method.

Software-implementation of brain-inspired computing approaches underlie many important modern-day computational tasks. Yet, traditional computing architectures physically separate the core computing functions of memory and processing. I will present an all-optical approach to overcome these restrictions by developing photonic spiking neurons interconnected via an integrated photonics network to photonic synapses. I will present our results in scaling to multi-element circuits and report on their optical performance in pattern recognition and data storage. Photonic implementations give access to the speed, bandwidth and power improvements inherent to optical systems, which will be attractive for the direct processing of data in the optical domain.

Recently, there have been a renewed interest on brain-inspired (neuromorphic) computing schemes that are directly implemented on a physical platform. In fact, such optical or electrical platforms allow performing important computational tasks at a speed much higher than the software-based counterparts. Here we propose to use neuromorphic silicon photonics to recover data integrity directly in the optical domain outperforming the electronic performances. We demonstrate a silicon photonic Feed Forward Network that can be trained to solve several tasks directly in the optical domain: linear and non-linear distortion recovering, demodulation of complex modulated data and error correction.

Electronic-photonic integration is the system-level solution to scaling bandwidth density at constant cost and energy. The end point is one interconnected, world-wide ‘data center’ with resources virtualized and provisioned as services. The IPSR-I consists of reports from 17 International Technology Working Groups that define the consensus timelines, applications and component technologies that enable the required scaling. Component performance will scale with integration. Parallelism is architectural scaling paradigm. Virtualization is functional scaling paradigm. This presentation will summarize the consensus requirements and solutions for information hardware evolution during the next two decades.

The silicon photonics platform is still missing a native source. Therefore, using a novel epitaxial process based on aspect ratio trapping and nano-ridge engineering we demonstrated an powerfull approach to fabricate GaAs-InGaAs lasers directly on a standard silicon substrate. In depth morphological and optical characterisation confirms the high quality of the material. We demonstrated lasing from DFB-type devices with etched gratings and with metal gratings. In the presentation we will also discuss the possibility for coupling to standard silicon waveguides and for extending the emission to longer wavelengths.

Currently, manufacturing processes, evolution of equipment and instrumentation are challenges generally affecting an industry that is determined to follow higher customization and individualization. Thus, the European H2020 project “iQonic” establishes a multi-sensorial component manufacturing and photonic system assembly hardware and software environment for zero-defect manufacturing. Based on laser photonics use cases such as quantum cascade lasers, high power diode laser stacks and others, a sensorial network aligned with the current industrial internet of things architectures utilizing edge devices will acquire production defect relevant data. This data represents descriptors for main sources of defects, in particular contamination and surface damages, as well as component irregularities such as geometry deviations. The near real time data, in conjunction with historian data, flows via a unified middleware layer from the sensorial network into a software based manufacturing model, based on artificial intelligence and a decision support system that allows for error compensation throughout the complete manufacturing chain, early malfunction detection on the component and system level, component-rework and re-assessment. Consequently, aiming for zero-defect manufacturing during various stages of production a key performance indicator (KPI) of iQonic is to lift the overall photonics assembly yield to 80%, decreasing the configuration time of the production environment and enabling for the use of recycled parts. Finally, the iQonic supply chain scalable and holistic approach is under development with the goal to provide flexibility, efficiency and sustainability to the manufacturing industry.

We review some of the basic principles, fundamentals, technologies, architectures and recent advances leading to thefor the implementation of Field Programmable Photonic Field Arrays (FPPGAs).

This Conference Presentation, "Wavelength-division-multiplexing-based electronic-photonic network for high-speed computing" was recorded at Photonics West 2020 held in San Francisco, California, United States.

This Conference Presentation, "A monolithically-integrated 2 × 25-Gb/s Si photonic WDM receiver with thermally-tunable ring-resonator filters" was recorded at Photonics West 2020 held in San Francisco, California, United States.

Silicon photonics is emerging as a generic platform technology for a broad variety of applications, from telecom and datacom to sensing and medical. But in many of those applications there is a need to enrich the basic silicon (or silicon nitride) waveguide platform with functions based on add-on materials, for improved performance or squarely new functionalities. The list of such new materials is long and so is the list of technologies to bring them on top of silicon. This proliferation of heterogeneous integration is somewhat in conflict with the need for standardization as needed to drive maturity up and cost down. Therefore a key question is how to build supply chains that combine the rich functionality of new materials for silicon photonics with manufacturing platforms with critical mass. This presentation will discuss the challenge and propose possible solutions.

Integrated photonics devices, based in subwavelength grating (SWG) metamaterials, have shown unprecedented performance in a wide variety of situations. Since their proposal and first experimental demonstration in 2010 designers have made use of the new degrees of freedom provided by these structures to design advanced devices with improved capabilities. The extended design space provided by SWG structures has been successfully used to engineer the refractive index, the dispersion and, more recently, the waveguide birefringence, thus allowing novel advanced device design. In this invited talk we will review some of the advances made by our group in the field

Silicon nanophotonics represents a scalable route to deploy complex optical integrated circuits for multifold applications, markets, and end-users. Most recently, applications such as optical communications and interconnects, sensing, as well as quantum-based technologies, among others, present additional opportunities for integrated silicon nanophotonics to expand its frontiers from laboratories to industrial product development. Within a wide set of functionalities that silicon nanophotonic chips can afford, the availability of low-loss optical input/output interfaces has been regarded as a major practical obstacle that hampers long-term success of integrated photonic platforms. Indeed, fiber-chip interfaces based on diffraction gratings are an attractive solution to resonantly couple the light between planar waveguide circuits and standard single-mode optical fibers. Surface grating couplers provide much more alignment tolerance in fiber attach compared with most conventional edge-coupled alternatives, while retaining the much-needed control of the fiber placement on the chip surface and wafer-level-test capability that the in-plane convertors lack. Here, we report on our recent advances in the development of high-performance fiber-chip grating couplers that exploit the blazing effect. This is achieved with well-established dual-etch processing in interleaved teeth-trench arrangements or using L-shaped grating-teeth-profile geometries. The first demonstration of the L-shaped-based grating coupler yielded a coupling loss of -2.7 dB, seamlessly fabricated into a 300-mm foundry manufacturing process using 193-nm deep-ultraviolet stepper lithography. Moreover, silicon metamaterial L-shaped fiber couplers may promote robust sub-decibel coupling of light, reaching a simulated coupling loss of -0.25 dB, while featuring device layouts (>120 nm) compatible with lithographic technologies in silicon semiconductor foundries.

In this presentation, I propose the approach towards identifying interesting material candidates suitable for nonlinear photonics, and present the results of some experimental studies performed in this direction. More specifically, I will talk about our studies of GaN waveguides with wide electronic bandgap, suitable for the applications in the visible and near-infrared spectral ranges. I will also present the results of our experimental realization of passive InGaAsP waveguides that have potentials of being used for wavelength conversion to beyond 2 micrometers, thus expanding the operation range of well-established InGaAsP laser sources to the longer wavelengths.

We describe development of spectrally tunable micro-engineered filters operating in the longwave infrared (LWIR) region from 8 to 12 μm based on using the guided-mode resonance (GMR) effect. The device structure consists of a subwavelength dielectric grating on top of a homogeneous waveguide using high index dielectric transparent materials, i.e., germanium (Ge) with a refractive index of 4.0 and zinc selenide (ZnSe) substrate with refractive index of 2.4. The filters are designed to reflect the incident broadband light at one (or more) narrow spectral band while fully transmitting the rest of the light. The tuning of the reflection wavelength is achieved by changing the angle of incidence of light by mechanically tilting the filter. Filters based on one-dimensional gratings are polarization dependent and those based on two-dimensional gratings are polarization independent at normal incidence of light. Both 1-D and 2-D gratings were designed and characterized. Anti-reflection coatings were applied on substrate interfaces to improve transmission over the entire spectral region. We carried out transmission measurements of these filters using an automated tunable room temperature quantum cascade laser (QCL) system operating from 7.3 to 12.9 μm, and a modified Fourier Transform Spectrometer with a custom designed chamber for normal incidence of light on the sample. We present detailed characterization experiments and compare the theoretical and experimental results.

We show that self-assembled films of horizontally aligned carbon nanotubes are a electrostatically tunable hyperbolic metamaterial using spectroscopic ellipsometry. We map the hyperbolic dispersion of plasmonic modes in aligned carbon nanotube films using transmission measurements of nanoribbon resonators and find good agreement with a theoretical model based on the optical properties dervied from the ellipsometry. Self-assembled films of carbon nanotubes are well-suited for applications in thermal emission and photodetection, and they serve as model systems for studying light–matter interactions in the deep subwavelength regime.

Tuning the macroscopic dielectric response on demand holds potential for actively tunable metaphotonics and optical devices. In recent years, graphene has been extensively investigated as a tunable element in nanophotonics. Significant theoretical work has been devoted on the tuning the hyperbolic properties of graphene/dielectric heterostructures, however, until now, such a motif has not been demonstrated experimentally. Here we focus on a graphene/polaritonic dielectric metamaterial, with strong optical resonances arising from the polar response of the dielectric, which are, in general, difficult to actively control. By controlling the doping level of graphene via external bias we experimentally demonstrate a wide range of tunability from a Fermi level of EF = 0 eV to EF = 0.5 eV, which yields an effective epsilon-near-zero crossing and tunable dielect

Photonic hyper-crystals combine the most interesting features of hyperbolic metamaterials and photonic crystals. Since the dispersion law of extraordinary photons in hyperbolic metamaterials does not exhibit the usual diffraction limit, photonic hyper-crystals exhibit light localization on deep subwavelength scales, leading to considerable enhancement of nonlinear photon-photon interaction. Therefore, similar to their conventional photonic crystal counterparts, nonlinear photonic hyper-crystals appear to be very promising in optical limiting and optical computing applications. Nonlinear optics of photonic hyper-crystals may be formulated in such a way that one of the spatial coordinates would play a role of effective time in a 2+1 dimensional optical spacetime describing light propagation in the hyper-crystal. Mapping the conventional optical computing onto nonlinear optics of photonic hyper-crystals results in a “hyper-computing” scheme, which may considerably accelerate computation.

We demonstrate that reshaping of electromagnetic fields in hyperbolic metamaterials with plasmonic components can be used to engineer strong tunable bulk second order nonlinear response in plasmonic composites with application in high resolution nonlinear tomography. In order to analyze nonlinear response of an anisotropic plasmonic metamaterial slab we compare numerical and analytical calculations with experimental results. The results open up possibilities to design tuneable frequency-doubling integratable metamaterials with the goal to overcome limitations associated with classical phase matching conditions in thick nonlinear crystals.

We report integrated nonlinear plasmonic components integrated on a silicon photonics platform at telecommunications wavelengths. While metals commonly introduce loss, here less than 1dB insertion loss is possible by rapid nano-focussing and defocussing. Metallic components are designed to focus light to a 10 nm scale where nonlinear processes are greatly enhanced. We discuss progress on four-wave mixing over micron-scale interaction lengths as well as new results on Raman scattering. The technique introduces the possibility of compact, broadband, and efficient nonlinear silicon photonic devices.

The active and nonlinear graphene properties are limited due to weak light-matter interaction between the ultrathin graphene and the incident light. In this work, we present enhanced nonlinear effects at the low terahertz (THz) range by designing a new patterned graphene hyperbolic metamaterial (GHMM). More specifically, it is demonstrated that the third harmonic generation (THG) can be significantly enhanced by the proposed GHMM due to the field enhancement at the resonance as well as the supported slow-light response that fosters strong light–matter interaction.

Materials such as Si, SiGe, Ge, SiN and AlN can be used for Mid-IR (3 up to 8µm). For LWIR which ranges from 8µm to 13µm, absorption limitations define the materials which can be used, such as Ge, SiGe, chalcogenides, ZnS.... Array waveguide grating devices, with SiGe waveguides cladded by Si or Ge waveguides capped by thick SiGe layers, have been designed and fabricated. They target the simultaneous detection of several gas using arrays of QCL sources. The index difference between the core and the claddings is around 0.5 on the 3-13 µm spectral range. To increase the miniaturization, the index difference has to be increased. So by using cladding material with lower index, new platforms called “Ge on insulator” have been developed such as SiGe on SiN, Ge on SiN, Ge on AlN,

In this work, we report interband cascade light emitting diodes (ICLEDs) based on InAs/GaAsSb superlattices emitting around 4.5 μm The ICLED structures were grown on InAs substrates by molecular beam epitaxy, which were composed of InAs/GaAsSb superlattice emitters, InAs/AlAsSb multi-quantum well (MQW) injection regions, and the GaAsSb/AlAsSb MQW tunneling regions. Both 5-stage and 2-stage ICLEDs were fabricated. The devices exhibited high output power, low series resistance and high wall-plug efficiency (WPE). At room temperature, radiances of 0.36 W/cm² sr and 0.19 W/cm² sr were achieved from the 5-stage and 2-stage ICLEDs respectively. At 80 K, the output power from the 5-stage ICLED reached 3.56 mW with 350 mA injection current, resulting in a WPE of around 0.5%. The efficiency was largely maintained with increasing injection. The thermal quenching of these ICLEDs from 20 K to 300 K was also significantly less than other types of devices emitting at similar wavelengths. These results demonstrate that ICLEDs have great potential for mid-infrared light emitting diode applications requiring large output power and high wall-plug efficiency.

Frequency combs are ideal candidates to realize miniaturized spectrometers without moving parts. ICLs are perfect for the realization of miniaturized spectrometers, due to their low power consumption and the possibility to build sensitive on-chip detectors using the same epilayer material. Here, we present an overview of our current work on ICL frequency combs. This includes the generation of self-starting frequency combs utilizing their gain nonlinearity, resulting in a dominant frequency modulation similarly to quantum cascade lasers frequency combs. Furthermore, we demonstrate the generation of 3ps pulses with a peak to average power ratio of over 40 via active mode-locking.

Mid-infrared (mid-IR) gas sensing technology has been widely received as a competitive choice for the newly emerging internet-of-things (IoTs) applications mainly due to its high sensitivity, selectivity and reliability. However, high cost and chip-integration challenges, on the contrary, still limits their potential development. Lead-salt materials are proposed to offer possible solutions to address these issues, and our previous works have demonstrated their outstanding photon generation and detection capabilities in the MIR region. In this work, towards the low-cost point, we demonstrate some preliminary experimental results for preparing lead-salt based high quality active MIR photonic materials. Using a modified oriented-attachment synthesis method, for the first time, PbSe films grown on amorphous glass substrates in the wet chemical process, presented a highly smooth surface having an uniformed crystal orientation in (111) direction. Further, their nanocrystal size can also be tailored to allow a broad range control of emission wavelength from 3.3 μm to 4.2 μm owing to the unique quantum size effects. In conclusion, this new material growth exploration opens a possible cost-effective path to conduct active photonic waveguide engineering to manipulate light-and-matter interactions in the MIR range for potential chip-integrated sensing applications (e.g., IoTs).

There is a trend for the development of mid-infrared laser spectroscopy with remote interrogation, multiplexed multi-point detection, and integrated photonics systems. The merging of semiconductor lasers with hollow-core fibers is one of the promising strategies for these purposes. In this talk I will discuss recent progress on mid-infrared laser spectroscopy performed in a novel type of hollow-core negative curvature fiber (HC-NCF). Sensitive CO, N2O, and H2CO detection between 2.3 and 3.6 µm using absorption spectroscopy will be presented. Photothermal sensing in the HC-NCF will also be discussed using the mid-infrared-pump and near-infrared-probe scheme recently proposed by our group.

The mid-IR wavelength range, i.e. 2-25 μm, houses the vibrational spectra of most gasses and large molecules found in complex structures such as tissue, plastics or food. When designing an upconversion system for imaging or mid-IR detection, several aspects should be considered. Upconversion has several advantageous features which makes it an interesting option to consider for many mid-IR applications. Main advantages include, low-noise detection even at elevated temperatures, an almost instantaneous response time, phase preservation, and the ability to perform upconversion imaging. The χ⁽²⁾ crystal properties impact the performance of the system significantly. Design aspects related to the choice of crystal as well as different applications is presented.

We review our work on SOI and Ge-on-Si PICs for the mid-infrared, covering the 2-8 m wavelength range. We demonstrate the integration of III-V semiconductors on the SOI platform for 2-4m wavelength range integrated lasers and spectrometers, as well as demonstrate tunable quantum cascade lasers by butt-coupling a 5 m wavelength range quantum cascade gain chip to a Ge-on-Si tunable filter. Chip-based mid-IR spectroscopic sensors (based on NDIR spectroscopy, photo-thermal spectroscopy and absorption spectroscopy) will be discussed as well.

Augmented low index waveguides consist of a dual core waveguide layer where the transverse electric (TE) mode is confined to the high index region and the transverse magnetic (TM) mode is confined to the lower index core. The result is a large difference in propagation constants between the TE and TM modes which has applications for on-chip polarization manipulation. In this paper we will demonstrate how this concept can be used to realize polarization rotation, polarization beam splitters and polarizers in the silicon photonics platform.

For next-generation on-chip optical communications, the combination of wavelength- and mode-division multi-plexing has been proposed as way to achieve high aggregate bandwidth on a single multimode silicon bus waveguide. In this application, microring resonators are used to multiplex and demultiplex the different wavelength and mode channels. The designs of the microrings ultimately determine the throughput and power consumption of the circuit. In this work, we perform a comprehensive numerical comparison of the two designs that have already been demonstrated (the point-coupled and racetrack microring resonators) with a new, waveguide-wrapped design. The proposed design reduces the size of the microring cavity, which reduces the spatial footprint and increases the free spectral range (bandwidth), without heavily increasing loss and intermodal crosstalk (power budget). We believe that efficiency improvements to next-generation optical communications circuits like these can help meet the growing global demand for bandwidth without adding to the growing cost of operating them.

Plasmonics is an emerging alternative to photonics. Plasmonics promises ultra-compact size, fast speed, operation across a broad spectral range and a new level of CMOS integration. Yet, plasmonics also has a reputation for being a high-loss technology. In this review, we will discuss opportunities for plasmonics in the field of optical communications, microwave photonics or THz sensing. As practical examples we will highlight latest results achieved with 100 GHz bandwidth plasmonic modulators and detectors or new plasmonic THz detection schemes.

In ordinary consciousness, noise is associated with the term “hindrance”; it is considered as a nuisance that can lead to communication or signal transmission failure or prevent the detection of a weak signal to be measured. However, under certain conditions the impact of noise can be counter-intuitively a resource. In nonlinear systems, noise can induce novel regimes leading to the formation of synchronized structures, coherence between the output and the input of resonators or even to the amplification of weak signals. In other words, noise can play a constructive role, with potential benefits for signal processing or measurement for instance. Single or coupled Nano-Opto-ElectroMechanical resonators whose design is based on suspended photonic crystal membrane could be used as a toy-system to pursue two main goals: stochastic amplification and chaos. As such noise-aided processes might have a strong impact in noise-assisted applications including signal processing or sensing.

In this work, we address a chip-scale polarimeter in which the measurement frame remains optimal over a wavelength range of 200 nm in the presence of Gaussian and Poisson shot noise. The optimization includes equalized variances of each Stokes parameter, and minimal equally weighted variance. The proposed device contains only four photodetectors, which is the minimum number required for full-Stokes reconstruction. It includes broadband asymmetric power splitters and phase shifters. Notably, the broadband phase shifters are designed based on the subwavelength grating waveguides.

Single photon sources by heralding time correlated photons are described. By intermodal four wave mixing (FWM) in a silicon photon circuit, we generate a herald photon at 1260 nm and the heralded one beyond 2 um, with a coincidence to accidental ratio larger than 50 and a single photon purity of 0.75. The discrete band intermodal phase matching does not require further filtering to improve the purity of the single photon. Moreover, the intermodal FWM exhibits high controllability of the signal/idler wavelengths, that can be generated far from the Raman and pump noise, with improved noise filtering.

The combination of edge coupling and a polarization rotator/splitter (PRS) device is an attractive way to achieve receiverside fiber coupling in a 400 Gbits/s connector via Coarse Wavelength Division Multiplexing (400G CWDM 8 MSA)¹. This requires low-loss and polarization insensitivity over the O and E bands. We present a Si/SiN/polymer integrated photonic concept of such a system. Our simulated coupling system shows a loss between the input fiber and the fundamental TE mode in the silicon waveguide ranging from -0.8 dB to -1.4 dB for an arbitrary polarization state over the entire O and E bands.

We report the first experimental quantification of optically induced magnetization in plasmonic Au nanoparticles due to the inverse Faraday effect (IFE). The induced magnetic moment is large under typical ultrafast pulse excitation and can easily exceed the magnetic moment in comparably sized magnetic nanoparticles by more than order of magnitude. Furthermore, the magnetization and demagnetization kinetics are instantaneous within a sub-picosecond timescale, supporting a mechanism of coherent transfer of angular momentum from the optical field to the electron gas. Our results open the door to all-optical sub-wavelength strategies for optical isolation that do not require externally applied magnetic fields.

The two next-generation technologies poised to revolutionize our society are 3D displays and efficient energy conversion, and nanophotonics is the key to both. While tunable devices enable 3D displays, LiDAR, virtual reality, and such other applications, refractory nanophotonic devices enable efficient thermophotovoltaic energy conversion. Both of these nanophotonic devices can be realized by exploiting the phenomenon of many-body effects. While electronic correlation leads to a huge optical tunability, parity-time symmetric interaction between photonic resonators results in frequency-selective thermal emitters necessary for efficient thermophotovoltaics. This talk will describe tunable nanophotonic devices based on charge density waves in 1T-tantalum disulfide and frequency-selective thermal emitters based on hybrid plasmonic-photonic resonators.

Raman imaging is recognized as a powerful label-free approach to provide contrasts based on chemical selectivity. Nevertheless, Raman-based microspectroscopy has drawbacks mostly due to its inherent overwhelming data size, which slows imaging speeds, and non-trivial post-processing, in particular for non-specialists in vibrational spectroscopy. In parallel, compressive sensing has shown a paradigm shift approach where one can computationally reconstruct accurate information from highly undersampled data. Following the compressive sensing spirit, compressive Raman microspectroscopy has emerged as a potential approach to speed up the imaging and concomitantly simplify the post-processing analysis. In this contribution, I will discuss the concepts and assumptions in compressive Raman, in particular focusing on current challenges for fast and high-sensitivity imaging of challenging biological specimens.

Using nanostructured waveguide surfaces via materials ranging from noble metals (e.g., gold) to graphene quantum dots gives rise to so-called surface enhanced infrared absorption (SEIRA) features, which amplify molecular signatures up to a factor of 1,000. Hence, even trace concentrations of molecular constituents may be probed via their vibrational signatures in a label-free direct assay format.

New narrow-gap two-dimensional (2-D) semiconductors exemplified by black phosphorus and tellurene are promising material candidates for mid-IR optoelectronic devices. In particular, tellurene, atomically thin crystals of elemental tellurium, is an emerging narrow-gap 2-D semiconductor amenable to scalable solution-based synthesis and large-area deposition. It uniquely combines tunable bandgap energies, high carrier mobility, exceptionally large electro-optic activity, and superior chemical stability, making it a promising and versatile material platform for mid-infrared photonics. Here we discuss the design and experimental realization of integrated photonic devices based on tellurene and other 2-D semiconductors specifically for the mid-IR spectral regime based on a chalcogenide glass (ChG) photonic platform.

Optical refractive index (RI) sensors exploiting selective co-integration of plasmonics with silicon photonics in Lab-on-achip configurations are expected to disrupt Point-of-Care (POC) diagnostics, delivering performance and economic breakthroughs. Propagating surface-plasmon-polariton modes offer superior sensitivity due to their extreme overlap with the surrounding medium. In parallel, low-loss photonics act as the hosting platform with which the plasmonic losses can be sustained while allowing for multiplexed layouts via in-plane SPP excitation schemes. However, merging plasmonics with silicon photonics in a cost-effective manner, requires a truly CMOS-compatible manufacturing process. Herein, we demonstrate experimentally, the highest bulk-sensitivity among all the plasmo-photonic interferometric RI sensors, while taking the leap forward in the development of a CMOS-manufactured plasmo-photonic sensing platform merging Si₃N₄ photonics and aluminum plasmonics. The proposed structure relies on a butt-coupled interface between Si₃N₄ waveguides and a 70 μm long plasmonic stripe, deployed in one branch of a Mach-Zehnder Interferometer (MZI) serving as the sensing transducer that detects local changes in the refractive index. The lower MZI arm (reference arm) exploits the low-loss Si₃N₄ platform to deploy a MZI-based variable optical attenuator followed by a thermo-optic phase shifter to optimize the sensor performance achieving resonance extinction ratio values at the MZI output of more than 35 dB. Experimental evaluation of a gold-based sensor revealed a bulk refractive index sensitivity of 1930 nm/RIU. In addition, we experimentally demonstrate that the proposed plasmo-photonic waveguide platform can migrate from gold (Au) to Aluminum (Al), demonstrating the first step towards a fully CMOS compatible plasmo-photonic interferometric sensor.

Miniaturized silicon photonics spectrometers have great potential for mass market applications like medicine and hazard detection. However, the performance of state-of-the-art silicon spectrometers is limited by fabrication imperfections and temperature variations. In this work, we present a fundamentally new strategy that combines machine learning algorithms and on-chip spatial heterodyne Fourier-transform spectroscopy to identify specific absorption features operated under a wide range of temperatures in the presence of fabrication imperfections. We experimentally show differentiation of four different input spectra with unknown temperature variations as large as 10 °C. This is about 100x increase in operational range, compared to state-of-the-art retrieval techniques.

We demonstrate significant improvements in the inference accuracy of diffractive optical neural networks and report that a five-layer, phase-only (or amplitude/phase) modulation diffractive network can achieve 97.18% (97.81%) and 89.13% (89.32%) blind-testing accuracy for MNIST and Fashion-MNIST datasets, respectively. Moreover, the integration of diffractive neural networks with electronic deep neural networks is investigated. Using a single fully-connected layer on the electronic part and a five-layer, phase-only diffractive neural network at the optical front-end, we achieved blind-testing accuracies of 98.71% and 90.04% for MNIST and Fashion-MNIST datasets, respectively, despite a >7.8-fold reduction in the number of pixels at the opto-electronic sensor-array.

To overcome the energy and capacity constraints in telecom and datacom networks, introduction of energy-efficient optical circuit switching (OCS) to the conventional electrical packet switching network is widely considered. In the OCS, large-port-count optical switches are essential. We have been working on optical switches based on CMOS-compatible silicon photonics that offer fast switching, compactness, low power consumption, and low-cost. Using our 45-nm CMOS process, we have recently demonstrated a low-loss 32 x 32 silicon photonics switch, and their performance improvements of wide operation bandwidth, polarization-independent operation, etc. We review the recent progress of our silicon photonics switches.

We propose a 2D scanning optical phased array circuit that reconciliates the requirements of resolution and range in automotive LiDAR. Using only the wavelength of the laser source to scan in both x and y directions, we generate a discrete pixelated pattern in the far field, with both the required resolution and a sufficiently long Rayleigh range. We start from a 2D dispersive optical phased array consisting of wavelength-dependent grating coupler antennas and long delay lines with sufficient angular resolution, and then combine these into a larger array to achieve the required range specifications.

Narrow-linewidth semiconductor lasers, micro-optics, silicon photonics (SiP), low noise electronics and high-density packaging are key elements for the development of compact high-end light sources for sensing.

A laser module for the interrogation of an RFOG (Resonant Fiber-Optic Gyroscope) includes three distributed feedback lasers coupled with micro-lenses to a multi-component SiP chip that performs beat note detection and several other functions. The lasers and SiP chip are packaged in a 2.6 cm³ multi-layer ceramic package, a 4x volume reduction over a first generation module. The package interfaces with 92 electrical pins and two fiber pigtails, one carrying the signals from a master and slave lasers, another carrying that from a second slave laser. The complete laser source including electronics is 60 mm in diameter and 23 mm in height, a 10x volume improvement over a previous version. The master laser can be locked to the RFOG resonator with a loop bandwidth greater than 1 MHz. The slave lasers are offset frequency locked to the master laser with loop bandwidths greater than 100 MHz. This high performance source is compact, automated, robust, and remains locked for days.

A lighter version of this laser module for FM-CW LIDAR applications produces an output optical frequency that varies linearly as a function of the electrical drive. A triangular modulation at 100 kHz with a greater than 1 GHz amplitude has been demonstrated with a linearity noise near 1 MHz as measured through a 150 m unbalanced interferometer.

In this work, we design a Si-based Fresnel-zone lens for a hybrid 3D integrated circuit (3D IC) solution. The 3D IC solution consists of two layers of transceiver modules which are mounted at several points on an optical printed circuit board (OPCB) for seamless transmission of signal through each layer to the OPCB and vice versa. Each transceiver module is made up of a Si-subcarrier (Si layer), transceiver IC, laser diode (VCSEL) and photodiode (PD). The transceiver IC, LD and PD are flip-chip bonded to the Si-subcarrier. Fresnel-zone lens are designed on the transmission surface of each of the Si-subcarriers to improve coupling efficiency, transmittance through the silicon substrate, reduce surface scattering, and improve focusing. Each of the Si-subcarrier with the transceiver modules are flip-chip bonded together and also flip-chip bonded to the optical PCB. A 2-level and 4-level Fresnel-zone lens are designed at 1.3μm and 1.55μm. Based on design parameters such as coupling efficiency, transmittance, less design complexity, and ease of fabrication, the 4-level Fresnel zone lens was selected as the optimal design for 3D IC and optical PCB applications. The optimal 4-level Fresnel-zone lens are designed for λ=1.3μm, where the focal length, f is 350μm, and diameter, D, is 167μm; and for λ=1.55μm, where the focal length, f is 350μm, and diameter, D, is 169.2μm. Also the plots of coupling efficiency and transmittance are provided for applications in 3D IC optical interconnects.

We present a phase compensation method for an optical phased array (OPA) to manipulate a sharply defined optical beam. Undesirable initial phase distribution caused by non-uniformity of fabrication processes and variation in the characteristics of phase shifters is measured by utilizing phase-shifting digital holography, where a light wave from a waveguide in arrayed waveguides is used as a reference wave and light waves from the other waveguides are used as object waves. The initial phases can be compensated by using the measured result without falling into local optimal solutions. A numerical simulation showed that the initial phases were correctly measured and compensated by using the proposed method. Applications of the proposed compensation method to a fabricated OPA with 16-channel electro-optic polymer waveguides results in obtaining a sharply defined optical beam.

Vertical stacks based on high-power semiconductor lasers and low-voltage high-current AlGaAs/GaAs and InGaAs/AlGaAs/GaAs thyristors have been developed and studied for generating current pulse in low-impedance load circuits based on semiconductor lasers. Pump current pulses with an amplitude up to 200 A for AlGaAs/GaAs thyristors and up to 70 A for InGaAs/AlGaAs/GaAs thyristors were realized in broad area diode lasers and 3-stripe diode laser mini bars, with optical pulse duration of 40-600 ns and a total peak power of about 78 W. The feasibility of generating current pulses with an amplitude of 16 A and a duration of 2.5 ns is shown, which makes it possible to obtain laser pulses with a peak power of 8 W and a duration of 2 ns. It is shown that the parallel joint of single thyristors allows one to multiply the increase in the current pulse amplitude, while maintaining efficiency and duration.