This PDF file contains the front matter associated with SPIE Proceedings Volume 11689, including the Title Page, Copyright Information, and Table of Contents.

Electronics and photonics have long had a complementary coexistence across multiple application areas. Nonetheless, an ideal partnership of these two realms was made challenging in large part by the enormous frequencies of lightwaves. About two decades ago, this limitation was overcome with the invention of the laser frequency comb. Combs provide a coherent link between electronics and photonics, and because the link is bidirectional, performance attributes previously unique to each can now be shared. Their implementation has been transformative for time keeping, frequency metrology, precision spectroscopy, microwave-generation, ranging and other technologies. More recently still, high-Q nonlinear optical microresonators, have enabled chip-scale frequency combs. I will review efforts to fully integrate comb systems around these new ‘microcombs,’ along with the physical principles of the devices themselves. Finally, I will consider the revolutionary impact this chip-scale unification of the optoelectronic spectrum can have on photonic instrumentation and consumer products.

Introduction to SPIE Photonics West OPTO conference 11689: Integrated Optics: Devices, Materials, and Technologies XXV.

We report on composite hybrid plasmonic waveguides (CHPW) which shows, record experimental attributes such as normalized Purcell factor approaching 10^4, 10-dB amplitude modulation with <1 dB insertion loss and fJ-level switching energy, and photodetection sensitivity and internal quantum efficiency of -54 dBm and 6.4 % respectively. These devices involve amorphous-based, CHPWs, with no crystalline material. The ability to support multiple optoelectronic phenomena while providing performance gains over existing plasmonic as well as dielectric counterparts offers a clear path towards reconfigurable, monolithic plasmonic circuits.

Periodic photonic configurations as photonic crystals (PhCs) and subwavelength grating (SWG) waveguides are gaining a renewed interest for the development of biosensing structures. By performing a proper design, these periodic configurations allow a significant sensitivity increase while keeping a compact footprint, what is achieved by exploiting concepts such as the slow-wave effect, the increase of the light-matter overlap or the interference of dispersion engineered modes.

On-chip Raman sensing enabled by large-scale photonic integration is a promising technology for biological and healthcare applications. In this contribution we give a review the current status of on-chip Raman sensing with a particular focus on the ultimate performances. We discuss the limitations in terms of detection limit and the different paths currently followed to get around them.

Miniaturization of Fourier transform spectrometers must necessarily deal with the problem of the mechanical scan of an interferometer, which is the core element of this technology. Several small-scale FT spectrometers with no moving parts have been demonstrated over the last years, although they all rely on advanced integrated photonics technology. We have shown previously that spectrum of an unknown radiation can be accurately measured with the simplest of the optofluidic systems: a droplet evaporating on a partially reflective substrate. This principle allows to devise a miniaturized FT spectrometer with a spontaneous evaporation-driven scan. Here, we show that such optofluidic spectrometer can be employed for the readout of a plasmonic nanostructured optical fiber sensor, allowing to devise a plasmonic sensing setup where either radiation source, sensor and readout spectrometer are all integrated in an optical fiber. The system performance is analogous to that of a macroscopic plasmonic setup, but it can be obtained with a dramatically reduced cost and dimensions.

Optical spectroscopy is among the most important chemical analysis techniques, due to its high specificity and long-term stability. For spectroscopic analysis of gas compositions, the mid infrared (mid-IR) region is particularly important, owing to the rovibrational resonances in that spectral range. Hence, there is great interest in miniaturizing and reducing the power consumption of optical spectroscopic sensors, but until recently the mid-IR range has been out of reach. We demonstrate spectroscopic sensing of carbon dioxide using an integrated silicon waveguide at the strong absorption peak at 4.23 µm wavelength. We show different measurement principles that leverage the power of integrated optics in innovative ways.

We use a system known as FLOWER (frequency locked optical whispering evanescent resonator) to rapidly detect trace amounts of the chemical warfare agent surrogates DIMP and DMMP. We use sorbent polymer layers covalently bound to the surface of the microtoroid cavity to selectively adsorb target gases. As the target gas diffuses into the polymer layer, a measurable change in the resonance frequency of the toroid occurs. We demonstrate 80 ppt (part per trillion) sensing of DIMP; two orders of magnitude better than what can be achieved using mass spectroscopy.

Gas sensors have wide applications including industrial process control, environment monitoring, safety control, etc. The distribution of these sensors enables data generation for the emerging trend of big data and internet of things. In this work, chip-based non-dispersive infrared (NDIR) gas sensors are demonstrated. Silicon substrate-integrated hollow waveguide (Si-iHWG), which is formed through silicon wafer etching and bonding, is used as optical channel and gas cell. A high sensitivity of 50 ppm for CO2 sensing is demonstrated. The Si-iHWG chip-based sensor with compactness, low cost, versatility, and robustness provides a promising platform for miniaturized gas sensing in various application scenarios.

Photonic Integrated Circuits (PICs) are expected to disrupt the industry similar to what Integrated Circuits did in the electronics industry by shrinking size, weight and cost while increasing performance at the same time. Many optical functions can be integrated in a PIC ranging from a simple beam combiner to a fully integrated optical frequency comb. LIGENTEC's technology addresses today’s challenges of Integrated photonics with low propagation loss, ease of optical coupling and short development cycles. We will present our novel SiN platform for PICs, it’s main functional building blocks and their performance, show effective ways for optical I/Os and a pathway to heterogeneous integration of active elements. Finally, we will discuss application examples in LiDAR, Quantum Computing and RF-optical links in Metrology.

Boosted by novel applications, to satisfy the scalable growth in both network traffic volume and connected endpoints while decreasing the cost and the energy consumption, transparent optical metro edge nodes and DC networks (DCNs) based on fast optical switches have been considered, featuring the data rate and format transparency and eliminating the power consuming O/E/O conversions. We present novel WDM photonic integrated switches with nanoseconds reconfiguration time and polarization independent operation. The WDM photonic integrated switches are capable to switching in the wavelength, space, and nanoseconds time domain to provide full flexibility and the required speed to achieve high throughput networks. Application to dynamic optical metro networks and optical DCN architectures based on distributed nanoseconds WDM photonics integrated switches will be presented.

Silicon modulators are used to generate frequency agile electro-optical frequency combs. Applications are discussed for both fine resolution dual comb spectroscopy and data communications based on wavelength division multiplexing transmission.

A reconfigurable reflective arrayed waveguide grating (R-RAWG) has been designed, fabricated and tested in a silicon nitride platform. The R-RAWG has a number of advantages if compared to a traditional arrayed waveguide grating (AWG) as smaller footprint and the capability to correct to phase errors induced by fabrication defects. To implement this design, we have used tunable reflective michelson loops that produce a broadband response without the need of a modified or additional fabrication process. This approach opens the possibility to implement this design in almost any fabrication platform. By controlling the amplitude and phase of each arm, more than 12 different spectral shapes have been obtained with more than 20 dB of extinction ratio. The control is based on a new method using optimization algorithms borrowed from machine leaning developed using only the power spectrum response of one output to adapt all the variables. The reconfiguration of the band shape, the possibility to adapt the filter to the desired spectrum in one or multiple bands and the fabrication-friendly implementation for mass production make this device suitable for multiple applications as LIDAR, spectroscopy, OCT, Microwaves, Telecommunications among others.

Modern design of photonic devices is quickly and steadily departing from classical geometries to focus more and more on non-trivial structures and metamaterials. These devices are governed by a multitude of parameters and the optimal design requires to simultaneously consider different figure of merits. In this invited talk we will present our recent work on the application of machine learning tools to the multi-objective optimization of multi-parameter photonic devices. In particular, we will demonstrate the potentiality of dimensionality reduction for the analysis of the complex design space of subwavelength metamaterials devices.

Neuromorphic computing has emerged as a highly-promising compute alternative, migrating from von-Neuman architectures towards mimicking the human brain for sustaining computational power increases within a reduced power consumption envelope. Electronic neuromorphic chips like IBM’s TrueNorth, Intel’s Loihi and Mythic’s AI platform reveal a tremendous performance improvement in terms of computational speed and density; at the same time, neuromorphic photonic layouts are constantly gaining ground in exploiting their large component portfolio for enabling GHz-bandwidth and low-energy neurons. Progressing in tight synergy with appropriate training techniques, this evolution has already started to translate into performance improvements in end-to-end applications, highlighting the practical perspectives of the new neural network hardware when effectively synergized with new training frameworks. Herein, we present a complete portfolio of neuromorphic photonic subsystems and architectures, highlighting their utilization in practical application scenario for time series classification and fiber transmission links. Our work extends along feed-forward and recurrent photonic NN models, demonstrating experimental results together with the required training methods for bridging the gap between software-deployed NNs and the photonic hardware. We report on the experimentally validated performance of a 10GHz photonic time series classification engine, presenting also preliminary results on how photonic neurons can replace DSP modules in end-to-end fiber transmission schemes. The perspectives of these layouts to yield energy and area efficiency benefits are discussed through a detailed energy and area breakdown of neuromorphic photonic technologies, highlighting a promising roadmap when plasmo-photonic hardware is adopted.

We present fully apodized and perfectly vertical surface grating couplers in 300 nm silicon waveguides. We achieve ultrahigh coupling efficiency of -0.35 dB at 1550 nm for an optical fiber with 10.4 µm mode-fiber-diameter. To this end, we followed a two stage process in which, we first optimized a pool of periodic grating couplers using machine learning techniques, and then apodized them over 100 parameters using the gradient based adjoint- method. Using a simple fabrication tolerance analysis, we also show that segment variations mostly causes a wavelength shift for the maximum coupling efficiency of the apodized grating couplers, similar to those typically observed for periodic grating couplers.

Despite tremendous progress in the integrated photonics ecosystem over recent years, and the commercial success of many products, there remain some important challenges and opportunities. We discuss some of the key simulation challenges related to the design, simulation, and optimization of advanced components such as lasers, isolators, and novel passive components created with photonic inverse design methods. We also discuss system level simulation challenges such as handling spatial correlations when performing statistical analysis and dealing with thermal management.

Classical and quantum photonics with superior properties can be implemented in a variety of old (silicon, silicon nitride) and new (silicon carbide, diamond) photonic materials by combining state of the art optimization and machine learning techniques (photonics inverse design) with new fabrication approaches.

Compared with electronic integrated circuits, photonic integrated circuits have many advantages and arise as a promising candidate for our next-generation computation and communication systems. However, the feature size of photonic integrated circuits is still large for on-chip large-scale and high-density integration. Inverse design method, powered by advanced algorithms, has been adopted to greatly reduce the footprint of photonic components because it searches for the optimal photonic structures in the full structural parameter space. This talk will cover our recent efforts on inverse-designed photonic components with reduced feature size, including polarization rotators, reflectors, photonic welding points, waveguide crossings, and photonic jumpers. These components will contribute to construction and development of advanced photonic chips with significantly enhanced integration density, scale, and functionality.

Multimode silicon photonics have drawn tremendous attention because the introduction of higher-order modes greatly enhances the capacity of mode-division-multiplexing (MDM) data transmission systems as well as improves the flexibility of on-chip photonic device designs. As the cornerstone of multimode silicon photonics, plentiful multimodemanipulation photonic devices have been developed successfully. On the other hand, more and more emerging applications have been stimulated by higher-order modes introduced in multimode silicon photonics. This paper gives a review for our recent processes in the development of multimode silicon photonic devices. Keywords: mode, multiplexer, conversion, bend, filter, silicon, waveguide.

This presentation will present an overview of wave guiding in thin film lithium niobate where surprising polarisation effects can be encountered. Polarisation conversion can occur inherently and this can lead to surprising leakage losses for both TE and TM polarisations and can significantly impact linear functionality including enabling single polarisation guiding in straight waveguides, challenges with achieving low-loss waveguide bends and also efficient second harmonic generation. A number of applications harnessing these effects will also be presented.

Efficient and reliable on-chip optical amplifiers and light sources can enable versatile integration of various active functionalities on the silicon platform. Here, we discuss our recent results of ultra-high on-chip optical gain in erbium-based hybrid waveguides with a monolithic, CMOS-compatible and scalable atomic-layer deposition process. The unique layer-by-layer nature of atomic-layer deposition enables atomic scale engineering of the gain layer properties and straightforward integration with silicon integrated waveguides. We have demonstrated up to >20 dB/cm net modal gain per unit length, the highest performance achieved from erbium-based planar waveguides integrated on silicon. Our results show significant advances towards efficient on-chip amplification, opening a route to large-scale integration of various active functionalities on silicon.

In this work, we report on the development of ALD-grown ultralow loss host Al₂O₃ planar waveguides on Si and then successful realization of ALD-grown Er³⁺ doped on-chip Al₂O₃ waveguide-based high-gain amplifier devices. Both thermal and plasma enhanced ALD processes have been employed in the optimization processes. Optimization of both Al₂O₃ and Er₂O₃ growth conditions is performed for fine-tuning the optical properties of respective films. Systematic characterization of both films has been carried out by making use of spectroscopic ellipsometry, XRD, FTIR, and XPS techniques. The Er₂O₃ layers are sandwiched between the Al₂O₃ layers to achieve controlled erbium ion doping with the homogenous distribution. The effects of the growth parameters of Al₂O₃ and Er₂O₃ including deposition temperature, RF plasma power, TMA pulse time, Er(thd)3 pulse time, and O₂ pulse time are optimized. With this work, we propose a method for precise control of doping ion concentration and its distribution. As a demonstrator, single-mode ridge waveguide amplifiers are realized by lithography from the active planar structures. ALD deposited chip-scale singlemode Er³⁺ doped Al₂O₃ ridge waveguide amplifiers with a small-signal gain of more than 13 dB/cm over the C band are realized. The reported ALD based growth process can further be adapted for active ion doping of different oxide systems with precise concentration and profile control, thus offering new opportunities for active on-chip applications.

Establishing a photonic integrated circuit (PIC) process is expensive, and unreachable for most companies. The foundry model (FM), in which a small number of generic foundries (GFs) provide optimized manufacturing facilities to a great mass of fabless circuit designers, lowers the costs and makes PIC technology widely accessible. The downside of GF platforms is the fixed process flow, which limits the design freedom on the physical level. Thus, the PIC performance has to be tweaked and optimized on a circuit level. In this work, we optimize the output power of a laser by circuit level design only. Two methods are investigated experimentally. Firstly, the mirror reflectivity is mapped in order to find an optimum cavity design which maximizes the wall-plug efficiency (WPE). An increased WPE enables a higher output power, since the lower thermal dissipation limits the heating. A WPE around 5 % at a 4.5-mW output power was observed. Secondly, booster semiconductor optical amplifiers (SOAs) can be placed at the laser output, and the saturation power can be increased by tapering the active waveguide. Around 60 mW of output power was achieved for a 500-µm long SOA with a 2-µm to 4-µm linear taper. In conclusion, we have shown that lasers on the considered generic foundry platform can be optimized from a circuit level perspective. Due to the flexibility of the FM, this can potentially benefit a wide range of applications, such as optical communications, sensing, lidars, spectroscopy, and many others.

Recent progress in developing tunable mid-IR (2.6 um range) integrated hybrid lasers, are demonstrated. the hybrid laser includes gain chips based on AlGaInAsSb/GaSb quantum wells and tunable reflectors based on micron-scale silicon on insulator integrated photonics platform. The devices exhibit milliwatt-level average power, 10 mW of peak powers and tuning ranges up to 60 nm. Factors limiting tuning range, spectral purity and maximum power are discussed. The demonstrated platform enables realization of tunable lasers for a wide range of applications requiring high performance light sources with emission wavelengths from 1.8 µm to 3 µm and beyond.

This Conference Presentation, “Physics and applications of epsilon-near-zero materials,” was recorded for the Photonics West 2021 Digital Forum.

In this talk, I will present our recent development on the “Meta”-optical fiber integrated with optical plasmonic nanocircuits and epsilon-near-zero (ENZ) materials. I will present the integrated plasmonic network (e.g. directional coupler and resonator) powered by the core mode of optical fiber. I will also discuss the first experimental demonstration of optically confined ENZ resonance excitation in an optical fiber waveguide uniformly coated with AZO nanolayer. The integration of plasmonic/ENZ nanocircuits and optical fiber will open the path to revolutionary ultracompact in-fiber optical devices for optical communication, imaging, sensing/laser applications. The authors acknowledge the supports partially by the Air Force Office of Scientific Research (AFOSR, Award number: FA9550-19-1-0274) and Defense Advanced Research Projects Agency (grant number N66001-17-1-4047).

We present on recent progress on a hybrid tellurite glass and silicon nitride photonic platform. We show low loss waveguides and Q factors < 10^6 in microring resonators. We also show rare-earth-doped active devices, including erbium-doped and thulium-doped waveguide amplifiers and thulium-doped microring lasers. Using the same approach, we demonstrate nonlinear functionalities including efficient four-wave-mixing, supercontinuum generation and third harmonic generation in compact microring resonators and waveguides. The platform is highly promising for compact and low-cost passive, active and nonlinear photonic integrated circuits for applications in computing, communications, sensing and metrology.

Luminescence quenching due to ion cluster formation in erbium ion doped amorphous aluminium oxide, limits the maximum doping concentration that can be incorporated into the material and, consequently, the maximum achievable optical gain. By controlling the reactive sputtering deposition parameters, layers with different morphologies can be deposited. In this work, we investigate low propagation loss poly-crystalline aluminium oxide thin films and the effect of erbium doping on the crystallinity. We have developed a reactive sputter process to reproducibly obtain high refractive index (n~1.72 at 633 nm) poly-crystalline thin films with very low slab waveguide losses from the near-UV to the midinfrared wavelength range. Slab waveguide losses as low as 1.8 dB/cm at 407 nm and less than 0.1 dB/cm at 1550 nm of wavelength have been experimentally characterized. Both the undoped and erbium doped layers were deposited by reactive sputter coating with, a set substrate temperature of 700 °C. Preliminary TEM analyses show no discernible change in the crystallinity of the doped layers with respect to their undoped counterparts. The high optical quality of this material, in combination with a potentially increased rare-earth ion doping concentration, could pave the way towards high-gain on-chip amplifiers in different wavelength ranges and efficient on-chip lasers.

As a novel layered noble metal dichalcogenide material, palladium diselenide (PdSe₂) has attracted wide interest due to its excellent optical and electronic properties. In this work, a strong third-order nonlinear optical response of 2D PdSe₂ films is reported. We conduct both open-aperture (OA) and closed-aperture (CA) Z-scan measurements with a femtosecond pulsed laser at 800 nm to investigate the nonlinear absorption and nonlinear refraction, respectively. In the OA experiment, we observe optical limiting behaviour originating from large two photo absorption (TPA) in the PdSe₂ film of β = 3.26 ×10^-8 m/W. In the CA experiment, we measure a peak-valley response corresponding to a large and negative Kerr nonlinearity of n₂ = -1.33×10^-15 m²/W – two orders of magnitude larger than bulk silicon. In addition, the variation of n₂ as a function of laser intensity is also characterized, with n₂ decreasing in magnitude when increasing incident laser intensity, becoming saturated at n₂ = -9.96×10^-16 m²/W at high intensities. Our results show that the extraordinary third- order nonlinear optical properties of PdSe₂ have strong potential for high-performance nonlinear photonic devices.

Periodic arrays of resonant dielectric nano- or microstructures provide perfect reflection across spectral bands whose extent is controllable by design. At resonance, the array yields this result even in a single subwavelength layer fashioned as a membrane or residing on a substrate. The resonance effect, known as guided-mode resonance, is basic to modulated films that are periodic in one dimension (1D) or in two dimensions (2D). It has been known for 40 years that these remarkable effects arise as incident light couples to leaky Bloch-type waveguide modes that propagate laterally while radiating energy. Perfect reflection by periodic lattices derives from the particle assembly and not from constituent particle resonance. We show that perfect reflection is independent of lattice particle shape in the sense that it arises for all particle shapes. The resonance wavelength of the Bloch-mode-mediated zero-order reflectance is primarily controlled by the period for a given lattice. This is because the period has direct, dominant impact on the homogenized effective-medium refractive index of the lattice that controls the effective mode index experienced by the mode generating the resonance. In recent years, the field of metamaterials has blossomed with a flood of attendant publications. A significant fraction of this output is focused on reflectors with claims that local Fabry-Perot or Mie resonance causes perfect reflection with the leaky Bloch-mode viewpoint ignored. In this paper, we advance key points showing the essentiality of lateral leaky Bloch modes while laying bare the shortcomings of the local mode explanations. The state of attendant technology with related applications is summarized. The take-home message is that it is the assembly of particles that delivers all the important effects including perfect reflection.

The subwavelength patterning of planar structures is now widely used in silicon photonics, enabling the synthesis of metamaterials with engineered optical properties, including refractive index, dispersion, and anisotropy. A wide range of integrated devices based on subwavelength grating (SWG) metamaterials have been demonstrated at telecom wavelengths, some with unprecedented performance. The benefits of SWG metamaterials can be leveraged not only in the typical telecom near-infrared bands, but also at the longer mid-infrared wavelengths. In this invited presentation, we will review our latest developments in SWG-based silicon and germanium photonic devices for the near- and the midinfrared.

We report a photonic RF arbitrary waveform generator and phase encoded signal generator using a soliton crystal micro-comb source with a free spectral range (FSR) of 48.9 GHz, that provides 80 wavelengths. We achieve arbitrary waveform shapes including square waveforms with a tunable duty ratio from 10% to 90%, sawtooth waveforms with a slope ratio of 0.2 to 1, and a symmetric concave quadratic chirp waveform with an instantaneous frequency of sub GHz. The phase encoded signal generator achieves a high pulse compression ratio of 30 and phase encoding rates from 2 to 6 Gb/s This work verifies the effectiveness of using microcombs for high-performance, broad bandwidth, nearly user-defined RF waveform generation.

We are demonstrating the use of Low temperature PECVD silicon nitride based materials used for applications ranging from non-linear functionalities in the C band, wavelength division multiplexing in the O band and post fabrication light based refractive index tuning for in-situ device trimming. These materials are demonstrated for waveguide ranging from 300 nm up to 1 micron in thickness with refractive indices varying between 1.9 and 2.55.

All-optical poling leads to an effective second-order nonlinearity (χ⁽²⁾) in centrosymmetric materials without the need for sophisticated fabrication techniques or material processing, through the periodic self-organization of the charges. The absence of the inherent χ⁽²⁾ in prevailing silicon-based platforms can be surmounted through all-optical poling. Using the induced effective χ⁽²⁾ in silicon nitride (Si₃N₄) waveguides, nonlinear frequency up-conversion processes, such as second-harmonic generation, were previously demonstrated on Si₃N₄. Here, we report near- and non-degenerate difference-frequency generation in all-optically poled Si₃N₄ waveguides. We show the agreement between the theory and the measurements and optimize achievable QPM bandwidth range, reaching conversion efficiency of 1 %/W.

Main complementary metal-oxide-semiconductor (CMOS)-compatible photonics platforms, i.e., silicon and silicon nitride, rely on Kerr nonlinearities for near-instantaneous modulation of optical signals. Kerr nonlinearities emerge due to the third-order susceptibility (χ⁽³⁾) and lead to several nonlinear optical processes, including the four-wave mixing (FWM). FWM is the underlying process of many applications, such as parametric amplification, optical sampling, all-optical wavelength conversion, and demultiplexing and therefore has an indispensable role in optical signal processing. The full potential of on-chip nonlinear processes can be efficiently unlocked by tuning the light-matter interactions at a greater extent via manipulating both material and structural properties of integrated photonic devices. We employ photonic crystal waveguides (PhCWgs) to engineer the structural properties of a waveguide by introducing two-dimensional periodicity in the plane of light propagation. In addition to structural engineering, the chosen material platform aims to bypass the limitations of existing CMOS-compatible platforms: the compositionally engineered ultra-silicon-rich nitride (USRN : Si7N3), eliminates two-photon absorption at 1.55 μm and possesses an order of magnitude higher Kerr nonlinearity compared to stoichiometric silicon nitride at telecommunication wavelengths. Here, we present four-wave mixing in a USRN-based, CMOS-compatible, PhCWg leading to on/off optical parametric signal gain reaching 3 dB, and a large instantaneous idler conversion efficiency of −1 dB experimentally. Enhancement of the Kerr nonlinearity in the presence of a sizable and near-constant group index allows us to demonstrate a large on/off gain per unit length of 333 dB/cm on an ultra-compact, 97 μm-long PhCWg.

Optical and acoustic waves can interact over the nonlinear effect of stimulated Brillouin scattering (SBS), which is a coherent process. By using traveling acoustic waves, we recently showed proof-of-principle experiments of Brillouin-based light storage. The particularity of Brillouin-based light storage is the strict phase-matching condition. This allows for different features: simultaneous storage at multiple wavelengths, cascaded storage at different spatial positions, and nonreciprocal storage with a GHz bandwidth. However, the delay time of this technique has so far been limited to the acoustic lifetime of about 10 ns. In this talk, I will discuss our recent results on coherent photon-phonon interaction. One focus will be on a proof-of-principle experiments on how to reinforce acoustic phonons. This enables us to overcome the obstacle of the limited acoustic lifetime by optically reinforcing the acoustic wave.

The heterogeneous integration of AlGaAs-on-insulator (AlGaAs-OI) has proven to be a highly efficient material platform for nonlinear photonics. When AlGaAs is bonded to silica, there is a large difference in refractive index which results in waveguides with a strong modal confinement and enhanced nonlinearities. This, in combination with low linear and nonlinear losses, makes AlGaAs-OI an ideal platform for exploring nonlinear phenomena. In this talk we present recent progress on the design, fabrication and testing of AlGaAs-OI waveguides for efficient second harmonic generation, supercontinuum generation and the creation of photon pairs.

The integration of cold neutral atoms with nanophotonic circuits offers significant potential as a light–mater interface for a wide range of applications ranging from studies of fundamental physics and quantum many– body physics to quantum networks. Here, we describe the design and realization of a novel platform where an efficiently–coupled microring photonic circuit on a chip is integrated with a cold atom system. This platform is fully compatible with laser cooling and trapping atoms, which allows for direct loading of cold atoms into an optical tweezer lattice formed on the microring circuit. Realizing strong atom–light interaction requires localizing atoms within the near field region of a whispering-gallery mode in a microring resonator. To this end, we estimate the positions of trapped atoms and consider a scheme to transport them to the closest site from the surface. This scheme can also be used for preparing for an array of individually trapped atoms. Such a platform holds promises for realizing a robust and scalable light–mater interface operating at individual quanta.

Optical phased array is an important device for beam steering. To achieve the optical phased array which has wide steering angle, it is necessary the narrow antenna pitch. In this report, we proposed and investigated numerically the plasmonic waveguides antenna which has the low crosstalk for wide steering angle in the optical phased array. It was found that the crosstalk at the antenna pitch 800 nm of the gap type plasmonic waveguide can be almost ignored by the numerical simulation. The steering angle 156 degrees much wider than that of the conventional waveguides was achieved at this antenna pitch.

The field of optofluidics as such emerged in the year 2000. It integrates principles and concepts of optics and microfluidics. Optofluidic devices are hollow components where, until now, just isotropic liquids with different properties have been used. This process makes the optofluidic component a tunable device. Optofluidic components include lenses, prisms and diffraction gratings, among others. The structure of an optofluidic grating consists of a long and thin serpentine microchannel where liquids are injected. Recently, we demonstrated that using isotropic liquids in an optofluidic grating enables it to be used as a refractometer. Here, we present the results when liquids showing an optical activity are injected in the optofluidic grating making it tunable. With this change now the gratings respond different to polarized light and thus are called polarization gratings. Some liquids with optical activity have been tested. Among them a liquid that consists of a mixture of penicillin and water has been used. Penicillin has a high Specific Rotation, [α]_D²⁰= +290^o+5^o (2% in H₂O). The fabricated grating microchannels had a square profile, with dimensions of 200 µm width, 500 µm depth and 5 mm length. The distance between the microchannels is 200 µm. The illuminating light had various wavelengths (632.8 nm, 543 nm and 468 nm) and polarization states such as linear, elliptical and circular. The states of polarization and diffraction efficiency of the first diffracted order, under the illuminating parameters, were studied.

In this work, we analyze passive parameters for a band of 1500 to 1600 nm in microring resonators (MRRs). Such analysis can be vital for estimating an appropriate parameter design exploration with potential applications on Wavelength Division Multiplexing (WDM) solutions. Using a coupled mode theory-based method, we found optimal design spaces for MRRs with radii from 5 to 10 µm and bus-ring gap from 0.12 to 0.21 µm. For All-Pass MRRs, we found an optimal design space where the transmittances in the resonant frequencies are down to 8% in the Through port, while for the Add-Drop MRRs, we found an optimal design space where for transmittances in the Drop port are from 0.77 to 1. We also found optimal design spaces for Q-factors between 2000 and 3800. To find the optimal ring/radius and bus-ring gap values inside the design spaces, we use the particle swarm optimization technique. The data obtained with the exhibited work also shows a modal analysis for the supermodes formed by the cross-section of the bus-ring interface and the impact of UV-lithography common fabrication errors, even due to wafer die positioning. With the latter, our work provides a comprehensive design space exploration and helps designers to know the effect that typical structural fabrication errors will have on the passive resonance.

Our team works on a new concept of smart glasses for augmented reality applications. Our retinal projector consists of a dense waveguide network to transport light on the surface of a glass and an electrode network to extract light. The laser beams are extracted through holographic elements that direct light into the eye. The images are directly created on the retina without optics. The emissive points (EPs) are defined as the intersections between dense waveguide and electrode networks. Design of the Emissive Point Distribution (EPD) is of primary importance in the imaging process. Previous results showed that EPs must be randomly distributed inside the pupil in order to obtain a good self-focusing effect. To evaluate self-focusing, we calculate the Signal-to-Noise-Ratio (SNR) of the point spread function and compare it to the Airy function. Our first EPD model considers waveguides and electrodes designed as a sum of cosine functions. At the inter- section point between a waveguide’s function and an electrode’s function, the composition of these two functions is canceled. We use Newton’s method to find this point. With this model, we can have a good SNR but the number of available pixels is low. Our second model is based on B-Spline curves to represent the waveguide and electrode networks. With this model we can easily locally modify the curves. We develop tools specially adapted for B-Spline curves to find intersections. We also establish properties on the minimum distance between two curves.

Using Synopsys® Software Suite, we developed a Process Design Kit (PDK) targeting the commercial software OptSim Circuit® for the design of integrated photonics devices on transparent materials. We combined the physical properties and optical parameters of the material from laser direct writing (LDW) experimental data in the literature with theoretical model to carry out numerical Finite Differences Time Domain and Beam Propagation Method simulations. The final PDK includes the main building blocks library, namely straight and bent waveguides, directional coupler, splitter, and mode-converter, which give the opportunity to easily design and simulate more complete layouts, simplifying the creation of complex photonic integrated circuits on transparent materials.

The transparent ITO/BaTiO₃/ITO Resistive Random-Access Memory (ReRAM) vertically integrated with bus waveguides situated underneath is successfully realized as a ReRAM-based microdisk resonator fabricated on lithium niobate (LiNbO₃) substrate. The radio-frequency sputtering technique was adopted for the subsequent depositions of the transparent ITO and BaTiO₃ layers, while a proton-exchange method was utilized to fabricate the bus waveguides immersed in LiNbO₃. The ReRAM-based microdisk resonator thus designed and fabricated has the novel functionality of memory and optical spectral filtering combined dually. As the ReRAM microdisk resonator is electronically switched between the two different memory states, or the high-resistance state (HRS) and low-resistance state (LRS), the output spectral observed at both the through and drop ports are noticeably shifted with one another before and after subjecting the ReRAM to a required forming process. Specifically, the spectral shift associated with the LRS state of ReRAM between the through and drop port terminal was approximately 0.4 nm, while roughly 0.6 nm was measured with the HRS state of ReRAM between the same two terminals. The resultant light wave filtering allows the spectrum of the interest to be selectively tuned as the ReRAM device dimensions are varied. Utilizing the different thin-film materials for ReRAM fabrication may also prove beneficial for spectral tuning. In light of different spectral shifts observed, the particular memory state of ReRAM could uniquely be interrogated by an optical means. Our discovery heralds a new era for realizing one of the novel optical memory devices reported to date.

Our team is currently developing an innovative and compact retinal projection display concept for augmented reality applications. This concept intends to break with conventional optics using a device based on an integrated photonics architecture. Designs and simulations of test structures have been presented in previous works. Here, we present experimental results obtained on stoichiometric Si₃N₄ integrated photonic circuits designed for λ = 532nm. The samples combine several building blocks such as grating couplers, Multi-Mode Interferometers (MMI) and dense waveguide arrays with several emissive areas. We used a goniometric characterization bench to perform far field measurements. For near field characterization, an imaging setup using a 4.5mm-focal lens system and a high-resolution CMOS camera was mounted on the goniometer. The power profiles of emissive points were measured in the near and far field. Regarding the dense waveguide arrays, their angular characterization confirms our simulations and allows us to emphasize the impact of trapezoidal-shaped waveguides on the emission angle. We measured a homogeneously distributed power profile across the waveguide distribution on the emissive areas. The power ratio of each emissive area remains relatively uniform. This is a promising result for our future work where light must be equally and uniformly distributed over the surface of the display.

We report the design and numerical analysis of a composite HfO₂-coated-Si₃N₄ waveguide pumped with femtosecond laser pulses at 1550 nm for mid-infrared wavelength generation at 4.0 µm. The principle of wavelength conversion is based on the degenerate four-wave-mixing in designed HfO₂-coated-Si₃N₄ waveguide. The waveguide design and the dispersion engineering to get the desired phase matching conditions have been discussed. The advantages of composite Si₃N₄-HfO₂ waveguide over Si3N4 strip waveguide include high damage threshold, better electromagnetic interaction and thus strong light confinement, and relatively longer wavelength conversion in the mid-infrared region. Such on-chip composite Si₃N₄-HfO₂ waveguide generating mid-infrared light at 4.0 µm holds considerable potential for the applications in a wide range of the mid-infrared nonlinear optical devices.

In this work, we present the design process and experimental evaluation of a 1×2 asymmetric power splitters based on the self-imaging principle that is applied on an ultra-low-loss 800nm thick Si3N4 platform. The asymmetry in the multimode interference region is induced by removing a rectangular piece from the edge of the coupler, prompting a disruption at the interference pattern and adjusting accordingly the splitting power ratio. The design of the MMIs operating in the 1500- 1600nm wavelength region was realized through 3D-FDTD calculation method and the experimental results agree with theory providing an error of 5% in splitting ratio and less than -0.6dB insertion losses.

Integrated tunable lasers based on the co-integration of InP-based SOAs with low-loss Si3N4 dielectric waveguides have emerged as promising solutions in applications where the control of light phase is fundamental. Μicrowave photonics, coherent communications and LIDARs are only some of the applications where sub-KHz linewidths have already been achieved. Nevertheless, the majority of these demonstrations are based on Si₃N₄ platforms featuring thicknesses lower than 300nm and providing modes with effective indices below 1.6 imposing a major restriction on the achievable FSR values and devices’ footprint. In this work, we present the design of Vernier ring-inspired reflectors based on an 800nm- thick Si₃N₄ platform providing a TE fundamental mode with an effective index close to 1.71 for a width of 800nm, a group index close to 2.08 at λ=1550nm wavelength, and propagation losses as low as 0.2dB/cm. The proposed thick- Si₃N₄ designs are based on a simple dual ring Vernier configuration achieving an experimental FSR near 38nm and a 15dB side-mode suppression. These results are in close agreement with the ones obtained theoretically through a detailed Transfer Matrix Formulation verifying the accuracy of the presented semi-analytical model. This simulation model is then employed for the prediction of the performance of more advanced structures such as triple cascaded and high-order Vernier Ring designs, towards extending the achievable FSR and SMSR metrics.