This PDF file contains the front matter associated with SPIE Proceedings Volume 10535 including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Fluorescence imaging provides a powerful approach to study fundamental life processes and has become an integral part of the toolbox for biologists. In order to study molecular interactions, single molecule imaging approaches require labeling the molecules with fluorescent reporters. The influence of these fluorescent labels to the molecular interactions have been unknown. In this talk, I will present a hybrid photonic-plasmonic nano-device as a new tool to study molecular interactions at the single molecule level. By coupling a single plasmonic nanoantenna with photonic crystal nanocavity, we can achieve both high quality factor and ultra-small mode volume, thus pushing the detection limit to the single molecule level while keeping the local heating effect at a negligible level.

Microring resonators find many applications for on-chip integrated optical sensors. Their spectral response contains resonance dips that shift due to variations of the optical path length of the microring probed. Numerous examples of such microring resonator sensors in the SOI, Si₃N₄ and SiON waveguide technologies have been reported for the detection of bulk refractive index variations and the label-free detection of biomarkers. Al₂O₃ is an alternative waveguide technology that exhibits low optical propagation losses, is transparent over a large spectral range extending from the visible to the mid-IR and permits co-doping with active rare-earth ions, which enables the co-integration of active devices on the chip. In this work an Al₂O₃ microring resonator sensor was developed for the label-free detection of protein biomarkers. The uncladded microring with a radius of 200 μm had a measured quality factor of 3.2 × 10⁵ at 1550 nm. Submerging the devices in water decreased the quality factor to 45 × 10³. This corresponds with propagation losses in the rings of 0.6 dB/cm and 5.7 dB/cm respectively. The bulk refractive index sensitivity of the sensor was determined by flowing NaCl dissolved in water in different concentrations. A sensitivity of 102.3 ± 0.5 nm/RIU with a corresponding limit of detection of 1.6 × 10^-6 RIU was demonstrated for TM polarized light. High affinity human monoclonal antibodies mAb S100A4 were immobilized on the sensor to detect the S100A4 protein biomarker down to 12 nM concentrations. These results demonstrate the feasibility of this material for label-free optical biosensors.

Following the Industrial advancements in the last few decades, highly flammable chemicals, such as ethanol (CH₃CH₂OH) and methanol (CH₃OH) are widely being used in daily life. Ethanol have some degrees of carcinogenic effects in human whereas acute and chronic exposer of methanol results blurred vision and nausea. Therefore, accurate and efficient sensing of these two vapors in industrial environment are of high priorities. We have designed a novel, ultra-compact chemical vapor sensor based on composite plasmonic horizontal slot waveguide (CPHSW) where a low-index porous-ZnO (P-ZnO) layer is sandwiched in between top silver metal and lower silicon layers. Different P-ZnO templates, such as nano-spheres, nano-sheets and nanoplates could be used for high-selectivity of ethanol and methanol at different temperatures. The Lorentz-Lorenz model is used to determine the variation of P-ZnO refractive index (RI) with porosity and equivalent RI of P-ZnO layer for capillary condensation of different percentage of absorbed vapor. An in-house, new divergence modified finite element method is used to calculate effective index and attenuation sensitivity. Plasmonic modal analyses of dominant quasi-TM mode shows a high 42% power confinement in the slot. Next, an ultra-compact MZI incorporating a few micrometres long CPHSW is designed and analysed as a transducer device for accurate detection of effective index change. The device performance has been studied for different percentage of ethanol into P-ZnO with different porosity and a maximum phase sensitivity of >0.35 a.u. is achieved for both the chemical vapors at a mid-IR operating wavelength of 1550 nm.

Tracking changes in a photonic integrated circuit is an essential task for many applications, such sensing or telecommunication systems. In particular, locking of laser to a microring resonator and tracking resonance shifts over time with high accuracy can improve several applications such as sensing and biosensing. In this work, we present a novel system to lock a laser to a silicon photonics microring resonance and track the changes in wavelength over time. An electronic digital feedback loop balances the power at outputs of the microring (at the through and the drop ports) by tuning finely the wavelength of the input laser. The silicon photonics chip is equipped with integrated photodiodes at each port of the microring. The low noise of photodiodes, together with the resolution of the tuning of the laser, allows achieving locking with less than 7 femtometers as residual noise at 1550 nm. The digital implementation of the feedback loop permits to reach bandwidth up to 1 kHz. Demonstration of the locking has been made with several different microring resonators, with Q-factor varying from 5000 to 60000.

Integrated Optical Fibre (IOF) allows for robust planar integration and seamless monolithic coupling. Fabrication is achieved through an adapted Flame Hydrolysis Deposition (FHD) technique, which forms a ruggedized glass alloy between the fibre and planar substrate. It has been previously demonstrated as a low linewidth external cavity lasers diode and a hot-wire anemometer, inherently suitable for harsh environments. This work looks at implementing the platform for harsh environment refractometry, in particular monitoring hydrocarbon fuels in the C14 to C20 range (e.g. Jet A1 and diesel). The platform uses SMF-28 fibre and direct UV written Bragg gratings to infer refractive index and thus the quality of the fuel. A challenge arises as the refractive index of these fuels are typically greater than the refractive index of the waveguide. Therefore, the guided mode operation of FBG refractometers is unsuitable. This work uniquely reports leaky mode operation and a regression analysis, inferring propagation loss through changes in amplitude of successive gratings. In effect, the proposed methodology utilises the imaginary part of the effective index as opposed to the real part, typically used by such sensors. Initial results have shown a 350 (dB/cm)/riu sensitivity is achievable above a refractive index of 1.45. This was measured for a SMF-28 fibre wet etched to 30 µm and planarized. Considering a 0.01 dB/cm propagation loss resolution, refractive index changes of the order 10-5 can be approached. Work will be presented on the fabrication of an IOF platform for refractometers as well as metrics for survivability in harsh environments.

In this communication, we report on the design, fabrication, and testing of Silicon Nitride on Insulator (SiNOI) and Aluminum-Gallium-Arsenide (AlGaAs) on silicon-on-insulator (SOI) nonlinear photonic circuits for continuum generation in Silicon (Si) photonics. As recently demonstrated, the generation of frequency continua and supercontinua can be used to overcome the intrinsic limitations of nowadays silicon photonics notably concerning the heterogeneous integration of III-V on SOI lasers for datacom and telecom applications. By using the Kerr nonlinearity of monolithic silicon nitride and heterointegrated GaAs-based alloys on SOI, the generation of tens or even hundreds of new optical frequencies can be obtained in dispersion tailored waveguides, thus providing an all-optical alternative to the heterointegration of hundreds of standalone III-V on Si lasers. In our work, we present paths to energy-efficient continua generation on silicon photonics circuits. Notably, we demonstrate spectral broadening covering the full C-band via Kerrbased self-phase modulation in SiNOI nanowires featuring full process compatibility with Si photonic devices. Moreover, AlGaAs waveguides are heterointegrated on SOI in order to dramatically reduce (x1/10) thresholds in optical parametric oscillation and in the power required for supercontinuum generation under pulsed pumping. The manufacturing techniques allowing the monolithic co-integration of nonlinear functionalities on existing CMOS-compatible Si photonics for both active and passive components will be shown. Experimental evidence based on self-phase modulation show SiNOI and AlGaAs nanowires capable of generating wide-spanning frequency continua in the C-Band. This will pave the way for low-threshold power-efficient Kerr-based comb- and continuum- sources featuring compatibility with Si photonic integrated circuits (Si-PICs).

Whispering gallery mode optical resonators integrated on silicon have demonstrated low threshold Raman lasers. One of the primary reasons for their success is their ultra-high quality factors (Q) which result in an amplification of the circulating optical field. Therefore, to date, the key research focus has been on maintaining high Q factors, as that determines the lasing threshold and linewidth. However, equally important criteria are lasing efficiency and wavelength. These parameters are governed by the material, not the cavity Q. Therefore, to fully address this challenge, it is necessary to develop new materials. We have synthesized a suite of metal-doped silica and small molecules to enable the development of higher performance Raman lasers. The efficiencies and thresholds of many of these devices surpass the previous work. Specifically, the silica sol-gel lasers are doped with metal nanoparticles (eg Ti, Zr) and are fabricated using conventional micro/nanofabrication methods. The intercalation of the metal in the silica matrix increases the silica Raman gain coefficient by changing the polarizability of the material. We have also made a new suite of small molecules that intrinsically have increased Raman gain values. By grafting the materials to the device surface, the overall Raman gain of the device is increased. These approaches enable two different strategies of improving the Raman efficiency and threshold of microcavity-based lasers.

Chalcogenide glasses (ChGs) exhibit high refractive indices, broad transparency windows, pronounced nonlinearities, and photo-sensitivity effects. Waveguides are fabricated in ChGs layers using dry etching, nano-imprint lithography, or direct laser-beam writing. Ultra-high stimulated Brillouin scattering amplification was demonstrated in ChG waveguides. Efficient Brillouin scattering requires tight confinement of guided optical and acoustic modes with large overlap. Here we present waveguides consisted of a ChG core and silica cladding. Devices are fabricated in silica-on-silicon wafers. The silica layer is dry-etched through a Cr hard mask. Etching defines either isolated trenches or isolated pedestals in the silica layer, with widths of 1-3 µm and heights between 0.5-2 µm. A 300 nm-thick layer of As2S3 glass is deposited onto the sample by thermal evaporation. Deposition partially fills the etched silica trenches with a ChG core region, or alternatively forms a core region on top of silica pedestals with air on three sides. A thin upper layer of resist is applied for protection. The waveguide structure provides two potential advantages: tight confinement of both guided optical and acoustic modes in small-area ChG cores, and no processing of the ChG layer following deposition. The end-to-end losses of a 4 mm-long device with a 600 nm-wide core were 20 dB. Losses are primarily due to coupling to/from fibers at the facets. Four-wave mixing between two continuous-wave pumps of 10 mW power was demonstrated, with efficiency on the order of -60 dB. The linear and nonlinear characterization of longer devices is ongoing.

We have designed and developed a nonlinear-optic wavelength converter with periodically poled LiNbO₃ (PPLN) waveguides for optical fiber communication systems. The wavelength conversion module comprises two parallel PPLN ridge waveguide devices for a polarization-independent operation. We demonstrate highly efficient wavelength conversions and amplifications based on a cascaded second harmonic generation (SHG) and difference frequency generation (DFG), and optical parametric amplifier (OPA). The wavelength conversion efficiencies and the signal gains more than 20 dB are achieved for both orthogonal transverse magnetic (TM) polarization and transverse electric (TE) polarization in the module.

The search for integrated photonic devices that enable modulation and active functions at speeds faster than those reached using electronics, continues to drive much of the research in photonics. One of the approaches to this task is to use the intrinsic electronic nonlinearity of metals. Plasmonic nanostructures and metamaterials have indeed shown strong nonlinear response leading to signal modulation at THz speeds. Furthermore, active polarization control is one of the major challenges facing an industry that aims at integrating photonic device at the nanoscale, as these tend to be based on weakly birefringent crystals that typically operate over micron scale lengths and microseconds. At the same time, hyperbolic metamaterials, such as nanorod-based plasmonic metamaterials or metal-dielectric multilayers, exhibit very highly anisotropy unachievable with natural materials resulting in efficient polarization conversion over sub wavelength distances. For instance, full linear to circular conversion has experimentally been shown with a 350 nm thick nanorod metamaterial slab. Here we show experimentally and theoretically that plasmonic nanorod metamaterials can provide intensity-dependent polarization rotation at ultrafast time scales, well within the THz frequency range. Time-resolved non-degenerate optical pump probe spectroscopy is used to provide experimental demonstration of the polarization rotation of a probe signal controlled by a control pump beam and reveal the associated rotation mechanism. The results provide new grounds for the development of optical functionalities that prove useful for all-optical ultrafast information processing in integrated photonic devices.

Aluminium Gallium Arsenide (AlGaAs) is regarded as a very promising material for non-linear optical applications thanks to its strong second and third order non-linear coefficients. Moreover, its bandgap can be easily increased to values above 1.3 eV by varying the percentage of Aluminium, which mitigates the two photon absorption at telecom wavelengths that typically hinders the use of silicon based devices for these applications. However, the major drawback of GaAs/AlGaAs waveguides lies in the relatively low modal confinement in the vertical direction that translates into high propagation losses. The integration of an AlGaAs core on a silica cladding layer (i.e. AlGaAs on Insulator or AlGaAs-OI) is a very new and promising material platform for non-linear photonics as it combines the superior non-linear properties of AlGaAs with the very strong modal confinement offered by the low refractive index of the silica cladding. To date the most challenging aspect of AlGaAs-OI has been in the fabrication of the platform itself. In this talk key aspects regarding the design, fabrication and testing of AlGaAs-OI waveguides for nonlinear applications shall be explored, focussing on the fabrication challenges and how they were overcome. In particular, we will review AlGaAs epilayer designs with stop-etch layers that allow effective removal of the GaAs substrate and dry etching chemistries for smooth and vertical waveguide sidewalls. We will also discuss how these different designs and fabrication techniques impact on the waveguide propagation losses and on the performance of micro-ring resonators for non-linear applications.

In this paper, the realization of hybrid Lithium Niobate-silicate glass waveguide is presented. A 300nm-thick ion-sliced lithium niobate thin film has been successfully reported on a glass substrate containing high refractive index strip created by a silver/sodium ion exchange. The obtained waveguides have been successfully characterized at a wavelength of 1.5 μm and showed a single mode behavior as well as a strong confinement. The use of such waveguides for electro-optic modulators or second harmonic generation is also discussed.

A silicon dual-ring modulator designed for chirp tuning in an intensity-modulated system is described and its performance is modelled. Previous experimental work using this device geometry partially demonstrates the advantages of the dual-ring approach. However, we provide here the first comprehensive theoretical treatment from which optimal operation parameters can be deduced. The device consists of two, over-coupled micro-ring resonators independently coupled to a MachZehnder interferometer and driven by a push-pull signal. Utilizing the interference effect provided by the Mach-Zehnder geometry, the device produces a large modulation depth and improved linearity, compared to single ring geometries, provided that the appropriate resonance detuning between the two micro-ring resonators and the correct phase condition are met. The differential drive configuration generates opposing signs of dispersion from the two rings leading to an adjustable modulation chirp that can be tuned into the negative or positive regime, or can be fixed at an essentially zero-chirp condition. System-level simulation is reported to validate the chirp tuning for a non-return-to-zero signal at a modulation rate of 28 Gb/s.

A photonic microwave sensor based on electro-optic (EO) polymer infiltrated silicon subwavelength grating (SWG) waveguide and bowtie antenna is designed and experimentally demonstrated. The microwave sensor receives wireless microwave signals via the bowtie antenna. The electrical field between the extension bars of the bowtie antenna modulates the light guided in the SWG based Mach–Zehnder interferometer (MZI). Thus, microwave signals can be detected by measuring the intensity variation of light from the MZI output. The EO polymer infiltrated SWG does not require ion implantation and has low optical propagation loss. Furthermore, compared to slotted silicon waveguides, the EO polymer poling efficiency on SWG structure can be greatly increased due to wider poling separations and thus the increased breakdown voltage. In order to achieve strong microwave field enhancement, the impedance of the bowtie antennas is tailored. The optimized bowtie antennas operate at 15 GHz and provide >1000X field enhancement while only occupy an area of 7.6 mm X 0.3 mm. Leveraging the folded SWG waveguide, high EO coefficient polymer, and large field enhancement from bowtie antenna, an ultra-sensitive and compact microwave photonic sensor has been demonstrated.

Novel sub-wavelength silicon photonic waveguides for label-free sensors are demonstrated in this article. We use silicon-on-insulator (SOI) waveguides that consist of sub-wavelength grating (SWG) structures, where the waveguides are made of small silicon arrays (180 × 180 nm² rectangles with 60 nm gaps). They are used to form microring and Bragg grating resonators which measure the change of refractive index by monitoring the resonant wavelength shift. Due to the high surface contact area and low optical confinement of the proposed waveguide, the sensitivity (both bulk and surface) can be significantly increased. The bulk sensitivity of 580 nm/RIU for the microring and 610 nm/RIU for the Bragg grating are better than other recently published resonator sensors. Moreover, a standard biological sandwich assay demonstrates an enhanced surface sensitivity of 2050 pm/nm for both devices. Theoretical models and experimental results are investigated, indicating the predominant losses are from the water absorption at 1550 nm and scattering by sidewall roughness.

The prospect of creating metamaterials with optical properties largely exceeding the parameter space covered by natural materials has been inspiring intense research efforts for more than a decade. Until recently, optical metamaterials were usually associated with plasmonic nanostructures. However, plasmonic metamaterials suffer from the intrinsic absorption losses of metals at optical frequencies. To overcome this problem, metamaterial research has shifted its focus towards nanoparticles composed of high refractive index dielectrics, which support electric and magnetic multipolar Mie-type resonances [1]. Similar to plasmonic nanoresonators, their resonance properties can be tuned by the nanoparticle design, making them versatile building blocks of functional photonic nanostructures with tailored optical response. Silicon in particular has emerged as a popular material choice, not only due to its high refractive index and very low absorption losses in the telecom spectral range, but also to its huge technological relevance. This talk will review our recent advances in controlling light with Mie-resonant metasurfaces - the two-dimensional counterparts of metamaterials - composed of Mie-resonant silicon nanoparticles. Such metasurfaces can impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front with high transmittance efficiency [2]. A focus of this talk will be on strategies to obtain dynamic control of the metasurface optical response [3]. [1] I. Staude & J. Schilling, Nature Photon. 11, 274–284 (2017). [2] K. E. Chong et al., Nano Lett. 15, 5369–5374 (2015). [3] M. R. Shcherbakov et al., Nat. Commun. 8, 17 (2017).

Using a new class of optomechanical waveguides that produce large Brillouin nonlinearities, we realize Brillouin lasers, Brillouin amplifiers, and Brillouin-based signal processing technologies in silicon photonics. Counterintuitively, the same nanophotonic silicon waveguides that greatly enhance both Kerr and Raman nonlinearities exhibit vanishingly small Brillouin nonlinearities. Only with the advent of new optomechanical waveguides—that guide both light and sound—have Brillouin interactions been transformed into the strongest and most tailorable nonlinearities in silicon. We summarize progress in the rapidly growing field of integrated Brillouin photonics, and explain how a variety of simulated lightscattering processes can be engineered to (1) create Brillouin-based optical amplifiers, (2) tailor optical susceptibility, and (3) create new signal processing technologies in silicon photonics. Finally, we harness Brillouin-based opticalamplification to create the first silicon-based Brillouin lasers and we discuss their performance characteristics.

Stimulated Brillouin scattering (SBS) in integrated photonic circuits enables a wide range of application from narrow-linewidth lasers, radiofrequency filters to signal processing. In this presentation, we focus on two specific applications: light storage based on acoustic waves and SBS-based distributed sensing. We demonstrate that storing optical data in acoustic waves is a powerful concept, enabling coherent storage in amplitude and phase with a broad bandwidth in planar waveguides without the need of a resonant structure. External control light pulses define position and storage time and allow for deliberate control of the flow of optically encoded information. We also show that it allows for the simultaneous storage at different frequency channels and that no cross talk between the channels is observed. This is enabled by our photonic chip platform which provides a record-high Brillouin gain in planar spiral waveguides. Localizing the Brillouin response to a very short scale allows for a distributed mapping of our waveguide structure. We use Brillouin optical correlation domain analysis, a technique inspired from radar technology, to scan our spiral and straight waveguides with a high spatial resolution of 800 µm. This enables short scale sensing of changes in the refractive index and accurate mapping of hybrid waveguide structures.

Direct UV writing is a technique capable of fabricating low-loss channel waveguides, couplers and Bragg gratings in planar silica devices by translating an appropriate substrate through a tightly focused UV beam. To date direct UV written waveguides have been primarily formed using 244nm laser light, relying on the photosensitivity provided by doping with germanium and boron. To induce sufficient refractive index change, necessary for wave guiding, the substrates also require hydrogenation prior to UV writing. Not only does this require additional processing but over time the hydrogen present within the silica out-diffuses, which can cause variation of the final written structures. Deep-UV light, with a wavelength of 213 nm, has previously been used to inscribe strong fibre Bragg gratings (FBGs) in hydrogen-free Ge-doped fibres. Here we present the use of a 213 nm UV laser to write planar waveguide devices without the need for hydrogen loading. Flame Hydrolysis Deposition (FHD) was used to deposit core and cladding layers of doped silica onto a thermally oxidised silicon wafer. Individual planar chips were diced from this wafer and a 5th harmonic Q-switched solid state laser operating at 213 nm wavelength was used to inscribe waveguides within the germanium-doped core layer of the chips without prior hydrogen loading. We shall present our latest results of direct deep-UV written waveguides, including; the characterisation of single mode waveguides, detailed fluence and loss measurements, induced refractive index change and the first demonstration of planar Bragg gratings and photonic structures written with 213nm light.

Hollow Core Anti-resonant fibers allow for guidance of mid-infrared light at low attenuation and can be used for a variety of applications, such as high power laser transmission and gas sensing. Recent work has seen the integration of silicon into such fibers with linear losses potentially as low as 0.1dB/m. Due to the change in refractive index difference of silicon via for example the free carrier plasma dispersion effect, the prospect of an all optical modulator using such a fiber has been proposed. Here, further work has been undertaken on the integration of functional materials inside hollow core fibers via the deposition of the TMD semiconductor material MoS₂, in its few-layered form. Through the use of a liquid precursor, a high quality MoS₂ film can be deposited over 30cm length of fiber, as confirmed via Raman spectroscopy. The transmission spectra of these novel composite material hollow core fibers has also been analysed, showing additional loss of around 5dB/m, despite being only around 2nm in thickness. This implies that the refractive index of the integrated material is potentially able to modify the guidance properties of the fiber sample. We will present a comparison of the composite material hollow core fibers we have fabricated to date and discuss the prospects for using these novel waveguides in the active manipulation of light, including optical switching, sensing and frequency generation.

KY(WO₄)₂ and other materials of the double tungstate crystal family have been used for decades in active optical applications because of their relatively high refractive index (n≈2-2.04 @ 1550 nm), high transparency window (0.3- 5 μm), excellent gain characteristics when doped with rare-earth ions and reasonably high thermal conductivity (~3.3 Wm^-1K^-1). Low-contrast (Δn<0.02) on-chip amplifiers and lasers in this material with good performance have been shown in recent years. Higher refractive index contrast can further improve this performance, and allow easier integration with other integrated optics platforms due to their smaller footprint. Because double tungstate materials cannot be directly grown on many prospected substrates, other methods to fabricate optical waveguides with a thickness of 1-2 μm need to be investigated. In this work, swift heavy ion irradiation has been used to produce a planar waveguide by introducing a buried layer of lower refractive index in the KY(WO₄)₂ at a depth of ~2.5 μm. After the irradiation, an annealing step was introduced to reduce the scattering losses. The refractive index profile, effective refractive indices and absorption spectra of the planar waveguides have been investigated for several annealing temperatures, and end-facet free-space coupling of 1550 nm has been used to measure the losses. For a fluence of 3·10¹⁴ ion/cm² of 9 MeV C ions, propagation losses <1.5 dB/cm have been demonstrated at 1550 nm after an annealing step at 350°C.

Rare earth ion doped potassium double tungstates (e.g. KY(WO4)2, KYb(WO₄)₂, and KGd(WO₄)₂) have long been used as laser and amplifier materials thanks to the high achievable gain provided by the rare-earth ions. This family of host materials is also very attractive for nonlinear optics due to their high nonlinear refractive index and Raman gain. Very efficient on-chip solid state lasers, frequency combs, supercontinuum sources and Raman lasers could be realized if high refractive index waveguides with the correct dispersion were developed.

To date, the demonstrated integrated devices in rare-earth ion doped potassium double tungstates have shown very promising results, including high gain in on-chip amplifiers and high efficiency and output power in on-chip lasers. These devices, however, were fabricated using low refractive index contrast waveguides, which are not suitable for ring resonators or to achieve anomalous dispersion. High refractive index contrast KY(WO₄)₂ waveguides with high confinement are therefore needed as building blocks for active devices.

In this work, pedestal disk resonators are proposed, based on a combination of swift ion irradiation, focused ion beam milling and a novel wet etching process. In-coupling of light into the first fabricated pedestal disks will be presented.

The packaging of photonic devices remains a hindering challenge to the deployment of integrated photonic modules. This is never as true as for silicon photonic modules where the cost efficiency and scalability of chip fabrication in microelectronic production facilities is far ahead of current photonic packaging technology. More often than not, photonic modules are still packaged today with legacy manual processes and high-precision active alignment. Automation of these manual processes can provide gains in yield and scalability. Thus, specialized automated equipment has been developed for photonic packaging, is now commercially available, and is providing an incremental improvement in cost and scalability. However, to bring the cost and scalability of photonic packaging on par with silicon chip fabrication, we feel a more disruptive approach is required. Hence, in recent years, we have developed photonic packaging in standard, highthroughput microelectronic packaging facilities. This approach relies on the concepts already responsible for the attractiveness of silicon photonic chip fabrication: (1) moving complexity from die-level packaging processes to waferlevel planar fabrication, and (2) leveraging the scale of existing microelectronic facilities for photonic fabrication. We have demonstrated such direction with peak coupling performance of 1.3 dB from standard cleaved fiber to chip and 1.1 dB from chip to chip.

Rare-earth ion doped potassium yttrium double tungstate, RE:KY(WO₄)₂, is a promising candidate for the realization of on-chip lasers and amplifiers. Two major bottlenecks difficult the realization of compact, high-contrast devices. Firstly, the crystal can only be grown on a lattice matched substrate, leading to a low (<2×10^-2) refractive index contrast between core and cladding. Secondly, the required thickness for the high-index contrast waveguides, ~1 μm, makes a lapping and polishing approach very challenging. In this work we propose a novel polishing stop that will permit to accurately control the final thickness of the KY(WO₄)₂ waveguide within a few tens of nanometers. A 1 mm thick KY(WO₄)₂ substrate is flip-chip bonded with an adhesive layer onto a SiO₂ substrate. Afterwards a low temperature pulsed laser deposited (PLD) Al₂O₃ layer - with the desired final thickness of the KY(WO₄)₂ waveguide core - is deposited on top of the assembly. The sample is then thinned using a multistep lapping and polishing procedure. Earlier work with a polishing stop made from SiO₂, showed a decrease of the polishing speed with a factor 3-4, allowing the termination of the process within a tolerance of a few tens of nanometers.

Direct wafer bonding is a key enabling technology for many current and emerging photonic devices. Most prior work on direct wafer bonding has, however, focused on the Si platform for fabrication of silicon-on-insulator (SOI) and micro-electromechanical systems (MEMS). As a result, a universal bonding solution for heterogeneous material systems has not yet been developed. This has been a roadblock in the realization of novel devices which need the integration of new semiconductor platforms such as III-V on Si, Ge on Sapphire, LiNbO₃ on GaAs etc. The large thermal expansion coefficient mismatch in the hetero-material systems limits the annealing to low temperatures to avoid stressed films. This work explores the use of Al₂O₃ as an intermediate layer for bonding heterogeneous materials. The key to achieve a stronger bond is to maximize the hydroxyl group density of the bonding interfaces. The use of Al₂O₃ helps achieve that, since it has a high hydroxyl group density (around 18 OH/nm² at RT) which is approximately 4 times that of a Si surface. This work optimizes the bonding process using Al₂O₃ by studying the contribution of Al₂O₃ deposition parameters. An optimized process is presented and applied to bond GaAs on Sapphire and InP on SiO₂/Si.

Fiber-chip grating couplers providing high-efficiency, robustness and cost-effectivity are recognized as a key building block for large-volume photonic applications. However, the efficiency of silicon-on-insulator (SOI) grating couplers is limited by the mismatch between the beam diffracted by the grating and the fiber mode, back-reflections at the grating-to-waveguide interface, and the power radiated towards the substrate. While the first two limitations can be overcome by grating apodization, the limited diffraction efficiency (directionality) towards the fiber remains a challenge. Typically, grating directionality is optimized by backside metallization, distributed Bragg mirrors, multi-level grating architectures or non-standard etching depths. However, these approaches yield comparatively complex structures, which in turn, come with the expense of extra fabrication costs, hindering the mass-scale development. Alternatively, the blazing effect has been exploited to provide remarkably high directionalities, relying on standard deep and shallow etch depths. Here, we report on the first experimental demonstration of an ultra-directional L-shaped fiber-chip grating coupler fabricated on 300 mm SOI wafer using 193-nm deep-ultraviolet lithography. The grating coupler is realized on a 300-nm-thick Si layer, combining standard full (300 nm) and shallow (150 nm) etch steps in an L-shaped arrangement. This approach yields a remarkably high grating directionality up to 98%. A single-step subwavelength-engineered transition provides an eight-fold reduction of the reflectivity, from ~8% to ~1%. We experimentally demonstrate a coupling efficiency of -2.7 dB, with a 3-dB bandwidth of 62 nm. These results open a new route towards exploiting the blazing effect for the large-volume realization of high-efficiency fiber-chip grating couplers in the low-cost 300 mm SOI photonic platform.

In this work, authors report for the first time on CMOS-compatible integrated micro-ring resonators with Bragg gratings coupled at both bus ends using a high quality Si3N4 film deposited by the liquid source CVD (LSCVD) method at ultra-low temperature of 150 ºC. Generally, the Si3N4 films deposited by either LPCVD or PECVD have demonstrated high tensile stress which prevents a thicker film deposition greater than 250 nm-thick with low loss state. Considering above, LSCVD is developed to fabricate the high quality Si3N4 films of several micrometers thickness without the limitation of cracking using the liquid SiN-X source at only 150 ºC, which guaranteed Kerr-based nonlinearity while featured high thermal compatibility with existing front-end electronic devices and silicon photonics especially those involving flexible/organic substrate. Furthermore, LSCVD deposition without needing SiH4 and NH3 chemistry also avoided the dangling Si-H and N-H bonds, which usually occur to PECVD and LPCVD and required extra 1200 ºC post-annealing to overcome such intrinsic absorption loss in C-band. We demonstrated high Q-factor ring resonators in this Si3N4 films, showing Q-value of over 1.3 × 10^5. A 3-dB bandwidth of around 70 nm for grating coupler was also achieved with 1550 nm central wavelength, while the coupling efficiency from fiber to grating is less than 4 dB. In this case, the measured spectral bandwidth can cover most of operating frequency of C-band and L-band. The LSCVD deposited Si3N4 is therefore a promising CMOS-compatible integration platform for nonlinear functional devices and circuits at telecommunication wavelengths.

In this paper we present silicon and germanium-based material platforms for the mid-infrared wavelength region and we report several active and passive devices realised in these materials. We particularly focus on devices and circuits for wavelengths longer than 7 micrometers.

Mid-Infrared (mid-IR) spectral range, spanning from 2 μm to 20 μm, is ideal for chemical sensing using spectroscopy thanks to the presence of vibrational absorption bands of many liquid and gas substances in this wavelength range. Indeed, mid-IR spectroscopy allows simultaneous qualitative and quantitative analysis by, respectively, identifying molecules from their spectral signature and relating the concentrations of different chemical agents to their absorption coefficient according to Beer-Lambert law. In the last years, photonic integrated sensors based on mid-IR spectroscopy have emerged as a cheap, accurate, and compact solution that would enable continuous real-time on-site diagnostics and monitoring of molecular species without the need to collect samples for off-site measurements. Here, we report the design, processing and characterization of a photonic integrated transducer based on selenide ridge waveguides. Evanescent wave detection of chemical substances in liquid phase (isopropyl alcohol, C₃H₈O, and acetic acid, C₂H₄O₂, both dissolved in cyclohexane) is presented using their absorption at a wavelength of 7.7 μm.

We present the first demonstration of ultrafast laser-inscribed waveguides in IG2 chalcogenide glass and their coupling to a mid-infrared quantum cascade laser. The fabrication parameter space has been investigated, resulting in optimized single-mode waveguides that have estimated propagation losses of 1 dB/cm at 7.8 μm. Higher order mode propagation was also observed. The refractive index modification caused by ultrafast laser inscription has been empirically quantified by comparison with modeled waveguide parameters, resulting in Δn = 0.0097–0.0143 over the pulse energy range investigated. We will present these findings, alongside our initial investigation into waveguide bend losses, which prepare the building blocks towards mid-infrared evanescent field coupling and integrated sensing applications.

The large transparency window of silicon (1.1 - 8 µm wavelength range) makes it a promising material for the implementation of a wide range of applications, including datacom, nonlinear and quantum optics, or sensing in the near- and mid-infrared wavelength ranges. However, the implementation of the silicon-on-insulator (SOI) platform in the mid-infrared is restricted by the absorption of buried oxide layer for wavelengths above 4 µm. A promising solution is to combine silicon membranes and subwavelength nanostructuration to locally remove the buried oxide layer, thus allowing access to the full transparency window of silicon. Additionally, structuring silicon with features smaller than half of the wavelength releases new degrees of freedom to tailor material properties, allowing the realization of innovative high-performance Si devices. Implementing Si membrane waveguides providing simultaneous single-mode operation at both near-infrared and mid-infrared wavelengths is cumbersome. Due to the high index contrast between Si and air cladding, conventional strip waveguides with cross-sections large enough to guide a mode in the mid-infrared are multi-mode in the near-infrared. Here, we exploit periodic corrugation to engineer light propagation properties of Si membrane waveguides allowing effective single-mode operation in near- and mid-IR. Single-mode propagation in the mid-IR is allowed by choosing a 500-nm-thick and 1100-nm-wide silicon waveguide. A novel waveguide corrugation approach radiates out the higher order modes in the near-IR, resulting in an effectively single-mode operation in near-IR. Based on this concept, we demonstrated Bragg filters with 4 nm bandwidth and 40 dB rejection.

The refractive index difference profile of optical fibers is the key design parameter because it determines, among other properties, the insertion losses and propagating modes. Therefore, an accurate refractive index profiling method is of paramount importance to their development and optimization. Quantitative phase imaging (QPI) is one of the available tools to retrieve structural characteristics of optical fibers, including the refractive index difference profile. Having the advantage of being non-destructive, several different QPI methods have been developed over the last decades. Here, we present a comparative study of three different available QPI techniques, namely the transport-of-intensity equation, quadriwave lateral shearing interferometry and digital holographic microscopy. To assess the accuracy and precision of those QPI techniques, quantitative phase images of the core of a well-characterized optical fiber have been retrieved for each of them and a robust image processing procedure has been applied in order to retrieve their refractive index difference profiles. As a result, even if the raw images for all the three QPI methods were suffering from different shortcomings, our robust automated image-processing pipeline successfully corrected these. After this treatment, all three QPI techniques yielded accurate, reliable and mutually consistent refractive index difference profiles in agreement with the accuracy and precision of the refracted near-field benchmark measurement.

Integrated photonics technology is set to revolutionize our access to powerful on-chip computing, nondestructive sensors and more. The major limitation of modern integrated photonics is losses that accompany the coupling of high index waveguides. For instance: Fresnel reflection on CMOS compatible Si waveguide interface is of 35% for the single facet and of 51% for both facets. These losses, of course, are minor in glass waveguides ( ~%4) [1, 2]. The light coupling from fiber into a planar waveguide with complicated shape is even lossier. The abrupt change in refractive index on the interface is in charge of disruptive reflection. To reduce the reflection, one can gradually change the refractive index at the interface. Here we propose to use metasurfaces which utilize the sub-diffraction properties of resonators [3, 4, 5]. First, we study the anti-reflection properties of the random structures on the facet of the waveguides [6]. In general, rough surfaces, as random process, can be defined mainly by two statistical functions: the height distribution and the autocorrelation function (ACF). Therefore, by tuning these two parameters we change the reflection properties of such a structure. Allowing an additional degree of freedom, anti-reflective random metasurfaces have numerous advantages. In addition, they can be easily manufactured on space compatible devices, high power lasers to list a few. References: [1] Alina Karabchevsky, James S Wilkinson, and Michalis N Zervas. Transmittance and surface intensity in 3d composite plasmonic waveguides. Optics express, 23(11):14407–14423, 2015. [2] A Karabchevsky and AV Kavokin. Giant absorption of light by molecular vibrations on a chip. Scientific reports, 6, 2016. [3] Shalin A. S. Optical Antireflection of a Medium by Nanostructural Layers // Progress in Electromagnetic Research B. 2011. V. 31. P. 45-66. [4] Shalin A. S., Nikitov S. A. Approximate Model for Universal Broadband Antireflection Nano-Structure // Progress in Electromagnetic Research B. 2013. V. 47. P. 127-144. [5] D. A. Baranov, P. A. Dmitriev, I. S. Mukhin, A. K. Samusev, P. A. Belov, C. R. Simovski and A. S. Shalin. Broadband antireflective coatings based on two-dimensional arrays of subwavelength nanopores // Appl. Phys. Lett. 106, 171913 (2015); [6] JA Ogilvy. Wave scattering from rough surfaces. Reports on Progress in Physics, 50(12):1553, 1987.

Many linear and nonlinear optics applications rely on micro-resonators (MRRs) with carefully designed dispersion and coupling rate coefficients. These parameters are however challenging to measure for MRRs based on high-confinement optical waveguides. In this paper, we report on the use of optical frequency domain reflectometry (OFDR) for the measurement of group velocity dispersion (GVD), coupling coefficients and round-trip loss, in high-Q (Q_i ∼ 0.3 × 10⁶) silicon-rich nitride MRRs. This technique allows for retrieving the GVD coefficients, intrinsic losses and coupling coefficients for each transverse mode in the resonator, thus providing very valuable feed-back information from experiments to the design flow step.

Photons carry linear momentum, and spin angular momentum when circularly or elliptically polarized. During light-matter interaction, transfer of linear momentum leads to optical forces, while angular momentum transfer induces optical torque. Optical forces including radiation pressure and gradient forces have long been utilized in optical tweezers and laser cooling. In nanophotonic devices optical forces can be significantly enhanced, leading to unprecedented optomechanical effects in both classical and quantum regimes. In contrast, to date, the angular momentum of light and the optical torque effect remain unexplored in integrated photonics. Here, we demonstrate the measurement of the spin angular momentum of photons propagating in a birefringent waveguide and the use of optical torque to actuate rotational motion of an optomechanical device. We show that the sign and magnitude of the optical torque are determined by the photon polarization states that are synthesized on the chip. Our study reveals the mechanical effect of photon’s polarization degree of freedom and demonstrates its control in integrated photonic devices. Exploiting optical torque and optomechanical interaction with photon angular momentum can lead to torsional cavity optomechanics and optomechanical photon spin-orbit coupling, as well as applications such as optomechanical gyroscope and torsional magnetometry.

Unavoidable statistical variations in fabrication processes have a strong effect on the functionality of fabricated photonic circuits and on fabrication yield. It is hence essential to measure and consider these uncertainties during the design in order to predict the statistical behavior of the realized circuits. Also, during the mass production of photonic integrated circuits, the experimental evaluation of circuits’ desired quantity of interest in the presence of fabrication error can be crucial. In this paper we proposed the use of generalized polynomial chaos method to estimate the statistical properties of a circuit from a reduced number of experimental data whilst achieving good accuracy comparable to those obtained by Monte Carlo.

We exploit quantum information processing on a traveling wave of light, expecting emancipation from thermal noise, easy coupling to fiber communication, and potentially high operation speed. Although optical memories are technically challenging, we have an alternative approach to apply multi-step operations on traveling light, that is, continuous-variable one-way computation. So far our achievement includes generation of a one-million-mode entangled chain in time-domain, mode engineering of nonlinear resource states, and real-time nonlinear feedforward. Although they are implemented with free space optics, we are also investigating photonic integration and performed quantum teleportation with a passive liner waveguide chip as a demonstration of entangling, measurement, and feedforward. We also suggest a loop-based architecture as another model of continuous-variable computing.

Nanowires offer new opportunities for nanoscale and integrated quantum optics; the quantum dot geometry in semiconducting nanowires as well as the material composition and environment can be engineered with unprecedented freedom to improve the light extraction efficiency. Quantum dots in nanowires are shown to be efficient single photon sources, in addition because of the very small fine structure splitting, we demonstrate the generation of entangled pairs of photons from a nanowire and discuss the limits to entanglement fidelity. Another type of nanowire under study in our group is superconducting nanowires for single photon detection, reaching efficiencies, time resolution and dark counts beyond currently available detectors. We will discuss our first attempts at combining semiconducting nanowire based single photon emitters and superconducting nanowire single photon detectors on a chip to realize integrated quantum circuits.

Quantum simulators are getting to the level of real devices, constituted by a quantum system which can be controlled in its preparation, evolution and measurement and whose dynamics can implement that of the target quantum system we want to simulate. In this context, photonics quantum technologies are expected to play an instrumental role in the realization of controlled quantum systems capable, in their evolution, to simulate a given complex system. I will present some of the main results obtained in this field in our laboratory by using integrated waveguide optical circuits that represent the hardware of a quantum simulator. These systems are constituted by interferometer arrays of beam splitters and phase shifters fabricated on single integrated platforms by femtosecond laser writing technique and have the potential of speeding-up the evolution from lab systems to the next generation of quantum optical devices for real-world applications. Using the mobility of photons we are able to create arbitrary interconnections within these systems and to mimic the main features of quantum phenomena of increasing complexity.

Single photon avalanche detectors (SPADs) operating in gated-Geiger mode at near infrared wavelengths have applications in quantum key distribution (QKD), eye-safe light detection and ranging (LIDAR), 3D image sensing, quantum enhanced imaging and photonic based quantum information processing. Whilst InGaAs SPADs are commercially available, the high cost and lack of integrated SPADs limit the applications. We have previously demonstrated vertical Geiger mode Ge on Si SPADs at 1310 and 1550 nm operating at 100 K where the Ge is used as an absorber and the lower noise Si is used as the avalanche gain region. At 100 K and 1310 nm a single photon detection efficiency of 4% was demonstrated with a dark count rate (DCR) of 5 MHz. Here we present first results on Ge on Si SPADs grown on top of silicon-on-insulator (SOI) substrates. Both vertical photodetectors and waveguide coupled detectors were investigated with designs aimed to reduce the DCR over previous results. Waveguides and avalanche regions were patterned in the top Si of a SOI wafer before being coated with silicon dioxide. Holes were then etched in the oxide to allow selective area growth of Ge inside these windows and on top of the Si waveguides for the waveguide coupled Ge SPADs. This approach reduces the threading dislocation density compared to bulk Ge growths which aids the reduction of the DCR. The fabricated devices have been tested at both 1310 nm and 1550 nm wavelengths and demonstrate improved performance over previous published results.

Bringing photonics and electronics into a common integration platform can unleash unprecedented performance capabilities in data communication and sensing applications. Plasmonics were proposed as the key technology that can merge ultra-fast photonics and low-dimension electronics due to their metallic nature and their unique ability to guide light at sub-wavelength scales. However, inherent high losses of plasmonics in conjunction with the use of CMOS incompatible metals like gold and silver which are broadly utilized in plasmonic applications impede their broad utilization in Photonic Integrated Circuits (PICs). To overcome those limitations and fully exploit the profound benefits of plasmonics, they have to be developed along two technology directives. 1) Selectively co-integrate nanoscale plasmonics with low-loss photonics and 2) replace noble metals with alternative CMOS-compatible counterparts accelerating volume manufacturing of plasmo-photonic ICs. In this context, a hybrid plasmo-photonic structure utilizing the CMOS-compatible metals Aluminum (Al) and Copper (Cu) is proposed to efficiently transfer light between a low-loss Si₃N₄ photonic waveguide and a hybrid plasmonic slot waveguide. Specifically, a Si₃N₄ strip waveguide (photonic part) is located below a metallic slot (plasmonic part) forming a hybrid structure. This configuration, if properly designed, can support modes that exhibit quasi even or odd symmetry allowing power exchange between the two parts. According to 3D FDTD simulations, the proposed directional coupling scheme can achieve coupling efficiencies at 1550nm up to 60% and 74% in the case of Al and Cu respectively within a coupling length of just several microns.

The demand for faster magnetization switching speeds and lower energy consumption has driven the field of spintronics in recent years. Whereas spin-transfer-torque and spin-orbit-torque interactions exemplify the potential of electron-spin-based devices and memory, the switching speed is limited to the ns regime by the precessional motion of the magnetization. All-optical magnetization switching, based on the inverse Faraday effect, has been shown to be an attractive method for achieving magnetization switching at ps speeds. Successful magnetization reversal in thin films has been demonstrated by using circularly polarized light. However, a method for all-optical switching of on-chip nanomagnets in high density memory modules has not been described. In this work we propose to use plasmonics, with CMOS compatible plasmonic materials, to achieve on-chip magnetization reversal in nanomagnets. Plasmonics allows light to be confined in dimensions much smaller than the diffraction limit of light. This in turn, yields higher localized electromagnetic field intensities. In this work, through simulations, we show that using surface plasmon resonances, it is possible to couple light to nanomagnets and achieve significantly higher opto-magnetic field values in comparison to free space light excitation for the same incident intensity. We use two well-known magnetic materials Bismuth Iron Garnet (BIG) and Gadolinium Iron Cobalt (GdFECo) and couple these nanomagnets to a plasmonic resonator made of Titanium Nitride. Our simulation results show 10 times enhancement in the opto-magnetic field for BIG and about 3 times for GdFeCo in the coupled structure compared to free-space excitation. Our simulations also show the possibility of having in-plane components of the opto-magnetic field in the coupled structure which might prove beneficial for switching in nanomagnets with canted magnetization.

Plasmonic technology has attracted intense research interest enhancing the functional portfolio of photonic integrated circuits (PICs) by providing Surface-Plasmon-Polariton (SPP) modes with ultra-high confinement at sub-wavelength scale dimensions and as such increased light matter interaction. However, in most cases plasmonic waveguides rely mainly on noble metals and exhibit high optical losses, impeding their employment in CMOS processes and their practical deployment in highly useful PICs. Hence, merging CMOS compatible plasmonic waveguides with low-loss photonics by judiciously interfacing these two waveguide platforms appears as the most promising route towards the rapid and costefficient manufacturing of high-performance plasmo-photonic integrated circuits. In this work, we present butt-coupled plasmo-photonic interfaces between CMOS compatible 7μm-wide Aluminum (Al) and Copper (Cu) metal stripes and 360×800nm Si₃N₄ waveguides. The interfaces have been designed by means of 3D FDTD and have been optimized for aqueous environment targeting their future employment in biosensing interferometric arrangements, with the photonic waveguides being cladded with 660nm of Low Temperature Oxide (LTO) and the plasmonic stripes being recessed in a cavity formed between the photonic waveguides. The geometrical parameters of the interface will be presented based on detailed simulation results, using experimentally verified plasmonic properties for the employed CMOS metals. Numerical simulations dictated a coupling efficiency of 53% and 68% at 1.55μm wavelength for Al and Cu, respectively, with the plasmonic propagation length L_spp equaling 66μm for Al and 75μm for Cu with water considered as the top cladding. The proposed interface configuration is currently being fabricated for experimental verification.

This paper review our recent work on silicon modulators based on free carrier concentration, working in the O-band of optical communications (1260 nm - 1360 nm) for short distance applications. 25 Gbit/s OOK modulation is obtained using a driving voltage of 3.3 V_pp , and QPSK dual-drive Mach-Zehnder modulator (DDMZM) operating in the O-band is demonstrated for the first time.

We review the recent advances reported in the field of integrated photonic waveguide meshes, both from the theoretical as well as from the experimental point of view. We show how these devices can be programmed to implement both traditional signal processing structures, such as finite and infinite impulse response filters, delay lines, beamforming networks as well as more advanced linear matrix optics functionalities. Experimental results reported both in Silicon and Silicon Nitride material platforms will be presented. We will also discuss the main programming algorithms to implement these structures and discuss their applications either as standalone systems or as part of more elaborated subsystems in microwave photonics, quantum information and machine learning.

Wavelength multiplexing (WMUX) channel transmission bandwidth should be sufficiently large to compensate for thermal drifts of the emitters at the transmitter side of the link all over their functional windows in terms of driving currents and operational temperature of the environment. As well as that, a nearly absolute thermal insensitiveness of the WMUX device performance itself has to be ensured across the link over the widest possible temperature range. In other terms, devices have to exhibit the smallest thermo-optic coefficient, in order to fulfill system specifications under any thermal condition applied to the optical link. In this paper, we present coarse wavelength division multiplexing (CWDM), echelle grating (EG) WMUX to operate in the O-band (1310 nm) designed accordingly to 4 x 20-nm-spaced standard and fabricated on 200-mm Silicon Nitride-on-Insulator (SiNOI). Taking advantage of PECVD SiN low thermooptic coefficient compared to crystalline silicon, thermally-insensitive demultiplexers can be obtained. The device show insertion losses as low as 1 dB, interchannel crosstalk averaging -25 dB, non-uniformity of 1.3 dB and a -1 dB and -3 dB bandwidths of nearly 10 nm and 13 nm, respectively. Such wide channel bandwidths allow the compensation of wavelength drifts due to the different thermal environments between the transmitter and the receiver as well as the detuning of emitters at the transmitter side of the link. The EG shows a quasi-absolute thermal insensitiveness in the temperature operation range from 20 °C up to 80 °C, highlighting the thermal robustness of such SiNOI EG devices. A thermally-dependent chromatic dispersion averaging less than 13 pm/K over different channels has been estimated, thus 6x times less than similar devices when realized on standard SOI.

In recent years, light emitting diodes (LEDs) have gained renewed interest for use in visible light communication links (VLC) owing to their potential use as both high-quality power-efficient illumination sources as well as low-cost optical transmitters in free-space and guided-wave links. Applications that can benefit from their use include optical wireless systems (LiFi and Internet of Things), in-home and automotive networks, optical USBs and short-reach low-cost optical interconnects. However, VLC links suffer from the limited LED bandwidth (typically ~100 MHz). As a result, a combination of novel LED devices, advanced modulation formats and multiplexing methods are employed to overcome this limitation and achieve high-speed (>1 Gb/s) data transmission over such links. In this work, we present recent advances in the formation of high-aggregate-capacity low cost guided wave VLC links using stacked polymer multimode waveguides and matching micro-pixelated LED (μLED) arrays. μLEDs have been shown to exhibit larger bandwidths (>200 MHz) than conventional broad-area LEDs and can be formed in large array configurations, while multimode polymer waveguides enable the formation of low-cost optical links onto standard PCBs. Here, three- and four-layered stacks of multimode waveguides, as well as matching GaN μLED arrays, are fabricated in order to generate high-density yet low-cost optical interconnects. Different waveguide topologies are implemented and are investigated in terms of loss and crosstalk performance. The initial results presented herein demonstrate good intrinsic crosstalk performance and indicate the potential to achieve ≥ 0.5 Tb/s/mm² aggregate interconnection capacity using this low-cost technology.

The double-periodic Si photonic crystal waveguide radiates guided slow light into free space as an optical beam. It also functions as a beam steering device, in which the steering angle is changed widely by the slight wavelength variant thanks to the large dispersion of slow light. A similar function is obtainable when the wavelength is fixed and the refractive index of the waveguide is changed. In this study, we integrated two kinds of heater structures in the waveguide and demonstrated the beam steering by the thermo-optic effect. For a p-i-p doped heater structure, we implanted a p-type dopant except around the waveguide core, and observed a beam steering angle Δθ = 26°, which is close to a theoretical value, with a relatively low heating power P = 1.6 W and high-speed response of 100 kHz order. However, the beam divergence increased up to δθ = 5°, which seemed to reflect the temperature nonuniformity in the Si slab. On the other hand, for the TiN heaters placed away from the waveguide core, we obtained a comparable steering angle with a narrower beam divergence of δθ < 0.3°. However, the required heating power was as large as P = 4.8 W, and the response speed was slow, reflecting its low heating efficiency and large heat capacity. We expect these problems to be solved by homogenizing the current and temperature distributions for the former and by optimizing the positioning of the heaters for the latter.

In this work, we show the possibility of combining grating couplers and mode converters, both with a high efficiency. The proposed devices are very compact with no extra fabrication efforts required. We have shown that the LP₀₁, LP_11a, LP_11b and LP_21b modes in an optical fiber can be successfully excited directly from the proposed grating couplers, which have the fundamental mode as an input from an integrated waveguide. It is shown the overall efficiency could be as high as 50%.

Steering the beam of a wave source has been demonstrated using mechanical and non-mechanical techniques. While mechanical techniques are bulky and slow, non-mechanical techniques rely on breaking the symmetry of the refractive index profile either using asymmetric structure or injecting a non-uniform current. In this contribution, we theoretically and experimentally demonstrated a new type of topological steering of light sources in which the phase offset is provided by Floquet-Bloch phase in periodic structure. It was shown that in periodic structures, there exist singular states in the radiation region of the band diagram that exhibit diverging quality factor. Thus light sources can operate at these states with lower power threshold. The existence of these singular states are topologically protected, and their momentum are very sensitive to any small perturbations, which is used to control the steering angle. By uniformly controlling some parameters in the system, such as a physical dimension or injecting current uniformly, the beam of the light source steers. Our experimental demonstrations open new paradigm in the implementation of light steering with applications in data communications, bio imaging and sensing.

Polymer optical sensors have attracted significant scientific interest due to the advantages of flexibility and low- cost mass-production possibilities. A main challenge in integration of all-polymer systems is interfacing sensor parts to light sources and detectors. Coupling strategies such as end-facet coupling, 45° mirrors coupler and gratings coupler have been investigated. However, facet polishing is complicated for large flexible foils, while 45° mirrors often require a metal reflection layer. Thus grating couplers have the biggest potential and are compatible with roll-to-roll processes. Polymers have higher thermo-optic-coefficients and thermal-expansion-coefficients compared to inorganic materials, making them very sensitive to temperature changes. Consequently, polymer grating couplers show a shift of the coupling angle with temperature and thus a decay of efficiency. We therefore present a temperature characterization of all-polymer based grating couplers on waveguides based sensors. Cost-effective manufacturing methods, including hot-embossing and spin-coating, were used for the fabrication of waveguides and gratings on PMMA foils. Single mode waveguides were realized by modifying the dimensions of their cross-section. Gratings with a period of 560 nm were subsequently bonded on the waveguides for input coupling. Thermal response was characterized by monitoring the coupling angle at different temperatures. Temperature dependences of the incident angle at two main peaks of 0.0027 °/K and 0.0054 °/K were determined respectively at the wavelength of 852 nm and a linear response over the evaluated range between 298 K and 323 K was observed, which opens up possible applications for on-chip temperature monitoring and thermal compensation when integrated with polymer sensors.

Using transparent conducting oxides (TCOs), like indium-tin-oxide (ITO), for optical modulation attracted research interest because of their epsilon-near-zero (ENZ) characteristics at telecom wavelengths. Utilizing indium-tin-oxide (ITO) in multilayer structure modulators, optical absorption of the active ITO layer can be electrically modulated over a large spectrum range. Although they show advances over common silicon electro-optical modulators (EOMs), they suffer from high insertion losses. To reduce insertion losses and device footprints without sacrificing bandwidth and modulation strength, slot waveguides are promising options because of their high optical confinement. In this paper, we present the study and the design of an electro-optical absorption modulator based on electrically tuning ITO carrier density inside a MOS structure. The device structure is based on dielectric slot waveguide with an ITO plasmonic waveguide modulation section. By changing the dimensions, the effective refractive indices for the slot mode and the off-sate mode of the plasmonic section can be matched. When applying electric field to the plasmonic section (on-state), carriers are generated at the ITO-dielectric interface that result in changing the layer where the electric field is confined from a transparent layer into a lossy layer. A finite difference time domain method with perfect matching layer (PML) absorbing boundary conditions is taken up to simulate and analyze this design. An extinction ratio of 2.3 dB is achieved for a 1-μm-short modulation section, at the telecommunications wavelength (1.55 μm). This EOM has advantages of simple design, easy fabrication, compact size, compatibility with existing silicon photonics platforms, as well as broadband performance.

We propose a new waveguide loss measurement method based on the reflected interferometric pattern from the waveguide. The loss of the waveguide is obtained by analyzing the fineness of the reflected interferometric pattern from the Fabry-Perot (F-P) cavity formed by the facets of a single-mode waveguide. In this method, a single mode lensed fiber and a circulator is used to direct the tunable laser into the waveguide under test and collect the reflected spectrum pattern through a photodetector. Comparing to the traditional transmission F-P interferometric method relying on double end fiber coupling, the proposed method requires only a single end coupling, considerably simplifying the coupling difficulty and the measurement system complexity. The fineness measurement is also free from the influence of background noise level, and reduces the coupling accuracy requirement. This method is low-cost, easy-to-operate and reliable, which can serve as an alternative method to measure the waveguide loss.

In this paper, we demonstrate a plasmonic planar lens structure that can achieve subwavelength focusing of the infrared electromagnetic radiation. The lens is composed of metallic binary slits with different dielectric fillings. The index modulation approach of the filling materials is used to achieve phase modulation of the wavefront of the incident wave. Using this approach, we could achieve a phase range of 0.43π. The structure can focus the incident infrared wave in the subwavelength scale. The focal length attained is 44.69 μm and the achieved Full width at half maximum (FWHM) is 4.28 um for an incident infrared wave of wavelength 8 um. The transmission through the structure is 25.64 % at the design wavelength. The used metal is copper and the dielectric filling materials are silicon and air. Copper has lower losses in the infrared range than the traditional metals used in visible Plasmonics. Silicon has a higher melting point than the common dielectric materials used in refractive index modulation of the visible Plasmonic lenses. This temperature stability is a very important feature when working in the infrared domain. Besides being specifically suitable for the infrared range, copper and silicon are also CMOS compatible. Therefore, the proposed structure is suitable for integration in many potential infrared applications such as thermal imaging, medical diagnosis, thermal photovoltaic cells and heat harvesting. In addition, the fact that many molecules have unique absorption spectra or signature in the infrared range would facilitate the analysis and study of many materials and biological molecules using infrared miniaturized spectrometers.

For constructing a quadrature phase interferometer for optical current sensors, we integrated various optical components on a single polymeric waveguide chip. To obtain stable output in quadrature interferometer, it is important to remove the scattered light inside the planar waveguide of integrated optics. In this work, we analyzed the mechanism of optical interference due to the radiated light, and improved the structure of optical waveguide device . After the improvement of waveguide structure, the sensor output signal was maintained within ±0.5% error range regardless of its operating point drift.

Polymer optical waveguides fabricated using the Mosquito method are expected to realize high bandwidth density 3-dimensional (3-D) on-board wiring. In the Mosquito method, the waveguides are fabricated by dispensing a liquid core monomer into a liquid cladding monomer using a microdispenser. Hence, for the on-board applications particularly 3-D wiring, the core position and alignment accuracies are important to couple the waveguides with the other optical components with high efficiency. We already succeeded in fabricating graded-index core multimode polymer optical waveguides with low propagation loss using the Mosquito method. However, the positions of the formed cores tended to deviate from the original design, since both the core and cladding monomers are in the liquid state during the Mosquito process.

In this paper, we apply a fluid analysis simulation using a COMSOL Multiphysics® in order to theoretically simulate the influence of several fabrication parameters on the core position. The calculated core height deviation from the designed height is dependent on the needle-tip height, because the core positions are influenced by the pressure distribution of cladding monomer caused by the monomer flow. Meanwhile, we find that the monomer wetting on the needle outer wall also affects the core height. When the effect of monomer wetting is taken into account, the simulated core heights are different from the results without the effect of monomer wetting and we can theoretically predict the height of the formed core. Finally, we confirm that the core height can be controlled by adjusting the needle-tip height setting in which the effect of the monomer flow and wetting theoretically calculated is taken into account in the Mosquito method.

An optical modulator is considered one of the most fundamental components in an optical data communication system as it acts as a linking device between the optical and electrical parts of the system. Electro-absorption (i.e. electro-optical) modulation is one popular scheme in designing optical modulators; however, minimizing the device footprint in siliconbased platforms acted as a challenge. Few years ago, “plasmonics” field emerged as a good candidate that could possibly further reduce silicon-based modulators’ footprint. Unfortunately, existence of metals introduced huge propagation losses. Recently, transparent conducting oxides (e.g. indium tin oxide “ITO”) have been intensively used as active media in electro-optical (EO) modulators. They have a metal-like plasmonic behavior with extremely lower losses.

Under no biasing voltage, ITO acts almost as a dielectric. However, by carefully tuning the biasing voltage, the free carrier concentration beneath the ITO surface is changed. This allows a dramatic alteration in the complex permittivity of the ITO reaching an epsilon-near-zero (ENZ) value at some point. At this region, the ITO acts as a metal and a plasmonic mode is present at an ITO-dielectric interface. A heavily doped silicon slab can be used as a contact for the gating voltage to be applied on in order to accumulate free carriers on the ITO surface.

In this work, an all-silicon indium tin oxide-integrated electro-optical modulator is designed. The modulator exhibits superior parameters (e.g. insertion loss and extinction ratio) that outperform the current modulators based on the same technology.

For several fields such as spectroscopy, metrology, and lithography, laser sources in the ultraviolet (UV @ 386 nm) or deep ultraviolet (DUV @ 193 nm) spectral range rely on broad band or pulsed laser systems such as excimer lasers. Highly brilliant semiconductor laser systems could advance these fields further as they are more reliable and easier to handle.

One way to achieve the UV emission is using a 772 nm emitting semiconductor master oscillator - power amplifier (MOPA) laser system whose emission is frequency doubled once or twice in a later step. The laser system will be built into a small and compact package and consists of a MO, which is a distributed feedback (DFB) ridge waveguide (RW) laser. The diffraction limited laser emission with a single spectral mode is coupled into the PA for the amplification of the output power up to 3 W. The PA is a semiconductor laser with a RW and a tapered section. Optical feedback can be minimized by using a micro-optical isolator, which is placed between MO and PA that allows a linewidth of < 3 MHz.

We will present further experimental results of the MOPA system in detail. This includes the emission characteristics, the spectral emission behavior, and the robust setup by applying several thermal cycles and shaking tests.

On the base of the same laser system, wavelengths of 780 nm or 785 nm could facilitate small rubidium atomic clocks or Raman spectroscopy respectively. Especially when using distributed Bragg reflector laser diodes an even smaller linewidth can be achieved.

Optical interconnects have been proposed to be the next generation interconnect solution to overcome the impending interconnect bottleneck. Large optical devices have hindered integration of electrical and optical components. Plasmonics have enabled nanophotonic components with sub-micron scale optical devices with similar size range as electronics and they promise to bridge the size gap between optical and electrical components. Surmounting research is suggesting that the electronics industry is starting to accept more variety materials in the fabrication process, the most important of which is graphene. The modulator is composed of a thin layer of silicon nitride – a few nm thick – sandwiched between two graphene sheets that are both electrically connected to the signal. Thin Al₂O₃ layers separate the graphene sheets from the ground electrodes on top and bottom. The electric field generated by applying a maximum of 5V on the graphene sheets changes the fermi level of graphene to switch between a highly lossy metal-like material and a dielectric material. Operating in the mid infrared regime, around 5 μm wavelength, when the Fermi level is located in the band gap, optical absorption is high. When the Fermi level is located away from the bandgap, absorption is minimized. Simulations show that the modulator exhibits over 7 dB / μm extinction ratio and less than 0.1 dB / μm propagation loss. By designing for 3 dB extinction ratio and less than 0.1 dB propagation loss, the footprint of the modulator is only 80 nm x 400 nm for feasible integration in future electronic chips without competing for space.

We demonstrate a compact efficient waveguide taper in Silicon Nitride platform. The proposed taper provides a coupling-efficiency of 95% at a length of 19.5 μm in comparison to the standard linear taper of length 50 μm that connects a 10 μm wide waveguide to a 1 μm wide photonic wire. The taper has a spectral response > 75% spanning over 800 nm (spanning O, C & L band) and robustness to fabrication variations; ±200 nm change in taper and end waveguide width varies transmission by <5%. We experimentally report a taper insertion loss of <0.1 dB/transition and reduction in the footprint of the photonic device by 50.8% for the proposed compact taper in comparison to the traditional adiabatic taper. To the best of our knowledge, the proposed taper is the shortest waveguide taper ever reported in Silicon Nitride.

Mode Division Multiplexing / De-Multiplexing (MD-MUX/De-MUX) is currently investigated as an effective and attractive technique for increasing channel capacity in optical communication networks. The core of such mode multiplexing is usually based on an optical mode converter. Different integrated optical structures have been proposed for mode conversion in planer technology. One of the difficulties in this direction is the design of a mode converter for higher order fiber modes where the energy is distributed in the two transverse dimensions of the guide cross section. In this work, we make use of the two dimensional multi-mode interferencein 2D multimode waveguide (2D MMI) for building a mode converter to convert a fundamental mode LP₁₀ of single mode fiber to the third order LP₂₁ mode in multimode fiber. The operating principle of the structure is based on using the 2D MMI with a proper length to create the 4 images on the SM input fiber into the output of the 2D symmetric MMI. The 4 images are distributed in the space in both the x and y directions as a 2x2 matrix form. For these images to form the field distribution of the fiber LP21 mode, a proper phase shift should be associated with each image. This is done using a section of phase shifters based on the control of the waveguide width that allows controlling its relative propagation constant. The proposed design is tested using the 2D Beam Propagation Method BPM. The obtained performance is quite encouraging.

Resolving spectrally adjacent peaks is important for techniques, such as tracking small shifts in Raman or fluorescence spectra, quantifying pharmaceutical polymorph ratios, or molecular orientation studies. Thus, suitable spectral resolution is a vital consideration when designing most spectroscopic systems. Most parameters that influence spectral resolution are fixed for a given system (spectrometer length, grating groove density, excitation source, CCD pixel size, etc.). Inflexible systems are non-problematic if the spectrometer is dedicated for a single purpose; however, these specifications cannot be optimized for different applications with wider range resolution requirements. Data processing techniques, including peak fitting, partial least squares, or principal component analysis, are typically used to achieve sub-optical resolution information. These techniques can be plagued by spectral artifacts introduced by post-processing as well as the subjective implementation of statistical parameters. TruRes™, from Andor Technology, uses an innovative optical means to greatly improve and expand the range of spectral resolutions accessible on a single setup. True spectral resolution enhancement of >30% is achieved without mathematical spectral alteration, dataprocessing, or spectrometer component changes. Discreet characteristic spectral lines from Laser-Induced Breakdown Spectroscopy (LIBS) and atomic calibration sources are now fully resolved from spectrally-adjacent peaks under otherwise identical configuration. TruRes™ has added advantage of increasing the spectral resolution without sacrificing bandpass. Using TruRes™ the Kymera 328i resolution can approach that of a 500 mm focal spectrometer. Furthermore, the bandpass of a 500 mm spectrograph with would be 50% narrower than the Kymera 328i with all other spectrometer components constant. However, the Kymera 328i with TruRes™ is able to preserve a 50% wider bandpass.

A method for increasing the extinction ratio of integrated optical Mach-Zehnder modulators based on LiNbO₃ via the photorefractive effect is proposed. The influence of the photorefractive effect on the X- and Y-splitters of intensity modulators is experimentally studied. An increase in the modulator extinction ratio by 17 dB (from 30 to 47 dB) is obtained. It is shown that fabricated modulators with a high extinction ratio are important for quantum key distribution systems.

A tunable slow light thermal modulator using 2D semiconductor metamaterial is presented and investigated. We have designed and simulated a terahertz (THz) semiconductor metamaterial (MM) waveguide system; The simulation results show the spectral properties and the group delay of the proposed 2D metamaterial can be tuned by adjusting temperature and the semiconductor used in the waveguide. Our calculations exhibit a significant slow-light effect, based on electromagnetically induced transparency (EIT) effect. By appropriately adjusting the distance between the sub radiant and supper radiant modes, a flat band corresponding to nearly constant group delay (of order of 71) over a narrow bandwidth of THz regime can be achieved. Our analytical results show that the group velocity dispersion (GVD) parameter can reach zero. The simulation results show the incident pulse can be slowed down without distortion owing to the low group velocity dispersion (LGVD). The outstanding result is that, the 2D semiconductor metamaterial is in a high decrease of the group velocity and therefore slow light applications. The proposed compact slow light thermal modulator can avoid the distortion of signal pulse, and thus may find potential applications in slow-light and thermal modulator devices and thermal applications.

Here, we demonstrate a new type of microphotoreactor formed by a liquid-core optofluidic waveguide fabricated inside aerogel monoliths. It consists of microchannels in a monolithic aerogel block with embedded anatase titania photocatalysts. In this reactor system, aerogel confines core liquid within internal channels and, simultaneously, behave as waveguide cladding due to its extremely low refractive index of ~1. Light is confined in the channels and is guided by total internal reflection (TIR) from the channel walls. We first fabricated L-shaped channels within silica aerogel monoliths (ρ= 0.22 g/cm³, n=1.06) without photocatalyst for photolysis reactions. Using the light delivered by waveguiding, photolysis reactions of methylene blue (MB) were carried out in these channels. We demonstrated that MB can be efficiently degraded in our optofluidic photoreactor, with the rate of dye photoconversion increasing linearly with increasing power of incident light. For photocatalytic transformation in this reactor system, titania particles were successfully embedded into the mesoporous network of silica aerogels with varying amount of the titania in the structure from 1.7 wt % to 50 % wt. The presence of titania and its desired crystalline structure in aerogel matrix was confirmed by XRF, XRD patterns and SEM images. Band gap of silica-titania composites was estimated from Tauc plot calculated by Kubelka-Munk function from diffuse reflectance spectra of samples as near expected value of ≈ 3.2 eV. Photocatalytic activity and kinetic properties for photocatalytic degradation of phenol in the channels were investigated by a constant flow rate, and longer-term stability of titania was evaluated.

We present a low chirp electroabsorption modulator integrated DFB laser (EML) fabricated by a selective area growth double stack active layer technique. A stable single mode operation can be obtained and the typical side mode suppression ratio (SMSR) is over 53 dB. The threshold current of the device is about 16 mA and the optical output power from the EAM fact is over 8 mW at an injection current of 80 mA. A static extinction ratio as high as 34 dB can be obtained when the bias voltage is approaching -5 V. The chirp parameters of the EML chip are measured with a fiber resonance method. Negative chirp parameters can be obtained when the reverse bias voltage increases to 1 V. A clear 25 Gb/s back to back eye diagram can be achieved and a 20 Gb/s eye diagram can be seen after the transmission of 25 km single mode fiber. The EAM can operate at 20 Gb/s with a dynamic extinction of 8.6 dB with a driving voltage as low as 0.65 V. The fabricated EML chip shows great advantages in very-short-reach systems as well as long distance applications.