This PDF file contains the front matter associated with SPIE Proceedings Volume 12004, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

We review our recent results on modulators and detectors for the 2μm range, which may become very relevant for future communications, and on the development of mid-IR broadband devices for sensing applications. We show Mach-Zehnder and Michelson based modulators operating at data rates up to 25 Gb/s and Ge based detectors operating up to 12.5 Gb/s. For longer wavelengths relevant for sensing applications, we present broadband waveguides and splitters, waveguide integrated bolometers, and the realisation of a mid-infrared sensor.

TiO₂ is a very promising material for integrated photonics due to its high refractive index (~2.3 at 633 nm), wide transparency window from the visible to the mid-infrared and high non-linear refractive index. However, to date, high propagation losses hinder its utilization in real-life applications. In this work, we carry out a systematic study of the different fabrication processes involved in the realization of TiO₂ channel waveguides, including RF sputter deposition, electron-beam lithography and thermal annealing, showing film losses below 1 dB/cm for wavelengths above 633 nm and channel losses of 1-1.5 dB/cm at 1550 nm.

We demonstrate a new post-processing approach to efficiently couple light in silicon nitride (Si3N4) photonic integrated circuits (PIC) via grating couplers. Thin-film coupons of apodised Si₃N₄ grating couplers functionalized with metallic bottom reflectors and adiabatic couplers are micro-transfer printed onto the input and output of Si₃N₄ waveguides, providing efficient coupling without jeopardizing the rest of the PIC. Two-dimensional FDTD simulations predict coupling efficiencies as large as 70% (-1.5dB) at a wavelength of 785nm. As a proof-of-concept, we report an experimental coupling efficiency of -4.6dB, which is 2.6dB better than the values obtained with standard designs of grating couplers.

We present ultra-low power stress optic actuators for high-speed switching in photonic integrated circuits using the standard silicon nitride TriPleX™ platform. The stress-optic actuator is created by a piezoelectric layer (lead zirconate titanate, PZT) on top of a Si₃N₄-based TriPleX™ waveguide in our standard Asymmetric Double Stripe (ADS) cross section. The top cladding thickness in between the actuator and the waveguide is chosen to achieve minimal optical loss (≤0.01dB/cm). The electrodes are placed on the top of- and directly below the PZT layer allowing the generation of a vertical electric field across the layer. This electrical field deforms the PZT layer by means of the piezoelectric effect. As a consequence of the PZT deformation stress is induced in the underlying waveguide. In this way, the refractive index of the waveguide is controlled by the stress-optic effect brought about by actuating the PZT layer. To demonstrate the stress-optic based phase actuation experimentally, a Mach-Zehnder Interferometer (MZI) is employed. The MZI is designed for operation at a wavelength of 1550 nm. We measure a half-wave voltage-length product (Vπ·cm) of 16 V·cm, while the half-wave-voltage length loss product (Vπ ·L·α) is 1.6 V·dB only. The 2π phase shift would be at 42 V. The measured response time is 4.25 μs. The quasi-DC power dissipation is able to go down to 1 μW. Compared with conventional thermo-optic actuators these characteristics show a dramatic improvement, being a factor of 50 faster in terms of switching speed and a factor of 100 000 lower in terms of quasi-DC power dissipation. This makes stress-optic actuators an attractive choice for the next generation integrated photonic circuits where ultra-low quasi-DC power dissipation and/or fast switching time and operation in the MHz range are required.

In this work, we study the eigenvalues and eigenvectors of a taiji microresonator that is made by a ring cavity with an embedded S-shaped waveguide. Specifically, we demonstrated that this system works on an exceptional point. This strongly affects the behaviour against perturbation of the counterpropagating modes inducing a peculiar splitting of the single Lorentzian transmission spectra. Precisely, we show that this splitting is proportional to the square root of the perturbation strength. Therefore, the taiji exhibits a higher sensitivity to a small perturbation with respect to a typical microresonator which shows a linear splitting.

Precise temperature measurement is highly desirable in many scientific, engineering, and industrial areas. Optical sensors based on Whispering-Gallery-Mode (WGM) microresonators offer the advantages of high sensitivity, high resolution, and small footprint. However, conventional sensing methods rely on tracking the changes in a single-mode, which limits the dynamic range of the measurement. We demonstrate an optical WGM barcode technique involving simultaneous monitoring of the patterns of multiple modes that can provide a direct temperature readout from the spectrum. This work lays the foundation for developing a high-resolution temperature sensor with superior sensitivity over a broad dynamic range.

We present a simple gas sensor based on planar polymer optical waveguides with MOF (ZIF-8) coating for carbon dioxide detection and sensing. The optical waveguides were made of PMMA and fabricated by hot embossing replication. A thin MOF film was uniformly grown on the waveguide sample surface through a simple solution method, which is crucial for the envisioned production of MOF-based sensing devices on large scale. The experimental results show that the produced optical elements exhibit high sensitivity and selectivity of CO₂ gas with rapid response time and excellent reversibility of adsorption and desorption of the gas molecules. The demonstrated planar polymeric sensing devices provide the potential to develop flexible onchip gas sensors in an inexpensive and reproducible way.

We review our work on implementing integrated QFC sources based on microring resonators for on-chip generation of two- and multi-photon time-bin entangled states, d-level frequency-entangled photon pairs, and multipartite d-level cluster states. We also present our recent progress on telecom-compatible, scalable, time-entangled two-photon qubits using on-chip Mach-Zehnder interferometers (MZI) in combination with spiral waveguides. Both approaches are highly cost-effective, efficient, and practical, since we coherently manipulate the time and frequency modes through standard fiber-linked components that are compatible with off-the-shelf telecommunications infrastructures. Our work paves the way for robust sources and processors of complex photon states for future quantum technologies.

VTT micron-scale silicon photonics platform can play a significant role in the second quantum revolution, supporting not only quantum photonics but also solid-state quantum systems. Quantum photonics can benefit from the unique properties of the platform, a distinctive example application being quantum key distribution, where we are developing receivers to support its large-scale deployment. On the other hand, we are using our photonic integration technology also to aid scaling-up superconducting quantum computers, by controlling and reading the qubits in the cryostat through classical optical links. I will cover all these developments showing our recent results, ongoing activities, and future plans.

Universal photonic processors (UPPs) are reconfigurable photonic integrated circuits able to implement arbitrary unitary transformations on an input photonic state. Femtosecond laser writing (FLW) allows for rapid and cost-effective fabrication of circuits with low propagation losses. A FLW process featuring thermal isolation allows for a dramatic reduction in dissipated power and crosstalk in integrated thermally-reconfigurable Mach-Zehnder interferometers (MZIs), especially when operated in vacuum, with 0.9 mW dissipation for full reconfiguration and 0.5% crosstalk at 785 nm wavelength. To demonstrate the potential of this technology we fabricated and characterized a 6-mode FLW-UPP in a rectangular MZI mesh with 30 thermal shifters.

Erbium-doped integrated DFB lasers on glass exhibit a thermal stability and a very narrow linewidth that has been proven useful for many applications ranging from DWDM and Optomicrowave transmissions to airborne LIDAR. If the technologies used for the Erbium-doped active waveguides can differ (alumina, phosphate and silicate glasses have been reported among others), the laser cavity is always obtained thanks to a long Bragg grating implemented on the chip surface. Realizing cm-long submicrometric structure is a challenge that has been successfully overcome, but having such fragile features exposed on the top of a device entails several problems of packaging when reliability is concerned. Until now, this key issue has been addressed by depositing a conformal thin-film on the device surface, which is a complicated task since the deposited layer should be conformal, match the proper refractive index and respect the thermal budget of the process flow. In this paper, we present a different approach for the realization of Er-doped DFB lasers on glass where the grating-based cavity is implemented on a passive wafer that is then flip-chipped and wafer bonded on an Erbiumdoped phosphate glass containing active ion-exchanged waveguides. First results proved that a stable emission at a wavelength of 1.55 μm has been achieved for a fiber-coupled output power of more than 1mW.

Short-distance optical communications and large-scale networks are central in telecom, datacom, and information processing technologies. Such applications require high transmission capacity, low energy consumption, implementation at the chip-scale level and cost-effective production. Silicon photonics (SiP) is well-positioned to tackle these growing needs. Indeed, photonic chips enable dense integration of complex functions through light-driven, compact, and high-performance devices. SiP is boosted by complementary metal-oxide-semiconductor (CMOS) processes and toolsets used for decades in the microelectronic industry. CMOS-friendly manufacturing, mature germanium (Ge) epitaxy and open-access foundry model are advantageous for monolithic integration, where a low-loss silicon (Si) platform is associated with advanced opto-electrical efficiency and fast response time. Optical detectors are key building blocks in the SiP library. They leverage progresses made in design strategies, material processing and seamless Si CMOS integration. In particular, chip-integrated silicon-germanium (Si-Ge) photodetectors are aiming for fast, sensitive, and energy-aware operation, with performances that are becoming competitive or even superior to existing and well-adopted III/V-based counterparts. In this work, we present recent advances in waveguide-integrated p-i-n photodetectors based on double silicon-germanium-silicon (Si-Ge-Si) heterojunctions. Hetero-structured Si-Ge-Si photodetectors with a butt-waveguide-coupling and a lateral p-i-n electrical junction are most promising to detect light on a silicon chip at near-infrared (near- IR) wavelengths. They rely on an unique integration approach that yields structures with compact footprints and properly engineered waveguide geometries. Such devices then benefit from improved modal confinement and overall control over the intrinsic region. They are also easy to fabricate and integrate with other passive and active components on a single chip. Si-Ge-Si p-i-n photodetectors were fabricated on 200 mm silicon-on-insulator (SOI) substrates using industrial-scale semiconductor manufacturing processes. Fabricated p-i-n structures were operated under low-voltages and in avalanche regime, respectively. In both situations, devices showed up a reliable high-speed, low-noise, and sensitive signal detection within a mainstream telecom waveband around 1.55 μm.

We successfully demonstrate a monolithic integrated dual-polarization (DP) IQ modulator on thin-film lithium niobate (TFLN) platform, which consists of IQ modulators, spot-size converters (SSCs) and a polarization rotator combiner (PRC). After coupled with polarization maintaining fibers, the measured insertion loss of the modulator is 12 dB. In addition, we experimentally achieve a 1.6 Tb/s net bitrate single-carrier DP-PS-256QAM transmission.

Planar lightwave circuits (PLCs) provide economical, high-capacity solutions for systems using wavelength-division multiplexing. To accommodate a higher volume of optical integration in a smaller footprint, PLC technology has trended towards higher refractive index contrast platforms resulting in tighter optical confinement. Further progress in the densification of photonic functionality, especially for multi-stage interferometric configurations, must rely on the development of advanced architectures to increase the density of functional units. We present a breakthrough approach to the synthesis of ultra-dense interferometric chains, reaching packing density of waveguides close to theoretical limits. The proposed framework is well suited for mixed parallel and sequential interferometric structures in low- or high-refractive index contrast platforms. The new methodology allows the addition of stages to an interferometric chain without appreciable increase in device footprint, thus creating a highly-optimized ultra-dense waveguide layout. To validate this approach, we designed and fabricated a 4-λ LAN multiplexer that comprises 7 interferometric stages in a silica-on-silicon platform with a refractive index contract of Δn = 2.0%. Despite the relatively low refractive index contrast, the device was realized in a footprint of only 0.15 cm². The multiplexer exhibits exceptional optical performance, including on-chip loss of 0.2 dB, negligible polarization-dependent loss, and a remarkably flat single-mode spectral response with no insertion loss penalty. This ultra-compact implementation, combined with the state-of-the-art optical performance characteristics, led to a wide deployment of the multiplexer in data center applications, and provided a rapidly-advancing roadmap for unprecedented densification of optical functionality in PLCs in any refractive index platform.

High quality factor bulk resonators made in different materials have demonstrated outstanding performance in key functionalities that are very challenging to achieve in planar photonics. However, they have made no significant technological impact mainly because of their stability and scalability limitations related to the way they are connected to the outside world using prisms or tapered fibers. Here, we show several demonstrations of efficient coupling of bulk resonators to integrated waveguides using different materials like lithium niobate or polymers. Preliminary results of a universal integrated coupler that can be implemented using silicon photonics are also presented.

We experimentally demonstrate bandwidth-tunable RF photonic Hilbert transformer based on an integrated Kerr microcomb source. The micro-comb is generated by an integrated micro-ring resonator with a free spectral range of 48.9 GHz, yielding 75 micro-comb lines in the telecom C-band. By programming and shaping the generated comb lines according to calculated tap weights, we demonstrate high-speed Hilbert transform functions with tunable bandwidths ranging from 1.2 GHz to 15.3 GHz, switchable center frequencies from baseband to 9.5 GHz, and arbitrary fractional orders. The experimental results show good agreement with theory and confirm the effectiveness of our approach.

We propose and theoretically investigate integrated photonic filters based on two coupled Sagnac loop reflectors (SLRs) formed by a self-coupled optical waveguide. Recently we investigated integrated photonic filters based on cascaded SLRs and coupled SLRs. Here, we advance this field by presenting a unique approach of using coupled SLRs formed by a self-coupled optical waveguide. This enables us to achieve high performance filter functions including Fano-like resonances and wavelength interleaving with a simpler design and a higher fabrication tolerance by tailoring coherent mode interference in the device. Our design takes into account the device fabrication issues as well as the requirements for practical applications. As a guide for practical device fabrication, an analysis of the impact of the structural parameters and fabrication tolerance on each filter function is also provided. The Fano-like resonances show a low insertion loss (IL) of 1.1 dB, a high extinction ratio of 30.2 dB, and a high slope rate (SR) of 747.64 dB/nm. The combination of low IL and high SR promises this device for Fano resonance applications. Our device also can achieve wavelength de-interleaving function with high fabrication tolerance which is attractive for optical interleavers that need a flat-top symmetric filter shape. Optical interleavers and de-interleavers are core elements for signal multiplexing and demultiplexing in wavelength division multiplexing optical communication systems. Versatile spectral responses with a simple design, compact device footprint, and high fabrication tolerance make this approach highly promising for flexible response shaping in a wide variety of applications.

We are developing a non-conventional retinal projector for augmented reality (AR) applications. In our concept, light at λ = 532 nm is guided in silicon-nitride (SiN) photonic integrated circuits (PICs) embedded in the lens of a pair of glasses. We use holographic elements to transmit the emissive points towards the user’s retina without using lenses. Pixels are formed in the eye using the self-focusing effect and the eye lens. The transparency of the device is an absolute requirement for our application. In this work, we present the fabrication and the characterization of our latest SiN PICs on transparent substrate. The device was fabricated by transferring the SiN PICs from a silicon to a glass substrate. We characterized the PICs and the free-space optical transmission properties of our device using in-house goniometers and a Modulation Transfer Function (MTF) setup. We found a 76% transparency at our wavelength and no image alteration. However, we measured significant waveguide propagation losses; solutions are discussed to tackle this problem. Our glass-substrate device is a major step towards a future prototype for our AR retinal projector.

Interferometric scattering microscopy is a newly emerging alternative to fluorescence microscopy in biomedical research and diagnostic testing due to its ability to detect nano-objects such as individual proteins, extracellular vesicles, and virions individually through their intrinsic elastic light scattering. To improve the signal-to-noise ratio, we developed photonic resonator interferometric scattering microscopy (PRISM) in which a photonic crystal (PC) resonator is used as the sample substrate. The scattered light is amplified by the PC through resonant near-field enhancement, which then interferes with the <1% transmitted light to create intensity contrast. Importantly, the scattered photons assume the wavevectors defined by PC’s photonic band structure, resulting in the ability to utilize a non-immersion objective without significant loss at illumination density as low as 25 W/cm². We demonstrate virus and protein detection, including highly selective capture and counting of intact pseudotype SARS-CoV-2 from saliva with sensitivity equivalent to conventional nucleic acid tests. The results showcase the promise of nanophotonic surfaces in the development of resonance-enhanced interferometric microscopies, and as a single step, room temperature, and rapid viral detection technology.

Detection of threat materials is an important capability for the military and homeland security to protect soldiers and civilians. Waveguide-enhanced Raman spectroscopy (WERS), a photonic integrated circuit sensing methodology, is being developed for field detection of materials related to chemical warfare agents, explosives, and narcotic threats. Low-fluorescence silicon nitride spiral waveguides with long path lengths are used to obtain high signal levels with nearinfrared excitation (785 nm and 1064 nm). Compact single-mode-fiber-coupled spectrometers with high sensitivity are being utilized for detection of the Raman scattered light. Thermoelectrically cooled charged coupled device (CCD) or InGaAs detectors (-15 °C) provide for low-noise and high-quantum-efficiency spectral measurement. Performance comparable to that obtained with large benchtop spectrometers is observed. The spiral waveguides are coated with functionalized polymer sorbents suitable for concentrating relevant classes of threat materials in the evanescent field of the waveguide. The sorbents are deposited using piezoelectric microdispensers to allow for controlled deposition of thin films without the need for spin-coating. Raman chemical imaging microscopy is used to characterize the uniformity of the sorbent polymers on the waveguides. Library spectral matching can be used in combination with the selectivity of the sorbent materials to provide discrimination of the materials absorbed by the polymer coatings. The ultimate objective is development of a prototype handheld WERS sensor system suitable for defense and security applications in the field. WERS development and spectral measurements will be presented.

Water quality monitoring faces technological challenges such as rapid and in-situ measurements, using reusable, compact and easy-to-clean devices. Glass integrated photonics is an attractive solution: it exhibits a high sensitivity to absorption or interferometric measurements, and glass is chemically compatible with aqueous environments. An innovative idea for pollution detection is to assess the bacterial cellular viability as a global indicator for pollutant toxicity. This study proposes an original concept of integrated opto-fluidic sensor which sorts and quantifies the dead or alive bacteria in a liquid sample. To ensure a robust label-free detection, the cells discrimination is provided by a selective trapping of the bacteria exploiting dielectrophoretic effects. This avoids the use of a functionalization layer. The device comprises a photonic circuit made by silver-sodium ion-exchange on glass. The sensing area co-integrates a single-mode waveguide and aluminum electrodes designed to generate dielectrophoretic forces. Both waveguide and electrodes can be encapsulated inside a polydimethylsiloxane microfluidic channel for the flow of the bacterial suspensions. In this study, charged polystyrene beads (Sigma-Aldrich, CLB9) dispersed in deionized water have been used to model dead bacteria. We observed an intensity modulation of the guided light (up to 8% of the output power) at a wavelength of 1550 nm, by selectively controlling the beads trapping. We also correlated the beads collection by microscopy imaging.

Photonic crystals can exhibit interesting optical properties such as peculiar dispersion, small group velocity, negative refraction and diffraction. Group velocity engineering in a certain wavelength range allows for enhanced nonlinear optical interactions, while higher light confinement achievable in photonic crystal waveguides leads to a reduced footprint for integrated photonic components. Silicon-based photonic crystals are relatively well studied,^1–3 however, they are not suitable for a monolithic integration with active devices. ^III-V semiconductors exhibit light-emitting properties, large Kerr nonlinearity and negligible two-photon absorption in the telecommunication regime, and therefore are more suitable for frequency conversion, all-optical signal processing, laser absorption spectroscopy and microcomb generation for correlation spectroscopy applications. In this work, we theoretically investigate the design and fabrication of photonic crystal waveguides based on an airbridge Al_0.18Ga_0.82 slab for frequency conversion using FWM. We demonstrate a suspended Al0.18Ga0.82 layer fabricated by HF-controlled wet etching of an AlGaAs heterostructure, which selectively etched top and bottom claddings of higher aluminum concentration AlGaAs leaving behind the core suspended in air. We show, by simulations, that the group-index values of 25 over a bandwidth of 22 nm around 1590 nm in a dispersion-engineered W1 photonic crystal defect waveguide are possible enabling this device to operate in the slow-light regime where we also demonstrate a phase mismatch of nearly zero. Future designs can be optimized for longer wavelengths in the mid-infrared (MIR) as a promising platform to realize compact, slow-light enhanced integrated photonic components for sensing and wavelength conversion, thanks to the low propagation loss of AlGaAs in the MIR regime.

The two unique features of the plasmonic isolator and the plasmonic modulator are their small size of about 10-100 μm and their technological compatibility with the Photonic Integrated Circuits (PIC). These features make them attractive as components for a denser and smaller PIC. An additional advantage of the plasmonic modulator is its ultra-fast operational speed, which exceeds 200 GHz. We have developed and experimentally demonstrated two fabrication technologies, which allow a substantial decrease of both the plasmonic propagation loss and the coupling loss. The developed technologies are based on the optimization of the out-of-plane confinement and the in-plane confinement for a surface plasmon. A low propagation loss of 0.7 dB/μm for a surface plasmon in a Co/TiO₂/SiO₂ plasmonic structure on a Si substrate and a moderate coupling efficiency of 4 dB per facet between a Co/TiO₂/SiO₂ and a Si nanowire waveguide were achieved.

The longwave infrared (LWIR) spectral region from 8 to 12 µm is widely used for day/night sensing and imaging applications as it corresponds to an atmospheric window as well as the peak region of the terrestrial blackbody emission. Some of these applications require use of compact spectrally tunable notch or bandstop filters. We are developing such spectral filters based on dielectric metasurfaces that utilize the guided-mode resonance (GMR) effect to provide a resonant wavelength that can be tuned by either changing the incidence angle or the grating period. We describe development of spectrally tunable micro-engineered filters with the device structure consisting of a subwavelength dielectric grating on top of a planar homogeneous layer using high-index dielectric transparent materials, i.e., germanium (Ge) with a refractive index of 4.0 and zinc selenide (ZnSe) with refractive index of 2.4. The filters are designed to reflect the incident broadband light at one (or more) narrow spectral band while fully transmitting the rest of the light. Filters based on one-dimensional (1-d) gratings are polarization dependent and those based on two-dimensional (2-d) gratings are polarization independent for normal incidence of light while polarization sensitive at non-normal incidence. The filter designs were carried out using the rigorous coupled-wave analysis (RCWA) algorithm. We designed, fabricated and characterized a number of filters by carrying out direct transmission measurements using a tunable quantum cascade laser (QCL) system. We will present the simulation and experimental results for both the 1-d and 2-d grating GMR filters.

Snapshot multispectral mosaic imagers are based on optical filters monolithically integrated directly on top of a standard CMOS image sensor, extending the traditional Bayer color imaging concept to multi- or hyperspectral imaging without a need for dedicated fore-optics. This overcomes the requirement for spatial or spectral scanning during acquisition by sensing an entire multispectral data cube at one discrete point in time, enabling the multispectral acquisition of scenes containing movement. The use of CMOS process technology based, monolithically integrated optical filters further enables the qualities of compactness, low cost, high acquisition speed, a limited spectral crosstalk and a high degree of design flexibility, differentiating it from other snapshot spectral cameras. However, the use of CMOS process technology also introduces process variability leading to peak wavelength variations and challenges in repeatable sensor-to-sensor behavior. In this paper we introduce a new compact snapshot multispectral mosaic imager with an improved deposition process. The new snapshot imager has 16 bands covering a wavelength range of 460-600nm, with a resolution of 272x512pixels for each band. The deposition process is based on in-line optical monitoring, dynamically compensating the depositions to reach a targeted optical performance. By depositing on a full batch of wafers in parallel on a rotating spindle, wafer-to-wafer variability is further reduced. Filter performance repeatability is further maximized by an improved intra-wafer layer thickness uniformity. Combining this with a deposition process tuned for optical materials also enables more complex filter stacks, such as multiple cavity and high OD filters.

Lanthanide super crystals are of interest to increase energy within solar cell technologies due to solar cells inability to absorb photons at longer wavelengths. Currently, efficiencies of solar cells are limited close to the Schockley-Queisser limit (30%) for c-Si based solar cell devices. Development of light absorbing meta-materials is essential to enhance photonic activities and is key for solar cell energetic enhancements and advancement.

Ridge waveguides were 3D printed using a stereolithography 3D printer and hydrogel resin formulation. The ridge waveguides were 13, 20 and 30 μm wide, 3-6 μm high and 4.4 mm long. The loss of the waveguides was measured using the cutback method and ranged between 0.28 and 1.2/cm (or 1.2 and 5.2 dB/cm) with transmittances up to 0.94 using 635 nm light. This work demonstrates a quick and inexpensive method to fabricate integrated photonic chips with the promise to fabricate more complex photonic devices.

Clean energy harvesting applications of metasurfaces employ perfect broadband absorbers with a high thermal stability. An evaluation of a set of several numerically investigated, refractory metal nitride (Zirconium Nitride - ZrN)-based, sub-wavelength broadband absorbers is carried out using wide-angle (0° ≤ θ ≤ 70°) and variously polarized (0° ≤ ϕ ≤ 90°) incident light. Following a metal-dielectric-metal configuration with the same order of dimensions, each absorber features a dielectric layer of SiO2, separating the top (nanostructure) and bottom (ground) layers made of ZrN. The choice of material is supported by a high melting point (2980 °C), interesting optical and plasmonic properties along with chemical and mechanical stability. Each of the proposed designs was first analyzed for geometrical parameters to achieve optimum absorption. The simulated output for the wavelength range 280-4000 nm, in terms of normally incident light for both TE and TM polarizations is presented alongside solar irradiance. The normalized impedance for each structure was computed for comparison with that of the free space. The analyses led towards an important consequence that while preserving the order of optimized dimensions for each geometry, only a few designs are independent of incident angle, insensitive to polarization variation and easy to fabricate. Out of the twenty absorber profiles investigated, the "cross nanoresonator" showed the highest absorbance of 99.61% at 613 nm, with an average of 94.60% for visible spectrum and 66.72% for 280- 4000 nm. The study adds confidence to the understanding that absorption is a function of both structure geometry and its dimensions.

Time-delay Reservoir Computing (TRC) are neural networks which thanks to their hardware simplicity are suited for photonic implementation. Here, we numerically investigated and experimentally tested a TRC based on a nonlinear single silicon microring resonator (MRR) coupled to an optical fibre loop which provides an external tuneable optical feedback. The work is inspired by the key role that MRRs demonstrate in integrated optical devices, together with the significant advantage they provide due to their fully passive nonlinearity. Insights about the computational properties of the system are provided as a result of the performance on multiple benchmark tasks.

Next-generation BSI CMOS Imager Sensors are strongly driven by novel applications in depth sensing, mainly operating in the NIR (940nm) spectrum. As a result, the need for higher pixel sensitivity while shrinking pixel pitch is more present than ever. In this work, we present a new technology platform based on ad-hoc nano diffractor geometries, integrated in the Back Side of BSI CIS that allow to drastically improve the QE of the sensor for pitches varying from 10 μm down to 2.2 μm, co-optimized for both optical and electronic pixel performance.

We have designed and fabricated micro-LiDAR chips based on 1D optical phased arrays (OPAs) that collimate light in the horizontal direction only. Thus, a cylindrical lens is needed for the vertical collimation. A part of the work demonstrates the analysis of 1D beam steering experiments through the direct outcoupling from the waveguide facets with two straight cylindrical lenses available commercially and a detailed analysis based on the parameters like Rayleigh range and beam divergence is presented. This work also demonstrates the characterizations of 3D printed curved cylindrical collimating lenses. A thorough analysis based on the experimental work resulted in certain suggestions to improve the collimation and to perform the beam steering in a better way.

Collection of light in photodetector focal plane arrays (FPAs) can be enhanced by microlenses or metasurfaces. We propose an alternative approach based on using microconical waveguide arrays integrated with mid-wave infrared (MWIR) FPAs which allows increasing photon collection efficiency with large angle-of-view (AOV). The light incident on FPA is collected by the wider base of microconical waveguides with diameter (D_t) and delivered to their narrow base with diameter (D_b) which is coupled to the photodetector mesa of FPA. A parameter to determine the light-concentrating ability is a power enhancement factor (PEF) defined as the ratio of the powers delivered to the same photodetector with and without the microconical waveguide. By using finite-difference time-domain modeling, the PEF and AOV parameters of the proposed structures are studied as a function of geometrical parameters of microcones. It is demonstrated that the maximal PEFs in excess of 100 require use of sufficiently elongated small-angle microcones with a wavelength-scale diameter of the narrow base. To demonstrate the light concentrating capability, slightly suboptimal microconical arrays with D_t/D_b = 60 μm/8 μm and with 150 μm length of microcones were fabricated in photoresist by using a nanoscribe tool directly on top of the front-illuminated Ni/Si Schottky-barrier short-wave infrared photodetectors with 22 μm mesas, and three-time enhancement in the photocurrent response was observed. Due to expected reduction of the thermal noise for compact photodetector mesas, the proposed approach permits increase of the SNR and the operation temperature of the MWIR imaging devices.

A new double line waveguide architecture produced in Nd³⁺ doped GeO₂-PbO glasses is presented for photonic applications. These glasses produced with the melt quenching technique have interesting characteristics that make them attractive for photonic applications: large transmission window (400–5000 nm), large polarizability, low melting temperature (1200° C) with respect to silicates, low cut-off phonon energy (~800 cm^-1 ), large mechanical resistance, high chemical durability and high refractive index (~2.0). The double line waveguides are written directly into Nd³⁺ doped GeO₂-PbO glasses using a Ti:Sapphire femtosecond (fs) laser, operating at 800 nm, delivering 30 fs pulses at 10 kHz repetition rate. The two written lines that form the double waveguide are formed by several collinearly overlapping lines. Results of the output mode profile, the M² beam quality factor at 632 and 1064 nm and refractive index change are presented, as well as the parameters used for laser writing. Double waveguides written with 4 and 8 overlapping lines, writing speed of 0.5 mm/s and pulse energy of 30 μJ demonstrated to be adequate parameters for writing; refractive index changes of ~10^-3 were found at 632 nm for all the cases. The present results demonstrated that Nd³⁺ doped GeO₂-PbO glasses with the new double line waveguide architecture are promising materials for the fabrication of passive and active components for photonic applications. Further investigation will focus on the influence of the writing parameters on the optical performance of the different waveguides, and evaluate the potential of the materials as optical amplifiers at 1064 nm.

Nd³⁺ doped TeO₂-ZnO glasses with double line waveguides produced by femtosecond (fs) laser writing technique are presented. The waveguides are written directly into these glasses using a femtosecond (fs) Ti:Sapphire laser, operating at 800 nm, delivering 30 fs pulses at 10 kHz repetition rate. Each written line is formed by several collinearly overlapping lines. When double line waveguides are produced, the light is guided in between the two lines and a negative refractive index change is produced in the region of the fs laser’s focus. However, as the absorption of the material at 800 nm (⁴ I_9/2 → ⁴ F _5/2 + ² H_9/2 transition of Nd³⁺) is in resonance with the fs laser, the heating of the material makes writing difficult. In this context, the use of several overlapping lines represents a good alternative as the velocity of the writing can be increased to avoid, heating. We report results of output mode profile, beam quality factor M² and refractive index change for, different parameters used for the fs laser writing. Pulse energies were 15μJ for 4 and 8 overlapping lines and 30 μJ for 2, 4 and 8 overlapping lines and the writing speed was 0.5 mm/s. The present investigation evaluates the best condition for the waveguides inscription, studying the influence of different parameters used in the writing process aiming at future photonic applications.

The reduction of optical loss for integrated photonics I/O is an important area of active research. Edge coupling (end-firing) is a key I/O technology, having advantages over grating couplers in terms of spectral bandwidth and lower insertion loss¹. Low-loss edge coupling into silicon waveguides will be critical to datacenters and telecommunications systems in order to help accommodate the aggressive growth of data analytics applications². In this work, we investigate the coupling losses from optical fiber (SMF-28) into on-chip silicon waveguides using silicon nitride edge couplers with varying chip facet angles. The expected losses were simulated using Three Dimensional Finite-Difference Time-Domain (3D-FDTD) modelling and measured experimentally to close the design-fabrication loop. The chips were produced within a state-of-the-art 300 mm CMOS foundry, using edge couplers from the foundry Process Design Kit (PDK). During optimization of the photolithography and dry etching process, the facet angle deviation from 90° was minimized. Insertion loss of the SiN edge coupler was investigated via transmission measurements utilizing both cleaved fibers and fiber V-grooves. Facet angles varied from approximately 75°–90° were tested for insertion loss and trends were consistent with the 3D-FDTD modelling. Measurements were performed over a range of 1450–1650 nm using a tunable laser source and optical power meter. In addition, facet insertion loss was isolated by using propagation loss data from an in-line testing tool that measured silicon waveguides propagation losses, on wafer and in the same wavelength band.

Lead Zirconate Titanate (PZT) is widely used for energy harvesting owing to its strong piezoelectric and electromechanical coupling coefficient as well as high temperature compatibility (Curie point ~ 370°C).^1-3 The heterogeneous integration of a PZT thin film on the Si photonics platform can compensate the lack of piezoelectricity in the centro-symmetric Silicon, and enable a wide range of electro-optomechanical applications combining the benefits of a strong piezoelectric material and a matured photonic platform.

In this work, we directly deposit a PZT film on silicon-on-insulator (SOI) using a transparent Lanthanide based seed layer making it photonics compatible,⁴ unlike the traditional PZT film grown with a metallic Platinum (Pt) buffer layer, which introduces unacceptable optical losses in the device.⁵ We fabricate unimorph micro- cantilever beams with the hybrid PZT-SOI chip and demonstrate its piezoelectric actuation. The laser Doppler Vibrometry (LDV) measurements on these suspended actuators give a deflection up to 40 nm with an applied RF voltage of V_pp = 10 V at the fundamental resonance frequency. Next, through numerical simulations, we show that a PZT actuator integrated with a directional coupler allows for a strong tuning efficiency.

Thus, we demonstrate a PZT film based actuator that can be directly integrated on the Si photonic plat- form. This opens the possibility of achieving an efficient electro-optomechanical coupling and low-power MEMS applications in Si photonic integrated circuits (PICs).

Self-written waveguides (SWWs) are established to connect different optical elements with each other. They enable a rigid and easy-to-manufacture low-loss optical connection, which can be employed in many optical configurations. To create an optical interconnect, a UV-curable monomer is applied in between two optical elements. If near-UV light is propagated through one end, the monomer starts to polymerize locally and self-traps the light beam due to the increasing refractive index. Subsequently, the surrounding resin can be cured using UV-flood exposure creating a rigid connection between the two components. In recent works, we demonstrated that this technique can be used to connect laser diodes with a polymer waveguide directly without using UV light exposure and that it is also possible to overcome alignment offsets with respect to the optical axis. Here, we investigated how these structures can additionally be used as integrated sensing elements. A detailed analysis of the thermal behavior of the SWWs was performed, which yields an increase of the optical transmission with increasing temperature. We also investigated the implementation of thin-film filters for splitting an SWW in multiple beams, which enables us to create a reference and a sensing arm for measurement applications or to use the filter for wavelength demultiplexing. We performed a detailed investigation of the thermal behaviour and implemented thin-film filters for more complex functional structures.

The need to predict data with less computational effort lead to studies to improve the training algorithms and Artificial Neural Networks (ANN) architectures. We demonstrated how to improve the performance and to increase the efficiency of the ANN by implementing a hybrid model where the parameterization is made by Genetic Algorithm (GA). In this work we applied the hybrid GA-ANN model for the analysis and synthesis of metamaterial based waveguides, composed of metallic and dielectric thin layers claddings surrounding a dielectric core. The parameter to be computed is the length propagation as a function of wavelength, metal filling ratio, refractive indexes of the metal and dielectric layers, waveguide core width and core refractive index. For the synthesis, one of the geometrical parameters becomes the ANN output. The proposed GA ANN was capable of predicting the propagation characteristics of new unseen configurations of metamaterial waveguides with low relative error.

Online solvers for a series of standard 1-D or 2-D problems in integrated optics will be discussed. Implemented on the basis of HTML/JavaScript/SVG with core routines compiled from well tested C++-sources, the quasi-analytical algorithms require a computational load that can be handled easily even by current mobile devices. So far the series covers the 1-D guided modes of dielectric multilayer slab waveguides and the oblique plane wave reflection from these, the modes of rectangular channel waveguides (in an approximation of effective indices), bend modes of curved multilayer slabs, whispering-gallery resonances (“Quasi-Normal-Modes”) supported by circular dielectric cavities, the hybrid modes of circular multi-step-index optical fibers, bound and leaky modes of 1-D complex multilayers, including plasmonic surface modes, and, with restrictions, quite general rectangular scattering problems in 2-D.