This PDF file contains the front matter associated with SPIE Proceedings Volume 9750, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Using the Mosquito method, we fabricate low-loss multimode polymer optical waveguides with graded-index (GI) perfect circular cores for the applications to on-board optical interconnection. We already developed the Mosquito method utilizing a microdispenser, as a fabrication technique for GI circular core polymer waveguides. In the Mosquito method, a liquid-state core monomer is dispensed from a syringe needle into a liquid-state cladding monomer while the needle horizontally scans. Originally we used siloxane based monomers. In this paper, novel organic-inorganic hybrid materials (SUNCONNECT®) are selected to confirm the applicability of wide-range polymers to the Mosquito method. Here, a dip is observed on the upper perimeter of the obtained core cross-sections particularly when using a straight needle. Such a core-shape deformation increases the coupling loss with circular-core optical fibers. So, the flow of core and cladding monomers while dispensing the core with the needle scan is visually observed. It is confirmed that the edge of the straight needle chips off the upper perimeter of the core when the core monomer is dispensed, leading to the dip. Therefore, the straight needle is replaced for a curved one to change the dispensing direction for eliminating the dip. It is experimentally found that an almost circular core (50-μm diameter with 1.09 vertical to horizontal ratio of diameter) is formed when a curved needle is used. Finally, we successfully demonstrate a 1.73-dB lower loss in a 5-cm long waveguide compared to the one having the core with a dip.

We present the experimental demonstration of a strip loaded waveguide on crystalline lithium niobate thin film. The structure consists in a 1 μm-wide and 200 nm-thick titanium dioxide strip waveguide on a 700 nm lithium niobate slab waveguide. It operates at the telecom wavelength for a TE-polarized light.

The linear electro-optic effect in lithium niobate is capable of realizing a variety of polarization transformations, including TE-to-TM and left-to-right circular polarization conversion. While most LiNbO₃ components are designed for operation in the third telecommunications window around 1.55 μm wavelength, current interest in quantum information processing and atomic physics, where the wavelengths of interest are in the visible and near-infrared, has placed new demands on endless polarization control devices. At short wavelengths, traditional Ti-diffused LiNbO₃ waveguides suffer from photorefractive degradation at optical power levels well below 1 mW. Proton exchanged waveguides have much higher power handling capability but can only guide light polarized parallel to the optic axis, and therefore are not applicable to polarization control. Zinc oxide diffusion is an alternative waveguide fabrication technology that guides both e- and o-waves with much higher power handling capability than Ti:LiNbO₃ waveguides. ZnO:LiNbO₃ waveguides exhibit a highly circular mode field with lower anisotropy than Ti-diffused waveguides. We report on the modeling, fabrication and testing of a polarization controller in ZnO-doped, x-cut lithium niobate operating at a wavelength of 780 nm.

The fabrication of on-chip optical isolators to protect integrated optical sources is one of the major challenges of research in integrated optics. Their operation principle is based on the control of the guided-wave polarization and the most common structures are composed of a polarization splitter, a non-reciprocal rotator based on the Faraday effect, and a reciprocal rotator. The reciprocal rotator is a device that rotates the wave polarization by 45°. This can be achieved by creating a relative phase shift between the waveguide’s two polarization eigen states or by twisting its optics axis thanks to an appropriate shaping of its core. In this work, we propose the design and simulation of a waveguide with optics axes tilted by 45° fabricated by two cascaded field-assisted ion exchanges on a glass substrate and an encapsulation. The dependences of the proposed design on process time, temperature, applied voltage and photolithography over-etching are investigated. The final device exhibits a 45.1° rotation of its optical axes and less than 5% variation on the C+L telecommunication band.

This paper deals with an experimental non-destructive technique for the measurement of polarization behavior of integrated optical waveguides. It is based on a high resolution polarimeter associated to an ellipsometric-type calibration which allows determining the full state of polarization of the output light. A magneto-optic perturbation is also added to generate TE/TM mode beating, whose spatial period is directly linked to the modal TE/TM birefringence. This equipment is first qualified by the measurement of modal birefringence in totally or partially buried ion exchanged waveguides. The results show that the value of the birefringence varies as a function of the diffusion aperture width or with the burying depth. By adding a magneto-optical cover layer, consisting in magnetic nanoparticles doped silica matrix obtained by a sol gel process ¹, we evidence a huge increase of the beating magnitude and a decrease of the modal birefringence.

The trade-off between extinction ratio (ER), insertion loss (IL), and energy consumption (E) is a common bottleneck for existing integrated optical modulators. In this work, we report an indium tin oxide (ITO) based hybrid-plasmonic modulator, consisting of a Si/ITO/HfO₂/Al/HfO₂/ITO/Si stack, that can alleviate such trade- off in device metrics. This is achieved by first use field symmetry matching technique to engineer the waveguide to support long-range propagation. Then, by electrostatically inducing the ITO layers to enter an epsilon-near-zero state, strong carrier absorption as well as disturbance to the field symmetry will render the otherwise low-loss waveguide highly absorptive. Using this strategy, amplitude modulation with ER = 4.83 dB/μm, IL = 0.03 dB/μm, and E = 14.8 fJ is achieved. Moreover, with a triode-like biasing scheme, the modulator attributes can be further manipulated and the same device can be dynamically reconfigured for phase and 4-quadrature-amplitude modulation, with actively device length of only 5.53 μm and 17.78 μm respectively.

We present an optical system which integrates a plasmonic sensing surface and an angular tracking system to enable a compact refractive index measurement. A refractive index change at the surface of the sensing membrane causes a change in the angle at which monochromatic light is transmitted through the membrane. This transmission angle is measured by the angular tracking system. We show good theoretical and experimental agreement of the transmission of the plasmonic sensing surface at different angular illumination of the membranes. Using this compact optical setup the embedded angular tracking system has an accuracy of <10^-4 deg. This corresponds to a sensitivity <10^-5 refractive index units. Finally we demonstrate this measurement technique using different concentrations of saline solution.

We introduce a compact plasmonic resonator that is capable of generating a Fano resonance in the transmission spectrum. The Fano resonance is observed with its unique lineshape. The proposed design is simple, compact, easy to fabricate and can be easily developed for different applications. The device structure is made of a gold layer, a metalinsulator- metal waveguide, and a rectangular cavity. As an application to the proposed plasmonic resonator, we introduce a gas sensor which is operational at the near infrared spectral range. The sensor possesses a high sensitivity of 1500nm/RIU at the telecom wavelength 1.55μm. FDTD simulation tools were conducted for the optimization of the device structure and obtaining the results.

Recently, unidirectional reflectionlessness was demonstrated in classical photonic structures at optical exceptional points. Here we introduce a non-parity-time symmetric plasmonic waveguide-cavity device consisting of two metaldielectric- metal stub resonators side coupled to a metal-dielectric-metal waveguide. We tune the geometric parameters of the structure to obtain the exceptional point and realize unidirectional reflectionlessness at the optical communication wavelength. We investigate the properties of the plasmonic exceptional point as well as the associated physical effects of level repulsion, crossing and phase transition. We also show that by properly cascading the plasmonic waveguide-cavity structures we can design a wavelength-scale unidirectional plasmonic waveguide perfect absorber.

Photonic integrated circuits that exploit nonlinear optics in order to generate and process signals all-optically have achieved performance far superior to that possible electronically - particularly with respect to speed. We review the recent achievements based in new CMOS-compatible platforms that are better suited than SOI for nonlinear optics, focusing on radio frequency (RF) and microwave based applications that exploit micro-resonator based frequency combs. We highlight their potential as well as the challenges to achieving practical solutions for many key applications. These material systems have opened up many new capabilities such as on-chip optical frequency comb generation and ultrafast optical pulse generation and measurement. We review recent work on a photonic RF Hilbert transformer for broadband microwave in-phase and quadrature-phase generation based on an integrated frequency optical comb. The comb is generated using a nonlinear microring resonator based on a CMOS compatible, high-index contrast, doped-silica glass platform. The high quality and large frequency spacing of the comb enables filters with up to 20 taps, allowing us to demonstrate a quadrature filter with more than a 5-octave (3 dB) bandwidth and an almost uniform phase response.

Polymer optical waveguides, especially single-mode waveguides are increasingly used for short distance communication, as well as for sensing applications. The realization of a working communication route requires different and sequentially realized steps. Generally, these steps are the packaging of semiconductor beam senders and receivers, the fabrication of an optical waveguide, the preparation of its end-facets, the alignment of different elements along their optical axis and the integration into a desired communication route. The development of a process, which integrates all these steps for planar surfaces, offers a reduction in time and an increase in flexibility. A sub-step toward such a highly automated system is the integration of optical waveguides into the planar surface. In this context, we are investigating the use of the micro-dispensing process to realize this integration step. We functionalize UV-curing adhesives as cladding for micro-optical cores as well as for inherent bonding to the substrate surface. For this purpose an optical characterization of the adhesives is necessary for an adequate core and cladding material combination. A ow behavior characterization is also relevant in order to analyze the used dispensing process with the selected adhesive. Finally, a mechanical characterization is done to test the adhesion of the core to the adhesive, as well as the adhesive to the substrate surface. In this paper we present a summary of the realized characterization of the selected polymer. Based on experiment results we infer limits and opportunities of this method.

I report a lattice-form tunable optical dispersion compensator whose number of operable channels is doubled with the use of an interleave filter. In this scheme, interleaved signals are introduced into two different inputs of the lattice-form compensator and are provided with the same dispersion value based on unitary properties of the compensator transfer matrix. Thus this configuration can activate inoperable bands that account for nearly half of the total bandwidth in existing lattice-form compensators. The proposed compensator was realized by connecting the silica waveguide-based interleave filter and dispersion compensator with fibers. The dispersion of -283 to 252 ps/nm was obtained over 40 GHz bandwidth with a period of 50 GHz.

Exploiting a controllable technique for red and blue shifting of quantum well’s bandgap energy, we have fabricated LED sources accessing a wide frequency spectrum along with all-optical intensity modulator devices. . We demonstrate bandgap tuning of InGaAsP multiple quantum well structures by utilizing an impurity free vacancy diffusion technique. Substantial modification of the bandgap energy toward the red and blue part of the spectrum has been observed using SiO₂ , SiO_yN_x , SiN_x capping layers and by controlling the associated oxygen and nitrogen content. The resulting degree of tuning, up to 120nm red-shift and 140nm blue-shift of the band to band wavelength emission, has been studied using room temperature photoluminescence, in agreement with the emission spectra obtained from semiconductor LED devices fabricated on this platform. The intensity modulator devices has been fabricated along with LED sources compatible for the selected frequency, designed to reach minimum material losses and residual amplitude modulation.

In this paper, the simulation, design and fabrication of a back-side coupling (BSC) concept for silicon photonics, which targets heterogeneous hybrid III-V/Si laser integration is presented. Though various demonstrations of a complete SOI integration of passive and active photonic devices have been made, they all feature multi-level planar metal interconnects, and a lack of integrated light sources. This is mainly due to the conflict between the need of planar surfaces for III-V/Si bonding and multiple levels of metallization. The proposed BSC solution to this topographical problem consists in fabricating lasers on the back-side of the Si waveguides using a new process sequence. The devices are based on a hybrid structure composed of an InGaAsP MQW active area and a Si-based DBR cavity. The emitted light wavelength is accordable within a range of 20 nm around 1.31μm thanks to thermal heaters and the laser output is fiber coupled through a Grating Coupler (GC). From a manufacturing point of view, the BSC approach provides not only the advantages of allowing the use of a thin-BOX SOI instead of a thick one; but it also shifts the laser processing steps and their materials unfriendly to CMOS process to the far back-end areas of fabrication lines. Moreover, aside from solving technological integration issues, the BSC concept offers several new design opportunities for active and passive devices (heat sink, Bragg gratings, grating couplers enhanced with integrated metallic mirrors, tapers…). These building boxes are explored here theoretically and experimentally.

We show the enhancement of the photoluminescence at λ = 1:5 μm in highly-doped (> 10²¹ cm^-3) Er-Al₂O₃ samples by controlling the vertical distance between the Er-ions using atomic layer deposition (ALD) technique. Er₂O₃ and Al₂O₃ were deposited on top of silicon in an alternating fashion with ALD. Five Er₂O₃-Al₂O₃ samples were fabricated by keeping the amount of Er₂O₃ constant but changing the thickness of the Al₂O₃-layers between the Er₂O₃-layers. The PL spectra of the samples reveal that the PL signal enhances up to 90% when the vertical distance (the number of Al₂O₃-layers) between the Er-ions increases. The PL enhancement can be related to the reduction of up-conversion signal at 532 and 650 nm in the Er-ions. Our results demonstrate that ALD is an excellent technique to fabricate and to optimize Er-doped materials due to its unique depositions properties.

An integrated on-chip optical device composed of a multiple quantum-well light-emitter and photodetector in the lightemitting transistor (LET) platform is fabricated. The two devices are 400 μm in length and electrically isolated by dry etching with 4.9 μm gap. The two facets are formed by cleaving for optical output. In this report, we discuss the characteristics of the two-section device and demonstrate the optical detection by the heterojunction phototransistor (HPT) under different operation points (I_B and V_CE) and injected optical powers. The collector current of the HPT is 74.88 mA without illumination and 83.87 mA under illumination of 7.46μW at V_CE = 3 V and I_B = 12 mA, which exhibits 12% increment. The responsivity of the InGaP/GaAs HPT can reach to 711.74 A/W. At the electrical modulation bandwidth of phototransistor fT is enhanced from 1.4 GHz to 1.51 GHz under illumination. This is attributed to the Franz-Keldysh photon-assisted absorption at base-collector junction of light-emitting transistor, which produces additional holes and electrons to enhance the current gain. Through the analysis of small-signal equivalent circuit models, we can show the transit time by de-embedding the circuit parasitic effect. Extracting those parameters can clearly know the thermionic emission lifetime in the quantum well.

We report on the design, fabrication and measurement of travelling-wave superconducting nanowire single-photon detectors (SNSPDs) integrated with polycrystalline diamond photonic circuits. We analyze their performance both in the near-infrared wavelength regime around 1600 nm and at 765 nm. Near-IR detection is important for compatibility with the telecommunication infrastructure, while operation in the visible wavelength range is relevant for compatibility with the emission line of silicon vacancy centers in diamond which can be used as efficient single-photon sources. Our detectors feature high critical currents (up to 31 μA) and high performance in terms of efficiency (up to 74% at 765 nm), noise-equivalent power (down to 4.4×10^-19 W/Hz^1/2 at 765 nm) and timing jitter (down to 23 ps).

We fabricate a series of reconfigurable waveguide interferometers using laser machining techniques and charac- terize them classically. The 3D nature of the ultrafast laser writing technique allows for the fabrication of unique multi-arm interferometers not possible in planar platforms. We demonstrate selectivity between multiple phase shifters in a single interferometer by patterning the chip surface using picosecond laser ablation in a separate step. Microfluidic elements for making practical measurements on-chip are incorporated by machining channels within the substrate to interact with waveguide modes. Our results provide a path toward practical implementation of quantum metrology protocols requiring multiple interferometer arms and tunable phases.

We report on our progress towards the integration of nonreciprocal optical elements in, for example, an integrated optical waveguide isolator on conventional semiconductor photonic platforms. Our approach uses an evanescent interaction with a magneto-optic iron garnet upper cladding. Specifically, cerium- and bismuth- substituted yttrium and terbium iron garnets were investigated. Device fabrication incorporates RF sputtering, mask lift-off to form a grating for a quasi-phase-matched interaction and thermal anneal. A non-reciprocal polarisation-mode conversion was observed.

Monolithic integration of nonreciprocal optical devices on semiconductor substrates has been a long-sought goal of the photonics community. One promising route to achieve this goal is to deposit high quality magneto-optical (MO) oxide thin films directly on a semiconductor substrate. In this article, we will review our ongoing progress in material development and device engineering towards enabling a monolithically integrated, high-performance magneto-optical nonreciprocal photonics platform. In particular, we will discuss our recent work which has led to a new pulsed laser deposition (PLD) technique of Ce or Bi substituted yttrium iron garnet (YIG) thin films with reduced thermal budget, simplified growth protocols and improved magneto-optical characteristics. These materials were incorporated in monolithic resonator and interferometer based isolator devices to demonstrate on-chip optical isolation with improved device figure of merit. Challenges and opportunities for monolithic magneto-optical devices will be discussed in the context of our latest material and device performance metrics.

Periodic structuration of magnetic material is a way to enhance the magneto-optical behavior of optical devices like isolators. It is useful to reduce the footprint of such integrated devices or to improve their features. However, the structuration and/or integration of efficient magnetic materials on photonic platforms is still a difficult problem, because classical magneto-optical materials require an annealing temperature as high as 700°C. A novel wafer-scale approach is to incorporate that material into an already structured template through a single step deposition at low temperature. Using the dip-coating method, a magneto-optical thin film (~300nm) of CoFe₂O₄ nanoparticles in silica matrix prepared by sol-gel technique was coated on a 1D and 2D TiO₂ subwavelength gratings. Such gratings were realized by the patterning of TiO₂ films obtained by a sol-gel process. It was confirmed by Scanning Electron Microscope images that the magneto-optical composite completely occupies the voids of the 2D structuration showing a good compatibility between both materials. This composite shows a specific Faraday rotation of about 200°cm^-1 at 1,5μm for 1% of volume fraction of nanoparticles. Spectral studies of the transmission and the reflection of a 1D TiO₂ grating filled with the MO composite have evidenced the presence of a guided-mode optical resonance at 1,55μm. The position of this resonance was confirmed by numerical simulations, as well as its quite low efficiency. Based on simulations results, one can conclude that an increase of the grating depth is required to improve the efficiency of the resonance.

A novel design of two-mode (DE)MUX based on multimode interference (MMI) couplers on InP substrate is proposed. A phase shifting section based on the thickness variation of the core layer is introduced in the (DE)MUX to realize a 100% mode conversion efficiency and multiplexing. The total length of the structure is only 549 μm, much shorter than other InP based mode (DE)MUXs. Simulations show that, the device crosstalk is below -20 dB and the insertion loss is lower than 1 dB for both of the fundamental mode and the first order mode within the whole C band. This new structure can be potentially integrated with other devices based on InP substrate to serve as a monolithic few-mode transmitter/receiver.

Advances in nuclear fuel reprocessing have led to a surging need for novel chemical analysis tools. In this paper, we present a packaged lab-on-chip approach with co-integration of optical and micro-fluidic functions on a glass substrate as a solution. A chip was built and packaged to obtain light/fluid interaction in order for the entire device to make spectral measurements using the photo spectroscopy absorption principle. The interaction between the analyte solution and light takes place at the boundary between a waveguide and a fluid micro-channel thanks to the evanescent part of the waveguide’s guided mode that propagates into the fluid. The waveguide was obtained via ion exchange on a glass wafer. The input and the output of the waveguides were pigtailed with standard single mode optical fibers. The micro-scale fluid channel was elaborated with a lithography procedure and hydrofluoric acid wet etching resulting in a 150±8 μm deep channel. The channel was designed with fluidic accesses, in order for the chip to be compatible with commercial fluidic interfaces/chip mounts. This allows for analyte fluid in external capillaries to be pumped into the device through micro-pipes, hence resulting in a fully packaged chip. In order to produce this co-integrated structure, two substrates were bonded. A study of direct glass wafer-to-wafer molecular bonding was carried-out to improve detector sturdiness and durability and put forward a bonding protocol with a bonding surface energy of γ>2.0 J.m^-2. Detector viability was shown by obtaining optical mode measurements and detecting traces of 1.2 M neodymium (Nd) solute in 12±1 μL of 0.01 M and pH 2 nitric acid (HNO3) solvent by obtaining an absorption peak specific to neodymium at 795 nm.

Rare-earth ion doped crystalline potassium double tungstates, such as KY(WO₄)₂, KLu(WO₄)₂ and KY(WO₄)₂, exhibit many properties that make them promising candidates for the realization of lasers and amplifiers in integrated photonics. One of the key challenges for the hybrid integration of different photonic platforms remains the design and fabrication of low-loss and fabrication tolerant couplers for transferring light between different waveguides. In this paper, adiabatic vertical couplers realized by flip-chip bonding of polymer waveguides to Si₃N₄ devices are designed, fabricated and tested. An efficient design flow combining 2D and 3D simulations was proposed and its validity was demonstrated. The vertical couplers will ultimately be used for the integration of erbium doped KY(WO₄)₂ waveguides with passive platforms. The designed couplers exhibit less than 0.5 dB losses at adiabatic angles and below 1 dB loss for ±0.5 μm lateral misalignment. The fabricated vertical couplers show less than 1dB losses in average for different adiabatic angles of Si₃N₄ tapers, which is in good quantitative agreement with the simulations.

In this paper, we report our recent progress in silicon-nitride-based optofluidic label-free biosensors using a surfacefunctionalized coupled-resonator optical waveguide (CROW) in the visible wavelengths. The working principle is based on far-field imaging of the CROW mode-field intensity distributions at a fixed probe wavelength. The imaged pattern variation reflects real-time analyte-binding information on the CROW surfaces. Our surface-functionalized 16- microring CROW reveals six eigenstates with distinctive mode-field intensity distributions. Our proof-of-concept sensing experiment at an arbitrarily chosen probe wavelength within the CROW transmission band shows a detection of streptavidin concentration down to 40 ng/ml.

Typical optical integrated circuits combine elements, like straight and curved waveguides, or cavities, the simulation and design of which is well established through numerical eigenproblem-solvers. It remains to predict the interaction of these modes. We address this task by a ”Hybrid” variant (HCMT) of Coupled Mode Theory. Using methods from finite-element numerics, the optical properties of a circuit are approximated by superpositions of eigen-solutions for its constituents, leading to quantitative, low-dimensional, and interpretable models in the frequency domain. Spectral scans are complemented by the direct computation of supermode properties (spectral positions and linewidths, coupling-induced phase shifts). This contribution outlines the theoretical background, and discusses briefly limitations and implementational details, with the help of an example of a 2-D coupled-resonator-optical-waveguide configuration.

For high quality optical coatings the knowledge of the losses of the deposited materials is essential. A precise measurement of low Im(n+iκ)≤ 10^-6 at an intended operation wavelength and with low intensity can be achieved in waveguide configurations, whereby leaky waveguide configurations allow one to analyze losses of high- and low-index media of H-L-stacks as well due to resonances in the angle-dependent reflection curve. Numerical investigations reveal that different leaky wave schemes, e.g. Bragg-, Bloch- and Antiresonant-Reflecting waveguides, comply differently with practical requests. Loss figure evaluation requires peculiar attention due to measurement accuracy and ambiguities, thus suitable constraints for layer data and a proper merit-function construction have to be used.

Graphene is different from most optical materials in that it is a thin material layer with a thickness as small as one atom. Graphene layers can be incorporated into optical simulations using either a surface conductivity material model or a volumetric permittivity material model; however, introducing graphene through a volumetric permittivity is computationally inefficient because it requires very fine discretization grids. We have recently developed a more efficient approach that enables the use of comparatively coarse grids by formulating a discretization of Maxwell’s equations (in the time or frequency domains) that combines a surface conductivity description of graphene layers with a volumetric permittivity description of other optical materials. This approach includes the full dispersion characteristics of graphene as specified by the Kubo formula. This paper demonstrates how the combined material description approach can be used to efficiently model state-of-the-art devices that take advantage of the energy confinement provided by surface plasmons. We show how to efficiently model TE and TM polarized surface plasmons, a surface plasmon waveguide switch, and an electro-optical modulator. This last example also includes electrical simulations of graphene and demonstrates how both optical and electrical simulations can be combined to produce a complete model of a graphene based device. For each example, we compare with previously published results, including experimental results.

Semi-guided light propagation across linear folds of slab waveguides is being considered. Radiation losses vanish beyond certain critical angles of incidence, as can be understood by arguments resembling Snell's law. One thus realizes lossless propagation through 90-degree corner configurations, where the remaining guided waves are still subject to pronounced reflection and polarization conversion. A step-like system of two of these sharp corners can then be viewed as a system akin to a Fabry-Perot interferometer, with two partial reflectors at a distance given by the vertical separation of the slab cores. The respective resonance effect enables full transmission of semiguided, laterally plane waves through the step structures. One obtains a configuration that optically connects guiding layers at different elevation levels in a 3-D integrated optical chip, without radiation losses, over large distances, and reasonably broadband. We show rigorous quasi-analytical results for typical high-contrast Si/SiO₂ structures. Although the full-transmission effect requires a symmetric system, here realized by slab waveguides with a silicon core sandwiched between thick silica substrate and cover layers, simulations for configurations with air cover show that a certain asymmetry can well be afforded.

The increasing demand for early detection of diseases drives the efforts to develop more and more sensitive techniques to detect biomarkers in extremely low concentrations. Electromagnetic modes at the surface of one dimensional photonic crystals, usually called Bloch surface waves, were demonstrated to enhance the resolution and constitute an attractive alternative to surface plasmon polariton optical biosensors. We report on the development of Bloch surface wave biochips operating in both label-free and fluorescence modes and demonstrate their use in ovalbumin recognition assays.

Micro-processing by using an ultrashort pulsed laser has been previously reported and developed in the past decade for fabricating micro devices. Using tightly focused short pulse laser beam, the laser intensity easily can reach more than 10¹³ W/cm². Under such conditions non-linear phenomena are triggered, hence multiphoton ionization and self-focusing are notably induced in a medium. Femtosecond laser enables micro-fabrication without critical heat damage owing to extremely shorter pulse width and very fast multi-photon absorption at the laser focal point, compared with longer pulse irradiation. In this report, a micro-voids array was created in optical fiber line by using a femtosecond laser to produce sensing area only at local micro-region of the fiber line. At sensing portion consisted of the voids array, transmitted light was partially scattered by voids after that the leaked light could be reflected on the interface of cladding and outsides, which held the incident angle depending on structures of the micro-voids array. Voids array played as a role of scattering sources to transmitted light and consequently it was expected that the transmitted light can be broadly leaked out from the fiber core to the cladding. Furthermore, optical losses attributed to the creation of micro voids were quantitatively obtained so as to figure out the sensor characteristics. Consequently the reflection region which was considered as a sensing area showed the re-coupling rate of 0.04 dB (3.03%) to insertion loss of 1.32 dB, and the incident angle existed between 67.2 -71.9°.

Polymer micro-bottle resonators are fabricated by means of a simple self-assembling process. High optical quality SU-8 negative resist is chosen as bottle material. SU-8 is dispensed onto a fiber stem and is kept in rotation during the UV photo-polymerization. Micro-bottles with different geometrical sizes have been obtained by changing the SU-8 dispensed volume, with a repeatability of about 2%. Planar waveguides is chosen as interrogation system for our SU-8 self-assembled micro-bottle resonators. The highest quality factor Q associated to the resonance peak in the transmission spectrum is about 3.8 × 10⁴.

Solder joining using metallic solder alloys is an alternative to adhesive bonding. Laser-based soldering processes are especially well suited for the joining of optical components made of fragile and brittle materials such as glasses, ceramics and optical crystals. This is due to a localized and minimized input of thermal energy. Solderjet bumping technology has been used to assemble a lens mount breadboard taking as input specifications the requirements found for the optical beam expander for the European Space Agency (ESA) EarthCare Mission. The silica lens and a titanium barrel have been designed and assembled with this technology in order to withstand the stringent mission demands; handling high mechanical and thermal loads without losing its optical performances. Finally a high-precision opto-mechanical lens mount has been assembled with a minimal localized stress (<1 MPa) showing outstanding performances in terms of wave-front error measurements and beam depolarization ratio before and after environmental tests.

In this study, we have proposed a novel type of localized surface plasmon resonance (LSPR) fiber optic sensor based on in-line/pico-liter micro-holes which can be experimentally fabricated into the fiber waveguide by using a second harmonic 400 nm femtosecond laser. A repetitive pulse train of 1 kHz with a pulse width of 350 fs was irradiated onto a MMGI fiber optic to make three holes that penetrate through the fiber core and work as spectroscopic-microfluidic flow cells. In order to induce the interaction between transmitted light and gold nanoparticles (GNPs) adhered on the inner surface of the flow cells, micro-holes were designed to be the width of approximately 50 μm, along a direction perpendicular to an optical axis of an optical fiber. GNPs with approximately 100 nm of particle diameter adhered onto the inner surface according to 3-aminopropyltriethoxy silane treatment. The transmitted light through the micro-holes was obtained by optical instruments consisted of a white light source and an optical spectrum analyzer. In order to obtain the reference spectrum, the optical spectrum was acquired before dipping the sensor into the GNPs solution. After 30 min of immersing the sensor portion into the GNPs solution, the optical spectrum was also obtained. The reference spectrum which was considered as the baseline, was set to zero and then, the absorbance spectrum was calculated. The absorbance peak at a wavelength of 537 nm occurred in an air condition in the sensing area, which seemed like the resonance peak based on the LSPR.

Polarization gratings, which have the important properties of being highly efficient for first order diffraction and having high polarization sensitivity, can be applied to beam splitters, displays, spectro-polarimeters, and so on. Usually, polarization gratings are fabricated utilizing the periodic anisotropy of liquid crystal molecules. However, high tolerance to light, heat, and humidity is required, in particular, for optical communication applications. Therefore, a polarization grating based on an inorganic material is more suitable than one based on an organic one. We propose a silicon polarization grating with form birefringence induced by an anisotropic surface microstructure with features shorter than the wavelength of light (sub-wavelength anisotropic structure), allowing the birefringence to be controlled through selection of the dimensions of the periodic structure. In this paper, we describe the design of sub-wavelength structures of half wave plates using a thin film of silicon. By optimizing the line width, the line spacing, and the thickness of the film, a transmittance of more than 99% at an incident wavelength of 1550 nm was obtained. A polarization grating based on this half wave plate was designed. The orientation of the half wave plate structure was rotated in a particular direction. Furthermore, we evaluated the wavelength dependence and incident angle dependence of the diffraction efficiency using a finite-difference time-domain method.

In this paper, we have proposed and demonstrated a high sensitive half ring laser sensor with a deep etched-sensing region based on III-V semiconductor. A whispering gallery mode propagates along the deep etched boundary of the HRL by the deep etched mirror at the edge of the HRL. In addition, the lasing direction of the proposed sensors is controlled by the reflection coefficient of the deep etched mirror at the side of the micro-cavity. The proposed sensors have advantages that an enhanced Q-factor by a stimulated emission and a controllable lasing direction for simplified alignment system. Additionally, the ultra-small variation of the effective refractive index according to molecules interactions could be sensitively detected with the proposed sensors using by a long evanescent field at the deep etched sensing region.

We report an electro-optic switch at 1.55 μm wavelength based on Mach-Zehnder Interferometer (MZI) in which, the MZI arms and the input-output 3-dB couplers are designed using plasmonic and photonic waveguides re- spectively. More than 90% photons are successfully converted into surface plasmons through tapering the both photonic as well as plasmonic waveguide. The plasmonic and photonic mode profiles, interaction between plas- monic and RF fields, confinement of plasmonic field in plasmonic waveguide, and trade-off between loss and confinement are thoroughly examined before the combined optical and electrical simulation of the switch. The switching voltage is less than 6 Volts, the MZI arm length is only 15 μm, the crosstalk is less than -35 dB, and the maximum switching speed is 11.55 ps. The footprint of the switch is only 290x50 μm2.

Optofluid system has been more and more attractive in optical sensing applications such as chemical and biological analysis as it incorporates the unique features from both integrated optics and microfluidics. In recent years, various optofluid based structures have been investigated in/on an optical fiber platform which is referred to as “lab in/on a fiber”. Among those integrated structures, femto-second laser micromaching technique plays an important role due to its high precision fabrication, flexible design, 3D capability, and compatible with other methods. Here we present a ferrofluid based optical fiber magnetic field sensor fabricated by femtosecond (fs) laser irradiation .With the help of fs laser micromaching technique, a micro-reservoir made by capillary tube assembled in a single mode optical fiber could be fabricated. The micro-reservoir functions as a fiber inline Fabry-Perot (FP) cavity which is filled by ferrofluid liquid. The refractive index of the ferrofluid varies as the surrounding magnetic field strength changes, which can be optically probed by the FP interferometer. A fringe visibility of up to 30 dB can be achieved with a detection limit of around 0.4 Gausses. Due to the fabrication, micro-reservoirs can be assembled with optical fiber and distinguished through a microwave-photonic interrogation system. A quasi-distributed magnetic field sensing application has been demonstrated with a high spatial resolution of around 10 cm.

Integrated Mach-Zehnder interferometers (MZI) based on semiconductors or glasses have been widely used as evanescent field sensors for the monitoring of liquid or gas concentrations. In these systems the upper cladding of the sensing arm is removed partially to form an interaction window by means of subtractive fabrication techniques like etching. The use of polymer materials implicates new options and challenges. Polymers are tunable in terms of refractive index and viscosity offering a great flexibility in design and fabrication in a certain range. They enable a cost-efficient and large-scale roll-to-roll manufacturing of integrated optics on flexible foils as substrate material. The foils can be pre-patterned for example by hot-embossing. Additive steps such as printing a pattern or dispensing a homogeneous layer of liquid monomer material followed by a UV induced polymerization can be used to define the optical structure. However, when a large scale fabrication is required, the reliable production of small lateral structures and thin layers is challenging. Thus the fabrication according to the classical MZI design including an interaction window is difficult so that new design approaches are required. We present here the design and systematic evaluation of MZI sensors without interaction window based on polymer materials. The phase shift at the recombining Y-splitter of the MZI upon a refractive index change of an analyte, which serves as upper cladding of the entire system, is generated by a geometrical asymmetricity of the MZI. The waveguides in the sensing and the reference arm have different width leading to different effective refractive indices and sensitivities. We consider theoretically the expected interference signal and show results from numerical simulations of the whole system using commercial software. The simulations include the material as well as propagation losses and give an overall optimal system length.

High-quality optical resonators underlie many important applications ranging from optical frequency metrology, precision measurement, nonlinear/quantum photonics, to diverse sensing such as detecting single biomolecule, electromagnetic field, mechanical acceleration/rotation, among many others. All these applications rely essentially on the stability of optical resonances, which, however, is ultimately limited by the fundamental thermal fluctuations of the devices. The resulting thermo-refractive and thermo-elastic noises have been widely accepted for nearly two decades as the fundamental thermodynamic limit of an optical resonator, limiting its resonance uncertainty to a magnitude ^10-12 at room temperature. Here we report a novel approach that is able to significantly improve the resonance stability of an optical resonator. We show that, in contrast to the common belief, the fundamental temperature fluctuations of a high-Q micro/nanoresonator can be suppressed remarkably by pure optical means without cooling the device temperature, which we term as temperature squeezing. An optical wave with only a fairly moderate power launched into the device is able to produce strong photothermal backaction that dramatically suppresses the spectral intensity of temperature fluctuations by five orders of magnitudes and squeezes the overall level (root-mean-square value) of temperature fluctuations by two orders of magnitude. The proposed approach is universally applicable to various micro/nanoresonator platforms and the optimal temperature squeezing can be achieved with an optical Q around 10⁶-10⁷ that is readily available in various current devices. The proposed photothermal temperature squeezing is expected to have profound impact on broad applications of high-Q cavities in sensing, metrology, and integrated nonlinear/quantum photonics.