During the last years, LETI has been developing integrated optics components for stellar interferometry imaging using its proprietary silica on silicon technology. Recent astrophysical results obtained with the three-telescope combiner IONIC3 on IOTA confirm the great interest of this kind of integrated devices in terms of overall performance and stability. In this paper, after a brief explanation of the stellar interferometry imaging technique, silica on silicon integrated optical components for stellar interferometry are presented.

Integrated reflecting mirrors based on total internal reflection are first proposed in this paper. They are design to be fabricated by ion-exchange process on a glass substrate. Theoretical modelling of parabolic and elliptic mirrors is presented. Surface and buried elliptic mirrors are fabricated at the same time as the rest of the guiding structure by a silver ion-exchange followed by a field assisted potassium exchange in the second case. Light coming out of a singlemode waveguide is focused outside the integrated component at distances of 500 μm. Light beam width of 13 μm at 1/e² of the maximum intensity were measured. Second, those mirrors are used to design an integrated laser Doppler velocimeter with ultra-high spatial resolution. Interference pattern of 22 x 33 x 10 μm³ with fringe spacing of 0.8 μm was produced at the focal point of the integrated mirrors in air. The fringe visibility measured in the center of the measuring volume is 1.

We demonstrate a 4-bit optical true time-delay module for synthetic aperture radars based on the integration of polymer channel waveguide and electro-optic Bragg gratings. The demonstrated device is a truly integrated module that eliminates the most difficult packaging problem associated with the delicate interfaces between optical fibers and optical switches. The total insertion loss of the 4-bit optical true-time-delay line is less than 3 dB with switching time <50 □s and driving voltage of 25 V.

In order to integrate various photonic functions and/or many channels into one chip, (Pb,La)(Zr,Ti)O₃ (PLZT) waveguide technologies have been developed. PLZT is one of the best candidates in terms of dense integration and device miniaturization due to its efficient voltage-induced index change and high refractive index. We have established a solid-phase epitaxy to grow low-loss PLZT thin film waveguides, since the formation of low optical propagation loss PLZT waveguides had been difficult with typical vapor phase growth techniques. PLZT waveguides with PLZT buffer layers are grown on Nb-doped semiconductive SrTiO₃ substrates for the effective overlap integral of the optical field and the electric field. Efficient control of light coupled in the waveguides is achieved by applying voltage between the top electrodes and the substrates to induce the excellent electro-optic properties of PLZT waveguides. In addition, optical switching devices, which are the key elements of various integrated devices, are fabricated in the PLZT waveguides, showing low-voltage drive and ultra-fast response characteristics. Further key developments such as matrix switches, switch-VOA arrays, and modulator arrays directed toward integrated photonics are also discussed.

In the last decade there was an increasing interest in the investigation and application of so called metamaterials, such as photonic crystals or photonic crystal fibers, where optical properties can be tailored by means of geometry data. Waveguide arrays are another typical example of metamaterials, where the evolution of electromagnetic fields can be controlled by the effective index of the individual guides and the coupling strength between two adjacent guides. In this paper, the formation of localized states at defects in waveguide arrays is investigated both, theoretically and experimentally. Depending on the relation of the effective waveguide index and the coupling strength different guiding scenarios at an array defect can be observed, which have no analogon in conventional integrated optics. The experimental investigations are realized in polymer waveguides fabricated by UV-lithography. Typical field distributions in the waveguide array are visualized by means of the detection of the fluorescence light above the sample. Using coupled mode theory the experimental results are simulated providing an analytical description.

Direct coupling from fibres to waveguides requires field matching to achieve high coupling efficiency. 3D on-chip tapers are well suited in principle, but practicability may depend on materials and geometrical structures used for the waveguide chip, especially when photonic crystal defect waveguides are involved. To adapt the spot size of the fibre mode to that of a waveguide with high index contrast, silicon micro-lenses can be used advantageously. Although positioning requires finer resolution with small foci this can be accomplished by state-of-the-art micro-positioning equipment. A theoretical description of the hybrid coupling concept and corresponding numerical results are presented, where the design covers the range from free-space ray-trace to FDTD at the chip-level. Experimental results for the characterisation of the optimised aspheric silicon micro-lenses are reported as well.

A thermo-optic switch using total internal reflection waveguide was fabricated for optical true time delay. Experimental result shows that the crosstalk in the bar state is as low as -42dB and the total insertion loss is only -4dB at the wavelength of 1.55&mu;m. A power consumption of 130mWand switching speeds of 2ms are obtained as well, which makes the device qualified to be used in the application of optical true time delay.

We studied various electrical and optical properties of Europium (1 atomic %) incorporated BaTiO₃ film on n-Si(100) substrate. The thin film structure was analyzed by X-ray diffraction. Film thickness and optical refractive index were measured with an ellipsometer. P-E hysteresis measurement shows the remnant polarization of 37 micro-C/cm² in BaTiO₃:Eu film. C-V measurements on the pure BaTiO₃ film show recovery of capacitance across sweeping voltage ranges with a narrow transition zone due to the polarization change. On the other hand, C-V and I-V measurements on the BaTiO₃:Eu film show that Europium incorporation increases positively charged states in the BaTiO₃ layer such that BaTiO₃:Eu/n-Si interface behaves like a leaky p-n junction.

Integrated optics has been extensively used from the beginning for telecommunication applications. Depending on the functions to implement, different technologies have been employed. Among all of them, glass ion exchange is the cheapest, since both substrate and technological requirement are not expensive. Ion exchange technology has some advantages that can be very important for sensors applications. After a brief presentation of the different possible ion exchange, we will present some integrated optics sensors realized on glass that have been made in the past few years. We will give details about the particularity required for every applications. Then, we will give some informations about biological applications and we will conclude with some limitations of this technology.

The large refractive index difference between silicon nitride and silicon dioxide allows silicon nitride/dioxide waveguides to have a small mode size and low radiation bending loss. Low radiation bending loss enables high quality (Q) factor microring resonators. In this paper, we will present a record high quality factor microring resonator using silicon nitride and silicon dioxide on a silicon wafer. The microring resonator was fabricated using a deep UV photolithography and etching process. The microring resonator was critically coupled to a straight waveguide. An intrinsic quality factor of 240,000 has been measured. We will also present our result of using on-chip high-Q microring resonators for liquid phase chemical sensing application.

Very compact and low-cost rotation sensors are strongly required for any moving systems in several applications. Integrated optical angular velocity sensors seem to be very promising in terms of low cost, compactness, light weight and high-performance. In the paper a new integrated optical angular velocity sensor having a passive resonant configuration is proposed. Preliminary results are really encouraging and demonstrate the possibility of using the sensor in gyro systems for satellite applications.

A novel waveguide geometry for an integrated optics bio-sensor suitable for fluorescence detection is presented. In particular, we propose a polymeric waveguide realized on a glass substrate. This new geometry is aimed to an efficient evanescent-wave excitation of the fluorophores and subsequent collection of the fluorescence emission with no need of optical filters. The absence of any optical filters simplifies the device operation and permits to avoid the losses resulting from the use of the filter itself.

We present the design of an innovating integrated planar structure adapted for intensity or phase measurements. It is based on the evanescent prism decoupling of the optical signal from a waveguide used as the sensing element. The device is formed by successive thin film sputtering deposition. A TiO₂ crystalline layer forms the gas sensing element from which light is coupled out by a planar high refractive index prism. We experimentally validate the structure.

Thanks to the maturing of rare-earths highly-doped materials, erbium-doped waveguide amplifiers (EDWAs) present a compact alternative to fibre amplifiers. While ion-exchanged EDWAs implemented on glass substrates provide the best passive characteristics, EDWAs based on thin films technologies offer higher integration degree and amplification efficiencies. This paper proposes the realization of an EDWA in a new configuration which combines all these advantages. Indeed, this optical amplifier consists of an erbium/ytterbium-codoped glass guiding layer reported on an ion-exchanged strip formed on a passive glass substrate. The electromagnetic principle of operation of this hybrid structure is presented. Then, all technological steps of realization are detailed including the report of the active layer by a low-temperature wafer bonding process. Finally, passive and active characterizations allow demonstrating the single mode operation and the amplification efficiency of the hybrid waveguide. Indeed, a high gain coefficient of 3.66±0.25 dB/cm is obtained in the 1.16-cm-long hybrid amplifier.

We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilized an all-epitaxially-grown orientation-patterned GaAs (OP-GaAs) crystal, 0.5-mm-thick, 5-mm-wide, and 11-mm-long, with a domain reversal period of 61.2 microns. By tuning either the near-IR pump wavelength between 1.75 and 2 microns, or the temperature of the GaAs crystal, the mid-IR output tuned between 2 and 11 microns, limited only by the spectral range of the OPO mirrors. The pump threshold of the singly-resonant OPO was 16 micro-J for the 6-ns pump pulses, and the photon conversion slope efficiency reached 54%. Also, we show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.

High coherence glass DFB lasers emitting in the 1550 nm window are useful for many applications, including eyesafe sensors and DWDM telecommunication systems. One of the key characteristic of lasers designed for sensor or telecommunications applications is their monomode behaviour. A standard DFB laser indeed emits two wavelengths located at both sides of the grating stop band. A quarter-wave phase shift is thus required in the center of the grating in order to make a single mode laser. In this paper, we present a new kind of phase shift, that was initially developped for semiconductor lasers but never applied to glass or fiber optics lasers. The main advantage of this technique is that the phase shift is realized during the waveguide photolithography process so that there is no need of any additionnal step. Moreover, its design ensures that the value of the phase shift can be very accurately set, which enables to realize a grating cavity with a unique lasing wavelength. Both theoretical and experimental results on these new phase shifted lasers are presented and a SMSR of more than 50dB is presented.

All-optical OR operation has been demonstrated using a semiconductor optical amplifier (SOA) and delayed interferometer (DI) at 20 Gb/s and 40 Gb/s. The DI is based on a polarization maintaining loop mirror. Q-factor of the operation is discussed through the numerical simulations. The results show the OR gate operation rate is limited by the carrier lifetime and the input pulse energy.

The Finite-Difference Time-Domain (FDTD) method is often a viable alternative to other computational methods used for the design of sub-wavelength components of photonic devices. We describe an FDTD based grid refinement method, which reduces the computational cell size locally, using a collection of nested rectangular grid patches. On each patch, a standard FDTD update of the electromagnetic fields is applied. At the coarse/fine grid interfaces the solution is interpolated, and consistent circulation of the fields is enforced on shared cell edges. Stability and accuracy of the scheme depend critically on the update scheme, space and time interpolation, and a proper implementation of flux conditions at mesh boundaries. Compared to the conformal grid refinement, the method enables better efficiency by using non-conformal grids around the region of interest and by refining both space and time dimensions, which leads to considerable savings in computation time. We discuss the advantages and shortcomings of the method and present its application to the problem of computation of a quality factor of a 3-D photonic crystal microcavity.

We present a finite-element simulation tool for calculating light fields in 3D nano-optical devices. This allows to solve challenging problems on a standard personal computer. We present solutions to eigenvalue problems, like Bloch-type eigenvalues in photonic crystals and photonic crystal waveguides, and to scattering problems, like the transmission through finite photonic crystals. The discretization is based on unstructured tetrahedral grids with an adaptive grid refinement controlled and steered by an error-estimator. As ansatz functions we use higher order, vectorial elements (Nedelec, edge elements). For a fast convergence of the solution we make use of advanced multi-grid algorithms adapted for the vectorial Maxwell's equations.

Multimode interference (MMI) devices have been developed for a large number of optoelectronic applications. Frequency domain methods have been widely used to simulate the behavior of this class of device at fixed operating wavelengths. However time domain models are becoming more popular in photonic simulation as bandwidths increase and account needs to be taken of material properties such as nonlinearity. By making physically consistent approximations, the time-domain beam propagation method provides simulation without incurring the large memory and computational penalties of other time domain numerical methods. In this paper we will compare these various approaches in the context of simulating MMI devices, provide guidelines for the selection of one approach in preference to the other and discuss the limitations and errors introduced by some of the common approximations made.

We present an analytical study of surface plasmon polariton (SPP) propagation about a circular bend formed by the interface between a metal and a dielectric with the metal occupying the inner volume. It is shown that in the short wavelength limit, the problem is essentially analogous to scattering from a 1D finite potential well, with standard expressions for the transmittance and reflectance. In certain cases, we find that propagation on nonplanar interfaces may result in lower losses than on flat surfaces, contrary to expectation. We also show that the same approach is valid when the metal occupies the outer volume, such that in the 1D approximation SPPs propagating around such bends do not radiate. An upper bound for the transmittance, valid even when our approximation breaks down, is also derived. This is found to depend nonmonotonically on the bend radius, allowing increased transmission with decreasing radius. We further present a numerical study using the finite- difference time-domain method and show that it is consistent with theoretical predictions. We also show that the introduction of a microcavity plasmon resonator could significantly enhance the transmission.

We present our simulation tool JCMmode for calculating propagating modes of an optical waveguide. As ansatz functions we use higher order, vectorial elements (Nedelec elements, edge elements). Further we construct transparent boundary conditions to deal with leaky modes even for problems with inhomogeneous exterior domains as for integrated hollow core Arrow waveguides. We have implemented an error estimator which steers the adaptive mesh refinement. This allows the precise computation of singularities near the metal's corner of a Plasmon-Polariton waveguide even for irregular shaped metal films on a standard personal computer.

Recent advances in semiconductor fabrication tools, which now support 100-nm pixilation and centimeter-scale spatial coherence, create intriguing new opportunities in integrated photonics. Application of the latest generation of fabrication tools allows for the implementation of broad new photonic device function based on 2D distributed diffractive structures such as holographic Bragg reflectors (HBRs) - devices that provide generalized spatial routing of signals within a planar waveguide circuit (e. g. silica-on-silicon) while at the same time providing powerful spectral filtering function. HBRs and other 2D distributed diffractive devices promise to open disruptive pathways to integrated photonic solutions characterized by high performance, small footprint, and extremely low cost especially when fabricated via stamping/nanoimprinting

We report a novel all-fiber, maskless lithograpic technology to form various concentric grating patterns for micro zone plate on azo polymer film. The proposed technology is based on the interference pattern out of the cleaved end of a coreless silica fiber (CSF)-single mode fiber (SMF) composite. The light guided along SMF expands into the CSF segment to generate various circular interference patterns depending on the length of CSF. Interference patterns are experimentally observed when the CSF length is over a certain length and the finer spacing between the concentric rings are obtained for a longer CSF. By using beam propagation method (BPM) package, we could further investigated the concentric interference patterns in terms of intensity distribution and fringe spacing as a function of CSF length. These intereference patterns are directly projected over azo polymer film and their intensity distrubution formed surface relief grating (SRG) patterns. Compared to photoresist films azo polymer layers produce surface relief grating (SRG), where the actual mass of layer is modulated rather than refractive index. The geometric parameters of the CSF length as well as diameter and the spacing between the cleaved end of a CSF and azo polymer film, were found to play a major role to generate various concentric structures. With the demonstration of the circular SRG patterns, we confirmed that the proposed technique do have an ample potential to fabricate micro fresnel zone plate, that could find applications in lens arrays for optical beam formings as well as compact photonic devices.

A new approach for constructing devices of various free spectral ranges (FSRs) is described. We show that devices with different FSRs can be built around the same aberration-free architecture based on elliptical grating facets. Elliptical facets, combined with double astigmatic point design, are demonstrated to lead to dramatic improvements in reflective grating performance compared to traditional flat facet designs. A discussion on the proper selection of the grating order for devices with various FSRs is given. The proposed theory was applied to manufacture devices with various FSRs. A standard silica-on-silicon process was used to fabricate interleavers with narrow FSR of 0.8 and 1.6 nm. Subsequently, we show how the above methodology can be used to scale the reflective grating design to devices with wide FSR. We applied the theory to produce coarse wavelength division multiplexing filters with FSR in excess of 500 nm. The filters exhibited insertion losses of 2.5 dB and polarization dependent losses of less than 0.2 dB. Applications of wide FSR devices in metro edge and access networks are discussed.

Press-patterning of polymers to yield optical structures is being pursued in optics and photonics to yield low-cost optical components. This is a promising technology for the low-cost and high-throughput fabrication of polymeric photonic components. The processing of such imprinted photonic components is usually done using a metallic shim where a pattern is generated on the shim by electroforming or electroplating. The shims are then used to replicate patterns on plastics and polymers under high temperatures and pressures. Under the correct conditions, the polymer flows and replicates a diffraction grating. Polymeric diffraction gratings and holograms have applications in a multitude of photonic applications for diffractive optics. This requires materials that are transparent in the visible region, and preferably have relatively high refractive indices in order to achieve a high diffraction efficiency. In addition, in order to facilitate processing by the press-patterning method that will be further described in this paper, polymeric materials that are amenable to spin-coating and show good thermoplastic behavior are also desired. Optically transparent, high-refractive index polyimides were tested for their ability to be processed and patterned using a press-patterning method. A process that allowed the materials to be patterned were developed, and measurements were taken to validate the results. Our initial results showed successful press-patterned polyimide films with grating structures having submicron line and trench widths and step heights of less than 0.5 microns.

In this paper, the realization and characterization of periodic segmented waveguides made by ion-exchange on glass is presented as well as their application to polarizers and wavelength duplexers. Segmented waveguides are of major interest for integrated devices because they allow tailoring the refractive index without changing the technological parameters. Indeed, a segmented waveguide, which is composed of a periodic succession of guiding and non-guiding zones, can be considered as a classical waveguide with a core refractive index that ranges from the segmented core to the substrate ones, depending on the segmentation ratio. Through this way, it is thus possible to avoid the use of more complex techniques that require a double-step lithography process. In the first part of the article, surface segmented waveguides made by ion-exchange on glass are studied and a linear relationship between the segmentation duty cycle and the maximum core refractive index of an equivalent continous waveguide is demonstrated. A simple correction on the duty cycle is needed to take into account the longitudinal diffusion. After a presentation of its principle of operation, in the second part of the article, we propose the realization and characterization by means of segmented waveguide of a polarizer with more than 30dB of extinction ratio at λ=1550nm. Finally, the design and first results obtained on a duplexer based on an asymmetric segmented Y-junction are presented.

We report on the non-lithographic laser writing fabrication of polymer waveguide fanout on a newly developed 4'- hydroxy-4-nitroazobenzene dye functionalized polymer film. It can avoid the time consuming costly error correction re-fabrication in conventional optical waveguide fabrication by lithographic techniques when encountering error due to imperfect fabrication. The laser writing correction of power splitting ratio on waveguide directional coupler and y-branch fanouts has been demonstrated.

Compact waveguide bends and splitters are important components to enable dense integration of many functions on a single photonic chip. A common approach is to use a waveguide material system in which a large refractive index contrast between the core and clad materials is available. This permits a small bend radius to be used while still achieving high optical efficiency for the bend. However, such material systems generally have higher propagation loss than is possible with low refractive index contrast material systems such as silica. In this presentation we examine an approach to make the bend size essentially independent of the core/clad refractive index contrast using total internal reflection from a planar interface. We show through both 2D and 3D finite difference time domain (FDTD) simulation that very high bend efficiencies are possible when the correct bend design principles are adhered to. We illustrate this in practice with single air interface bends (SAIBs) in a PFCB material system with approximately 1% refractive index contrast. We experimentally demonstrate 45 degree bends with 0.3 dB loss per bend, and discuss the effects of fabrication issues such as misalignment, etch undercut, and etch roughness.

The hybrid integration of passive and optoelectronic devices has been widely researched. One of the main applications of this technique is for the fiber to the home (FTTH) network. In bi-directional transceivers, integrated WDM filters have been used to separate or combine the optical signals. Thin film filter (TFF) embedded waveguide type is effective for an application requiring wide bandwidth and low loss. Although the insertion loss of TFF itself is quite low, significant loss occurs at the trench and it depends on the geometrical structure and fabrication errors of the trench waveguide. The conventional sawing method and deep reactive ion etching technique were used for trench fabrication. In the case of using DRIE process, fabrication error was reduced and position error of the trench was controlled within 1um. This method could also enhance the platform design flexibility. To reduce the coupling loss between input and reflection waveguides with high tolerance of filter position, a few mode waveguide and horn waveguide were proposed. The insertion losses of transmission and reflection were less than 0.5dB and 0.7dB respectively. The 1dB tolerance of filter position was improved to be nearly twice than that of the conventional waveguide.

More than 80% of all lab-on-a-chip systems rely on optical detection. In most cases this is done by external bulk optical elements. We present an approach where advanced multimode optical elements are integrated with a microfluidic system. In order to ease integration of the optical circuitry, the waveguide height and width are adapted to the dimensions of the microfluidic channels. Typical dimensions for the multimode waveguides are 40 μm x 40 μm. The integrated optical elements include tapers, waveguide crossings, and spectrometers. The devices are designed, simulated and subsequently fabricated in polymer on a silicon substrate. A glass lid bonded to the polymer layer seals the microfluidic channels and provides a top cladding for the waveguide circuitry. Arrays of specially designed components are evaluated to extract precise basic parameters like coupling and propagation loss. To increase compactness of the waveguide circuitry waveguide crossings with different angles are evaluated. It is found the angles down to 25° between the crossing waveguides show little (< 0.25 dB) excess loss. Integrated spectrometers using a reflective, concave echelle grating are fabricated and evaluated. It is shown that spectral range, resolution and linear dispersion of such miniaturized devices can be adapted to the needs of micro total analysis systems (μTAS).

A change in the Li/(Li+Ta) ratio in LiTaO₃ crystals from 0.485 (congruent) to ~0.5 (stoichiometric) results in a up to 130 times reduction in coercive fields for domain reversal and an elimination of the internal fields and domain backswitching. Dramatic differences in the fatigue behavior are also observed, that results in an electro-optic effect that is very sensitive to electrodes in stoichiometric compositions and rather insensitive in congruent compositions.

By using a direct-write e-beam technique with liquid phase epitaxy LiNbO₃ thin films, we have successfully produced sub-micron domain structures for achieving dynamically switchable filters in a periodically poled lithium niobate (PPLN) waveguide. Sub-micron domain (~200 nm) structures with a period ~1.2 um are realized in liquid phase epitaxy LiNbO₃ films on congruent LiNbO₃ substrates by using the direct-write e-beam domain engineering method. In comparison with single crystal congruent LiNbO₃ (CLN) and stoichiometric LiNbO₃ (SLN), we show that LPE LiNbO₃ is the most promising material for producing superior domain regularities and finer domain sizes than single crystals. A physical model is presented to qualitatively explain the observed differences in structure and regularity of the induced periodic domains among the three different materials we studied. We postulate that the higher Li/Nb ratio in LPE LN than in CLN enhances domain inversion initiation. Also, we believe that the vanadium incorporation and distortion due to the lattice mismatch between films and substrates enhance electron localization, domain wall pinning and domain nucleation in LPE materials, giving rise to better structures.

Recently large index contrast optical waveguides are considered for the fabrication of integrated optical components. Electro-optical waveguides are particularly interesting since they have the potential to be used for switching devices. In this paper we introduce a new method for fabrication of large index contrast lithium niobate waveguides. The waveguides are fabricated using crystal ion slicing and wafer bonding. This allows the fabrication of high refractive index contrast waveguides with lithium niobate as the core and silicon dioxide as the low refractive index cladding. Electrodes can also be deposited between the layers for applying an electric field to the waveguide in the vertical direction. The structure can be fabricated on any substrate. Waveguides with a thickness of 700nm suitable for single mode operation at lambda=1.55micron have been successfully produced. The thin films are analyzed using different analytical techniques including atomic force microscopy and Rutherford backscattering (RBS). The RBS spectrum shows that the crystal structure of the fabricated thin films is very similar to bulk lithium niobate and the quality of the crystalline waveguide is excellent. Optical waveguiding and electro-optical modulation is demonstrated using the prism-coupling method. It is shown that the fabricated waveguide refractive indices and electro-optic coefficients are identical to bulk lithium niobate crystals. These large index contrast waveguides are ideal for fabrication of devices such as electro-optic micro-ring resonators, Mach-Zehnder interferometric modulators with reduced half wave voltage and nonlinear optical waveguide devices for second harmonic generation or parametric amplification. It is shown that this waveguide structure is an ideal structure for the fabrication of integrated optical components due to the good optical properties of lithium niobate and large index contrast achieved by the fabrication method.

For applications such as fiber optic networks, wavelength conversion, or extracting information from a predetermined channel, are required operations. All-optical systems, based on non-linear optical frequency conversion, offer advantages compared to present systems based on optical-electronic-optical (OEO) conversion. Thanks to the large nonlinear susceptibility of AlGaAs (d14 = 90pm/V) and mature device fabrication technologies, quasi-phasematched non-linear interactions in orientation-patterned AlGaAs waveguides for optical wavelength conversion have already been demonstrated. However, they require long interaction length (~ centimeters) and a complex fabrication process. Moreover, the conversion efficiency remains relatively low, due to losses and poor confinement. We present here the design and fabrication of a very compact (~ tens of microns long) device based on tightly confining waveguides and photonic crystal microcavities. Our device is inherently phase-matched due to the short length and should significantly increase the conversion efficiency due to tight confinement and high cavity-Q value. We characterized the waveguides, measuring the propagation loss by the Fabry-Perot method and by a variant of the cutback method, and both give a consistent loss value (~5 dB/mm for single-mode waveguides and ~3 dB/mm for multimode waveguide). We also characterized the microcavities measuring the transmission spectrum and the cavity-Q value, obtaining Q's as large as 700.

In this paper, an original guided-wave optical pressure sensor that responds only to rapid pressure change is described. The proposed sensor is based on a conventional guided-wave optical pressure sensor using intermodal interference, with an added semi-closed space with a small hole under the bottom side of the diaphragm. By the addition of this semi-closed space, the sensor, unlike conventional sensors, can withstand high static pressure. When there is a sudden change in ambient pressure, pressure within the semi-closed space cannot quickly adjust due to the small hole that restricts fluid flow. So, pressure difference is induced on the diaphragm for a short while. Thus, the sensor shows a response only to changes in pressure, not to static pressure. We examined the step response of the sensor, that is, the output characteristics for sudden pressure change. The diaphragm dimensions of the fabricated sensor were 14 mmX14 mmX0.22 mm. Also, the volume of the semi-closed space was 14 mmX14 mmX1.8 mm, and the sectional area of the small hole was 93 umX25 um. In this experiment, the pressure in a 30 cmX28 cmX30 cm closed box, in which the fabricated sensor was placed, was suddenly increased by 0.78 kPa. Due to the pressure change, the output intensity decreased by approximately 20 % of the initial intensity level. Approximately 1.4 sec after the step-like change in pressure, output intensity returned to the initial level.

In this paper, an optical microphone using a silicon-based guided-wave optical pressure sensor as an opto-mechanical transducer is reported. The pressure sensor consists of a rectangular diaphragm and a straight waveguide on the diaphragm. The sensitivity of the sensor and the resonance frequency of the diaphragm are important factors to determine the characteristics of the microphone, and depend on the diaphragm dimensions. In this study, to examine a feasibility of the proposed optical microphone, the target values of phase sensitivity and resonance frequency were set at 1.6 mrad/Pa and 7 kHz, respectively. By design considerations, the diaphragm dimensions were determined to be 7 mmX7 mmX23 μm. After fabrication of the optical microphone, sound pressure from 5 to 25 Pa, with a frequency of 1 kHz, was applied to the fabricated microphone with a 7 mmX7 mmX27 μm diaphragm. During measurement, a lock-in detection was taken because the fabricated pressure sensor had an unexpected low sensitivity, which resulted in an extremely low S/N ratio. The measured output voltage from the lock-in amplifier was proportional to the sound pressure as expected although the lock-in detection is not practical for the microphone.

A beam steering type 1:4 optical switch with phase shifters in a silica arrayed-waveguide is proposed. It consists of collimating waveguide mirrors, an arrayed-waveguide which has deep trenches with polymer materials, and input/output waveguides. It can switch the output port of the incident light at high extinction ratio. The incident light is guided to the front mirror, collimated, and input to the arrayed-waveguide. Each waveguide in the arrayed-waveguide has the same length. The number of narrow trenches filled with polymer linearly increases in order. The refractive index of the polymer is set to the effective index of the single mode silica waveguide at certain temperature. The propagation direction of the output light from the arrayed-waveguide can be controlled by changing the temperature of the device because of the large thermo-optic coefficient of the polymer. The second mirror converges the light into one of the output waveguide. We designed two types of the switch which had 9 or 15 waveguides in the arrayed waveguide and they are under fabrication. The chip sizes are about 2.5 mm x 8.0 mm and 2.5 mm x 9.0 mm, respectively. The required temperature shift for the switching from one output port to the adjacent output port is 20 [K] when we use the polymer with a TO coefficient of -1.8x10^-4 [1/K].

We propose a 1 x 2 optical prism deflector switch which consists of two parabolic waveguide mirrors, multiple-stage micro prisms filled with polymer, and input/output waveguides. This type of switch has high extinction ratio characteristics compared with the interference-type switch. The number of prisms is 20 or 30, and the vertex angle of the prism is about 0.1 rad. The prisms are so thin that the coupling loss can be reduced. The waveguide mirror is formed by depositing Ag on the side wall of the deep trench in a slab waveguide. The light from the input waveguide reflects at the parabolic mirror to be the parallel light, propagates through the prisms and reflects at the other parabolic mirror to converge on the output waveguide. The prisms have thermo-optic (TO) coefficient of -1.3 x 10^-4/K while the slab waveguide has that of -6.7 x 10^-6/K. Therefore, by raising the temperature around prisms, the light is deflected through the prisms and the switch is brought into the cross state. On the other hand, without rise in temperature, the light goes straight. The distance between adjacent outputs waveguides is 30mm, corresponding to the change in the temperature of 30 K. The size of devise is 4.4 mm x 8.0 mm with 20 prisms and 3.3mm x 6.5mm with 30 prisms, respectively. With 20 prisms at a wavelength of 1555 nm, a minimum insertion loss of 0.65 was measured in bar state.

The novel compact arrowhead arrayed-waveguide grating (AWG) using v-bend waveguides in each arrayed waveguide is proposed and fabricated. The v-bend structure is useful to reduce bending area of a silica waveguide with low Δ (0.3%) to high Δ (0.8%) design. It is composed of curved single mode waveguides and a slab waveguide with an integrated elliptic metal mirror. The mirror structure in the v-bend waveguide is fabricated by the reactive ion etching of the deep trench with smooth and vertical side wall, and by the deposition of silver metal with chemical reaction. The proposed AWG with arrowhead shape has a footprint of only 1/10 of the conventional one with the same performance. The small footprint leads to low cost and to high-resolution because the small circuit is less subject to the fluctuation of the effective index of the substrate. In this paper, the 8-ch, 25 GHz spacing arrowhead AWG composed of the same v-bend structures in each arrayed waveguide in order to obtain the uniform propagation loss of the v-bend is fabricated with the effective index of 0.75 % silica and its property is reported. Its size of the slab and arrayed waveguide region is 1.3 mm × 15.5 mm and only 1/10 of the conventional type.

Optical interferometer displacement sensors are well known for their high resolution, up to 10^-7 m in a stabilised environment, over a wide measuring range which can reach several meters. Moreover, the measures are carried out without any mechanical contact with the target object. Two optical outputs are however needed to determine the displacement direction. A glass integrated sensor with only one optical output that still measures the displacement direction is proposed here. It is derived from a Michelson interferometer but is realised by ion-exchange on a glass substrate. A piezoelectric element placed over the reference arm produces a longitudinal acoustic wave that creates a small phase modulation on the reference light beam at a high frequency (1.28 MHz). A small modulation of the output signal is thus produced. The direction determination is based on the comparison between the phases of the excitation acoustic signal and of the high frequency part of the sensor's output signal after proper signal processing. A theoretical and an experimental demonstration of that principle are presented. A precision of 158 nm was obtained with a simple numerical signal processing.

We introduce and demonstrate a new design for mode multiplexing in proton-exchange lithium niobate waveguides using asymmetric Y-junctions. The coupling between the lowest two modes in the device is suppressed by modifying the Y-junction shape. Without increasing the device length, the mode contrast is enhanced by >3.4dB compared to conventional designs. The new design improves the performance of an important functional block in integrated optics.