Single-mode Planar Waveguides Research Articles

First- and second-order Bragg gratings in single-mode planar waveguides of chalcogenide glasses

First- and second order Bragg reflectors at telecommunication wavelength (1.5 /spl mu/m) were fabricated in single-mode monolayer (As/sub 2/S/sub 3/) and multilayer (AsSSe-AsS) chalcogenide glass (ChG) planar waveguides with near bandgap illumination using an interferometric technique. Reflectivities as high as 90% near 1555 nm, and index modulations up to 3/spl times/10/sup -4/ were achieved. The volume photodarkening effect is the principal mechanism involved in the formation of the Bragg gratings.

Sol−Gel-Based, Planar Waveguide Sensor for Water Vapor

A water vapor sensor based on a combination of sol-gel processing and planar optical waveguide technologies has been developed. The indicator erythrosin B was entrapped in a thin sol-gel film (thickness ∼100 nm) prepared from methyltriethoxysilane, dimethyldiethoxysilane, and tetraethoxysilane. This dye exhibits an increase in absorbance in the presence of liquid or gaseous water. The sol-gel layer containing the dye was deposited onto a sol-gel-derived, single-mode planar waveguide. Outcoupled light intensity measurements (at 514.5 nm) over a range of water vapor concentrations (in a nitrogen gas stream) yielded a response over a wide range of relative humidity (<1-∼70%) at room temperature. Response and reversal times were less than 1 min, which may make this sensor attractive for real-time monitoring applications.

Fabrication method of ion-exchanged waveguide integrated elements in shallow buried single-mode planar guides

A new fabrication method of waveguide integrated elements immersed in shallow buried single-mode planar waveguides fabricated in glass substrates is proposed in order both to avoid scattering losses, by minimizing the interaction of the propagating field with surface irregularities, and to improve fibre–waveguide coupling performance. Likewise, by a proper choice of the waveguide characteristics, which are related to the fabrication parameters, both a high-single-mode-transmission regime and a high optical power in the waveguide element are obtained.

Fabrication method of ion-exchanged waveguide integrated elements in shallow buried single-mode planar guides

Abstract A new fabrication method of waveguide integrated elements immersed in shallow buried single-mode planar waveguides fabricated in glass substrates is proposed in order both to avoid scattering losses, by minimizing the interaction of the propagating field with surface irregularities, and to improve fibre–waveguide coupling performance. Likewise, by a proper choice of the waveguide characteristics, which are related to the fabrication parameters, both a high-single-mode-transmission regime and a high optical power in the waveguide element are obtained.

Analysis of a deep waveguide Bragg grating

Spectral properties of a very deep Bragg grating operating in a first diffraction order on a single-mode planar waveguide have been studied theoretically. It is shown that the scattering loss can be low (a few percent), the reflectivity very high (over 90%), the reflection band is shifted against the ‘Bragg’ wavelength toward the shorter wavelengths, and its spectral shape is very different from that of a shallow grating. Inside a reflection band, a part of the input optical power penetrates through the grating even if it is infinitely long. These properties are predicted by modelling using two independent computer codes based on different modelling methods, namely the bi-directional mode expansion and propagation method (BEP), and a method of lines (MoL). The first method is discussed in some detail here. The work has been performed within the framework of European Action COST 240.

Experimental study of integrated-optics microcavity resonators: Toward an all-optical switching device

An integrated all-optical switch based on a high-Q nonlinear cylindrical microcavity resonator is proposed. The switch consists of single mode planar waveguides that allow coupling light in and out to a microresonator, exhibiting whispering gallery modes. Due to the high Q factor and the small dimensions, fast switching at low power is feasible for devices based on presently available nonlinear polymers as the active material. In this approach, the transmission of an integrated optical waveguide close to a microcavity has been measured and related to the resonances of the cylindrical microcavity.

The Electroactive Integrated Optical Waveguide: Ultrasensitive Spectroelectrochemistry of Submonolayer Adsorbates

Highly sensitive spectroelectrochemistry of adsorbed films on ITO is demonstrated with the electroactive integrated optical waveguide (EA-IOW). The EA-IOW, a single-mode planar waveguide coated with an ITO layer, is ∼10(4)-fold more sensitive to changes in absorbance occurring during electrochemical events versus a single-pass transmission spectroelectrochemical experiment, as demonstrated by reduction of surface-adsorbed methylene blue. Furthermore, the EA-IOW is selective to near-surface events, as it is relatively insensitive to absorbance by solutions of dissolved chromophores at <1 mM. The EA-IOW is also used to monitor the formation of Prussian Blue during the reduction of ferricyanide, an event that is not easily followed using current-detected cyclic voltammetry, due to interfering faradaic and non-faradaic electrochemical events. The optical background of the EA-IOW is potential-dependent and is explained by ion diffusion into the ITO and by voltage-dependent changes in optical constants for the material. Finally, the high sensitivity of the EA-IOW (relative to other evanescent-field-based spectroelectrochemical techniques) is discussed in terms of its design.

Novel bioaffinity sensors for trace analysis based on luminescence excitation by planar waveguides

We have developed a novel generation of optical bioaffinity sensors for ultra trace analysis. These sensors are based on luminescence generation in the evanescent field of high-refractive-index single-mode planar waveguides, With the waveguiding layers and the grating parameters chosen, very sharp discrimination of bulk against surface-confined excitation, in combination with high excitation intensities in the evanescent field, can be achieved, leading to unprecedented sensitivity. Experimental data of the optimization of the transducer parameters will be presented. Incoupling of excitation light is performed using diffractive gratings. Different methods for the detection of both transmitted and luminescence light will be presented. The transmitted excitation light can be detected either at the distal waveguide chip end or using a second outcoupling grating. Both isotropically emitted luminescence, collected by a lens located below the transducer substrate (‘volume detection’), and emission coupled back into the waveguiding layer can be monitored, the latter via a second outcoupling grating. First experimental results obtained in model bioaffinity assays will be presented, demonstrating the feasibility of the different detection methods mentioned above, as well as the superior sensitivity of our novel sensor configuration. In still preliminary experiments, 100 attomoles of fluorescently labelled DNA (16-mer oligonucleotide), applied at 100 femtomolar concentration, can be detected.

Sol−Gel-Based, Planar Waveguide Sensor for Gaseous Iodine

A novel sensor for gaseous iodine has been developed using a combination of sol-gel processing and planar integrated optical waveguiding technologies. The sensing principle is based on the detection of a charge transfer complex formed between iodine and phenyl groups that have been incorporated into a porous, methylated glass film. The glass film was prepared from siloxane precursors by the sol-gel method. Sensors were fabricated by coating the film over a single-mode planar waveguide. Light was coupled into and out of the laminate structure using integral grating couplers, and formation of the charge transfer complex was monitored as attenuated total reflection of the guided wave. The sensor exhibits a linear response to I(2) in the range of 100 ppb to 15 ppm with response and recovery times less than 15 s. The response is selective to 4 ppm iodine in the presence of 10 ppm chlorine and is stable for at least 3 months.

Improved propagation-mode near-field method for refractive-index profiling of optical waveguides

Experimental and theoretical improvements to the propagation-mode near-field technique for refractive-index profiling have been made. The measured near-field profile is deconvoluted with the transfer function of the optical imaging system in order to recover the actual near-field profile. Anew equation is also derived in order to use these data to reconstruct the refractive-index profile of the waveguide under consideration. The improved method, which is valid for all relevant wavelength ranges, is demonstrated in the determination of the refractive-index profiles of two single-mode planar waveguides.

Planar Fresnel lens photoimprinted in a germanium-doped silica optical waveguide

A gradient-thickness Fresnel lens was photoimprinted in the germanium-doped core layer of a single-mode planar waveguide on silica by exposure to ultraviolet light through a mask, which increases the refractive index in the lens region by approximately 5 x 10(-3). The lens is used to collimate the output of a standard single-mode optical fiber butt coupled to the waveguide at a wavelength of 1.3 microm. The method is applicable to the mass production of complex diffractive elements in a planar waveguide geometry.

Distributed single-mode fiber to single-mode planar waveguide coupler

Light transfer between a curved single-mode fiber and a single-mode planar waveguide is investigated experimentally in dependence on the refractive index and thickness of the planar waveguide and for different polishing depths. Marcuse's model is applied to treat theoretically the coupler, leading to a very good agreement with the experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Diffraction characteristics of superimposed holographic gratings in planar optical waveguides

A coupled-mode analysis of superimposed holographic transmission gratings in single-mode planar optical waveguides is presented. The diffraction characteristics are shown to be sensitive to the polarization of the incident wave, the angular separation of the output waves and the relative index modulation between the gratings. The coupling between gratings affects the diffraction efficiencies and decreases the angular and wavelength selectivities. Nevertheless, good channel separation and high fanout can be obtained together.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power-Dependent Coupling Characteristics of a Butt Joint between a Single-Mode Planar Waveguide and a Nonlinear Planar Waveguide with Different Film Thickness

An efficient coupling scheme between single-mode planar waveguides with different film thickness is proposed. The configuration consists of a tapered waveguide with nonlinear cladding. Power-dependent coupling efficiency of the configuration is analyzed by the beam propagation method. The numerical results show that this configuration has high coupling efficiency and is less sensitive to the offset between coupled waveguides when the input power is properly selected.

Highly efficient coupling between two planar waveguides with different refractive index profiles by using nonlinear cladding

An efficient butt-joined coupling scheme between single-mode planar waveguides with different refractive index profiles is proposed. The configuration consists of a tapered waveguide with nonlinear cladding. Power dependent coupling efficiency of the configuration is analyzed by the beam propagation method. The numerical results show that this configuration has high-coupling efficiency and is less sensitive to the offset between coupled waveguides if the input power is properly selected.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Lateral coupling between a silicon-oxinitride waveguide and an amorphous Si photodiode

We have measured the absorption coefficient at λ=850 nm for an amorphous Si (a-Si:H) p-i-n photodiode laterally coupled to a silicon-oxinitride single mode planar waveguide both for TE and TM modes. The experimental results are compared to calculations considering a five-layer system with a complex index of refraction for the absorbing layer. Theoretical and experimental results agree well considering the inaccuracies in the determination of the layer thicknesses.

Single polarization optical waveguide on silicon

A single polarization optical waveguide structure is introduced and demonstrated experimentally. The optical waveguide structure considered is a silicon nitride film deposited onto an oxidized silicon wafer so as to form a single-mode planar waveguide. Single polarization is achieved by choosing layer thicknesses, so that the attenuation due to substrate coupling for the TM mode is much larger than that for the TE mode. Calculations are presented to define ranges of design parameters over which TM attenuation can be 3-4 orders of magnitude higher than that for TE. In one sample having a TE loss of 0.28 dB/cm measured at a wavelength of 0.63 mu m a ratio of TM to TE attenuation of over 750 is experimentally demonstrated. >

Inverse scattering theory applied to the design of single-mode planar optical waveguides

An inverse scattering theory is used to design single-mode planar optical waveguides that have wider inhomogeneous cores than those obtained by direct scattering methods. The wave equation for the electric field in the core is transformed into a Schrodinger-type equation whose potential function q(x) is related to the refractive-index profile. The modal structure of the waveguide is characterized by the transverse reflection coefficient r(k); a single discrete propagating mode and continuous radiating modes are considered. The Gel’fand–Levitan–Marchenko inverse scattering theory is used to obtain the unique solution of q(x) from a rational-function representation of r(k).

Design of wide-core planar waveguides by an inverse scattering method

An inverse scattering method is used to design single-mode planar optical waveguides. Waveguides with wider cores compared with those designed by direct scattering methods are obtained, and a numerical example is given.

Relation between three mode field half-width definitions for single-mode planar waveguide and application to splice-loss evaluation

Two moment-related definitions for the mode-field half-width (MFHW) of a planar optical waveguide with an arbitrary index profile are proposed, and their relationships to the MFHW based on a Gaussian least-mean-square fit are derived. Various formulas for calculating splice loss for two identical planar waveguides under transverse offset and axial tilt are presented, including accurate formulas based on transmission coefficient, approximate formulas based on various MFHW definitions, and error formulas for using them both. Numerical data for symmetrical step-index slab waveguides show that for small misalignments, splice losses calculated from moment MFHWs are more accurate than those from the Gaussian MFHW, and error formulas can be used to obtain conservative estimates.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>