Properties Of Optical Waveguides Research Articles

Swift nitrogen ion irradiated waveguide lasers in Nd:YAG crystal

We report on the fabrication, fluorescence and laser properties of optical waveguides by swift nitrogen ion irradiation in Nd:YAG crystals. The confocal micro-luminescence investigations have concluded that the fluorescence features of the bulk material have been well preserved in the waveguide. Under 808 nm optical end-pumping, continuous-wave (cw) laser oscillation at 1064.2 nm has been demonstrated with laser slope efficiencies of 16% and pump power thresholds of 38.3 mW.

Plasmonic Coaxial Waveguides with Complex Shapes of Cross-Sections.

In this paper, we describe waveguide properties of new optical waveguides made of noble metals and filled with glass and air. Such waveguides are coaxial cables and differ from a conventional coaxial in the shape of their central rods. Coaxial waveguide with annular and elliptic central rods are considered. Numerical simulations demonstrate that these waveguides, having nanosize cross-section, support propagation of few comparatively low-loss modes, having phase velocity close to the speed of light and the fields localized in a small area outside a metal. We illustrate excitation of these coaxial modes by dipole-like sources.

Optical waveguide and nonlinear properties of Bi3NdTi3O12 thin films

Neodymium-substituted bismuth titanate (Bi3NdTi3O12, BNT) thin films were prepared on quartz substrates by a metal-organic solution deposition process. The crystalline structure was evaluated by X-ray diffraction. Waveguide property was investigated by using prism coupling technique and optical transmittance measurement. The optical nonlinearities of the film were measured by the top-hat Z-scan techniques and a large positive nonlinear refractive index, nonlinear refractive coefficient and two-photon absorption coefficient were determined to be 3.84 × 10−7 esu, 0.7523 cm2/GW and 4.81 × 104 cm/GW, respectively. These results reveal that the BNT film may be a kind of new multifunctional materials.

All-optical logic gates using semiconductor-based three-coupled waveguides nonlinear directional coupler

All-optical logic gates with nonlinear optical (NLO) properties of three-coupled identical waveguides have been proposed and designed theoretically in a unique semiconductor-based symmetric structure. The model uses the NLO interactions of the coupled waveguides, like Kerr effect and Two Photon Absorption (TPA). Unlike the previous studies, we take into account higher order NLO effects of semiconductors such as Free Carriers (FC) and loss to control the switching operation. These NLO phenomena lead to high functionality in a simple unique structure. Therefore, in this work, by setting the input intensity of the waveguides, the logic AND, OR, NAND, and NOR gates are designed in a unique structure with different lengths. Our analysis deals with continuous waves (CW) region and the results are valid for the ranges of short optical pulses with time duration longer than FC life time.

Optical properties of planar waveguides on ZnWO_4 formed by carbon and helium ion implantation and effects of annealing

We report on the optical properties of ZnWO(4) planar waveguides created by ion implantation, and the effect annealing has on these structures. Planar optical waveguides in ZnWO(4) crystals are fabricated by 5.0 MeV carbon ion implantation with a fluence of 1 × 10(15) ions/cm(2) or 500 keV helium ion implantation with the a fluence of 1 × 10(16) ions/cm(2). The thermal stability was investigated by 60 minute annealing cycles at different temperatures ranging from 260°C to 550°C in air. The guided modes were measured by a model 2010 prism coupler at wavelengths of 633 nm and 1539 nm. The reflectivity calculation method (RCM) was applied to simulate the refractive index profile in these waveguides. The near-field light intensity profiles were measured using the end-face coupling method. The absorption spectra show that the implantation processes have almost no influence on the visible band absorption.

Waveguide optical properties of polystyrene doped with p-nitroaniline derivatives

New copolymers of styrene with N-acryloyl p-nitroaniline or N-diethyl methylenemalonate p-nitroaniline chromophores were synthesized and characterized by size exclusion chromatography (SEC), thermal analyses (DSC, TGA) and reflectometry. The linear optical properties of the polystyrene copolymers and the polystyrene (PS) doped with p-nitroaniline derivative chromophores were investigated and were related to the chromophore content in the matrix by prism coupling at 633 nm. Thin films of the polymers with good optical quality were prepared by the spin coating method. The glass transition and decomposition temperatures and the refractive index profile of the copolymers were similar to those of the parent PS. On the other hand, the PS doped with p-nitroaniline derivative chromophores had lower glass transition temperatures attributed to the plasticizing effect of the chromophore and different refractive index profiles compared with the parent PS.

Slow light, open-cavity formation, and large longitudinal electric field on a slab waveguide made of indefinite permittivity metamaterials

The optical properties of slab waveguides made of indefinite permittivity ($\ensuremath{\varepsilon}$) materials (IEMs) are considered. In this medium, the real part of the transverse permittivity is negative while that of the longitudinal permittivity is positive. At any given frequency, the IEM waveguide supports an infinite number of transverse magnetic (TM) eigenmodes. For a slab waveguide with a fixed thickness, at most only one TM mode is forward wave. The remainder are backward waves which can have a very large phase index. At a critical thickness, the waveguide supports degenerate forward- and backward-wave modes with zero group velocity if loss is absent. Above the critical thickness, the waveguide supports complex-conjugate decay modes instead of propagating modes. The presence of loss in IEMs will lift the TM mode degeneracy, resulting in modes with finite group velocity. A feasible realization is proposed. The performance of the IEM waveguide is analyzed and possible applications are discussed, which are supported by numerical calculations. These slab waveguides can be used to make optical delay lines in optical buffers to slow down and trap light, to form open cavities, to generate strong longitudinal electric fields, and as phase shifters in optical integrated circuits. Although the presence of loss will hinder these applications, gain can be introduced to compensate the loss and enhance the performance.

Quality Standardization for Polydimethysiloxane-Based Optical Interconnect Production From Optical Aspects

The influences of waveguide materials, fabrication conditions, and packaging substrates on the optical waveguide properties of electrical-optical circuit boards have been investigated by systematic variation of these conditions. Pt catalyst in polydimethysiloxane, casting mould sidewall roughness, interlay thickness, and packaging substrates show sensitive impact on optical waveguide insertion loss and in terms of defined target of optical loss, the basic quality criteria can be defined before production.

Optical transmission properties of C-shaped subwavelength waveguides on silicon

Optical properties of C-shaped subwavelength waveguides in metallic (silver) films on silicon substrates are studied in the range of 0.6–6 μm. Power throughput and resonant wavelengths of several transmission modes are studied by varying the waveguide length (or metal thickness). Among three types of transmission modes, the fundamental order of the Fabry–Perot-type mode was shown to attain remarkably high power throughputs (as high as 12). With optimized design of the aperture, the resonant wavelength of this mode occurs in the 1–2 μm wavelength range, suggesting that such apertures can be utilized to achieve plasmonic-enhanced silicon photonic devices at telecommunication wavelengths.

Structural−Property Relationship in Pyrazino[2,3-g]quinoxaline Derivatives: Morphology, Photophysical, and Waveguide Properties

The objective of this contribution is to achieve crystalline one-dimensional organic micro/nanostructures by self-assembling for active waveguides and other optoelectronic nanodevices. To improve solid emitting performance for highly efficient waveguide fibers, our strategy here is to adopt nonplanar conjugated segments to minimize unfavorably intermolecular fluorescent quenching in solid state; meanwhile, long alkyl chains are added as structural group that controls molecular packing. With this intention, a series of molecules based on pyrazino[2,3-g]quinoxaline (PyQ) units were developed. The effects of the molecular geometry and symmetry on their optical properties, crystal dimensions, liquid crystals, and active waveguide properties were studied in detail to understand the structure−property relationship of organic conjugated molecules, which is of vital importance to rational design for organic self-assemblies toward optoelectronic applications. On a single molecular level, the molecular structures a...

Analysis of liquid-to-solid coupling and other performance parameters for microfluidically reconfigurable photonic systems

In this paper, we analytically investigate the coupling of light from liquid-core waveguides to conventional solid-core waveguides and a series of other optical properties of liquid waveguides in order to gauge the practicality of such a system for use in microfluidically reconfigurable photonic systems. A finite element model of the system was constructed and relevant properties such as mode field diameter, attenuation, bending loss, and efficiency of evanescent and end-fire coupling were investigated as a function of the liquid waveguide Peclet number and the relative difference in refractive index. For pure liquid systems we show that the mode field diameter decreases monotonically with increasing Peclet number and that bending losses could be significantly reduced by increasing the Peclet number. More critically, we observed irreversible evanescent coupling, in which the light coupled in the solid waveguide is entrapped within the solid rather than coupled back into the liquid waveguide. This effect was caused by the lengthwise variation in the propagation constant of the liquid core due to downstream diffusion. We demonstrate that coupling efficiencies as high as 84% can be obtained for fluid based end-fire coupling by taking advantage of the tunable mode field diameter. By developing techniques for coupling light between liquid and solid states we hope to be able to overcome the drawbacks of solid waveguide systems (e.g. unchangeable structure and properties) and liquid waveguide systems (e.g. diversion and attenuation) yielding a new paradigm for reconfigurable photonics.

Structure and properties of optical waveguides in stoichiometric LiNbO3 crystals

The structures of proton-exchanged and implanted waveguides are studied by X diffraction analysis and vibration spectroscopy. On the basis of the absorption’s spectroscopy data in the visible region and the data on the shift of the fundamental absorption edge in the nearultraviolet region, a comparative analysis of technologically conditioned variations in the nonlinear optical properties of proton-exchanged and implanted waveguides in stoichiometric LiNbO3 crystals is conducted.

Structural and optical characterization of c-axis textured BaTiO3 thin films on MgO fabricated by RF magnetron sputtering

In this paper, BaTiO3 thin films were prepared by RF magnetron sputtering on MgO substrates and their properties such as the crystal structure and optical waveguide properties were investigated. The optimum deposition parameters, such as substrate temperature, deposition pressure, gas flow ratio, the RF power and the after annealing temperature, were obtained in order to get the best BaTiO3 film quality. The XRD results show that highly c-axis textured BaTiO3 thin films were successfully grown on MgO substrate. Films obtained under the optimum deposition parameters, substrate temperature of 650°C, RF power of 50 W, deposition pressure 18 mTorr and gas flow ratio O2/(Ar+ O2) of 15% namely, reaches a full width at half maximum intensity (FWHM) of BaTiO3 (002) XRD peak of 0.25°. The FWHM of BaTiO3 (002) XRD peak was further reduced to 0.24° via post-treatment with furnace annealing (at 800°C for 2 h) which indicates the film crystal quality is further improved. The bright and sharp TE modes measured by m-line spectroscopy of the BaTiO3 film were observed indicating its possible application in optical waveguide.

Analytical modal analysis of bent slot waveguides

We analyze modal properties of dielectric optical bent slot waveguides by using the multilayer formulation of the well-known classical analytical model of bent waveguides based on the Bessel-Hankel functions. Unlike the previously studied approximate model based on the Airy functions, this model is valid for all values of bend radii. The present approach allows quick and accurate computations of propagation constants, mode profiles, and field-power densities for the 2D bent slot waveguides with very small radii. Using this model we characterize the optimal slot position inside the bent core to maximize the field enhancement in the slot. Such modal analysis is quite useful for the design of devices involving bent slot waveguides. Moreover the results obtained by the present 2D rigorous analytical model can also be used for benchmarking other numerical tools.

Investigation on optical properties of Bi2.85La0.15TiNbO9 thin films by prism coupling technique

Layered-perovskite ferroelectric Bi2.85La0.15TiNbO9 (LBTN) optical waveguiding thin films were grown on fused silica substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) revealed that the film is highly (00l) textured. We observed sharp and distinct transverse electric (TE) and transverse magnetic (TM) multimodes and measured the refractive indices of LBTN thin films at 632.8 nm. The ordinary and extraordinary refractive indices were calculated to be nTE=2.358 and nTM=2.464, respectively. The film homogeneity and the film-substrate interface were analyzed using an improved version of the inverse Wentzel–Kramer–Brillouin (iWKB) method. The refractive index of the film remains constant at n0 within the waveguiding layer. The average transmittance of the film is 70% in the wavelength range of 400–1400 nm and the optical waveguiding properties were evaluated by the optical prism coupling method. Our results showed that the LBTN films are very good electro-optical active material.

Optical properties of Bi 2.25La 0.75TiNbO 9 thin films grown on fused silica substrates by PLD

Layered-perovskite ferroelectric Bi 2.25La 0.75TiNbO 9 (LBTN-0.75) optical waveguiding thin films have been prepared on fused silica substrates by pulsed laser deposition (PLD). X-ray θ–2 θ scans revealed that the films are single-phase perovskite. The optical properties, such as the wavelength dependence of the transmittance and the refractive index, were determined. The average transmittance of the film is 75% in the wavelength range of 200–1100 nm and the band gap E g = 3.46 eV. The optical waveguiding properties of the films were characterized by using prism coupling method. The distinct m-lines of the guided transverse electric (TE) and transverse magnetic (TM) modes of the LBTN-0.75 films waveguide have been observed. The film homogeneity and the film–substrate interface were analyzed using the inverse Wentzel–Kramer–Brillouin (iWKB) method.

Planar Optical Waveguides Based on Thin ZnO Layers

Zinc oxide ZnO is a semiconductor material with a wide broad-band gap of 3.4 eV. It displays attractive properties permitting to apply it in sensor techniques as well as in systems of integrated optics. Data quoted in literature indicate that it is transparent in a visible range. It is characterized by a high value of the refractive index (n ≈ 2) [1–6], which is a favorable feature of the waveguide in systems of integrated optics [3]. The primary aim of the investigations is to develop in future a photonic sensor structure attained in compliance with the techniques of integrated optics applied as sensors of selected gases, e.g. NH3, NOx, . . . Gas sensors constructed on the basis of integrated optics are particularly desirable in environments liable to considerable hazards of explosion, i.e. in industry [1]. An innovation of the solution suggested by us is the construction of a sensor structure in compliance with the techniques of integrated optics, comprising a waveguide layer, a sensor layer and input-output elements, viz. Bragg’s gratings, all mounted on common substrate. The subject matter of the present paper is to investigate the optical waveguide properties of ZnO layers depending on the applied deposition technology and their thermal treatments [7–18].

Role of nanostructure on the optical waveguiding properties of epitaxial LiNbO3 films

High-quality LiNbO3 (LN) epitaxial films have been grown on (0 0 1)Al2O3 substrates by pulsed laser deposition. The deposition conditions have been optimized using experimental designs to promote the growth of highly (0 0 1)-oriented, phase pure and light-guiding LN films. The structural and nanostructural properties have been investigated by x-ray diffraction reciprocal space mapping and the guiding properties have been investigated by m-line spectroscopy and measurements of the light propagation losses. In particular it is shown that the film composition, the state of strain, the film thickness, the film roughness, the lateral extension of the crystallites building up the film as well as the mosaicity can be determined by a careful examination of the x-ray reciprocal space maps associated with simulation of the diffracted intensity distribution in reciprocal space. The guiding properties have been correlated with the nanostructural properties of the films: whereas light guiding has been clearly observed in single-crystal-like films, the existence of a mosaic structure, made of nanocrystalline domains, is shown to be detrimental to the guiding properties.

Rib waveguides based on Zn-substituted LiNbO 3 films grown by liquid phase epitaxy

The fabrication of epitaxially grown Zn-substituted LiNbO 3 (Zn:LiNbO 3) waveguide films and rib waveguides is reported and detailed investigations about microstructure, morphology and optical waveguide properties are provided. Zn:LiNbO 3 films were grown on congruent X-cut LiNbO 3 substrates by a modified liquid phase epitaxy in solid–liquid coexisting solutions. The homogeneously Zn-substituted films exhibit high crystalline perfection and extremely flat surfaces with averaged surface roughness of rms = 0.2–0.3 nm. At the film/substrate interface a Zn-containing transient layer has been observed, which allows the growth of elastically strained Zn:LiNbO 3 film lattices. X-ray diffraction reciprocal-space measurements prove the pseudomorphic film growth. The refractive index difference between substrate and film depends on the zinc substitution content, which increase with rising growth temperatures. For films with 5.3 mol% Zn (Δ n o ≈ +5 × 10 −3) only ordinary ray propagation was observed, while for films with 7.5 mol% Zn (Δ n o ≈ +8 × 10 −3, Δ n e ≈ +5 × 10 −3) both modes, TM and TE propagate. Stress-induced refractive index changes are in the order of Δ n ≈ 10 −4. In rib waveguide microstructures singlemode propagation with nearly symmetrical field distribution has been observed. To demonstrate the potential of the proton exchange-assisted dry-etching technique interferometer microstructures were fabricated.

Formation and characterization of a near-stoichiometric LiNbO_3 waveguide by MeV oxygen implantation

We report the fabrication and optical properties of planar and channel waveguides on z-cut near-stoichiometric LiNbO(3) crystal formed by 6.0 MeVO(3+) implantation at a dose of 5x10(14) ions/cm(2). The properties of the planar waveguide are characterized by use of prism coupling and the reflectivity calculation method. It is found that the effective refractive indices of the transverse magnetic modes increase but the transverse electric ones decrease when an appropriate heat annealing treatment is performed. We also find that only transverse magnetic polarized light could be guided in this waveguide effectively, although the dark mode could be detected in both the transverse electric and the transverse magnetic directions.