Thin-film Optical Waveguide Research Articles

Electro-optic beam deflector using epitaxial Pb(Zr,Ti)O3 waveguides on Nb-doped SrTiO3

Pb(Zr,Ti)O 3 (PZT) thin-film optical waveguides were grown on Nb-doped SrTiO3 substrates by solid-phase epitaxy to fabricate an electrode/waveguide/conductor structure. The propagation loss was relatively large for a PZT waveguide on a lightly Nb-doped SrTiO3 as compared with the propagation loss of 4 dB/cm for the structure using undoped SrTiO3. An electro-optic beam deflection device was fabricated by preparing a prism electrode on the surface of the PZT waveguide on a lightly Nb-doped SrTiO3 substrate. Efficient deflection of the coupled laser beam in the PZT waveguide as large as 11 mrad was observed by applying 35 V between the prism electrode and the substrate.

Fabrication of thin-film waveguide QPM-SHG devices by domain-inverted liquid-phase epitaxy

The ferroelectric domain-inversion phenomenon observed in a liquid-phase epitaxially grown LiNbO 3 was applied as a new fabrication technique of a quasi-phase-matched second-harmonic generation device. A periodic domain-inverted LiNbO 3 thin-film optical waveguide was fabricated by forming a periodic groove structure on a Mg-doped LiNbO 3 substrate using proton-exchange and selective etching techniques followed by domain-inverted liquid-phase epitaxy. Generation of blue light with a 440 nm wavelength was demonstrated by first-order quasi-phase matching.

Thin Film Waveguide Sensor for Measurement of the Absorption Coefficient of Hemoglobin Derivatives

A simple method for determining the absorption coefficient of oxyhemoglobin and deoxyhemoglobin in human blood is proposed. The method is based on a variation of the complex propagation constant of guided wave in a thin-film optical waveguide. On the waveguide layer, a serial multi-channel sample chamber is constructed to vary the interaction length between the evanescent field and the sample, and the dependence of the sensor response on the interaction length is investigated for various concentrations of two hemoglobins. The response of this sensor is linearly proportional to the interaction length and the concentration of the two hemoglobins. The attenuation constant due to the evanescent field absorption between the channels is experimentally obtained with the designed sensor, and the absorption coefficient is determined by the proposed method. The determined absorption coefficients coincided with those obtained by conventional transmission measurement.

Dip-coated thin-film polycarbonate optical waveguides

We report on our systematic and detailed study of fabrication and characterization of polycarbonate thin-film optical waveguides. Various waveguide properties, such as refractive index, optical loss, waveguide thickness, dispersion as a function of temperature of waveguides and substrates, and the effect of thickness gradient on optical guiding losses, have been reported. A comparative study of the properties of waveguides fabricated with dioxane and tetrahydrofuran as solvents is also presented.

Synthesis and Characterization of Highly Oriented Sol-Gel (Pb, La) TiO3 Thin Film Optical Waveguides

The preparation and the optical characteristics of highly oriented PLT thin films are investigated. PLT films fabricated on MgO(100) and c-plane sapphire substrates have highly grown in (100) and (111) orientations, respectively. PLT films with high La content have a near cubic structure and weak anisotropy of refractive indices. The optical propagation losses of PLT films decrease as the La content of the films increases due to a complex interaction of surface roughness reduction and a reduction in the anisotropy refractive index. However, optical scattering in thicker sol-gel PLT thin film waveguides occurs by the internal scattering mechanism from the defects and the interfaces rather than by the surface scattering mechanism.

Er/sup 3+/-doped Al/sub 2/O/sub 3/ thin films by plasma-enhanced chemical vapor deposition (PECVD) exhibiting a 55-nm optical bandwidth

We report the first deposition of Er/sup 3+/-doped aluminum oxide thin-film optical waveguides by plasma-enhanced chemical vapor deposition (PECVD). The aluminum and erbium precursors used for the deposition of the thin films were trimethyl-aluminum and Er tri-chelate of 2,2,6,6-tetramethylheptane-3,5 dione respectively. The samples show broad, room-temperature photoluminescence at /spl lambda/=1.533 /spl mu/m. The Er/sup 3+/ concentration ranged from 0.01-0.2 at%. The full width half maximum (FWHM) of the Er/sup 3+/ emission spectrum is 55 nm, considerably broader than in silica glass. The radiative lifetime has been measured at 50-mW pump power.

Active optical thin-film waveguide sensor for ion sensing

In this paper, an active PVC optical thin-film waveguide sensor is proposed which can select a specific ion and measure its concentration. The waveguide was fabricated using the plasticized poly(vinyl chloride) (PVC), bis ethyl hexyl phthalate (BEHP), lipophilic anionic dye (LAD-3), and ionophores (K23E1 for calcium, or C14DD16C5 for sodium) in which the PVC membrane plays important roles for both incident light propagation and selective ion sensing. In order to investigate the applicability of this sensor to Ca 2+ and Na + measurement, the sensor was applied to sample solutions whose CaCl 2 concentration was gradually altered. Also, we applied it to a NaCl solution. In this experiment, we found that this PVC thin-film waveguide possessed good light propagation for argon laser light at 488 nm. Also, the comparison of the experimental responses between the active waveguide sensor and a commonly utilized waveguide sensor (evanescent waveguide spectrometry), indicated that the sensitivity of the active waveguide sensor is obviously higher than that of the conventional waveguide sensor. These findings suggested that the proposed PVC waveguide ion sensor is applicable to the determination of various ions with high sensitivity.

Guided-wave couplers and amplifier based on the second-order Bragg interaction

Guided radiated wave coupling by means of a second-order surface relief grating etched onto a thin-film optical waveguide is investigated for the transverse magnetic mode. The necessary governing equations derived from a quasi-optic analysis are summarized. The quasi-optic analysis is an asymptotically exact perturbation procedure that is valid, in particular, for amplitudes of the grating that are small relative to the film thickness. The interference effect in the guided waves is employed to deduce the design criteria for optimizing the performance of the output and the input couplers, the frequency-selective reflector, and the surface-emitting amplifier. The device characteristics are found to be insensitive to small changes in the physical parameters about their designed values.

PZT Electro-Optic Waveguide Devices Fabricated by Solid-Phase Epitaxy

ABSTRACTHigh quality epitaxial PZT optical waveguides have been grown by solid-phase epitaxy based on metal alkoxide solution process. Optical propagation loss was 4 dB/cm in epitaxial PZT thin film optical waveguides grown on SrTiO3 substrates. Epitaxial PZT optical waveguides were grown on Nb doped conductive SrTiO3 substrates, since considerable reduction in drive voltage will be expected when top electrode / optical waveguide / conductive substrate structures are realized. Propagation loss was relatively large, as compared with the structure using non-dope insulative substrates. Preliminary electrooptic deflection devices were fabricated by preparing prism electrodes on the surface of the PZT optical waveguides. Efficient deflection/switching of coupled laser beam in the PZT optical waveguides as large as 26 mrad was observed by applying 70 volts between prism electrode and Nb doped SrTiO3 substrates.

Laser operation of an Nd:Gd3Ga5O12 thin-film optical waveguide fabricated by pulsed laser deposition

We report the laser operation of a thin-film waveguide structure grown by the pulsed laser deposition technique. A 2.7-μm-thick crystalline film of neodymium doped Gd3Ga5O12 (Nd:GGG) lases at a wavelength centered at 1.06 μm when pumped by a Ti:sapphire laser at 808 nm.

Quasioptics of second-order Bragg interaction in a thin film optical waveguide

For the transverse magnetic mode, the second-order Bragg interaction of the guided and the radiated waves is considered for a thin film dielectric waveguide with a corrugated film–cover interface. A set of four canonical equations for the deexcitation and the excitation of the guided waves are derived by employing a quasioptical technique. The governing equations are applied for the treatment of a surface-emitting distributed feedback laser. Some design criteria are obtained for optimizing the performance of the laser. When these design criteria are used, the laser characteristics are insensitive to small changes in the physical parameters about their designed values. Numerical results are presented to illustrate the performance of the laser. The shape of the surface relief grating is found to play a vital role in determining the gain threshold and the gain margin of the laser.

Characterisation of GaLaS chalcogenide glass thin-film optical waveguides, fabricated by pulsed laser deposition

The fabrication of stoichiometric thin-film optical waveguides of GaLaS via a pulsed laser deposition technique is reported. Stoichiometric films are grown by ablating GaLaS bulk glass with a KrF excimer laser (λ = 248 nm) at an incident laser flux ⩾ 3.5 J/cm 2. The composition of the films is determined by energy-dispersive X-ray analysis and the refractive index is measured by a dark-mode prism coupling technique. Photoinduced structural rearrangement of the as-deposited films leads to a blueshift in the visible absorption edge and a permanent refractive index change, Δ n, of −1%. On the basis of these results, grating structures have been written with both blue light, and e-beam addressing, and their suitability for integrated optical structures assessed.

Growth of crystalline Gd 3Ga 5O 12 thin-film optical waveguides by pulsed laser deposition

Crystalline thin-film optical waveguides of gadolinium gallium garnet (Gd 3Ga 5O 12) have been deposited onto heated yttrium aluminium garnet (Y 3Al 5O 12) substrates by a pulsed laser deposition technique. The refractive indices of the films have been inferred from dark-mode prism coupling measurements and are in excellent agreement with the bulk crystal.

Photorefractive damage in LiNbO3 thin-film optical waveguides grown by liquid phase epitaxy

Photorefractive damage in LiNbO3 thin film optical waveguides grown by liquid phase epitaxy (LPE) was evaluated by the in-plane scattering method at the irradiation wavelength of 514 nm. We were particularly interested in comparing films grown from a Li2O–B2O3 flux and a Li2O–V2O5 flux, and investigating the effect of Mg and Fe doping. Two powerful tools were used for data analysis: the Glass model and the ray model, which estimates the refractive index change. The LPE film grown from the Li2O–B2O3 flux showed a much higher resistance to photorefractive damage than the LPE film grown from the Li2O–V2O5 flux. The photorefractive effect was suppressed by Mg doping and enhanced by Fe doping as in the bulk crystal. The refractive index change in the 0.7 mol % Mg-doped LPE film grown from the Li2O–B2O3 flux was small enough (10−5 at most) to induce no beam fanning. Conventional Ti-indiffused, H+-exchanged, and annealed H+-exchanged waveguides were used as reference samples.

Epitaxial growth of Fe-doped sapphire thin films from amorphous Al oxide layers deposited on sapphire substrates

Thin films of amorphous Al2O3, about 280 nm thick, with Fe-cation concentrations of 0–4 at. % were deposited onto alpha-alumina [0001] substrates. Epitaxial regrowth of the thin films was found to occur during a postannealing process at temperatures of 950 and 1400 °C. The regrowth quality was determined by Rutherford backscattering spectrometry and ion channeling measurements. Perfect regrowth was found in the undoped samples after annealing at 1400 °C with a minimum backscattering yield of 2% in the Al sublattice. Furthermore, ion channeling angular scans revealed that Fe dopants occupied the substitutional sites of Al sublattice upon thermal anneal. This simple method of incorporating dopants into single-crystal alumina has potential in the fabrications of thin-film planar optical waveguides.

Optical thin films for waveguide applications

The development of optical thin films for waveguide applications will enable a variety of new and highly useful optoelectronic functions. Many difficulties must be overcome, however, before optical films can be used in photonics applications. Properties such as polycrystallinity, surface topography, and refractive-index homogeneity can affect the performance of optical thin film waveguides to a much greater extent than in other thin film applications because of the long optical interaction lengths. Even a small degree of polycrystallinity in anisotropic media, for example, can be a significant source of optical scattering. We review recent results of epitaxial lithium tantalate thin films grown as waveguide structures on sapphire and gallium arsenide substrates. Highly oriented crystalline structures with useful optical properties have been demonstrated. Although many challenges still remain before optical thin films are used widely as waveguides, modern thin film technology is beginning to provide the tools and capabilities to make these concepts a reality.

Pulsed laser deposition of Ga-La-S chalcogenide glass thin film optical waveguides

Thin film optical waveguides of the chalcogenide glass Ga-La-S have been deposited on substrates of CaF2 and microscope glass by the technique of pulsed laser deposition. The chalcogenide properties of photobleaching, photodoping, and photoinduced refractive index changes have been observed and preliminary experiments carried out. The refractive index and thickness of the layer were verified using a waveguide ‘‘dark mode’’ analysis technique.

Liquid phase epitaxial growth of LiNbO 3 thin film using Li 2O-B 2O 3 flux system

LiNbO 3 thin film optical waveguides were fabricated by liquid phase epitaxy. In order to improve the crystallinity and optical transparency of the film, a 5 mol% MgO-doped LiNbO 3 substrate and Li 2O-B 2O 3 flux system were used instead of a conventional combination of LiTaO 3 substrate and Li 2O-V 2O 5 flux system. Dependence of film properties on the melt composition was investigated in detail. As a result, high crystallinity with a small linewidth of 11.4 arc sec in the X-ray rocking curve, and good surface morphology with perfect mirror surface were realized by choosing a suitable melt composition. The chemical composition of the grown film was estimated to be nearly stoichiometric from results of several characterizations, and the Li/Nb ratio of the film could not be widely changed by changing the Li 2O/Nb 2O 5 ratio in the melt. The as-grown film shows a perfect transparency for the wavelength down to the fundamental absorption edge resulting in a small guided optical wave propagation loss of less than 1 dB/cm at a wavelength of 458 nm. Ferroelectric domain inversion phenomena at the film-substrate interface, and preliminary results of trial on controlling film properties by Mg, Zn, Na and Ti doping are also shown and discussed.

Enhancement of Photoelastic Constant of Optical Thin-Film Waveguide Assisted by Surface Acoustic Wave

In the present research, we propose a method of controlling the photoelastic constant using surface acoustic waves. A Bragg diffraction is carried out to determine the photoelastic constants of Nb2O5. As a result, it is confirmed that the photoelastic constant of Nb2O5 thin film undergoing a sputtering process, during which surface acoustic waves were excited on the substrate, was about 3 to 6 times larger than those of thin films on which surface acoustic waves were not excited.

Sensitivity analysis of a thin-film optical waveguide biochemical sensor using evanescent field absorption

A multichannel thin-film optical waveguide sensor for determining aqueous biochemical concentration with a high dynamic range of measurement is proposed. The sensitivity dependence of the proposed sensor on interaction length and waveguide thickness is investigated for dye solutions and three different hemoglobin concentration levels of carboxyhemoglobins. The sensitivity is inversely proportional to the waveguide thickness while proportional to the interaction length. As a consequence the variability of the interaction length makes the proposed sensor a flexible tool for concentration measurements. Moreover, an efficient method for determining the absorption coefficient is discussed.