Ion-exchanged Channel Waveguides Research Articles

Single mode integrated-optical wide-band channel waveguides and junction splitters in KTiOPO4 for visible light

Single mode integrated-optical wide-band channel waveguides (SOWCWs) have been defined as a novel type of channel waveguides. The wavelength ranges (bandwidths) of both single mode operation in the channel waveguide and efficient junction-splitting using the same channel waveguides, that is for constant combining or splitting of light in integrated-optical devices like Y junctions, can easily comprise the entire visible wavelength region. In this case, the SOWCW is a real single mode white light channel waveguide. The optical bandwidths of both Rb↔K ion-exchanged channel waveguides in KTiOPO4 (KTP) as an example of SOWCWs and Rb:KTP Y junctions in comparison with those of conventional titanium-indiffused channel waveguides and Y junctions in LiNbO3 have been theoretically calculated and experimentally verified. The channel waveguide attenuation, the coupling efficiency to single mode fibers, and the splitting ratio of Y junctions, especially, show no significant wavelength dependence in the Rb:KTP case. Use of SOWCWs could open up new directions of integrated optics. As an example, the basic three-color-mixing device is chosen from a variety of possible applications in the field of integrated-optical color image generation.

Light-induced refractive index changes in singlemode channel waveguides in KTiOPO 4

Light-induced changes of the effective refractive index in Rb ↔ K ion-exchanged singlemode channel waveguides in KTiOPO 4 have been investigated in the visible wavelength region dependent on time, guided optical mode intensity and temperature. A hypothesis for the explanation of the light-induced effects is suggested. Thermooptic and pyroelectric effects are discussed. The light-induced refractive index changes do not restrict the function of integrated-optic components in the visible.

Determination of ion-exchanged channel waveguide profile parameters by mode-index measurements

We report a method for characterizing ion-exchanged channel waveguides in terms of the diffusion depth, width, and surface-index change from mode-index measurements. The method is then used to study the effect of the diffusion time and the mask width on these parameters in K(+)-Na(+)-exchanged guides in BK7 glass. It is observed that the mask width affects the waveguide dimensions in ways not reported in earlier studies. Our results reveal that the diffusion depth depends on the mask opening and saturates with time to a maximum value for a given mask width. The lateral-diffusion rate and the side diffusion beneath the mask are independent of the mask width, which indicates that the lateral electric field associated with the metallic mask plays an important role in such diffusion. We discuss the implications of this behavior to modeling and fabricating integrated optical devices.

Singlemode channel waveguides and electrooptic modulators in KTiOPO/sub 4/ for the short visible wavelength region

Single-mode channel waveguides at short visible wavelengths have been fabricated in KTiOPO/sub 4/ by Rb/spl rlhar2/K ion exchange in mixed melts of RbNO/sub 3/-KNO/sub 3/-Ba(NO/sub 3/)/sub 2/. The technological parameters have been chosen by means of theoretical WKB- and calculations concerning the singlemode region of the effective channel waveguide index N/sub 00/ at the given wavelength. Great diffusion anisotropy and small dispersion of the surface refractive index change guarantee singlemode operation of the very same channel waveguide from the blue up to the red. Typical attenuation of about 2.0 dB/cm for TM- and 1.5 dB/cm for TE polarization was obtained at /spl lambda/=0.5145 /spl mu/m. Light-induced refractive index changes (photorefractive effect) have been determined as a function of time, wavelength, guided optical mode intensity and temperature. The light-induced effects in Rb/spl rlhar2/K ion-exchanged channel waveguides in KTiOPO/sub 4/ are about two orders of magnitude smaller than those in annealed proton-exchanged channel waveguides in LiNbO/sub 3/. Electrooptic phase modulators have been successfully investigated concerning dynamic V/sub /spl pi// measurements, the electric-optical field overlap and dc-drift phenomena. Design, fabrication and experimental results of integrated-optic Mach-Zehnder-interferometer modulators for short visible wavelengths are presented. >

Waveguide polarizers processed by localized plasma etching

We develop a downstream localized plasma-etching process that permits in situ monitoring of light throughput in a semiconductor-clad channel waveguide as the semiconductor thickness is trimmed. Hydrogenated amorphous silicon films are deposited on ion-exchanged channel waveguides by plasmaenhanced chemical vapor deposition. We then employ the localized plasma-etching process to maximize accurately the extinction ratio between TE and TM polarizations propagating in the clad waveguide. We achieve polarization extinction ratios of greater than 30 dB for both TE-pass and TM-pass polarizers.

Numerical simulation of ion-exchange in glass for integrated optical components

A numerical model based on the finite-element method for solving the nonlinear diffusion equation of ion-exchange in glasses is presented. The model is applied to the calculation of the concentration profile for a Ag/sup +/-Na/sup +/ ion-exchanged channel waveguide. The calculated concentration profile is in good agreement with a measured refractive-index profile of a waveguide fabricated with the same parameters as used in the calculations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-loss erbium-doped ion-exchanged channel waveguides

We report the fabrication of ion-exchanged channel waveguides in an Er-doped Na-modified BK-7 glass. The buried waveguides were elliptical in cross section, having approximate cross-sectional dimensions of 10 microm x 30 microm. Characterization of the optical properties of the waveguides revealed that they are single mode in the 10-microm dimension and multimode in the 30-microm dimension and exhibit a total waveguide loss, absorption plus scattering, of 0.8 dB/cm at 0.633 microm.

Nondestructive two-dimensional refractive-index profiling of integrated-optical waveguides by an interferometric method

We describe an interferometric method that uses an interference microscope that permits the determination of the complete two-dimensional refractive-index profile of integrated optical waveguides, provided that the form of the one-dimensional depth profile is known. Results are reported for potassium-sodium ion-exchanged channel waveguides and are shown to be in good agreement with theory.

Waveguide polarizers with hydrogenated amorphous silicon claddings

We have fabricated TE- and TM-pass waveguide polarizers with polarization isolations of 42 and 35 dB, respectively. The devices were fabricated by the growth of hydrogenated amorphous silicon claddings on K(+)-Na(+) ionexchanged channel waveguides in glass. Cladding thicknesses were accurately tuned to permit optimum coupling of either a TE or a TM mode to the cladding. We have also demonstrated that a waveguide polarizer attenuation as high as 760 dB/cm can be measured by using a photothermal deflection technique.

Accurate analysis of ordinary and grating-assisted ion-exchanged glass waveguides

Finite difference and finite element methods, and the coupled mode theory are combined to study in detail the ion-exchanged glass channel waveguides. Ordinary and grating-assisted waveguides are analyzed. The effect of various device parameters on waveguide behavior is investigated. Design curves to make waveguides with required characteristics are provided.

Scalar finite-element evaluation of cut-off wavelength in glass wave guides and comparison with experiment

The scalar finite-element method is used to analyze ion-exchanged glass channel waveguides. Cut-off wavelengths for fundamental and first-order modes are calculated and the single-mode region is determined. The results are compared with the experimentally measured values.

A general model for fabrication processes of channel waveguides by ion exchange

A general theoretical approach to the modeling of several different process steps in fabrication of ion-exchanged channel waveguides is presented. All of the commonly used fabrication processes are included, and the nature of the ion source and the effect of external electric voltage are taken into account. The model uses a numerical finite-difference calculation of diffusion in the glass with boundary conditions and electrical current distribution chosen according to the process being modeled. A single computer program includes the model, and can be used for simulating a fabrication process with different successive process steps. Several calculated examples are given, all with experimentally obtained parameters for Ag+ -Na+ exchange in Corning 0211 glass.

Simulation of tapered transitions in ion-exchanged channel waveguides

Tapered transitions in the ion-exchanged glass waveguide are modeled to predict the index profile, propagation constant, and modal field along the taper. Results are in excellent agreement with the experimental data in Ag(+)-Na(+) exchanged tapers fabricated by a two-step process in BK7 glass.

Effect of annealing on diffused channel waveguides

Mode size measurements of the Ag(+)-Na(+) ion-exchanged channel waveguides in BK7 glass show a square root dependence on the annealing time in contrast to the linear variation predicted in the literature.

Nonlinear-optical effects in ion-exchanged semiconductor-doped glass waveguides

We have measured nonlinear-optical effects in ion-exchanged channel waveguides fabricated in semiconductor-doped glass. The nonlinearity is manifested as optically induced saturable absorption displaying a resonant enhancement. The relaxation time of the nonlinearity was found to be tens of picoseconds. The relaxation time also exhibited wavelength dependence. Waveguide transmission and pulse-probe experiments using a picosecond mode-locked dye laser were used to carry out these measurements.

Fabrication of ion-exchanged channel waveguides directly into integrated circuit mask plates

Optical channel waveguides have been fabricated into integrated circuit lithography mask plates by silver-sodium ion exchange. The process combines the advantages of Ag thin-film ion sources and the accurate and reliable patterning of chromium films on mask plates. The process is potentially suitable for cheap mass production, since no lithography is needed during the actual waveguide fabrication. The tailoring of waveguide cross sections by modifying the electric field distribution inside the glass is also presented.