Passive glass waveguides made by ion-exchange technique are potential candidates for integrated optics (IO) applications. The authors review the advantages in the technology as applied to fabrication of useful single-mode structures. Progress in process, fabrication, modeling, and waveguide performance using different monovalent cation systems and glass compositions is described with emphasis on fiber-compatible single-mode structures prepared from molten baths. It is shown how a systematic study allows a correlation between the process parameters and the waveguide characteristics so desirable in assuring reproducible characteristics of the devices. >

Ion-exchanged glass waveguides: a review

Various factors that can effect thermal blooming in stagnation zone situations are examined, including stagnation-zone motion, longitudinal air motion in the neighborhood of the stagnation zone, and the effects of scenario noncoplanarity. Of these effects, only the last offers reasonable hope of reducing the strong thermal blooming that normally accompanies stagnation zones; in particular, noncoplanarity should benefit multipulse more than cw beams. The methods of treating nonhorizontal winds hydrodynamically for cw and multipulse steady-state sources are discussed. Aspects of pulse “self-blooming” are also considered.

Time dependent propagation of high-energy laser beams through the atmosphere, 4

A systematic study of waveguides fabricated by K/sup +/-Na/sup +/ exchange in soda-lime silicate and BK7 glasses is presented. The measured K/sup +/ concentration profile, the refractive index profile, and the diffusion profile obtained by solving the one-dimensional diffusion equation are correlated to explain the differences in the index profiles in the two glasses. The mobility of the potassium ions was measured by fabricating waveguides using electromigration. Surface waveguides formed by diffusion from a molten KNO/sub 3/ salt bath were buried by applying an electric field. Single-mode channel waveguides for operation at a wavelength of 1.3 mu m that exhibit excellent mode matching with conventional optical fibers, achieving a fiber-waveguide insertion loss of less than 1 dB for a 20-mm-long waveguide, have been obtained. >

Fiber-compatible K/sup +/-Na/sup +/ ion-exchanged channel waveguides: fabrication and characterization

The formation of a spatial relief reproducing that of the anode as a result of the thermal poling of glasses and glass-metal nanocomposites in a strong electric field has been studied by atomic force microscopy. The anode surface patterns exhibited either a square grid or a rectangular grating with a depth of 120 nm, a strip width of 0.5 μm, and a period of 1 μm manufactured using electron-beam lithography and ion etching on the surface of an n-type single crystal silicon wafer. The relief depth formed on the surface of poled samples varied within 5–15 nm, depending on the experimental conditions. The mechanism of relief formation in this system is discussed.

Submicron-resolved relief formation in poled glasses and glass-metal nanocomposites

We have measured the surface index change and birefringence in K+–Na+ ion-exchanged waveguides and compared the results with theory. The contribution to the index change caused by the polarizability/volume changes (Δnp) is calculated using two theoretical models which use empirical relations based on the glass composition. In both cases, we encounter large discrepancies between the predicted and measured values which are attributed to the inherent deficiency in the models, which assume free expansion of the glass in calculating the volume changes. Recognizing that the net volume change is much smaller, we accurately measure its value and show that both models can be used to predict Δnp with the same accuracy, provided that the correct volume change is used. We show that the limitation in accuracy is dictated by measurement errors and uncertainties in the values of the ionic radii and polarizabilities. We also present a unique and systematic method for determining the compressive stress generated in the glass resulting from ion exchange.

Modeling of the index change in K(+)-Na(+) ion-exchanged glass.

An approximate method for analyzing planar optical Y-junctions is presented. The junction structure is replaced by a discrete succession of bounded waveguide segments, and the presence of waveguide bends is assumed. Using this approximation, single-mode symmetrical Y-junctions operated as power dividers are investigated numerically. It is shown that strong mode conversion occurs between the guided and radiation modes of the local normal mode. A perturbation analysis shows that reflected fields are negligible. Reliable values of the transmitted power are obtained. >

Analysis of single-mode optical Y-junction by the bounded step and bend approximation

The swelling due to the exchange of smaller ions for larger ions is investigated on sodium-potassium ion-exchanged glass waveguides. The dependence of the swelling on the time and the temperature of ion exchange is well explained by diffusion theory. It is shown that the mode index increases with increased swelling.

Characteristics of swelling of sodium-potassium ion-exchanged glass waveguides

The relation between the ordinary and extraordinary index profiles of ion-exchanged glass waveguides is investigated on the basis of the stress-optic law and the Clausius–Mossotti relation. For K+ exchange and Ag+ exchange, the experimental results are consistent with our analysis. The values of the coefficient that relates the ordinary and extraordinary index profiles are presented.

Relation between the ordinary and extraordinary index profiles of ion-exchanged glass waveguides

In the measurement of 3-D shape by projecting a regular pattern on the object surface, it is required to extract feature points with a high accuracy and to determine their mutual relations. In this paper, 45-deg rotated checker-pattern projection is proposed, and a method for extracting and tracking the crossing point is presented in which the geometrical properties of the rotated checker pattern are utilized. If the pattern projector and the camera are on the same horizontal plane, a large brightness difference is produced between the horizontal and nonhorizontal (vertical and slant directions) neighbors of the crossing-point pixel. By utilizing this property, crossing points are extracted. The projection profile of the brightness pattern along the vertical direction has a triangular form, and the location of the extremum of the profile gives the vertical coordinate of the crossing point. By utilizing this profile, the crossing points are classified (segmentation). On the basis of the result of segmentation, the crossing points are successively tracked and their mutual relations are determined. To demonstrate the usefulness of the method, the experiment of 3-D shape measurement was made. The error of the measurement was less than 2 mm, which is due to the error in extracting the crossing point (i.e., 1 pixel at the maximum). In the measurement of a cylinder, the measurement was made along the circumference. It is shown that the measurement of the position of the crossing point on the reference plane is not required if the rotation of the object is utilized.

Rotated checker‐pattern projection and its cross‐point extraction and tracking for 3‐D object profilometry

A honeycomb waveguide network for parallel signal processing, consisting of single-mode symmetrical Y junctions, is proposed. In this waveguide network, input guided-wave amplitudes are divided and then combined with the amplitudes of the adjacent waveguides. It is shown that the operations of spatial filtering, such as smoothing, edge extraction, and edge enhancement, can be performed. An example of the honeycomb waveguide network is discussed.

Hiroshi Hirai

Papers

Analysis of single-mode optical Y-junction by the bounded step and bend approximation

Characteristics of swelling of sodium-potassium ion-exchanged glass waveguides

Relation between the ordinary and extraordinary index profiles of ion-exchanged glass waveguides

Rotated checker‐pattern projection and its cross‐point extraction and tracking for 3‐D object profilometry

Honeycomb optical-waveguide networks for parallel signal processing