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A deep domain inversion (DI) technique for X-cut LiNbO3 is reported. DI regions as deep as 70 μm, i.e., deep enough for virtually any guided-wave application, were obtained by electric-field poling, with even deeper DI regions possible. As an application of the DI technique, a bandpass traveling-wave Mach–Zehnder modulator is demonstrated with a 15 GHz bandwidth centered at 21 GHz.

The fluorescence spectrum of Er-indiffused LiTaO3 was measured and revealed strong anti-Stokes fluorescence (ASF) with upconverted green and red emissions when the 4F9/2 manifold of an Er3+ ion was pumped by either a 632.8 or a 647 nm laser. Investigation into the dependence of fluorescence intensity on pump intensity and depth profiling of the Stokes and anti-Stokes fluorescences revealed that the ASF is attributed mainly to energy transfer upconversion within Er3+ cluster sites. Postindiffusion processing in molten LiNO3 was found to be effective in suppressing the upconversion via decrease of the cluster site concentration.

A complete structural phase diagram of annealed proton-exchanged X-cut LiTaO3 is presented, to relate refractive index change to proton-induced lattice deformation. From this diagram, explanations for the previously observed phenomena of index increase upon annealing and index decrease with increasing proton concentration (above a certain value) are derived. We have analyzed the evolution of index profiles during postexchange annealing, describing how the presence of multiple phases within a waveguide can lead to large index variations and buried index profiles. Finally, we identify at least two high-concentration phases that exhibit large temporal instabilities.

The influence of annealed proton exchanged (APE) waveguides on domain inversion in Z‐cut LiNbO3 is reported. For this study, pyrophosphoric acid is used to fabricate planar APE waveguides, both before and after creating domain inversion through the application of an external electric field at room temperature. Domain inversion produced in this manner is shown to sustain the APE process. However, domain inversion is not producible in portions of the substrates having APE waveguides on both crystal faces. The implication of this result for integrated optic device fabrication is discussed.

We report on the variation of the refractive index of a GaAs/AlGaAs multiquantum well of well width 6.5 nm and barrier width 19 nm, introduced by zinc impurity‐induced disordering. We employ a structure consisting of several uncoupled, multiquantum well ridge waveguides with tapered disordering across the transverse direction. The refractive index changes have been deduced as a function of the interdiffusion length of Ga/Al by the use of an interference technique. We measured a maximum index change of 0.083 and 0.062 for significant disordering (Ld=6.6 nm) at 35 and 100 meV below the band edge of the undisordered multiquantum well, respectively.

We compare the photorefractive effect in proton‐exchanged (PE) and annealed proton‐exchanged (APE) LiNbO3 optical waveguides at the irradiation wavelength of 488 nm. We measure the intensity dependence of the saturated index change, the build‐up time constant, and the photorefractive sensitivity in PE and APE waveguides. In APE waveguides the photorefractive sensitivity is about three times that of PE waveguides up to an irradiation intensity of 100 W/cm2. The contribution of the dark conductivity to the photorefractive effect in PE and APE waveguides is found to be dominant in the intensity range used in our experiments.

We report the first simultaneous quasiphase matched second harmonic generation (SHG) of blue (433 nm) and green (532 nm) light in LiNbO3 channel waveguides. Up to 0.45 mW (0.25 mW) of blue (green) light was obtained stimultaneously with an efficiency of 22%/W (28%/W). This result is made possible by using a 6.8 μm period domain inversion grating which serves as a first‐order (second‐order) grating for green (blue) generation simultaneously. We also show that further enhancement in the SHG performance can be obtained by choosing the appropriate grating depth.

We have studied the effect of nonuniformity in graded index, channel waveguide dimensions on the phase‐matching condition for guided‐wave nonlinear frequency conversion. Both theoretical and experimental results using normalized waveguide parameters and quasi‐phase matching for second‐ harmonic generation in annealed proton‐exchanged LiNbO3 waveguides show the existence of an optimum waveguide design which is insensitive to inhomogeneities in the waveguide dimensions. Application of such a waveguide design using normalized approach can significantly relax the fabrication tolerance, leading to nonlinear guided‐wave devices with long interaction lengths and useful conversion efficiencies.

We have fabricated fiber‐compatible, low‐loss, wavelength and polarization insensitive 3 dB 2×2 cross couplers by Ag+‐Na+ ion exchange in glass. The couplers were designed using the adiabatic invariance condition for graded‐index channel waveguides. An excellent agreement between theory and experiment is demonstrated.

We report on the fabrication and the characterization of low‐loss, single‐mode GaAs/AlGaAs single heterostructure ridge waveguides and a linear electro‐optic phase modulator on silicon substrate. The waveguides and the phase modulator were grown by molecular beam epitaxy and were characterized at a 1.3 μm wavelength. The average TE mode propagation loss of 1.24 dB/cm, obtained for a 6‐μm‐wide ridge waveguide, is the lowest loss so far reported. The measured phase shift efficiency of the phase modulator was 3.5°/V mm.

A novel self‐aligned buried‐ridge striped planar (BRSP) GaAlAs/GaAs diode laser structure is presented. The structure was grown by two‐step liquid phase epitaxy using preferential growth and melt etch. A Ga1−y Aly As layer with a wide range of Al concentration (y>0.05) is selectively grown outside the ridge and can be an effective melt‐etching mask. As a result, the BRSP structure can incorporate virtually all effective index steps, i.e., the positive, negative, and complex index steps. The threshold current of the BRSP structure is between 70 and 100 mA. The BRSP structure may prove to be of importance in the realization of linear array lasers.

A simple method is described for fabricating fibers with large strain birefringence starting with standard MCVD preforms. The method is illustrated using borosilicate fibers. The birefringence and polarization properties are measured in a long fiber and the birefringence is also measured using a fiber slice and polarizing microscope.

An experimental integrated optical version of the Mach‐Zehnder interferometer switch, analogous to the microwave balanced bridge, is reported. The bridge is formed by 3‐μm‐wide Ti‐diffused strip waveguides in LiNbO3 and the switch utilizes electro‐optical tuning to achieve 3‐dB operation of the directional couplers. The switching voltage required to switch between the states, corresponding to a π phase shift in one arm, equals 14.8 V. The cross talk between channels that corresponds to the extinction ratio when operated as an on‐off modulator is −21.6 dB.

We report a high‐efficiency PpinN GaAs/AlGaAs waveguide phase modulator for high‐speed operations. By introducing p‐ and n‐GaAs layers beside the intrinsic GaAs layer of a P‐i‐N double heterostructure, the absorption edge‐related effect, hardly used in P‐i‐N phase modulators, is utilized. We demonstrate a high phase shift efficiency of 37.5°/V mm at 1.3 μm wavelength. Although this corresponds to the highest expeirmental value reported for reverse‐biased GaAs/AlGaAs phase modulators, our device operates with a low junction and a very low dynamic capacitance.

We have observed the formation of growth strains due to interfacial dislocations in thin films made by the diffusion of niobium into LiTaO3. These dislocations become significant for films wherein Δn0≳0.01; their effect is to increase the scattering loss of the optical guided waves in the film.

Previous results on dielectric optical waveguides made by diffusing niobium into LiTaO3 have been extended. It is shown that the propagation constants of the thin‐film waveguide modes can be accurately calculated assuming that the refractive index decreases as the square of the distance into the film. Low‐loss single‐mode embedded strip guides made by electron resist masking techniques are also described.

Single‐mode fibers which maintain linear polarization are described. The fibers are birefringent and linear polarization is maintained along either of the two principal axes. The birefringence arises from the deliberate enhancement of anisotropic strains.

Al(0.3)Ga(0.7)As/Al(0.05)Ga(0.95)As double-heterostructure light-emitting diodes (LEDs) were successfully grown for the first time by liquid phase epitaxy on a GaAs-coated Si substrate that was prepared by a sequential process of migration-enhanced epitaxy and molecular beam epitaxy. The edge-emitting LEDs had diode ideality factors of 1.54 at a forward-biased voltage higher than 0.9 V and external quantum efficiencies of 0.0033 W/A per facet. This efficiency is 50 times higher than the previously reported value, and is on the same order as that of AlGaAs homojunction LEDs fabricated on the GaAs substrates by liquid phase epitaxy.

Calculations for a simple three‐layer slab model show that sufficient anisotropic strain birefringence can be introduced into germanosilicate, phosphosilicate, and borosilicate single‐mode fibers to reduce the coupling between orthogonally polarized modes to a level of practical interest for single‐mode single‐polarization propagation.

Single‐mode buried channel waveguides with circularly symmetric mode field distribution compatible with conventional single‐mode fibers at 1.3 μm wavelength were fabricated and characterized for the first time using a novel single‐step ion exchange process from silver films. The technique is relatively simple and eliminates the gold electrode deposition used in previously reported fabrication methods.

A narrow ridge was ion‐beam etched on an outdiffused LiNbO3 crystal to form a single‐mode waveguide confining the beam in both transverse dimensions. Electrodes were evaporated along the ridge to produce a very efficient electro‐optic phase modulator requiring a power of 20 μ W/MHz of bandwidth and a voltage of 1.2 V to produce a modulation index of 1 rad.

We describe a means of eliminating undesired surface guiding in titanium‐diffused strip waveguides on LiNbO3. Surface guiding for light of the extraordinary polarization, normally produced when the crystal is diffused in dry argon or oxygen, can be eliminated entirely by adding water vapor to the diffusion gases. Infrared absorption measurements show that hydrogen enters crystals diffused in a wet atmosphere. Although the mechanism for the prevention of surface guiding is not fully understood, we suggest that the presence of excess hydrogen reduces lithium mobility.

Observation of optical guidance in an epitaxial mixed‐crystal film (NH4)xK1−xH2PO4 grown on a (100) KDP substrate is reported. The film thickness was ∼38 μ. The ordinary and extraordinary indices of the film for x=0.07 at 589.3 nm were nfo=1.5105 and nfe=1.4695. The difference in corresponding indices between the film and the substrate was 10−3. When the film waveguide was excited by a Gaussian He–Ne laser beam, the distribution of energy across the output face of the crystal confirmed one‐dimensional guiding in the epitaxial film.

We report a novel electrolytic process that is used to fabricate reproducible, low loss, single mode waveguides. By precisely controlling the current pumped through high purity Ag and Pt electrodes in molten NaNO3, as well as its duration, a high degree of accuracy over the release and hence the control of Ag+ concentration is achieved. The inherent capability of the process to generate very low level of silver ion concentration with high precision implies much higher time of diffusion, thus removing the time criticality factor faced by the existing processes while fabricating single mode waveguides.

Symmetrical buried waveguides with fiberlike refractive index profiles using Ag+‐Na+ exchange have been realized in soda‐lime‐silicate glass substrates. A simple scanning electron microscope technique to determine the silver ion (refractive index) profile is also reported.

A single‐heterostructure optical waveguide at 1.3 μm wavelength in GaAs/AlGaAs, grown on Si by molecular beam epitaxy, is demonstrated. 6‐μm‐wide ridge waveguides with 0.25 μm ridge height had single modes and the measured average propagation loss was 11.7 dB/cm. The principal loss was mainly due to the relatively large free‐carrier concentration in the guiding layer. It is expected that lower free‐carrier concentration (∼1015 cm−3) will lead to waveguides with propagation loss of less than 3 dB/cm.