Waveguide mode filters fabricated using laser-induced forward transfer.

Titanium (Ti)-in-diffused lithium niobate waveguide mode filters fabricated using laser-induced forward transfer followed by thermal diffusion are presented. The mode control was achieved by adjusting the separation between adjacent Ti segments thus varying the average value of the refractive index along the length of the in-diffused channel waveguides. The fabrication details, loss measurements and near-field optical characterization of the mode filters are presented. Modeling results regarding the device performance are also discussed.

Latent light-assisted poling of LiNbO3.

The observation of latent light-assisted poling (LAP) in lithium niobate single crystals is reported. More specifically, the nucleation field is reduced and remains reduced for an extended time period (up to several hours) after irradiation with ultrafast (approximately 150 fs) laser light at a wavelength of 400 nm. The maximum nucleation field reduction measured using latent-LAP (62%) was significantly higher in comparison with regular non-time-delayed LAP (41%) under identical irradiation conditions in undoped congruent lithium niobate crystals. No latent-LAP effect was observed in MgO-doped crystals for the experimental conditions used, despite the strong effect observed using regular LAP. The latent-LAP effect is attributed to the formation of a slowly decaying photo-induced space-charge distribution which assists local ferroelectric domain nucleation. The dynamics of latent-LAP are compared with the dynamics of photorefractive grating decay, recorded in lithium niobate crystals of different doping, confirming the space charge hypothesis.

Spectral and electro-optic response of UV-written waveguides in LiNbO3 single crystals.

An experimental study of the spectral and electro-optic response of direct UV-written waveguides in LiNbO3 is reported. The waveguides were written using c.w. laser radiation at 275, 300.3, 302, and 305 nm wavelengths with various writing powers (35-60 mW) and scan speeds (0.1-1.0 mm/sec). Spectral analysis was used to determine the multimode and single mode wavelength regions and, the cut-off point of the fabricated waveguides. Electro-optic characterization of these waveguides reveals that the electro-optic coefficient (r33) decreases for longer writing wavelengths, with a maximum of 31 pm/V for 275 nm and, is reduced to 14 pm/V for waveguides written with 305 nm.

Direct-writing of inverted domains in lithium niobate using a continuous wave ultra violet laser.

The inversion of ferroelectric domains in lithium niobate by a scanning focused ultra-violet laser beam (lambda = 244 nm) is demonstrated. The resulting domain patterns are interrogated using piezoresponse force microscopy and by chemical etching in hydrofluoric acid. Direct ultra-violet laser poling was observed in un-doped congruent, iron doped congruent and titanium in-diffused congruent lithium niobate single crystals. A model is proposed to explain the mechanism of domain inversion.

Tunable two-dimensional hexagonal phase array in domain-engineered Z-cut lithium niobate crystal.

An optical phase array with tunable phase step is demonstrated. The phase array consists of a two-dimensional hexagonal lattice of inverted ferroelectric domains fabricated on a Z-cut lithium niobate substrate. The electro-optically tunable phase step is obtained by the application of an external electric field along the z axis of the crystal via transparent electrodes. Theoretical analysis and experimental results are presented, showing that a tunable and flexible adaptive optical illuminator device can be realized by combining the electro-optic tunability with the Talbot effect. Generation of a multiplicity of light patterns is shown.

Photorefractive adaptive transmission system.

A photorefractive system based on the combined operation of a strontium barium niobate input amplifier and a self-pumped barium titanate phase-conjugator crystal is presented and analyzed. Amplified real-time phase-conjugate wave-front generation in this system is demonstrated. The system's ability to all-optically, temporally modulate a weak probe signal and to transmit it back to its source by means of amplified dynamic phase conjugation demonstrates its potential in adaptive optical transmission schemes.

Excimer laser use for microetching computer-generated holographic structures.

Excimer-laser microetching of a variety of materials is applied to the fabrication of surface-relief optical microstructures of arbitrary morphology, with particular emphasis on computer-generated holographic structures. High-definition, high-radiation-intensity selective laser ablative etching in conjunction with step-and-repeat (period) replication or raster (pixel) scanning is used. To support such developments, the characteristic etching properties of a wide range of solid materials, from metals to semiconductors and polymers, are studied. Optical-interconnect and generic object holograms are produced by means of this alternative one-step holographic information-recording method.

Direct ultraviolet writing of channel waveguides in congruent lithium niobate single crystals.

We report the fabrication of optical channel waveguides in congruent lithium niobate single crystals by direct writing with continuous-wave ultraviolet frequency-doubled Ar+ laser radiation (244 nm). The properties and performance of such waveguides are investigated, and first results are presented.

Etching and printing of diffractive optical microstructures by a femtosecond excimer laser.

Diffractive optics fabrication is performed by two complementary processing methods that rely on the photoablation of materials by ultrashort UV laser pulses. The spatially selective ablation of materials permits the direct microetching of high-quality surface-relief patterns. In addition, the direct, spatially selective transfer of the ablated material onto planar and nonplanar receiving substrates provides a complementary microprinting operation. The radiation from the ultrashort pulsed excimer laser results in superior quality at relatively low-energy density levels, owing to the short absorption length and minimal thermal-diffusion effects. Computer-generated holographic structures are produced by both modes of operation. Submicrometer features, including Bragg-type structures, are microprinted onto planar and high-curvature optical-fiber surfaces, demonstrating the unique ability of the schemes for complex microstructure and potentially nanostructure development.

Multiwatt continuous-wave adaptive laser resonator.

We present, for what we believe is the first time, results of continuous-wave diode-pumping of a Nd:YVO (4) laser with an adaptive gain-grating resonator. The system is shown to produce more than a 7-W output in a TEM>(00) single longitudinal mode with a laser beam propagation parameter M(2) of <1.3 and <1.1 in the x and y axes, respectively. We demonstrate the self-adaptive abilities of the resonator by spatial correction of an intracavity aberrator for both injected and self-starting versions of the cavity.

Photosensitivity of lead germanate glass waveguides grown by pulsed laser deposition.

We report very large photoinduced refractive-index changes Dn, of the order of ~10(2), in lead germanate glass waveguides grown by pulsed-laser deposition. The magnitude of Dn was derived from measurements of diffraction efficiency for gratings written by exposure to 244-nm light through a phase mask, whereas the sign of Dn was determined from ellipsometric data. Results are shown for films grown under oxygen pressures ranging from 1 chi 10(-2) to 6 chi 10(-2)mbars (1.33mbars=1 Torr).

High-phase-conjugate reflectivity (<800%) obtained by degenerate four-wave mixing in a continuous-wave diode-side-pumped Nd:YVO(4) amplifier.

High-phase-conjugate reflectivities of >800% have been achieved through degenerate four-wave mixing in a cw diode-side-pumped Nd:YVO(4) amplifier. Reflectivity curves are shown as a function of input pump-beam intensity for three values of small-signal amplifier gain, and comparison is made with a numerical simulation.