Broadly tunable laser-diode-based mid-infrared source with up to 31 microW of power at 4.3-microm wavelength.

High-power single-spatial-mode near-IR laser diodes are mixed in periodically poled LiNbO(3) (PPLN) to generate broadly tunable mid IR-radiation. Conversion efficiencies to the mid IR up to 0.017%/W are demonstrated, and up to 31 microW of power is generated at the spectroscopically important 4.3-microm wavelength. We achieved broadband mid-IR tunability by mixing a wavelength-tunable laser-diode pump source with a fixed-wavelength master oscillator power amplifier laser-diode signal source in a PPLN sample that has a poling period that varies from 21.0 to 22.6 microm in the direction transverse to the beam propagation. We generated mid-IR radiation from 4.1 to 4.3 microm with these laser sources, using a fixed 22.0-microm period region of the sample.

Two-dimensional Er:YSGG microlaser array pumped with a monolithic two-dimensional laser diode array.

We have demonstrated one- and two-dimensional Er:YSGG microlaser arrays at 2.8-microm output wavelength with power levels up to 900 mW cw. The one-dimensional microlaser arrays are based on conventional edge-emitting laser diodes, and the two-dimensional microlaser arrays are based on surface-emitting monolithic two-dimensional laser diode arrays with 45-deg deflectors.

Automated phase sensing and control of an external Talbot cavity laser with phase-contrast imaging.

We describe a novel phase-sensing and control system, based on phase-contrast imaging, operating within a linear external cavity laser consisting of 18 GaAlAs edge-emitting gain stripes. The system is used to achieve single-spatial-mode operation and diffraction-limited output from the linear cavity, which uses diffractive coupling at a Talbot plane to achieve coherent operation.

Tolerances in microlens fabrication by multilevel etching and mass-transport smoothing.

A method is developed for the quantitative assessment of microlens deficiencies caused by inaccuracies in the multistep mesa fabrication or by incomplete mass-transport smoothing. Analytical expressions are obtained and tolerable imperfections are deduced for the practical effort-saving fabrication of highperformance micro-optical elements.

Intracavity phase correction of an external Talbot cavity laser with the use of liquid crystals.

Arrays of GaAlAs emitters have been diffractively coupled by using an external Talbot cavity to support a single spatial mode; however, element-to-element phase differences distort the desired spatial mode. To enable element-to-element phase correction, we incorporated a 20-element array of tunable liquid-crystal phase shifters into a 20-element GaAlAs external Talbot cavity laser. Using the tunable phase shifters, we corrected spatial mode distortions, which resulted in 663 mW of nearly diffraction-limited power.

Modal analysis of linear Talbot-cavity semiconductor lasers.

A modal analysis at threshold is presented for linear Talbot-cavity semiconductor lasers with a finite number of array elements. The analysis self-consistently calculates the array supermode profiles and the loss each incurs owing to imperfect Talbot imaging, including edge diffraction losses. It is found that the decrease in mode discrimination between supermodes incurred by fabricating larger arrays can be offset by reducing the near-field fill factor.

Optical characterization of grating surface emitting semiconductor lasers.

We describe an apparatus for measuring the optical characteristics of grating coupled surface emitting semiconductor lasers. These measurements include far and near field measurements, spectrum, and total power. The far field can be determined with an absolute accuracy of 0.01 degrees .

Cross-induced polarization changes in single-mode fibers.

The polarization changes induced by a strong wave on a copropagating weaker wave in a single-mode birefringent fiber are investigated. Quantitative analysis and measurements are presented for the dependence of these polarization changes on the relative input state of polarization of the two waves as well as on their frequency separation.

Brillouin-gain spectra for single-mode fibers having pure-silica, GeO(2)-doped, and P(2)O(5)-doped cores.

Brillouin-gain spectra are measured for pure-silica core, GeO(2)-doped core, and P(2)O(5)-doped core single-mode fibers with different index profiles. A narrow-linewidth semiconductor laser operating at 828 nm is used as the pump light source. The spectral shape of the Brillouin gain is found to be strongly related to the refractive-index profiles. The Brillouin linewidths evaluated experimentally are 90 and 215 MHz for a step-index single-mode fiber and a graded-index single-mode fiber, respectively. The Brillouin Stokes shifts depend on the core/clad-ding dopant materials and their concentrations and range from 20 GHz for the P(2)O(5)-doped core fiber to 21.6 GHz for the puresilica core fiber in the 0.8-microm-wavelength region.

Parametric interaction of a modulated wave in a single-mode fiber.

Parametric interaction in a single-mode fiber between a carrier and its two sidebands was observed. This interaction leads to gain or loss in the two sidebands depending on the relative phase between them and is approximately linearly dependent on the carrier power. A maximum gain of 1.4 was observed at a carrier power of 11 mW.

Contrast detection and its dependence on the presence of edges and lines in the stimulus field.

The influence of sharp luminance discontinuities (dark lines and edges) in the stimulus field on the contrast sensitivity has been measured using sinusoidal gratings. Merely by changing the position of edges or lines in the stimulus field, it is possible to alter the contrast sensitivity by a factor of 3 or more. The distance from which such a discontinuity can affect the contrast sensitivity depends on the spatial frequency of the grating itself, and can be up to several degrees for gratings of low spatial frequency. No difference could be found between the effect of edges and the effect of very thin (5 min of arc) dark lines on the contrast sensitivity. The apparently conflicting experimental results in the literature concerning the relationship between the number of periods in a grafting and the contrast sensitivity, and especially concerning the influence that the surround of the grating has on this relationship, can be ascribed to the effect of these luminance discontinuities. In all cases where the number of periods was reported to have a large effect on the contrast sensitivity (up to a factor 10), the position of edges or lines in the stimulus field was also varied when the number of periods was changed. The change in the contrast sensitivity is no more than a factor 2 to 3 when there are no lines or edges in the grating surround.