M. Hempstead

Optical anisotropy of dispersed carbon nanotubes induced by an electric field

Carbon nanotubes dispersed in ethanol are aligned by an electric field. Due to the orientation of these elongated particles, the dispersion exhibits anisotropic behavior. Transmission experiments show rotation of the linear polarization of an incident laser beam. Alignment and relaxation times and the influence of the magnitude of the electric field have been measured.

Channel waveguide laser at 1 μm in Yb-indiffused LiNbO 3

We report laser action in a Ti-diffused LiNbO3 waveguide doped with trivalent Yb ions by thermal indiffusion. Lasing was observed at 1008, 1030, and 1060 nm with thresholds as low as 15-mW launched pump power. We reduced photorefractivity, which initially permitted only intermittent lasing, by annealing the sample in wet O2. The annealed sample lased continuously in a cavity formed by high-reflectivity mirrors; however, with a 7% output coupler the output power exhibited instabilities. The greatest value of the output power observed under these conditions was consistent with a slope efficiency of ~16% with respect to absorbed power.

Non-photorefractive CW Tm-indiffused Ti:LiNbO 3 waveguide laser operating at room temperature

We report laser operation at 1.81 /spl mu/m and 1.85 /spl mu/m in a Tm/sup 3+/:LiNbO/sub 3/ Ti-diffused waveguide doped by thermal indiffusion at high temperature. We believe this is the first time lasing has been seen in Tm:LiNbO/sub 3/ at room temperature. Continuous-wave operation was achieved at room temperature with a threshold of 42 mW launched pump power. The output power was observed to be stable, without any sign of photorefractive damage.

Tunable coupled-cavity waveguide laser at room temperature in Nd-diffused Ti:LiNbO3

We report on a Y-junction channel waveguide laser, operating at room temperature, in Nd-diffused Ti:LiNbO(3). Pumping was performed with a cw Ti:A1(2)O(3) laser operating at 816 nm. With feedback provided only by the polished end faces of the device, a cw lasing threshold of ~39-mW launched pump power was obtained, with a slope efficiency of ~35%. Using 95% reflectivity mirrors at the waveguide ends, we reduced the lasing threshold to ~4 mW, with a slope efficiency of ~2.6%. Tuning of the lasing signal over a range of 2.3 nm around a center wavelength of 1092.7 nm was demonstrated, with a monolithically integrated phase modulator.

Waveguide lasers operating at 1084 nm in neodymium-diffused lithium niobate

The authors report the demonstration of waveguide lasers in lithium niobate into which the active element neodymium has been introduced by thermal diffusion. The waveguides were fabricated using conventional Ti indiffusion and optical feedback was provided by the polished endfaces alone. The absorbed power threshold of one waveguide laser was estimated at 13+or-3 mW for pumping at 814 nm, and its slope efficiency in terms of total lasing output as a function of absorbed pump power was estimated to be 55+or-8%. Laser output powers in excess of 100 mW were observed.<<ETX>>

1.7 μm excited state absorption measurement in erbium‐doped glasses

We have measured, for the first time, the complete 1.7µm excited state absorption spectrum in erbium doped glasses. The spectrum is obtained by measuring the gain of an erbium doped waveguide in the 1400-1800 nm region. Using the measured spectra, we estimate the 1.5µm uniform upconversion rate by calculating the spectral overlap between the 1.5µm emission and 1.7µm ESA cross sections. The technique is applied to erbium-doped, ion-exchangeable silicate glasses, yielding upconversion constants in the range of 1-10 x 10 -18 cm 3 /s.

Relief gratings on Er/Yb-doped borosilicate glasses and waveguides by excimer laser ablation

Relief gratings have been fabricated on Er/Yb-doped borosilicate glass substrates by laser ablation using a 193 nm excimer laser and a modified Mach-Zehnder interferometer. The grating fabrication process was quantified using diffraction efficiency measurements and related to the incident energy density. Diffraction efficiencies and grating profiles are presented for gratings fabricated using different pulse energy densities and number of pulses, and optimised fabrication conditions are proposed. Finally, relief gratings were applied to ion-exchanged channel waveguides and spectral transmission measurements are presented.

Integrated Q-switched multiple-cavity glass waveguide laser

A novel Q-switching scheme, using rapid variation of the path difference between the cavities of a multiple-cavity resonator, is described. A thermooptic phase modulator was used to switch the cavity loss of a Y-junction glass waveguide laser between high and low states. Q-switched pulses with durations of 5 mu s and peak powers of 70 mW were obtained.<<ETX>>

Advanced materials for fibre and waveguide amplifiers

Abstract Recent research into optical fibre and waveguide amplifiers has been characterized by steady progress. Advances in the lowest fibre loss 1.5 μm telecommunications window, where newly installed optical networks operate, include erbium-doped materials with flatter gain spectra and planar amplifiers in a broad range of materials including oxide glasses, dielectric crystals and semiconductors. At 1.3 μm, substantial improvements have been made in praseodymium-doped fluoride fibre amplifiers and chalcogenide glasses have shown promise for enhanced gain efficiency.

900-nm Nd:Ti:LiNbO(3) waveguide laser.

We report what is to our knowledge the first laser operation of Nd(3+) -doped LiNbO(3) near 900 nm. An absorbed power threshold of 26 mW was obtained when the device was pumped at 814 nm. The design of the waveguide geometry to favor laser operation at this wavelength is demonstrated.