Picosecond pulse amplification in a core-pumped large-mode-area erbium fiber.

Amplification in a single-clad, large-mode-area erbium fiber as an alternative to double-clad Er-Yb amplifiers is presented. Both signal and pump are coupled through a mode-matched splice into the fundamental mode, which ensures preferential gain in the fundamental mode while minimizing the amplified spontaneous emission (ASE). The 875 microm(2) effective area of the Er fiber enables amplification of 6 ps pulses at 1.55 microm wavelength by approximately 33 dB in a single stage to >25 kW peak power with low nonlinear pulse distortion and a diffraction-limited output beam with M(2)<1.1.

Simultaneous direct amplification and compression of picosecond pulses to 65-kW peak power without pulse break-up in erbium fiber.

Picosecond pulses at 1.56 micro mm wavelength are directly amplified with a diffraction limited beam quality in a core-pumped Er fiber with an 875 micro m(2) effective area. The interplay between nonlinear spectral broadening and anomalous fiber dispersion compresses the input pulse duration during amplification so that 42 nJ energy pulses with approximately 65 kW peak power are achieved without pulse break-up.

Distributed suppression of stimulated Raman scattering in an Yb-doped filter-fiber amplifier.

Suppression of stimulated Raman scattering (SRS) is demonstrated in a cladding-pumped fiber amplifier. The Yb-doped amplifier fiber design incorporates a high-index ring that resonantly couples SRS wavelengths out of the gain material, thus filtering the gain. Modeling shows that fiber asymmetry plays an important role in the filtering spectrum.

Environmentally stable Kerr-type mode-locked erbium fiber laser producing 360-fs pulses.

We demonstrate an environmentally stable Kerr-type mode-locked erbium fiber laser producing 360-fs near-bandwidth-limited pulses. Environmentally stable operation is possible in the presence of nonpolarization-maintaining fiber components provided that their overall length is short compared with the length of the polarization-maintaining fiber components. The pulses are generated at a stable repetition rate of 27 MHz and have an energy content of 60 pJ.

Generation of pulses shorter than 200 fs from a passively mode-locked Er fiber laser.

The generation of stable bandwidth-limited pulses as short as 180 fs with pulse energies as high as 100 pJ is demonstrated with a passively mode-locked Er fiber. These are to our knowledge the shortest and most intense pulses directely produced from a mode-locked Er fiber laser to date. A wide stability regime is achieved by using a dispersion-compensated cavity and employing nonlinear polarization evolution for passive amplitude modulation.

Femtosecond accumulated photon echo in Er-doped fibers.

We report the observation of accumulated photon echo in Er-doped fibers. We also demonstrate time reversal and autoconvolution of femtosecond pulses, which suggest that Er-doped fibers are a promising medium for femtosecond time-domain optical signal processing.

GaAs Clusters in the Quantum Size Regime: Growth on High Surface Area Silica by Molecular Beam Epitaxy.

Molecular beam epitaxy has been used to grow microcrystalline clusters of gallium arsenide (GaAs) in the size range from 2.5 to 60 nanometers on high-purity, amorphous silica supports. High-resolution transmission electron microscopy reveals that clusters as small as 3.5 nanometers have good crystalline order with a lattice constant equal to that of bulk GaAs. Study of the microcrystallite surfaces by x-ray photoelectron spectroscopy shows that they are covered with a shell (1.0 to 1.5 nanometers thick) of native oxides of gallium and arsenic (Ga(2)O(3) and As(2)O(3)), whose presence could explain the low luminescence efficiency of the clusters. Optical absorption spectra of the supported GaAs are consistent with the blue-shifted band edge expected for semiconductor microcrystallites in the quantum size regime.

Two-photon absorption as a limitation to all-optical switching.

Two-photon absorption can place a fundamental limitation on waveguide all-optical switching devices. We have derived a general criterion to describe this limitation that must be satisfied by all materials. As a specific example, we have experimentally evaluated this criterion for a lead-glass fiber.

Second-harmonic generation in single-mode and multimode fibers.

We report efficient second-harmonic generation in several commercially available telecommunication-grade single-mode and multimode optical fibers. We have investigated the effect of standard dopants such as germanium, phosphorous, and fluorine, and find that the efficient second-harmonic generation is associated with germaniarelated photosensitive color centers. We observed a 1.5% conversion efficiency in single-mode fibers with germanium-, phosphorous-, and fluorine-doped cores and high hydroxyl levels.