V. Pruneri

49 mW of cw blue light generated by first-order quasi-phase-matched frequency doubling of a diode-pumped 946-nm Nd:YAG laser

We report highly efficient blue-light generation by frequency doubling of a high-power cw diode-pumped 946-nm Nd:YAG laser. A periodically poled lithium niobate crystal, 6 mm long and with a period of 4.6 µm, was used in the experiment. 49 mW of blue light was generated with a conversion efficiency of 4.6%. The measured effective nonlinear coefficient (d,eff~19pm/V) and the temperature-bandwidth (Delta.T~3°C) of the crystal are close to the theoretical limits.

Photorefractive index gratings in SnO2:SiO2 optical fibers

Permanent photorefractive gratings with considerable refractive index modulations (~3×10–4) were written in silica optical fibers doped with very low levels of SnO2(~0.15 mol %) using ultraviolet (UV) laser radiation at 248 nm. The photoinduced refractive index change does not show any sign of saturation even for long exposure times (i.e., total fluence >20 kJ/cm2). A comparison with GeO2:SiO2 fibers shows that under similar UV intensities saturation takes place for shorter exposure time and comparable refractive index changes are obtainable for GeO2 concentrations ~10 mol %.

Parametric fluorescence in periodically poled silica fibers

We report the observation of quasiphase matched parametric fluorescence from a periodically poled silica fiber. A pair-photon production rate of more than 100 MHz around 1532 nm was achieved in second-order nonlinear gratings for 300 mW of pump power at 766 nm. These results are very promising for the realization of reliable all-fiber single-photon sources for quantum cryptography systems and metrology applications.

Dynamics of the second-order nonlinearity in thermally poled silica glass

We study the temporal evolution of both the second-order nonlinear coefficient and of the nonlinear thickness in thermally poled silica-glass slides by using a high-resolution all-optical technique. A time delay in the nonlinearity formation is observed, followed by an increase to a maximum, and a final decrease. The thickness is shown to increase at a rate that differs significantly from that reported for the corresponding ionic charge fronts. Our measurements also show strong dependencies on sample thickness and these can be attributed to different electric fields in the depletion region.

Optical parametric oscillation in periodically-poled lithium niobate based on continuous-wave synchronous-pumping at 1.047µm

A singly resonant optical parametric oscillator is reported that uses a periodically poled LiNbO(3) crystal and is synchronously pumped by a cw mode-locked 1.047-microm Nd:YLF laser. Picosecond pulses were tunable from 1.67 to 2.806 microm. Mean output powers of 120 mW (90 mW) were obtained for the signal (idler) wave with an overall slope efficiency of 61% at a pump depletion of 75% when the oscillator was operating at three times above threshold.

Broad-band second-harmonic generation in holey optical fibers

Holey fibers are shown to have an ideal geometry for efficient parametric processes due to their tailorable modal properties. These fibers can have the additional advantage of single-mode operation at all the interacting wavelengths. We demonstrate theoretically that by appropriate choice of holey fiber geometry, these fibers can be up to four orders of magnitude more efficient for second harmonic generation than conventional poled fibers.

Self refractive non-linearities in chalcogenide based glasses

Abstract We report third order non-linear absorption and refraction measurements at 1.20 and 1.52 μm on selected gallium–Lanthanum sulfide-based glasses (Ga:La:S) showing negligible non-linear absorption and a refractive non-linearity close to one hundred times that of SiO 2 . Their potential use in telecommunication as base materials for all-optical switching practical devices is evaluated resulting in large figures of merit. The addition of a glass modifier to the Ga:La:S matrix has improved thermal and optical properties, resulting in ease of fibre drawing. The non-linear optical response of this new variant of the Ga:La:S family is studied.

Efficient frequency doubling of 1.5 /spl mu/m femtosecond laser pulses in quasi-phase-matched optical fibers

Summary form only given. We report on the fabrication of second order nonlinear gratings up to 7.5 cm long for quasi phase matched (QPM) SHG of 1.5 /spl mu/m and their use for ultrashort pulsed frequency conversion. It is shown that periodically poled glass fibres (PPGF) are very promising for QPM-SHG and parametric processes involving highpower laser sources.

Bragg gratings in ternary SiO2:SnO2:Na2O optical glass fibres

Bragg gratings have been written in an optical fiber with a core made from ternary SiO(2): SnO(2): Na(2)O glass and a SiO(2) cladding. The presence of Na(2)O allows for higher concentrations of SnO>(2) , which are believed to be responsible for the photorefractive response of this composition. In these preliminary experiments significant refractive-index modulations, up to 6.2x10(-4) , have been achieved with a 248-nm excimer laser and a phase mask to write gratings for reflectivity at ~1.5microm . The induced refractive-index changes show enhanced temperature stability, and there is no sign of any erasure up to temperatures exceeding 600 degrees C.

ENHANCED PHOTOSENSITIVITY IN GERMANOSILICATE FIBERS EXPOSED TO CO2 LASER RADIATION

We report a novel method to increase the UV photosensitivity of GeO(2): SiO(2) optical fibers based on exposure to CO(2) laser irradiation before grating writing. Fibers treated with a CO(2) laser can produce gratings with refractive-index modulation two times greater and a Bragg wavelength that can be 2 nm longer than those of untreated fibers. Experiments on GeO(2): SiO(2) preform samples treated with a CO(2) laser in a way similar to the fibers showed a marked increase of the 242-nm absorption band, which is associated with an increase of germanium oxygen-deficient centers and is believed to be responsible for the higher photorefractive response.