Electric-field thermally poled optical fibres for quasi-phase-matched second harmonic generation

We report on quasi-phase-matched frequency doubling to the blue in electric-field poled optical fibres. An increase of a factor of ~10 in the conversion efficiency in comparison with the previous results is obtained. Our experiments show that the structure of the induced nonlinear grating is not uniform, both longitudinally and transversely. For this reason the value of the effective nonlinear coefficient is still far from the optimum expected from the measured value, through Maker's oscillation, for a uniformly poled fibre

Frequency doubling in Ga:La:S optical glass with microcrystals

Second harmonic generation in gallium-lanthanum-sulphide (Ga:La:S) and GeS2+Ga:La:S glasses is investigated. It is shown that microcrystals of Ga:La:S and of alpha-phase of gallium-sulphide (alpha-Ga2S3), whose presence in the glass matrix is revealed by x-ray diffraction analysis, are responsible for the frequency doubling process

532nm pumped optical parametric oscillator in bulk periodically poled lithium niobate

We report a quasi-phase-matched optical parametric oscillator pumped by the second harmonic of a single frequency Q-switched Nd:YAG laser. Both the frequency doubling to 532 nm and the parametric oscillation are performed in periodically poled lithium niobate crystals with a nonlinearity of ~15 pm/V. The OPO has been operated in 'singly resonant' and 'doubly resonant' configurations. The threshold in the singly resonant case was ~0.14 J/cm2, more than one order of magnitude below the damage limit. OPO tuning from 945 nm to 1225 nm was achieved by changing both the period of domain reversal (from 6.8 to 6.85µm) and the temperature of the crystal

55% conversion efficiency to green in bulk quasi-phase-matching lithium niobate

High voltage and liquid electrodes were used for periodic poling of lithium niobate. A sample with a period of 6.80 µm was used for first-order frequency doubling of 1064 nm Q-switched Nd:YAG light with an average power conversion of 55%, implying greater than 90% power conversion at the peak of the pulse. The effective nonlinear coefficient for both Q-switched and continuous-wave measurements was ~15 pm/V

Low-threshold picosecond optical parametric oscillation in quasi-phase-matched lithium niobate

We report a singly resonant optical parametric oscillator in periodically poled lithium niobate. synchronously pumped by the second harmonic of an amplified 10 µs pulse train from a continuous wave mode-locked Nd:YLF laser. Pulses of ~2 ps duration have been generated over the tuning range from 883 to 1285 nm with a typical threshold of 200 mW average power within the 10 µs envelope. The M2 beam quality factor for the generated signal was ~1.1, indicating absence of any significant photorefractive damage

Enhanced photosensitivity in germanosilicate fibres exposed to CO₂ laser radiation

We report a novel method to increase the UV photosensitivity of GeO2:SiO2 optical fibers based on exposure to CO2 laser irradiation before grating writing. Fibers treated with a CO2 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 GeO2:SiO2 preform samples treated with a CO2 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

100 MHz Amplitude and Polarization Modulated Optical Source for Free-Space Quantum Key Distribution at 850 nm

We report on an integrated photonic transmitter of up to 100 MHz repetition rate, which emits pulses centered at 850 nm with arbitrary amplitude and polarization. The source is suitable for free space quantum key distribution applications. The whole transmitter, with the optical and electronic components integrated, has reduced size and power consumption. In addition, the optoelectronic components forming the transmitter can be space-qualified, making it suitable for satellite and future space missions.Comment: 6 figures, 2 table

Second-harmonic generation in highly textured LiNbO3 films prepared by pulsed laser deposition

LiNbO3 films have been deposited on (001) sapphire substrates by pulsed laser deposition, in an oxygen environment. Films grown at substrate temperatures of 650°C are crystalline, strongly textured, and show a degree of twining that is lower the higher the oxygen pressure is in the range of 0.5-1 Torr. Values of the nonlinear optical coefficients d33 and d31 of the films, measured via second-harmonic generation, are close to those for the bulk LiNbO3 single crystal. The dependence of both the degree of twining and the nonlinear optical response on the film thickness suggests that the films become closer to single domain for larger thickness. © 2000 American Institute of Physics.Peer Reviewe

Parametric fluorescence in periodically poled silica fibres

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

Electric field poling of quasi-phase-matched optical fibers

Electric field poling of silica glass provides the prospect of efficient second-order nonlinear interactions in optical fibres. Recent advances in quasi-phase-matched second harmonic generation in electric field poled silica fibres are reviewed