Gunnar Arvidsson

Blue light generated by frequency doubling of laser diode light in a lithium niobate channel waveguide

Blue light was generated in a LiNbO/sub 3/ channel waveguide by frequency doubling radiation from a laser diode in a guided to guided wave interaction, utilizing first-order quasi-phase-matching in a periodically domain inverted structure. A fabrication method that does not depend on the use of titanium was used. A periodic pattern of silicon oxide on the positive c-face of LiNbO/sub 3/ was used in combination with a heat treatment to achieve a periodic outdiffusion and domain reversal in the surface layer. A channel guide was subsequently formed by proton exchange.<<ETX>>

Fabrication of periodically domain-inverted channel waveguides in lithium niobate for second harmonic generation

A method to produce periodically domain-inverted channel waveguides in LiNbO/sub 3/ is reported. With this type of waveguide, using quasi-phase matching (QPM), arbitrary wavelengths can be frequency doubled by choosing the appropriate period. It is concluded that, with improved fabrication methods, it will be possible to generate milliwatts of blue light with a diode laser as pump, which is of considerable interest. >

Wet etching of proton-exchanged lithium niobate-a novel processing technique

It is known that in proton-exchanged wave-guides in lithium niobate,1 the crystal structure is modified. We demonstrate that proton-exchanged regions on the c+-face can be etched away selectively using a mixture of HF and HNO3. In this way it is possible to form, for example, a groove with a smooth bottom surface. The unexchanged c+-face of lithium niobate is only very slowly etched by this acid.

Influence of randomly varying domain lengths and nonuniform effective index on second-harmonic generation in quasi-phase-matching waveguides

The degradation of second-harmonic generation in quasi-phase-matching waveguides, when random errors occur in the domain boundary position and when the effective index varies along the waveguide, is studied theoretically. Two models for random errors are used, one assuming independent shifts of the domain boundaries and one assuming independent domain lengths. Only the influence of random errors following the statistics in the second model might be of any significance in practical implementations. It is shown that in this case the normalized output power is a decreasing function of the product of the number of domains and a relative variance of the stochastic disturbances. If the difference in effective indices between the interacting modes varies along the waveguide, the same kind of ripple that has been observed in birefringence phase matching occurs.

Frequency doubling in Ti:MgO:LiNbO 3 channel waveguides

Second-harmonic generation (SHG) in channel waveguides fabricated by titanium diffusion into MgO-doped lithium niobate is studied. A conversion efficiency for SHG of 2.4%/W has been obtained for a 16-mm-long waveguide by using a Nd:YAG laser as pump source. The conversion efficiency is lower than the theoretical prediction. This difference is attributed to inhomogeneities along the waveguide. The channel waveguides used carried several modes at the second-harmonic wavelength; those modes, phase matched above room temperature (~80°C), showed substantially lower sensitivity for photorefractive damage than others phase matched at room temperature.

Periodic Structures For Phase-Matching In Second Harmonic Generation In Titanium Lithium Niobate Wave Guides

Use of periodic modulation of lithium niobate waveguide properties to achieve phase-matching for second harmonic generation has been investigated both theoretically and experimentally. The mathematical description has been reduced to the same form of differential equations as for the unperturbed case, but with a modified coupling coefficient. A compact expression for the conversion efficiency has been derived for the case when simultaneous modulation of both the linear and nonlinear properties are taken into account. For the case of modulation of only the linear properties, second harmonic light has been obtained experimentally.

Second-harmonic generation in quasi-phase-matching waveguides with a multimode pump

Second-harmonic generation of blue light in quasi-phase-matching waveguides is analyzed with respect to the linewidth of the pump radiation. From the coupled-wave equation, when the pump linewidth is small, the conversion efficiency is shown to be enhanced by a factor of 2, compared with a single-mode case. A degradation of 3 dB occurs for a linewidth of three times the acceptance bandwidth. We also analyze the influence of the pump spectrum on measurements when the frequency response of a waveguide is evaluated by tuning the fundamental wavelength or by measuring the spectrum of the generated second-harmonic radiation.

Influence of various imperfections on the conversion efficiency of second-harmonic generation in quasi-phase-matching lithium niobate waveguides

The generation of coherent blue light by frequency doubling of radiation from semiconductor lasers in quasi-phase-matching lithium niobate waveguides has recently been demonstrated, but with a conversion efficiency significantly lower than the theoretically predicted value. We have experimentally investigated the performance of some quasi-phase-matching waveguides by measurements of the second-harmonic power and the integral of the second-harmonic power with respect to the fundamental wavelength at a wavelength scan. These experimental results are combined with a theoretical analysis. It is concluded that the inhomogeneities in the effective index, the absence of domain inversion in some regions along the waveguide, and the suppression of the nonlinearity that is due to the proton exchange process are the most important imperfections to deal with in the future optimization of the domain inversion process and the waveguide formation.

Postfabrication changes and dependence on hydrogen concentration of the refractive index of proton‐exchanged lithium tantalate waveguides

Postfabricationchanges and dependence on hydrogen concentration of the refractive index ofproton-exchanged lithium tantalate waveguides

Near- to mid-infrared picosecond optical parametric oscillator based on periodically poled RbTiOAsO(4).

We describe a Ti:sapphire-pumped picosecond optical parametric oscillator based on periodically poled RbTiOAsO(4) that is broadly tunable in the near to mid infrared. A 4.5-mm single-grating crystal at room temperature in combination with pump wavelength tuning provided access to a continuous-tuning range from 3.35 to 5microm , and a pump power threshold of 90 mW was measured. Average mid-infrared output powers in excess of 100 mW and total output powers of 400 mW in ~1-ps pulses were obtained at 33% extraction efficiency.