Germano Montemezzani

Tailoring of infrared photorefractive properties of Sn 2 P 2 S 6 crystals by Te and Sb doping

The photorefractive properties of Sn2P2S6 crystals doped with Te and Sb in the near-infrared wavelength range up to 1064 nm are reported. The main photorefractive parameters, i.e., two-wave mixing gain, effective electro-optic coefficient, diffusion length, concentration of traps, and response time, are compared with conventional nominally pure Sn2P2S6. Te-doped Sn2P2S6 shows the fastest response with the smallest decrease of the photorefractive efficiency with increasing wavelength in the near infrared. Sb doping, on the other hand, inhibits photorefraction in the near infrared. Sn2P2S6:Te and Sn2P2S6:Sb crystals both show a high two-wave mixing gain Γ at 633 nm, and 10 and 20 cm−1. Te-doped Sn2P2S6 shows a photorefractive gain of 4.5 cm−1 at 1064 nm. Response times at 1064 nm of 20 ms have been measured for the intensity 6 W/cm2, which is 2 orders of magnitude shorter than in Rh-doped BaTiO3.

Stoichiometric LiTaO3 for Dynamic Holography in Near UV Wavelength Range

LiTaO3 single crystals with near-stoichiometric composition are grown using a double crucible Czochralski method equipped with an automatic powder supply system. Their photorefractive properties are compared with those of LiTaO3 crystals grown from the congruent composition melt. Two beam coupling experiments show that nearly stoichiometric LiTaO3 crystals exhibit considerably higher photorefractive gain, speed and sensitivity than conventional congruent crystals. Due to the relatively large photoconductivity observed at near UV wavelengths, stoichiometric crystals are further characterized by small photogalvanic fields, making them very attractive for dynamic holography in this wavelength range.

Planar achromatic multiple beam splitter by adiabatic light transfer

We introduce a novel achromatic and robust scheme for n-fold multiple beam splitting based on adiabatic light transfer in a planar geometry of coupled waveguides (WGs). The concept is experimentally verified for a one-to-three beam splitter by using a reconfigurable light-induced WG structure at two operating wavelengths. The demonstrated planar-type achromatic beam splitter opens new opportunities for the realization of ultra-high bandwidth on-chip photonic devices.

Optical and Electro-Optical Properties of Sn 2 P 2 S 6

We report on the rotation of the indicatrix in the mirror plane and the refractive indices of Sn₂P₂S₆ single crystals in the wavelength range 550-2200 nm at room temperature. Electro-optical properties of Sn₂P₂S₆ were also measured by direct interferometric technique for electric fields applied parallel to the crystallographic x-axis that lies near the spontaneous polarization vector. The room temperature free electro-optical coefficient r₁₁₁ ^T reaches 174plusmn10 pm/V at lambda=633 nm and shows only weak dispersion in the wavelength range between lambdaap0.6... 1.3mum. The temperature dependence of the electro-optical coefficients near the structural phase transition at T_C=65degC is well described by a Curie-Weiss law with a peak value r₁₁₁ ^Tcong4500 pm/V

Third column electro-optical coefficients of monoclinic Sn 2 P 2 S 6

All coefficients of the third-column of the unclamped electro-optic tensor of Sn2P2S6 single crystals are determined by direct interferometric techniques. It is found that the largest coefficient r113T for electric field parallel to the z-axis is ≈ 67 pm/V at the wavelength of 633 nm and room temperature.

All-Optical Control of Nonlinear Pattern Modes by Periodic Photonic Structures

We present experimental studies on manipulation of modulational instability in a nonlinear dissipative feedback system by a one- and two-dimensional periodic photonic lattice. In particular, we study the control of intrinsic instability modes of a photorefractive single feedback mirror system, by an optically induced lattice with variable parameters. By tuning the lattice strength and periodicity, we can induce patterns of particular geometry, suppress the modulational instability modes, or control the pattern orientation in the transverse plane.

Dynamical light induced waveguides by interband photorefraction

Dynamical waveguides are produced via the interband photorefractive effect in a pure KNbO3 crystal by illumination with ultraviolet light. The guiding of a red laser beam is demonstrated. Buildup- and decay times of the waveguides are on the order of a few μS. By reconfiguring the waveguide, different waveguide structures, such as a Y-branch, are easily realized

Low drive voltage electro-optic Bragg deflector using a periodically poled lithium niobate planar waveguide

An electro-optic Bragg light deflector is demonstrated in a thinned, periodically poled lithium niobate planar waveguide confined between two silica layers on a silicon substrate. More than 97% of diffraction efficiency is obtained with an operating wavelength of 633 nm for the two orthogonal light polarizations with a drive voltage of about 5 V. The temporal electric drift and the response time of the component are also studied.

Robust and broadband frequency conversion in composite crystals with tailored segment widths and χ (2) nonlinearities of alternating signs

We propose an efficient, robust, and broadband nonlinear optical frequency conversion technique, which uses segmented crystals constructed in analogy with the composite pulses in nuclear magnetic resonance and quantum optics. The composite crystals are made of several macroscopic segments of nonlinear susceptibilities of opposite signs and specific thicknesses, which are determined from the condition to maximize the conversion efficiency with respect to variations in the experimental parameters. These crystals deliver broadband operation for significantly lower pump intensities than single bulk crystals. We demonstrate this technique by numerical simulation of sum-frequency generation in MgO:LiNbO3 crystal.

Fs laser ablation of DAST

High rate femtosecond laser ablation of the highly nonlinear active organic crystal DAST has been demonstrated. The threshold fluence and the ideal fluence range for damage free ablation at several wavelengths have been determined and the quality of the produced grooves has been investigated.