Detlef Kip

Modulation Instability and Pattern Formation in Spatially Incoherent Light Beams

We report on the experimental observation of modulation instability of partially spatially incoherent light beams in noninstantaneous nonlinear media and show that in such systems patterns can form spontaneously from noise. Incoherent modulation instability occurs above a specific threshold that depends on the coherence properties (correlation distance) of the wave packet and leads to a periodic train of one-dimensional filaments. At a higher value of nonlinearity, the incoherent one-dimensional filaments display a two-dimensional instability and break up into self-ordered arrays of light spots. This discovery of incoherent pattern formation reflects on many other nonlinear systems beyond optics. It implies that patterns can form spontaneously (from noise) in diverse nonlinear many-body systems involving weakly correlated particles, such as atomic gases at (or near) Bose-Einstein condensation temperatures and electrons in semiconductors at the vicinity of the quantum Hall regime.

Observation of staggered surface solitary waves in one-dimensional waveguide arrays.

The observation of nonlinear staggered surface states at the interface between a substrate and a one-dimensional self-defocusing nonlinear waveguide array is reported. Launching of staggered input beams of different power in the first channel of the array results in formation of localized structures in different channels. Our experimental results are confirmed numerically.

Fabrication and application of holographic Bragg gratings in lithium niobate channel waveguides

Permanent refractive-index gratings in waveguide devices are of high potential for optical communication systems that make use of the high spectral selectivity of holographic filters, e.g. dense wavelength division multiplexing (DWDM), optical sensors, or narrow-bandwidth mirrors for integrated waveguide lasers. In this contribution we review our results on holographically recorded refractive-index gratings in Cu-doped LiNbO3 channel waveguides. Elementary holograms are recorded with green light and read in reflection geometry in the insensitive infrared wavelength region around 1.5 μm. To enable long-term stability of the Bragg gratings a thermal fixing technique is applied. In this way strong and almost permanent refractive-index gratings are obtained and their application as narrow-bandwidth filters for DWDM applications is demonstrated. In comparison with Bragg gratings in silica fibres, the electro-optic effect in LiNbO3 allows for a direct wavelength tuning and a fast, reliable electrical switching of these gratings.

Direct laser writing of surface reliefs in dry, self-developing photopolymer films.

Fabrication of surface reliefs is achieved by raster scanning dry photopolymer films under a focused laser beam. The formation of the structure takes place subsequent to illumination without any chemical treatment or wet processing. Computer-generated optical elements can be recorded quickly, easily, and at low cost. The technology is particularly well suited for rapid prototyping and design purposes. These photopolymer films have potential in photonics applications, such as diffractive optical elements and waveguide structures.

(1+1)-Dimensional modulation instability of spatially incoherent light

We present a comprehensive study of the one-dimensional modulation instability of partially spatially incoherent light in noninstantaneous self-focusing media. For this instability to occur, the nonlinearity has to exceed a specific threshold that depends on the coherence properties of the beam. Above this threshold a uniform-intensity partially spatially coherent wave front becomes unstable and breaks up into periodic trains of one-dimensional stripes.

Observation of two-dimensional multimode solitons.

We present the first experimental observation of (2+1) -dimensional multimode (composite) solitons. A single-hump component and a double-hump (dipole-type) component are jointly self-trapped as a composite soliton in a biased photorefractive crystal.

Low-loss planar optical waveguides in strontium barium niobate crystals formed by ion-beam implantation

Planar optical waveguides have been formed in strontium barium niobate single crystals by either proton or heliumion implantation. The profiles of the ordinary and the extraordinary refractive indices are deduced from dark-line mode spectroscopy. Optical barriers with depths to Deltan(e) = 2.6% for protons and Deltan(e) = 5.5% for helium are obtained. By proton implantation we find a very low intensity loss of 0.4 cm(-1) for ordinarily and a higher value of 2.7 cm(-1) for extraordinarily polarized light at 632.8 nm. For helium-implanted waveguides both values are ~4 cm(-1).

Optical channel waveguides in Nd:YVO4 crystal produced by O+ ion implantation

In this letter, we report on optical channel waveguides in Nd:YVO4 crystals produced by photographic masking and following direct O+ ion implantation at 3.0MeV. Annealing treatments of the samples are performed to improve the waveguide stability and to reduce losses. An increase of the ordinary refractive index induced by the implantation is believed to be responsible for waveguide formation. Quasi-TM guided modes are observed, while no quasi-TE ones are detected. The optical damping coefficients are of 0.43, 0.63, and 0.54cm−1 for channel waveguides with widths of 4, 5, and 6μm, respectively. The result of modal analysis is in agreement with the experimental data.

Self-stabilized holographic recording in LiNbO3:Fe crystals

Abstract We describe the self-stabilized holographic recording in Fe-doped LiNbO 3 crystals reaching almost 100% diffraction efficiency using weak interfering beams of 514.5 nm wavelength, even for relatively low light pattern modulation values. The evolution of the recording process is shown to be adequately described by a simple mathematical formulation based on Kogelniks coupled-wave theory in spite of the dynamic nature of the recording process. Crystal parameters computed from this experiment are compared to the available data from literature.

Nonvolatile holographic storage in iron-doped lithium tantalate with continuous-wave laser light

Holograms have been recorded in congruent LiTaO(3):Fe with continuous-wave laser light by use of a two-step process. Blue gating light (lambda=488 nm) sensitizes the crystals for holographic recording with red light (lambda=660 nm) of a diode laser. Refractive-index changes of as much as 1.0x10(-5) are achieved for intensities of the red light of 1 W/cm(2) . The saturation values are proportional to the intensity of the writing light. Nondestructive readout with red light is possible, and the holograms remain erasable for blue light.