M. Wesner

Observation of bright spatial photorefractive solitons in a planar strontium barium niobate waveguide

We have obtained stationary bright spatial solitons in a planar photorefractive strontium barium niobate waveguide for visible light ranging from 514.5 to 780 nm. Even for larger wavelengths (lambda=1047 nm) strong self-focusing of the beam was observed; however, input power had to be some orders of magnitude higher than for visible light for self-focusing to occur. Furthermore, we found transient self-trapping of red light (lambda=632.8 nm) that corresponds to the formation of bright quasi-steady-state solitons.

Observation of dark spatial photovoltaic solitons in planar waveguides in lithium niobate

We have obtained photovoltaic lenses and dark spatial solitons in planar optical waveguides in lithium niobate doped with iron and copper. For TE modes of lower indices the photovoltaic nonlinearity only partly decreased the width of a dark notch within the outcoupled image of the recording light beam. The corresponding time to reach a steady state of this light-induced change ranged from about 0.1 to 30 s depending on the waveguide sample. For higher modes we observed a full compensation of the divergence of the dark notch on a time scale of some minutes. In some cases this was followed by an extinction of the dark solitons because the light was over-defocused in the highest modes.

All-Optical Signal Routing Using Interaction of Mutually Incoherent Spatial Solitons

We propose an all-optical switch or router that is based on the interaction of counterpropagating mutually incoherent spatial optical solitons. The concept is demonstrated experimentally by nonlinear collision of spatial solitons in a photorefractive planar waveguide in strontium barium niobate.

Observation of two-dimensional spatial solitons in iron-doped barium-calcium titanate crystals

Since the discovery of photorefractive spatial solitons [1, 2], these non-diffracting waves have been the subject of an intense research effort, because they are particularly interesting for building alloptical diodes, transistors, switches, and all-optical computers. Until now steady-state bright spatial solitons have been observed in BTO [3], SBN [4], InP:Fe [5], KNbO3 [6], KLTN [7], and BaTiO3 [8] crystals. Barium–calcium titanate (BCT) [9, 10] is a promising photorefractive material and an alternative to BaTiO3, which is much easier to grow and does not have any phase transition within the temperature range from 120 C to 100 C. This crystal also possesses slightly larger electrooptic coefficients r13 (20 pm/V) and r33 (130 pm/V) compared to BaTiO3. However, no studies of photorefractive spatial soliton formation have been reported so far in BCT crystals. In this contribution, we investigate photorefractive spatial soliton formation in iron-doped BCT crystals and observe, for the first time to our knowledge, the formation of steady-state two-dimensional (2D) screening solitons in this material. Samples of the congruently melting composition Ba0:23Ca0:77TiO3 are grown in the crystalgrowth laboratory of the Department of Physics at the University of Osnabr€uck [9, 10]. The dimension of our sample that is doped with 290 ppm Fe is 5 5 5 mm3. All surfaces are polished to optical quality. On both faces normal to the c-axis of the crystal, electrodes are prepared with silver paste. The light propagates along the a-axis in our experiment. Our experiments are conducted in a standard setup for soliton formation, in which an external electric field E0 is applied along the ferroelectric c-axis. A frequency-doubled Nd:YAG laser (l 1⁄4 532 nm) is used as the light source. Because of the low dark conductivity of our sample sd 6 10 14 W 1 cm 1 [9], a background illumination is necessary to tune the degree of saturation of the nonlinearity. This ordinarily polarized background light of the same wavelength 532 nm is made spatially incoherent by passing it through a rotating diffuser. The ratio r between the soliton light intensity (extraordinary polarization) and the background irradiance is r 5. The soliton intensity is always kept below 50 mW/cm2 to minimize photovoltaic self-defocusing. Figure 1 shows a characteristic result of 2D soliton formation. In this experiment, the beam intensity is I 30 mW/cm2. The beam diameter at the crystal’s input face is din 14 mm. Without an external electric field E0 applied, the beam width d increases during propagation due to both, phys. stat. sol. (a) 189, No. 1, R4–R5 (2002)

Dark spatial optical solitons in lithium niobate waveguides

We have realized dark spatial photovoltaic solitons at wavelength of 632.8 nm in Fe and Cu - doped planar optical waveguides in lithium niobate. It has been shown that for lowest TE modes the photovoltaic nonlinearity only partly compensated the light diffraction effect at the experimental conditions used. The development time of corresponding light-induced photovoltaic lenses ranged from 0.1 s to 30 s depending on the waveguide sample. For the highest TE modes we observed the exact compensation of diffraction effects in the time scale of some minutes followed in some cases by the termination of dark solitons formed because of the light overdefocusing.

Bright photorefractive spatial solitons in barium-calcium titanate crystals

We report the experimental investigation both, of the one - dimensional and two - dimensional bright screening spatial solitons in a promising photorefractive crystal of barium - calcium titanate doped with iron. The effects of the partial trapping of the spatially incoherent ordinarily polarized background light within the soliton - induced planar waveguide as well as the regular oscilations of the light beam intensity and width during the beam self - focusing are observed. For the crystal sample, doped with higher dose of iron (290 ppm), we also find the self - defocusing of light beams due to the light - induced negative photovoltaic lens in the absence of the externally applied electric field.

Formation of photorefractive spatial solitons in barium-calcium titanate crystals

The one-dimensional bright spatial screening solitons in a promising photorefractive crystal of barium-calcium titanate doped with iron are experimentally investigated. The effects of the regular oscillations of the light beam intensity and width during the beam self-focusing and in the soliton regime are observed. For the crystal sample, doped with higher dose of iron (290 ppm), we also find the self-defocusing of light beams due to the light-induced negative photovoltaic lens in the absence of the externally applied electric field. (Summary only available)

Electrical fixing of waveguide channels using dynamic self-focusing in strontium-barium niobate crystals

Summary form only given. We investigate the electrical fixing of one- and two-dimensional waveguides in both bulk samples and planar waveguides of strontium-barium niobate (SBN60). Planar waveguides are fabricated by He/sup +/ implantation, resulting in an about 5 /spl mu/m-thin waveguiding layer. Electrical fixing of waveguide channels is achieved as follows. Firstly, all crystals are homogeneously polarized by applying an electric field along the c-axis. After this, the samples are illuminated with focused extraordinarily polarized light (514.5 nm) propagating perpendicular to the c-axis. A typical diameter of the focused beam on the input face is 10 /spl mu/m. Thus the beam diffracts strongly during propagation through the sample. Either a one-dimensionally focused beam (for fixing planar waveguides in bulk samples) or a two-dimensionally focused beam (for fixing channel waveguides in bulk or waveguide samples, respectively) is used. At the same time, the whole crystal is illuminated by an ordinarily polarized background beam from the top. The intensity ratio of focused and background beam is about 100.

Infrared photorefractive effects in ion-implanted SBN waveguides

Summary form only given. The nonlinear response of photorefractive crystals at wavelengths around 1.3 and 1.5 /spl mu/m is of importance for applications in all-optical telecommunication systems. However, in general most photorefractive crystals are sensitive only for visible light. Previous attempts to extend the nonlinear response up to 1550 nm have been made in KNbO/sub 3/. In our contribution we investigate the properties of strontium-barium niobate SrBaNb/sub 2/O/sub 6/ (SBN) crystals in the near infrared up to telecommunication wavelengths.

Bright photorefractive spatial solitons in optical waveguides on SBN

The steady-state bright spatial solitons have been realized in a planar photorefractive strontium-barium niobate waveguide for visible light, ranging from 514.5 to 780 nm. The build-up time of the steady-state condition was about 1 s. For the wavelength of 1047 nm, the strong self-focusing of a light beam was observed. In the time scale of several tens of milliseconds the transient self-trapping of red light was observed, which corresponds to the regime of quasi-steady-state solitons. The interaction of the steady- state spatial solitons has also been demonstrated at He-Ne laser wavelengths.