Lutz Beckers

Structural and optical characterization of epitaxial waveguiding BaTiO3 thin films on MgO

Epitaxial waveguide structures of c-axis oriented BaTiO3 thin films on MgO(001) have been grown by pulsed laser deposition. The structural properties of the samples have been characterized by Rutherford backscattering spectrometry/ion channeling (RBS/C), x-ray diffraction, and atomic force microscopy. We found excellent crystalline quality even up to thicknesses of a few microns. This has been confirmed by RBS/C minimum yield values of 2%–3%, a full width at half maximum of 0.36° of the BaTiO3 (002) rocking curve, and a rms roughness of 1.1 nm for a 950 nm BaTiO3 film. The out-of-plane refractive index was measured to be close to the extraordinary bulk value with the birefringence being about one third of the bulk value. Waveguide losses of 2.9 dB/cm have been demonstrated.

A highly long-term stable silicon-based pH sensor fabricated by pulsed laser deposition technique

Abstract A highly long-term stable pH sensor based on a capacitive electrolyte insulator semiconductor heterostructure has been developed. The pH-sensitive gate insulator material Al2O3 has been deposited by means of the pulsed laser deposition technique. The basic characteristics of the sensor device, such as pH sensitivity, stability, selectivity, sensor drift and response time have been investigated using capacitance/voltage measurements. Furthermore the physical structure and the stoichiometric composition of the deposited Al2O3 layers have been studied by Rutherford backscattering spectrometry, ion channeling and transmission electron microscopy. According to the results obtained during a measurement period of more than 600 days, the sensor possesses a high pH sensitivity of about 56 mV/pH including a small baseline drift of the sensor signal of less than 1 mV per day.

Epitaxial BaTiO3 thin films on MgO

Abstract The epitaxy of thin films of BaTiO3 is motivated by the potential integration of electrooptical functions onto silicon. An epitaxial buffer layer of MgO on Si will be needed for optical waveguide formation and for enabling the growth of BaTiO3. In a first step, epitaxial waveguide structures of c-axis oriented BaTiO3 thin films on MgO (001) have been grown by pulsed laser deposition (PLD). The structural properties of the samples have been characterized by Rutherford backscattering spectrometry/ion channeling (RBS/C) and X-Ray diffraction (XRD). We found excellent crystalline quality even up to a thickness of a few microns. Waveguide losses of 2.9 dB cm−1 have been demonstrated.

Blue‐light second‐harmonic generation in ion‐implanted KNbO3 channel waveguides of new design

We report phase‐matched second‐harmonic generation in KNbO3 channel waveguides. The guides were fabricated by one single homogeneous He+ ion irradiation and specially structured photoresist on the KNbO3 crystals serving as an implantation mask. The mask enabled the formation of channel guides with a trapezoidal‐shaped cross section providing simultaneous confinement of both TE and TM modes. 2.6 mW second‐harmonic blue‐light at 441 nm was generated in a 5.8‐mm‐long guide for an incident fundamental power of 280 mW.

Photorefractive effect in proton-implanted Fe-doped KNbO 3 waveguides at telecommunication wavelengths

We report on photorefractive two-beam coupling in proton-implanted Fe-doped KNbO3 waveguides at wavelengths from 632.8 to 1550 nm. Exponential gain coefficients of 11 and 0.9 cm-1 were measured at wavelengths of 632.8 nm and 1550 nm, respectively. Photorefractive response times as low as 120 µs are reported at 632.8 nm for a pump power of 4 mW. It is shown that proton irradiation increases the effective trap density, decreases the response time, and extends the photorefractive sensitivity of Fe-doped KNbO3 crystals toward near-infrared wavelengths.

Mode propagation losses in He + ion-implanted KNbO 3 waveguides

The losses of ion-implanted potassium niobate (KNbO3) waveguides are evaluated theoretically and experimentally in dependence on wavelength, irradiation dose, waveguide thickness, and waveguide width. Irradiation-induced absorption and tunneling are identified as the main sources of loss. The contributions from surface scattering and intrinsic material absorption are shown to be small. The attenuation due to irradiation-induced absorption and tunneling is calculated from the experimentally determined complex refractive-index profile. The optical loss is minimum in the red part of the spectrum and increases toward the blue because of absorption and toward the infrared because of tunneling. A minimum loss of less than 0.2 cm-1(1 dB cm-1) was measured in an ion-implanted KNbO3 waveguide at a wavelength of 0.633 μm. On the basis of a theoretical model we give guidelines for the formation of optimized waveguides for specific applications, e.g., second-harmonic generation.

The refractive index distribution nc(z) of ion implanted KNbO3 waveguides

Abstract We have analysed by means of dark and bright light spectroscopy the c-polarised mode spectra of KNbO 3 planar waveguides. These waveguides were fabricated by He + ion implantation with ion doses from 2.5 × 10 14 to 3 × 10 15 cm −2 and ion energies from 1 to 2.9 MeV. A quantitative model is derived to correlate the index profile of n c with the implantation parameters. The results are in excellent agreement with profiles observed by measuring the surface reflectivity of wedge polished samples. The test of the mode spectra after partial surface stripping by ion sputtering does not evidence irregular structures in the index profile.

Birefringence phase-matched blue light second-harmonic generation in a KNbO3 ridge waveguide

Ridged channel waveguides in KNbO3 were fabricated by a technique using He+ ion implantation, photolithographic masking, and subsequent Ar+ ion sputtering. A continuous-wave second-harmonic output power of 14 mW at 438 nm was obtained with an in-coupled fundamental power of 340 mW in a 0.73 cm long waveguide. Phase matching was provided by material birefringence without need of periodic poling.

Linear and nonlinear optical properties of KNbO3 ridge waveguides

Ridged channel waveguides in KNbO3 were produced using He+ ion implantation, photolithographic masking, and subsequent Ar+ ion sputtering. We investigated the linear and nonlinear optical characteristics of the waveguides. The effective mode indices are derived from the refractive index profiles using the effective index method. The losses are investigated as a function of wavelength and of the geometrical parameters channel width and ridge height. A minimum loss of 2 dB cm−1 is measured at a wavelength of 0.633 μm. We investigated the power handling capabilities at visible and near-infrared wavelengths. Second-harmonic generation in these waveguides is studied both theoretically and experimentally with regard to its dependence on the guide fabrication parameters. Phase-matching configurations for blue light second-harmonic generation are evaluated on the basis of the dispersion of the effective mode indices. Overlap integrals are calculated on the basis of the field distributions derived from the refract...

Potassium niobate waveguides : He+ implantation in bulk single crystals and pulsed laser deposition of thin films

Abstract We present a new mask design and implantation scheme, which uses a single ion implantation step of 2 MeV He ions at a dose of 7×10 14 to 3×10 15 He cm −2 to form channel waveguides in single crystal KNbO 3 . The special processing of the photoresist mask enables the formation of channel waveguides with a trapezoidal-shaped cross section, providing for the first time simultaneous confinement of both TE and TM modes in a permanent KNbO 3 channel waveguide. Second-harmonic blue light (2.6 mW) at 441 nm was generated in a 5.8 mm long guide for a fundamental power of approximately 200 mW. In the second part of the paper, we demonstrate the deposition of single crystal KNbO 3 films on SrTiO 3 and BaTiO 3 /MgO substrates by Pulsed Laser Deposition (PLD). Technologically interesting optical materials such as BaTiO 3 and KNbO 3 are difficult to grow as single crystals of large dimensions. Thin film techniques can overcome this problem by synthesizing these materials on commercially available substrates.