Titanium Indiffusion Research Articles

Fabrication of titanium in-diffusion waveguide in the PIN-PMN-PT single crystal

Fabrication of the optical waveguide is essential for the application of high-performance relaxor ferroelectric single crystals in broadband integrated electro-optic devices. Here, a multimode titanium in-diffusion planar waveguide is demonstrated in a rhombohedral phase Pb(In1/2Nb2/3)O3–Pb(In1/2Nb2/3)O3–PbTiO3 (PIN-PMN-PT) single crystal. Influences of titanium in-diffusion on the crystalline phase and composition were carefully studied. Guided modes in the planar waveguide were characterized by prism couple measurements. Using the inverse Wentzel-Krames-Brillouin method, the refractive index profile in the waveguide was constructed. The results show that the PIN-PMN-PT crystal retains its single crystal structure and excellent electro-optic response after titanium in-diffusion. The mode refractive index change between the diffused layer and substrate crystal is approximately 3%, which is sufficient to constrain the energy of transmitted light. Moreover, the titanium-diffused PIN-PMN-PT waveguide is confirmed to be a graded optical waveguide with a Gaussian index profile. Our work indicates that the titanium in-diffusion is a feasible way to fabricate waveguides in PIN-PMN-PT crystals, which is of great significance for their application in integrated photonic devices.

Z+/Z- lithium niobate optical waveguide sensitivity related to pyroelectric effect.

Lithium niobate crystal is widely used for the design and fabrication of integrated electro-optic modulators. As a ferroelectric material, one sees its spontaneous polarization change with temperature variations. This phenomenon, known as the pyroelectric effect, induces strong waveguide transmission variations for waveguides realized on Z-cut wafers. Waveguides made by titanium in-diffusion either on the Z+ or Z- side of the crystal show a significant difference in temperature behavior. Experimental data, enlightened by numerical simulations, help to show why Z- waveguides are more immune to temperature changes than Z+ ones.

Design and Modeling of Titanium Indiffused LiNbO<SUB>3</SUB> Waveguides for Optimum Coupling to Communication Grade Fiber

Design and Modeling of Titanium Indiffused LiNbO<SUB>3</SUB> Waveguides for Optimum Coupling to Communication Grade Fiber

Mode Coupling Between Substrate Integrated Waveguide and Coplanar Waveguide for Traveling-Wave Electrooptical Modulator

A traveling-wave electrooptical modulator that makes use of a mode coupling mechanism between a substrate integrated waveguide (SIW) and coplanar waveguide (CPW) is proposed for millimeter-wave (mmW) radio-over-fiber applications. In this structure, SIWs are added at the input/output ports of conventional modulators from which mode conversion and signal transfer take place between lossy CPW traveling-wave electrodes and low-loss mmW SIW terminals. Such a gradual coupling from SIW to CPW in the modulation path creates a nonuniform field overlap integral and gives the ability of using the modulator at higher frequency. A laser micromachining technique for a transparent LiNbO3 substrate and a titanium in-diffusion technique for achieving a good optical field confinement are used to fabricate the SIW and optical waveguide, respectively. The bending structure of the SIW, fabrication of pad resistors, and broadband transitions are considered in the proposed modulator. 7-GHz bandwidth was measured for the proposed modulator at 60 GHz.

Design of Symmetric and Asymmetric 2×2 all Optical Ti: LiNbO3 Machzehnder Interferometric Switches

All optical switches based on electro-optic effect have been in consideration for fast communication and internet serviced networks with higher bandwidth. In this, we have designed and reviewed basic 2×2 all optical switches based on Machzehnder interferometer [Papadimitriou et al., Journal of Lightwave Technology, 21(2), 2003, 354–405] with symmetric and asymmetric (tapered) interferometric arms. All structures have been designed on a channel profile of titanium indiffusion on a lithium niobate substrate [Wooten et al., IEEE Journal of Selected Topics in Quantum Electronics, 6(1), 2000, 69–82]. All considered structure have been analysed for optimizing their sizes and corresponding driving voltages with insertion losses in the range of 3.0–4.5dB and maximum design tolerance up to ±1.5% only.

A novel approach for the analysis of distributed partially proton-exchanged Ti:LiNbO3waveguides

Proton exchange is becoming widely accepted as a complementary technique to titanium indiffusion for the fabrication of optical waveguides on LiNbO3. In this paper, we propose, for the first time to our knowledge, a novel approach to analyze optical distributed waveguides formed by local index variation, combining two processes, titanium (Ti) indiffusion, and localized proton exchange (PE), yielding the distributed parameter waveguides. We present a straightforward extension of the ray-approximation method (RAM) covering the computation of a single diffusion effective index, as well as multiple successive diffusions with a specific graded index profile. The efficiency of the method is shown by varying some of the optical distributed waveguide parameters, such as the index modulation or the proton-exchanged depth. The simulation results in particular show that the evolution of the transmission spectrum is in good agreement with previous experimental results.

Light propagation in double-periodic nonlinear photonic lattices in lithium niobate

Single- and double-periodic one-dimensional photonic lattices are formed in lithium niobate using both titanium in-diffusion and holographic grating recording. We investigate linear band structures and diffraction properties of such superlattices and observe a decrease of discrete diffraction with increasing modulation depth of the second superimposed lattice. In weakly modulated superlattices with tailored diffraction properties, our results demonstrate the formation of discrete solitons having a propagation constant inside the extra mini-gap formed inside the Brillouin zone.

Characterization of erbium doped lithium niobate crystals and waveguides

Optical planar waveguides have been fabricated by the titanium in-diffusion process in lithium niobate crystals activated with erbium ions. The waveguides were studied by m-line technique in order to recover the index profile. The effect of the Ti in-diffusion on the structural and spectroscopic properties of the lithium niobate crystals was investigated by Raman and photoluminescence spectroscopies. The presence of titanium has only minor effects on the vibrational properties of the crystal, and no change in the emission properties of the erbium ions is observed.

Design Methodology for Ti:LiNbO3 Waveguides

The purpose of this work was to develop a design methodology for the fabrication of waveguides in LiNbO3 operating in the single-mode regime at several wavelengths, with specific characteristics required to optimize integrated devices. To achieve this, it is necessary to obtain the relations between the optical characteristics of the waveguides and their respective fabrication conditions, and to introduce models of the waveguide formation process. The relations between fabrication conditions and optical characteristics of planar waveguides realized by titanium in-diffusion are documented extensively in the literature. However, reports on the characterization of waveguide fabrication processes, performed in a systematic way, could not be found, resulting in the need to combine information from several sources. Discrepancies among results from different researches are evident, resulting from different experimental methodologies and calibrations of equipment. Therefore, aiming at extracting a consistent data set, optical characterization techniques for the refractive index profile were employed to study series of samples.

Discrete diffraction and spatial gap solitons in photovoltaic LiNbO3 waveguide arrays

We investigate, experimentally and theoretically, light propagation in one-dimensional waveguide arrays exhibiting a saturable self-defocusing nonlinearity. We demonstrate low-intensity "discrete diffraction", and the high-intensity formation of spatial gap solitons arising from the first band of the transmission spectrum. The waveguide arrays are fabricated by titanium in-diffusion in a photorefractive copper-doped lithium niobate crystal, and the optical nonlinearity arises from the bulk photovoltaic effect.

Characterization of Ti : LiNbO3 waveguides by micro-raman and luminescence spectroscopy

Raman and luminescence spectroscopies are used for non destructive characterization of titanium-diffused LiNbO3 waveguides at the classical resolution of confocal microscopy (0.5×0.5×3 μm). The broadening of Raman lines near the surface permits one to measure the depths of lithium out-diffusion and titanium in-diffusion. The contrast of polaron luminescence makes it possible to control routinely the waveguides just after the diffusion process. Vertical scans give the thickness of the chemically-reduced layer near the surface of the wafer, whereas horizontal scans across the waveguides reveal screening effects by the titanium stripes against surface reduction.

Optical near-field measurements of guided modes in various processed LiNbO3 and LiTaO3 channel waveguides

Scanning near-field optical microscopy (SNOM) technique has been used in collection mode to probe the evanescent field at the surface of channel waveguides fabricated in LiNbO 3 and LiTaO 3 either by ion exchange, titanium in-diffusion or ion implantation. A specific sample holder has been developed on a commercial system. The intensity distribution of guided modes in the different waveguides, and the associated topographical images, have been obtained and compared among them, giving relevant information about the structure of the various waveguides. The effective index of guided modes has been deduced from the measurement of the intensity variation of the evanescent field as a function of the distance from the waveguide surface.

Oscillateur paramétrique optique intégré : revue des réalisations sur niobate de lithium polarisé périodiquement

To realize an IOPO, one need a good nonlinear substrate in which it is possible to realize low-loss waveguides and fulfill the phase-matching conditions. In this paper, I will present the problems researchers have faced, the techniques they have used and the results they have obtained by using either proton exchange or titanium indiffusion to create waveguides in periodically poled lithium niobate.

Ridge waveguides in lithium niobate fabricated by differential etching following spatially selective domain inversion

Ridge structures have been fabricated in z-cut LiNbO3 using the technique of differential etching following spatially selective domain inversion. Waveguides within these ridges have been achieved using the techniques of ion beam implantation, proton exchange, and titanium indiffusion. Using this last method, guides with losses <0.8 dB cm−1 have been realized for light at a wavelength of 1.3 μm. We briefly discuss applications for these structures.

Characterization and performance evaluation of coupled multiwaveguide arrays

A new and effective nonintrusive method for characterization of N coupled waveguides is presented. The method is able to furnish readily the coupling parameters of most significance, and furnishes in addition, a way of assessment of overall device quality and performance. The procedure is based on a semi-empirical implementation of coupled mode theory, by means of which different functions are defined for different input configurations. In a well-functioning device, all these function should attain a common single minimum, out of which the coupling coefficient and additional parameters of the device are deduced. Devices were fabricated on Z-cut LiNbO/sub 3/ crystals by in-diffusion of titanium. The method was applied in order to measure the wavelength and polarization dependence of the coupling coefficient.

Topotaxial Reaction Fronts in Complex Ba-Ti-Si Oxide Systems Studied by Transmission Electron Microscopy

Processes and interface structures occurring during BaTiO 3 sintering in the presence of the sintering aid SiO 2 are studied by model experiments. The formation of fresnoite Ba 2 TiSi 2 O 8 and different Ti-rich barium titanates by solid state reactions proceeding at the (001)BaTiO 3 /SiO 2 interface is followed by XRD and TEM. High resolution transmission electron microscopy (HRTEM) permits the structure to be studied of the various solid-solid reaction fronts involved. The observations indicate, e.g., a certain topotaxial reaction mechanism at the Ba 4 Ti 13 O 30 /BaTiO 3 (001) and Ba 6 Ti 17 O 40 / BaTiO 3 (001) reaction fronts, which comprises the outdiffusion of barium, the indiffusion of titanium and oxygen, and a restacking of the BaTiO 3 {111 }planes.

Thermal fixing of holographic gratings in planar LiNbO 3 :Ti:Fe waveguides

:Ti:Fe waveguides are thermally fixed during hologram recording at elevated temperatures. Different guides are fabricated by titanium indiffusion using iron-doped and nominally pure y-cutLiNbO3 substrates and characterization is performed by dark-mode spectroscopy. The refractive index modulation of gratings written and simultaneously fixed at 180 °C is investigated as a function of propagation depth, titanium and iron concentration. The experimental results are compared with those obtained for unfixed holograms recorded at room temperature.

Phase-conjugate waves generated by anisotropic four-wave mixing in LiNbO3and LiTaO3optical waveguides

We report on anisotropic four-wave mixing in planar optical LiNbO 3 and LiTaO 3 waveguides fabricated by indiffusion of titanium and iron layers. The generation of phase-conjugate waves in the waveguides is demonstrated, and the experimental results are compared to numerical solutions of the corresponding system of coupled wave equations. We observe a different behaviour of the phase-conjugate wave power on pump power in LiNbO 3 and LiTaO 3 waveguides, respectively. While the reflectivity of the signal beam saturates in LiTaO 3 for strong pump beams, there is a distinct increase in LiNbO 3 .

Second-harmonic generation efficiency in periodically poled LiNbO/sub 3/ waveguides

Quasi-phase-matched second-harmonic generation efficiency in periodically poled LiNbO/sub 3/ using titanium indiffusion, has been theoretically investigated. This permits clarifying how the involved guided modes convert the triangle-shaped form of the ferroelectric polarization in the crystal, via the overlap integral between this form and these modes, into an effective periodic nonlinear coefficient. As a consequence, the periodic function that really permits the quasi-phase-matching operation is the modulation of this effective nonlinear coefficient, the shape of which can be far from a triangular shape, as shown using different cases of mode profiles.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Mach-Zehnder interferometer made of strip-loaded outdiffusion guide

The electro-optic (EO) characteristics of the strip-loaded outdiffusion guide (SLOG) [1] are presented. A Mach-Zehnder interferometer using the SLOG technique is fabricated for test. The results show that the EO effect is greatly enhanced and the extinction ratio is also larger compared to those made by the conventional titanium indiffusion technique. Moreover, the fabrication takes less time, yet the waveguide has no surface guide and less damage. Experimental and computer-simulated results are also shown for comparison. © 1992 John Wiley & Sons, Inc.