Kazumi Kawamoto

Dependence of Lattice Constant Deviation and Refractive Index on Proton Concentration in Proton-Exchanged Optical Waveguides on a Single Crystal of LiNbO3

The lattice constant deviation and refractive index change of proton-exchanged optical waveguides fabricated on a single crystal of LiNbO3 are discussed in relation to the proton concentration. The exchange rate x of Li+ with H+ has been determined by nuclear reaction analysis and the lattice constant deviation has been measured by means of the double crystal X-ray diffraction method. The value of x in the samples proton-exchanged with the benzoic acid/lithium benzoate melts is in the range of 0.55 0.55. The dependence of the refractive index change on x is very similar to that of the lattice constant deviation. Reasons for the refractive index change caused by proton exchange are discussed.

RELATIONSHIP BETWEEN PROPAGATION LOSS AND CRYSTALLINITY IN PROTON-EXCHANGED AND ANNEALED LINBO3 OPTICAL WAVEGUIDES

The propagation loss of proton-exchanged and annealed LiNbO3 optical waveguides was studied in relation to the change in the crystal phase. With annealing at relatively low temperatures (≤325°C) or for a short time (at 375 or 400°C, ≤15 min), the propagation loss increases. Annealing at relatively high temperatures (375 to 400°C) for a longer time (30 to 45 min) greatly reduces the propagation loss. The reasons for the increase in propagation loss with insufficient annealing is the deterioration of crystallinity due to changes in the crystal phase and the coexistence of two different crystal phases.

The dependence of the diffusion coefficient on the proton concentration in the proton exchange of LiNbO3

The concentration-dependent diffusion coefficient for proton-lithium counter-diffusion is studied in this paper. Depth profiles of the proton concentration for proton-exchanged LiNbO3 were measured by secondary ion mass spectroscopy (SIMS). The concentration-dependent diffusion coefficient for the proton-lithium counter-diffusion was calculated by the Boltzmann-Matano method and the relationships between the diffusion coefficient, the proton-exchange process, and the crystal phases in proton-exchanged LiNbO3 were examined. To confirm the validity of the diffusion coefficient calculated from the SIMS data, the depth profiles of the proton concentrations were numerically computed with the calculated diffusion coefficient and the exponential dependence of the diffusion coefficient on the content of lithium benzoate for dilution was reproduced.

An Optical Deflector Using Collinear Acoustooptic Coupling Fabricated on Proton-Exchanged LiNbO3.

We fabricated a collinear acoustooptic deflector on proton-exchanged LiNbO3 with the objective of achieving high-speed seeking and track-following in optical disk drives. In order to obtain a high-efficiency deflector, we studied the electromechanical coupling coefficient Keff2 in proton-exchanged LiNbO3 experimentally and found that proton exchange greatly reduces Keff2 but annealing can gradually restore the value of Keff2. The collinear acoustooptic deflectors fabricated under suitable annealing conditions had optimum properties for an optical pickup application. The other effects of the annealing are also discussed in detail.

Magnetooptical Signal Calculation with Simplified Substrate Birefringence Model

Uniform birefringence is introduced into a simple scalar magnetooptical signal simulation model for polycarbonate substrates. Several effects of vertical and lateral birefringence such as astigmatism, elliptical polarization distribution, reduction of the signal amplitude and DC offset, are discussed.

Noise properties of quasi-phase-matched second-harmonic radiation pumped by a laser diode with a grating feedback

The noise properties of quasi-phase-matched second-harmonic radiation with a grating feedback are studied for three different optical configurations. In multimode operation at a relatively low feedback rate from the grating to the laser diode the relative intensity noise for second-harmonic radiation is large. In single-mode operation at a high feedback rate it can be reduced to less than −130 dB/Hz. The critical value of feedback rate for the single-mode operation is the least, ∼8%, in the self-phase-matched configuration. The mechanism of second-harmonic noise under the multimode operation and the differences in the noise properties for these three configurations are also discussed.

FABRICATION OF A PERIODICALLY DOMAIN-INVERTED STRUCTURE IN LINBO3 THIN FILM BY A DOMAIN-TRANSFER TECHNIQUE

A new technique to fabricate a periodically domain‐inverted structure in LiNbO3 is reported. This structure, fabricated by Ti indiffusion on a LiNbO3 substrate, is transferred in a LiNbO3 thin film grown by liquid phase epitaxy. As the growth temperature decreases below 690 °C, the cross section of the inverted domain changes from a reversed trapezoidal to a rectangular shape.