A refractive index sensor based on a three-layered polymeric waveguide was proposed and demonstrated. A high-index
thin film in TiO<sub>2</sub> was placed on top of the waveguide in the sensing region, playing the role of strengthening the
evanescent field to enhance the sensitivity of the sensor. The refractive index of the analyte applied to the surface of the
sensor was estimated by observing the count of the polarimetric interference between the TE and TM polarizations,
which is manifested as a periodic variation in the optical output of the sensor. For a fabricated sensor involving a 20 nm
thick TiO<sub>2</sub> film, the sensitivity was found to be equivalent to 1.8x10<sup>-3</sup> RIU. It was found to be enhanced by increasing the
thickness of the high-index overlay to a certain degree.
The investigation of physical properties of new relaxor ferroelectric material of (1-x)Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-xPbTiO<sub>3</sub> (PMN-PT) single crystal has been carried out. It has been established the opportunity of existence of this crystal in two modifications, having tetragonal unit cell (space group P4mm) and cubic perovskite one (space group Pm3m) accordingly. Their lattice parameters were found. It has been established a thermal stability of the PMN-PT single crystals in wide temperature range (20-950°C). The results of optical investigations have shown, that the crystals have good transparency in wide spectral area from the visible to IR range. Dispersion of refractive index of PMN-PT crystal are calculated by the dispersion theory and Kramers-Kronig' relationship. Using interferometry method, extremely large linear electro-optic coefficients r<sub>13</sub>~33 pm/V and r<sub>33</sub>~80 pm/V were characterised for the crystal, having tetragonal unit cell. It has been discussed prospects of the material while creating different optical systems.
We have demonstrated all-optical wavelength-selective single- and dual-channel dropping and wavelength conversion in a periodically poled Ti:LiNbO<sub>3</sub> waveguide which has two second-harmonic phase-matching peaks by cascaded sum and difference frequency generation (cSFG/DFG). Less than -17 dB of channel dropping extinction ratio was observed with coupled pump power of 325 mW and the wavelength conversion efficiency was measured to be -7 dB with coupled pump power of 233 mW.
The Nd:YVO4 single crystal was successfully grown by the Edge-defined film-fed growth (EFG) method. The crystal grown process was described in detail. The absorption and photoluminescence according to concentration of Nd ions in the Nd:YVO4 crystal have been measured. The wavelength of stronger absorption peak appeared around 596 nm, and that of the photoluminescence was the stronger at 879 nm.
Er and Mg co-doped LiNbO<sub>3</sub> single crystal with a melt concentration of 1, 3 mol% MgO and 0.6 mol% Er<sub>2</sub>O<sub>3</sub> have been grown by the micro-pulling down method to study the Er and Mg incorporation into the LiNbO<sub>3</sub> matrix. Compositional uniformity of the grown crystals was estimated. The influence of Er ions on the optical properties of Mg:LiNbO<sub>3</sub> single crystals was investigated.
Device performance of Ti:LiNbO3 10Gbps intensity modulator and 5Gbps phase modulator has been measured over various temperature in terms of insertion loss and bias drift voltage. Insertion loss and DC bias drift changed by 0.4dB and 0.45V, respectively, whether RF&DC port is open or short.
Stimulated Brillouin Scattering, observed in an optical transmission system using fibre lasers as signal sources, was suppressed by external phase modulation. The threshold power of SBS in a single mode fibre with 8.3-micrometers diameter was as low as 2 dBm due to a narrow spectral linewidth of a fibre laser. At 20 MHz phase-modulation, modulation voltages above 5.3V suppressed the first order Stokes more than 25 dB. RF spectrums of the fibre laser phase-modulated at or above 5.3V showed multiple sets of sideband components higher than the carrier frequency component in amplitude. The minimum spectral bandwidth of a fibre laser with 20 kHz bandwidth was broadened to 120 MHz at this modulation condition. The results signified broadening of the effective spectral linewidth of the fibre laser by phase modulation.