Enhanced 355-nm generation using a simple method to compensate for walk-off loss.

We theoretically and experimentally investigated a novel walk-off-compensation method for efficient ultraviolet beam generation. Through theoretical investigation, we described in detail how the power of a generated UV beam can be enhanced by the method; thus, we obtained a brief expression for the output power which has a prediction error of about 30%. In addition, we found that the beam quality can also be enhanced using this method. Through experiments using an alpha barium borate crystal as a walk-off compensator, we found that the power of the generated ultraviolet beam increased 1.9 times.

Mode tailoring in a ridge-type periodically poled lithium niobate waveguide.

We present a simple and powerful method for mode generation and transformation in a ridge-type periodically poled lithium niobate (PPLN) waveguide by the use of second-order nonlinear effect and local-temperature-control technique. We show that a Hermite-Gaussian (HG) mode wave (among HG(00) to HG(22)) can be selectively generated via the quasi-phase-matching (QPM) nonlinear process in a PPLN waveguide by tuning the wavelength of fundamental wave or the temperature of the waveguide. As well, it is demonstrated that HG mode can be transformed into Laguerre-Gaussian (LG) one via combination of HG modes which are simultaneously generated in a single PPLN waveguide with local-temperature-control technique.

A linearly-polarized Nd:YVO4/KTP microchip green laser.

We described the principle and the fabrication of a Nd:YVO(4)/KTP microchip for the linearly-polarized green laser and verified its availability by manufacturing and characterizing the green laser using the microchip. Under the driving condition having the modulation frequency of 60 Hz and the duty ratio of 25%, the laser showed the stable linear polarization, the maximum average power of 37 mW, yielding the high electrical-to-optical efficiency of 10.9%.

Characteristics of a multi-mode interference device based on Ti:LiNbO3 channel waveguide.

We have analyzed the multi-mode interference effect depending on the wavelength and the polarization states of input beam in a multi-mode Ti:LiNbO(3) waveguide at about 1300 nm region. The transmitted optical signal of a Ti:LiNbO(3) waveguide shows the periodic oscillation as a function of input wavelength. The measured average periodicity of the oscillation in TM and TE polarization beams were about 18 nm and 48 nm, respectively. Actually, the periodicity is determined by the refractive index difference between the two modes (fundamental and first modes). Therefore, we have explained the experimental results with the theoretical calculations which are derived from a quasi-analytical technique based on the effective-refractive- index method and the equation of coupling length determined by the mode phase factor in the multi-mode waveguide.

Wavelength filtering characteristics of Solc filter based on Ti:PPLN channel waveguide.

We have analyzed the Solc filtering characteristics in a periodically poled Ti:LiNbO3 (Ti:PPLN) multimode waveguide. The single- and dual-wavelength filtering were achieved under the optimized guiding condition for the TEM(00)-like mode and two mode (TEM(00)- and TEM(01)-like mode), respectively. The full width at half-maximum of the filter was about 0.21 nm at both guiding conditions. We found that the origin of two peaks of the dual-wavelength Solc filter in the two-mode guiding condition is the different effective refractive index between the TEM(00)- and TEM(01)-like modes. The wavelength difference of two peaks is about 0.8 nm at room temperature.

Low loss high mesa optical waveguides based on InGaAsP/InP heterostructures.

Low loss high mesa optical waveguides were fabricated on InGaAsP/InP heterostructures by utilizing inductively-coupled-plasma reactive ion etching (ICP-RIE) and electron beam lithography technique. The fabrication process was optimized by measuring sidewall roughness of deep-etched waveguides. Atomic force microscope loaded with carbon nanotude was used to obtain three-dimensional image of the etched sidewall of waveguides. The obtained statistical information such as rms roughness and correlation length was used to theoretically calculate scattering loss of waveguides. Several waveguides with different number of sharp bends and the length were fabricated and their propagation losses were measured by modified Fabry-Perot method. The measured propagation losses were compared with theoretically calculated losses.