Changsoo Jung

All-optical AND and NAND gates based on cascaded second-order nonlinear processes in a Ti-diffused periodically poled LiNbO(3) waveguide.

All-optical AND and NAND gates have been demonstrated in a Ti-diffused periodically poled LiNbO(3) channel waveguide which has two second-harmonic phase-matching peaks by cascaded sum-frequency-generation/difference-frequency-generation (cSFG/DFG) and sum-frequency-generation (SFG) processes. The conversion efficiency of signal to idler (AND gate signal) was approximately 0 dB in cSFG/DFG process. In the second SFG process, more than 15 dB extinction ratio between signal and dropped signal (NAND gate signal) has been observed.

Second-harmonic generation in periodically poled lithium niobate waveguides fabricated by femtosecond laser pulses

The authors have demonstrated the second-harmonic generation (SHG) in optical channel waveguides which were fabricated in periodically poled lithium niobate (PPLN) by tightly focused femtosecond laser (781nm) pulses. The measured quasi-phase-matched wavelength and 3dB bandwidth for SHG in a 44.8-mm-long PPLN waveguide which has a domain period of 16.6μm were about 1563 and 0.25nm, respectively. The value of the index difference between the fundamental and harmonic wavelengths in laser written waveguide was inferred to be 0.047.

All-optical wavelength conversion and tuning by the cascaded sum- and difference frequency generation (cSFG/DFG) in a temperature gradient controlled Ti:PPLN channel waveguide.

All-optical single and multiple wavelength conversion and tuning by the cascaded sum- and difference frequency generation (cSFG/DFG) have been demonstrated in a temperature gradient controlled periodically poled Ti:LiNbO3 (Ti:PPLN) channel waveguide. Up to 4 channels of wavelength division multiplexed (WDM) signals which have 100 GHz channel spacing were simultaneously wavelength converted at a 16.8 degrees C temperature difference between both end faces in a Ti:PPLN waveguide. The 3 dB signal conversion bandwidth was measured to be as broad as 48 nm at single channel conversion. The maximum wavelength conversion efficiency and optical signal to noise ratio of wavelength converted channel were approximately -16 dB and -20 dB at a total pump power level of 810 mW.

Broadening of the second-harmonic phase-matching bandwidth in a temperature-gradient-controlled periodically poled Ti:LiNbO3 channel waveguide.

We have demonstrated broadening of the phase-matching bandwidth in a periodically poled Ti:LiNbO3 (Ti:PPLN) channel waveguide Lambda = 16.6 microm) by using a temperature-gradient-control technique. With this technique, we have achieved a second-harmonic phase-matching bandwidth of more than 13 nm in a 74-mm-long Ti:PPLN waveguide, which has a 0.21-nm phase-matching bandwidth at a uniform temperature.

Channel-selective wavelength conversion and tuning in periodically poled Ti:LiNbO 3 waveguides

All-optical wavelength-selective single- and dual-channel wavelength conversion and tuning has been demonstrated in a periodically poled Ti:LiNbO(3) waveguide that has two second-harmonic phase-matching peaks by cascaded sum and difference frequency generation (cSFG/DFG). The wavelength conversion efficiency was measured to be -7 dB with coupled pump power of 233 mW.

Simultaneous forward and backward terahertz generations in periodically poled stoichiometric LiTaO3 crystal using femtosecond pulses

Forward and counterpropagated backward terahertz generations were demonstrated via difference frequency generation using a femtosecond laser. By cooling the crystal to reduce terahertz losses, we achieved the terahertz generations of 1.36 and 0.65THz. Temperature-dependent measurements showed gradual intensity increase of the terahertz pulse and red shift of the center frequency as the temperature decrease from 255to143K, although there were insignificant decreases of the spectral bandwidth.

Reshaping of a second-harmonic curve in periodically poled Ti:LiNbO3 channel waveguide by a local-temperature-control technique

We have demonstrated reshaping and bandwidth control of a second-harmonic (SH) curve in a periodically poled Ti:LiNbO3 (Ti:PPLN) waveguide (Λ=16.6μm) by using a local-temperature-control technique. With this technique, we have achieved several useful shapes of the SH curve such as an almost ideal sinc function, and double and multipeaks in a 74-mm-long Ti:PPLN waveguide, which has a prechirped SH curve at room temperature. More than 60% improvement of SH conversion efficiency and a 5nm broadening of SH phase-matching bandwidth were achieved.

Backward Terahertz Generation in Periodically Poled Lithium Niobate Crystal via Difference Frequency Generation

We have investigated the terahertz radiation generated by femtosecond laser pulses in a periodically poled lithium niobate crystal. Two different types of terahertz radiation, forward and backward, could be generated in quasi-phase-matching structures. The generation of these two different types of radiation is due to difference frequency generation under the quasi-phase matching condition. A broadband femtosecond optical pulse contributes to wave mixing, which occurs between two components of an ultrashort laser pulse and a terahertz pulse, in a quasi-phase-matching crystal. We observed a backward terahertz radiation at approximately 1.3 THz and the frequencies of terahertz radiations are easily controlled by varying the domain structures.

A linearly-polarized Nd:YVO 4 /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%.

Efficient Single-Pass Optical Parametric Generation and Amplification using a Periodically Poled Stoichiometric Lithium Tantalate

A high-conversion efficiency, nanosecond pulsed optical parametric generation and amplification with repetition rate of 20 kHz based on a periodically poled MgO-doped stoichiometric lithium tantalate was presented. Pumped by a Q-switched