Research on digital image conversion by using photon mixing

本文研究了利用非线性晶体中的非线性光子混频实现红外到可见光谱的频率转换。为了实现高效和频，对LiNbO_3晶体的相位匹配特性进行了详细的研究。实验研究了GaP晶体中光波与太赫兹（THz）波的频率转换。1）从红外到可见光的频率转换我们研究了LiNbO_3、MgO：LiNbO_3和周期极化LiNbO_3（PPLN）晶体中SFG的相位匹配特性。在LiNbO_3和MgO：LiNbO_3晶体中，SFG的红外转换范围主要由晶体温度决定。另一方面，由于可以通过控制畴周期来实现准相位匹配，因此可以在PPLN中获得宽调谐的信号频。在畴控PPLN中，1.5 ~ 5μm的红外辐射可以被转换为可见光，通过对红外图像进行空间数字化，提出了一种新的导波SFG结构，用于数字图像转换。2）光波与太赫兹波的频率转换。GaP晶体在太赫兹波段具有很强的非线性光学效应和低损耗特性，是一种很有吸引力的频率转换材料。我们发现，在0.98 μm处抽运光，可以实现光频和差频相互作用的共线相位匹配。我们研制了一种波长为0.98 μ m的KTP晶体光参量振荡器。利用双波长OPO输出在GaP中混频，成功地产生了0.5-2.2THz的可调谐THz波。

We have investigated a frequency conversion from infrared to visible spectrum by using a nonlinear photon mixing in nonlintear crystals. To achieve an efficient sum frequency generation (SFG), a phase matching property of LiNbO_3 crystals was studied in detail. Also, we have experimentally investigated the frequency conversion between optical waves and terahertz (THz) waves in a GaP crystal.1) Frequency conversion from infrared to visible spectrumWe have investigated the phase matching properties for SFG in LiNbO_3, MgO : LiNbO_3, and periodically poled LiNbO_3 (PPLN) crystals. In LiNbO_3 and MgO : LiNbO_3 crystals, the infrared conversion range for SFG is determined mainly by the crystal temperature. On the other hand, we can obtain widely tunable SFG in PPLN because that the quasi-phase-matching can be achieved by controlling the domain period. Infrared radiation woth 1.5-5μm can be converted to the visible in domain-controlled PPLN.We proposed a new structure of the guided-wave SFG for a digital image conversion by digitalizing the infrared image spatially.2) Frequency conversion between optical and THz waves.The frequency conversion between optical and THz waves can be possible by SFG and difference frequency generation (DFG). GaP crystal is an attractive material for the frequency conversion because of the large uonlinear optical effect and the low loss property at the THz-wave region. We have found that the collinear phase-matching was achieved by selecting the pumping wavelength at 0.98 μm for SFG and DFG interaction. We developed an optical parametric oscillator (OPO) with KTP crystal at the wavelength range of 0.98 um. Tunable THz waves were successfully generated in the range of 0.5-2.2THz by mixing a dual wavelength OPO output in GaP.