Research on digital image conversion by using photon mixing

我们研究了在非线性撕裂晶体中利用非线性光子混合实现从红外到可见光的频率转换。为了实现高效和频(SFG)，详细研究了LiNbO_3晶体的相位匹配特性。1)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，由于可以通过控制磁区周期来实现准相位匹配，因此在PPLN中可以获得宽可调的单频光纤。通过对红外图像进行空间数字化，提出了一种用于数字图像转换的导波单频光纤陀螺结构。2)光波和太赫兹波之间的频率转换，通过单频光纤和差频产生实现了光波和太赫兹波之间的频率转换。GaP晶体在太赫兹波段具有较大的非线性光学效应和较低的损耗，是一种极具吸引力的频率转换材料。结果表明，选择0.98mSFG和DFG相互作用的泵浦波长，可以实现共线相位匹配。研制了0.98um波段KTP晶体光学参量振荡器。通过在GaP中混频双波长OPO输出，成功地在0.5-2.2THz范围内产生了可调谐的太赫兹波。

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.