Research on generation of lightwave with ultra-wide sidebands and its conversion to THz electromagnetic wave

(A)超宽带光学边带的产生：研制了LiTaO_3晶体周期域反转准速度匹配(QVM)电光相位调制器，在16 GHz的调制频率下产生了3 THz以上的超宽带光学边带。提出并研制了一种新的LiTaO_3晶体倾斜周期域反转行位相光栅电光偏转器。利用拉曼-纳特衍射产生了超宽带调制边带。利用傅里叶变换光学进行了超快偏转。(B)太赫兹边带的控制：对电光产生的相位调制边带和锁模激光器产生的边带进行了光谱分辨、空间分离、选择和/或用液晶空间相位调制器进行相移，然后进行复合。产生了重复频率等于调制频率倍数的脉冲序列。(C)产生相干太赫兹光学拍频：…更多来自两个单模激光器的光波的叠加在两个激光器的不同频率处表现出强度拍频，这很容易被制成太赫兹。然而，由于激光的位相扩散，从光学拍频产生的太赫兹电磁波退相干。因此，必须确定频差为THzi量级的两个激光器的相位关系。即选择注入锁定：保证调制边带或锁模边带彼此相干。DBR激光二极管可以选择性地锁定到其中一个注入的边带。通过将两个半导体激光器锁定在THz相隔的边带上，可以产生相干的THz光拍频。ii.倍频自相关负反馈：通过非共线倍频自相关可以检测到光拍相位的偏差。通过将拍频相位偏差负反馈到激光相位，维持拍频相干性。该方案用微波延迟线和混频器代替倍频自相关得到了成功的验证。较少

(a) Generation of ultra-wide optical sidebandsi.Electro-optic phase modulators with quasi velocity matching (QVM) by periodic domain inversion of LiTaO_3 crystal have been developed, Ultra-wide optical sidebands over 3THz have been generated a modulation frequency 16GHz.ii.A new electro-optic deflector with traveling phase grating by tilt periodic domain inversion of LiTaO_3 crystal has been proposed and developed. Ultra-wide modulation sidebands have been generated by Raman-Nath diffraction. Ultrafast deflection has been done with the help of Fourier transform optics.(b) Control of THz sidebands : Both electro-optically generated phase modulation sidebands and sidebands from modelocked laser have been spectrally resolved, spatially separated, selected and/or phase shifted by liquid crystral spatial phase modulator and then recombined. The pulse trains with the repetition rate equal to a multiple of modulation frequency have been generated.(c) Generation of coherent THz optical beat : … More Superposition of lightwaves from two single-mode lasers exhibits intensity beat at the difference frequency of the two lasers which can easily be made to be THz. However, THz electromagnetic wave generated from the optical beat decoheres due to phase diffusion of the lasers. It is therefore essential to fix the phase relation of two lasers with frequency difference of the order of THz.i.Selective injection locking : Modulation sidebands or mode-locked sidebands are guaranteed to be coherent.with each orther. DBR laser diode can be selectively locked to the one of the injected sidebands. By locking two laser diodes to the sidebands separated by THz, coherent THz optical beat can be generated.ii.SHG autocorrelation negative feedback : Deviation of optical beat phase is show to be detected by non-collinear SHG autocorrelation. By negative feedback of the beat phase deviation to the one of the laser phase, the beat coherency is sustained. The scheme has been successfully demonstrated by using microwave delay-line and mixer in place of SHG autocorrelation. Less