Wavefront Manipulation Of Periodic Structures And Its Applictions

Integrated optics is a very promising signal processing and treatment technology, and is generally considered to be a break-through just like the current integrated circuit system. To achieve the integration of the light, its foundation is light processing and tuning. There are many methods of light manipulation, but an impotant basis is light wavefront control. In this thesis, I would study the wavefront manipulation based on several periodic structures. We propose to adjust the optical and acoustic wavefronts by using periodically artificial micro-structured materials (such as periodically poled lithium niobate, PPLN). The wavefront evolution and field distribution are investigagted. At last, the applications of such technology in Liqiud Crystal (LC) photo-alignment and nanopartical clean-up are also discussed.1. We have studied the phenomena and physical laws of periodically tuned optical wavefront. A new type of surface phonon polariton mode has been proposed. In ionic-type phononic crystals (ITPCs), such as PPLN, a kind of spoof phonon will be generated due to the additional polarition caused by piezoelectric effect, which is actually the wave front tuning in the longitude. The "phonon" will be coupled with the external electromagnetic field to form a polariton, which plays a role in wavefront manipulation, result in the dielectric response moving to longer wavelength respect to ionic crystal. In fact, ITPC is a counterpart of ionic crystal in Microwave band. Thererfore, we proposed a new kind of surface phonon polariton (SPhP) in this region. We have studied the field distribution and propagation behavior, and analyzed the parameters impact of its propagation distance. Then, we put forward a long range surface phonon polariton (LRSPhP). We think our research has opened a window in microwave or terahertz subwavelength optics.2. Lithium niobate is also a piezoelectric material. In addition to build an ITPC as mentioned above, it is also a kind of excellent materials for ultrasonic transducers. As sound is a kind of classical wave, it exhibits many similar phenomena just like light. Therefore, we propose an acoustic Talbot effect based on PPLN. Talbot effect is a near-field diffraction phenomenon, which is first found in optics. Optic Talbot effect requires two necessary conditions, namely the coherent light source and a periodic structure. However, PPLN is both coherent sound source and periodic modulation in the transverse direction, equivalent to combine the two essential components of the conventional optic Talbot effect together. Acoustic Talbot effect will be generated by such lateral periodically modulated sound, result in a quasi-two-dimensional acoustic standing wave. We have analyzed the detailed evolution of the sound field (only real part), especially in some fractional Talbot distance (LT). In addition, we proposed that this quasi-two-dimensional acoustic field has very attractive applications in acoustic fine particle interaction and agglomeration, such as PM2.5.3. Talbot effect is a very beautiful optical phenomenon. Complex two-dimensional (2D) field distribution can be generated only by a simple one-dimensional (1D) structure, such as1D grating. The unique2D field distribution is called Talbot carpet. Talbot effect can not only be used in acoustic clean-up as proved above, but also has a promising application in LC. The introduction of Talbot self- imaging in photo-alignment can realize complex patterned LC orientation only with a simple1D grating photo mask. This is a quite simple and efficient complex patterned LC alignment technique, which can be used to prepare various micro-structural LC tunable devices. In our experiment, an obliquely-placed grating is used, so that the Talbot carpet tilts correspondingly to be projected onto a vertical plane. When this light expose on a vertical placed sample, Talbot carpet patterned orientation is transferred into the LC cell through photo-alignment technique. This interesting LC alignment structure can be used in tunable Mach-Zehnder interferometer (MZI) array. There are many other application prospects in integrated optics, and even quantum optics.