The Study On The Key Technology Of Multi-spectral Imaging Based On Electrically Tunable Liquid Crystal

In this thesis, the electrically adjusting of the optical performances of liquid crystal (LC) structure, based on the field controlling effect of LC dielectric behavior, is realized through constructing smart LC electro-optic structure and then orderly modulating the refractive index (RI) of LC material and its spatial distribution. According to the elastic continuum theory of LC materials, a mathematic model, which is used to predict and describe the formation of specific RI spatial distribution of LC molecules driven by applied electric field, is proposed. A series of electrically controlling LC components are designed and fabricated, and then the major electro-optic and optical performances of the LC devices are acquired. The proposed electrically controlling LC micro-optical technology will have important applications in the miniaturized high-speed moving platform (terminal) guidance technology. The main works are as follows.1. An electrically tunable LC lens with a single circular patterned electrode is effectively designed and fabricated by adopting the polyimide (PI) layer as initial LC molecules constraint and electrical insulation structure, and through fabricating the inner electrodes, which are directly contact with LC materials. Because the electric field is directly applied over the LC structure, the operating voltage is decreased remarkably, and then the electric field intensity is enhanced obviously, and thus the LC molecules are driven and controlled more easily. The typical parameters of the LC lens include:the optical aperture of 2.0 mm, the lowest operating voltage of 1.1Vrms (being significantly less than the common value), the MTF being more than 0.5 at different driving voltage, and the transmittance of more than 40% in the wavelength range of 0.3～1.1μm. The model constructed based on common geometric optics and LC elastic continuum theory, is used to analyze the formation of the RI gradient distribution of LC materials, and consequently, a simple focal length formula and the correspondent phase distribution function are obtained, which are equivalent to the complex conventional relations.2. A LC microlens array of 128 X 128 is designed and fabricated based on the basic method mentioned above. The top patterned electrode is composed of 128 X 128 micro-circular holes. The diameter of each micro-circular hole is 50μm, and the center-to-center distance between neighboring lenses is 150μm, and the thickness of LC layer is 20μm. The typical parameters of the LC microlens include:the optical aperture of single lens being 50μm, the variance range of the focal length being 50～400μm, the operating voltage being 1.2～5.0 Vrms, and the maximum focal spot size of 10μm. Experiments show that the multi-sub-images can be effectively acquired through the LC lens array fabricated.3. A cylinder LC microlens array of 128×128 is designed and fabricated. The top patterned electrode is composed of 128×128 micro-rectangular holes. The size of each micro-rectangular hole is 60×200μm2, the center-to-center spacing between neighboring lenses is 110μm, and the thickness of LC layer is 20μm. The typical parameters of the LC cylinder lens array include:the tunable focal length in the range of 60～450μm, and the operating voltage in the range of 1.4～5.0 Vrms. An analysis model about the RI gradient distribution of LC material is established successfully. The issues such as the white light focusing, the far-field white light interference, and the monochromatic laser interference, are discussed carefully through employing the model constructed.4. A terahertz (THz) LC lens is designed and fabricated by using fused quartz substrate materials. The typical parameters of the THz LC lens include:the optical aperture of 1.0 mm, the threshold voltage of 1.15 Vrms, and the minimum focal length of 10.0 mm. Based on the THz-TDS technology and the model of the RI gradient distribution of LC materials, the THz beam penetrating and focusing characteristics of the lens are measured and analyzed in detail. Experiments show that the lens already demonstrates an obvious focusing operation to THz beams with a wavelength of 118μm when the applied voltage over the lens is 15 Vrms.5. Based on the frequency response properties of LC material, the frequency control technology of LC devices is proposed so as to further lower the operating voltage of LC devices. According to the dielectric response behavior of LC material, an equivalent circuit and a frequency driving model of LC imaging components are established efficiently. The typical parameters of the LC device include:the frequency range of the driving signal being in 0.1～100 KHz, the operating voltage being less than 1.0 Vrms, the tunable range of the focal length being 300～500μm, and the response time of the LC micro-structure being sub-milliseconds scale. 6. Based on an electrically tunable LC microlens array, a prototyped Shack-Hartmann wavefront detection structure is designed and fabricated. The structure has dual-mode imaging feature (wavefront and intensity image), and thus can be used to effectively improve detection sensitivity and dynamic measurement range of wavefront, and then reduce the crosstalk between arrayed micro-structures.