Study On Electrically Tunable Mid-long-wavelength Infrared Imaging Detection Technology

Spectral imaging is an advanced information acquirement means of combination targets' images and the spectrum of electromagnetic beams out from targets,which can be used to obtain both the common geometric appearance and also the spectral radiation clue of targets.So far,the spectral imaging technology has been widely used in several fields including geological survey,environmental testing,agricultural estimation,military reconnaissance,and biomedical imaging,and thus demonstrate a broad application prospects.The study on electrically tunable spectral chip-level-imaging detection technology in mid-long-wavelength infrared regions has been conducted in this dissertation,and the electrically tunable mid-long-wavelength infrared filter based on the key architecture of liquid crystal Fabry-Perot(LC-FP)has been designed and fabricated successfully.According to the electrically controlled birefringence of nematic LC materials and the multi-beam interference in FP cavity,the particular spectral imaging based on wavelength selection and adjustment can be realized through the developed LC-FP filter.The LC-FP filter demonstrates some remarkable advantages including: ultra-small,smart,low cost,low power consumption,and high reliability,etc.The main work of this dissertation is as follows.The director distribution algorithm of nematic LC materials is used to simulate the relationship between the driving voltage signal and the equivalent refractive index of LC materials fully filled into a prefabricated micro-cavity;The multi-beam interference theory is used to simulate the spectral transmission behavior of the LC-FP filter at different driving voltage signals;According to the simulation results,the depth of the FP cavity and other key parameters are determined.The architectures of the electrically tunable mid-long-wavelength infrared LC-FP filter have been constructed.The zinc selenide(ZnSe)materials with a very high transmittance in the mid-long-wavelength infrared regions are chosen as the electrode substrates of the LC-FP devices.Moreover,the nano-aluminum(Al)film is chosen to make high reflective mirrors as well as electrodes.As a key parameter of the filter,the thickness of the Al film,crucially determines the performances of the filter.The reasonable Al film thickness is determined by experimental testing of the spectral transmission properties of the LC-FP filter with different Al film thickness.A 2×2 arrayed LC-FP filter,and a cascaded LC-FP filter,are fabricated based on the standard microelectronic process.The cascaded LC-FP filter is constructed by closely stacking two FP microcavities with different depths and fully filled by nematic LC materials.The cascaded LC-FP filter presents better spectral selection performances than common LC-FP filter with a single FP microcavity.The transmission spectra of the LC-FP filter are obtained using a Fourier transform infrared spectroscopy.The transmission spectra of the LC-FP filter obtained by a Fourier transform infrared spectroscopy under different driving voltage signals are compared and analyzed carefully.A spectral imaging test platform based on a blackbody and an infrared camera is established.The infrared images of the target obtained by the LC-FP filter at different driving voltage signals are compared and discussed.The consistence of both the spectral transmission measurements and the spectral imaging experiments demonstrates that the needed spectral selection and spectral adjustment in the mid-long-wavelength infrared regions can be carried out by the LC-FP filter,effectively.Further improvement methods of the LC-FP filter are planned for overcoming several current problems of the LC-FP filter.