Active coherent beam combination has been a hot area of research for several years. Particular algorithm module is used to stabilize the phase difference between beamlets, and make them coherent. The phase noise increases with the raising power of laser output. Under low power condition, we simulate the phase noise of high power laser amplifier by the Arbitrary Function Generators (AFGs), and send them to the phase modulators to destabilize the phase, to test the performance of the phase lock algorithm. The experimental results show the feasibility.
Liquid crystal based phase only spatial light modulator has attracted many research interests since last decades because of its superior advantage. Until now the liquid crystal spatial light modulator has been applied in many fields, but the response speed of nematic LC limited its further application. In this paper, an optically addressed phase only LC spatial light modulator was proposed based on polymer network liquid crystal. Morphology effect on the light scattering of PNLC was studied, which was mainly consisted of fiber and fiber bundles. The morphology nearly determined the light scattering and electro-optical property. Due to the high threshold voltage, to address the PNLC phase modulator was also concerned. Optical addressing method was proposed, in which BSO crystal was selected to replace one of the glass substrate. The response speed of PNLC was so fast that the reorientation of liquid crystal director will follow the change of effective voltage applied on LC layer, which was related with the voltage signal and especially with electron transport of photo-induced carriers due to diffusion and drift. The on state dynamic response of phase change was investigated. Based on this device, beam steering was also achieved by loading 488nm laser strip on the optical addressed phase only spatial light modulator.
A near infrared tunable liquid crystal birefringent filter is developed by cascading a series of optical elements including the wide range wire-grid polarizers, the nematic liquid crystal retarders and the quartz retarders. The center wavelength of the filter's bandpass could be randomly selected or scanned in the designed spectral range with almost exactly the same out-of-band suppression by harmoniously adjusting the driving signals. The tuning range of the filter is 900nm~1700m, the clear aperture is over 50mm, and the bandwidth FWHM is about 15nm @900nm.The filter provides more flexible functions such as random wavelength selection and arbitrary spectral scanning step. Due to the excellent imaging quality and the relatively wide angle-of-acceptance with a large aperture, the filter enable snapshot spectral imaging sensors and compact systems without any moving parts, which is of great use in a wide variety of applications such as remote sensing for environmental monitoring, agriculture census, and mineral resources detection.
In this thesis, the currently feedback control algorithms used in the polarization controller, including
simulated annealing algorithm and gradient algorithm were analyzed. On this basis, a new method of polarization
control feedback algorithm based on fast locating algorithm was proposed to solve the defects of the original algorithm,
such as poor convergence and long time consuming search. It can reduce convergence time and improve the response
speed of the polarization controllers. This new endless polarization control algorithm using 4-plate polarization
controller was proposed and demonstrated. The results showed that the response time of the polarization controller was
less than 1ms. The control of polarization was achieved and the output polarization state was stable while the light
intensity fluctuated less than 2%, which could run endless reset freely.
Thermal injuries are a serious medical problem in the China. The accurate determination of burn degree is difficult for
scatheless diagnose and a precondition of treating burn wounds. Multi-spectral photographic analysis is expected to play
an important role in determining burn wound degree, the Liquid Crystal Tunable Filter has a capability of selecting the
observing wavelength instaneously with high spectral resolution and excellent imaging quality in visible and
near-infrared spectrum band. Taking advantage of this filter, we have developed a LCTF imaging spectrometer prototype
instrument at visible wavelength bands for burn wound diagnose.
In this paper, spectral analysis experiments were first performed on KUNMING mice and burn injury patients to find the
characteristic reflective spectral curves at 400nm-1800nm, the imaging spectrometer prototype instrument using LCTFs
which are sensitive to radiation in 420nm-750nmwavelength bands was built based on spectral analysis results. The
spectral imaging experiments on burn injury patients have verified the excellent properties of the prototype instrument,
including high quality spectral images with spectral resolution of less than 7nm and continuous selection of the output
wavelength. The burn areas of patients were marked with different colors which represents as different burn degree and
the spectral imaging system has thus been proven to have the ability to classify the burn areas through comparing their
reflective spectral curves with characteristic spectrum of the different burn degree in spectral database in the future.
Finally, the application of the LCTF imaging spectrometer to burn wound diagnose are summarized based on the results
of spectral imaging experiments on burn injuries.
A liquid crystal tunable filter (LCTF) with large aperture is developed using PDLC liquid crystal. A small scale imaging
spectrometer is established based on this tunable filter. This spectrometer can continuously tuning, or random-access
selection of any wavelength in the visible and near infrared (VNIR) band synchronized with the imaging processes.
Notable characteristics of this spectrometer include the high flexibility control of its operating channels, the image cubes
with high spatial resolution and spectral resolution and the strong ability of acclimation to environmental temperature.
The image spatial resolution of each tuning channel is almost near the one of the same camera without the LCTF. The
spectral resolution is about 20 nm at 550 nm. This spectrometer works normally under 0-50°C with a maximum power
consumption of 10 Watts (with exclusion of the storage module). Due to the optimization of the electrode structure and
the driving mode of the Liquid Crystal cell, the switch time between adjacent selected channels can be reduced to 20 ms
or even shorter. Spectral imaging experiments in laboratory are accomplished to verify the performance of this
spectrometer, which indicate that this compact imaging spectrometer works reliably, and functionally. Possible
applications of this imaging spectrometer include medical science, protection of historical relics, criminal investigation,
disaster monitoring and mineral detection by remote sensing.
LC-based spectral imaging is a novel spectral imaging technology using the liquid crystal tunable filter(LCTF),
which is a miniaturized device based on the electrically controlled birefringence of nematic liquid crystal.
Continuously tuning electrically controlled through a spectral coverage is realized using LCTF under low voltages.
Spectral imaging system based on LCTF is a miniaturized, multi-functional and real-time system with high spatial
resolution and spectral resolution, which means that more and further information about the Earth and its resources
can be acquired for new applications in large-scale mapping and environmental monitoring.
LC-based tunable filter with large aperture has been developed utilizing the effect of electric controlled
birefringence. Spectral test indicates that this filter can operate on the visible band with average 20 nm FWHM. A
small scale spectral imaging system is established based on this tunable filter. Spectral imaging experiments on
certain number of samples show that this system can provide continuously, and random-access selection of any
wavelength, and has a higher level of resolving power in respect of both imaging and spectral tuning in the visible
band, which indicates a brilliant application potentiality in environmental protection, resource detection.
The design and performance test of a cholesteric liquid crystal depolarizer (CLCD) is presented. This new depolarizer is a wedge-shaped cell filled with cholesteric liquid crystal material. By placing a CLCD in its path, the incident light beam is divided into a great number of micro beams in space, and each micro light beam has different polarization state and orientation, hence achieving the depolarization effect. Over a conventional optical depolarizer, the CLCD is easy built and insensitive to the polarization orientation of incident light.