Light wave becomes extremely distorted when it passes through a turbid medium. Indeed, the inhomogeneity of scattering medium and the mode dispersion of multimode optical fiber (MMF) always distort the propagation of light waves since they divert the propagation direction and disorder the spatial relationship of rays from the object. This becomes a big challenge for the applications of biological tissues endoscopic imaging. To overcome this problem, many methods based on computational optical imaging schemes have been reported and such a research has become a hot topic in recent years. These methods include the computational ghost imaging, the digital phase conjugation, the speckle correlation, the wavefront shaping, and the optical transmission matrix, etc. In this paper, we report our recent works on computational optical imaging based on digital wavefront modulation, which might be useful for the applications of endoscopy. On one hand, we propose a round-trip imaging method based on the optical transmission matrix of scattering medium, where the light wave is distorted twice. The object is recovered directly from the distorted output wave, while no scanning is required during the imaging process; one the other hand, by modulating the amplitude instead of the phase of the incident light wavefront, we propose a high-speed binary amplitude-only modulation method to focus and scan light through an MMF based on the digital micro-mirror device (DMD). This method can also be extended to focus and scan light at multiple planes along the axial direction by just modifying the input wavefront accordingly.
Thermal therapy (or hyperthermia) is one of the effective operations for tumor treating and curing. As tumor tissues are more susceptible to heat than normal tissues, in thermal therapy operations, temperature on operation area is a crucial parameter for optimal treating. When the temperature is too low, the tumor tissues cannot be killed; otherwise, the temperature is too high, the operation may damage normal tissues around the tumor. During thermal therapy operation, the heating power is normally supplied by high-frequency EM field, so traditional temperature sensors, such as thermal couples, thermistors, cannot work stably due to EM interference. We present a multi-function endoscope optical fiber temperature sensor system. With this sensor setup based on principle of fluorescence life time, the temperature on operation point is detected in real time. Furthermore, a build-in endoscope centers in the fiber sensor, thus the operation area can be viewed or imaged directly during the operation. This design can navigate the operation, particularly for in vivo operations. The temperature range of the sensor system is 30°C-150°C, the accuracy can achieve to 0.2°C. The imaging fiber buddle is constituted of more than 50k fibers. As the sensor probe is very thin (around 4 mm in diameter), it can also be assembled inside the radiofrequency operation knife. With the presented sensor system in clinic operation physicians can check the temperature in the operation point and view the operation area at the same time.
The fabrication technology of refractive microlens array (MLA) with self-assembly of drops of various thermoplastic optical polymer solutions is reported. In order to develop a conventional drop-on-demand type ink-jet printing method for fabricating high quality microlens array, Firstly, we tried to prepare a series of optical polymer inks. These inks compose of high quality optical polymers, polymethylmethacrylate (PMMA), dopant, and functional organic molecules such as laser dye, nonlinear organic dye, and rare earth ion chelates with a suitable organic solvent. Effects of surface tension on the polymer solution drops induced the self-formation of microlenses. This process exhibited a completely self-assembly characteristic without any chemical and photochemical post-treatment. The resulting microlens array displayed diameters varying from 1mm to 5mm and focal lengths from less than one millimeter to a few millimeters. Observation with an atomic force microscope reveals that the surface roughness of the lens is 0.9 nm. The transmittance spectrum of the lens is also measured.
Shaft calibration is an important technique during installation and maintenance of a rotating machine. It requires unique and high-precision measurement instruments with calculation capability, and relies on experience on heavy, high-speed, or high-temperature machines. A high-precision laser alignment system has been designed using PSD (Position Sensing Detector) to change traditional manual way of shaft calibration and to make the measurement easier and more accurate. The system is comprised of two small measuring units (Laser transmitter and detector) and a hand operated control unit or a PC. Such a laser alignment system has been used in some actual shaft alignment with offset resolution 1.5μm and angular resolution 0.1°.
Since the gradient index material has important applications at photoelectric system, imaging system, and integrated-optical system. Now, researches on gradient index material containing silver ions are more popular, it is difficult to get glass with high silver content as silver ion is extruded from molten glass at the molten temperature. Two-step ion-exchange process including Ag +- Na+ and Na+ - Ag + ion-exchange is used to get gradient index. This paper is based on the research in our lab, by adjusting the glass composition to get a series of sodium-rich glass then drawing the fusioned glass into fiber with diameter of 1mm used for ion-exchange. We used mixed molten salt for ion- exchange, then we researched on the choice of silver salt, the advantage and disadvantage of mixed molten salt and single molten salt, and the coloring up problem after ion-exchange.
The gradient index (GRIN) inhomogeneous materials optical glass micro-lens and polymer microlens and arrays were investigated in our Lab, in recent years. The different series of GRIN lenses have been fabricated using ion-exchanged in the special glass material. The GRIN lenses are done in applications for using to construct micro-optic devices. We analyzed and demonstrated results on propagation and imaging properties of GRIN lenses. On the other hand, we have also developed a drop-on-demand ink-jet printing method to produce micro-lens array using nano-scale polymer droplets involved with a uniform ultraviolet (UV) light and heat solidifying process. The experimental setup for manufacturing polymer microlens array and the measurement results of performance parameter are also given.
A pressure and temperature sensing system based on fiber-optic Bragg grating sensors for the oil and gas downhole is reported in this paper, the weak pressure sensitivity is enhanced and the cross-sensitivity of temperature and pressure measurands is overcome by an optimally designed mechanical enhancing and compensating structure, the working principle, experimental setup and testing results are also given.
In this paper, a measuring method utilizing Modulation Transfer Function (MTF) to evaluate the imaging performance of fiber optical plates, is proposed. As a kind of relay optical component in optical imaging systems, optical fiber transfer image plates have become more important and more available. By digital simulating the discrete MTF values, algorithm for MTF measure of fiber plates is studied. And MTF experimental results for the performance evaluation of fiber plates with knife-edge effect compared CCD test, are also discussed.
We start from Kukhtarav equations and Gauss's law which describe the photorefrective effect in a photorrefractive medium in which electroncs are the sole charge carries, plus the wave equation for the slowly varying amplitude of the optical field , In steady state and two dimensions the distributions of the nonlinear refractive index in a photorefective cystals under the conditions of supporting low intensity spatial solitons are studied theoretically. It is shown that steady state spatial bright solitons of TEMn0(n=2,2,3...)modes and modulated TEMn0 mode Gaussian waveform can form and induce planar array waveguides in photorefractive crystal.
We propose a novel method of transform spectral measurement, based on the diffraction of light through the side of a waveguide fabricated in photorefractive crystal where a holographic grating is recorded by holography. The optical spectrum can be obtained by Fourier transform for the interference pattern, which is formed by lights diffracted from counter-propagating mode in the waveguide. Changing the periodic length of the holographic Bragg grating recorded in the waveguide can widen the range of measurable spectrum. This spectral measurement method is well suited as high- resolution wavelemeter, terminal network spectrum monitor and spectral measurement advice for fiber-grating sensor.
In this paper, we will introduce some of SLMs research and applications in our laboratory, mainly the Liquid Crystal Light Valve(LCLV), CRT-LCLV and photorefractive crystal devices and their application.
A study on self-pumped phase conjugate properties in BaTiO3 crystal is presented. The relation between phase conjugate reflectivity and the input position as well as incident angle is investigated quantitatively, with experimental results given. The conclusion is helpful to improve the research work on interconnection and associative memory using BaTiO3..
We have developed a new device called electrically addressed cathode-ray tube coupled liquid crystal light valve as an input interface hardware in our hybrid pattern recognition system. A photorefractive bismoth silicon oxide crystal is used as dynamic holographic filter. An implementation of real-time hybrid optical pattern recognition using optical joint transform correlator which includes two type spatial light modulators, lase sources, CCD sensor and microcomputer is described. Theoretical analysis and initial experimental results are present.
In this paper , a binary joint transform correlator (BJTC) based on an electronically-addressed spatial light modulator is described. The system mainly includes a cathode-ray-tube coupled liquid crystal light valve (CRT —LCLV) , a CCD camera , and a microcomputer. On the base of theoretical analysis ,results of digital simulation and initial experiments are presented , and show that the correlator has good discrimination.
This paper investigates the spatial polarization characteristics of real-time holography and two- wave mixing in eosin both in theory and experiment, and we utilize these features to realize optical storage and pattern recognition.
Two types of spatial light modulators are described. One is optically addressed CdS/CdTe- LCLV. Another one is electrically addressed CRT-LCLV. Detailed description is given of the structure and fabrication. To demonstrate their ability of application in optical data processing. Some practical examples are shown.
Dynamic global interconnections between processors in massively parallel computers are a highly desirable feature. Such as photorefractive materials can be used to store holographic gratings that implement interconnection links between individual processing elements of two distinct planes. In this paper we detail the energy transfer between two coupled beams writing holograms in EOSIN film. A type of holographic routing architecture which uses a LCLV is presented. Spatial polarization characteristics and temporal modulation coupling are investigated.
This paper deals with two-wave mixing in eosin doped gelatin film. Some chemical and physical properties of eosin are shown. The basic two-wave mixing equation and real-time holographic characteristics are discussed. The higher order diffraction is observed. The experimental results also are given.
In this paper, we developed and demonstrated a liquid crystal light valve and photorefractive spatial light modulators, utilizing these devices to build up a real-time correlation pattern recognition system. The performance parameters of these devices were measured, and some of the experimental results are given.
We have studied that the dynamic behavior of our national products Bi12SiO20, Fe:KNbO3, etc., for real-time holographic recording and display. The potential applications of these crystals to image storage and freezing, real-time interferometry, and optical switching are described. The results of experiments are also given.
This paper describes photorefractive self-pump phase conjugation in BaTiO3and multi-wave
mixing in Bi12SiO20 spatial light modulators, and furtherly utilizes these systems to impletment optical
image storage, wavelength conversion, image subtraction and optical image shifting. The
operational principle and experimental results are also presented.
The applications and development of hybrid image processing have attracted significant attention in recent. This paper describes a multifunction optoelectronic hybrid processor that can inplemente several operations . This new system is appropriate for real-time automatic pattern recognition. An effective approach and architecture are provided for the robotic vision. In the system utilizing the joint transform techniques and the resulting Fourier transform of the object image and reference image was detected by the CCD camera and then sent it into digital image preprocessor . At the same time Fourier spectrum of the edge-enhanced images are obtained pass coherent optical image processing through a liquid crystal spatial light modulator as a real-time interface device ( a incoherent-to-coherent irrge flCC ) . Thus classification and correlation of the object pattern are carried out by using both of digital and analogy inge processing. The preliminary experimental results are given. 1 .
This paper, based on our studying multi-wave mixing in photorefractive crystals Fe: LiNb03[ 1] , we have set up a real-time parallel image, logic " ex OR" operation system, and performed real-time associative memory experiment. The results of our experiment is also given.
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