TAILIEUCHUNG - Optoelectronics Devices and Applications Part 9

Tham khảo tài liệu 'optoelectronics devices and applications part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Using the Liquid Crystal Spatial Light Modulators for Control of Coherence and Polarization of Optical Beams 309 1 p x1 x2 2 S0 S0y f z2 Y S0 exp I T 2 1 S0y exp V 2ƠX z2 2 y 7 P x J 2 2J 8 S0 - S0 y where z X - x2 . Now we consider the propagation of the electromagnetic beam characterized by the cross-spectral density matrix W x1 x2 through a thin polarization-dependent screen whose amplitude transmittance is given by the so-called Jones matrix Yariv Yeh 1984 T x l x x i Viyx x iyy x 9 with elements tịị x being the random generally complex functions of time. It can be readily shown Shirai Wolf 2004 that the cross-spectral density matrix of the beam just behind the screen is given by the expression W x1 x2 T xi W X1 x2 T x2 10 where the dagger denotes the Hermitian conjugation and the angle brackets again denote the average over the statistical ensemble. Taking into account Eq. 10 with due regard for definitions given by Eqs. 3 and 4 it becomes obvious that in general x1 x2 x x2 and P x P x . This fact can be used to realize the modulation of coherence and polarization by means of a random polarization-dependent screen. To minimize the light loss the elements of the matrix T x must be of the form tj x exp rp x 11 where px is some real random function. To provide the desired statistical characteristics of modulation the function p x has to be generated by computer. The most appropriate candidate for physical realization of such a computer controled random phase screen is the LC-SLM. 3. Elements of the theory and design of LC-SLMs The LC represents an optically transparent material that has physical properties of both solids and liquids. The molecules of such a material have an ellipsoidal form with a long axis about which there is circular symmetry in any transverse plane. The spatial organization of these molecules defines the type of LC Goodman 1996 . From the practical point of view the most interesting type is so-called nematic LC for which the molecules have a

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