Development of a stable electro-optical modulator

The activity of the sun can be studied through the measurement of its magnetic field. The measurement of the polarization state of the sunlight in a narrow spectral bandwidth can be related to the magnetic fields strengths and directions over the active sunspots. Measuring the polarization state can be done using the vector magnetograph. The essential component of the vector magnetograph is the polarization modulators. Electro-optical modulators are used as dynamic retarders. KDP (potassium dideuterium phosphate) crystals provide variable retardation which can be controlled by the applied voltage. KDP's have a high contrast ratio but suffer some problems; they require a high voltage and have a limited modulation lifetime. The KDP modulator forms the heart of the polarimeter assembly which is used for carrying out accurate measurements of linear polarization of the sun. It is therefore important to study the optical and electrical behavior of the KDP crystals so that the ultimate goal of making stable electro-optical modulators in the laboratory is achieved. A number of activities were performed in coating and testing the KDP crystals. A summary of these activities is given

MEMS Micro-Translation Device with Improved Linear Travel Capability

A microscopic translation device for a microelectromechanical system includes a pair of linear stator assemblies disposed in spaced relation to define an elongate channel. Each assembly is formed by a plurality of stators arranged in a row along the channel. A shuttle member is disposed between the stator assemblies for translating movement along the channel. The shuttle member includes a plurality of rotors extending outwardly from opposite sides. The shuttle is grounded through the stator assemblies and includes a mounting area for an object to be translated. Electrical lines are individually connected to alternate stators of a plurality of groups of the stators. A current supply sequentially supplies current through the electrical lines to the alternate stators so as to effect charging of the stators in a predetermined sequence. This produces a tangential capacitive force that causes translation of the shuttle

Generalized Design of Diffractive Optical Elements Using Neural Networks

Diffractive optical elements (DOE) utilize diffraction to manipulate light in optical systems. These elements have a wide range of applications including optical interconnects, coherent beam addition, laser beam shaping and refractive optics aberration correction. Due to the wide range of applications, optimal design of DOE has become an important research problem. In the design of the DOEs, existing techniques utilize the Fresnel diffraction theory to compute the phase at the desired location at the output plane. This process involves solving nonlinear integral equations for which various numerical methods along with robust optimization algorithms exist in literature. However all the algorithms proposed so far assume that the size and the spacing of the elements as independent variables in the design of optimal diffractive gratings. Therefore search algorithms need to be called every time the required geometry of the elements changes, resulting in a computationally expensive design procedure for systems utilizing a large number of DOEs. In this work we have developed a novel algorithm that uses neural networks with possibly multiple hidden layers to overcome this limitation and arrives at a general solution for the design of the DOEs for a given application. Inputs to this network are the spacing between the elements and the input/output planes. The network outputs the phase gratings that are required to obtain the desired intensity at the specified location in the output plane. The network was trained using the back-propagation technique. The training set was generated by using GS algorithm approach as described in literature. The mean square error obtained is comparable to conventional techniques but with much lower computational costs

Phase 9 Fiber Optic Cable Microbending and Temperature Cycling Tests

Optical fibers represent the back bone of the current communications networks. Their performance in the field lacks long term testing data because of the continuous evolution of the manufacturing of fibers and cables. An optical fiber cable that is installed in NASA's KSC has experienced a dramatic increase in attenuation after three years of use from 0.7 dB/km to 7 dB/km in some fibers. A thorough study is presented to assess the causes of such an attenuation increase. Material and chemical decomposition testing showed that there are no changes in the composition of the fiber which might have caused the increase in attenuation. Microbending and heat cycling tests were performed on the cable and individual fibers. It was found that the increase in attenuation is due to microbending caused by excessive stress exerted on the fibers. This was the result of manufacturing and installation irregularities

Performance optimization and light-beam-deviation analysis of the parallel-slab division-of-amplitude photopolarimeter

A division-of-amplitude photopolarimeter that uses a parallel-slab multiple-reflection beam splitter was described recently [Opt. Lett. 21, 1709 (1996)]. We provide a general analysis and an optimization of a specific design that uses a fused-silica slab that is uniformly coated with a transparent thin film of ZnS on the front surface and with an opaque Ag or Au reflecting layer on the back. Multiple internal reflections within the slab give rise to a set of parallel, equispaced, reflected beams numbered 0, 1, 2, and 3 that are intercepted by photodetectors D0, D1, D2, and D3, respectively, to produce output electrical signals i0, i1,i2, and i3, respectively. The instrument matrix A, which relates the output-signal vector I to the input Stokes vector S by I = AS, and its determinant D are analyzed. The instrument matrix A is nonsingular; hence all four Stokes parameters can be measured simultaneously over a broad spectral range (UV–VIS–IR). The optimum film thickness, the optimum angle of incidence, and the effect of light-beam deviation on the measured input Stokes parameters are considered

Performance optimization and light-beam-deviation analysis of the parallel-slab division-of-amplitude photopolarimeter

A division-of-amplitude photopolarimeter that uses a parallel-slab multiple-reflection beam splitter was described recently [Opt. Lett. 21, 1709 (1996)]. We provide a general analysis and an optimization of a specific design that uses a fused-silica slab that is uniformly coated with a transparent thin film of ZnS on the front surface and with an opaque Ag or Au reflecting layer on the back. Multiple internal reflections within the slab give rise to a set of parallel, equispaced, reflected beams numbered 0, 1, 2, and 3 that are intercepted by photodetectors D0, D1, D2, and D3, respectively, to produce output electrical signals i0, i1,i2, and i3, respectively. The instrument matrix A, which relates the output-signal vector I to the input Stokes vector S by I = AS, and its determinant D are analyzed. The instrument matrix A is nonsingular; hence all four Stokes parameters can be measured simultaneously over a broad spectral range (UV–VIS–IR). The optimum film thickness, the optimum angle of incidence, and the effect of light-beam deviation on the measured input Stokes parameters are considered

Rotation-Invariant Synthetic Discriminant Function Filter for Pattern Recognition

The ring synthetic discriminant function (RSDF) filter for rotation-invariant response is discussed for pattern recognition. This method uses one half of a slice of the Fourier transform of the object to generate the transfer function of the filter. This is accomplished by rotating the one half of a slice in the Fourier domain through 2π rad about the zero-frequency point of the Fourier plane. This filter has the advantage of always matching at least one half of a slice of the Fourier transform of any rotation of the image. An analytical discussion of the filter construction and correlation results are presented along with simulated correlation results for a particular target image. These results and established metrics are used for comparison with benchmark algorithms