Volume holograms as frequency-selective elements
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Diffraction efficiency
Volume hologram
Optical coupling between preferential-order volume diffraction grating couplers fabricated on independent substrates is demonstrated. The coupling efficiency between gratings is quantified as a function of both grating and waveguide fabrication technology and relative angular position of the two substrates. A maximum grating-to-grating coupling efficiency of 31% is reported for coupling between two nonoptimized, nonfocusing, unpatterned volume grating couplers.
Diffraction efficiency
Electromagnetically induced grating
Waveguide
Ultrasonic grating
Guided-mode resonance
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Poly(tBOC)styrene is a sensitive (<0.5-mJ/cm 2 ) photodeformable holographic medium that supports high-efficiency surface relief gratings and moderate efficiency index gratings. The development of the holograms is especially simple, requiring only that the medium be heated to ~100°C for 2 min. The diffraction efficiency for the first order in reflection is higher than 10% for spatial frequencies below 500 lines/mm, but there is no regime where a linear relationship exists between exposure and efficiency. This medium is eminently suitable for the production of holographic optical elements intended for use in the ultraviolet. An off-axis zone plate made by aluminizing a relief hologram fully depletes the zero-order beam and produces a first-order focused spot within 30 % of the diffraction limit. Such tightly focused beams can be used for ablating patterns in many materials.
Diffraction efficiency
Polystyrene
Reflection
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Holograms show promise as optical interconnects both for electronic intra and interchip applications and for numerical optical computing. We are concerned with applications where it is desirable to store many interconnects in the same hologram while maintaining good diffraction efficiency. To deal with the problem of low-diffraction efficiencies present in holographic materials with many superimposed exposures, resonant mirrors are added to reflect the light back and forth through the hologram, thus increasing reconstruction efficiency. Up to 100% efficiency is possible in lossless multiexposure holograms.
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Volume Holographic Gratings is designed and fabricated to obtain a simple, lightweight and cheap light deflector. The entire process, starting from the chemical preparation of the photosensitive material, to the recording of Volume Holographic Gratings and their appropriate characterization, is reported. The recording material was a new photopolymer sensitive to light at 532nm. Results showed that the recorded Volume Holographic Grating presents a very high value of the diffraction efficiency, up to 94%. In addition, a flexible material is used to write Volume Holographic Gratings.
Diffraction efficiency
Volume hologram
Characterization
Holographic Data Storage
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We consider several aspects of holographic optical interconnects. First we outline the various categories of holographic interconnects. We then show that obtaining a large number of superimposed holographic interconnects, all of high efficiency, in one hologram is difficult with present materials. Resonant mirrors around the hologram are suggested as a solution. It is shown that, with four mirrors around a lossless hologram of low diffraction efficiency, it is possible to choose mirror reflectivities to provide 100% diffraction efficiency. Angular beam widths and a recommended configuration are also presented.
Diffraction efficiency
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Optimum conditions for the generation of high-efficiency hologram gratings are presented. The most efficient phase holograms were obtained for exposures 10 to 20 times larger than those for optimally exposed amplitude holograms. Hologram gratings produced on Agfa Gevaert 8 E 70 recording plates diffracted 40 percent of the incident radiation into the holographic image. This experimentally obtained efficiency is 60 percent of the theoretical maximum for a hologram with a geometric parameter Q of 4.6.
Diffraction efficiency
Multiple exposure
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Diffraction efficiency
Volume hologram
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One of the factors determining the diffraction efficiency of the grating of a surface-relief hologram is the refractive index of the material. The refractive index of the photopolymer constituting a reproduced grating is smaller than that of the photoresist constituting the master grating. To reproduce the grating with a high diffraction efficiency, we studied how to optimize the grating shape. We found that a grating 0.5 μm wide required a master grating 0.9 μm wide to get the highest diffraction efficiency and that the reproduced grating had to be at least 1 μm deep. We fabricated a master and stamp and replicated gratings with a diffraction efficiency of 78 ±5%.
Diffraction efficiency
Electromagnetically induced grating
Ultrasonic grating
Photoresist
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In this paper, we study the diffraction properties of tunable cascaded VHGs by using the two-dimensional coupled wave theory and two-dimensional Runge-Kutta methods. The intensity distributions of the diffracted and transmitted beams are given, the total diffraction efficiency is calculated for multiple cascaded finite-sized VHGs. It is shown that the diffraction characteristics depend on the grating parameters such as the number of the cascaded VHGs and the sizes of each VHG, and the effects of the buffer gaps between two cascaded VHGs is also discussed. It demonstrates the possibility of shaping beam and improving the beam quality by controlling the grating parameters and the layers number of the VHGs. The analysis of this paper also will be valuable for novel applications of finite-sized VHGs.
Diffraction efficiency
Volume hologram
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A hybrid hologram is constructed which combines the flexibility of a computer-generated hologram (CGH) with the high-diffraction efficiency of volume phase holograms. The new hologram is constructed by using a spatially filtered wave front from a conventional 246- × 256-cell CGH as the object wave for the recording of a volume hologram. Theoretical and experimental results show that simultaneous high-diffraction efficiency and reconstruction fidelity are possible.
Diffraction efficiency
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