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991.
Design of the Optimum Holographic Optical Element Lens Using the Hologram Computer-Aided Design Tool
A hologram CAD (computer-aided design) tool capable of designing holographic optical element (HOE) is described. We have been developing this tool which is specialized for holograms. An optimum HOE lens with high diffraction efficiency and diffraction limited imaging characteristics is designed with the tool by applying a computer generated hologram (CGH) which generates an aspherical wave. The imaging characteristics of the HOE lens are experimentally verified and desirable results are obtained.This paper was originally presented at the 2nd International Conference on Optical Design and Fabrication, ODF2000 which was held on November 15-17, 2000 at the International Conference Center, Tokyo, Waseda University, Japan. 相似文献
992.
Fast Computation of Fresnel Holograms Employing Difference 总被引:1,自引:0,他引:1
Hiroshi Yoshikawa 《Optical Review》2001,8(5):331-335
We propose an approximation method that can calculate the Fresnel hologram 16 times faster than the conventional method. To compute the hologram, an object is assumed to be a collection of self-illuminated points and the fringes from each object point are superposed. The distance between object point and sampling point on the hologram is used to obtain the phase of the light. Since a sampled hologram usually has small pixel intervals, the difference of the distance values between adjacent pixels is also small and its n-th order difference can be assumed to be constant. Therefore, the distance value at a certain pixel can be obtained from its neighbor with simple additions. The distance error can be reduced less that one wavelength with practical parameters. A hologram, which has a horizontal parallax only, 1.3 Mega-pixels and 1,000 object points, can be calculated in less than one second with a personal computer. 相似文献
993.
By introducing a convergent lens in the phase mask setup and by tilting appropriately the fiber from the phase mask, a linearly chirped fiber grating with an appropriate chirp can be obtained conveniently. Using this method, two groups of fiber gratings, each of them is composed of 8 overlaped linearly chirped fiber gratings but with different center reflection wavelength separations (~0.8 nm and ~1.6 nm, respectively) are fabricated. Experimental results show that, the compensators based on the two groups of fiber gratings can be used to compensate for the dispersion of 8×2.5 Gb/s transmission over 100 km of standard single-mode fiber for multiple channels in optical time-division multiplexing (OTDM) and densed wavelength division multiplexing (DWDM). 相似文献
994.
995.
M. P. Sampedro M. A. Cerezo Jcome D. Ramírez Martínez M. Mndez Otero M. Palomino Ovando 《Crystal Research and Technology》2006,41(7):683-688
It is, well know that some, optical materials to change his refractive index when these exposed to light, depending on particular conditions, they can generate several distributions of refractive index. In this work, an experimental periodic arrangement of refractive index generated on the Bi12TiO20 photorrefractive crystal is presented, the initial condition used was generated by superposing two He‐Ne laser linearly polarized beams in a perpendicular direction to the external field applied to the crystal at 632.8 nm. The diagrams of bands generated with this arrangement is studied, based on the similarities presented by the periodic refractive index with the photonic bandgap (PBG) diagrams one‐dimensional superlattices composed of alternating layers of two distinct materials. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
996.
Suppression of the interactions between fibre gratings used as dispersion compensators in dense wavelength-division multiplexing systems
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Chirped fibre Bragg gratings (CFBGs) are required to be concatenated to compensate
the fibre dispersion in the dense wavelength-division multiplexing (DWDM) systems.
When the channel spacing is small, the performance of CFBGs is degraded, which
restricts the usage of fibre gratings. The origin of the interactions between the
gratings is analysed and methods of suppressing the interactions are also proposed. 相似文献
997.
The near sotichiometric Ce:LiNbO3 (Ce:SLN) crystals were grown by the top seeded solution growth (TSSG) method by adding K2O flux to Li2O‐Nb2O5 melt. Their UV‐vis absorption spectra and IR spectra were measured and discussed to investigate their defect structure. The results showed that the grown crystals were near stoichiometric and Ce ions in the crystals located the Li site. Photorefractive properties of Ce:SLN crystals were studied by two‐wave coupling experiment. The results of the two‐wave coupling experiments of the crystals showed that as the CeO2 doping concentrations increased, the diffraction efficiency increased, photoconductivity decreased and the writing time and erasure time increased. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
998.
The system of L-band 2×10 Gb/s WDM transmission over conventional single mode fibre with 600 km by chirped fibre Bragg gratings dispersion compensation
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A chirped fibre Bragg grating according to ITU-T suggested L-band
(2nd channel $\lambda _{1}=1570.83$~nm; 80th channel $\lambda
_{2}=1603.57$ nm) with more than 1800 ps/nm single channel dispersion
compensation is presented in this paper, of which the cladding mode
loss, the delay curve ripple and the power fluctuation of the
reflected spectrum are less than 0.5 dB, 50 ps and 0.25 dB,
respectively. With this new FBG as dispersion compensation device, a
$2\times 10$ Gb/s wavelength division multiplexing (WDM) L-band
transmission of 600 km based on conventional single mode fibre (G.652
fibre) is performed without forward error correction. The bit error
rate (BER) is less than 10$^{ - 12}$ and the power penalties of the
2{nd} and 80{th} channel of L-band are 1.8~dB and 2.0~dB,
respectively. 相似文献
999.
The spectral focusing characteristics of a grazing-incidence flat-field spectrometer with a spherical variable-line-spacing grating in the 5-40nm spectral range are presented. The spectrometer can be used for any object at a distance in the 50mm-infinity range from the grating apex with a diffracted spectrum sharply focused on an almost flat focal plane at a constant distance from the grating apex. 相似文献
1000.
We investigate diffraction of light at phase holographic-type gratings recorded by a piezoactive ultrasonic wave in gyrotropic cubic photorefractive crystals. We show that the efficiency of diffraction at a holographic grating can be increased substantially by applying a d.c. field to a crystal under the conditions of a longitudinal electrooptical effect; elliptical polarization of diffracted light is determined by electrically induced anisotropy of a crystal in the piezofield of a photorefractive grating, by the external electric field, detuning of phase synchronism, gyrotropy of the crystal, ultrasound frequency, and the time of recombination of charge carriers. 相似文献