Variable curvature mirror (VCM) is a simplified active optical component being capable of changing its curvature radius.
Curvature radius variation within a wide range requires that the VCM should be able to generate a large saggitus
variation. Besides that, the surface form accuracy should be maintained above a reasonable level. In this paper, a
piezoelectric actuation based prototype VCM is designed, constructed and experimentally tested. The thickness of the K9
plane mirror is only 3mm over the full aperture of 100mm. Six piezoelectric actuators are fixed into a base plate and the
head of each actuator is connected to an annular ring through the screw thread. With such a structure, the force provided
by each actuator can be transformed to the mirror backside through this annular ring. With each actuator generating the
same force, the curvature radius can be changed in a uniform way. At the mean time, the surface form accuracy could be
adjusted one point by point to compensation asymmetric modes as well. Mathematical analysis and FEA (finite element
analysis) are used together to demonstrate the theoretical correctness. Besides that, the prototype VCM is successfully
constructed and experiments have been carried out to give a quantitative assessment on the saggitus variation.
In recent years, cylindrically symmetric vector beams are widely used in many fields, such as high-resolution
microscopy, micro printing and nonlinear optics et al. The intensity and polarization of cylindrically symmetric vector
beams are symmetrical around the optical axis. Radially polarized beam and azimuthally polarized beam are the most
common cylindrically symmetric vector beams. In this paper, first by using numerical methods it is calculated that the
cylindrically symmetric vector beams can be obtained by overlapping two optical vortices or by overlapping an optical
vortices with topological charge of two and a plane wave. Then, a radially polarized beam and azimuthally polarized
beam were experimentally obtained by overlapping a right-circularly polarized plane light and a left-circularly polarized
optical vortices with topological charge of two, which is obtained by using a reflective liquid crystal spatial light
modulator (SLM) and a quarter-wave plate. The experimental results show that, by using this method, different kinds of
cylindricany symmetric vector beams can be obtained very simply and easily, and could be switched to each other at
video rate, and has higher energy conversion efficiency (up to 60%).
In optical trapping, annular beam as a kind of hollow beam is used to increase the axial trapping efficiency as well as the
trapping stability. In this paper, a method for producing an annular beam by a system consisting of a single axicon and a
pair of lens is proposed. The generated beam was also used as the optical tweezers. We use the geometrical optics to
describe the propagation of light in the system. The calculated intensity distribution in three-dimensional space after the
system shows a good agreement with the experimental results. The advantages of this method are simplicity of operation,
good stability, and high transmittance, having possible applications in fields like optical microscopic, optical
manipulation and electronic acceleration, etc.
Rewritable collinear holographic image storage was realized in a genetically mutated bacteriorhodopsin BR-D96N film by using its photochromic property. For a BR-D96N film with 3.0 optical density, under 632.8nm, 700mW/cm2 recording light (optical reference ratio is about 1:1.2), the optimum recording time is about 3s, and optimum reconstruction light intensity is about 50mW/cm2, and the safe-time of the hologram is about 10min. The experiment shows that, in collinear holographic storage system, simple optical setup, small volume, low environmental effect and the high density storage can be realized; and it is proved that the BR-D96N film has advantages like short storage time, high
light sensitivity, high reversibility, long-term stability and easy used, which can be used as a high sensitive dynamic
rewritable collinear holographic storage media.
A diarylethene derivative, 1,2-bis[2-methyl-5-(3-fluorophenyl)-3-thienyl] perfluorocylcopentene, is synthesized and dispersed into PMMA to prepare a polymeric film. The film shows good color recycling between switching of irradiation of UV light and red light. Under the excitation of linear polarized light, an apparent characteristic of photoinduced anisotropy is observed in the diarylethene/PMMA film, which implies polarization modulation gratings can be recorded in this holographic medium apart from recording of intensity modulation gratings. We experimentally make a comparison among four types of polorization holograms recording for their reconstruction images, which shows that the orthogonal circular polarization hologram has both high signal-to-noise ratio and high diffraction efficiency. Based on the polarization gratings scheme, we demonstrate the polarization multiplexing holograms reocording and retrieval in the diarylethene/PMMA film and the combination with the angular multiplexing scheme.
To test the dynamic photorefractive grating during holographic recording, as usual, the signal wave is blocked from time to time and simultaneously the diffracted beam of the reference wave is tested. This kind of measurement destroys the continuity of the holographic recording and increases the random noise and results in bad repeatability and reliability. In this paper, the phase-conjugate technique is used to overcome the above drawbacks. The reference wave and the object wave are much stronger than the probe beam propagating along the counter-direction of the reference wave. Thus the real-time and non-destructive testing of the dynamic holograms can be obtained by measuring the phase-conjugate wave of the object wave.
Self-enhancement effect and oscillatory characteristic of diffraction are observed during the holographic recording in LiNbO3:Ce:Cu crystal. Both phenomena are owing to the dynamic diffraction characteristics of photorefractive volume holograms or gratings. On the basis of the experimental results and the above concept, two methods, i.e., the self-enhancement effect and the optimal switching from the recording step to the fixing step, are correspondingly suggested for the production of persistent holograms with high fixed diffraction. By use of our recently presented time-space dynamic theory of two-center holographic recording, the experimental results are theoretically analyzed and numerically simulated. The simulations are in good agreement with the experimental results. It is shown that the self-enhancement in both steps of recording and fixing can obviously enhance the recorded and fixed hologram and thus the nonvolatile diffraction efficiency. And it is also indicated that switching after the first diffraction maximum leads theoretically to fixed diffraction of as much as 100% with a suitable switching time. This optimal switching provides a completely new method to obtain high persistent diffraction of the nonvolatile holographic storage in doubly doped LiNbO3 crystals.
Photoinduced anisotropic properties of pyrrylfulgide are studied. From measurement of the photoinduced spectrum of dichroism, the birefringence spectrum is evaluated by Kramers-Kronig relations. At optimal exposure of 13 ~ 20J/cm2 a maximum photoinduced dichroism (Dperpendicular - Dparallel) of about 0.1 and a maximum photoinduced birefringence (nperpendicular - nparallel) of about 8×10-4 are achieved. We exploit this photoinduced anisotropy and use a pyrrylfulgide/PMMA film to demonstrate optical image processing such as contrast reversal, image subtraction and summation, low-pass filtering and edge-enhancement. From the spectra of dichroism and birefringence the spectrum of the diffraction efficiency for polarization holography is calculated. We demonstrate that diffracted images with high signal-to-noise-ratio (SNR) can be obtained by holographic recording with orthogonal polarization.
Optical data storage is a frontier in the information science. Currently, there are mainly two kinds of storage materials, i.e., thermal-optic and photonic materials. The storage methods are divided into serial and parallel modes. In the market, the mature technique is CD-RW, which uses the thermal-optic material and serial method. The storage density of the CD-RW is restricted by the size of material particles, the conduction of heat, etc. Besides, the recording speed is seriously limited by the process of heating. Photonic materials and parallel method will be the trend in the optical data storage. Because it is based on the photon reaction on the molecule scale, the storage density and speed will be greatly increased. In this paper, a new kind of organic photochromic material -- pyrrylfulgide was studied. A parallel optical data storage system was established. Using the pyrrylfulgide/PMMA film as a recording medium, micro-images and binary digital information could be recorded, readout and erased in this parallel system. The recorded information on the film can be kept for at least 8 months in dark at room temperature. So far, the storage density is 3 x 107 bit/cm2.
The photochromic retinal protein bacteriorhodopsin (BR) modified by genetic method is considered as a promising material for optical and holographic recording because of its effective photochemistry, high stability and unique reversibility. The parallel image recording can largely increase the speed of data writing and reading in comparison with the bit-type recording. Here, we established a micro-imaging system with BR-D96N biofilm as recording medium. The optical image loaded on a LCSLM was illuminated by an argon laser (514 nm) and was micro-imaged on the BR film with a high resolution lens. The BR film was mounted in a two dimensional micropositioning system for accurately addressing. The recorded images were readout by a CCD camera under weak illumination of 514 nm laser. In this system, we can record 1000 frames of microimages on the BR film with each frame having an area of 460μm × 350μm. This system can be developed into a two dimensional parallel digital optical data storage setup.
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