Holographic elements fabricated based on photoalignment technology have advantages such as polarization sensitivity, high diffraction efficiency and small volume. Their applications range is becoming increasingly widespread. A liquid crystal (LC) holographic polarization variable line-space (H-PVLS) grating is fabricated in this paper. H-PVLS was analyzed from the perspective of microstructure and macroscopic properties. The microstructure at different positions of H-PVLS indicates the variable spacing properties of the fabricated holographic elements. Spectral analysis indicates that the variable spacing properties of H-PVLS results in a larger wavelength bandwidth compared to PVG under the same conditions. The anomalous dispersion properties of the fabricated components were also measured. These results of photoalignment-based H-PVLS grating provide valuable enlightenment to the development of near-eye displays and have the potential to improve the visual experiences.
For the waveguide displays, low diffraction efficiency and narrow response bandwidth at high spatial frequency limit the development of coupling elements. In this paper, a dual-monomer, with higher and lower refractive index modulation separately, allyl propionate H-PDLC system is proposed. After experimental optimization, the diffraction efficiency of prepared high transmittance (more than 90% in the visible spectrum) H-PDLC gratings is up to 91%, and the response bandwidth is 99 nm at 973 lp/mm. By increasing the proportion of initiator and changing the radiation conditions, the diffraction efficiency is optimized to 75.4% and the response bandwidth is 29 nm at 2941 lp/mm. The experiments demonstrate that the high-frequency H-PDLC gratings have considerable application prospects as coupling elements for augmented reality optical waveguide display systems.
Lensless imaging technology can recover real scenes from highly multiplexed measurements without the focusing lens, effectively reducing the size and cost of the camera. Current reconstruction algorithms based on iterative optimization are hard to generate high-quality results due to the superposition and inevitable loss of the valid information. In order to improve the quality of the generated results, we propose a two-stage network. The first stage generates preliminary scene mapping results. The second stage uses a modified U-net network to construct a backbone network that suppresses the use of error information measured in the Point Spread Function (PSF). Meanwhile, the multiple attention modules are used at different scales of the network to extract the effective feature information in the PSF and reformulate the image information. In addition, a dual-scale discriminator structure is proposed to further improve the image quality. The results of experiments in the mask-based lensless imaging system captured dataset show that the method produces realistic results.
As an important diffractive optical element, the holographic grating has always been favored by users for its high diffraction efficiency and low cost. Especially in recent years, its value in the near-eye display waveguide structure has been further improved and explored. This paper derives a set of interference field theoretical models suitable for flexible curved radius grating, through the modification of the traditional two-wave interference principle. Based on this, the morphological law of the required interference pattern can be simulated. On the other hand, when we change the radius of flexible grating, the focus position of the diffraction field can be changed correspondingly, so as to achieve the purpose of quantitative focusing. Experiments show that the different degrees of bending of flexible curved radius grating can effectively adjust the focal length of the holographic element, and its diffraction efficiency can always be maintained above 88%. What’s more, the imaged brightness uniformity consistent, no interference of diffraction ghost lines, pave the way for the subsequent research on the key technologies of different surface-shaped curved waveguides.
With large storage capacity, low cost and long storage life, optical holographic storage technology has great application potential to meet the demands of quick data exchange and cold data storage. Accurate and standardized testing procedure of disc storage life about new optical storage media materials has become an important challenge. In view of the new optical storage technology, we discuss and analyze the applicability and limitations of the application of holographic optical disk life test through the existing domestic and foreign disc test standards. Because of materials changing in the holographic disc, we propose and optimize an aging test model and test procedure based on several discs aging test models. And also hope to provide a reference for the establishment of life test standards for holographic optical storage discs.
Holographic displays enable the formation of a three-dimensional particle field distribution and is promised to be one solution of the key problems in present virtual and augmented reality displays. The biggest challenge in the computer-generated holography (CGH) is the high consuming calculation time and the restricted field of view due to the micro display screen. In order to solve the above mentioned problems, we propose a method for machine learning accelerated lensless holographic projection, which is based on the reconstruction of complex amplitude image from phase-only CGH. The runtime of generating the phase-only CGH is half of traditional iterative method. The complex amplitude image can achieve the maximum diffraction bandwidth of the spatial light modulator (SLM). The feasibility of this method is verified by experiments.
Diffusive photopolymer is one of the fastest developed fields on the application of the holographic optical storage, and has the advantages of huge data capacity and low coat. Based on the extended model of the nonlocal polymerization-driven diffusion, the photophysical mechanism of the dual monomer system in the photopolymer holographic material is introduced. The diffusion coefficient, polymerization rate and diffusion rate are determined experimentally to provide the conditional parameters in the model. Quantitative analysis of photopolymer formulation, refractive index modulation and diffraction efficiency. This analysis can improve material performance and provide a basis for the development of next-generation holographic storage materials. A nonlocal diffusion model is used to predict theoretically the grating evolution. The model has been developed to account for both nonlocal spatial and temporal effects in the medium, which can be attributed to polymer chain growth and corresponding polymeric kinetics equations are given. We find the relationship between these equations and refractive index modulation, and obtain a diffraction efficiency equation which is appropriate for transmission volume grating. The proportion of dual monomer in chemical reaction system was optimized, and the high optical transparency of photopolymer film were obtained.
In order to study the new holographic recording medium, four kinds of photopolymer materials containing TMPTA monomers are studied. The three-dimensional interference fringe information was successfully recorded in the photopolymer film samples, which proved that it has good holographic recording and high resolution ability. The experimental results show that when the recording angle is 30°, the diffraction efficiency is as high as 93.5%@532nm and the refractive index modulation is as high as 3.07×10-3. As a holographic recording medium, it has high resolution ability and high diffraction efficiency, the material is possible suitable for permanent storage of holograms and big data, besides it has strong advantages and potential applications in the large-scale 3D display, big data storage, holographic anticounterfeiting, holographic printing and other fields.
In order to study a new holographic recording medium, this paper prepares a kind of holographic photoinduced polymer material based on a double monomer and a composite photoinitiator. Add different photoinitiator, such as red bengal (RB), titanium (irgacure 784, Ti) and a mixture of the two in the photopolymer materials, and then perform holographic exposure. We found that the compound photoinitiator improved the diffraction efficiency, light sensitivity, and transmittance to some extent compared with a single photoinitiator. Combined with the diffusion kinetics, we studied the effects of the two kinds of photoinitiators on the photoinduced polymers, and the ratio of the composite photoinitiators was optimized. The holographic parameters such as diffraction efficiency under different exposure intensities, different exposure time, different thickness and different wavelength are tested, it is shown that the exposure conditions have a great influence on the diffraction efficiency. At the same time, this material is sensitive to both green light and red light. The experiment results show that the reconstructed image is clear and bright, which indicates that the photoinduced polymer is suitable for dual-wavelength multiplexing holographic storage.
In this paper, we reported a method to fabricate 2D hexagonal lattice Holographic Polymer-dispersed Liquid Crystal (HPDLC) grating with variable period by using cylindrical waves interfere with plane waves. In order to separate polymer from liquid crystal syrup, a 532nm laser with an exposure intensity of 16mw/cm2 was used to expose. Two steps exposure techniques was adopted in the experiment with the expose time of 2s and 60s in the separate steps to form the 2D gratings. In the second exposure step, the sample was rotated by anti-clockwise 60° to form 2D hexagonal lattice structure within H-PDLC grating. The theoretical equations for describing the variable period grating is analyzed. What’s more, the diffraction efficiency and other characteristics of this grating is also studied experimentally. The experimental result shows that fabricated grating with the continuously changing periods varying from 1.679 micrometer to 2.051 micrometer within the radius of 6 mm circle sample area, which is corresponded to the theoretical simulation quite well. The first-order diffraction efficiency was tested around18.3%. The intensity of transmission beam increased from 15.6% to 73% when applied with the driving voltage from zero to the maximum of 90 V. This 2D grating has the potential application in diffractive optics such as a tunable multi-wavelength organic laser device etc.
Different higher education backgrounds in China and Germany led to challenges in the curriculum design at the beginning of our cooperative bachelor program in Optoelectronics Engineering. We see challenges in different subject requirements from both sides and in the German language requirements for Chinese students. The curriculum was optimized according to the ASIIN criteria, which makes it acceptable and understandable by both countries. German students are integrated into the Chinese class and get the same lectures like their Chinese colleagues. Intercultural and curriculum challenges are successfully solved. The results are summarized to provide an example for other similar international programs.
The University of Shanghai for Science and Technology (USST), the Coburg University of Applied Sciences and Arts (CUASA) and the OTH Regensburg, University of Applied Sciences (OTHR) established an English taught international cooperative bachelor program in the area of Engineering Physics/Optoelectronics. Students from China study their first four semesters at USST. They continue their studies in Germany for the last three semesters, including an internship and a bachelor thesis, graduating with a Chinese and a German bachelor degree. Students from Germany study their third and fourth semester at USST to gain international experience. While the first cohort of Chinese students is currently in Germany, the second cohort of German students is in Shanghai. Up to now the feedback regarding this study program is completely positive, thus it is planned to develop it further.
Dark field illumination in high throughput colony selection device is reported in this paper. It improves the contrast of image in the premise of uniform illumination. Three important factors including angular distribution of light radiation, number of LED circle array and distance between the target and the LED circle source were analyzed, which affect illumination uniformity of dark field illumination. The simulation result shows that the illumination uniformity is 93.16% when the angular distribution of light radiation is 75°, the number of LED circle array is 3, and the distance between the target and the LED circle source is 61mm. In addition, Experimental system was set up in order to test designed dark field illumination, which matches with the project requirement and simulated results very well.
Multi-wavelength sensitive holographic polymer dispersed liquid crystal (H-PDLC) grating and its application within
image splitter for autostereoscopic display are reported in this paper. Two initiator systems consisting of photoinitiator,
Methylene Blue and coinitiator, p-toluenesulfonic acid as well as photoinitiator, Rose Bengal and coinitiator, Nphenylglycine
are employed. We demonstrate that Bragg gratings can be formed in this syrup polymerized under three
lasers simultaneously including 632.8nm from He-Ne laser, 532nm from Verdi solid state laser, and 441.6nm from He-
Cd laser. The diffraction efficiency of three kinds of gratings with different exposure wavelength are 57%, 75% and
33%, respectively. The threshold driving voltages of those gratings are 2.8, 3.05, and 2.85 V/μm, respectively. We also
present the results for the feasibility of this proposed H-PDLC grating applied into image splitter without color
dispersion for autostereoscopic display according to experimental splitting effect.
This paper reports on the investigation of the electrically controlled multifocus, multi-imaging characteristics of an on-axis holographic polymer-dispersed liquid-crystal (H-PDLC) Fresnel lens. The Fresnel lens is examined within a PDLC cell through the analysis of interference fringes generated by on-axis plane and spherical waves. Experiments are conducted to investigate the multifocus and multi-imaging phenomena of the H-PDLC Fresnel lens, and a corresponding geometrical optical analysis is also provided. It is then demonstrated that the H-PDLC Fresnel lens is a plane-surface diffractive optical device which modulates the phase of incident light through a periodic change of refractive index and forms multiple symmetrical images. Its diffraction properties, which can be controlled electrically, have further potential applications in this field.
The optical chopper array based on Holographic Polymer Dispersed Liquid Crystal (H-PDLC) working at high
frequencies, for example 1KHz, 2KHz, and its application in an improved Frequency Division Multiplexed Fluorescence
Confocal Microscope (FDMFCM) system are reported in this article. The system is a combination of the confocal
microscopy and the frequency division multiplexing technique. Taking advantages of the optical chopper array based on
H-PDLC that avoids mechanical movements, the FDMFCM system is able to obtain better Signal-Noise Ratio (SNR),
smaller volume, more independent channels and more efficient scanning. What's more, the FDMCFM maintained the
high special resolution ability and realized faster temporal resolution than pervious system. Using the proposed device,
the FDMFCM system conducts successful parallel detection of rat neural cells. Fluorescence intensity signals from two
different points on the specimen, which represent concentration of certain kind of proteins in the sample cells, are
achieved. The experimental results show that the proposed H-PDLC optical chopper array has feasibility in FDMFCM
system, which owes to its unique characteristics such as fast response, simple fabrication and lower consumption etc.
With the development of H-PDLC based devices, there will be prospective in upgrading FDMFCM system's
performance in the biomedical area.
An experimental investigation on a novel electrically controlled optical chopper based on holographic polymer dispersed
liquid crystal (H-PDLC) gratings is presented in this paper. In order to realize the chopping function, a corresponding
electrical driving source and controlling circuit are developed for the phase type H-PDLC grating, so that the H-PDLC
chopper can not only modulate a light beam with variable frequencies at different duty ratios but also generate other
types of waveform modulation such as the sinusoidal modulation to replace the traditional rectangular modulation.
Experimental results on one-channel, two-channel and four-channel
H-PDLC optical choppers showed that, in
comparison with the mechanical chopper counterpart, this device had the advantages of (1) lower noise without
mechanical moving part, (2) higher conveniences in terms of changing its operational frequencies, duty ratios and
modulation curves, and (3) multi-channel modulation capability. Therefore, it will have a great potential for applications
that requires frequency modulations such as frequency modulated confocal microscopy system.
Tunable photonic crystals (PCs), which are infiltrated with nematic liquid crystals (LCs), tune photonic band gap
(PBG) by rotating directors of LCs when applied with the external electrical field. Using the plane wave expansion
method, we simulated the PBG structure of two-dimensional tunable PCs with a triangular lattice of circular column,
square column and hexagon column, respectively. When PCs are composed of LCs and different substrate materials
such as germanium (Ge) and silicon (Si), the influence of structural parameters including column shape and packing
ration on PBG is discussed separately. Numerical simulations show that absolute PBG can't be found at any
conditions, however large tuning range of polarized wave can be achieved by rotating directors of LCs. The
simulation results provide theoretical guidance for the fabrication of field-sensitive polarizer with big tunable band
range.
Based on double random phase encoding method (DRPE), watermarking technology may provide a
stable and robust method to protect the copyright of the printing. However, due to its linear character,
DRPE exist the serious safety risk when it is attacked. In this paper, a complex coding method,
which means adding the chaotic encryption based on logistic mapping before the DRPE coding, is
provided and simulated. The results testify the complex method will provide better security
protection for the watermarking. Furthermore, a low-noise multiple watermarking is studied, which
means embedding multiple watermarks into one host printing and decrypt them with corresponding
phase keys individually. The Digital simulation and mathematic analysis show that with the same
total embedding weight factor, multiply watermarking will improve signal noise ratio (SNR) of the
output printing image significantly. The complex multiply watermark method may provide a robust,
stability, reliability copyright protection with higher quality printing image.
A novel two channel multi-frequencies division multiplexed confocal fluorescence microscopy (FDMCF) system based
on the holographic polymer dispersed liquid crystal (H-PDLC) optical chopper modulation is reported. The characteristic
of unique FDMCF system is that within the FDMCF system, the
multi-channel exciter laser beams are modulated with
different carrying frequencies, after the fluorescence signals are collected, and through data analyzing process, the
FDMCF system can realize the multiply points parallel detection synchronously with high temporal and spatial
resolution. Besides, combined with the electrically controlled H-PDLC grating array working as the optical chopper to
replace the mechanical chopper, it can improve and develop the FDMCF system from two channels to unlimited system.
The paper has done the experiments to demonstrate the two-channel FDMCF system based on H-PDLC modulation and
analysis the benefits from the electrically-controlled integrated electro-optical H-PDLC devices.
Base on the theory of the thick grating, volume phase grating (VPG) is analyzed numerically in light of thick grating theory and the characteristics of VPG’s gain spectrum in connection with the variation of parameters are presented, based on which a novel dynamic gain equalizer (DGE) is designed. Simulation shows that the DGE designed can work well.
In this paper, we have developed a novel optical switch based on the electronically switchable Bragg gratings (ESGB) in holographical polymer dispersed liquid crystals (H-PDLC), which is adopted in the U.S. Patent (NO.09/963, 939). This optical switching can be produced by the superposition of H-PDLC Bragg gratings with different spatial frequencies and very high diffraction efficiency. It can provide switching speeds faster than 5ms, so that the technique can be widely applied in telecommunication to improve the transmission speed effectively.
The holographically-formed polymer dispersed liquid crystal (H-PDLC) has been widely studied in recent years. In this paper, we analyze the major factors contributing to the efficiency of volume gratings base on the basic optical theory. With regard to the feature of the special exposure material-PDLC, we have conducted some experiments to investigate the impacts of four major factors, such as different recipes of PDLC, exposing time of PDLC cells, thickness of film and the degree of two laser beams, which contribute to obtain the higher diffraction efficiency. As a result, under the same conditions, it is found that the most significant affecting factor is the recipe of PDLC. The diffraction efficiency is enhanced substantially after new chemistry reagent is mixed into the polymer precursors. Shorter cure time and comparative smaller degree of two laser beams give rise to higher diffraction efficiency. Finally, using 17degree of two laser beams, 50mw power of laser with the wavelength of 441.6 nm and exposing time about 30 seconds, we can obtain about 90% efficiency of the H-PDLC volume grating. Furthermore, we researched the relationship between the applied voltage and the diffraction efficiency.
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