In angle multiplexing, the angle between the reference light and the object light is slightly changed in different
recordings. In reconstruction, only the reference beam with an accurate angular position can retrieve the corresponding
object beam due to the characteristics of Bragg condition. Accordingly, a suitable angular separation of the reference
beam should be decided for angle multiplexing. A larger angular separation will decrease the storage density, and a
smaller angular separation will increase the cross-talk noise in small bi-angles. In general speaking, only one condition
of full angle of lights is involved to calculate the angular separation with coupled-mode theory or with experiment. Thus
the angular separation is fixed in the whole procedure of angle multiplexing. As a result, the angular separations of most
multiplexed holograms are either larger or smaller. Only one hologram is multiplexed in the critical angular condition. In
this paper, angle multiplexing with different angular separations were performed to quantitatively demonstrate the effect.
The possible method to deal with the issue was also proposed.
The performance of a flashlamp pumped miniature 2.94 μm Er:YAG laser is optimized by using a mathematical model.
The model is based on the rate equations with spectroscopic data including energy transfer processes. Using this model,
we can explain the experimental phenomenon that the laser pulse slightly extends beyond the pumping pulse in some
cases. A method of optimizing the reflectivity of the output coupler was also presented.
We proposed a novel optical geometry for holographic data storage in which a phase input pattern was involved. The
input phase pattern was derived from an amplitude pattern by iterative Fourier transform algorithm. Two important
parameters of reconstructed images, diffraction efficiency and image quality, were discussed and measured. Our
geometry exhibited uniform holographic recording as well as uniform erasing. Moreover, the loss of light due to
absorption in the input pattern was minimized. The little light loss also ensured a higher diffraction efficiency of the
reconstructed image.
KEYWORDS: Digital holography, Holograms, Image encryption, Holography, 3D image reconstruction, Computer programming, Modulators, Digital imaging, Digital recording, Modulation
We propose a novel optical encryption approach using a lenticular lens array (LLA) as a deterministic phase
modulator and the single-shot digital holographic scheme. In the proposed scheme, the input amplitude image is
encrypted and interferes with the reference wave phase, which is modulated by a LLA, then recorded holographically by
a digital CCD camera to form an encrypted hologram. A decryption key is obtained from the key hologram using
numerical reconstruction. The image is decrypted using a digital holographic approach after which the encrypted
hologram is multiplying the numerical reconstructed key for decryption. The experimental results show that only an
encrypted hologram is needed. Moreover with this approach, the decryption procedure can be rapidly accomplished
using a personal computer, presenting a decrypted image of satisfactory image quality. Finally the selective sensitivity of
the key rotation is also investigated.
We discuss a method for the recording of multiple images in a photorefractive LiNbO3 crystal which needs only a
single object beam without any reference beam. The object beam is modulated by a lenticular lens array sheet to produce
a set of sub-object beams. These beams are angularly separated on the recording plane but are made to overlap by light
scattered light by the photorefractive LiNbO3 crystal. The result is that only a single beam is needed to record multiple
holograms. Experimental results show that four holograms can be stored in a photorefractive LiNbO3:Fe crystal 30 mm
X 30 mm X 1 mm in size at the same time. The proposed method makes it especially simple to produce one-beam
write/read multiple holograms.
In this work, a novel approach for numerical wave-front reconstruction in arbitrary phase step digital holography is
presented. We present a simple and effective approach for digital holography microscopy that can be used for the 3D
reconstruction of micro-structure images. The experimental results demonstrate that only two digital holograms and a
simple estimation are required for the twin-image suppression and numerical reconstruction. The advantages of this
approach are its simplicity, in that only one estimate equation need be applied, and its effectiveness, in that the exact
phase profile of a micro lens array is presented, without blurring due to numerical reconstruction or aberration caused by
the quadratic phase micro objective lens.
Refractive-index mismatch in conventional confocal microscopy produces severe degradation on axial resolution of
sectioning image because the spherical aberration is generated in specimen. In this study, we propose a polarized
photon-pairs confocal laser scanning microscope (PCLSM) in which a two-frequency linear polarized photon-pairs
(LPPPs) laser beam is produced. The common-path propagation of LPPPs integrated with optical heterodyne technique
not only can reduce the spherical aberration but also decreases scattering effect in specimen at same time. Therefore, the
better axial and lateral resolutions of the sectioning image are produced simultaneously. In the experiment, a verification
and comparison between PCLSM and conventional confocal laser scanning microscope (CLSM) on the ability of
cancellation of spherical aberration induced by cover glass are demonstrated experimentally. Finally, the ability of
PCLSM which can decrease the spherical aberration based on the common-path propagation of LPPPs associated with
polarization gating, spatial coherence gating and spatial filtering gating is discussed.
This paper proposes a technique of realizing sub-wavelength focusing spot on surface by modifying the spatial phase in far-field. This focusing spot will use to detect the spectrum of the monolayer biomolecules on the planar surface. Taking the advantage of modifying spatial phase and polarization of incident laser beam, the field distribution in near-field (near focal point) can be changed and can achieve to the smallest spot size of sub-wavelength under the reasonable adjustment of the phase and polarization of incident beam in far-field. Although nano-scale light sources can produce by labelling dye on nanoparticles, quantum dots etc., but technically it is not easy to finely manipulate nanoparticles. On the contrary, using the planar thin film of matured, reliable fabrication processes, not only the near-field twisted electromagnetic of nanostructure can be eliminated, but also fixing the biomolecules on planar surface makes its arrangement to have the consistent direction, thereupon the overall behavior of molecular vibration is simple, pure, and advantageous to detect the vibrational spectra of the monolayer molecules on surface.
In this paper we propose a novel method to perform multiplexing. In our setup, we use only one beam of light to illuminate and pass through the object pattern and to image it into a photorefractive lithium niobate crystal. Image information is recorded in the crystal in the form of gratings due to fanning effect. We can read the image information using another collimated or white-light reading beam. To record multi-images in the same crystal, the object beam of each recording should be tilted to the last object beam for avoiding crosstalk. As a result, we can record multi-images in a lithium niobate crystal, and read them separately without crosstalk.
Random-phase-multiplexing storage using photorefractive crystals is one of the most important topics in the field of photorefractive optics. To achieve random phase recording, we can use a diffuser to encrypt the reference light in a holographic recording setup. To decrypt the recorded pattern, the same diffuser used in encryption must be used in the reconstruction light, and it must be set in the original orientation. In this way, a number of 2-D patterns can be stored in a single photorefractive crystal with a single diffuser set at different orientations for different patterns. A merit in this recording method is that the encryption is virtually not possible to be decrypted if the original diffuser for encrypting is not available. In this paper, we proposed a way to decrypt the encrypted information in a photorefractive lithium niobate crystal without the possession of the original diffuser. In this method, we suppose somehow we know one of the patterns stored in the crystal, and then we retrieve the original diffuser with this pattern. And ultimately all the other patterns stored in the crystal are decrypted and retrieved with this retrieved diffuser.
We present a setup that transfers 2-D images between two ports. By using a photorefractive LiNbO3 crystal and a BaTiO3 crystal, we are able to transfer images either way without making any change in the experimental layout. The resolutions of the device are 10.1 and 6.4 lp/mm for the two transferring directions, respectively.
We propose and demonstrate a new way to image a coherent pattern through a thick dynamic phase distorting medium using a photorefractive LiNbO3 crystal. The method involves only one beam of light- the object light. Making use of photorefractive fanning effect, gratings are formed in the LiNbO3 crystal through the interference between the fanning light and the image light. In this way, the undistorted image is recorded in the crystal. The intensity distribution of the image can then be reconstructed at any time later. An undistorted image can be obtained under the condition that the period of the fluctuation time in the medium is much shorter than the response time of the crystal. Since this method uses only one beam of light, its layout is simpler and thus it avoids some aberrations due to the constraint in the layout in other methods, such as the aberration due to oblique incident light.
A photon pair density wave (PPDW) is initiated and compared with the conventional defused photon density wave (DPDW) to verify its optical properties generated by correlated parallel polarized pair photons propagating in a scattering medium. An optical heterodyne signal is generated by the scattered correlated pair photons in the scattering
medium. However, the phase delay of the signal depends upon the beat frequency and the distance between source and detector. This is similar to DPDW at the lower modulated frequency of laser source in frequency domain. Spherical wave fronts of constant attenuated intensity and the phase delay of PPDW are observed in a homogenous
scattering medium by using a lock-in amplifier. The assumption that polarized photon pairs propagating as photon density wave in a multiple scattering medium is verified experimentally. Optical properties of PPDW in the scattering medium are demonstrated successfully.
We demonstrate an optical setup being capable of transferring a two-dimensional picture in either way from one plane to another. The transferring takes place only when the receiving port sends a requesting signal. This setup consists of a LiNbO3 crystal for the purpose of four-wave mixing, and a BaTiO3 crystal for the purpose of producing self pumped phase conjugate wave. The characteristic of this setup is that it does not require any change in the experimental arrangement when the transferring direction of the picture is reversed. Finally, this setup can perform not only static but also dynamic image transferring.
We present a general survey on phase conjugators including self-pumped phase conjugator (SPPC) and mutually pumped phase conjugator (MPPC) in photorefractive BaTiO3 crystal along with some recent results on two high-performance phase conjugators using pentagon-shaped BaTiO3 crystal. We also describe two unconventional conjugators with highly ordinary polarized and purely ordinary polarized incident beams. Finally, an application of phase conjugators in one- and two-way 2-D image transfer in optical interconnection is presented.
The angular distribution of the photon pairs of a Zeeman laser scanning confocal microscope (ZLSCM) is measured in turbid media. By scanning the pinhole at different locations on a focal plane, the angular distribution of the snake photon pairs that is contributed by the object plane in the scattering medium is measured. The narrower width of the angular distribution of the snake photon pairs implies the better performance of the depth resolution of ZLSCM in turbid media. In this study, the dependence between depth resolutions of ZLSCM with respect to different vol. % concentrations of the scattering medium is observed. In addition, the correlation between angular distribution and depth resolution in different concentrations is also demonstrated and discussed.
Photorefractive phase conjugators are well known working with extraordinarily polarized light waves with respect to the crystal forming the conjugator. We demonstrate here experimentally a photorefractive phase conjugator, which works with an incident light beam predominantly polarized in ordinary state. The conjugate waves are, however, extraordinarily polarized. Good quality conjugate waves were still observed even when the intensity ratio f the o- component to the e-component in the incident beam is more than one thousand.
Mutually pumped phase conjugator with +c-face incident geometry is first demonstrated in a photorefractive pentagon-shaped 0 degree(s)-cut BaTiO3 crystal. Designed choosing the geometry such as the orientation between two mutual incoherent beams and the crystal's c-axis a novel configuration can be formed in the crystal when the mutually pumped phase conjugation established. This configuration provides more efficient interaction, which offer with fast response and high stability, and even high resolution. Two very stable and rather fast phase-conjugate signals with 22% reflectivity can be generated in 0.3 s. Two images with fine structure as high as 8.8 micrometers can be resolved.
Self-pumped photorefractive phase conjugators only work with extra-ordinarily polarized waves (e-waves) with respect to the photorefractive crystal used in the conjugator. This is because photorefractive effect is prominent only with e-wave in crystals. Ordinarily polarized waves (o-waves) do not only give rise to this kind of photorefractive effect but often suppress the e-wave photorefractive effect when both of them are directed into the crystal. In this paper, we propose another photorefractive phase conjugator, which although works with e-waves too, is very insensitive to the suppressing effect of a beam of o-waves occupying the same propagation channel.
We have demonstrated a double phase conjugator with orthogonal incident polarizations that generates both extraordinary and ordinary polarized conjugate waves simultaneously in the same photorefractive crystal, with its polarization state preserved. The e-conjugate waves are yielded by photorefractive backscattering in the crystal, and the o-conjugate waves take place due to the coupling of the incident e-waves and o-waves through circular photogalvanic effect.
Phase conjugate phenomenon and mechanism with BaTiO3 photorefractive crystals have been investigated using various cw sources and all the way down with ultrashort pulses of the femtosecond region. Our laser sources support all the various pulsewidths at a wide range of different spectral regions.
Incoherent optical pattern recognition has been demonstrated with a simple setup using photorefractive BaTiO3 crystal. The input patterns to be identified can be transmitted into the system with complete incoherent light. The setup does not required pre-fabricated filters for its operation and thus is a real-time system. The working principles of the systems are the photorefractive beam fanning effect and the degenerate four-wave mixing.
A multi-function optical computing system performing the NOR and NAND operations with two photorefractive BaTiO3 crystals is proposed. Instead of using the interference between the input signals and local incoherent erasing, we use incoherent erasing techniques in the construction of this system. The multi-function system works with different polarization states of the input optical waves. The system works with different polarization states of the input optical waves. The system is able to accept temporally incoherent and spatially incoherent signals. Optical experimental result with spatially incoherent optical images demonstrating the incoherent parallel processing capabilities and the multi-function logic operations of the system are shown.
We have discovered for mutually pumped phase conjugator (MPPC) with a novel configuration 'ray' in a 0 degree-cut nominally undoped photorefractive BaTiO3 crystal which phase conjugates two mutually incoherent beams simultaneously. Both beams incident +c face of the crystal make a non-zero obtuse angle to the crystal's +c axis, respectively. This leads to an effective mutual coupling as two fans emanating from the input beam shave a large interaction region. This novel MPPC exhibits phase conjugation with three internal reflection sand is remarkably insensitive to angular and lateral positional changes of the two input beams. We refer to this phase conjugator as 'ray of mutually pumped phase conjugator'. The temporal responses, positional and angular acceptance, and the variations of the phase-conjugate reflectively with input beam power ratio have also been determined. These characteristics make this mutually pumped phase conjugator particularly interesting for practical applications such as for injection locking lasers and for optical free space communications.
Self-Pumped Phase Conjugate signal with femtosecond laser pulse is observed. The pulse width of the incident laser pulses is about 126 femtosecond , the repetition rate is 110 MHz, and the wave-length is about 797 nm. The characters of the conjugate pulse are determined with an autocorrelator and a beam-profile analyzer. The quality of the conjugate pulses is found to be good by the well known phase distortion method.
In the development of an automatic signature verification system, the primary problem that must be resolved first is to find out a stable signature feature. In this paper, a simple and flexible distortion measurement approach is proposed to resolve the instability problem of signatures. The total distortion between an input signature and a template signature is a combination of both static and dynamic distortions. We also select some features from the fast Fourier transform (FFT) spectrum by a window function and a special weighting function. The linear correlation is used to find out the similarity between the spectrum of an imput signature and the spectrum of the template signature. Experimental results have shown that the two- layers' decision process has a high verification rate.
We propose here a simple way to synthesize a shift, rotation and limited size correlation filter, making use of the idea of synthetic discriminant functions (SDF). The SDF is synthesized by superimposing four 2nd order circular harmonics of a training reference pattern in 4 different sizes. Computer simulation experiments have shown that the filter is indeed shift, fully rotation and limited size invariant over a size range from 1 to 1.75. The invariant range can be increased if more training patterns are used.
Making use of the beam fanning effect in a BaTiO3 crystal, we propose two simple setups to perform the function of an optical image-combiner/OR-gate and an optical AND gate, respectively. The optical image combiner combines two patterns, mutually coherent or mutually incoherent, from two input channels into a single coherent one. Experimental results have shown that the response time of these devices ranges from 0.01 to 2.5 s. In the image-combiner/OR-gate device, three optical waves are involved. The first two carry the input signals into a 45-deg-cut BaTiO3 crystal; the third one brings the output out of the BaTiO3 crystal to the output plane. The AND-gate device, however, requires only two input beams.
KEYWORDS: Image segmentation, Inspection, Databases, Telecommunications, Optical character recognition, Optical communications, Detection and tracking algorithms, Personal digital assistants
In this paper, a segmentation method of knowledge-radicals for on-line handwritten Chinese characters (OLHCC) is proposed. Using the methods of finding local minimum and finding minimum of sum in local regions, some segmentation lines are obtained. We use a trick called `line segment shortening' to improve the above mentioned methods if overlapped radicals exist in a character. Based on the common writing habits of people, the decision algorithms are proposed to identify the correctness of segmentation lines. Our experimental results are conducted on ten databases of 5401 frequently used Chinese characters that users wrote according to their habits. An average suitable segmentation rate of more than 94% has been obtained, which shows that our algorithm is reliable.
In this paper, we describe an intelligent stroke extraction method based on modified polygonal approximation. Since a Chinese character is written stroke by stroke, we can regard Chinese characters as a collection of strokes. Therefore, if the strokes are extracted properly, the complexity for recognizing handwritten Chinese characters will be simplified. Using a thinning algorithm to find out the strokes of an input Chinese character has been suggested by many proposed papers. However, the thinning result is very sensitive to noise and the thinning process is time-consuming. Hence, a method for extracting strokes with robustness to noises and time-saving is highly desired. In this paper, we propose a stroke extraction method based on modified polygonal approximation. This method is more efficient and accurate in extracting strokes than any others.
The system consists of two mutually orthogonal linearly polarized laser beams carrying the Fourier spectra of a reference pattern and an input pattern into a photorefractive crystal, respectively. The image of every reference pattern in the input would appear at the output plane regardless of whether it is moving or not. However, a still non-reference pattern presented at the input plane would not show up at the output plane. Therefore stationary noise pattern never shows up in the output plane.
A scheme capable of demonstrating shift- and rotational-invariant associative memory is presented. The scheme can be implemented both digitally and optically. In optical implementation, we use one holographic spatial frequency filter and one ordinary hologram of the reference pattern. A BaTiO3 crystal is also employed in the experiment. In the digital implementation of the scheme, in addition to the rotational invariance it is shift invariant too. However, the optical implementation exhibits shift invariance only when the BaTiO3 crystal is sufficiently large.
A method of performing shift- and rotational-invariant associative memory is proposed. The method can be implemented both optically and digitally with computers. The method is detailed and some results of the digital implementation are presented. The experimental results show that the original reference pattern is recovered by partial inputs in any orientation. If the input is not the original reference pattern or a partial version of it, the results produced by this method are unidentifiable.
A simple way to synthesize a shift, fully rotational and limited size invariant composite matched spatial filter for a coherent optical correlator is proposed. We use circular harmonic components of the same order of a reference pattern in different sizes as the training images instead of using the whole reference pattern in different orientations and different sizes as is reported by other workers. This saves much labor and time in the synthesis of the filter. In this article, we have synthesized a simple filter containing four second order circular harmonic components of the alphabetic letter `E' in four relative sizes 1, 1.17, 1.33, and 1.5. Results of computer simulation have shown that this filter is shift, fully rotational and limited size invariant over the size range from 1 to 1.5. Computer simulation has also shown that this filter possesses discriminating ability.
Optical demonstration of phase-only circular harmonic filtering using a binary CGH in a standard Fourier transform correlator is reported here. The experimental results have confirmed the computer simulated results1 in that the phase-only circular harmonic filtering produces smaller side-lobes and more prominent correlation peaks with the target.
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