In digital holographic microscopy, wavefront aberrations suppressions techniques are very matured from the perspective of the reference wave, i.e. aberrations was suppressed by numerically manipulating the reference wave. There are techniques that deal with the noises that arise from the object arm, but were mostly numerical procedure in the reconstruction stage. We found out that a better approach would be suppressing the noises, particular scattering noise from the object arm, prior to the recording stage via phase conjugation technique. By using phase conjugation technique, it is possible to trace back to the object plane where scattering is minimum; hence, achieving optical noise suppression prior to the recording stage.
In digital holography, techniques of noise suppression from the perspective of reference arm have been maturely developed. The object counterpart, however, is still in its infancy. Self-pumped phase conjugation technique which involves a BaTiO3 crystal was introduced unto reflective-type digital holographic microscopy to suppress scattering noise derived from the object arm, prior to recording stage. A phase distorter was introduced as scattering source, and signal-to-noise ratio was calculated. Furthermore, induced method was proposed to speed up the response time.
In this work, we propose an innovative method for digital holographic microscopy named as photorefractive phaseconjugation digital holographic microscopy (PPCDHM) technique based on the phase conjugation dynamic holographic process in photorefractive BaTiO3 crystal and the retrieval of phase and amplitude of the object wave were performed by a reflection-type digital holographic method. Both amplitude and phase reconstruction benefit from the prior amplification by self-pumped conjugation (SPPC) as they have an increased SNR. The interest of the PPCDHM is great, because its hologram is created by interfered the amplified phase-conjugate wave field generated from a photorefractive phase conjugator (PPC) correcting the phase aberration of the imaging system and the reference wave onto the digital CCD camera. Therefore, a precise three-dimensional description of the object with high SNR can be obtained digitally with only one hologram acquisition. The method requires the acquisition of a single hologram from which the phase distribution can be obtained simultaneously with distribution of intensity at the surface of the object.
KEYWORDS: Digital holography, Holography, 3D image reconstruction, Amplifiers, Microscopy, Holograms, Glasses, Digital imaging, Objectives, Refractive index
This paper applies the Mach-Zehnder interferometer with an objective lens and an offset lens to magnify the
wavefront of an object image, while compensating for the quadratic phase caused by the objective lens and achieving
digital holographic microscopy. 1) The single-exposure method and simple arbitrary micro phase step (AMPS)
approach are applied to suppress the zero-order and conjugate image interferences caused by holograph reconstruction.
Through this process the best conditions for conjugate imaging suppression can be identified via the relative light
intensity distribution and noise suppression of the numerically reconstructed object wavefront.
A deterministic phase-encoded encryption system, which adopts a lenticular lens array (LLA) sheet as a phase modulator
(key), based on arbitrary two-step phase-shift interferometry (PSI), with an unknown phase step, is presented. The
principle of encryption and decryption which is using a LLA in arbitrary unknown two-step PSI is given. With the aid of
key holograms (right key), it can be theoretically shown that only the reconstructed object wavefront term will be left in
the image plane, and all the accompany undesired terms be eliminated. Thus the hidden information of object wavefront
in this encryption system can be numerically and successfully decrypted using arbitrary unknown two-step PSI with right
key. For comparisons, computer simulations are carried out to verify the principle of encryption and decryption without
key, with wrong key and with right key, respectively.
This work presents the working principle for digital holography with arbitrary phase-step reconstruction using multiple
holograms. The arbitrary phase-step of the reference wave can be easily estimated with two different approaches -blind
searching algorithm (Meng et al.) and the limited area algorithm (Hsieh et al.). Using these approximations, the
magnitude-contrast images are reconstructed without dc term and twin-image blurring, but the phase-contrast images are
filled with phase distortion. Computer simulations are carried out to verify the proposed approach and optical
experiments are performed to validate it. The optical results and spatial resolutions using different estimation of the
phase-step are presented and discussed herein.
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.
KEYWORDS: Digital holography, Holograms, 3D image reconstruction, Holography, 3D metrology, Phase measurement, Spatial frequencies, Charge-coupled devices, Digital recording, Wave propagation
We develop a novel holographic reconstruction method that requires only an off-axis Fresnel digital hologram
without the need for additional phase-retrieval elements in the experimental setup. With this approach we can reconstruct
numerical phase profiles without twin-image blurring, using only an off-axis digital hologram. Furthermore numerical
reconstruction and twin-image suppression can be rapidly accomplished with a personal computer. Not only is twin-
image suppression easier but the constraints characteristic of the conventional phase-shifting digital holographic-based
scheme that employs multiple exposures can be overcome. The experimental results clearly show that complex spatial
frequency information about the object to be measured is not lost during numerical reconstruction and that the profile of
the phase object can be exactly measured and presented.
This work presents a novel method for optical decrypted key production by screen printing technology. The key is
mainly used to decrypt encoded information hidden inside documents containing Moire patterns and integral
photographic 3D auto-stereoscopic images as a second-line security file. The proposed method can also be applied as an
anti-counterfeiting measure in artistic screening. Decryption is performed by matching the correct angle between the
decoding key and the document with a text or a simple geometric pattern. This study presents the theoretical analysis and
experimental results of the decoded key production by the best parameter combination of Moire pattern size and screen
printing elements. Experimental results reveal that the proposed method can be applied in anti-counterfeit document
design for the fast and low-cost production of decryption key.
In this work we present a single exposure method for recording multiple holograms in reflection holography. In this
novel method, the input pattern is a segmented image composed of alternating slices of several original images and
modulated by a lenticular lens array sheet. A set of object beams can be produced simultaneously, which are angularly
separated on the recording plane and overlap one reference beam at the same time. Therefore, only one exposure is
needed for holographic recording multiple holograms. Experimental results show that a lenticular lens array sheet placed
as a modulator in the path of the object beam provides a simple yet effective ingredient of creating multiple images for
single-exposure holography. The proposed method is especially useful for one-step write/read multiple holograms and
for stereoscopic display applications.
We propose a novel optical holographic encrypted data storage scheme based on phase encoding multiplexed scheme. In the proposed data storage scheme, patterns of encrypted images are stored holographically in a photorefractive LiNbO3:Fe crystal by using lenticular lens array (LLA) sheet phase-encoded multiplexing.
Experimental results show that rotating a LLA placed as a phase modulator in the path of the reference beam provides a simple yet effective method of increasing the holographic storage capabilities of the crystal. Combining this rotational multiplexing with two-axis tilting multiplexing offers not only further data storage
capabilities but also data encryption possibilities.
We propose a cost-effective, compact, and robust optoelectronic sensing system for measuring ballistic impact velocity and distribution of the projectile motion. The key elements consisted of this system are four photo-gates hybridized by compound one-dimensional prism array and analog/digital electronic components. The number of light sources and photodetectors used in a photo-gate was reduced to one pair of that. The time interval passing each pair can be measured precisely (~10-8 s). The average velocity and location of projectile are carried out according the measured time intervals. The system can precisely measure the velocity of a bullet as it leaves a gun barrel and the velocity toward the trajectory outside the firearm. Furthermore, the system uses a commonly found low-powered laser pointer as light source. Compared with other optoelectronic sensing systems that use high-powered lasers, our system is both economical and safe.
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.
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.
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.
We propose a new holographic memory scheme based on random phase-encoded multiplexing in a photorefractive LiNbO3:Fe crystal. Experimental results show that rotating a diffuser placed as a random phase modulator in the path of the reference beam provides a simple yet effective method of increasing the holographic storage capabilities of the crystal. Combining this rotational multiplexing with angular multiplexing offers further advantages. Storage capabilities can be optimized by using a post-image random phase plate in the path of the object beam. The technique is applied to a triple phase-encoded optical security system that takes advantage of the high angular selectivity of the angular-rotational multiplexing components.
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.
We have discovered for mutually pumped phase conjugation (MPPC) of two incoherent beams which are all remarkably insensitive to angular and lateral positional changes in either of the two input beams or in the photorefractive BaTiO3 crystal itself. By designed choosing the geometry such as the orientation between the pump beam and the crystal's c-axis the grating can be dominated and two lasers can be coupled efficiently. Three novel configurations can be formed in photorefractive crystals when the MPPC occurred. These configurations are part of a family of mutually pumped phase-conjugate mirrors (MPPCMs) all of which have similar internal beam paths within the crystal having three internal reflections. These configurations provide broad interaction, which offer with more efficient, and large angular and positional acceptance, and even high resolution and stability. We also experimentally demonstrate our discovery of a new double mutually pumped phase- conjugate mirror (DMPPCM) which phase conjugate three incident beams in pairs operating as two MPPCMs in the same crystals at the same time but in different orientations. These characteristics make these configurations particularly interesting for practical applications such as for phase locking lasers and for optical free space communications.
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.
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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