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We developed compressive self-interference digital holographic approach that allows retrieving three-dimensional information of the spatially incoherent objects from single-shot captured hologram. The Fresnel incoherent correlation holography is combined with parallel phase-shifting technique to instantaneously obtain spatial-multiplexed phase-shifting holograms. The recording scheme is regarded as compressive forward sensing model, thus the compressive-sensing-based reconstruction algorithm is implemented to reconstruct the original object from the under sampled demultiplexed sub-holograms. The concept was verified by simulations and experiments with simulating use of the polarizer array. The proposed technique has great potential to be applied in 3D tracking of spatially incoherent samples.

Terahertz frequency range spans from 0.1 to 10 THz. Terahertz radiation can penetrate nonpolar materials and nonmetallic materials, such as plastics, wood, and clothes. Then the feature makes the terahertz imaging have important research value. Terahertz computed tomography makes use of the penetrability of terahertz radiation and obtains three-dimensional object projection data. In the paper, continuous-wave terahertz computed tomography with a pyroelectric array detectoris presented. Compared with scanning terahertz computed tomography, a pyroelectric array detector can obtain a large number of projection data in a short time, as the acquisition mode of the array pyroelectric detector omit the projection process on the vertical and horizontal direction. With the two-dimensional cross-sectional images of the object are obtained by the filtered back projection algorithm. The two side distance of the straw wall account for 80 pixels, so it multiplied by the pixel size is equal to the diameter of the straw about 6.4 mm. Compared with the actual diameter of the straw, the relative error is 6%. In order to reconstruct the three-dimensional internal structure image of the straw, the y direction range from 70 to 150 are selected on the array pyroelectric detector and are reconstructed by the filtered back projection algorithm. As the pixel size is 80 μm, the height of three-dimensional internal structure image of the straw is 6.48 mm. The presented system can rapidly reconstruct the three-dimensional object by using a pyroelectric array detector and explores the feasibility of on non-destructive evaluation and security testing.

In this paper, a hybrid method of phase retrieval and off-axis digital holography is proposed for imaging of the complex shape objects. Off-axis digital hologram and in-line hologram are recorded. The approximate phase distributions in the recording plane and object plane are obtained by constrained optimization approach from the off-axis hologram, and they are used as the initial value and the constraints in the phase retrieval for eliminating the twin image of in-line holography. Numerical simulations and optical experiments were carried out to validate the proposed method.

Terahertz waves of which frequency spans from 0.1 to 10 THz bridge the gap between the infrared spectrum and microwaves. Owing to the special features of terahertz wave, such as penetrability and non-ionizing, terahertz imaging technique is a very significant and important method for inspections and detections. Digital holography can reconstruct the amplitude and phase distributions of a sample without scanning and it already has many successful applications in the area of visible and infrared light. The terahertz in-line digital holographic multi-plane imaging system which is presented in this paper is the combination of a continuous-wave terahertz source and the in-line scheme of digital holography. In order to observe a three dimensional (3D) shape sample only a portion of which appears in good focus, the autofocusing algorithm is brought to the data process. The synthetic aperture method is also applied to provide the high resolution imaging effect in the terahertz waveband. Both intrinsic twin images and defocused objective images confuse the quality of the image in an individual reconstructed plane. In order to solve this issue, phase retrieval iteration algorithm is used for the reconstruction. In addition, the reconstructed amplitude image in each plane multiplies the mask of which the threshold depends on the values of the autofocusing curve. A sample with simple artificial structure is observed which verifies that the present method is an authentic tool to acquire the multi-plane information of a target in terahertz waves. It can expect a wide application in terahertz defect detecting, terahertz medical inspection and other important areas in the future.

Terahertz radiation lies between the microwave and infrared regions in the electromagnetic spectrum. Emitted frequencies range from 0.1 to 10 THz with corresponding wavelengths ranging from 30 μm to 3 mm. In this paper, a continuous-wave Terahertz off-axis digital holographic system is described. A Gaussian fitting method and image normalisation techniques were employed on the recorded hologram to improve the image resolution. A synthesised contrast enhanced hologram is then digitally constructed. Numerical reconstruction is achieved using the angular spectrum method of the filtered off-axis hologram. A sparsity based compression technique is introduced before numerical data reconstruction in order to reduce the dataset required for hologram reconstruction. Results prove that a tiny amount of sparse dataset is sufficient in order to reconstruct the hologram with good image quality.

A photonic microwave down-conversion approach is proposed and experimentally demonstrated based on a Mach-Zehnder modulator paralleled with a phase modulator. The incident radio frequency signal and the local oscillator signal are feed to the MZM and PM, respectively, and these two modulated optical signals interfere in the coupler. The useless higher-order sidebands are removed by a tunable optical band-pass filter. The principle of microwave frequency down-conversion is analyzed theoretically, the MZM and PM paralleled frequency down-conversion system is built. Then the performance of system is tested, and the experimental results show that the spurious-free dynamic range achieves 104.8 dB:Hz2/3. Compared to the conventional MZM-MZM cascaded system, the SFDR has been improved by 16 dB. The MZM and PM paralleled frequency down-conversion system can balance the intensity of the two coherent beams easily, and only single DC bias is needed. The proposed method possesses simple structure and high dynamic range.

Digital holographic microscopy has been widely used for the imaging of micro-objects and biological samples. Lensless in-line digital holographic microscopy is capable of wide field-of-view imaging. However the spatial resolution of the reconstructed images is limited by the pixel size of the detector. The relative position shift between the sample and the detector can effectively improve the resolution in the traditional sub-pixel shifting method, but it requires a high precision of translation stage. To overcome this problem, we propose a method based on the point source scanning to realize sub-pixel shifting. High precision sub-pixel shifting is achieved easily by using the geometric between point source and detector. Through moving the point source, multiple holograms with sub-pixel shifts are captured. These holograms are merged together to obtained a high resolution hologram by a synthesizing algorithm. Then, the high resolution reconstructed image of the object can be obtained by the angular spectrum algorithm. The feasibility of the proposed method is demonstrated by simulation and experiments. A USAF resolution test target was used as the object. Compared with the traditional digital holography, a higher resolution reconstructed image is obtained by our method. The proposed method has the advantages of simple recording setup and lower precision requirement of the translation stage. It can achieve the wide field-of-view and high resolution imaging.

Terahertz (THz) continuous-wave digital holography is an advanced interference imaging technique that can reconstruct quantitative distributions of amplitude and phase of the sample in real time with high resolution. In this paper, a reflective off-axis holographic system is presented. A Gaussian fitting method is applied to enhance the hologram contrast and Laplacian of Gaussian filter is used to obtain the reconstructed distance automatically. Furthermore, spectrum filtering method and angular spectrum algorithm are used to obtain the complex amplitude of the one-yuan chinese metal coin. The results confirm the prospective application of terahertz digital holography in the surface morphology for reflective samples.

For traditional dual-plane on-axis digital holography, the robustness is lower because it is difficult to maintain the stability of the phase difference between the object beam and the reference beam, and it may be invalid when the objects are on the surface of a medium with uneven thickness. An improved dual-plane digital holographic method based on Mach–Zehnder interferometer is presented to address these problems. Two holograms are recorded at two different planes separated by a small distance. Then, the zero-order image and conjugated image are eliminated by Fourier domain processing. In order to enhance the robustness of the system, the object is illuminated by a stochastic beam that is a speckle wave produced by a diffuser. Simulated and experimental results are shown to demonstrate that the proposed method has greater robustness than the traditional dual-plane on-axis digital holography and it can be used to imaging on the irregular surface of a transparent medium.

A new type femtosecond laser tracker is one high precision measurement instrument with urgent need in science research region and industrial manufacture field. This paper focuses on the operational principle and the structure development of the femtosecond laser tracer, and the method of error compensation as well. The system modules were studied and constructed. The femtosecond frequency comb module was firstly analyzed and developed. The femtosecond laser frequency comb performed perfectly high precise distance measurement for laser tracker. The experimental result showed that the stability of repetition rate reached 3.0×10 -12 @1s and the stability of carrier envelop offset reached 1.0×10 -10 @1s. The initial experiment showed that measurement error was less than 1ppm. Later the error compensation module was introduced, and the optoelectronic aiming and tracking control module was built. The actual test result showed that the stability of miss distance was better than 2.0 μm, the tracking speed could reach 2m/s.

Lightwave, as a kind of electromagnetic wave, possesses a frequency much higher than the response frequency of the current photodetectors, so the complex amplitude of the lightwave cannot be measured directly due to the loss of the phase information. Some invisible optical concepts such as phase, wavefront etc. are difficult to understand for the undergraduate students. To make the wavefront of the light wave visible, a digital holographic teaching apparatus, as a kind of comprehensive experimental platform, is developed by our teachers and students under the support of Daheng Science & Technology company. Digital holography (DH) can retrieve the quantitative amplitude and phase information of the object wavefront, which makes the wavefront display possible. In the teaching apparatus, the digital hologram is recorded by the off-axis lensless Fourier transform (LFT) digital holographic system, and the reconstruction of the hologram is achieved by the inverse Fourier Transform. The system is controlled by the Labview software. Except the quantitative amplitude and phase information, the spectrum of the hologram in the spatial-frequency domain etc. can also be visualized in the user interface of the apparatus. This can help students intuitively comprehend many optical content including phase, optical interference, diffraction, optical Fourier transform and diffraction propagation calculation et al., which has the characteristics of being open, flexible and systematic. Furthermore, the analytical and manipulative ability of students can be effectively advanced, and students can also generally understand the actual demand, work pattern and product sales of the company.

In the Optics of University Physics, two most important concepts are interference and diffraction, which reflect the wave nature of the light. The corresponding content is relatively abundant, such as Young’s Double-slit Interference, One-slit Diffraction, Grating Diffraction. But they are not easy for undergraduates to comprehend. So in order to show the two phenomenon visually, the related demonstrative experiment equipment are well-developed, but they are independent with each other. The students can accept them separately, but in the same time ignore the connection between them two. Actually, interference and diffraction are consistent in essence from the view of coherent superposition and redistribution of the light intensity. The difference only depends on the specific parameters. The objective of our paper is to analyze the condition for two slits to produce interference and diffraction phenomenon. Also, apply the knowledge of Fourier Optics to analyze the Fresnel diffraction. This would be a good example for the theory of grand unification in physics. Firstly, the intensity distribution is deduced for two-slit interference, one-slit Fraunhofer diffraction, two-slit Fraunhofer and Fresnel diffraction applying complex-amplitude integration method. In the same time, the simulated experimental results by MATLAB are shown. Secondly, the experimental results are given to verify the analysis. Finally, a new idea is presented to realize an equipment of demonstrative experiment for teaching.

Fluorescence microscopy is widely used in various of practical applications now. High resolution optical sectional microscopic imaging utilized by confocal two- or multi-photon fluorescence mi croscopy has became an essential tool in biological researches. However, optical aberrations introduced by nonhomogeneity refractive index of tissues degraded the resolution and brightness of the images. Here we present the implementation of self-interference digital holographic adaptive optics in fluorescence microscopy. Wavefront sensing and correction is achieved by holographic recording and numerical processing approach, dispenses with Shack-Hartmann sensor and deformable mirror-based complicated system. The operation speed of the system is enhanced using off-axis Fourier triangular holography. Both the influenceof the size and axial position of the guide star on th e quality of the corrected images are investigated. ,1752'8&7,21 High resolution fluorescence microscopes (FM) are widely used for three-dimensional imaging of biological samples.Diffraction-limited resolution can be achieved by use of high numerical aperture (NA) objective and multiphoton excitation in confocal FM, and used for bi ological researches [1]. The resolution of such systems are highly depends onthe performance of the scanning point source in the tissue volume. However, the nonuniform refractive index of biological tissues often introduces aberrations to the wavefront, thus distorts the light and the final image.Adaptive optics (AO) techniques have been successful applie d in microscopy to correct the aberrations and improve the imaging resolution [2,3]. Shack-Hartmann sensor and deformable mirror are commonly used as the wavefront sensor and modulator in conventional AO system, which makes the system less robust and the spatial bandwidth of measurable aberration is limited by the subaptures of the devices. AO system based on indirect methods of wanvefornt measurement that depend on numerical processing of the final images, such as the phase retrieval methods [4] and the image optimization methods [5] have been proposed. However, the extended acquiring time of such systems restrict high speed measurement, as well as the use of deformable mirror still limit the bandwidth of the wavefront correction.On the other hand, a close-loop AO system based on a holographic sensing method is proposed [6]. The wavefront sensor and corrector hardware are both replaced by numerical processing of digital hologram in [7]. However, such systems cannot be used in FM as the light source is spatially incoherent. Incoherent digital holographic adaptive optics (IDHAO) is proposed as a new AO method in self-interference holographic framework [8,9], where the aberrations are compensated point by point by calculating the convolution between the extended hologram and a point source hologram.IDHAO is seen to be particularly robust and efficient with essentially unlimited dynamic range of measurable aberration.However, there are still some limitations in the method, such as the recording speed is relative slow because three or fourholograms have to be captured to solve the twin image problem both in the point source and extended holograms. The single exposure recording method has been proposed [10], but still not being applied in adaptive microscopic imaging of fluorescent samples yet. In this paper we present the implementation of self-interference digital holographic adaptive optics in fluorescence microscopy. Nonhomogeneity refractive index distribution of biological tissues is simulated. The hologram of extended

The imaging character of microsphere is determined by its refractive index and size. In this paper, it is demonstrated that the spherical aberration(S) and numerical aperture (NA) of the microsphere are different with different refractive index or different radius. The relationship between the focal length and refractive index is obtained by numerical simulation. It is shown that the focal length decreases with the increase of the refractive index. The focal length and diameter possesses a linear relation，which is matched with the theoretical result. It is also found that the photonic nano-jet may appear when the refraction index and size of the microsphere are chosen properly. The microsphere has great potential in the laser processing of surfaces materials and super-resolution detection of nano structure etc. So the study on the microsphere imaging has great significance.

Digital holography is the product of the optical holography, computer technology and photoelectric detection technology, and has the advantage of high-speed, real-time, full field of view, non-contact and quantitative phase contrast imaging. However, the numerical aperture of the hologram is limited due to the smaller sensitive area of the photoelectric sensor and the larger pixel size, and it is uneasy to meet the practical requirement on the imaging resolution. An approach is presented to achieve the high-resolution digital holographic imaging based on a spatial light modulator(SLM). An amplitude spatial light modulator is placed between the object and the CCD in the lensless Fourier transform digital holographic imaging system. The distribution of a diffraction grating is loaded into the SLM. In this way, more light including the high-frequency content, diffracted from the object, can be collected by the CCD. The standard resolution target is used as the object. The reconstructed image is obtained by the Fresnel diffraction propagation algorithm, which exhibits three diffraction orders. The results show that the resolution is improved from 62.5 μm to 31.3 μm.

Dual wavelength digital holography is an effective technique for the measurement of object profile with the discontinuities especially for an object of thickness greater than single wavelength. However; phase information of the two reconstructed images obtained by two different wavelengths usually can’t match precisely. As a result, signal to noise ratio (SNR) of reconstructed image of the equivalent wavelength increases and the real phase information of object can’t be measured accurately. It is because in space multiplex system, the focal plane asymmetry is produced due to the discrepancy between the two wavelengths through the splitter and CCD front lens, which worsens the mismatching of the two phase information. In this paper, the method of refocusing two holograms with autofocusing algorithm based on the gradient square criterion is proposed. The matching error can be decreased easily since two real distances for the reconstruction of object information are obtained. Considering the advantages of autofocusing algorithm, the phase of sample can be measured quickly with accuracy. This method provides a basis for real-time reconstruction of dual wavelength digital holography in micro-structure measurement field. Finally, the off-axis Fresnel digital holography is implemented with Mach-Zehnder setup to verify the effectiveness of the proposed method and the three-dimensional morphology of phase grating is measured successfully.

The terahertz (THz) imaging is an advanced technique on the basis of the unique characteristics of terahertz radiation. Due to its noncontact, non-invasive and high-resolution capabilities, it has already shown great application prospects in biomedical observation, sample measurement, and quality control. The continuous-wave terahertz in-line digital holography is a combination of terahertz technology and in-line digital holography of which the source is a continuous-wave terahertz laser. Over the past decade, many researchers used different terahertz sources and detectors to undertake experiments. In this paper, the pre-process of the hologram is accomplished after the holograms’ recording process because of the negative pixels in the pyroelectric detector and the air vibration caused by the chopper inside the camera. To improve the quality of images, the phase retrieval algorithm is applied to eliminate the twin images. In the experiment, the pin which terahertz wave can’t penetrate and the TPX slice carved letters “THz” are chosen for the samples. The amplitude and phase images of samples are obtained and the twin image and noise in the reconstructed images are suppressed. The results validate the feasibility of the terahertz in-line digital holographic imaging technique. This work also shows the terahertz in-line digital holography technique’s prospects in materials science and biological samples’ detection.

A 1×4 optical splitter based on annealed proton exchanged (APE) waveguides is designed and fabricated. The beam propagation method and refractive index profile of APE waveguide are analyzed numerically. The symmetry of the optical splitter is reformed and optimized by adding straight waveguide in the cascaded Y-branch structure. The relationship between the length of the straight waveguide and the beam-slipper coefficient is obtained. The function of the 1×4 optical splitter is simulated by the commercial software BeamProp (RSoft). And the result indicates that the output uniformity of the optical splitter is improved when the length of the straight waveguide is 1935μm. Furthermore, the polarization-maintaining is gained in the 1×4 optical splitter since only the TE mode can propagate in the APE waveguide in X-cut LiNbO 3 crystal. Finally, the optical splitter is fabricated and tested experimentally and the results show good agreement with the simulation.

A phase shifting digital holography with pre-magnification is designed. In order to fully utilize the bandwidth of the camera, a four-step phase-shifting digital holography is adopted to retrieve the complex distribution of the object. To further enhance the resolution of the reconstructed image without phase aberration, two microscope objectives (MOs) are placed in front of the object and the reference mirror. The MO in the reference arm provides parallel beam at the PZT plane thus improve the precision of the phase shifting. A 1951 USAF negative resolution target is used as the sample. Experiment result demonstrates the feasibility of the proposed method.

Phase-only spatial light modulator (SLM) based on liquid crystal on silicon (LCOS) is a kind of device based on electrically controlled birefringence effect to realize phase modulation. Due to its low cost, programmable, high resolution, fast response time, LCOS has been widely used in multi-channel imaging, adaptive optics, diffraction optical elements (DOEs), dynamic holographic, optical tweezers and other fields. It is necessary to numerically evaluate the modulation characterization of LCOS before application. Firstly, the phase modulation characterization of the LCOS (PLUTO HED6010XXX by Holoeye Company) was measured based on the Twyman-Green interferometer, and the curves of both phase shift and normalized intensity as grey level functions were obtained. Experimental results indicated that phase modulation of the LCOS could be achieved to 3.99π, and the root-mean-square value (RMS) of normalized intensity was less than 0.01, which demonstrated that LCOS could be regarded as a phase-only modulation device. This method is also suitable for the evaluation of modulation characterization of other LCOS devices. Secondly, a phase pattern of thin lens written onto LCOS was demonstrated. Because of the pixel structure of LCOS, the theory of discretization of lenses was studied. Both simulation and experimental results were obtained. The experimental results proved that the convergence character of the lens written onto LCOS was similar to optical lenses. In the experiment, the measured focal length was in a good agreement to the theoretical deduction, and the relative error (RE) of which was below 1%. Both simulation and experimental results showed that LCOS could be used as lens to converge the plane wave, and replace the optical lens successfully.

Starting with the numerical calculation of the Fourier spectrum of the orthogonal phase-coded beam, a fundamental study on hybrid phase-coding and spatial multiplexing shows that there will be a complex and serious fluctuation in both intensity and phase distribution in the reference beam if a Fourier transform configuration is used for setting up the reference beam. In order to maintain phase-only modulation and orthogonality in the reference beam pattern, we suggest that the phase modulator should be imaged to the recording plane.

Fresnel Incoherent Correlation Holography (FINCH) enables holograms to be created from incoherent light illumination of 3D objects. The optical setup of FINCH is usually simple and compact owe to its in-line geometry while the reconstruction of hologram suffers from the obstruction of zero-order item and twin image. Phase-shift technology is combined with FINCH in order to obtain zero-order-free and twin-image-free reconstruction. Three-step phase-shifting is adopted in all the publications of FINCH and the application of other multi-step phase-shift technology in FINCH are not investigated yet. The Fresnel holograms are sequentially recorded with different multi-step phase-shifting (including four, three, and two-step) to form the complex hologram and the quality of the reconstructed images are compared by simulations and experiments respectively in this study. Several parameters including resolution, SNR and normalized cross-correlation are applied to evaluate the quality of reconstruction images. Although various noises would be introduced by the optical elements and the experimental environment in practice, four-step phase-shifting provides the best quality of the reconstructed image but the system resolution is not different from others. In addition, the influence of different phase shift plus to the quality of reconstruction images in the three-step phase-shifting FINCH is investigated and the results show that the quality of reconstruction images which use the π/2 is better than that 2π/3.

The reconstructed amplitude distribution of digital holography suffers from the contamination of speckle noise. We introduced and demonstrated an approach using phase SLM (spatial light modulator) to reduce speckle noise in digital holography. Multiple holograms were recorded through different illumination angle via SLM modulation. The speckle noise in the reconstructed image is suppressed by averaging these fields. The modulation interval of SLM exceeds the minimum angle of uncorrelated speckle pattern. Both reflective and transmissive experiments were conducted using USAF test target as the sample. The results show that the speckle noise was obviously suppressed and the contrast dropped to 36% of the initial value using 25 different angles. With the help of SLM modulation of illumination angle, the operation speed, accuracy and stability of the experiment has been greatly improved.

In the anticancer research with traditional Chinese medicine, many medicinally effective components can only dissolve in higher polar organic solvents, such as ethanol, dimethyl sulfoxide (DMSO) etc. However, organic solvents may directly interfere with the accuracy of therapeutic efficacy evaluation. Therefore the study on effects of organic solvents with different concentrations on Hela cells is of great significance. The digital holography is a non-destructive and non-contact method to image the transparent sample without staining and with the high precision and high resolution. In this paper, the digital holography is proposed to replace the methyl-thiazol-tetrazolium (MTT) or the Giemsa dye method. Based on the pre-magnification off-axis Fresnel digital holographic theory, an inverted microscopy system is built to obtain the phase-contrast images of the Hela cells, which are added different concentrations of organic solvents. Compared to the control group, there is significantly differences with the shapes of Hela cells with different organic solvents. The size of cell with ethanol 25% is no significantly difference with the control group. But the sizes of cells in the solutions with ethanol 12.5% and 50% are smaller than the control group. Next, the sizes of cells in the solutions with DMSO 12.5%, 25% and 50% are great smaller, compared with the control group. The results show that the digital holography has high practical value in detecting the changes in the shape of cells and is helpful in the choice of organic solvents for further apoptosis study.

Due to the finite size of the hologram aperture in digital holography, high frequency intensity and phase fluctuations along the edges of the images, which reduce the precision of phase measurement. In this paper, the apodization filters are applied to improve the phase measurement in the digital holography. Firstly, the experimental setup of the lensless Fourier transform digital holography is built, where the sample is a standard phase grating with the grating constant of 300μm and the depth of 150nm. Then, apodization filters are applied to phase measurement of the sample with three kinds of the window functions: Tukey window, Hanning window and Blackman window, respectively. Finally, the results were compared to the detection data given by the commercial white-light interferometer. It is shown that aperture diffraction effects can be reduced by the digital apodization, and the phase measurement with the apodization is more accurate than in the unapodized case. Meanwhile, the Blackman window function produces better effect than the other two window functions in the measurement of the standard phase grating.

Imaging fiber bundle is a necessary element in a conventional endomicroscopy imaging system. The combination of a proximal spatial light modulator as a means of achieving beam scanning and an imaging fiber bundle for light delivery and collection enables the wavefront at the distal end of the fiber bundle to be synthesized, controlled and scanned. In this way the endomicroscope is very different from conventional systems which use proximal scanning mirrors or distal scanning heads. Thus, it is necessary to investigate the effect of primary parameters, such as diameter of each core, core-core separation and phase mask applied to the face of the imaging fiber bundle on the characteristics of focusing spot. These effects were simulated by numerically generating distal wavefronts and propagating them using the method of angular spectrum of plane-wave. The axial and lateral resolution and SNR were introduced to evaluate the characteristics of the focus. The imaging system could be optimized and reduced constraints on the imaging fiber bundle used based on these results.

The quality of the microfluidic chip will influence the separations, injections, reactions and measurements of samples in the microfluidic system, it is essential to detect the structure such as the width, depth and roughness for evaluating its performance. Aiming at this requirement, digital holography microscope method is developed to achieve the quantitative, non-contact phase imaging with the full field. Firstly, the digital image plane holographic microscopy is designed, and the complex amplitude of the whole wave field is reconstructed by the angular spectrum method. The two-step phase subtraction and surface fitting methods are combined to eliminate the phase aberration, and the unwrapped phase information is extracted using the least-squares phase-unwrapping algorithm. Meanwhile, we acquire the profile parameters of the microchannel using white light interferometer, and the results demonstrate that the digital image plane holographic microscopy is feasible and effective for the profile measurement of microchannels in the microfluidic chip.

The liquid crystal spatial light modulator is becoming a more and more important device due to its wide applications. During its characterization, the phase modulation is the most important one. In this paper, the modulation characterization of a PLUTO phase-only spatial light modulator based on liquid crystal on silicon (LCOS) is studied by applying the lensless Fourier transform digital holography. In the digital holography, the LCOS is used as a reflected sample which modulates the phase of the incident wavefront with respect to the addressed gray level and gives the information of entire active region. This result is then compared with the result obtained by using conventional Michelson Interferometric method and both results are in good accordance with each other. At last the same holographic set up is used for the imaging of phase grating as a reflected object which is addressed to the LCOS and the clear profilometry of the grating is achieved.

Digital holography is widely used as a high resolution metrological technique in many domains. As a coherent imaging method, the speckle noise is inherent in the system and degrades image quality and optical resolution. An improved fiber-space-hybrid lensless Fourier-transform digital holography system is proposed. Multiple holograms are recorded with different oblique illumination. All hologram are reconstructed individually using the same program and each reconstructed image has a different speckle pattern. The oblique illumination system is optimized by an automatic two dimensional scanning of the fiber tip. Thus only a limited illumination area of light spot is demanded. By averaging the reconstructed images, the speckle noise of the reconstructed image is reduced. We demonstrate the effectiveness of the technique experimentally. The proposed system is convenient and practical. It can lead to a high quality result automatically.

Wave-front coded system is proposed to improve the depth of field and is proven effective. Although there are researches interested in modulation transfer function (MTF), the sampling interval is not specified. We start from the basic model of wave-front coded system and investigate the sampling interval of the optical transfer function (OTF). Then, the simulation of imaging process is performed in computer and the result is illustrated.

A key problem for the digital holography is to improve the resolution of digital holographic system. We present a system for long-range digital holographic imaging with improved resolution using synthetic aperture method. Imaging system is formed by three sub-apertures, and each sub-aperture receiver contains independently telescope lenses and a CCD device. Through every sub-aperture system, a hologram is obtained. Subsequently, we numerically reconstruct the intensity image and get a synthetic image with the resolution improved. The theoretical analysis and simulated experiment show that the method is reasonable and efficient.

In this paper, dual-wavelength digital holography is demonstrated by both numerical simulation and experiment. Simulations were done for two wavelengths of 500 nm and 550 nm. The objects are a wedge prism with a height of 2.5 μm and four abrupt steps. Three-dimensional (3D) reconstruction profiles of the original objects are obtained in the simulations. We find that dual-wavelength phase unwrapping is a fast and robust method for removing 2π discontinuities compared to software algorithm-based methods. In the experiment, two lasers of the different wavelengths 632.8 nm and 671 nm are used to obtain a larger beat wavelength. The object is a phase grating. In dual-wavelength phase unwrapping, two individual phase images are obtained by using each wavelength, respectively, and the phase image for beat wavelength is obtained by subtracting one single wavelength phase image from the other and then adding 2π whenever the resultant value is less than zero. In the final synthetic image, 3D profile of the phase grating is obtained after removing, the discontinuities by reducing the noise of the beat wavelength phase image. The experiment results demonstrate the effectiveness of the dual-wavelength phase unwrapping in digital holography.

DIW (Dynamometer Inertia Weight) of 'chassis dynamometers for automobile emissions testing' is a total inertia weight of all rotating components in the chassis dynamometer. Total Inertia weight is a inertia device simulates translational and rotational kinetic energy of a traveling vehicle which is equivalent to the mass of the car. DIW is an important technical indicator, whether it is accurate or not will affect the calibration of all technical characteristics of 'chassis dynamometers for automobile emissions testing'. In this paper,first of all, we introduce a new method to measure the Dynamometer Inertia Weight, that is, coast-down testing with twice constant-force loading method, and we derivate a formula to calculate the Dynamometer Inertia Weight from kinetic energy conservation law. Secondly, we have done a lot of coast-down testings with twice constant-force load method. After analyzing the data, we found out the factors that affect the testing processes and the accuracy of testing results. Finally, after comparing twice constant-force loading method with the take-down flywheel method and twice constant-power loading method, we know that this coast-down testing with twice constant-force loading method is better than other methods in stability and repeatability and testing data will be more accurate. It's a accurate and convenient way to measure the DIW of 'chassis dynamometers for automobile emissions testing'.

The single wavelength off-axis reflection digital holographic microscopy (DHM) can be applied in micron optical tomography measurement through the pre-magnification method. The pre-magnifying surface profile of the object is imaged by the lens placed in front of the object to be measured, and then is recorded by the CCD camera. The Reconstructed image can be got through Fresnel Diffraction calculation, the 3D surface shape information of the object was shown after the phase filtering and unwrapping process to the reconstruction image. The result in this experiment proves that off-axis reflection digital holographic microscopy can be applied to actual measurement of micron object, to achieve the tomography without touching or breaking the object.

The lensless Fourier transform digital holography has been widely employed in microscopic imaging. It enables quantitative phase analysis for both reflection and transmission objects. The phase image is obtained in the numerical reconstruction procedure. The in-focus reconstruction distance could be determined according to the extremum of the autofocusing criterion function, which is commonly applied in finding the in-focus amplitude image of the object. Then the reconstruction distance for the phase image is considered to be equal to the one for the amplitude image. When the object is a pure phase sample, such as the living cell, the minimum value of the autofocusing criterion function should be found to determine the in-focus reconstruction distance. However, in the experiment, the in-focus amplitude image is often not an ideal uniform bright field, so this method will result in some deviation. In this contribution, two derivatives-based criterion functions are applied to the phase image directly to accomplish the in-focus phase contrast imaging, which is more intuitive and precise. In our experiments, the set-up of the lensless Fourier transform digital holography is established firstly. Then the living cervical carcinoma cells are detected. The phase aberration is corrected by two-step algorithm. The final autofocusing results verify the algorithm proposed in this paper.

The linear canonical transform(LCT) is a parameterized linear integral transform, which is the general case of many well-known transforms such as the Fourier transform(FT), the fractional Fourier transform(FRT) and the Fresnel transform(FST). These integral transforms are of great importance in wave propagation problems because they are the solutions of the wave equation under a variety of circumstances. In optics, the LCT can be used to model paraxial free space propagation and other quadratic phase systems such as lens and graded-index media. A number of algorithms have been presented to fast compute the LCT. When they are used to compute the LCT, the sampling period in the transform domain is dependent on that in the signal domain. This drawback limits their applicability in some cases such as color digital holography. In this paper, a Fast-Fourier-Transform-based Direct Integration algorithm(FFT-DI) for the LCT is presented. The FFT-DI is a fast computational method of the Direct Integration(DI) for the LCT. It removes the dependency of the sampling period in the transform domain on that in the signal domain. Simulations and experimental results are presented to validate this idea.

Multi-aperture telescope is proposed to achieve high angular resolution without fabricating a large diameter monolithic primary mirror. Due to the array structure, the multi-aperture telescope has almost the same cut-off frequency as an equivalent diameter telescope, but decrease in the area of light collecting, which is the reason that the direct output image of multi-aperture telescope is blurred and low contrast. The additive noise level is another reason for low image quality. The Wiener filter is sensitive to noise because of the zero value out of the cut-off frequency in optical transfer function. An alternative image deblurring method is total variation (TV) blind deconvolution. The TV method is an iterative algorithm and preserves the edge information well. The most important characteristic of TV blind deconvolution is that the algorithm is still working with high noise level and produces reasonable result.

In this paper we study the dynamics of refractive index modulation in a dual-monomer photopolymer through grating growth under different experiment stages. By using different sets of parameters for vinyl monomers (NVC) and acrylate monomers (POEA) respectively, a composite dual-monomer model, extended from the uniform post-exposure (UPE) model for single monomer photopolymer, is proposed and fitted with the experiment data very well. Further discussions indicate that the dominant contribution to the total index modulation is made by NVC monomers, and a brief explanation of the function of POEA monomers is given.

In this paper, the quality of the reconstructed images by general plane, Gaussian, speckle imaging, and speckle reference beams, is investigated by numerical simulation and preliminary experiments, and is quantitatively evaluated using the signal to noise ratio (SNR) and the loss of signal to noise ratio (LSNR) for the purpose of comparing experimental results. The results of numerical simulation show that with plane reference, the quality of reconstructed images are very good and with Gaussian beam the noise of the reconstructed images is restrained but the boundary information is also weakened. What is worthy to be noticed, the results of both numerical simulation and preliminary experiments show that with speckle reference, the quality of the images is not good; although with the speckle imaging reference that is the image of the random phase, the situation is a little better. So, it is necessary to improve the quality of the reconstructed images when the random-phase multiplexing technology is to be used for high density storage. And in order to implement high-density holographic storage with high reconstruct quality, the reference beam must be optimized.

As the lensless Fourier transform digital holography is applied into the microscopic phase-contrast imaging on the live cells, the motion of the cells will lead to the non-coplanarity phenomena between the object and the reference source. This could result in the imaging aberration. An effective and robust autofocus procedure based on the phase distribution is presented in the paper. With the initial measurement of the distance between the reference source and the hologram, the optimum parameters corresponding to the phase-contrast image can be achieved by a single hologram, combined with the linearity fitting. The lensless Fourier transform digital holographic system is built and the experiments on the phase-contrast imaging of the live cervical carcinoma cells are performed. Finally, the good experiment results are demonstrated. Both the theoretical analysis and the experimental investigation verify the feasibility and validity of the automatic procedure for the non-coplanar aberration compensation.

The temperature variation of the testing sample can result in the density change of the surrounding air, and then the refractive index of the air is altered accordingly. Therefore, the temperature can be obtained by detecting the phase. In this contribution, the digital holography is presented to measure the temperature distribution, which can achieve the fullfield and non-destructive detection. The phase distribution can be determined by applying a single fast Fourier transform to the digital hologram. In the experiment, the LFT digital holography system is built and employed to inspect the temperature field of an electric soldering iron. The phase images are obtained, showing the temperature distributions around the iron with different position and time. The experimental results demonstrate the feasibility and effectiveness of the digital holography for the temperature measurement.

For the reconstruction in the in-line digital holography, there are three terms overlapping with each other on the image plane, named the zero order term, the real image and the twin image respectively. The unwanted twin image degrades the real image seriously. A hybrid phase retrieval algorithm is presented to address this problem, which combines the advantages of two popular phase retrieval algorithms. One is the improved version of the universal iterative algorithm (UIA), called the phase flipping-based UIA (PFB-UIA). The key point of this algorithm is to flip the phase of the object iteratively. It is proved that the PFB-UIA is able to find the support of the complicated object. Another one is the Fienup algorithm, which is a kind of well-developed algorithm and uses the support of the object as the constraint among the iteration procedure. Thus, by following the Fienup algorithm immediately after the PFB-UIA, it is possible to produce the amplitude and the phase distributions of the object with high fidelity. The primary simulated results showed that the proposed algorithm is powerful for solving the twin image problem in the in-line digital holography.

Surface roughness is crucial guideline to the surface quantity of work piece. This paper demonstrates a simple approach for measurement of surface roughness by using digital holography imaging method based on reflection off-axis lensless Fourier transform (LFT) holography. The surface profiles of the standard roughness sample plates which have the different arithmetic average height values are used as the measurement sample. Comparing the arithmetical average height values of the roughness sample plates obtained from the experiment with the given parameters, the results are in good agreement. It has shown that the method is reasonable and efficient.

Coast-down time measuring system can measure the time when speed values of Chassis Dynamometers for Automobile Emissions Testing change from initial velocity to end velocity under different load in a given speed range. This coast-down time will represent characters of Chassis Dynamometers for Automobile Emissions Testing such as Dynamometer inertia weight, constant load coast-down time, variable load coast-down time, Chassis Dynamometers for Automobile Emissions Testing can be calibrated by comparing these coast-down time with theoretical values. Working principle of coast-down time measuring system is a photoelectric sampler of coast-down time measuring system collects speed values information of Chassis Dynamometers for Automobile Emissions Testing. Then, determine speed values through calculation. When the velocity is equal to initial velocity V b value, measuring system starts a timer. When speed reaches end velocity V e value, measuring system stops the timer. So time interval is coast-down time from V b to V e . It is obvious that accuracy of coast-down time measurement lies on whether start and end velocity can be judged accurately and determined quickly, whether accuracy of timing can be admitted, and lies on how long these can be done. Coast-down time measuring system with photoelectric sampler proposed in this paper involves all the above factors, as well as improves measurement accuracy of coast-down time.

Optical sparse-aperture system can be designed to obtain high resolution in astronomical object imaging with several independent small-aperture telescopes. However, the images from separated telescopes are not only overlapped but also have same phase. Ordinarily, the phase of each sub-aperture can be obtained by wave-front sensing technology, such as phase retrieval algorithms, but this method requires more than one CCD and interfere the wave front. In this work, we use the differences between PSFs from each sub-array to get the type and size of the co-phase error. Finally, submit the results to mechanical system as a feedback for phase retrieval. We used Golay-3 system as an example to verify the above conclusions. The output is consistent with the pre-set value within the allowable error. The results show that this method is feasible and reasonable.

The newly emerging hand vein recognition technology has attracted remarkable attention for its uniqueness, noninvasion, friendliness and high reliability. It is unavoidable to produce small location deviation of human hand in the practical application; however, the existing recognition methods are sensitive to the hand shift or rotation. The test sample is matched with a series of registered images after affine transformation including the shift or rotation by most of researches, this affine transform method can remedy the location deviation to some extent, but the limited range for hand shift and rotation brings users much inconvenience and the computational cost also increases greatly. Aiming at this issue, a hand vein recognition algorithm based on local SIFT (Scale Invariant Feature Transform) analysis is developed in this contribution, which has practical significance due to its translation and rotation invariance. First, the hand vein image is preprocessed to remove the background and reduce image noises, and then SIFT features are extracted to describe the gradient information of hand vein. Many one-to-more matching pairs are produced by the common matching method of SIFT features, thus the matching rule is improved by appending a constrained condition to ensure the one-to-one matching, which is achieved by selecting feature point with the nearest distance as the optimal match. Finally the match ratio of features between the registered and test images is calculated as the similarity measurement to verify the personal identification. The experiment results show that FRR (False Rejection Rate) is only 0.93% when FAR (False Acceptance Rate) is 0.002%, and EER (Equal Error Rate) is low to 0.12%, which demonstrate the proposed approach is valid and effective for hand vein authentication.

The Rayleigh-Sommerfeld formula(RS) has proved accurate for evaluating diffraction of the optical field from a planar aperture. Thus the FFT based direct integration method for the RS(FFT-DIRS) can provide a more exact reconstructed image from sampling points of the diffraction field of the object than the numerical method for the Fresnel formula(FR) that is an approximation of the RS. Although the FFT-DIRS has been proposed and studied in some literatures, an important problem remains to be solved, that is the effect of sampling on it. Sampling of the object diffracted field leads to a periodic or quasi periodic shifting of the reconstructed image. If these spatial replicas overlap, the desired image can not be recovered without the aliasing noise. So the overlapping period plays an important role in employing the FFTDIRS for the practical applications. In this paper, a formula of this overlapping period is obtained through the relationship between the RS and the FR. Then the validity of this formula at different distances is investigated by the experimental results.

Using transmissive-writing and orthogonal-readout scheme, a dual-channel wavelength division multiplexer on the bases of two volume holographic gratings is demonstrated for the first time. The two gratings locate in different areas of a piece of doubly doped LiNbO3 photorefractive crystal, so that each grating can reach the maximal diffraction efficiency of the crystal. The gratings are recorded in the crystal by using green laser. During the readout, the input infrared light is incident on a surface of the material perpendicularly, and the light beam diffracted by one of the two channels emerge from a surface adjacent the input one. The two diffracted beams both propagate normally to the output surface. This makes it easier to couple the communication light beams into and out of the device. The filter works at the third window of optical communication with a channel space of 0.72 nm.

Digital holography combines the advantages of the optical holography and the digital image processing as a method for recording and reconstructing amplitude and phase of a wave field. Traditional reconstruction algorithms can only obtain image with the fixed pixel size. By directly discretizing the Reyleigh-Sommerfeld (RS) integral formula, a new reconstruction algorithm is proposed. Experiment result shows that the reconstruction pixel size and pixel number can be controlled with the proposed algorithm. Key words: digital holography, reconstruction algorithm 1. INTRODUCTION The principles of holography were developed originally by Dennis Gabor in 1948 as a method for recording and reconstructing amplitude and phase of a wave field. In combination with modern CCD sensor and image processing systems, digital holography microscopy (DHM) is a revolutionary technology which combines the advantages of the optical holography and the digital image processing as a method for recording and reconstructing the amplitude and phase of a wavefield. The technique allows one to use a single recorded hologram to obtain multi-focus, marker-free, quantitative phase contrast imaging of living tissues with high lateral resolution and the optical thickness axial resolution on the order of several nanometers. DHM has found many applications, the most typical being high-resolution deformation measurement, shape measurement, vibration analysis, and DHM microscope. The ever increasing computation power of personal computer makes digital holography more practical and attractive. The process of digital holography is separated into two steps: hologram recording and object field reconstruction. In the recording process, a CCD camera is used to record and sample the special continuous interference pattern on the hologram plane. Object field reconstruction is performed numerically by propagation simulation of the wavefi eld back to the object pl ane. The post-processing in this step, such as phase retrieval, wavefront propagation, shape and deformation measurement, object recognition, among others, all belong to the field of signal processing. The last decade has seen great advance of digital signal processing techniques. Digital signal processing is advantageous over analog means in its manageability of noise and the flexibility of algorithm design. The propagation simulation of the wave field requires appropriate mathematical tools and proper understanding of sampling from the optical domain to the discrete numerical domain. Currently three