Effect of Wavefront Properties on Numerical Aperture of Fresnel Hologram in Incoherent Holographic Microscopy

Fresnel incoherent correlation holographic （FINCH） microscopy is a recently developed new technique, which employs a spatial light modulator （SLM） as the beam splitter. Light originating from the same object point is split into two beams by the wavefront-division phase mask displayed on SLM, and a Fresnel-zone plate-like hologram is formed by the interference of the two beams. The numerical aperture NAH of the recorded Fresnel hologram is introduced as a comprehensive parameter for evaluating the imaging characteristics in the FINCH scheme. The effect of wavefront properties on NAH of the hologram is investigated theoretically in the sense of optimizing imaging resolution. The variation trends of NAH are described and an optimal NAH is achieved by implementing an appropriate phase mask for a given recording distance between SLM and CCD; thus optimized imaging resolution and signal-to-noise ratio are demonstrated experimentally.     

Bounding box extraction from spherical hologram of elementary object to synthesize hologram of arbitrary three-dimensional scene with occlusion consideration (Invited Paper)

A novel method to extract a bounding box that contains the three-dimensional object from its spherical hologram is proposed. The proposed method uses the windowed Fourier transform to obtain the angular distribution of the quasi-collimated beams at each position in the spherical hologram and estimates the bounding box by accumulating the quasi-collimated beams in the volume inside the spherical hologram. The estimated bounding box is then used to realize occlusion effect between the objects in the synthesis of the three-dimensional scene hologram.     

Fresnel hologram reconstruction of complex three-dimensional object based on compressive sensing

Reconstruction the computer generated Fresnel hologram of complex 3D object based on compressive sensing （CS） is presented. The hologram is synthesized from a color image and the depth map of the 3D object. With the depth map, the intensity of the color image can be divided into multiple slices, which satisfy the condition of the sparsity of CS. Thus, the hologram can be reconstructed at different distances with corresponding scene focused using the CS method. The quality of the recovered images can be greatly improved compared with that from the back-propagation method. What＇s more, with the sub-sampled hologram, the image can be ideally reconstructed by the CS method, which can reduce the data-rate for transmission or storage.     

Acceleration method for computer generated spherical hologram calculation of real objects using graphics processing unit(Invited Paper)

Graphics processing unit （GPU） based fast calculation method for computer generated spherical hologram （CGSH） of a real-existing object is proposed. Three-dimensional （3D） point cloud is constructed by capturing a real-existing object from multiple directions using a depth camera. The GPU based calculation is used in both hologram generation part and numerical reconstruction part of the CGSH. The improved calculation efficiency is verified by comparing the computation speed between central processing unit （CPU） based and GPU based imDlementation.     

Optical reconstruction of 3D images by use of pure-phase computer-generated holograms

A three-dimensional （3D） object reconstruction technique that uses pure-phase computer-generated holograms （CGHs） and a phase-only spatial light modulator （SLM） is proposed. The full parallax CGHs are generated by the point source method and the wave-oriented method without paraxial approximation. Different from conventional CGHs, the pure-phase information on the hologram plane is loaded on the SLM to reconstruct the 3D diffusive objects without considering the reference wave. This technique is more efficient in its utilization of the space-bandwidth product of the SLMs. Numerical simulations and experiments are performed, and the results show that our proposed method can reconstruct 3D diffusive objects successfully.     

Improvement of Quality of Reconstructed Images in Multi-Frame Fresnel Digital Holography

A modified reconstruction algorithm to improve the quality of reconstructed images of multi-frame Fresnel digital holography is presented. When the reference beams are plane or spherical waves with azimuth encoding, by introducing two spherical wave factors, images can be reconstructed with only one time Fourier transform. In numerical simulation, this algorithm could simplify the reconstruction process and improve the signal-to-noise ratio of the reconstructed images. In single-frame reconstruction experiments, the accurate reconstructed image is obtained with this simplified algorithm.     

The reconstruction of diffractive object digital hologramat a short distance

By using a spherical wave as the reference wave, we recorded the in-line phase-shifting digital hologram of the 25th element of Chinese standard No. 3 resolution test pattern, and gave the corresponding numerical reconstructed results. Some problems concerning with the digital hologram recording and reconstruction of the diffractive object at a short distance are discussed. The experimental result shows that the resolution of the reconstructed image is better than 10μm, which is the limit by using this experimental arrangement.     

Data-embedded-error-diffusion hologram (Invited Paper)

This paper describes a method for converting a complex Fresnel hologram into a phase-only hologram that can be embedded with large amount of data. Briefly, each row of pixels in the hologram is scanned sequentially in a left-to-right direction. The magnitude of each visited pixel is set to a constant, and its phase is embedded with the data. Subsequently, the error is diffused to the neighborhood pixels. The phase hologram realized with such means, which is referred to as the data-embedded-error-diffusion （DEED） hologram, is capable of preserving high fidelity on the content of the hologram and the embedded data.     

Particle digital in-line holography with spherical wave recording

In this paper, we propose a method of digital in-line holography of particle. A diverging spherical beam is used for illumination in recording hologram, the complex amplitude distribution generated by particle field at a single plane located in the Fresnel diffraction region is recorded by CCD, and a plane beam for reconstructing hologram, then, the magnified image can be obtained by numerical reconstruction in computer. This procedure can be interpreted by Fourier optical theory and the theoretical analysis have been done in detail, the experimental results, the air freshener being subject, are also given.     

One step hologram calculation for multi-plane objects based on nonuniform sampling (Invited Paper)

The nonuniform sampling method in hologram plane is proposed to reconstruct objects on multi-plane simultaneously. The hologram is nonuniformly sampled by decomposing it into several parts with various sampling rates. The hologram is calculated based on the nonuniform fast Fourier transform （NUFFT） algorithm. In the experiment, we load this nonuniformly sampled hologram on phases-only spatial light modulator （SLM）, and by illumination with collimated light objects with different sampling rates are reconstructed at different distant planes simultaneously. Both of the numerically simulation and optical experiments are performed to demonstrate the feasibility of our method. The experiment also shows that our proposed nonuniform sampled hologram for multi-plane objects is calculated by only one step, better than conventional method that needs several steps of calculation proportional to the numbers of object planes.     

Dual-channel phase-shifting interferometry for microscopy with second wavelength assistance

Dual-channel phase-shifting interferometry for simultaneous phase microscopy is presented. Red and blue light beams are used for microscope illumination. A 45 tilted beamsplitter replicates the object and reference waves in red light together with the object wave in blue light into two parallel beams. The two resulting quadrature phase-shifting interferograms in red light and the object waves in blue light are generated in the two channels. The two interferograms are recorded simultaneously by a color charge-coupled device (CCD) camera, and can be separated via RGB components of the recorded color patterns without crosstalk. As a result, the phase of tested specimen can be retrieved. The feasibility of the proposed method is demonstrated by test performed on a microscopic specimen.     

The spectral combination characteristic of grating and the bi-grating diffraction imaging effect

This paper reports on a new property of grating, namely spectral combination, and on bi-grating diffraction imaging that is based on spectral combination. The spectral combination characteristic of a grating is the capability of combining multiple light beams of different wavelengths incident from specific angles into a single beam. The bi-grating diffraction imaging is the formation of the image of an object with two gratings: the first grating disperses the multi-color light beams from the object and the second combines the dispersed light beams to form the image. We gave the conditions necessary for obtaining the spectral combination. We also presented the equations that relate the two gratings’ spatial frequencies, diffraction orders and positions necessary for obtaining the bi-grating diffraction imaging.     

The recording of digital hologram at short distance and reconstruction using convolution approach

By adopting in-line lensless Fourier setup and phase-shifting technique, we recorded the phase-shifting digital hologram at short distance. As the Fresnel diffraction condition is no longer valid, the convolution approach is chosen for the reconstruction. However, the simulated reference wave for the reconstruction would suffer from severe under-sampling due to the comparatively large pixel size. To solve this problem, sinc-interpolation is introduced to get the pixel-size of the hologram reduced prior to the reconstruction. The experimental results show that an object image of high fidelity is obtained with this method.     

Fast reconstruction of digital holograms for extended depths of field

Past research has demonstrated that a static, three-dimensional(3D) object scene can be directly recorded as a complex digital hologram. However, numerical reconstruction of the object scene, which may comprise multiple sections located at unknown distances from the hologram, is a complicated and computation-intensive process.To the best of our knowledge, we propose, for the first time, a low complexity method that is capable of reconstructing a complex hologram, such that sections at different depths in the 3D object scene can be automatically reconstructed at the correct focal distances and merged into a single image for an extended depth of field. We demonstrate an order of magnitude increase of the depth of field for binary objects. With the use of a graphical processing unit, the reconstruction of a 512 × 512 complex hologram can be accomplished in about 100 ms,equivalent to around 10 frames per second.     

High-quality three-dimensional holographic display with use of multiple fractional Fourier transform

In order to realize holographic display of three-dimensional （3D） objects and suppress zero-order light, conjugate image, and speckle noise, a novel method is proposed based on multiple fractional Fourier transform （M-FrFT） for cMculating holograms of 3D objects. A series of kinoforms are generated by adding pseudorandom phase factor （PPF） to object planes in calculating each kinoform, and generating the PPF randomly again in the next kinoform calculation. The reconstructed images from kinoform sequence are superposed together in order to suppress the speckle noise of reconstructed image and improve the contrast and detail resolution of the reconstructed images. The qualities of reconstructed images from single amplitude hologram, single kinoform, and kinoform sequence calculated by M-FrFT are compared. The effects of suppressing speckle noise are analyzed by calculating the speckle index of numerical reconstructed images. The analytical results illustrate that, with the proposed method for 3D holographic display, the zero-order light, conjugate image, and speckle noise can be suppressed, and the qualities of reconstructed images can be improved significantly.     

Enhancement of spatial resolution of ghost imaging via localizing and thresholding

In ghost imaging, an illumination light is split into test and reference beams which pass through two different optical systems respectively and an image is constructed with the second-order correlation between the two light beams. Since both light beams are diffracted when passing through the optical systems, the spatial resolution of ghost imaging is in general lower than that of a corresponding conventional imaging system. When Gaussian-shaped light spots are used to illuminate an object, randomly scanning across the object plane, in the ghost imaging scheme, we show th√at by localizing central positions of the spots of the reference light beam, the resolution can be increased by a factor of 2~(1/2) same as that of the corresponding conventional imaging system. We also find that the resolution can be further enhanced by setting an appropriate threshold to the bucket measurement of ghost imaging.     

Optical attenuator based on phase modulation of a spatial light modulator

In this Letter, we propose an optical attenuator based on the phase modulation of a spatial light modulator(SLM). In this system, we use two polarized beam splitters(PBSs) to control the polarized light and one SLM to modulate the phase of the polarized light. In the initial state, the light beam is divided into p-light and s-light when it passes through the first PBS. When the light passes through the second PBS, s-light is reflected and p-light is detected by the CCD camera. By loading different grayscales on the SLM, p-light changes its polarized state to s-light. The light power can be attenuated during the loading process. Our experiment shows that the system can obtain a wide optical attenuation from 1–27.2 d B. When loading two grayscales,the SLM has a fast switching time of 25 ms under a low actuated voltage of 5.5 V. The response time of the optical attenuator depends on the switching time of the SLM. Therefore, the system can also have a fast response time. By using the method of spatial multiplexing and adding two mirrors in the system, it can also be extended into a 1 × 2 optical switch. The results verify its feasibility. The optical attenuator has wide applications in photonic signal processing and fiber-optic communication.     

Coherence of a squeezed sodium atom laser generated from Raman output coupling

The coherence of a squeezed sodium atom laser generated from a Raman output coupler, in which the sodium atoms in Bose-Einstein condensate （BEC） interact with two light beams consisting of a weaker squeezed coherent probe light and a stronger classical coupling light, is investigated. The results show that in the case of a large mean number of BEC atoms and a weaker probe light field, the atom laser is antibunching, and this atom laser is second-order coherent if the number of BEC atoms in traps is large enough.     

Entanglement COncentration of Entangled Squeezed Vacuum States

By analysing the action of a beamsplitter on squeezed vacuum states(SVSs),it is found that,if the two input light beams of the beamsplitter have the same squeezing amplitude and phase,the output state is a two-mode SVS,If the two input light beams of the beamsplitter have the same squeezing amplitude but a phase difference of π,the output state is a direct porduct state of two single-mode SVS.Based on these results,we propose to distill a maximally entangled SVS from a partially entangled SVS by using a 50/50 beamsplitter and photodetectors.     

Numerical Investigation and Optimization of SBS-Based Slow-Light Using Filtered Incoherent Pump

The performance of stimulated Brillouin scattering （SBS）-based slow light using a novel spectrally-sliced broadband incoherent pump source is numerically studied. The profile of the pump-power spectrum is determined by the transmission spectra of the optical filter followed by the polarized broadband incoherent pump source. We also investigate the performance of Gaussian-type and super-Gaussian-type filtering under different spectrally-sliced
bandwidths and pump power levels for 2.5Gbit/s return-to-zero pulse （50% duty-cycle）. The pulse broadening is characterized by the full width of half maximum （FWHM） and the rms pulse width, respectively. However,the results obtained by the two kinds of measurement methods deviate from each other with increasing pump power. Compared with the regular Gaussian-type filtering, the pulse broadening can be significantly reduced using super-Gaussian-type filtering at the cost of a small reduction in delay time. Furthermore, the maximum improvement in pulse broadening of ＆#8710; BFWHM =28.4% and ＆#8710; B RMS =10.4% is achieved by using a five-order super-Gaussian-type filter and a pump power of 500mW.