Dynamic Changes in the Bacterial Community During the Fermentation of Traditional Chinese Fish Sauce (TCFS) and Their Correlation with TCFS Quality.

This study revealed for the first time the dynamic changes of the bacterial community during the fermentation of traditional Chinese fish sauce (TCFS) using high-throughput sequencing. In the early phase of TCFS fermentation, Shewanella (approximately 90%) within Proteobacteria was the dominant bacteria. Then, Halanaerobium (3%-86%) within Firmicutes rapidly replaced Shewanella as the dominant genus until the 12th month. Lactococcus (3.31%) and Bacillus (45.56%) belonging to Firmicutes were detected abundantly in the 3rd and 9th months after fermentation, respectively. In the late phase (12-15 months), Tetragenococcus within Firmicutes replaced Halanaerobium as the most dominant bacteria (29.54%). Many other genera including Pseudomonas, Psychrobacter, Tissierella, Carnobacterium and Gallicola were abundantly present in the 15th month after fermentation. Furthermore, the relationships between the bacterial community and major functional substances of TCFS, including amino nitrogen (AAN), free amino acids (FAAs), total soluble nitrogen (TSN), and trimethylamine (TMA), were investigated by partial least squares regression (PLSR). Tetragenococcus was positively correlated with the formation of TMA, while Halanaerobium showed the opposite result, suggesting that Tetragenococcus might be a good starter for TCFS fermentation. These results contribute to our knowledge about bacterial participation in the process of TCFS fermentation and will help improve the quality of fermented seafood.

Optical interconnects based on high-contrast all-dielectric nano-post arrays.

In this paper, we present a compact solution for optical interconnects in optoelectronic integrated neural networks using high-contrast all-dielectric nano-post arrays. The nano-post arrays are made of amorphous silicon, which has a high refractive index and high transmittance in the near infrared. The radius of each post is changed to generate different phase delays. Deflection and convergence of the light are realized by proper design of the phase profile of the nano-post array. Connection efficiencies are calculated by numerical simulations and compared with those of zone plate interconnects. Simulation results show that the proposed nano-post arrays can have superior performance over zone plates in applications that require short focal length and high efficiency.

Design of two-dimensional diffractive optical elements for beam shaping of multicolor light-emitting diodes.

To achieve a cellular network in visible light communication, the illumination areas covered by red, green, and blue light-emitting diodes (LEDs) forming a white LED should be of the same size with uniform intensity distribution. In this paper, the iterative algorithm for the design of multicolor-oriented two-dimensional diffractive optical elements (DOEs) is improved. Simulation results indicate that almost the same size of the diffraction patterns of the DOE illuminated by multicolor LEDs is achieved with good uniformity of the intensity distribution.

Phase-difference-based compression of phase-only holograms for holographic three-dimensional display.

In holographic three-dimensional (3D) display, holograms for reconstructing 3D scenes require huge storage space and high transmission bandwidth. Holographic data must be compressed for practical applications. The holograms for 3D display are commonly represented in pure-phase format. Existing hologram compression techniques are generally not designed to handle phase-only holograms. In this paper, we propose a phase-difference-based compression method to compress phase-only holograms for holographic 3D display. Phase-only holograms are decomposed into grayscale images representing the phase distance and binary images containing the sign information of the phase difference. The grayscale images can be better handled by common image compression algorithms since their pixel values are proportional to the phase distance reflecting the distance between complex amplitudes. The binary images are compressed by lossless bi-level image coding. The compressed grayscale images and binary images can be synthesized to recover the phase-only holograms and reconstruct the 3D scenes. The advantages of the proposed method over existing image coding standards are verified by numerical simulations.

Design of diffractive optical elements for subdiffraction spot arrays with high light efficiency.

Spot arrays beyond the diffraction limit are required in many optical applications, and the shaping of a light beam into subdiffraction spot arrays can be implemented by diffractive optical elements (DOEs). However, the low light efficiency of spot arrays is undesired in many applications. In this paper, a modified Gerchberg-Saxton algorithm is presented for generating DOEs to realize subdiffraction spot arrays with higher light efficiency. In the simulation, the spot size is reduced to approximately 70%-90% of the diffraction-limited spot, and the corresponding light efficiency is within the range of 20% to 50%. The experimental results are also shown to demonstrate the effectiveness of the proposed algorithm.

Design, fabrication, and testing of zone-plate interconnects for a compact optoelectronic integrated neural coprocessor.

We have designed, fabricated, and tested a set of scalable compact optical elements for use in the compact optoelectronic integrated neural (COIN) coprocessor. The COIN coprocessor is an implementation of a feed-forward neural network that uses optical interconnects to transmit information from one layer of neurons to the next. Optical interconnection elements based on Fresnel-zone-plate concepts have been fabricated using standard lithographic processes, thereby allowing large arrays to be fabricated with a single exposure. This paper discusses the design trade-offs that must be considered for effective use of such elements in a COIN coprocessor, and the fabrication and testing of a set of such optical interconnection elements. It was found that the behavior of the fabricated zone plates correlated well with the design simulation, and that this type of optical element is indeed suitable for use in the COIN coprocessor.

Evaluation of organic light-emitting diodes as light sources for a compact optoelectronic integrated neural coprocessor.

Organic light-emitting diodes (OLEDs) are a most promising candidate for light sources of the compact optoelectronic integrated neural (COIN) coprocessor because of their easy integration with the silicon electronics. However, the optical properties of OLEDs are different from those of vertical-cavity surface-emitting lasers, which were previously used in the COIN system. The interconnect behavior of the COIN coprocessor is unknown if OLEDs are employed. In this paper, we build a mathematical model of the interconnect scheme of the COIN coprocessor and investigate the influence of the spectral bandwidth, light-emitting area, and angular emission profile of OLEDs by numerical simulations. The simulation results show that OLEDs with properly selected properties can be used as the light sources for the COIN coprocessor.

Holographic projection with higher image quality.

The spatial resolution limited by the size of the spatial light modulator (SLM) in the holographic projection can hardly be increased, and speckle noise always appears to induce the degradation of image quality. In this paper, the holographic projection with higher image quality is presented. The spatial resolution of the reconstructed image is 2 times of that of the existing holographic projection, and speckles are suppressed well at the same time. Finally, the effectiveness of the holographic projection is verified in experiments.

Diffractive optical element with same diffraction pattern for multicolor light-emitting diodes.

The wavelength-division multiplexing technique can be utilized in visible light communication to increase the channel capacity when a multicolor mixed white LED is used as light source. In such an application, the illumination area of LEDs should be invariant to the incident wavelength, so as to decrease interference within the adjacent regions. Diffractive optical elements (DOEs) can be used in the optical transmitter system to shape the diffraction patterns into polygons. However, traditional DOEs illuminated by a multicolor mixed white LED would result into diffraction patterns with unequal sizes. In this paper, a hybrid algorithm which combines particle swarm optimization with a genetic algorithm is proposed for multicolor oriented DOEs design. A DOE is designed and fabricated for blue and red LEDs, and experimental results show that diffraction patterns with rather good uniformity as well as quasi-equal size for red and blue LEDs are obtained.

Precise design of two-dimensional diffractive optical elements for beam shaping.

Diffractive optical elements (DOEs) for beam shaping are widely used in many fields, and there are many kinds of optimization algorithms to design the DOEs for beam shaping. However, only the intensity distribution of the selected sampling points is controlled by these optimization algorithms. The intensity distribution of other points on the output plane is always far away from the ideal distribution. The reason is that the sampling interval on the output plane is not small enough. In this paper, a new modified GS algorithm is presented with a small enough sampling interval on the output plane. A two-dimensional DOE for beam shaping is designed, and the simulation results and the experimental results demonstrate the good performance of this algorithm.

Interferometric spherical surface testing with unknown phase shifts.

A general method is presented for spherical surface testing with unknown phase shifts based on a physical model of the interferometer cavity, which describes the phase shifts taking into account the rigid cavity motions and the radial imaging distortion of the interferometer. The captured interferograms are processed frame by frame with the regularized frequency-stabilizing method, so as to get the phase shifts between the frames. These phase shift data are subsequently fitted, and the initial estimations for the wavefront, direct current and interference contrast terms are calculated by the least-squares method. Specially, a simple way is proposed to find reasonable initial guess for numerical aperture (NA) of the test beam (when NA is unknown), so as to ensure the effectiveness of the above phase shift fitting procedure. Then, the wavefront result is further refined in an iterative way, by fitting the sequence of interferograms to the physical model of the interferometer cavity with the linear regression technique. Finally, the wavefront result related to the actual surface profile is retrieved after removing the aberrations due to the surface misalignment and the imaging distortion. Both simulations and experiments with the ZYGO interferometer have been carried out to validate the proposed method, with experimental accuracies better than 0.004λ RMS achieved. The proposed method provides a feasible way to spherical surface testing without the use of any phase-shifting devices, while retaining good accuracy and robust convergence performance.

Image magnification in lensless holographic projection using double-sampling Fresnel diffraction.

Since the diffraction angle is limited by the spatial resolution of the spatial light modulator (SLM), the size of the optical image of the lensless holographic projection with a SLM is very small. Using a divergent spherical beam to illuminate a SLM is an effective method to physically increase the projection angle; nevertheless, the sampling ranges of the existing Fresnel diffraction algorithms with fast Fourier transform keep unchanged. In this paper, a double-sampling Fresnel diffraction algorithm to enlarge the sampling range is proposed when using a divergent spherical beam to illuminate a SLM, and the magnification of the optical image is realized in lensless holographic projection. The hologram can be easily optimized by the Gerschberg-Saxton algorithm. Simulation and experimental results with enlarged optical image are presented successfully.

Two-step resonant diffraction grating designed for three-color separation in Fresnel diffraction region.

A two-step resonant diffraction grating is designed to separate the distributions of the wavelengths of 633, 532, and 488 nm in the Fresnel diffraction field using an analytical solution of the modal method, which can give a physical explanation for mode propagation in the grating region and interference at the interfaces. The energy efficiencies are 76.1% for 633 nm, 83.5% for 532 nm, and 75.6% for 488 nm at TE polarizations. The field distributions are captured by a color CMOS detector with a microscope, and the experimental results show the grating has a good color-separation performance.

Phase extraction from interferograms with unknown tilt phase shifts based on a regularized optical flow method.

A novel method is presented to extract phase distribution from phase-shifted interferograms with unknown tilt phase shifts. The proposed method can estimate the tilt phase shift between two temporal phase-shifted interferograms with high accuracy, by extending the regularized optical flow method with the spatial image processing and frequency estimation technology. With all the estimated tilt phase shifts, the phase component encoded in the interferograms can be extracted by the least-squares method. Both simulation and experimental results have fully proved the feasibility of the proposed method. Particularly, a flat-based diffractive optical element with quasi-continuous surface is tested by the proposed method with introduction of considerably large tilt phase shift amounts (i.e., the highest estimated tilt phase shift amount between two consecutive frame reaches 6.18λ). The phase extraction result is in good agreement with that of Zygo's MetroPro software under steady-state testing conditions, and the residual difference between them is discussed. In comparison with the previous methods, the proposed method not only has relatively little restrictions on the amounts or orientations of the tilt phase shifts, but also works well with interferograms including open and closed fringes in any combination.

Orthogonal-reference-pattern-modulated shift multiplexing for collinear holographic data storage.

A novel hybrid shift multiplexing method for collinear holographic data storage (CHDS) by using orthogonal reference patterns (RPs) is proposed, analyzed, and demonstrated. For this method, holograms are multiplexed by not only shifting the media but also using different RPs. Compared with the traditional method, the shift pitch for the hybrid method is substantially reduced because of the selectivity introduced by different RPs. The interpage cross talk due to Bragg mismatch and degeneracy for multiplexing holograms in the same volume by using orthogonal RPs is also attenuated by utilizing the shift selectivity of the hologram. A 1.5 µm shift pitch is experimentally achieved by using three amplitude RPs in a system that would be 4.5 µm with only one RP. This new method offers an alternative to significantly increase the data density and transfer rate of the CHDS system given that the media has ideal properties.

Channel analysis of the volume holographic correlator for scene matching.

A channel model of the volume holographic correlator (VHC) is proposed and demonstrated to improve the accuracy in the scene matching application with the multi-sample parallel estimation (MPE) algorithm. A quantity related to the space-bandwidth product is used to describe the recognition ability in the scene matching system by MPE. A curve is given to optimize the number of samples with the required recognition accuracy. The theoretical simulation and the experimental results show the validity of the channel model. The proposed model provides essential theoretical predictions and implementation guidelines for using the multi-sample parallel estimation method to achieve the highest accuracy.

Improving signal-to-noise ratio by use of a cross-shaped aperture in the holographic data storage system.

A cross-shaped aperture is proposed to improve signal-to-noise ratio (SNR) in the holographic data storage system (HDSS). Both simulated and experimental results show that higher SNR can be achieved by the cross-shaped aperture than traditional square or circular apertures with the same area. A maximum gain of 20% in SNR is obtained for the optimized cross-shaped aperture. The sensitivities to pixel misalignment and magnification error are also numerically compared.