Shift multiplexing with a two-dimensional lens array

We propose a new shift multiplexing method to reduce the cross-talk noise and increase the holographic storage density. We use spherical waves emerging from a two-dimensional lens array as reference beams to multiple holograms. The theoretical results indicate that the sidelobes of the diffraction intensity can sharply be reduced to near-zero and the spatial separation of adjacent holograms can also be reduced, resulting in higher holographic storage density than conventional shift multiplexing methods.     

Practical limitation for continuous-variable quantum cryptography using coherent States

In this Letter, first, we investigate the security of a continuous-variable quantum cryptographic scheme with a postselection process against individual beam splitting attack. It is shown that the scheme can be secure in the presence of the transmission loss owing to the postselection. Second, we provide a loss limit for continuous-variable quantum cryptography using coherent states taking into account excess Gaussian noise on quadrature distribution. Since the excess noise is reduced by the loss mechanism, a realistic intercept-resend attack which makes a Gaussian mixture of coherent states gives a loss limit in the presence of any excess Gaussian noise.     

参考光波面质量对全息存储质量影响的数值模拟研究

采用数值模拟方法研究了不同种类参考光波面质量对再现图像质量的影响.针对全息实验实际情况,对二值图像建立了傅里叶变换全息图记录和读出的物理模型,分别考察采用一般平面波参考光、高斯光束球面波参考光和散斑参考光时的读出图像质量,并以信噪比损失作为衡量图像质量的定量工具.模拟结果表明,在理想平面波参考光和球面波参考光的情形,全息读出图像质量非常好,与输入图像相比信噪比损失在0.6dB以下.但是对于散斑参考光,尽管其极优的位移选择性提供了高密度存储的可能性,但再现图像质量明显变差,信噪比损失在5dB以上,实现有效的数据存储位密度将是十分困难的.为了兼顾存储密度和再现质量,应该考虑优化参考光的途径.     

Crosstalk Noise Reduction in Shift-Multiplexed Holographic Storage System Using Multiple Point Sources

We propose and analyse a new method to reduce cross-talk noise in a shift multiplexed holographic storage system using multiple point sources. The normalized diffraction efficiency is given analytically with respect to the shift distance. The noise-to-signal ratio is defined and calculated to value the cross-talk of the system. The numerical results show that using multiple point sources can effectively decrease the cross-talk.     

Effect of excess noise on continuous variable entanglement sudden death and Gaussian quantum discord

A symmetric two-mode Gaussian entangled state is used to investigate the effect of excess noise on entanglement sudden death and Gaussian quantum discord with continuous variables. The results show that the excess noise in the channel can lead to entanglement sudden death of a symmetric two-mode Gaussian entangled state, while Gaussian quantum discord never vanishes. As a practical application, the security of a quantum key distribution （QKD） scheme based on a symmetric two-mode Gaussian entangled state against collective Gaussian attacks is analyzed. The calculation results show that the secret key cannot be distilled when entanglement vanishes and only quantum discord exists in such a QKD scheme.     

Experimental study on polarization holographic storage in genetic mutant BR-D96N film

The information storage is developing toward high speed access and massive stor-age capacity. Optical holographic storage has not only high speed parallel data access and high addressing speed without mechanical motion but also high storage density with multiplexed volume holographic storage[1]. In recent years, optical holographic storage is studied intensely in the field of information storage. It has been shown that the polari-zation of light could also be recorded with polarization hologra…     

Some factors affecting the magnitude of comodulation masking release

This paper examines some of the factors that can affect the magnitude of comodulation masking release (CMR). In experiment I, psychometric functions were measured for the detection of a 1-kHz sinusoidal signal in a "multiplied" narrow-band noise centered at 1 kHz (reference condition) and the same noise with two comodulated flanking bands added. The functions were slightly steeper for the comodulated than for the reference masker. Thus CMRs measured at a high percent correct point were slightly (0.4 dB) larger than CMRs measured at a low percent correct point. Large individual differences were found for the reference masker but not for the comodulated masker. Experiment II compared CMRs obtained with narrow-band Gaussian noise and multiplied noise, using a single flanking band. For a flanking band remote from the signal frequency, the CMRs were smaller and more variable for the multiplied noise than for the Gaussian noise. This variability arose mainly from individual differences in the reference condition. Experiment III compared growth-of-masking functions for a signal centered in Gaussian noise and multiplied noise. Thresholds were lower for the multiplied than for the Gaussian noise, and the differences were greatest at high noise levels. The results are consistent with the idea that, for multiplied noise, some subjects can detect a change in the distribution of the envelope of the stimulus, when the signal is added to the masker. Such subjects have low thresholds in the reference condition, and give small CMRs. Other subjects are relatively insensitive to this cue. They have higher thresholds in the reference condition, and give larger CMRs. For Gaussian noise, thresholds for the reference condition are relatively stable across subjects and CMRs tend to be substantial, even for flanking-band frequencies remote from the signal frequency.     

Quantum-Error-Rejection for Hyperentanglement Transmission without Calibrated Reference Frames

In quantum communication, the channel noise and the misalignment of the reference frames between the communication parties will lead to the failure of quantum state transmission. Here an alignment-free spatial-polarization hyperentanglement transmission scheme is provided for hyperentangled photons. In this scheme, before the spatial-polarization hyperentanglement is transmitted through the fiber channel, it is first encoded as a time-bin entanglement with the same polarization. After the photons pass through the noise channel, the polarization errors caused by reference frames misalignment and channel noise can be corrected by time-bin entanglement. In principle, by implementing this scheme, the communication parties can share the original hyperentangled state, and the success probability can approach unity. The scheme is robust to random channel noise and reference frames misalignment, and the decoherence effect caused by the misalignment of the reference frames between the communication parties can be completely suppressed by implementing this scheme.     

Sliced orthogonal nonlinear generalized decomposition based fringe-adjusted joint transform correlation

A sliced orthogonal nonlinear generalized (SONG) decomposition based version of modified fringe-adjusted joint transform correlator (MFJTC), SBFJTC, is proposed. In SBFJTC scheme, the reference and input scenes are decomposed into a set of binary slices through SONG decomposition. MFJTC filtering of each pair of binary slices, corresponding to the same gray level of reference and input scene, is performed and then the outputs are added. Numerical simulations show that the proposed scheme delivers a better correlation performance and robustness to the white additive Gaussian noise, substitutive noise and nonoverlapping noise than that of both of the FJTC and the MFJTC.     

Detection of binary images in noise

Detection of binary images in noise is considered in the light of statistical detection theory, with particular reference to information storage systems. The different disturbances are classified into system noise and transparency noise. The receiver operating characteristics (ROC) have been obtained when the scanned binary image is corrupted by additive white Gaussian noise and multiplicative speckle. It is shown that improvement in ROC with signal-to-noise ratio (SNR) is less pronounced in the presence of speckle.     

Experimental investigation of noise-assisted information transmission and storage via stochastic resonance

We present experimental results on the information transmission and storage via stochastic resonance in circuits designed and built around Schmitt triggers (STs). First, we investigate the performance of a transmission line comprised of five STs and show it to exhibit stochastic resonance. Each ST in the line is fed with white Gaussian noise, and the first ST is driven by a non-return-to-zero pseudo-random bit sequence with sub-threshold amplitude. Parameters such as bit error rate (Q-factor) are measured (calculated) and shown to exhibit a minimum (maximum) for an optimum amount of noise. Interestingly, we find that system performance degrades with the number of STs as if the system were linear and impaired only by additive Gaussian noise. We then propose and build a 1-bit storage device based on two STs in a loop configuration. We demonstrate that such a system is capable of storing one bit of information only in the presence of noise, and that there is a regime where the efficiency of such a device increases with increasing noise.Our results point to the feasibility of building ‘blocks’ that can transmit, store and eventually process information, whose performance is not only robust against noise, but can actually benefit from it.     

The Improvement of Performance for Continuous-Variable Quantum Key Distribution with Imperfect Gaussian Modulation

Gaussian modulation is one of the key steps for the implementation of continuous-variable quantum key distribution (CVQKD) schemes. However, imperfection in the Gaussian modulation may introduce modulation noise that can deteriorate the performance of CVQKD systems. In this paper, we mainly investigate how to improve the performance of a CVQKD system from different aspects. First, we explore the several different origins, impacts and monitoring schemes for the modulation noise in detail. Then, we discuss the practical performance of a CVQKD system with an untrusted noise model and neutral party model, respectively. These analyses indicate that the neutral party model should be reasonably regarded as a general noise model, which will passively and greatly raise the performance of the system. Further, we propose a dynamic auto-bias control scheme to actively resist the modulation noise which comes from the drift of bias point of the amplitude modulator. Together these methods contribute to the improvement of the practical performance of CVQKD systems with imperfect Gaussian modulation.

     

Cross-talk in phase encoded volume holographic memories employing unitary matrices

The cross-talk noise in phase encoded holographic memories employing unitary matrices is theoretically investigated. After reviewing some earlier work in this area, we derive a relationship for the noise-to-signal ratio for phase-code multiplexing with unitary matrices. The noise-to-signal ratio rises in a zigzag way on increasing the storage capacity. Cross-talk is mainly caused by high-frequency phase codes. Unitary matrices of even orders have only one bad code, while unitary matrices of odd orders have four bad codes. The signal-to-noise ratios of all other codes can in each case be drastically improved by omission of these bad codes. We summarize the optimal orders of Hadamard and unitary matrices for recording a given number of holograms. The unitary matrices can enable us to adjust the available spatial light modulators to achieve the maximum possible storage capacity in both circumstances with and without bad codes. PACS 42.40.Lx; 42.40.Ht; 42.40.Pa     

Reduction of parasitic interferences in digital holographic microscopy by numerically decreased coherence length

Due to the large coherence length of laser light, optical path length (OPL) resolution in laser based digital holographic microscopy suffers from parasitic interferences caused by multiple reflections within the experimental setup. Use of partially coherent light reduces this drawback but requires precise and stable matching of object and reference arm’s OPLs and limits the spatial frequency of the interference pattern in off-axis holography. Here, we investigate if the noise properties of spectrally broadened light sources can be generated numerically. Therefore, holograms are coherently captured at different laser wavelengths and the corresponding reconstructed wave fields are numerically superimposed utilizing variable weightings. Gaussian and rectangular spectral shapes of the so synthesized field are analyzed with respect to the resulting noise level, which is quantified in OPL distributions of a reflective test target. Utilizing a Gaussian weighting, the noise level is found to be similar to the one obtained with the partially coherent light of a superluminescent diode. With a rectangular shaped synthesized spectrum, noise is reduced more efficient than with a Gaussian one. The applicability of the method in label-free cell analysis is demonstrated by quantitative phase contrast images obtained from living cancer cells.     

基于CCF-TLS-ESPRIT算法的低频振荡在线辨识

低频振荡在线辨识需用到广域测量系统(WAMS)的采集信号,而WAMS采集的信号中常伴有高斯白噪声,经过常规的低通滤波处理后会产生高斯色噪声,从而影响辨识的精度.针对在线辨识中的色噪声问题,提出以互相关函数(CCF)来代替实测信号,从而抑制色噪声,并结合总体最小二乘-旋转不变技术参数估计(TLS-ESPRIT)算法进行模态辨识.仿真结果表明,CCF-TLS-ESPRIT算法能够有效辨识出色噪声环境中的系统低频振荡模态,并具有一定的效率.     

Cross talk between holograms of finite contrast in a phase-code multiplexing system

The cross talk between holograms recorded in a phase-code multiplexing system is analyzed. The signal-to-noise ratio (SNR) is derived for the original image of a finite contrast ratio in the presence of a phase-shift error of the reference beam. It is shown that one particular code in the Walsh-Hadamard code set can be the dominant cross-talk noise source. We experimentally measured the SNR of the holograms recorded in an 8-bit phase-code multiplexing system by varying the contrast ratio of the original image. We show good agreement between experiment and theory. The existence of one bad code is also shown experimentally.     

Study of cross-talk of parallel Fabry–Perot sensors in path-matching differential interferometry

Cross-talk in multiplexing parallel Fabry–Perot sensors in a path-matching differential interferometry (PMDI) can be limited by corresponding path-matching read-out systems. Nevertheless, improper design in cavity lengths of Fabry–Perots can result in serious cross-talk. This paper presents a spectrum analysis to design the parallel Fabry–Perot sensors quantitatively without cross-talk. The spectrum analysis used to solve the cross-talks in a multiple parallel Fabry–Perot system is proved to be an efficient tool. To the author's knowledge, cross-talk problems were first investigated in a multiple parallel Fabry–Perot system quantitatively and experimentally. In a spectrum analysis, the spectrum transfer function in a broadband light source and a Fabry–Perot cavity are simulated by a Gaussian distribution spectrum and a low-finesse reflectivity, respectively. After integrating the whole spectrum system with respect to the wave number, the cross-talk terms can be removed by assuming zero. It is concluded that the cavity length differences between two Fabry–Perots should be longer than the coherence length of a broadband light source to diminish cross-talk effects. Experimental results for two parallel Fabry–Perots in PMDI are presented and compared with theoretical predictions. This study shows good agreement between experimental results and theoretical predictions, indicating that spectrum analysis can be applied properly to the design of two- or multiple-parameter sensors.     

Technique for referencing of fiber-optic intensity-modulated sensors by use of counterpropagating signals

We present a new all-optical fiber-referencing scheme for intensity-modulated sensors. It consists of a closed loop traversed by sensing and reference optical signals in opposite directions. With the proposed scheme the noise induced by power fluctuations of the optical source and mechanical perturbations can be greatly reduced. We experimentally demonstrate the efficiency of the scheme and discuss its use in a sensor array.     

离散调制连续变量量子密钥分发的安全边界

对一种结合离散调制和反向协调,适用于长距离传输的连续变量量子密钥分发四态协议的安全性进行了严格证明.这种协议中Alice发送的态与高斯调制协议中的有一定差异,这种差异可以等价成信道衰减和额外噪声.另外,由于Alice不可能做到精确调制,这会导致其发送的相干态中含有噪声.把这种调制引起的噪声看作光源的噪声,并推导出了在光源噪声不能被窃听者所利用的条件下的安全码率的下界.为了避免实验上快速、随机的控制本地振荡光的相位,还将无开关协议和四态协议相结合,分析了其安全性.     

Squeezed-state purification with linear optics and feedforward

A scheme for optimal and deterministic linear optical purification of mixed squeezed Gaussian states is proposed and experimentally demonstrated. The scheme requires only linear optical elements and homodyne detectors, and allows the balance between purification efficacy and squeezing degradation to be controlled. One particular choice of parameters gave a tenfold reduction of the thermal noise with a corresponding squeezing degradation of only 11%. We prove optimality of the protocol, and show that it can be used to enhance the performance of quantum informational protocols such as dense coding and entanglement generation.