Multichannel method for absolute shape measurement using projected fringes

The multichannel approach is combined with the reduced temporal phase unwrapping scheme for rapid shape measurement. The shape is measured using projected fringes and optical triangulation. Fringes are projected using a colour video projector and recorded by a CCD-camera. Using a colour video projector and a colour video camera makes it possible to use the red, green and blue channels individually. This is the multichannel method. In each channel, the blue, green and red carries fringe maps with different fringe pitch. A short sequence of phase-stepped images is projected and acquired sequentially in time. This reduces measurement time by a factor of three when compared to using one channel. From the acquired images, it is possible to calculate absolute phase using the reduced temporal phase unwrapping analysis scheme. For each channel, it is also possible to calculate fringe contrast and fringe amplitude. Therefore, it is possible to retrieve the colour of an object without acquiring an extra image. The method is demonstrated by measuring the shape of two generally coloured and complex shaped objects.     

Coherent summation of power of nanosecond relativistic microwave oscillators

The possibility of developing a two-channel nanosecond relativistic microwave oscillator with a phase stability in each channel sufficient for coherent summation of their electromagnetic fields is demonstrated experimentally. In experiments, vacuum diodes of two independent superradiant backward wave oscillators operating in 10-GHz frequency range were connected to a common voltage source with a subnanosecond pulse rise time, which ensured the fixation of the initial phase of electromagnetic oscillations. The measured values of the phase difference jitter of the channel electromagnetic oscillations amount to several percent of the oscillation period.     

Active phasing a nine-element 1.14 kW all-fiber two-tone MOPA array using SPGD algorithm

We demonstrated active phase locking a nine-element 1.1 kW all-fiber master-oscillator power amplifier (MOPA) array using the stochastic parallel gradient descent (SPGD) blind optimization algorithm. Two spectrally combined single-frequency seed lasers, which provide potential ability to suppress the stimulated Brillouin scattering effect, are employed as a master oscillator for the nine MOPA channels. The nine laser beams are tiled side by side into a 3×3 laser array with a fill factor of 40% in the near field. When the SPGD controller is enabled, the metric function is increased 4.1 times, and a visibility more than 90% of the interference pattern at the receiving plane is obtained. The computed phase residual error is less than λ/15, despite the phase fluctuation of each channel.     

Flat-top interleavers with chromatic dispersion compensator based on phase dispersive free space Mach-Zehnder interferometer

In this paper, novel interleavers using circular cavities (CC) in a Mach-Zehnder interferometer (MZI) has been presented and demonstrated for the first time, in which CCs act as phase dispersive mirrors which exhibit a periodic dependence on the frequency of light. Three implementation schemes have been proposed and investigated. Theoretical analysis shows the spectral characteristics of each scheme in a 50-GHz channel spacing application. Furthermore, the chromatic dispersion (CD) of each output comb can be flattened within passband by appending an additional CC. The result shows that the proposed designs with novel interferometer technique can simultaneously provide flat top passbands, high isolation stopband and low CD value as well.     

数字正交检波中的数据处理方法

详细讨论了数字正交检测中的数字处理方法,通过时域插值和选择适当的数字滤波器,可以降低对A DC采样速率的要求.最后给出NMR实验结果.     

Pilot-based cross-phase modulation compensation for coherent optical orthogonal frequency division multiplexing long-haul optical communications systems

A pilot-based nonlinearity compensator (PB-NLC) is shown in this Letter to be an effective method for compensating cross-phase modulation (XPM) in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An unmodulated pilot tone is transmitted at the center of each OFDM channel to detect phase errors caused by the Kerr effect, which converts intensity fluctuations from all channels to phase errors. The pilots are then used to cancel the XPM phase errors for each OFDM channel at the receiver after each channel's self-phase modulation (SPM) has been compensated, using its intensity waveform to determine its SPM. Numerical simulations of a 58 Gb/s single polarization 2375 km system with inline dispersion compensation show that the signal quality, Q, at the optimal launch power is increased by 2.4 dB if SPM compensation is used before the PB-NLC. This contrasts with only a 0.9 dB improvement if the PB-NLC is used without an SPM compensator for the same link. This shows the PB-NLC can effectively mitigate XPM but not SPM.     

Full off-axis red-green-blue digital holographic microscope with LED illumination

We developed a new full off-axis red-green-blue (RGB) digital holographic microscope with an LED illumination. A decisive advantage of the use of LED illumination is a large image quality improvement due to its partially coherent nature. The off-axis configuration enables the fast recording of the holographic data in each spectral channel. The digital holographic refocusing and the optical phase map computation are successfully demonstrated. The multiwavelength operation provides a significant improvement of the collected information for colored samples.     

COULOMB CORRECTION OF THE p-4He LOW ENERGY SCATTERING PHASE SHIFTS

A simple approach of Coulomb correction to the p-⁴He low energy scattering phase shifts is proposed,in which the channel radius of each partial wave is taken as an adjustable parameter.By using the Coulomb correction the n-⁴He scattering observables predicted from p-⁴He scattering phase shifts are in excllent agreement with experiment.Our calculations show that the neutron polarization depends sensitively on the channel radius of p waves and the obtained channel radius are adeguate to the different sets of phase shifts.     

An asymmetric single-channel color image encryption based on Hartley transform and gyrator transform

A novel asymmetric single-channel color image encryption using Hartley transform and gyrator transform is proposed. A color image is segregated into R, G, and B channels and then each channel is independently Hartley transformed. The three transformed channels are multiplied and then phase- and amplitude truncated to obtain first encrypted image and first decryption key. The encoded image is modulated with a conjugate of random phase mask. The modulated image is gyrator transformed and then phase- and amplitude truncated to get second encrypted image and second decryption key. The asymmetric (decryption) keys, random phase mask, and transformation angle of gyrator transform serve as main keys. The optoelectronic encryption and decryption systems are suggested. Numerical simulation results have been demonstrated to verify the performance and security of the proposed security system.     

深海走航抛弃式测量仪器时变信道对传输性能的影响

由于环境的要求,深海走航抛弃式测量仪器信号传输大多使用有线信道,然而,信道的电阻抗随放线长度不断变化,严重影响了深海走航抛弃式测量仪器信道传输的稳定性.本文以国家海洋技术中心自主研发的走航抛弃式温度、盐度、湿度(XCTD)剖面仪的传输信道为原型,提出了一种动态分析有线信道对传输信号幅值和相位影响的方法.首先推导出各电路参数随信道长度变化的规律,建立简化的传输电路模型和该模型的传输函数.通过定性分析得出传输频率、分布电容和缠绕电感对信号相位的影响.利用MATLAB软件分析XCTD在动态放线过程中信道对信号幅值和相位的影响.研究结果可进一步指导抛弃式走航测量系统的电路设计,提高测量数据的精度和信号传输的稳定性.     

高能量粒子再分布模型在CFETR上的应用

在中国聚变工程实验堆(CFETR)设计参数下,利用一种高能量粒子(EP)物理简化模型分析了磁流体动力学(MHD)不稳定中新经典撕裂模(NTM)引起的粒子再分布和损失。相位矢量旋转法利用EP相空间中小间隔区域内跟踪探测粒子对来判定粒子轨道随机与否,即记录连接矢量旋转角的方法标记该区域是否存在KAM面破缺,以此为据修正相空间的粒子分布函数和判断粒子损失。利用相空间探测粒子对相位矢量旋转法标记一定NTM幅度下的随机区域分布并迭代得到稳态分布剖面。对捕获粒子区域的共振岛探测结果表明,低频或零频率扰动不会与高能量α粒子形成有效共振,MHD扰动和有效碰撞效应可能使捕获-通行轨道边界附近形成损失通道。     

Phase-only sampled 45 channel fiber Bragg grating written with a diffraction-compensated phase mask

A novel phase-only sampled 45 channel fiber Bragg grating (channel spacing, 100 GHz) with high interchannel and intrachannel reflection uniformity and precise dispersion matching capability to an 80 km SMF-28 fiber is demonstrated. This grating is fabricated by the side-writing technique, in which phase information of continuous phase-only sampling is completely incorporated into a diffraction-compensated phase mask.     

Time reversal communication in a time-varying sparse channel

Recently time reversal (TR) communications has been extended to time-varying channels. The basic idea is to implement it on a block-by-block basis such that within each block the channel remains time-invariant and subsequently is updated using detected symbols (decision-directed mode). Using experimental data (12-20 kHz) collected in shallow water, this letter investigates three different block-based TR approaches: (1) without explicit phase tracking, (2) with phase tracking, and (3) exploiting channel sparsity. The TR approaches then are compared to a conventional adaptive multichannel equalizer. It is found that approach (3) generally provides the best performance and robustness.     

多抖动法主振荡功率放大器相干合成技术

 采用多抖动相位控制方法实现了两路和三路1 Ｗ量级光纤放大器的相干合成,对实验结果进行了详细分析。实验中,将种子光源输出激光分为两路（或三路）,分别通过光纤放大器进行功率放大,并采用多抖动法实现相干合成。控制系统开环时,远场光斑条纹模糊不清,两路和三路合成时条纹对比度分别为0.19和0.12;系统闭环时,远场光斑条纹清晰可见,对比度提高到0.93和0.81,合成效率分别为80%和77%。此外,对两路和三路的合成效果进行了比较,指出了各路的控制资源对合成效果的影响。     

Experimental demonstration of tripartite entanglement and controlled dense coding for continuous variables

A tripartite entangled state of bright optical field is experimentally produced using an Einstein-Podolsky-Rosen entangled state for continuous variables and linear optics. The controlled dense coding among a sender, a receiver, and a controller is demonstrated by exploiting the tripartite entanglement. The obtained three-mode "position" correlation and relative "momentum" correlation between the sender and the receiver, and thus the improvements of the measured signal to noise ratios of amplitude and phase signals with respect to the shot noise limit are 3.28 and 3.18 dB, respectively. If the mean photon number n equals 11 the channel capacity can be controllably inverted between 2.91 and 3.14. When n is larger than 1.0 and 10.52, the channel capacity of the controlled dense coding is predicted to exceed the ideal single channel capacity of coherent and squeezed state light communication, respectively.     

Computer-generated kinoforms of real-existing full-color 3D objects using pure-phase look-up-table method

A computational method based on pure-phase look-up-table (LUT) is proposed for generating kinoforms of full-color real-existing three-dimensional (3D) objects. The principle of the pure-phase LUT method is described. 3D depth as well as color information of a full-color 3D object is obtained by the full-color 3D profile measurement approach based on binocular vision. The obtained full-color 3D data is decomposed into red (R), green (G), and blue (B) channels, and kinoforms of each channel are calculated from the depth map and color information of the corresponding channel using the pure-phase LUT method. In order to reduce the speckle noise of reconstructed full-color 3D image, sequential kinoforms of each color channel are generated by adding dynamic-pseudorandom phase factor into the object domain. Numerical reconstruction and optical reconstruction with a phase-only spatial light modulator (SLM) show that, with the proposed method, full-color holographic 3D display of real-existing full-color 3D objects is available.     

Design of multi-channel optical code-division multiple-access encoders and decoders based on sampled fiber Bragg gratings

An encoding/decoding scheme of multi-channel optical code-division multiple-access (OCDMA) system using sampled fiber Bragg gratings (SFBGs) is proposed and numerically investigated. A multiple-phase-shift (MPS) technique based SFBG is first developed as a dense wavelength-division multiplexing (DWDM) device to accommodated multiple channels. The OCDMA scheme is achieved through phase coding/encoding on each individual channel of the SFBG and the auto correlative ratio for each user is larger than 14.3 dB. The whole system exhibits enhanced performance in terms of the capacity and security since the OCDMA technique is simultaneously implemented for all channels using the single SFBG.     

Coherent underwater communication using passive time reversal over multipath channels

Passive time reversal exploits underwater acoustic channels’ spatial and temporal diversity. It can refocus multipath propagated signal at the receiver and can be realized simply by the passive phase conjugation (PPC) method. By the temporal focusing, time delay spread caused by multipath propagation is mitigated for spectral efficient coherent communications. However, the PPC method is unable to eliminate multipath and is limited by channel variations. An adaptive equalizer is therefore needed to compensate residual multipath after refocusing and to track channel temporal variations. Spatial diversity is obtained by using a vertical receiving array. In this paper we used 4-hydrophone array and demonstrated that the adaptive decision feedback equalization in conjunction with PPC significantly decreased the bit error rate.     

Efficient procedure to compute the microcanonical volume of initial conditions that lead to escape trajectories from a multidimensional potential well

A procedure is presented for computing the phase space volume of initial conditions for trajectories that escape or "react" from a multidimensional potential well. The procedure combines a phase space transition state theory, which allows one to construct dividing surfaces that are free of local recrossing and that minimize the directional flux, and a classical spectral theorem. The procedure gives the volume of reactive initial conditions in terms of a sum over each entrance channel of the well of the product of the phase space flux across the dividing surface associated with the channel and the mean residence time in the well of trajectories which enter through the channel. This approach is illustrated for HCN isomerization in three dimensions, for which the method is several orders of magnitude more efficient than standard Monte Carlo sampling.     

Modified model for four-wave mixing-based wavelength conversion in silicon micro-ring resonators

A modified model for wavelength conversion based on the four-wave mixing (FWM) in a silicon micro-ring resonator is presented. Unlike previous contributions, the nonlinear phase shifts caused by self-phase modulation and cross-phase modulation are also taken into account in the present theoretical analysis besides the linear propagation loss and the nonlinear losses caused by two-photon absorption and free-carrier absorption. Analysis shows that the nonlinear phase shifts will cause different red shifts for the pump and signal (or converted) resonant wavelengths, and consequently an additional wavelength difference between the signal transmission dip and the efficiency peak, which will increase/decrease the conversion efficiency of the signal channel far from/near the pump. The conversion efficiency and the conversion peak width of each signal channel are both affected by the micro-ring radius and coupling coefficient. A broader conversion peak width can be obtained by using a micro-ring resonator with a smaller Q factor.