Reversible waveform conversion between microwave and optical fields in a hybrid opto-electromechanical system

We present a scheme of reversible waveform conversion between microwave and optical fields in the hybrid opto-electromechanical system. As an intermediate interface, nanomechanical resonator optomechanically couples both optomechanical cavities in the optical and microwave frequency domains. We find the double-optomechanically induced transparency and achieve coherent signal waveform bi-directional transfer between microwave and optical fields based on quantum interference. In addition, we give an analytical expression of one-to-one correspondence between the microwave field and the optical output field, which intuitively shows the reversible waveform conversion relationship. In particular, by numerical simulations and approximate expression, we demonstrate the conversion effects of the three waveforms and discuss the bi-directional conversion efficiency and the bandwidth. such a hybrid opto- and electro-mechanical device has significant potential functions for electro-optic modulation and waveform conversion of quantum microwave-optical field in optical communications and further quantum networks.     

光场压缩态的产生及其在亚散粒噪声光学测量和量子信息中的应用

光场压缩态是一种非经典光场,它在超标准量子极限（SQL）的高精度光学测量、超低噪声光通信及量限通信等有着广泛应用前景,是物理学和信息科学交叉前沿研究课题,文章介绍了光场压缩态的产生及它在亚散粒噪声光学测量（sub-shot-noise=limit opical measurement）和量子信息中的重要应用。     

Soliton-based ultra-high speed optical communications

Multi-terabit/s, ultra-high speed optical transmissions over several thousands kilometers on fibers are becoming a reality. Most use RZ (Return to Zero) format in dispersion-managed fibers. This format is the only stable waveform in the presence of fiber Kerr nonlinearity and dispersion in all optical transmission lines with loss compensated by periodic amplifications. The nonlinear Schrödinger equation assisted by the split step numerical solutions is commonly used as the master equation to describe the information transfer in optical fibers. All these facts are the outcome of research on optical solitons in fibers in spite of the fact that the commonly used RZ format is not always called a soliton format. The overview presented here attempts to incorporate the role of soliton-based communications research in present day ultra-high speed communications.     

Optical theorem detectors for active scatterers

We develop a new theory of the optical theorem for scalar fields in nonhomogeneous media which can be bounded or unbounded. It applies to arbitrary lossless backgrounds and quite general probing fields. The derived formulation holds for arbitrary passive scatterers, which can be dissipative, as well as for the more general class of active scatterers which are composed of a (passive) scatterer component and an active, radiating (antenna) component. The generalization of the optical theorem to active scatterers is relevant to many applications such as surveillance of active targets including certain cloaks and invisible scatterers and wireless communications. The derived theoretical framework includes the familiar real power optical theorem describing power extinction due to both dissipation and scattering as well as a novel reactive optical theorem related to the reactive power changes. The developed approach naturally leads to three optical theorem indicators or statistics which can be used to detect changes or targets in unknown complex media. The paper includes numerical simulation results that illustrate the application of the derived optical theorem results to change detection in complex and random media.     

Three-dimensional modulations on the states of polarization of light fields

Light fields with spatially structured states of polarization(SoPs) are gathering increasing attention because of their potential applications from optical imaging and micromanipulation to classical and quantum communications. Meanwhile,the concepts within structured light fields have been extended and applied to acoustic, electron, and matter waves. In this article, we review recent developments of the SoP modulation of light fields, especially focusing on three-dimensional(3 D) modulations on the SoPs of light fields. The recent progress and novel implementations based on 3 D spin-dependent separation are discussed. Following the discussions to this physical phenomenon, we then describe recent developments on the vector fields with 3 D structured SoP and intensity distributions, namely, 3 D vector fields. The discussed phenomena inspire us to explore other structured light fields for the expansion of applications in biomedical, information science,quantum optics, and so on.     

Plasmon lasers: coherent light source at molecular scales

Plasmon lasers are a new class of coherent optical frequency electromagnetic wave amplifiers that deliver intense, coherent and directional surface plasmons well below the diffraction barrier. The strongly confined electric fields in plasmon lasers can enhance significantly light‐matter interactions and bring fundamentally new capabilities to bio‐sensing, data storage, photolithography and optical communications.     

A secure transmission scheme on link level for optical fiber communication systems

In secure communication systems, a very important problem is how to prevent wiretapping. Lots of researches on cryptography give good solutions on secure communications. But if a wire tapper can detect the existence of the transmitted information and get enough eavesdropped frames, cryptanalysis techniques can help to blindly recover the frame structures, error-control coding parameters and passwords. In this paper we propose a novel secure transmission scheme on the link level for optical fiber communication systems. Based on the blind frame synchronization technique, we propose to drop the traditionally strict frame structures in fiber communications and conceal the error-correcting-encoded blocks among random data, so that wire tappers cannot get enough coded packets to analyze and recover the transmitted information. Therefore, the proposed method is very suitable for secure communications and military communications.     

Why optical data communications and why now?

Our focus here is on data communications within IT equipment and in IT data centers. Optical communications is not new. Thus the obvious question is likely; why a paper entitled, “Why optical data communications and why now?”. The reasons are twofold. First, optical data communications is more necessary now than it has ever been in the past. It is not excessive to even consider that it will be required in the not too distant future. Second, the advances in the broad field of photonics and optics have brought optical communications nearly to the point that it can finally cross over the threshold to be less expensive than electronic signaling. In this paper we make the case why we must aggressively pursue optics for data communications at all length scales within the data center. The summarization of this paper is that optical communications is inevitable, and we offer reasons why we believe this is true.     

Fiber optic cables for undersea communications

Areas for potential use of low-loss optical fibers in undersea communications are discussed, along with constraints that should be satisfied in incorporating these fibers into practical cables. Recent progress in construction of optical cable units with low attenuation, small diameter, low specific gravity, high tensile strength, and extended flexural endurance is described. Design concepts for six undersea optical cables, with a variety of diameters and capabilities, are presented in detail. Guidelines are discussed for the design of such cables. Related operational requirements on the cable, such as power transfer, are examined to show how unconventional approaches can allow advantages of the optical data link to be more fully utilized.     

光脉冲在微环耦合谐振光波导中传输线性特性的数值仿真

利用传输矩阵法得到了微环耦合谐振光波导色散关系的一般表达式,并由色散关系出发讨论了光脉冲在微环耦合谐振光波导中传输时的线性特性,包括带宽、群速度、色散和线性相位变化,这些特性对微环耦合谐振光波导在光通信和光传感领域的应用有重要意义. 关键词： 微环光波导 光脉冲线性特性 传输矩阵法 数值仿真     

Double Security Level in Optical Communication Systems Using Combined Modulation Formats

A new optical communication system exhibiting a double security level is presented. Information coding is based on combined modulation formats of two data streams over the same optical carrier. Incoherent and coherent optical encryption algorithms are presented and are theoretically analyzed. The optical encryption method is transparent to data bit rates. Furthermore, it requires "on-line" data decoding with no possibility of recording and further processing. The incoherent scheme is very practical and can be implemented in existing optical communications systems, using currently available technology. Computer experiments of the incoherent method indicate less than 25 dB of signal to noise ratio required for 10-9 bit error rate and ineligible information decoding time of more than 10 8 years.     

光纤激光模场及表征技术进展

在光纤通信、光纤激光器和光纤传感等领域的实际应用中,需要重点关注光纤中的模式问题。模分复用是提高光通信信息容量的有效方法,模间干涉是大多数光纤传感的基本方法,高功率光纤激光的光束质量控制的关键技术之一就是模式控制,因此,对光纤模式理论、模式产生及转换、模式表征技术开展研究具有重要的研究意义和实际应用价值。论文讨论了光纤的模式及光束质量,分析了多种模式发生及转换的方法,将模式表征方法归结为非相干、相干和低相干测量法。光纤模式表征是目前的研究热点,在多种表征方法中,空间和频谱成像法（S2）和双重傅里叶变换法（F2）具有显著的优越性,可不需要提前知道光纤的几何参数,就可获得模场分布、模式功率占比、群时延等特性。研究表明F2法更适合于表征高功率光纤激光的模场特性。     

Image information transfer via electromagnetically induced transparency-based slow light

In this work, we experimentally demonstrate an image information transfer between two channels by using slow light based on electromagnetically induced transparency(EIT) in a solid. The probe optical image is slowed due to steep dispersion induced by EIT. By applying an additional control field to an EIT-driven medium, the slowed image is transferred into two information channels. Image intensities between two information channels can be controlled by adjusting the intensities of the control fields. The similarity of output images is further analyzed. This image information transfer allows for manipulating images in a controlled fashion, and will be important in further information processing.     

Atomic-vapor-based high efficiency optical detectors with photon number resolution

The ability to detect very weak optical fields with high efficiency (>99%) and to distinguish the number of photons in a given time interval is a very challenging technical problem with enormous potential payoffs in quantum communications and information processing. We propose to employ an atomic vapor as the active medium, prepared in a specific quantum state using laser radiation. The absorption of a photon will be aided by a dressing laser, and the presence or absence of an excited atom will be detected using the "cycling transition" approach perfected for ion traps. By incorporating an appropriate up-conversion scheme, our method can be applied to a wide variety of optical wavelengths.     

Twisted optical communications using orbital angular momentum

Angular momentum, a fundamental physical quantity, can be divided into spin angular momentum(SAM) and orbital angular momentum(OAM) in electromagnetic waves. Helically-phased or twisted light beams carrying OAM that exploit the spatial structure physical dimension of electromagnetic waves have benefited wide applications ranging from optical manipulation to quantum information processing. Using the two distinct properties of OAM, i.e., inherent orthogonality and unbounded states in principle, one can develop OAM modulation and OAM multiplexing techniques for twisted optical communications. OAM multiplexing is an alternative space-division multiplexing approach employing an orthogonal mode basis related to the spatial phase structure. In this paper, we review the recent progress in twisted optical communications using OAM in free space and fiber. The basic concept of momentum, angular momentum, SAM, OAM and OAM-carrying twisted optical communications,key techniques and devices of OAM generation/(de)multiplexing/detection, high-capacity spectrally-efficient free-space OAM links, fiber-based OAM links, and OAM processing functions are presented. Ultra-high spectral efficiency and petabit-scale freespace data links are achieved benefiting from OAM multiplexing. The key techniques and challenges of twisted optical communications are also discussed. Twisted optical communications using OAM are compatible with other existing physical dimensions such as frequency/wavelength, amplitude, phase, polarization and time, opening a possible way to facilitate continuous increase of the aggregate transmission capacity and spectral efficiency through N-dimensional multiplexing.     

Fiber optic cables for undersea communications

Abstract

Areas for potential use of low-loss optical fibers in undersea communications are discussed, along with constraints that should be satisfied in incorporating these fibers into practical cables. Recent progress in construction of optical cable units with low attenuation, small diameter, low specific gravity, high tensile strength, and extended flexural endurance is described. Design concepts for six undersea optical cables, with a variety of diameters and capabilities, are presented in detail. Guidelines are discussed for the design of such cables. Related operational requirements on the cable, such as power transfer, are examined to show how unconventional approaches can allow advantages of the optical data link to be more fully utilized.     

全光纤量子通信系统中的高速偏振控制方案

偏振控制在光通信中是至关重要的技术, 关系着通信系统的稳定性和误码率. 本文提出一种基于双向Sagnac环工作方式的全光纤高速偏振控制方案, 通过调节环中一个光纤电光相位调制器的相位差而精确控制光场偏振方向, 并且实现了单个端口输出各种偏振态, 无需后续耦合操作. 相位控制精度为10^-3 rad, 最大消光比可达30 dB, 工作速率可达2 GHz. 由于本方案的精度、调制速度和稳定性都很高, 并采用了器件简单、成本低廉的全光纤光路, 易于集成, 在量子保密通信等光通信领域中有很好的应用前景. 关键词： 光纤偏振控制器 Sagnac环 量子通信     

On the relation between the wave aberration function and the phase transfer function for an incoherent imaging system with circular pupil

The consideration is carried out in its general formulation: the wave aberration function is represented in terms of classical aberrations (the Zernike polynomials), the phase transfer function (argument of the complex optical transfer function) is defined by a chain of transformations originating from the generalized pupil function. Quasi-analytical quadrature formulas are derived that link the optical transfer function and the phase transfer function with the aberration terms. It is shown that the phase transfer function contains information on the odd-order aberrations, which can be retrieved from coefficients to the Taylor expansion of the derived quadrature relation. Received 16 June 2001     

Optical transfer functions of Kerr nonlinear cavities and interferometers

We present the optical transfer functions for third-order nonlinear cavities that involve an optical carrier frequency and its modulation sideband fields. Our approach is based on linearized transformations and provides a convenient tool to calculate squeezed light sources as well as complex interferometer topologies, containing subsystems that involve intensity dependent phase shifts, i.e., optical Kerr media. As the result we present the noise spectral density of a Michelson interferometer with Kerr nonlinear arm cavities and resonant sideband extraction and find that quantum noise can be squeezed by arbitrary amounts even outside the cavity linewidth. Such a system might apply for future gravitational wave detectors or simply for a continuous wave source of squeezed states.     

Analysis of complex axis control loop in satellite laser communications

Satellite laser communication involves communications between GEO satellites and LEO satellites. The optical link can be built by the accurate pointing and tracking, which often employs the combination effect of coarse pointing assembly and fine pointing assembly. In order to achieve this goal with double rotated wedged-plate lenses and fast steering mirror that perform the scanning function of the coarse pointing assembly and the fine pointing assembly, mathematic model of transfer function of control loop is obtained by analyzing the total control loop for such complex axis. One can also get the optimized programs between coarse and fine pointing assembly.