Chaotic wavelength division multiplexing for optical communication

We demonstrate wavelength division multiplexing with chaotic subcarriers in two pairs of one-way-coupled Nd:YVO4 microchip lasers. Two individual digital messages are encoded on two chaotic carriers with different wavelengths in two transmitters by the chaotic masking method, and the mixed signals are sent to two receivers. Dual synchronization of chaos is used to obtain the original chaotic waveforms in the receivers. Two messages are decoded by filtering the difference of the laser outputs between the transmitter and the receiver by use of a low-pass filter for each pair of lasers. The message recovery can be achieved more easily when messages with small amplitude and low frequency are used.     

Multiple-image encryption by wavelength multiplexing

We introduce the technique of wavelength multiplexing into a double random-phase encoding system to achieve multiple-image encryption. Each primary image is first encrypted by the double phase encoding method and then superposed to yield the final enciphered image. We analyze the minimum separation between two adjacent multiplexing wavelengths through cross talk and the multiplexing capacity through the correlation coefficient. Computer simulations are performed to demonstrate the concept. This technique can be used for hiding multiple images as well.     

Birefringent sensor enhancement by wavelength multiplexing

The usable non-repetitive measuring range of birefringent fibre-optic based sensors is increased by wavelength multiplexing and demultiplexing. The theory involved along with experiments demonstrating the principle are discussed.     

密集波分复用(DWDM)、光学交叉互连(OXC)和全光通讯网络(AON)

本文介绍了全光网（AON）的基本结构和特点，介绍了全光网的两种关键部件－密集波分复用（DWDM）和光学交叉互连（OXC），讨论了各种方案的物理模型、工作原理和应用，并展望了光通讯的发展趋势。     

Cyclic polling-based dynamic wavelength and bandwidth allocation in wavelength division multiplexing passive optical networks

Cyclic polling-based dynamic wavelength and bandwidth allocation algorithm supporting differentiated classes of services in wavelength division multiplexing （WDM） passive optical networks （PONs） is proposed. In this algorithm, the optical line terminal （OLT） polls for optical network unit （ONU） requests to transmit data in a cyclic manner. Services are categorized into three classes： expedited forward （EF） priority, assured forwarding （AF） priority, and best effort （BE） priority. The OLT assigns bandwidth for different priorities with different strategies. Simulation results show that the proposed algorithm saves a lot of downstream bandwidth under low load and does not show the light-load penalty compared with the simultaneous and interleaved polling schemes.     

Transmission of two-dimensional images by wavelength multiplexing

Wavelength multiplexing is a method for encoding spatial information into spectral information. Previously, each point of a one-dimensional image corresponds to a specific wavelength. All wavelengths together can be transmitted in scrambled fashion through a single light fiber. Decoding into the original image is achieved by sending the transmitted light through a spectroscope. This process again displays the various wavelengths at various positions along a line. In this project, two-dimensional spatial information or grey tone images are encoded into a spectral distribution. After transmission through a light fiber this spectrum can be decoded into the original two-dimensional image. Four different encoding versions are presented, which use serial transmission parallel transmission, shifted light coupling or spatial pulse modulation.     

Technical study of visible light wavelength division multiplexing using polymer optical fiber

Visible light wavelength division multiplexing (VWDM) experiment was performed using polymer optical fiber (POF). Lights of two different wavelengths (650 and 530 nm) were sent to a single POF. Red light (650 nm) was used for 100-Mb/s full duplex IP data transmission and green light (530 nm) was used for voice signal transmission. Light sources are light-emitting diodes (LEDs). A POF coupler (splitter) and the prisms were employed as multiplexer and demultiplexer, respectively. The channel isolation and insert loss were measured, which are 20.5 and 17.65 dB for 650-nm channel respectively, and 19.16 and 20.55 dB for 530 nm one respectively.     

Polymer waveguide module for visible wavelength division multiplexing plastic optical fiber communication

We report a polymer waveguide module that provides bidirectional communication over a single plastic optical fiber (POF) with dual visible wavelength LEDs. The module is constructed using light-induced self-written waveguides, which enables a three-dimensional optical circuit for visible wavelength division multiplexing to be fabricated by an extremely simple process. We demonstrated 250 Mbits/s communication using a pair of these modules that each contained one green (lambda = 495 nm) and one red (lambda = 650 nm) LEDs by measuring the bit error rates. The results indicate that the system could transmit over more than 20 m of POF in full duplex mode.     

碳纳米管光学天线的有效波长和谐振特性

将经典金属自由电子气模型应用于金属型碳纳米管, 基于光学天线有效波长理论, 得出了金属型碳纳米管光学天线响应的有效波长与碳纳米管介电特性之间的普适关系. 在对碳纳米管介电特性进行第一性原理计算的基础上, 以金属型4 Å碳纳米管为例, 进一步研究了金属型碳纳米管光学天线响应的有效波长与入射波长之间的关系, 以及金属型碳纳米管光学偶极子天线的谐振特性. 通过将已有传统金属光学天线和碳纳米管天线有效波长的研究结果进行对比, 验证了本文理论的正确性. 结果表明, 碳纳米管光学天线响应的有效波长与入射波长呈近似线性关系, 与传统金属材料构成的同直径光学天线相比, 碳纳米管天线显示出了更强的波长压缩能力, 并且在可见光到红外波段内易于发生谐振. 该研究方法可为碳纳米管光学天线研究提供新的思路.     

适用于隧道环境的二元相控阵天线系统

为了满足在隧道环境中实现高速率、高质量无线通信的迫切需求,研究了适用于隧道环境的高增益天线,提出了利用二元相控阵天线系统提高隧道内信号传输质量的新方法。相控阵天线系统由两个高增益天线单元及一个移相器组成,通过移相器调整其中一个天线单元的相位,使隧道内合成电场的最小值幅值达到最大,提升信号的平均场强。仿真结果表明：与单个天线发射信号相比,在3 000 m隧道轴向传播范围内,相控阵天线系统发射信号合成电场的最低电平最少提升了19.6 dB;与两个天线同时发射信号相比,最低电平最少提升了12.4 dB,取得较好分集优化效果,消除多径效应导致的深度衰落,解决了隧道环境中存在的通信问题。

     

Photonic ratchet superlattices by optical multiplexing

We present a method based on incremental holographic multiplexing to create a refractive index ratchet distribution into a photorefractive crystal as an example for the generation principle of such complex multiperiodic lattices. The implemented technique follows a finite optical series expansion of the desired index modulation. To analyze the induced lattice, we determine the phase retardation of a probe beam at the back face of the crystal by digital holography analysis. Our result depicts a first example to optically explore the fascinating phenomena of ratchet resembling systems.     

应用波分复用改善像束传像系统像质的研究

本文通过分析空间波分复用系统中包散元件的色散平均效应,用线扩散传递函数研究了像束传像性质,由光学成像的本征理论用像束成像信息量分析了波分复用改善像束传像像质的机制,并从实验上验证了上述分析结论.     

Performance analysis of dense wavelength division multiplexing secure communications with multiple chaotic optical channels

The performance of dense wavelength division multiplexing secure communications with multiple chaotic optical channels is numerically analyzed in this paper. Taking the multiplexing of three chaotic optical channels as an example, we investigate the effects of second-order dispersion coefficient and nonlinear coefficient of fiber, channel spacing, message amplitude and bit rates on chaotic synchronization and multiplexing communications. Chaotic synchronization quality and Q-factor of the recovered message decrease with the increasing fiber length. A 1.25 Gbits/s non-return-to-zero (NRZ) sequence can be securely transmitted up to 60 km under the influence of the other two chaotic optical channels. Compared with the fiber dispersion, the cross-phase modulation is the primary factor which deteriorates the quality of communications. The results also show that the quality of communications is unlimited to the channel spacing as long as chaotic synchronization can be maintained. In addition, the effect of the amplitude of encrypted message on Q-factor and the confidentiality is demonstrated.     

Absolute polar duty cycle division multiplexing over wavelength division multiplexing system

The performance of absolute polar duty cycle division multiplexing (AP-DCDM) over wavelength division multiplexing (WDM) system is presented based on the simulation results. The AP-DCDM signal has narrower bandwidth than conventional time division multiplexing (TDM) signal, which makes its implementation in WDM system advantageous. In this paper, characteristics of AP-DCDM and TDM signals in WDM system are compared at the speed of 40 Gbit/s per channel, for the minimum allowed channel spacing and the chromatic dispersion tolerance. The results clearly show that AP-DCDM performs significantly better than TDM. By using AP-DCDM, 1.28 Tbit/s (32 × 40 Gbit/s) was successfully transmitted over 320 km standard single mode fiber. Spectral efficiency of 0.64 b/s/Hz was achieved by using 10 Gbit/s transmitters and receivers without polarization multiplexing.     

Pulsed digital micro-holography of femto-second order by wavelength division multiplexing

Wavelength division multiplexing (WDM) used in a pulsed digital micro-holographic system to record ultra-fast processing of the order of femto-second is reported for the first time, where a BBO crystal is used to generate harmonic wave of the incident laser wave, and both of the basic and the frequency doubled waves are time-delayed and introduced to a Michelson’s interferometer to record two sub-holograms with different spatial frequencies on a single frame of a CCD by WDM. In the experiment, an ultra-fast dynamic process of air ionization induced by a single femto-second laser pulse is holographic recorded by this system, and both of intensity and phase difference images digitally reconstructed are obtained through Fourier transformation and digital filtering, which shows clearly the dynamic process of formation and propagation of the plasma, with a time resolution of the order of femto-second.     

Multicolour spatial frequency analysis by optical multiplexing

The Fourier transforms of colour transparencies have been separated spatially according to their colour content. The use of a different spatial carrier for each colour enables simultaneous detection of the spectra as well as reconstitution of an image after different spatial filtering processes have been performed on different colour spectra.     

Tunable optical add-drop multiplexer based on long-period fiber gratings for coarse wavelength division multiplexing systems

We propose and experimentally demonstrate a voltage-controllable add-drop multiplexer with a tunable coupler based on long-period fiber gratings (LPFGs). The tunable coupler is based on cladding mode coupling between two parallel LPFGs with divided coil heaters, which controls the resonant wavelength positions of the two LPFGs. The wavelength tunability of the tunable coupler is measured to be -0.45 nm/degrees C in the temperature range from 20 to 120 degrees C. The large tuning range of optical signals (approximately 50.54 nm) from 1502.32 to 1552.86 nm, which covers both the short (S) and the conventional (C) bands, is achieved. The channel isolation is as high as approximately 40 dB. It has several advantages, including a broad tuning range of wavelength in both the S- and C-bands, high channel isolation, no backreflection, and so on.     

激光波长合束精度研究

对双光束波长合束精度进行了研究。用镀有特制光学薄膜的滤光片对波长为532和515 nm的两束激光进行合束,并对合束精度进行检测。基于此系统,建立了对应理论模型,并对合束及检测的误差来源和大小进行全面分析。两光束指向稳定性均为50 μrad时,合束精度理论值为14.69″,指向稳定性所占比例为99.26%,系统对质心定位等不稳定因素（误差变化< 3倍）抗性极好,精度变化< 2.4‰;指向稳定性提高到23.51 μrad时,合束精度理论值为7.09″,指向稳定性所占比例为96.77%,系统仍有较高抗干扰能力,精度变化< 1%。分析表明,影响近场小功率合束精度的因素有激光指向稳定性、机械调节和质心定位误差,其中激光指向稳定性是主要因素。通过调节各因素的比例,可对合束的抗干扰能力进行控制。     

Volume three-dimensional flow measurements using wavelength multiplexing

Optically distinguishable seeding particles that emit light in a narrow bandwidth, and a combination of bandwidths, were prepared by encapsulating quantum dots. The three-dimensional components of the particles' displacement were measured within a volume of fluid with particle tracking velocimetry (PTV). Particles are multiplexed to different hue bands in the camera images, enabling an increased seeding density and (or) fewer cameras to be used, thereby increasing the measurement spatial resolution and (or) reducing optical access requirements. The technique is also applicable to two-phase flow measurements with PTV or particle image velocimetry, where each phase is uniquely seeded.