OPTICAL COMMUNICATIONS USING SURFACE ACOUSTIC WAVES

The efficient and accurate evaluation of the transmission performance of high-capacity optical communication systems has always attracted significant research attentions. The enhanced Gaussian noise (EGN) model is considered as an excellent solution to predict the system performance taking into account linear and nonlinear transmission impairments. Since the conventional form of the EGN model is complicated and intractable for a fast computation, the closed-form simplification has been regarded as a direction to significantly reduce the computational complexity. However, the accuracy of such a closed-form EGN model becomes a main concern in the application of ultra-wideband optical communication systems. In this work, we have investigated the accuracy of the closed-form EGN model for ultra-wideband optical fiber communication systems, where the performance of the system using electronic dispersion compensation, multi-channel nonlinearity compensation and full-field nonlinearity compensation has been evaluated in terms of symbol rate, number of channels and signal power. Our work will provide an insight on the application of the EGN model in next-generation ultra-wideband long-haul optical fiber communication networks.

光纤通信已经成为目前通信网络发展的主流方向。但是随着光纤通信系统向着超远距离、超大容量、超高速率的方向发展，光纤色散已经成为其巨大的阻碍。如何有效地控制光通信系统中产生的色散，使光信号在大容量、高速率、长距离传输中无误码地到达接收端，已经成为人们迫切需要解决的问题。对光通信系统中的色散进行监测并进行动态补偿的研究，使得超大容量、超长距离、超高速率的光纤通信系统成为可能，有助于最终实现全光智能自动交换网络。在众多测量光纤色散的方法中，调制相移法具有结构简单，可靠性强等优点。本文中，我们对使用调制相移法测量光纤色散进行了研究和仿真，讨论了在不同光纤长度和不同调制频率下，影响调制相移法测量结果精度的因素。通过适当地选取调制频率，我们可以使用调制相移法测得不同光纤长度下色散的精确值。另外在本文中，我们通过仿真验证了调制相移法可以测量具有任意色散–波长曲线的光纤。因此在实际应用中，调制相移法是可以应用于高精度光纤色散的测量。 Optical fiber communication is the mainstream of communication development at present. However, with the development of optical fiber communication system which trending towards ultra-long length, ultra-large capacity and ultra-high speed, fiber dispersion turned to be a great obstacle. How to control the dispersion created in the optical communication system effectively while force optical signal to reach the receiving end in high-capacity, high-rate and error-free long-distance transmission has increasingly become a research focus of optical fiber communication systems. It is a great significance to research about monitor and dynamic compensate dispersion in the optical communication systems, so that the ultra-large capacity, ultra-long length and ultra-high speed optical fiber communication systems would not be impossible, all-optical intelligent network with automatic switching functions would come true. Among the varieties of methods to measure fiber dispersion, the phase-modulation shift method is the unique one, which has the advantages of simple structure, high reliability. In this paper, we make a research and simulate to use the phase-modulation shift method, meanwhile we also discuss about the factors which affect the accuracy of the results in the different fiber lengths and modulation frequencies. By the means that selecting appropriate modulation frequency, we can use modulation phase shift method to measure the exact value of dispersion comes out from different lengths of fiber. Moreover, this paper also proves that the phase-modulation shift method is able to measure the optical fiber with arbitrary dispersion-wavelength curve, which is already verified by our simulation. Therefore, the phase-modulation shift method is well to be applied to take practice in the high-precision fiber dispersion measurement.

The design, fabrication, optical and mechanical characteristics, and reliability of several kinds of the latching-type single-mode-fiber (SMF) switch are reported. Practical applications of these switches to optical fiber communication systems and optical testing and sensing systems are also demonstrated. In the developed switches, a movable fiber is actuated by the magnetic attraction force produced between permanent magnets and a micromagnetic-alloy pipe fixed around the fiber. The ultralight micropipes (0.13 (i.d.)-0.18 (o.d.)/spl times/5/sup L/ mm, 400 /spl mu/g) were successfully massproduced by a fiber-micromachining technique based on metallizing and etching of sacrificial fibers. We used a refractive-index-matching oil in the switches to reduce insertion loss and reflected light. The several hundred fabricated 1/spl times/2 standard SMF switches exhibited excellent optical characteristics, such as typical insertion loss of 0.36 dB, return loss of 49 dB and crosstalk of -70 dB. They exhibited stable latching-type operation with loss changes of below 0.1 dB during 10/sup 5/ switching operations with minimum driving power of 9 mW and switching time of 2 ms. The switches were subjected to endurance (10/sup 8/ switching operations), heat cycles, shock and vibration, and long-term (6.5 years) intermittent operation tests, and revealed no significant optical or mechanical degradation. A 1/spl times/8 latching-type SMF switch was constructed using seven 1/spl times/2 switches cascaded in three stages and uniform insertion losses of below 0.7 dB and return losses of over 47 dB at each of eight ports were obtained. The 1/spl times/2 and 1/spl times/8 switches have been applied to NTT's optical communication systems. We fabricated a compact and cost-effective wavelength switch by installing microfilter chips in the 1/spl times/2 switch and confirmed stable latching-type wavelength switching between 1.3- and 1.55-/spl mu/m optical signals. We also designed and fabricated a polarization-maintaining switch using polarization maintaining and absorption reducing (PANDA) fibers and confirmed stable polarization maintaining switching operations. These switches are applicable not only to optical fiber communication systems, but also to optical testing and sensing systems.

Nowadays, the coherent optical communication system plays an important role in communication field because of large capability and bandwidth. A coherent optical communication, based on high-order modulation and digital signal processing technologies, consists of optical transmitters, optical fiber lines, optical amplifiers and optical receivers. In the high-speed coherent optical communication system, the phase noise from the transmitter laser and the local oscillator laser can significantly degrade the performance of the signal transmission and detection, especially for the systems using high-order modulation format, such as m-ary phase shift keying (mPSK) and m-ary quadrature amplitude modulation (m-QAM). Therefore, investigations on laser phase noise compensation algorithm based on digital signal processing technologies has become more and more significant. In this work, a multi-ring carrier phase recovery algorithm is developed for compensating the laser phase noise in optical fiber communication systems using high-order modulation formats. Degradations on the performance of communication systems due to the laser phase noise have been investigated. The system performance using the proposed algorithm and the conventional Viterbi-Viterbi algorithm were also evaluated in 9-channel and 15- channel, 32-Gbaud, Nyquist-spaced QPSK, 16-QAM, 64-QAM and 256-QAM coherent transmission systems with considering the impact of the laser phase noise. It is found that the phase noise leads to stricter constraints on the linewidths of transmitter-side and receiver-side lasers, and it can greatly degrade the achievable information rates in communication systems. Besides, compared to the conventional Viterbi-Viterbi algorithm, which is usually applied in the QPSK system, our proposed algorithm can also well mitigate the laser phase noise in 16-QAM, 64-QAM and 256-QAM optical communication systems.
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Study on the regulation of amplitude for the optical soliton through nonlinear effects in the optical communication system

The aim of this research is the development and analysis of digital signal processing techniques for enhancing performance in coherent optical communication systems. While much of the current digital techniques are identical to those found in the digital wireless literature, we will investigate improvements in performance to be obtained by tailoring modulation and DSP post-processing algorithms to the optical. The combination of polarization-multiplexing and quadrature phase shift-keying (PM-QPSK or DP-QPSK) is emerging as one the most promising solutions to reach bit rates of 100 Gbps and higher. At the receiver end, the use of digital signal processing (DSP) [1, 2] results in significant deployment improvement over the traditional implementation. This application note shows a practical design of a 100 Gbps DP-QPSK transmission system using coherent detection with digital signal processing for distortion compensation.

An optical communications system is described which is capable of transmission and detection of 1-Gbċs <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> pulse-code modulation (PCM) word patterns. Modulation of an argon laser beam is obtained with a lithium tantalate (LiTaO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> ) modulator rod using a traveling-wave interaction. The high-speed electrical modulation signal is obtained by a multiplexing of four separate information channels.

This paper presents a silicon device (m.i.s.t.), with an optical threshold, which can operate as a digital optical switch. Its operation and characteristics are presented. A good correlation between theory and the experimental results is obtained. The responsivity and sensitivity of 0.9 AW?1 and 3.9 × 10?4 mA/?V are obtained, respectively. Possible applications in fast optical digital isolation and in optical communication systems are envisaged.

In this paper, a compressed sensing based scalable video coding using discrete wavelet transform (DWT) for space applications is presented. The proposed method is aimed at reducing the requirement of on-board memory, station contact time and data archival volume. Compressive sensing (CS) has been applied to encode the distributed wavelet coefficients into linear measurements. Since prior knowledge of the compressively sampled measurements is not available, a modeler is employed to determine the context of the measurement vector. Based on the statistics provided by the context modeler, the samples are entropy coded for transmission. A part of the compressive sampling measurements with near uniform distribution are encoded through adjusted binary coding, and the rest are encoded through Golomb-Rice coding. Run length encoding is implemented for exploiting the redundancy in the binary data further. At the receiver end, the original spatial signal is reconstructed from the CS samples by approximate message passing (AMP) algorithm and inverse discrete wavelet transform (IDWT) for video decompression. Simulation of the proposed approach has demonstrated an efficient compression of the video cubes with lower complexity at the transmitter end.

The implementation of timing recovery circuits in multigigabit/s optical regenerators becomes increasingly difficult because of the complexity of nonlinear circuit elements at such high data rates. We propose and demonstrate a new method of data regeneration without nonlinear retiming circuits. In the proposed scheme, the clock is superimposed on the data signal at the transmitter end and is separated from the composite signal at the receiver end by means of a novel microstrip directional filter for data regeneration. This scheme offers significant reduction in circuit complexity over conventional regenerator designs and has less pattern dependence and systematic jitter since the clock is not derived from the baseband data. A compact regenerator at 2.4 Gbit/s has been implemented using this technique and transmission over 35 km of dispersion-shifted fiber (DSF) with a 1550-nm DFB laser has been demonstrated.

In this paper, a microwave photonic dual band radar based on a photonic-assisted de-chirp processing receiver is proposed. The dual band operation is realized independently and simultaneously with a single set of hardware. At a transmitter end, two linear frequency-modulated signals separately located in C-band and Ku-band are transmitted, echoes are collected and sent to a receiver to implement photonic-assisted de-chirp processing. At the receiver end, a main modulator with a special structure, which consists of four parallel sub-modulators, is employed. The echoes and reference signals of C-band and Ku-band are applied to two pairs of sub-modulators of the main modulator, which are biased at the peak points for C-band and biased at the null points for Ku-band. In this case, the intermediate frequency signals of C-band and Ku-band produced by de-chirp processing locate at two different frequencies. Thus operation in different bands based on a unified system is achieved. An experiment operating in C-band and Ku-band with a bandwidth of 700 MHz and 3600 MHz is conducted. The results verify the concept of the dual band radar and show the potential of photonic technology to improve the performance of modern radar system.

The performance of many digital systems today is limited by the interconnection bandwidth between chips. Although the processing performance of a single chip has increased dramatically since the inception of the integrated circuit technology, the communication bandwidth between chips has not enjoyed as much benefit. Most CMOS chips, when communicating off-chip, drive unterminated lines with full-swing CMOS drivers. Such full-swing CMOS interconnect ring-up the line, and hence has a bandwidth that is limited by the length of the line rather than the performance of the semiconductor technology. Thus, as VLSI technology scales, the pin bandwidth does not improve with the technology, but rather remains limited by board and cable geometry, making off-chip bandwidth an even more critical bottleneck. In order to increase the I/O Bandwidth, some efficient high speed signaling standard must be used which considers the line termination, signal integrity, power dissipation, noise immunity etc In this work, a transmitter has been developed for high speed offchip communication. It consists of low speed input buffer, serializer which converts parallel input data into serial data and a current mode driver which converts the voltage mode input signals into current over the transmission line. Output of 32 low speed input buffers is fed to two serializer, each serializer converting 16 bit parallel data into serial data stream. Output of two serializers is fed to LVDS current mode driver. The serial link technique used in this work is the time division multiplex (TDM) and point-to-point technique. It means that the low-speed parallel signals are transferred to the high-speed serial signal at the transmitter end and the high-speed serial signal is transferred to the low-speed parallel signals at the receiver end. Serial link is the design of choice in any application where the cost of the communication channel is high and duplicating the links in large numbers is uneconomical.

The quality of shortwave channels may vary considerably due to the time-specific changes of the transmission conditions. So the correct transmission of a continuous data stream, e.g. digitized speech signals output by a vocoder cannot be guaranteed under adverse conditions even by means of complex error correction measures or costly high transmitter power. This results in the loss of vocoder data-the transmission of speech information is partly or fully interrupted which impairs intelligibility. For this reason we propose a voice transmission system as a solution to the problem of correct voice data transmission. It is a method that offers quasi-real-time behaviour for channels that are subject to no interference or only slight interference, and that offers complete and correct data transmission with reduced real-time behaviour (mailbox operation) in the presence of strong or long-term interference and fading. To reach intelligibility at the transmitter end, the vocoder data are first divided into intelligible blocks, e.g. into coherent words between two speech pauses and stored in a buffer. The blocks are then transferred to the lower layers of the ISO/OSI reference model where an ARQ protocol is employed which leads to correct data transmission. At the receiver end, the blocks can then be listened to individually or as a whole and, if necessary, repeated once or several times (mailbox operation). This method was tested over a radio link of 800 km between Rostock University and Rohde & Schwarz Munich laboratory. 1200 bps vocoders from Comsat Co. and XK 2100 transceivers with packet radio protocol (PRP) RSX.25 from Rohde & Schwarz were used.

Bit error rate (BER) performances of DPSK are researched for space uplink optical communication system. Considering further phase fluctuation effect based on the traditional atmospheric turbulence model, BER performance versus transmission power, zenith angle, frequency deviation, divergence angle and transmission diameter are discussed for different wavelengths. Simulations, especially, indicate that considering the phase fluctuation effect, BER performance is sensitive for low frequency deviation. It also confirms that wavelength of 1550nm on communication system is still a good choice for the better BER performance. This work is helpful for enhancing transmission quality and the design of space optical communication system.

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