Equivalent Noise Models in Fiber Optical Communication Systems

An equivalent noise model of optical receiver amplifiers as shown in Fig.1 has been given in many fiber optical communication literatures. It is proved in this paper that this equivalent noise model is neither equivalent to the original one nor measurable. The main reason is that the position of the input impedance in this noise model is not the same with its in the typical noise model,but the same S vn , S in with the typical noise model are used. So the equivalent noise model above is wrong and is not fit to be taken into application.

Fiber Grating Ring Laser in All Optical Communication System

Erbium fiber grating ring laser (EFRL) witn an integrated travelling wave and low polarization mode noise is reported. Through modulated experiment of a successful 2.488 Gb/s RZ data, it is shown that the EFRL is a promising alternative to DFB lasers for high-speed transmission applications.

Dispersion Monitoring Techniques in High Bit-rate Optical Communication Systems

For the efficient dynamic dispersion compensation, it is essential to monitor the dispersion accurately. The existing main dispersion monitoring techniques in high bit-rate optical communication systems are presented as well as their operating principles and research progress. The advantages and disadvantages of these methods are analyzed and discussed.

Toward Low-Cost Flexible Intelligent OAM in Optical Fiber Communication Networks

Low-cost,flexible and intelligent optical performance monitoring and management is a key enabling technology for network quality guarantee,especially in the era of explosive growth of communication capacity and network scale.However,to the best of our knowledge,it is extremely challenging to implement real-time performance monitoring and operations,administration and maintenance(OAM) in a highly complex dynamic network.In this paper,we propose an innovative optical identification(OID) scheme that can realize both performance monitoring and some advanced OAM sub-functions.The basic concepts,applications,challenges and evolution directions of this OID tool are also discussed.

2.5 Gbit/s monolithic ICs for optical fiber transmitter and receiver in 0.35 μm CMOS process

2.5 Gbit/s monolithic integrated circuits （ICs） for optical fiber transmitter and receiver in 0.35 μm CMOS （complementary metal-oxide-semiconductor transistor） process are presented. The transmitter, which includes a 4： 1 multiplexer and a laser diode driver （LDD）, has four 622 Mbit/s random signals as its inputs and gets a 2.5 Gbit/s driving signal as its output; the receiver detects a 2.5 Gbit/s random signal and gets four 622 Mbit/s signals at the output. The main circuits include a trans-impedance amplifier （TIA）, a limiting amplifier, a clock and data recovery （CDR） unit, and a 1： 4 demultiplexer （DEMUX）. Test results prove the logic functions of the transmitter to be right, and the 10% to 90% rise and fall times of transmitter＇s output data eye diagram are 211.1 ps and 200 ps, respectively. The sensitivity of the receiver is measured to be better than 20 mV. The root mean square jitter of the DEMUX＇s output data is 15.6 ps and that of the clock after 1： 4 frequency dividing is 1.9 ps. Two chips are both applicable to 2.5 Gbit/s optical fiber communication systems.

Beyond 100 Gb/s Optical OFDM Transmitted in Optical Long-Haul System

100 G Ethernet is considered to become the next generation Ethernet standard for IP networks.Typical 100 Gb/s transmission systems and their performance are presented.Comparision and analysis for 100 Gb/s transmission systems have been discussed.It is demonstrated that optical OFDM can be used in future 100 Gb/s/ch and long-haul system.

Remote I/O Unit for Optical Fiber Demmunication

Abstract:Based on optical fiber technology, the main electric circuit of the remote I/O unit controller is studied. And the application of the system is illustrated.

Flipped-Exponential Nyquist Pulse Technique to Optimize PAPR in Optical Direct-Detection OFDM Systems

In this paper, we describe a novel technique based on the flipped-exponential （FE） Nyquist pulse method for reducing peak-to-average power ratio （PAPR） in an optical direct-detection orthogonal frequency-division multiplexing （DD-QFDM） system, The technique involves proper selection of the FE Nyquist pulses for shaping the different subcarriers of the OFDM. We apply this technique to a DD-OFDM transmission system to significantly reduce PAPR. We also investigate the sensitivity of a received OFDM signal with strong nonlinearity in a standard single-mode fiber （SMF）.

STUDY ON MINE FIRE-RESISTANT OPTICAL FIBER CABLE KL5004

This paper introduces a new-developed mine fire-resistant optical fiber cable (OFC)KL5004,its structural characteristics, main feature, the theory about fire resistance and its application in high output and efficiency mine.

Design and Implementation of Optical Fiber Test Equipment

In order to meet the needs of the rapid development of optical fiber communication technology, combined with the thinking of the Internet of Things, a new idea of designing an optical fiber test equipment using Raspberry Pi is proposed. At the same time, the design of a multi-parameter measuring device for optical fiber signals based on Flask was completed.

Optical 64QAM-OFDM Transmission Systems with Different Sub-Carriers

In this paper, the transceiver performance of optical 64QAM-OFDM signals with different sub-car- riers is studied. Firstly, we build a 40Gbit/s optical coherent 64QAM-OFDM transmission system. 64QAM-OFDM optical signals with 16, 32, 64, 64, 128, 256 and 512 sub-carriers are transmitted over 100 km single mode fiber (SMF). Then, the optical spectrum diagrams before and after transmission, the bit error rate (BER) and constellation diagrams of received signals were compared. The simulation results show that, with the number of sub-carriers increasing, the value of PAPR will gradually increase and the quality of the received optical signals will deteriorate. Moreover, with the number of sub-carriers increasing, the computational complexity will increase when digital signal processing (DSP) is used. Therefore, we should choose the optimal number of sub-carriers, and the PAPR influence and BER are also considered for achieving effective transmission.

A flexible receiver with fiber optical parametric amplifier in OCDMA-FSO communication system

A new receiver is proposed, which uses the fiber optical parametric amplifier(FOPA) in optical code division multiple access(OCDMA) over free space optic(FSO) communication system. The noise tolerance as the performance index in this receiver is derived. The receiver can not only improve the noise tolerance but also change the pump data conveniently for adapting to the length variation of the coding sequence under a complex and fast-changing weather condition. The influence of different factors on the noise tolerance is analyzed, and a significant improvement of about 18.77 d B for the noise tolerance can be achieved when the pump power and the length of coding sequence are 5 W and 256, respectively.

Exploiting the Faster-Than-Nyquist Concept in Wavelength-Division Multiplexing Systems Using Duobinary Shaping

This paper begins with Nyquist wavelengthdivision multiplexing （WDM） and then introduces fasterthanNyquist. In fasterthanNyquist a certain amount of intersymbol interference （ISI） is accepted, which violates the fundamental principle of Nyquist WDM. This results in muchrelaxed transceiver bandwidth and simpler spectral design. However, in fasterthanNyquist, implementation complexity is shifted from the transmitter side to the receiver side. Therefore, successful application of fasterthanNyquist depends on innovation in the receiver structure. In this paper, we discuss the guidelines for implementing suboptimum, lowcomplexity receivers based on fasterthanNyquist. We suggest that duobinary shaping is a good technique for trading off achievable spectral efficiency, detection performance, and implementation complexity and might be preferable to Nyquist WDM. Experiments are conducted to verify robustness of the proposed technique.

Recent progress on high-speed optical transmission

The recently reported high spectral efficiency （SE） and high-baud-rate szgnal transmission are all Daseo on digital coherent optical communications and digital signal processing （DSP）. DSP simplifies the re- ception of advanced modulation formats and also enables the major electrical and optical impairments to be processed and compensated in the digital domain, at the transmitter or receiver side. In this paper, we summarize the research progress on high-speed signal generation and detection and also show the progress on DSP for high-speed signal detection. We also report the latest progress on multi-core and multi-mode multiplexing.

Research of Homodyne Optical Fiber Communication System and Associated Technologies

Because it has the advantages of high sensitivity, and it is easy to demodulate and convenient to select in FDM system, the coherent optical fiber communication system is much suitable to be used in long distance optical communication systems and in optical fiber WANs. There are two major patterns in coherent optical fiber communication: heterodyne and homodyne. Compared with the heterodyne scheme, the homodyne optical fiber communication system has the following advantages: (1) The sensitivity of the homodyne receiver is higher than that of the heterodyne receiver. As we know, the PSK homodyne optical fiber communication system has the highest sensitivity in coherent optical fiber communication systems. So it is much suitable to be used in long distance optical communication systems or in FDM systems. (2) Because the homodyne receiver only uses the baseband to demodulate the transmitted signals, it occupies much narrower frequency domain than the heterodyne receiver does, which makes it more suitable to be used in multichannel systems. (3) The demodulation pattern used in homodyne receiver is much easier than that used in the heterodyne receiver, since it only needs the baseband demodulation. Usually we construct a homodyne receiver with an optical phase locked loop (OPLL). The research of the OPLL began at 1960′s and the study of the homodyne receiver has been made gradually. In 1984, the first homodyne optical fiber communication system was demonstrated in BTRL, in which the signal laser and the local laser were all 1.5 μm He Ne gas lasers, and the OPLL used was a balanced one. In 1989, L.G.Kazovsky demonstrated experimentally a homodyne receiver in Bellcore using two 1.3 μm Nd:YAG lasers as the signal laser and the local laser and also using a balanced OPLL. Because the linewidth of the normal semiconductor laser is too large and its frequency stability is much poorer, it is very difficult to construct a homodyne receiver with the semiconductor lasers. At the end of 1989, the first Dissertation completed Jul. 1992homodyne optical fiber communication system using two 1.5 μm external cavity semiconductor lasers as the signal laser and the local laser, respectively, was finished in AT&T Bell Lab by J. M. Kahn, in which the OPLL was also a balanced one. In China, the research of the homodyne optical fiber communication system was funded by the National Seventh Five Year Program and by the National Natural Science Foundation. The difficulties to construct a homodyne optical fiber communication system are listed as follows: (1) In homodyne communication systems, the signal laser′s frequency should be stable to avoid the penalty of the receiver′s BER and the crosstalk to other channels in a FDM system, and the local laser could be tuned widely and easily to cover all the signal lasers′ frequency domain. Both the signal laser and the local laser should be narrow in linewidth to decrease the influence of the laser′s phase noise on the BER of the receiver. (2) The modulation pattern used should be studied and chosen carefully because the requirements of different kinds of modulation on the laser, the receiver and the channel are different. (3) Since the construction of the linear OPLL (the balanced) and the nonlinear OPLL (the Costas OPLL, or the Decision Driven OPLL) are rather different, their requirements on the linewidths of the lasers are different too, we should study the theory and the construction of the OPLL carefully to select the suitable scheme to realize. (4) In a multichannel system (such as a FDM system), the influence of crosstalk between channels on the homodyne system should be researched carefully. The technology used to stabilize the channel interval should also be studied. In this thesis, the homodyne optical fiber communication system has been theoretically analyzed, the technical difficulties of constructing the system have been studied. Several kinds of external cavity semiconductor laser have been researched experimentally. Compared

The Study on Heterodyne and Phase Diversity Coherent Optical Fiber Communication Systems and Their Components

The research in Coherent Optical Fiber Communication Systems (COFCS) using long waveband semiconductor laser diodes as transmitter and local oscillator has evolved gradually from an esteric subject studied in just a few communication laboratories around the world to the field demonstration stage. This is mainly because of the possibility of receiver sensitivity improvement reaching 10～20 dB, that of frequency division multiplexing (FDM) with very fine frequency separation and the possibility of using electronic equalization network to compensate for the effect of optical pulse dispersion in the Single Mode Fiber (SMF). The author of the dissertation has engaged in the study on COFCSs since 1987. Undergoing 3 years of hard work, the finished research work includes two parts: Part I is the study on heterodyne COFCSs and their key components; Part II is the study on two branch phase diversity COFCS and its components. In the first part, using the Lamb′s semi classical theory and the model of vector field, the effects of various kinds of parameters, such as cavity detuning, cavity′s Q factor and the transverse magnetic field strength, on the intramode beat frequency tuning characteristics are analyzed. On the basis of the theoretical analysis, the equipment of 1 523 nm He Ne Stabilized Transverse Zeeman Lasee (STZL) with high frequency stability and certain continuous single frequency tuning range, has been established domestically for the first time. With the development of long waveband semi conductor laser diodes fabricated domestically, the author mainly deals with the long waveband COFCSs using semiconductor laser diodes as transmitter and local oscillator. To counter the poor spectrum characteristics of the conventional double heterojunction semi conductor laser diodes, the characteristics of 1.5 um InGaAsP GRINROD External Cavity Semi conductor Lasers (ECSL) in the case of strong and weak feedback conditions, is experimentally studied. Then the GRINROD Dissertation completed Apr.1991ECSLs with complete closed and compact structure are developed. Using this kind of lasers and other components made domestically, the long waveband large deviation FSK heterodyne single filter/ envelope detection systems and small deviation FSK heterodyne single filter/delay line frequency discriminator detection system are achieved for the first time. In those experiments, the frequency modulation characteristics, line width, single frequency continuous tuning range and frequency stability of the GRINROD ECSL are measured by means of IF spectrum. Meanwhile, the IF receiving circuits are optimized for obtaining stable transmission properties. The main research achievements in part II are the theoretical analysis of the diversity COFCSs. Firstly, the Bit Error Rate (BER) performance of two branch homodyne phase diversity ASK, DPSK and two branch homodyne phase polarization DPSK receivers are analyzed by means of characteristic function model. In the analysis, the effects of pre and post detection filters on the system performance are especially studied. Secondly, the impacts of the phase noise, shot noise, polarization mismatch and imbalance of branch circuits on the two branch homodyne phase diversity ASK receiver, and that of modulation frequency deviation on FSK receiver are analyzed in terms of Gaussian approximation. Lastly, an improved all fiber 90 degree optical hybrid is fabricated. Utilizing the hybrid and 1.5 um InGaAsP GRINROD and grating ECSLs, a low IF, two branch phase diversity FSK coherent optical fiber transmission system is experimented for the first time in China. Guan Kejian Born in Jan. 1963. He received his Ph. D degree in Apr. 1991, in Radio Engineering, Beijing Uni versity of Posts and Telecommunications.

A novel 3-stage structure for a low-noise, high-gain and gain-flattened L-band erbium doped fiber amplifier

The configuration of the novel three-stage L-band erbium-doped fiber amplifier with very large and flat gain and very low noise figure presented in this paper uses the forward ASE (amplified spontaneous emission) from the first section of the EDF (erbium-doped fiber) and the backward ASE from the third section of the EDF (both serve as the secondary pump sources of energy) to pump the second EDF. To improve the pump efficiency, the power of the pump is split into two parts (with a ratio of e.g. 2:7). The characteristics of this L-band EDFA are studied on the basis of the Giles Model with ASE.

Optimal Higher-order Dispersion Management Methods in WDM Transmission Systems

In order to reduce the four-wave mixing crosstalk and avoid the signal waveform distortion in long-haul dense-wavelength division multiplexing systems,helpful methods on how to choose suitable local parameters in higher-order dispersion managed line are presented, which are used to increase the system capacity and improve the system performances.

Optical PPM-CDMA Communication System with Optical Hard Limiter

An optical PPM CDMA communication system with an optical hard limiter in front of the correlator of a receiver is proposed in order to reduce multi user interference. The performance of the system is evaluated when the effects of both multi user interference and photo detector shot noise are considered. An upper bound on the bit error rate is derived. The comparison of the performance of the above receiver with that of the optical PPM CDMA system without an optical hard limiter is made. Simulation results show that the performance of the system with an optical hard limiter is superior to that of the conventional one.