数字激光器在模拟光纤通信中的应用

本文尝试用数字光纤通信用激光器代替模拟光纤通信用激光器,通过加入温度控制,预失真补偿电路等线性补偿方法以及通过输入端加入AGC,固定衰减器等动态范围补偿的方法,使数字光纤通信用激光器在线性度以及动态范围两方面得到很大的提高,达到模拟光纤通信用激光器的水平,完全可以应用于短波,超短波以及微波模拟光纤通信中.     

Novel amplified fiber-optic recirculating delay line processor

The application of optical amplifiers (OAs) to fiber-optic delay line signal processing is demonstrated. Both erbium-doped fiber amplifiers (EDFAs) and semiconductor optical amplifiers (SOAs) are applicable. Analytical results are presented for both amplified and unamplified fiber-optic recirculating delay lines (AFORDLs and UFORDLs). In the AFORDL an OA is inserted in the fiber loop. It is shown that the active AFORDL structure is capable of realizing all-fiber filters not possible with the passive UFORDL. This result is significant because it shows that the OAs can function beyond just the trivial optical loss compensation to provide extra flexibility not available in passive designs. An AFORDL design is presented which has a pole near +1 and a zero at -1 in the Z-plane resulting in useful characteristics in the magnitude and phase responses. The results suggest that extension of the concept to higher-order filters has the potential to lead to the realization of more complex optical processors     

Fiber loop optical buffer

Fiber loop optical buffers enable data storage for discrete time intervals and therefore appear suitable for applications in optical asynchronous transfer mode (OATM)-based networks where data are transmitted in cells of fixed length. In this paper, the feasibility and the limitations of optical data storage in a fiber loop optical buffer are studied theoretically and experimentally, A model of a fiber loop buffer, incorporating semiconductor laser amplifiers (SLA) as switching gates, is described. The two major interfering quantities are cross talk and amplified spontaneous emission of the SLA gates. To limit the impact of cross talk on the signal quality, an on/off ratio of the SLA gates of at least 30 dB is required. The paper describes the optimum operation conditions, which enable data storage for more than 100 circulations even for data rates in the range from 10 to 160 Gb/s     

Fiber chromatic dispersion equalization at the receiving terminalof IM-DD ultra-long distance optical communication systems

We have evaluated the effect of fiber chromatic dispersion equalization at the receiving terminal for transoceanic optical communication systems. We used a 1000-km fiber loop with 31 Er-doped fiber amplifiers for the experiments, and measured the bit-error-rate characteristics after 9000-km transmission. Accumulated chromatic dispersion originating from the discrepancy between the signal wavelength and the system zero dispersion wavelength was equalized by the equalization fiber at the receiving terminal. We used both normal and anomalous dispersion fibers at the receiving end. The results have shown that the equalization method of the fiber chromatic dispersion at the receiving terminal is useful with some limitations for ultra-long distance optical communication systems     

Performance evaluation of the different types offiber-chromatic-dispersion equalization for IM-DD ultralong-distanceoptical communication systems with Er-doped fiber amplifiers

We have evaluated the transmission performance of different fiber-chromatic-dispersion-equalization methodologies for ultralong distance IM-DD optical communication systems that use Er-doped fiber amplifier repeaters. The experiment used a 1000 km fiber loop consisting of 30 dispersion-shifted fiber spans and 31 Er-doped fiber amplifiers. We changed the insertion point of the normal single-mode fiber for equalization to change the shape of the accumulated chromatic dispersion. Comparison of the longest transmission distance and the width of the 9000 km transmissible window are discussed for several types of dispersion equalization. The results indicate that the best type of the dispersion equalization for ultralong distance IM-DD optical communication systems is to install dispersion-shifted fibers with short sections of normal single-mode fibers to compensate the accumulated dispersion     

All-Optical AGC of EDFA Based on SOA

We propose a novel all-optical method for automatic gain controlling of transients in erbium-doped fiber amplifiers (EDFAs) using a semiconductor optical amplifier (SOA)-based negative feedback loop for adjusting the EDFA pump power. A dynamic model for the EDFA-SOA system is developed and used for numerical simulation of the transient behavior of this system. Simulation results for EDFA-SOA performance of the proposed method are presented. It is shown that using this method, it is possible to significantly reduce the transient effects, without producing power oscillations on the surviving channels     

Gain peak wavelength measurements using a polarization scrambledfiber loop configuration

We present a quick and accurate method to measure the gain peak wavelength (GPW) of concatenated optical amplifiers in a long haul optical fiber communication system. This method utilizes a simple fiber-amplifier loop with polarization scrambling. We verify that the GPW of an amplifier is completely determined by the operating gain per unit erbium doped fiber length and changes linearly with compressed gain near 1.558 μm. The data presented, indicates how the GPW can be controlled for a broad range of operating gains by adjusting the erbium fiber length. The temperature and pump power dependence of GPW were found to be negligible for typical undersea system amplifier conditions. The gain bandwidth for concatenated amplifier systems appears to be a function of compression not operating gain, implying that wavelength division multiplexing systems requiring a flattened gain response should take this into consideration     

The experimental study of the effect of fiber chromatic dispersionupon IM-DD ultra-long distance optical communication systems withEr-doped fiber amplifiers using a 1000 km fiber loop

We have evaluated the transmission performance difference of ultra-long distance optical communication systems with Er-doped fiber amplifier repeaters due to fiber chromatic dispersion effect. A 1000 km fiber loop with 31 Er-doped fiber amplifiers was used for the experiments. We have changed the system zero dispersion wavelength by changing the length of the normal single-mode fiber at the end of the fiber loop, and measured the bit-error-rate after transmission. Comparison of the longest transmission distance and the width of the 9000 km transmissible window were discussed for various system zero dispersion wavelengths. The results have shown that the difference between the gain peak wavelength of the amplifier chain and the system zero dispersion wavelength caused degradation of the system performance, and the degree of the degradation was almost symmetrical from the gain peak wavelength     

Design of Logical Topology with Effective Waveband Usage in IP-over-WDM Networks

We deal with the problem of designing the logical topology in IP-over-WDM networks. Many conventional methods for designing the logical topology assume that a constant number of wavelengths will be available on each fiber. But it is not necessary to utilize all wavelengths on each fiber in building an effective logical topology on a WDM network. Instead, several wave-bands may be considered for introduction while deploying additional wave-bands and their corresponding optical amplifiers when additional wavelengths are actually required. In this case, the number of wavelengths available on the respective fibers depends on the number of optical fiber amplifiers deployed on each fiber. In this paper, we propose a heuristic algorithm for the design of a logical topology with as few optical fiber amplifiers as possible. Our results indicate that our algorithm reduces the number of optical fiber amplifiers with a slight increase of average packet delays.     

Optical time domain reflectometry in optical transmission linescontaining in-line Er-doped fiber amplifiers

Optical time domain reflectometry (OTDR) in an optical transmission line containing in-line Er-doped fiber amplifiers is investigated. The proposed Er-doped fiber amplifiers are based on optical circulators, which support both OTDR and digital signal transmission. The measurable limit of OTDR fault location in optical transmission lines containing in-line amplifiers is discussed. Fault location and 1.8-Gb/s digital signal transmission are demonstrated in a 316.9 km, optical transmission line constructed with three in-line Er-doped fiber amplifiers     

Optimum configuration for cascaded fiber amplifiers in attenuationlimited transmission systems

Fiber amplifiers play an important part in optical transmission systems to overcome the impact of attenuation. Together with the transmitter and receiver the positions of amplifiers on the optical path as well as the design of the amplifiers itself determine the bit error probability of the digital communication link. We present a simple method how to derive the optimum configuration for an optical transmission link with cascaded fiber amplifiers for an attenuation limited system. The bit error probability is calculated in dependence of the positions of the line amplifiers and the lengths of the doped fibers for systems with and without booster and optical preamplifier. In a first step we search the optimum configuration by numerical minimization of the bit error probability for a given transmission length, transmitter power and optical receiver. We have found a very simple rule how to determine the lengths of the transmission fibers and the doped fibers of the amplifiers for the minimum bit error probability when the length of the first transmission fiber is given. Therefore, the search for the optimum configuration reduces to the search of the appropriate length of the first transmission fiber which results in an enormous reduction of computing effort. We have investigated the effect on the bit error probability when one deviates from the optimum configuration. For the case, when the transmission length is reduced me have found that the bit error probability decreases always, when the lengths of the single transmission fibers are cut     

MEMS可调式光衰减器性能测试及其分析

采用微细加工的方法研制出了一种可调式微机械光衰减器 ,对该衰减器的性能进行了测试 ,并对影响其光学性能的因素作了分析。测试表明 ,该衰减器的插入损耗<3dB ,衰减范围 0～ 4 0dB ,回波损耗 <- 45dB ,衰减精度可达 0 1dB。     

Propagation of signal and noise in concatenated erbium-doped fiberoptical amplifiers

Signal propagation and noise accumulation in lightwave systems using saturated optical amplifiers as repeaters are analyzed. Numerical simulations of amplified spontaneous emission in concatenated erbium-doped fiber amplifiers indicate that a reach beyond 10000 km is possible with a 1.55-μm system in the absence of fiber nonlinearities. Distributed optical amplifiers are shown to have low noise, but require higher pump power than lumped amplifiers. Three operating modes of an amplifier lightwave system are identified and their relative signal power efficiency and noise performance are described     

A novel in-service surveillance scheme for optically amplified transmission systems

We propose here a novel surveillance scheme for an optically amplified transmission system which allows simultaneous in-service fault identification for fiber and optical amplifiers. While requiring additional fiber Bragg gratings of designated wavelengths to be integrated with optical amplifiers, the monitoring light source is derived from the unused spectra of ASE and no dedicated light source is needed as in conventional OTDR technique. We have further demonstrated the scheme's feasibility with a 100-km, three-EDFA optical transmission system.     

Signal linewidth broadening due to nonlinear Kerr effect inlong-haul coherent systems using cascaded optical amplifiers

Signal spectral linewidth broadening due to the interaction between nonlinear Kerr effect and spontaneous emission from optical amplifiers in long-haul coherent optical fiber communication systems using optical amplifiers is examined theoretically and experimentally. By theoretical consideration and recirculating-loop experiments, it is shown that this effect becomes an essential limitation on maximum transmission length in transoceanic coherent optical fiber submarine cable systems     

Oscillation based test method of parameterization of open loop op amp and its authentication

The analytical design of differential amplifiers, the building blocks of an op-amp, requires an elegant, handy and computationally simple experimental method of measuring the d.c.super-gain of these blocks. This paper presents such an oscillation based test (OBT) by putting the Op.Amp. under test in the close loop of state variable filter. The oscillation frequency of the linearized system directly yields the d.c. open loop gain, the dominant pole and the second order non-dominant pole of test Op.Amp. The d.c. open loop gain of DUT is further authenticated by a novel method of frequency domain analysis using a super attenuator. The authentication is positive with 95 percent confidence level (ɛ, 0 percent, 9.64 percent) thereby establishing the validity of OBT method.     

喇曼光纤放大器的几项关键技术

喇曼光纤放大器具有优越的宽带性能 ,是现代宽带通信的较理想放大器。它的实用化得益于一些关键性技术的发展。对喇曼光纤放大器的最新发展进行了研究 ,对其中的关键性技术进行了分析、对比 ,以期有利于今后的实用化研制工作     

拉曼光纤放大器的特性与前景

通过对拉曼光纤放大器（FRA）的研究和分析,揭示了FRA的有关特性。结合光纤通信的需求和FRA的特性分析了FRA的应用前景和潜在问题,并介绍了FRA的最新发展状况。     

Transmission of 2-ps optical pulses at 1550 nm over 40-km standardfiber using midspan optical phase conjugation in semiconductor opticalamplifiers

We demonstrate transmission of 2-ps optical pulses at 1550 nm over 40 km of standard fiber by employing midspan optical phase conjugation in semiconductor optical amplifiers (SOAs). The second-order group-velocity dispersion of the fiber is completely compensated and the third-order dispersion becomes a major transmission limitation. This experiment shows that the midspan optical phase conjugation system using SOAs is applicable to ultrahigh bit rates greater than 100 Gb/s     

Improved Automatic Filtered Power Control Pumping Method for Uniform Shortpass Band in Optical Fiber Communications

To form a low noise figure and uniform shortpass band in optical fiber communications an improved automatic filtered power control (AFPC) pumping method is proposed here. A modulated single laser signal was entered in a closed feedback loop, in which the erbium-doped fiber amplifier (EDFA) was used as a part of the AFPC loop. Owing to the constant filtered signal and the quadrature phase shift delay inside the feedback loop, an optical pass band was uniformly formed. This EDFA attains high performance with a low noise figure simultaneously. The method was successfully applied to the fabrication of practical 12.0 m length of erbium-doped fiber pumped at 980 nm wavelength and 20 dBm power. Experiments prove that the signal gain of the loop remain flat in the range of 18.2 to 22.4 dB with a worst case error of ±0.5 dB and the noise figure was reduced by 2.2 dB at optimal, which correspond to a shortpass range of 40 nm band pass from 1525 nm to 1565 nm in wavelength. Of course, it should be possible to extent the system performance to all pumping configurations for semiconductor optical amplifiers. This provides the simplest and most economical way to transmit a well-defined band of modulated laser signal and to reject all other unwanted radiation.