Cascaded optical communication systems with in-line semiconductoroptical amplifiers

The optimization of the performance of installed standard-monomode fibers based optical transmission systems with in-line semiconductor optical amplifiers (SOA's) is reported in this paper. Both solitons and nonreturn-to-zero (NRZ) signals are studied and their capacities are compared. This investigation is based on numerical simulations by solving the nonlinear Schrodinger equations with the split-step method while the SOA is simulated with two different models that we show to be in a good agreement, transmissions over distances of the order of several hundreds of kilometers are shown to be possible, and very long distances can be reached especially if in-line sliding filters are used     

Long-haul coherent optical fiber communication systems usingoptical amplifiers

Studies on long-haul coherent optical fiber communication systems with in-line optical amplifier repeaters are made theoretically and experimentally. By theoretical calculation it was found that coherent systems can achieve wider dynamic range for an amplifier input power as compared with the intensity-modulation direct-detection (IM-DD) systems. The feasibility of such systems using traveling-wave semiconductor laser amplifiers (TWSLAs) and erbium-doped fiber amplifiers (EDFAs) was investigated, and 546 km, 140 Mb/s CPFSK transmission using TWSLAs and 1028-km, 560-Mb/s CPFSK transmission using EDFAs were successfully demonstrated     

On the bit error rate of lightwave systems with optical amplifiers

The problem of evaluating the performances of communication systems with optical amplifiers and a wideband optical filter is addressed. Exact probability of error expressions for optical signals in presence of amplifier spontaneous noise and photodetector shot noise are given and compared with those predicted by Gaussian approximations for amplitude shift keying (ASK), frequency shift keying (FSK), or differential phase shift keying (DPSK) modulations, both for ideal photodetectors and for the case where shot noise is significant     

Lightwave subcarrier CATV transmission systems

The design and performance of multichannel amplitude-modulated (AM) vestigial-sideband (VSB) lightwave cable television (CATV) systems are described. Requirements on linearity and noise are derived, and factors limiting the performance of the laser transmitters and receivers are discussed. For the high-performance lasers the carrier-to-noise ratio and composite second- and third-order distortions are acceptable for video trunk systems. Impairments because of fiber reflections and dispersion and mode partition fluctuations in the laser are discussed. Feedforward, feedback, and predistortion are discussed; difficulties with each prevent immediate application. The use of LiNbO₃ external modulators and high-power solid-state lasers is considered. The third-order distortion and insertion loss of the modulator more than counteract the high available laser power (100 mW), making this alternative unattractive unless a third-order linearizer can be implemented     

Energy enhancement of dispersion-managed solitons in optical fibertransmission systems with lumped amplifiers

We simulated dispersion-managed soliton propagation in optical fiber transmission systems with lumped amplifiers and loss. The energy enhancement of dispersion-managed solitons can be more or less than in the lossless case, depending delicately on the amplifiers arrangement. In all cases, there is a maximum enhancement factor beyond which the dispersion-managed soliton no longer exists and which also depends delicately on the arrangement     

水下无线光通信系统中可变增益放大器的实现

为了减小水下无线光通信系统中接收信号的动态范围,采用可变增益放大器,论述了基于数字模拟转换器和数字电位器实现可控增益的两种方法,并对基于数字电位器实现的方法进行了仿真实验.结果表明,该方法能有效压缩信号的动态范围,并使其趋于稳定.     

OTDR in optical transmission systems using Er-doped fiber amplifiers containing optical circulators

Fault location in optical amplifier transmission systems is described. Optical time-domain reflectometry (OTDR) cannot be used for an optical transmission line containing traditional Er-doped fiber amplifiers (EDFAs) because they contain optical isolators. The authors propose an OTDR scheme that uses new EDFAs containing optical circulators and return transmission lines. The new EDFAs support both OTDR and digital signal transmission. A 280.9 km transmission line containing three of the proposed EDFAs was constructed and tested. Experimental results demonstrated the feasibility of OTDR fault location and 1.8-Gb/s digital signal transmission.<>     

Dispersion compensation with phase-sensitive optical amplifiers

Recently, we proposed a novel approach to combating the pulse-broadening effect of group-velocity dispersion (GVD) in a fiber-optic communication link (IEEE Photon. Technol. Lett., vol. 5, pp. 669-672, 1993). In our scheme, linear loss in the fiber is balanced by a chain of periodically spaced, phase-sensitive optical amplifiers. In this paper, we present a detailed analysis of pulse propagation in such a fiber line showing that, due to attenuation in the quadrature orthogonal to the amplified quadrature, it is possible for a pulse to propagate without significant broadening over lengths many times longer than the usual dispersion length of the fiber. An averaged equation for pulse evolution over distances longer than the amplifier spacing is derived. The effect of optical-phase fluctuations between the propagating pulse and the amplifiers is also considered. Since our proposed scheme does not rely on the formation of solitons in the fiber, it can be implemented in both the positive and negative GVD regions, and it does not require a minimum peak power for the pulses     

Sampling pulses with semiconductor optical amplifiers

We demonstrate three techniques to measure the instantaneous frequency and intensity of optical pulses using semiconductor optical amplifiers (SOAs). Four-wave mixing, gain-saturation, and interferometric switching through a nonlinear optical loop mirror are three mechanisms by which sampling is done. We have experimentally measured the intensity and chirp profiles of pulses with energies as low as 10 fJ. Since the nonlinearity in the SOA is relatively slow, these measurement techniques are most appropriate for picosecond pulses often found in telecommunication applications. The temporal resolution of these methods are limited by timing jitter, which was ≈0.5 ps for the mode-locked laser diodes we used in our experiments, and by the width of the switching window     

Semiconductor optical amplifiers

Reviews some of the recent advances in semiconductor laser amplifiers and highlights some of the device and system issues connected with the use of optical amplifiers. Particular attention is given to noise properties, system applications (i.e. in-line amplifiers, power amplifiers, and receiver preamplifiers), and nonlinear effects. Finally, semiconductor amplifiers are compared with fiber amplifiers     

Semiconductor optical amplifiers

An overview of semiconductor optical amplifier characteristics and their potential applications is presented. The latter consist of nonregenerative repeaters, optical receiver preamplifiers, power amplifiers and amplifier/modulators, general optical gain blocks, narrowband tunable amplifiers, and bistable amplifiers     

Erbium-doped fiber amplifiers with wavelength-selective optical feedback

An optically-controlled fiber ring laser behaving as a low-speed all-optical inverter was demonstrated. Applications in fault location for lightwave systems, nonlinear optical circuitry and simple logic functions are described. Two inverters using erbium-doped fiber amplifiers were cross-coupled to form an all-optical guided-wave set/reset hip-hop that had greater than 40-dB extinction ratio and a state transition time of 1.6 ms.     

Structural modification of semiconductor optical amplifiers for wavelength division multiplexing systems

In this paper, the semiconductor optical amplifier is analyzed for in-line and pre-amplifier for wavelength division multiplexing (WDM) transmission having minimum crosstalk and power penalty with sufficient gain. It is evaluated that the cross gain saturation of the SOA can be reduced by settling crosstalk at lower level and also minimizing the power penalty by slight increase in the confinement factor. At an optimal confinement factor of 0.41069, high amplification is obtained up to saturation power of 20.804 mW. For this confinement factor, low crosstalk of −9.63 dB and amplified spontaneous emission noise power of 119.4 μW are obtained for −15 dBm input signal. It has been demonstrated for the first time that twenty channels at 10 Gb/s WDM can transmit up to 5600 km by use of this optimization. In this, cascading of in-line SOA is done at the span of 70 km for return zero differential phase shift keying modulation format with the channel spacing of 100 GHz. The optical power spectrum and clear eye are observed at the transmission distance of 4340 and 5600 km in RZ-DPSK system. The bit error rate for all channels increases more than 10⁻¹⁰ with the increase in launched input power.     

Lightwave scalar network analyzer employing optical heterodyne detection

A new system for measuring the transmittance and reflectance characteristics of lightwave components is described. By employing frequency-tracked narrowband detection after optical heterodyning, a resolution bandwidth as narrow as 3 MHz with a dynamic range of 50 dB is achieved at a scanning speed of 1 GHz/s. The shot-noise-limited sensitivity of the system is also discussed.<>     

Long-distance optical soliton transmission with lumped amplifiers

A soliton transmission method using lumped amplifiers is presented which is named the preemphasis method. An N=1 soliton with relatively high amplitudes (1.2<A<1.4), which is used as an input soliton, plays an important role in the lumped-gain soliton transmission system. The initial soliton pulse width can be preserved after propagation over long distance despite the existence of fiber loss. It is shown that with the lumped gain, the soliton pulse can propagate over more than 9000 km when the repeater spacing is 31 km and fiber loss is 0.22 dB/km     

Fibre optical parametric amplifiers with circularly-polarised pumps

A fibre optical parametric amplifier with orthogonal circularly-polarised pumps requires only half the pump power of an amplifier with linearly-polarised pumps to achieve a given gain. The gain is also independent of the polarisation of the input signal.     

Erbium-doped-fiber optical limiting amplifiers

A novel configuration of an erbium-doped-fiber optical output-limiting amplifier (OLA) is presented which is realized by simply introducing a differential lump-loss between the signal and the pump power at a particular point along the fiber. The OLA exhibits an input-power dynamic range in excess of 40 dB and the capacity to control optically the level of the constant-output signal     

Lightwave subscriber loop systems toward broad-band ISDN

The state-of-the-art of lightwave subscriber loop systems is reviewed. An approach is described for deriving an architecture for subscriber loop systems that can accommodate technological trends in broadband ISDN such as asynchronous transfer mode (ATM) and synchronous digital networks. Key component technology is discussed, namely, optical fibers and cables, splicing and connectors, and switching     

Bit-dependent degradation caused by stimulated Brillouin scatteringin CPFSK coherent optical repeaterless systems with booster amplifiers

An interesting phenomenon due to stimulated Brillouin scattering (SBS) is experimentally found in a CPFSK heterodyne system with a booster amplifier. We find that the demodulated waveform amplitudes of just a few distinguished bits are strongly suppressed leading to a significant increase in BER. It is confirmed that the BER degradation can be reduced by adjusting the threshold voltage bias of the receiver decision circuit