Suppression of beat noise from optical amplifiers using coherentreceivers

Coherent optical fiber communications have been studied intensively because of their high receiver sensitivity and high-frequency selectivity. With the advent of an erbium-doped fiber amplifier (EDFA), however, the first advantage seems to have become less attractive. Nevertheless, the combination of the EDFA and coherent techniques offers a number of attractive features. In this paper, we show both theoretically and experimentally that the excess beat noises (common-mode and image-band beat noises) from optical amplifiers can be suppressed by using coherent receivers such as a balanced receiver and a double-stage phase-diversity (DSPD) receiver. The noise figure (NF) of the excess-noise-suppressed coherent receivers with an optical preamplifier is shown to be 0 dB. Bit-error-rate (BER) formulas are also discussed     

Influence of EDFA''''s Characteristics on Performance of All Optical Network

The characteristic of EDFA in WDM system is analyzed. The simulation system based on the architecture of the China Information Network (CAINONET) is introduced, and the influence of noise figure, gain unflatness and output power of EDFA on the BER performance and scale of network is investigated. Moreover, the influence of noise figure is studied with different crosstalk . Meanwhile, it is indicated that it is important to apply the "node isolation principle" in the optical network. The research results can provide the valuable reference for the practical construction of all optical network .     

Theory of burst-mode receiver and its applications in opticalmultiaccess networks

In this paper, a unified theory for the newly developed optical burst-mode receiver is presented. Based on this theory, an analysis of the performance of the receiver is given both theoretically and experimentally. The theoretical model agrees well with the experimental results. This theory can quantitatively explain the bit error rate (BER) performance of burst-mode receivers. Several potential applications of burst-mode receivers are also illustrated, including applications in supervisory system for erbium-doped fiber amplifier (EDFA) trans-oceanic optical links and various high-speed all-optical multiaccess packet networks     

Performance analysis of an optical serial-to-parallel converterwith erbium-doped fiber amplifier

In this paper, we develop a performance analysis of an surface-emitting second harmonic generation (SESHG) optical serial-to-parallel converter using an erbium-doped fiber amplifier (EDFA) as a preamplifier. The analysis is complicated by the fourth-order nonlinearity that acts on the signal plus amplified spontaneous emission (ASE) noise to create many beat noises at the binary decision device. However, we demonstrate that Gaussian approximation for the beat noise statistics is reasonable. We calculate the BER of the system as a function of the SHG nonlinear cross section (A^NL), EDFA gain, the bandwidth of the optical filter that band-limits the ASE noise, and the timing pulse-to-data pulse power ratio. We find that for reasonable values of these and other parameters, the EDFA/SESHG serial-to-parallel converter combination should be able to operate at or below a BER of 10^-12. We find that small increments (0-2 dB) in the signal power that is input to the EDFA are enough to compensate the effects of ASE noise for most of the parameter variations we consider. From this point of view, the ASE noise has little effect on system performance. However, when the input power is fixed, we show evidence in terms of BER that the ASE noise plays a significant role, particularly in the high A^NL, high gain case. Also in this case, we show that the optimal timing pulse-to-data pulse power ratio is somewhat different from the value that is optimal for the system without an EDFA     

Theoretical and experimental study of 10 Gb/s transmissionperformance using 1.55 μm LiNbO3-based transmitters withadjustable extinction ratio and chirp

This paper has experimentally and theoretically investigated transmission performance depending on chirping and extinction ratio for a 10 Gb/s transmission system with the standard single-mode fiber. The transmission performance can be dramatically degraded or improved by adjusting chirp and extinction ratio in a 1.55 μm LiNbO₃ modulator-based transmitter and erbium-doped fiber amplifier (EDFA)-pin diode receiver configuration. To estimate the transmission performance, bit error rate (BER) characteristics rather than eye-opening penalty (EOP) have been calculated by solving the nonlinear Schrodinger equation with including the model of chirping and extinction ratio for the transmitter, and noise and intersymbol interference for the receiver. This simulation can predict the measured BER characteristics well enough to see interplaying between chirping and extinction ratio     

Influence of the nonlinear phase and ASE noise on DPSK balanced optical receiver in optical fiber communication system

The analytical expression of bit error probability in a balanced differential phase-shift keying(DPSK) optical receiver considering nonlinear phase noise and EDFA ASE noise is given,which is very useful to estimate the performance of DPSK balanced and unbalanced receiver in optical communication system.Through analysis,if only nonlinear phase noise is considered,both the balance and unbalanced receivers have the same performances.But if adding the ASE noise of EDFA,the balanced receiver is better.     

Bit error rate analysis of OTDM system based on moment generationfunction

The performance of optical time division multiplexing (OTDM) system is limited by a complex combination of noise. In this paper we present a theoretical framework for the optical receiver in OTDM system based on the moment generation function. The proposed receiver model is showed to be more accurate in predicting the bit error rate (BER) performance than the former ones. Its validity is also verified by the experimental results     

Application of the saddle point method for the evaluation of crosstalk implications in an arrayed-waveguide grating interconnection

The effect of in-band crosstalk can pose severe limitations in an optical network. In this paper, the implications of in-band crosstalk induced by an arrayed-waveguide grating (AWG) router in a passive N/spl times/N optical interconnection are analyzed with non-Gaussian statistics using a numerical model. The model is based on the saddle point approximation and takes into account fluctuations of the transfer function's sidelobes induced by the phase errors in the grating arms, phase noise, polarization variations, bit misalignment, and shot and thermal noise. The influence of these effects on the interconnection's bit error rate (BER) is analyzed. The validity of the Gaussian assumption for the crosstalk noise statistics is discussed. Finally, the model is used to examine the mean crosstalk requirements for various numbers of network nodes.     

Accurate modeling of optical multiplexer/demultiplexerconcatenation in transparent multiwavelength optical networks

This paper presents an accurate theoretical model for the study of concatenation of optical multiplexers/demultiplexers (MUXs/DMUXs) in transparent multiwavelength optical networks. The model is based on a semianalytical technique for the evaluation of the error probability of the network topology. The error-probability evaluation takes into account arbitrary pulse shapes, arbitrary optical MUX/DMUX, and electronic low-pass filter transfer functions, and non-Gaussian photocurrent statistics at the output of the direct-detection receiver. To illustrate the model, the cascadability of arrayed waveguide grating (AWG) routers in a transparent network element chain is studied. The performance of the actual network is compared to the performance of a reference network with ideal optical MUXs/DMUXs. The optical power penalty at an error probability of 10^-9 is calculated as a function of the number of cascaded AWG routers, the bandwidth of AWG routers, and the laser carrier frequency offset from the channel's nominal frequency     

UWB-TR接收机性能分析

在确定STR接收机模型的基础上,采用对接收机输出噪声进行高斯近似的方式对UWB-STR接收机性能进行了分析,得到UWB-STR接收机的误码性能表达式。表明该种接收机误码性能不仅与信噪比有关,而且与噪声输入带宽和积分时间有关,其特性可类推到其他类型的自相关接收机。最后与其他现有文献的结论进行了对比及修正,并提供了UWB-ATR的误码性能表达式。     

TWC and AWG based optical switching structure for OVPN in WDM-PON

Considering the influence of more random atmospheric turbulence,worse pointing errors and highly dynamic link on the transmission performance of mobile multiple-input multiple-output(MIMO)free space optics(FSO)communication systems,this paper establishes a channel model for the mobile platform.Based on the combination of Alamouti space-time code and time hopping ultra-wide band(TH-UWB)communications,a novel repetition space-time coding(RSTC)method for mobile 2×2 free-space optical communications with pulse position modulation(PPM)is developed.In particular,two decoding methods of equal gain combining(EGC)maximum likelihood detection(MLD)and correlation matrix detection(CMD)are derived.When a quasi-static fading and weak turbulence channel model are considered,simulation results show that whether the channel state information(CSI)is known or not,the coding system demonstrates more significant performance of the symbol error rate(SER)than the uncoding.In other words,transmitting diversity can be achieved while conveying the information only through the time delays of the modulated signals transmitted from different antennas.CMD has almost the same effect of signal combining with maximal ratio combining(MRC).However,when the channel correlation increases,SER performance of the coding 2×2 system degrades significantly.     

Flexible decision-aided maximum likelihood phase estimation in coherent optical phase-shift-keying systems

Decision-aided maximum likelihood (DA-ML) phase estimation has been applied in coherent optical communication systems due to its high computational efficiency. However, conventional DA-ML scheme only assumes constant phase noise within each observation block, thus causing block length effect (BLE) which degrades system performance. In this paper, we take into account the time-varying laser phase noise and propose a flexible DA-ML phase estimation method for carrier phase recovery in coherent optical phase-shift-keying systems so as to eliminate BLE. Weighted coefficients based on ML criterion are introduced to strengthen the estimation accuracy. The statistical property of phase estimation error is derived, and the bit error rate (BER) performance is also evaluated. Numerical simulation results show that our flexible DA-ML scheme is very robust against time-varying phase noise. Compared with conventional DA-ML receiver, it can significantly reduce the phase estimation variance, improve the BER performance and increase the laser linewidth tolerance. By adopting the flexible DA-ML method with a relatively larger block length, BLE can be effectively eliminated. Thus, the BER performance can be significantly improved without carefully finding out the optimum block length or the optimum forgotten factor.     

High-Bit-Rate Dense SS-WDM PON Using SOA-Based Noise Reduction With a Novel Balanced Detection

The major drawback of incoherent broadband sources (BBSs) is their inherent intensity noise. Semiconductor optical amplifiers (SOAs) can be exploited at the transmitter to mitigate this noise. Optical filtering at the receiver, however, leads to the return of most of suppressed noise. Wider filtering at the receiver is the best known strategy to maintain performance gains, at the price of reduced spectral efficiency due to the tradeoff between noise cleaning and adjacent channel crosstalk. We introduce a novel balanced receiver for wavelength division multiplexing (WDM) systems that maintains greater noise cleaning and leaves spectral efficiency unchanged. Unlike standard receivers, our balanced scheme does not filter the desired signal. In this paper, we first demonstrate that the newly proposed receiver is equivalent to standard WDM receivers when no SOA for noise cleaning is present at the transmitter. Although a 2.9-dB power penalty is incurred, network capacity is unchanged, i.e., bit error rate (BER) floors due to intensity noise are the same. When SOAs are employed to mitigate severe intensity noise, we show that our receiver outperforms the wide filtering strategy by two orders of magnitude. Dense WDM capacity is demonstrated up to 10 Gb/s using a thermal source, a saturated SOA, and the balanced detection scheme. A BER of 10^-6 is achieved at 10 Gb/s; further improvement is possible using low overhead forward error correction or a better SOA design. This demonstrates the ability of spectrum-sliced wavelength division multiplexing (SS-WDM) passive optical networks (PONs) to operate at 10 Gb/s at good spectral efficiency. Error performance better than 10^-9 is achieved up to 8 Gb/s with 30-GHz optical channel bandwidth and 100-GHz spacing.     

A study of green wavelength-division multiplexed optical communication systems using cascaded fiber bragg grating

This paper studies the performance analysis of wavelength-division multiplexed optical communication systems (WDM). First, flat-gain erbium doped fiber amplifiers (EDFAs) are seriously needed to obtain proper and equal amplification of all channels. Such amplifiers can be designed by intrinsically modifying the host material or extrinsically using proper filters. In this research, we benefit from both the intrinsic and extrinsic methods to achieve sharp flat EDFA output gain using cascaded fiber Bragg gratings (FBGs). Second, the performance of our technique has been evaluated through calculating the bit error rate (BER) and signal-to-noise ratio (SNR) of a WDM system embedded with the reported EDFA flattening system. The parametric simulations of the FWHM of FBGs, SNR, optical power and the transmission distance have shown a noticeable improved performance. Sending data via an optical WDM system will be proven from comprehensive simulations to achieve high quality signal transmission spectrums, increased transmission distances and low power consumption. By extension, the reported design using cascaded FBGs can also be generalized to equalize the gain of any arbitrary profile.     

Performance of open-loop all-optical chaotic communication systems under strong injection condition

A numerical investigation of the performance of an open-loop optical chaotic communication system for the isochronous synchronization solution has been carried out, under strong optical injection conditions achieved using antireflective coating at the input facet of the receiver laser in combination with an optical erbium-doped fiber amplifier (EDFA). Different message encoding techniques have been considered and tested at multigigabit rates and for different levels of optical injection to the receiver. The effects induced by the amplified spontaneous emission (ASE) noise of the EDFA to the performance of the chaotic communication system have also been studied. The performance of all the examined encryption methods for the 1 Gb/s bit-rate messages was quite satisfactory and was characterized by Q-factor values that exceeded 10, after synchronizing in the strong injection regime. For higher message bit rates, the Q-factor values for all methods decrease considerably due to the residual frequency components of the chaotic carrier that are now more significant in the message spectral region. The effect of the amplifier's ASE noise to the system's performance was deteriorated as long as the EDFA chaotic input was kept in relatively high power levels.     

Design and experimental characterization of EDFA-based WDM ring networks with free ASE light recirculation and link control for network survivability

We theoretically and experimentally investigate the performance of erbium-doped fiber amplifier (EDFA)-based WDM ring networks with free amplified spontaneous emission (ASE) light recirculation. We show that, with proper network and amplifier design, the lasing light generated by free ASE recirculation within the looped network provides an effective gain clamping technique, ensuring limited signal power excursions under WDM channels add-drop operations. Considering a ring network composed of eight fiber sections and eight EDFAs, maximum signal power overshoots below 2.5dB have been measured under 23/24 WDM channels drop. Optical signal-to-noise ratio (OSNR) analysis and bit-error rate (BER) measurement at 10 Gb/s confirm acceptable performances and negligible penalties due to polarization effects and relative intensity noise transfer from laser light to WDM signals. We also propose and demonstrate a new link control technique which overcomes the main limiting factors of such networks, respectively, related to OSNR degradation, stability and survivability to fiber and EDFA breakages.     

Highly Utilized Fiber Plant with Extended Reach and High Splitting Ratio Based on AWG and EDFA Characteristics

In this paper, we propose a hybrid time‐division multiplexing and dense wavelength‐division multiplexing scheme to implement a cost‐effective and scalable long‐reach optical access network (LR‐OAN). Our main objectives are to increase fiber plant utilization, handle upstream and downstream flow through the same input/output port, extend the reach, and increase the splitting ratio. To this end, we propose the use of an arrayed waveguide grating (AWG) and an erbium‐doped fiber amplifier (EDFA) in one configuration. AWG is employed to achieve the first and second objectives, while EDFA is used to achieve the third and fourth objectives. The performance of the proposed LR‐OAN is verified using the Optisystem and Matlab software packages under bit error rate constraints and two different approaches (multifiber and single‐fiber). Although the single‐fiber approach offers a more cost‐effective solution because service is provided to each zone via a common fiber, it imposes additional losses, which leads to a reduction in the length of the feeder fiber from 20 km to 10 km.     

An Innovative Receiver for Incoherent SAC-OCDMA Enabling SOA-Based Noise Cleaning: Experimental Validation

We propose a new low complexity receiver for spectral amplitude optical coded division multiple access (SAC OCDMA) that enables intensity noise reduction using semiconductor optical amplifiers (SOAs). Compared to the standard receiver requiring two optical filters at the receiver side, our receiver requires only one optical filter. While a 1.4-dB power penalty in incurred, network capacity is unchanged, i.e., BER floors due to intensity noise have the same level. The primary motivation for the low complexity receiver is not reduced component count, but rather modifying the receiver so that promising SOA noise mitigation techniques might be employed to increase system capacity. SOA noise cleaning suffers from a major limitation: filtering after the SOA can negate most of the signal enhancement, the so-called post SOA filtering issue. The only solution to date for the post-SOA filtering effect in SAC-OCDMA is prohibitively complex McCoy , J. Lightw. Technol., vol. 25, no. 1, pp. 394–401, Jan. 2007, i.e., requiring multiple SOAs per client. We demonstrate that our proposed receiver drastically limits the client side filtering, thus maintaining noise suppression and overcoming the post-SOA filtering effect. We compare BER at up to 10 Gb/s with and without noise cleaning. When a noise cleaning module is used, BER improvement of several orders-of-magnitude is observed when only a few users are active in the network. Examination of the noise properties, however, leads us to conclude that highly populated networks will have diminished improvement.      

Gain equalization of EDFA cascades

Investigates the impact of wavelength-dependent erbium-doped fiber amplifier (EDFA) gain spectrum on multichannel direct-detection lightwave transmission systems employing multiple amplifiers. An analysis is presented which quantifies the constraints imposed by received power imbalance, signal-to-noise ratio (SNR), and receiver sensitivity on an EDFA cascade. Expressions are derived which relate the system constraints to the EDFA gain imbalance, bit rate, number of channels, and receiver dynamic range. Results demonstrate that when four-wave mixing (FWM) is compensated in an 11-channel system, received power imbalance can impose a significant constraint on transmission distance when the EDFA gain imbalance is greater than 1 dB or when bit rate is less than 1.8 Gb/s. In addition, performance of the preemphasis gain equalization technique is studied for multichannel systems employing APD or p-i-n/FET direct-detection optical receivers. Simple expressions are derived which can be used to quantify the increase in transmission distance obtained when employing preemphasis equalization. Results indicate that equalization of the received power spectrum can provide a two- to four-fold increase in the transmission distance when using APD receivers, compared to a one- to two-fold improvement with p-i-n/FET receivers. Analytic results are compared with results obtained by proven simulation methods and found to be in good agreement     

掺铒光纤放大器的非线性色散效应

给出一种模型来考虑非线性色散对光通信系统的影响。数值结果表明 ,考虑非线性色散时 ,光脉冲的传播速度比不考虑非线性色散时的传播速度要快 ,而脉冲展宽是一样的