Amplified Spontaneous Emission Noise Research Articles

Signal-Noise Interaction in Optical-Fiber Communication Systems Employing Nonlinear Frequency-Division Multiplexing

We address the properties of nonlinear-Fourier-transform (NFT)-based fiber-optic communications systems and, particularly, study how the presence of noise deteriorates the performance of these systems. Similarly to the case of linear Fourier modes evolving independently under the action of chromatic dispersion alone, NFT-based systems employ so-called ``nonlinear modes,'' forming a nonlinear spectrum, as data carriers, and these nonlinear modes evolve independently in an uncoupled manner under the joint action of nonlinearity and dispersion. However, the influence of amplified-spontaneous-emission (ASE) noise on these nonlinear modes is still relatively poorly studied. In this paper, dealing with a continuous nonlinear spectrum, we scrutinize the properties of the effective noise emerging in the nonlinear Fourier domain. We also show that in the transmission stages, where the signal peak power is relatively high (e.g., at the receiver, in back-to-back transmission, or at short distances), the performance of an NFT system is mostly degraded not by the inline ASE noise, but by the imperfections of the digital sampling and the forward and backward NFT algorithms, i.e., by the NFT processing noise.

Using machine learning in an open optical line system controller

The reduction of system margin in open optical line systems (OLSs) requires the capability to predict the quality of transmission (QoT) within them. This quantity is given by the generalized signal-to-noise ratio (GSNR), including both the effects of amplified spontaneous emission (ASE) noise and nonlinear interference accumulation. Among these, estimating the ASE noise is the most challenging task due to the spectrally resolved working point of the erbium-doped fiber amplifiers (EDFAs), which depend on the spectral load, given the overall gain profile. An accurate GSNR estimation enables control of the power optimization and the possibility to automatically deploy lightpaths with a minimum margin in a reliable manner. We suppose an agnostic operation of the OLS, meaning that the EDFAs are operated as black boxes and rely only on telemetry data from the optical channel monitor at the end of the OLS. We acquire an experimental data set from an OLS made of 11 EDFAs and show that, without any knowledge of the system characteristics, an average extra margin of 2.28 dB is necessary to maintain a conservative threshold of QoT. Following this, we applied deep neural network machine-learning techniques, demonstrating a reduction in the needed margin average down to 0.15 dB.

A Novel Nonlinear Noise Power Estimation Method Based on Error Vector Correlation Function Using Artificial Neural Networks For Coherent Optical Fiber Transmission Systems

In this paper, we propose a promising nonlinear noise power estimation method based on correlation functions using artificial neural networks (ANN), which is robust against both amplifier spontaneous emission noise and the symbol patterns. Error vector correlation (EVC), together with the amplitude noise correlation (ANC) and the phase noise correlation (PNC), is used as the input of ANN in the proposed method. 378 cases of 224 Gb/s polarization-multiplexed 16-quadrature amplitude modulated (PM-16-QAM) signal transmitted over a wide range of conditions by varying launch power, OSNR and transmission distance are used to train and test the ANN. With the launch power varying from 0 to 8 dBm and the transmission distance as long as 2400 km, the results of tested samples demonstrate that the maximum absolute deviation (MAD), mean absolute error (MAE) and root mean square error (RMSE) of the estimated nonlinear noise power are 0.65 dB, 0.20 dB and 0.27 dB, respectively. In order to verify the independence of symbol patterns, 150 new cases with 30 pseudo-random binary sequence (PRBS) seeds are used to test the trained ANN. The results show that the MAE, MAD and RMSE of estimated nonlinear noise power are 0.86 dB, 0.25 dB and 0.33 dB respectively, meaning that the trained ANN is valid even if the test samples are not covered by the trained process. The results in this work verified that the ANN with EVC, ANC and PNC as input can make the trained model feasible to accurately estimate the nonlinear noise power in high speed optical coherent communication systems.

Delay-Tap-Sampling-Based Chromatic Dispersion Estimation Method With Ultra-Low Sampling Rate for Optical Fiber Communication Systems

A cost-effective chromatic dispersion (CD) estimation method is proposed, which is based on the delay-tap sampling (DTS) technique in combination with periodic training sequences (PTS). By performing equivalent sampling of PTS, DTS-based CD estimation at ultra-low sampling rate can be realized, significantly reducing the cost and high-speed requirements of analog to digital converters (ADCs). In contrast to the existing Nyquist DTS-based CD estimation method, we construct the CD lookup table in the CD over-compensated region, which can be suitable for a dynamic range of OSNR conditions. The CD lookup table built from the simulation can be used in the experimental system with similar configurations directly, indicating that the suggested method is reasonable and highly feasible. Besides, with only 1.25 GSa/s sampling rate of ADCs (about 1/30 of the Nyquist sampling rate which is 40.28 GSa/s), both 20.14 GBaud quadrature-phase-shift-keying (QPSK) simulation and experimental systems demonstrate the feasibility of the method, with a 28 ps/nm maximum CD estimation error for the simulation and a 35 ps/nm maximum CD estimation error for the experiment when OSNR is fixed to 18 dB. Furthermore, we also investigate the robustness of our method under the condition of different amplifier spontaneous emission (ASE) noise and nonlinear noise. The proposed method shows great potential for making a remarkable cost reduction in CD monitoring.

Enhancement of Spectral Efficiency FSO Links Using Linear Polarizer-Based MLPolSK Detection

This paper proposes the enhancement of spectral efficiency (SE) by linear polarizer based multilevel linear polarization shift keying (MLPolSK) detection in free-space optical (FSO) communication. At the transmitter end, in order to improve SE of FSO links, the various linear state of polarizations (SOPs) with an equal magnitude-spacing of x- or y-polarization are modulated for MLPolSK signal. At the receiver end, the cascaded polarization-independent semiconductor optical amplifier (SOA) and linear polarizer are introduced to detect MLPolSK signal. Polarization-independent SOA is applied to effectively mitigate the turbulence induced scintillation effect by the gain saturation without the distortion of polarization. Linear polarizer with high extinction ratio (ER) is used to transform various SOPs into the signal with an equal intensity-spacing of x- or y-polarization. Besides, the amplified spontaneous emission (ASE) noises are reduced by the polarization of ASE noises by linear polarizer. Finally, MLPolSK is detected by a single photodiode (PD) and decided by multilevel-thresholdings. In experiments, the performance of the proposed technique is evaluated under turbulence channels, which are emulated using Mach–Zehnder modulator (MZM)-based fading simulator. Experimental results show that the SE is improved up to 3 bit/s/Hz under the effective scintillation mitigation using the proposed technique.

Mode- and wavelength-multiplexed transmission with crosstalk mitigation using a single amplified spontaneous emission source

We propose to use the low-coherence property of amplified spontaneous emission (ASE) noise to mitigate optical crosstalk, such as spatial, polarization, and modal crosstalk, which currently limits the density of photonic integration and fibers for dense space-division multiplexing. High optical crosstalk tolerance can be achieved by ASE-based low-coherence matched detection, which avoids dedicated optical lasers and uses spectrally filtered ASE noise as the signal carrier and as a matched local oscillator. We experimentally demonstrate spatial and modal crosstalk reduction in multimode fiber (MMF) and realize mode- and wavelength-multiplexed transmission over 1.5-km MMF supporting three spatial modes using a single ASE source. Performance degradation due to model dispersion over MMF is experimentally investigated.

Instantaneous Dynamics of a Fiber Optical Parametric Oscillator Within Its Initiating Process

A fiber optical parametric oscillator (FOPO) is an effective way of generating new wavelength lasers in non-conventional wavelength bands, but the complex nature behind it is challenging for both theoretical and experimental studies. Luckily, dispersive Fourier transformation, which has been emerging in recent years, provides us with a good method of demystifying this complexity. In this letter, we capture and report, for the first time, the instantaneous dynamics of the initiating process in a fiber optical parametric oscillator. We directly observe that the initiating process experiences three stages. The FOPO fully establishes the parametric oscillation during nearly 2000 round-trips, i.e., nearly 93 $\mu \text{s}$ . In the meantime, the spectrum of the amplifier spontaneous emission noise gradually narrows down and evolves into the characteristic spectrum of the parametric oscillation. In order to start parametric oscillation, the pump power needs to exceed a certain threshold, after reaching which the power of the residual pump decreases while the signal and idle light grow. As we expect, due to the four-wave mixing effect, the signal and idle light are completely synchronous. Moreover, the stability of the oscillation is very sensitive to a slight fluctuation of the pumping pulses.

Reduction of amplified spontaneous emission noise using a statistical signal adaptive filter

This paper proposes a statistical signal adaptive filter (SSAF) based on adaptive total variation to reduce amplified spontaneous emission (ASE) noise in optical amplifiers, e.g. erbium doped fiber amplifiers. Non-return-to-zero on–off keying signal to noise ratio (SNR) is degraded by ASE noise. However, this can be improved by squeezing ASE using the proposed SSAF after photodetection to effectively remove the noise by analyzing the signal movement statistically. We obtained 4-dB SNR gain by reducing ASE beat noise compared with not applying SSAF. Simultaneous optical bandpass filter and SSAF application reduced the 2-dB power penalty for a 20-km optical link more than when only SSAF was used.

Single-carrier QAM/QNSC and PSK/QNSC transmission systems with bit-resolution limited DACs

Quantum Noise Stream Cipher (QNSC) is a physical layer encryption scheme to increase the security of fiber optics transmission. With the same launch power, the higher encryption constellation adopted, the higher security achieved. However, higher constellation modulations are limited by the bit resolution of DAC at transmitters, especially for the commercial transmission system adopting QPSK or 16QAM only. In the paper, we investigate the effect of bit-resolution limited DAC in QNSC system. We conduct simulation analysis in two scenarios. First, in an optical back-to-back condition with high OSNR, a QNSC system is influenced by quantization noise of DAC. Second, in an optical back-to-back condition with low OSNR, a QNSC system is affected by quantized noise of DAC and amplified spontaneous emission (ASE) noise of amplifier. Simulation results show that, the same as ASE noise, quantized noise can also mask the signal to ensure the security of QNSC system. Eve can eavesdrop just after transmitter to avoid interference of ASE noise, but cannot avoid the impact of quantization noise of DAC. The quantization noise introduced by low resolution DAC can still increase the difficulty of eavesdropping. Moreover, as long as the total noise remains unchanged, the transmission performance for Bob will not be affected

ASE narrow-band noise pulsing in erbium-doped fiber amplifier and its effect on self-phase modulation.

In this paper, we report a study of the features of polarized and unpolarized narrow-band amplified spontaneous emission (ASE) in a low-doped erbium fiber at 976-nm pumping. We demonstrate that ASE noise can be treated as a train of Gaussian-like pulses with random magnitudes, widths, and inter-pulse intervals. ASE noise can also provide a statistical analysis of these three parameters. We also present the data that reveal ASE noise's role in optical spectrum broadening through self-phase modulation of light propagating in a communication fiber. In particular, the data show that the ASE noise derivative defines the broadening's spectral shape.

A novel Michelson interferometer of high interference degree with the application of bi‐direction erbium‐doped fiber amplifier

AbstractIn this paper, a novel Michelson fiber high‐interference optical structure has been proposed. When an optical amplifier is applied into the interference optical path, the signal‐to‐noise ratio (SNR) of the signal light in the optical path is reduced by the amplifier generates amplifier spontaneous emission (ASE) noise. Through this new type of optical path, the ASE in the interference optical path can be suppressed, the SNR of the signal light can be improved, and a higher degree of interference can be achieved.

Combined Effect of ASE Noise and SRS Induced Crosstalk on the BER Performance of a Single Span WDM System with Raman Amplifier Using Heterodyne Coherent Detection

AbstractAnalysis is presented to evaluate numerically the combined effect of amplified spontaneous emission (ASE) and stimulated Raman scattering (SRS) on the bit error rate performance of a WDM transmission system with Raman amplifier using heterodyne receiver. The results are compared with those for a WDM system reported with direct detection receiver for different system parameters. It is observed that coherent heterodyne system is less affected by the crosstalk due to combined effect of ASE and SRS compared to direct detection. It is noticed that allowable transmission distance is 170 km, and 166 km of WDM channels for 8, and 16, respectively, when coherent heterodyne receiver is and with pump power of 10 mW and channel bandwidth of 12.5 GHz. The corresponding transmission distance is 60 km and 10 km, respectively, for direct detection system already reported.

Ultrafast all-optical digital comparator using quantum-dot semiconductor optical amplifiers

In this investigation, three types of 160 Gb/s all-optical digital comparators using quantum-dot semiconductor optical amplifiers (QD-SOAs) are constructed. These configurations have different combination patterns of logic gates and QD-SOAs. Based on numerical simulations, we investigate and evaluate the performance of the devices in terms of the number of logic gates and QD-SOAs, and the value of the extinction ratio (ER). In addition, we demonstrate the effect of amplified spontaneous emission (ASE) noise on the ER and Q-factor. The results show that two of the three configurations are superior to the other configuration in terms of circuit complexity, value of ER, and sensitivity to injection current. Moreover, these two configurations achieve ER values over 10 dB and Q-factor over 9, even when intense ASE noise is considered. The proposed configurations have several advantages such as high quality, easy configuration, insensitivity to injection current, and strong noise robustness, which are favorable for practical applications. This investigation also facilitates the specification of the pros and cons of each configuration, and the determination of the appropriate comparator according to the desired requirements.

Performance Analysis of Multi-User Optical Steganography Transmission System Based on Filtered Amplified Spontaneous Emission Noise

We propose a multi-user optical steganography transmission system based on the filtered amplified spontaneous emission (ASE) noise for the first time. The stealth signal can be hidden in the public channel in the time and frequency domain. The proposed multi-user transmission system can improve the capacity of stealth channel through increasing the number of stealth users, in order to overcome the major limitation of the single stealth channel transmission based on the ASE noise. Meanwhile, system performance of optical steganography system is theoretically analyzed and simulation demonstrated. The signal-to-noise ratio (SNR) of the stealth channel and the public channel are derived and analyzed. The interaction between the public channel and the stealth channel is investigated based on bit rate, transmission distance, optical bandwidth of the stealth user, and power spectral density of the ASE noise, which can affect the capacity of the stealth channel. In addition, the additional layer security of the stealth channel is analyzed in the proposed multi-user optical steganography system, and simulation results show that this approach is efficient and the security of the stealth user can be guaranteed.

Deep Neural Network Based Chromatic Dispersion Estimation With Ultra-Low Sampling Rate for Optical Fiber Communication Systems

Fast and low-cost chromatic dispersion (CD) estimation is very important for fiber link that is dynamically reconfigurable in the next-generation optical networks. In this paper, a novel CD estimation method based on the deep neural network (DNN) with ultra-low sampling rate is proposed for the optical fiber transmission systems. The method can estimate CD for under-sampled signals by the trained DNN with a weighted average. To demonstrate the feasibility of the method, the simulation of a 28-GBaud five-channel optical fiber transmission system with 100–2000-km SSMF transmission is carried, where the sampling rate of the analog-to-digital converter (ADC) at the receiver is only 500 MHz. The results show that the maximum mean absolute error (MAE) of the estimated CD is less than 75 ps/nm with the reference cumulative CD from 1600 to 32000 ps/nm for QPSK and 16QAM signals. Meanwhile, the robustness of the proposed method is verified for amplifier spontaneous emission (ASE) and nonlinear (NL) noise. Furthermore, we experimentally demonstrated that the maximum MAE is less than 75 ps/nm when the transmission distance varies from 100 to 800 km in 20-GBaud QPSK optical fiber transmission system. In conclusion, the proposed DNN-based CD estimation method shows great potential for the cost-effective under-sampled systems.

Transparent intersatellite optical wireless communication link with double sideband-suppressed carrier modulation and coherent homodyne detection

In this paper, we present an intersatellite optical wireless communication (IsOWC) link with double sideband-suppressed carrier (DSB-SC) modulation and coherent homodyne detection (CD), which enables transparent transport of multiband radio frequency (RF) signals. The performance of transparent multiband IsOWC link employing DSB-SC/CD and phase modulation with CD (PM/CD) is investigated. The theoretical model considers the finite extinction ratio (ER) of a Mach-Zehnder modulator (MZM) and the saturation property of an optical booster amplifier. The expressions of RF gain, noise figure (NF) and third-order spurious-free dynamic range (SFDR) are derived considering the third-order intermodulation product and amplifier spontaneous emission noise for both architectures. Numerical results for RF gain, NF, and third-order SFDR are given for demonstration. Results indicate that DSB-SC/CD can provide higher linearity and better sensitivity than PM/CD. The performance of the DSB-SC/CD scheme is obviously influenced by the ER of MZM. The gain of the optical preamplifier and the power of a local oscillator optical signal should be optimized to obtain satisfactory performance.

QPSK Training Sequence-Based Both OSNR and Chromatic Dispersion Monitoring in DWDM Systems

We design a quadrature phase-shift keying training sequence (QPSK-TS) for monitoring both optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD) in a dense wavelength division multiplexing (DWDM) system. By applying fast Fourier transform on the QPSK-TS, a comb-like spectrum with discrete peaks can be obtained. OSNR can be calculated by measuring the power of the amplified spontaneous emission (ASE) noise in the gaps between these peaks. Moreover, we search the optimal order in the fractional domain to calculate the CD after applying fractional Fourier transform on the QPSK-TS signal. The proposed method shows large ASE noise and optical nonlinearity tolerance in simulation results ( $ 1.0 dB error within 24 dB after transmission over 1000 km with 3 dBm per channel launch power, and $ 90 ps/nm error within 33400 ps/nm). Furthermore, the experimental results demonstrate high accuracy of the proposed method ( $\leq$ 1.0 dB error within 28 dB and $ 40 ps/nm error within 1670 ps/nm after 100 km single channel transmission).

Effects of fiber nonlinearity on error vector magnitude and bit error ratio for advanced modulation formats

Fiber nonlinear (NLI) noise, as well as amplified spontaneous emission (ASE) noise, degrades the performance of coherent optical fiber communications. We find that the temporal distribution of NLI noise, which is unlike that of ASE noise and depends on the waveform of signal pulse, has an impact on the estimation of error vector magnitude (EVM) and bit error ratio (BER). The influences of NLI noise, as well as ASE noise, on EVM and BER are analyzed for quadrature phase-shift keying and M-ary quadrature amplitude modulation systems. Modified theoretical formulas are proposed to estimate EVM and BER for the system under the effect of NLI noise, ASE noise, or mixing of these two noises. For system with mixing of ASE and NLI noises, according to our model, the optimal channel power for the best EVM is not corresponding to the best optical-signal-to-noise ratio. Our model is validated by numerical simulations.

Optimum Power in a Multi-Span DWDM System Limited by Non-Linear Effects

Limitations imposed by Four-Wave Mixing (FWM), Amplified Spontaneous Emission (ASE), dispersion and Stimulated Raman Scattering (SRS) on a multi-spam DWDM system are theoretically studied. In this work, expression for the linear dispersion parameter D has been defined as a function of number of channels in order to separate FWM and SRS effects and calculates both maximum fibre length and optimum power. Additionally, our simulation results consider the effect of ASE noise from Erbium Doped Fibre Amplifiers (EDFAs). This theoretical analysis yields a set of design criteria from optimized multi-span DWDM systems.

Performance evaluation and optimization of multiband phase-modulated radio over IsOWC link with balanced coherent homodyne detection

In this paper, we present a multiband phase-modulated (PM) radio over intersatellite optical wireless communication (IsOWC) link with balanced coherent homodyne detection. The proposed system can provide the transparent transport of multiband radio frequency (RF) signals with higher linearity and better receiver sensitivity than intensity modulated with direct detection (IM/DD) system. The expressions of RF gain, noise figure (NF) and third-order spurious-free dynamic range (SFDR) are derived considering the third-order intermodulation product and amplifier spontaneous emission (ASE) noise. The optimal power of local oscillator (LO) optical signal is also derived theoretically. Numerical results for RF gain, NF and third-order SFDR are given for demonstration. Results indicate that the gain of the optical preamplifier and the power of LO optical signal should be optimized to obtain the satisfactory performance.