Amplified Spontaneous Emission Noise Research Articles

Noise equalization scheme based on probabilistic shaping and complex-valued ANN for dual-polarization continuous spectrum NFDM system with high-order modulation formats

In dual-polarization continuous spectrum nonlinear frequency division multiplexing (DP-CS NFDM) systems, the presence of noise destroys the independence between subcarriers in the nonlinear spectral domain (NSD). Additionally, as the modulation order and the number of subcarriers increase, the signal power increases and the effect of noise on the performance of the system becomes more severe. In this paper, we propose a noise equalization scheme based on probabilistic shaping (PS) and complex-valued neural network (c-ANN) for dual-polarization transmission CS NFDM system with high-power signals. The scheme utilizes PS to reduce the distribution probability of high-power constellation points of the signal with high-order modulation format, to decrease the peak-to-average power ratio of the continuous spectrum subcarriers and the average power of the signal, which can achieve the suppression and equalization of the amplifier spontaneous emission (ASE) noise and the processing noise. In addition, the scheme uses the c-ANN to effectively reduce the correlation between subcarriers caused by the noise and improve the system performance. The effectiveness of the proposed scheme is verified in the DP-CS NFDM system, and the simulation results show that the Q-factor gain is enhanced by roughly 1.1 dB and 0.8 dB for the number of subcarriers of 128 and 256, respectively, compared to the classic nonlinear Fourier transform (NFT) scheme. Among them, with different noise figure (NF) and satisfying the 7% forward error correction (FEC) threshold, the 512QAM signal with an entropy of 8 after equalization increase the transmission distance by 80 km longer than that of uniform 256QAM signals for the number of subcarriers of 128. Compared with the joint scheme based on PS and real-valued neural network (r-ANN), this scheme has better equalization performance at the same complexity, and the complexity can be reduced by 50% under the same performance.

Co-LSTM-based fiber link modeling with ASE noise tracking for long-haul coherent optical transmission.

In this Letter, a novel, to the best of our knowledge, channel modeling scheme based on cascading chromatic dispersion-nonlinearity feature decoupling modules is proposed with the center-oriented long short-term memory (Co-LSTM) network structure adopted for modeling nonlinearity of each optical fiber span. By tracking the amplified spontaneous emission (ASE) noise at the output of each fiber span, the Co-LSTM-based channel modeling scheme achieves high waveform accuracy for long-haul coherent optical transmission compared with the conventional split-step Fourier transform method (SSFM) while saving calculation time by almost one order of magnitude.

Joint equalization of frequency offset and phase noise using two-stage cascaded extended Kalman filter for discrete spectrum 16/64APSK NFDM systems.

For the discrete spectrum nonlinear frequency division multiplexing (DS-NFDM) 16/64 amplitude phase shift keying (APSK) system, the inevitable laser impairments including frequency offset (FO) and carrier phase noise (CPN) would cause different rotations of the received signal constellations. In addition, the combined effect of FO and amplifier spontaneous emission (ASE) noise induces the eigenvalue shift, accordingly the residual channel impairment (RCI) is inevitably yielded. To address the above problems, we deduce the joint impairment model of FO, CPN and RCI, and then propose a joint equalization scheme using two-stage cascaded extended Kalman filter (TSC-EKF) for these impairments. It performs frequency offset compensation in the first stage, subsequently carries out joint equalization of CPN and RCI in the second stage. Meanwhile, the minimum Euclidean distance and phase difference between the received symbols and the ideal 16/64APSK constellations are ingeniously fused to calculate the innovations of TSC-EKF. The effectiveness has been verified by 2 GBaud DS-NFDM 16/64 APSK simulations and DS-NFDM 16APSK transmission experiments. The results demonstrate that when performing the joint equalization of FO, CPN and RCI, the maximum FOE range of TSC-EKF scheme achieves 1.2 and 9.6 times as that of nonlinear frequency domain (NFD) scheme and fast Fourier transform -Like (FFT-Like) scheme, respectively. Furthermore, its maximum LW tolerance reaches 3.3 times as that of the M-th power scheme. Importantly, the complexity of TSC-EKF is 63.4% as that of NFD scheme and on an order of O(N).

Combined intra symbol frequency domain averaging channel estimation for polarization division multiplexed coherent optical OFDM/OQAM systems

Intrinsic imaginary interference (IMI) induced by chromatic dispersion (CD) and polarization mode dispersion (PMD) seriously degrades the performance of optical orthogonal frequency division multiplexing offset-quadrature amplitude modulation (O-OFDM/OQAM) systems. Therefore, effective channel estimations are required for such systems to maintain good transmission performance. In the previous publications, both the full loaded (FL) and the half loaded (HL) frequency-domain channel estimation methods for polarization-division-multiplexed (PDM) coherent optical OFDM/OQAM (CO-OFDM/OQAM) systems have been proposed. However, for these frequency-domain methods, the channel frequency-domain responses caused by the correlation of the amplified spontaneous emission (ASE) noise are not considered. In this paper, we systematically discuss the frequency-domain channel transmission model for PDM CO-OFDM/OQAM systems. With the analysis of the correlation of the ASE noise, we propose a combined intra symbol frequency-domain averaging (CISFDA) channel estimation method for PDM OFDM/OQAM systems. Compared with the full-loaded frequency-domain channel estimation (FL-FD) method, the CISFDA method promotes the system robustness against the ASE noise and fiber nonlinear effect significantly. The proposed method is validated by numerical Monte Carlo simulations of the PDM CO-OFDM/OQAM system. Our new algorithm outperforms the FL-FD method in the 36 Gb/s PDM OFDM CO-OFDM/OQAM system, and the transmission distance is improved by 500 km with the bit-error-rate (BER) target at 3.8×10-3.

ASE noise mitigation with digital frequency offset loading for discrete spectrum nonlinear frequency division multiplexing systems.

We propose an amplified spontaneous emission (ASE) noise mitigation scheme utilizing digital frequency offset loading (DFO-loading) for discrete spectrum nonlinear frequency division multiplexing (DS-NFDM) systems. Firstly, based on the one-to-one mapping relationship between frequency offsets and eigenvalue positions, the transmitter side encodes 4-bit information onto 16 kinds of different digital frequency offsets. Then, a sliding window-assisted eigenvalue position (SWA-EP) decoding technology is further proposed to substitute the classical channel equalization and carrier phase recovery processes, with the purpose of recovering the original information. The numerical and experimental results demonstrate that, compared with b-coefficient 16 quadrature amplitude modulation (QAM) scheme, Q-factor gains are 2.1 dB under 15 dB optical signal-to-noise ratio (OSNR) and 1.8 dB after 800 km fiber transmission, respectively. Moreover, its complexity is only 0.6% of the b-coefficient scheme. The DFO-loading scheme offers an effective and low-complexity way to mitigate ASE noise of DS-NFDM system.

A Transponder Aggregator With Efficient Use of Filtering Function for Transponder Noise Suppression

Colorless, directionless, and contentionless reconfigurable optical add/drop multiplexing (CDC-ROADM) provides highly flexible physical layer network configuration. Such CDC-ROADM must operate in multiple wavelength bands which are being increasingly implemented in optical transmission systems. The operation in C+L bands requires switch devices used in CDC-ROADM to also be capable of multiband operation. Recent studies on wavelength division multiplexing (WDM) systems have pointed out the impact of amplified spontaneous emission (ASE) noise generated by signals of different wavelengths, which causes OSNR degradation. Therefore, it is desirable to filter out the ASE noise from different transponders when multiplexing multiple wavelengths at the transmitter side, especially in a system with non-wavelength selective combiners such as directional couplers and multicast switches. The use of transponder aggregators with filtering functions, such as the M × N wavelength selective switch (WSS), is preferable for this filtering. However, the downside of these devices is that it is difficult to provide economical multiband support. Therefore, we propose an economical transponder aggregator configuration by allowing a certain amount of ASE superposition and reducing the number of filtering functions. In this paper, we fabricated a prototype of the proposed transponder aggregator by combining silica-based planar lightwave circuit technology and C+L band WSS, both commercially available, and verified its feasibility through transmission experiments. The novel transponder aggregator is a practical solution for a multiband CDC-ROADM system with improved OSNR performance.

Three-dimensional wave optics and fluid dynamics modeling of a Rb flowing-gas diode-pumped alkali amplifier

Modeling of the efficiency and output beam quality of a Rb flowing-gas diode-pumped alkali amplifier (DPAA) based on a 3D computational fluid dynamic model coupled to a wave optics model for amplified beam propagation is reported. Both end and two-way side pumping schemes were considered and compared for two cases of buffer gas composition where either a He/CH4 mixture or pure He was used as a buffer gas. Dependencies of the DPAA efficiency and of the output beam quality on different flow and laser parameters were found. For the end pumping scheme and He/CH4 buffer gas, the amplifier efficiency is almost independent of the gas velocity, whereas beam quality deteriorates at low flow velocities. For side pumping, both efficiency and beam quality are independent of the flow velocity. The effect of amplified spontaneous emission (ASE) on the efficiency of the DPAA is moderate and leads to a decrease in the efficiency of the amplifier by a maximum of ∼10% compared to the case when ASE is not taken into account. The ASE noise to signal ratio in the end-pumped amplifier was found to be negligible, while in the side-pumped amplifier, the ASE noise power at the output was comparable to the power of the coherent amplified output beam. The presented results show that end pumping is preferable to side pumping in terms of efficiency, output beam quality, and ASE noise to signal ratio. The maximum efficiency of the amplifier with end pumping using pure He as a buffer gas is significantly lower than that for the amplifier using He/CH4 buffer gas. However, despite the low efficiency, an amplifier using pure He has higher output beam quality. The maximum efficiency of a two-way side-pumped amplifier with pure He as a buffer gas does not exceed 0.01. Thus, such an amplifier cannot be used for efficient energy extraction.

Experimental demonstration of 201.6-Gbit/s coherent probabilistic shaping QAM transmission with quantum noise stream cipher over a 1200-km standard single mode fiber.

A probabilistic shaping (PS) quadrature amplitude modulation (QAM) based on Y-00 quantum noise stream cipher (QNSC) has been proposed. We experimentally demonstrated this scheme with data rate of 201.6Gbit/s over a 1200-km standard single mode fiber (SSMF) under a 20% SD-FEC threshold. Accounting for the 20% FEC and 6.25% pilot overhead, the achieved net data rate is ∼160Gbit/s. In the proposed scheme, a mathematical cipher (Y-00 protocol) is utilized to convert the original low-order modulation PS-16 (22 × 22) QAM into ultra-dense high-order modulation PS-65536 (28 × 28) QAM. Then, the physical randomness of quantum (shot) noise at photodetection and amplified spontaneous emission (ASE) noise from optical amplifiers are employed to mask the encrypted ultra-dense high-order signal for further improving the security. We further analyze the security performance by two metrics known in the reported QNSC systems, namely the number of masked signals (NMS) of noise and the detection failure probability (DFP). Experimental results show it is difficult or even impossible to extract transmission signals from quantum or ASE noise for an eavesdropper (Eve). We believe that the proposed PS-QAM/QNSC secure transmission scheme has the potential to be compatible with existing high-speed long-distance optical fiber communication systems.

Frequency offset modeling in presence of ASE noise and corresponding low-complexity solution for discrete spectrum modulated nonlinear frequency division multiplexing system

For discrete spectrum modulated nonlinear frequency division multiplexing (DS-NFDM) transmission, the combined effect of laser frequency offset (FO) and amplifier spontaneous emission (ASE) noise would cause a perturbative shift of eigenvalues and corresponding spectral distortion. Moreover, the classical 4th-power feedforward frequency offset estimation (FOE) scheme is not suitable for DS-NFDM system with low baud rate. In this paper, we firstly deduce an FO impairment model with ASE noise in nonlinear Fourier domain (NFD). Meanwhile, we have proposed a training sequence-assisted FOE (TS-FOE) scheme, which effectively reduces the impact of ASE noise. The 2 GBaud DS-NFDM 16QAM simulation results illustrate that this scheme achieves an FOE error within 1 MHz using a training sequence (TS) with length of 64. Besides, its FOE range achieves [−Rs/2, +Rs/2], where Rs denotes the baud rate of signal. Furthermore, the effectiveness of TS-FOE scheme has been verified by 2 GBaud NFDM QPSK experimental system. The results demonstrate that when optical signal-to-noise ratio (OSNR) is set 13 dB, the TS-FOE scheme presents stable FO compensation performance for different FOs within 1 GHz, and the corresponding bit error rates (BERs) are all below the 7% hard decision forward error correction (HD-FEC) threshold. Meanwhile, its complexity is on the order of OL and related with the length L of TS, which is as one thousandth as that of angle search FOE scheme.

Efficient Three-Step Amplifier Configuration Algorithm for Dynamic C+L-Band Links in Presence of Stimulated Raman Scattering

We propose an efficient three-step amplifier configuration algorithm to improve and maintain the generalized signal-to-noise ratio (GSNR) performance of dynamic C+L-band links in presence of amplifier spontaneous emission (ASE) noise, Kerr nonlinearity and stimulated Raman scattering (SRS) using erbium-doped fiber amplifiers (EDFA). In step 1, we derive sub-optimal signal power profiles at the beginning of each span using the local optimization global optimization (LOGO) strategy [1] that takes into account ASE noise and Kerr nonlinearity. The effect of SRS, which is the dominant impairment in wideband transmissions, is compensated through amplifier gain pre-tilt of each span in step 2. In step 3, we use the closed-form inter-channel stimulated Raman scattering Gaussian noise (ISRSGN) model [2] to compute the GSNR of a multi-span link as a function of the inline amplifier gains and tilts and propose an iterative gradient ascent optimization algorithm to maximize the mean GSNR and minimize its standard deviation across the C- or L-band. Simulation studies for homogeneous-/heterogeneous-span links, static full-channel loading and dynamic loading due to gradual channel additions or sudden fiber cuts show that compared with other GSNR profile optimization methods, the proposed algorithm can achieve similar GSNR performance but only require execution time in the order of seconds. The effectiveness of the proposed algorithm in restoring/improving GSNR performance for an 8-span C+L-band link is experimentally verified for a scenario imitating a sudden fiber cut induced-channel disruptions. We further show that different optimization functions such as maximizing the minimum GSNR across the C+L band can be used in practical settings, and thus the proposed algorithmic framework is adaptable to different network control and management objectives.

Performance analysis of an SDM-WDM multicore optical fiber link

Analytical evaluation of inter-channel and inter-core coupling induced crosstalk including Amplified Spontaneous Emission (ASE) noise in a single mode 7-core homogeneous multi-core optical fiber (MCF) based Space Division Multiplexed Wavelength Division Multiplexing (SDM-WDM) communication system with distributed Raman amplifier is presented. The Stimulated Raman Scattering (SRS) induced crosstalk impairment including ASE noise and inter-core and inter-channel coupling induced crosstalk at the output of any core with excitation into other core of the MCF is investigated. Signal to Crosstalk plus Noise Ratio (SCNR) is determined at the output of photo detector of the excited core. Finally, Bit Error Rate (BER) performance results are evaluated for different system parameters, viz. WDM channel number, channel spacing, propagation distance, pump power etc. It is noticed that BER deteriorates with SRS induced crosstalk and ASE noise, which is worsened further by the effect of inter-core crosstalk (IC-XT). The maximum acceptable propagation distance for a desired value of BER and other system parameters considering inter-channel crosstalk (Ich-XT), IC-XT including SRS induced crosstalk and ASE noise is also evaluated analytically. For example, to maintain a particular BER (10E-9, say) we need to increase the input signal power from 2.5dBm to 5.5dBm while increasing the WDM channels from 12 to 16 considering only the SRS and ASE noise. On the other hand, we need to increase the input signal power from 5.5dBm to 9.0dBm to increase the WDM channels from 12 to 16 when the IC-XT is added up with the SRS and ASE noise. The maximum allowable pump power considering the collective impact of Ich-XT and IC-XT including SRS and ASE noise is determined for a given value of BER (10E-9). Power penalty versus WDM channel spacing at a given BER value (10E-10), link distance and pump power at different WDM channels is also evaluated and presented.

Maximizing Revenue With Adaptive Modulation and Multiple FECs in Flexible Optical Networks

Flexible optical networks (FONs) are being adopted to accommodate the increasingly heterogeneous traffic in today’s Internet. However, in presence of high traffic load, not all offered traffic can be satisfied at all time. As carried traffic load brings revenues to operators, traffic blocking due to limited spectrum resource leads to revenue losses. In this study, given a set of traffic requests to be provisioned, we consider the problem of maximizing operator’s revenue, subject to limited spectrum resource and physical layer impairments (PLIs), namely amplified spontaneous emission noise (ASE), self-channel interference (SCI), cross-channel interference (XCI), and node crosstalk. In FONs, adaptive modulation, multiple FEC, and the tuning of power spectrum density (PSD) can be effectively employed to mitigate the impact of PLIs. Hence, in our study, we propose a universal bandwidth-related impairment evaluation model based on channel bandwidth, which allows a performance analysis for different PSD, FEC and modulations. Leveraging this PLI model and a piecewise linear fitting function, we succeed to formulate the revenue maximization problem as a mixed integer linear program. Then, to solve the problem on larger network instances, a fast two-phase heuristic algorithm is also proposed, which is shown to be near-optimal for revenue maximization. Through simulations, we demonstrate that using adaptive modulation enables to significantly increase revenues in the scenario of high signal-to-noise ratio (SNR), where the revenue can even be doubled for high traffic load, while using multiple FECs is more profitable for scenarios with low SNR.

Gaussian blur aided blind phase search algorithm in low SNR QAM transmission system

Probabilistic constellation shaping (PCS) reduces the required SNR compared with the uniform distribution system to achieve the same mutual information (MI). However, severe amplified spontaneous emission (ASE) noise degenerates the performance of the conventional blind phase search (BPS) algorithm, showing an unpleasant MI penalty and reducing the shaping gain. In this paper, we reveal that the MI impairment comes from the misjudgment of phase noise estimation by the conventional BPS algorithm interfered by severe ASE noise. To cope with this problem, we propose a Gaussian blur-aided BPS (GBA-BPS) algorithm by introducing an unequal weight filter with an efficient solution of variance configuration into the conventional BPS. Details about why the GBA-BPS algorithm outperforms the conventional BPS algorithm are elaborated based on the spectrum analysis of the phase noise estimated by both schemes. Evaluated on a 50-GBaud PCS-64QAM system, the proposed GBA-BPS algorithm with a 31-tap filter effectively mitigates the misjudgment of phase noise estimation, achieving a maximum MI gain of 0.5 and 0.25 bits/symbol compared with conventional BPS when the SNR is 16 dB and 18 dB respectively. The proposed GBA-BPS is a significant improvement over conventional BPS and it is more suitable for carrier phase recovery in low SNR systems.

Fiber grating loop ring-down strain sensors using overlap spectrum demodulation and machine learning algorithm

The fiber grating loop ring-down (FGLRD) can be used in strain sensors to reduce costs and enhance system sensitivity. Introducing the overlap spectrum demodulation technology in the FGLRD can improve the system's linearity and expand the measurement range. However, there is always strong amplified spontaneous emission (ASE) noise owing to erbium-doped fiber amplifiers (EDFAs) in the FGLRD structure. The noise increases the difficulty of detecting the output ring-down spectrum and reduces the detection accuracy. This study proposes a machine learning algorithm for data processing of chirped FGLRD strain sensors based on overlap spectrum demodulation. It uses a global average pooling one-dimensional convolutional neural network algorithm to construct a data recognition model. The experimental results show that the method can improve the recognition accuracy and reduce the recognition errors caused by ASE noise compared to the conventional ring-down spectral peak detection method. The model accuracy was 100 % for the training and test sets and 98 % for the validation set. The loss value was close to 0.06, and the recognition time was approximately 0.5 ms.

Liquid crystal based active wavelength filter for phase-sensitive optical time domain reflectometry.

This study proposes a liquid-crystal-based active wavelength filter for phase-sensitive optical time domain reflectometry to mitigate the amplified spontaneous emission (ASE) noise and accurately match the passband with the light source. The validity of the proposed system was verified using comparative experiments with conventional passive optical filters. The experiment showed an increase in signal-to-noise ratio (SNR) of up to 2.21 dB compared with passive filters. Additionally, the proposed system can effectively eliminate ASE noise, resulting in an SNR of 12.99 dB.

Stimulated Brillouin Scattering Threshold in Presence of Modulation Instability for Optical Pulse in Long Optical Fiber

A theoretical and experimental study on the stimulated Brillouin scattering (SBS) threshold for optical pulse in the presence of modulation instability (MI) in long optical fiber is presented. The effects of MI on the SBS gain and threshold are analyzed based on the coupled-wave equation. An analytic expression is obtained to calculate the SBS threshold in the presence of MI. Numerical simulation is conducted to study the effects of the repetition rate and amplified spontaneous emission (ASE) noise on the SBS threshold for optical pulses. An experiment is conducted, and the results agree well with the theoretical analysis. The results clearly reveal how MI affects the Brillouin gain and SBS threshold of optical pulses in long optical fiber. The SBS threshold is affected by the ASE noise level and the repetition rate of the optical pulse. The study is helpful for the power evaluation of interferometric fiber sensing systems and optical power transmission systems.

Nonlinear Spectrum Modulation in the Anomalous Dispersion Regime Using Second- and Third-Order Solitons

We study the robustness of a nonlinear frequency-division multiplexing (NFDM) system, based on the Zakharov-Shabat spectral problem (ZSSP), that is comprised of two independent quadrature phase-shift keyed (QPSK) channels modulated in the discrete spectrum associated with two distinct eigenvalues. Among the many fiber impairments that may limit this system, we focus on determining the limits due to third-order dispersion, the Raman effect, amplified spontaneous emission (ASE) noise from erbium-doped fiber amplifiers (EDFAs), and fiber losses with lumped gain from EDFAs. We examine the impact of these impairments on a 1600-km system by analyzing the Q-factor calculated from the error vector magnitude (EVM) of the received symbols. We found that the maximum launch power due to these impairments is: 13 dBm due to third-order dispersion, 11 dBm due to the Raman effect, 3 dBm due to fiber losses with lumped gain, and 2 dBm due to these three impairments combined with ASE noise. The maximum launch power due to all these impairments combined is comparable to that of a conventional wavelength-division multiplexing (WDM) system, even though WDM systems can operate over a much larger bandwidth and, consequently, have a much higher data throughput when compared with NFDM systems. We find that fiber losses in practical fiber transmission systems with lumped gain from EDFAs is the most stringent limiting factor in the performance of this NFDM system.

Simple amplifier configuration algorithm for dynamic C + L-band systems in the presence of stimulated Raman scattering

We propose a simple two-step amplifier configuration algorithm based on signal power across different channels to improve the generalized signal-to-noise ratio (GSNR) performance of dynamic C + L-band links in the presence of amplifier spontaneous emission (ASE) noise, Kerr nonlinearity, and stimulated Raman scattering (SRS) using erbium-doped fiber amplifiers (EDFA). In step 1, ASE noise and Kerr nonlinearity are taken into account to derive sub-optimal signal power profiles at the beginning of each span using the local optimization global optimization (LOGO) strategy. The effect of SRS is compensated through amplifier gain pre-tilt in step 2. Simulations for links with homogeneous/heterogeneous spans, static full-channel loading, and dynamic loading due to gradual channel additions for C + L-band upgrades show that the proposed algorithm can achieve similar GSNR performance, but requires much less execution time, compared to other iterative methods that target for improving the GSNR across the C + L band, thus making it a fast and efficient GSNR management strategy for future dynamic C + L-band networks.

Optical sensor using space-domain active fiber cavity ringdown technique

A novel active fiber cavity ringdown (FCRD) technique using frequency-shifted interferometry (FSI) is proposed for the first time. Using this scheme, external parameters can be monitored in the space domain by measuring the ringdown distance instead of ringdown time. A bidirectional erbium-doped fiber amplifier (Bi-EDFA) is employed to compensate the inherent cavity loss for achieving higher sensitivity. And two band-pass filters are used to reduce the amplified spontaneous emission (ASE) noise of the Bi-EDFA. Compared with the well-known time-domain active FCRD scheme, our proposed method enables us to avoid using pulsed laser needed in time-domain active FCRD, it uses continuous-wave laser to inject into the fiber cavity and stabilize the optical power in the fiber cavity, which can suppress the baseline drift of ringdown signal caused by the gain fluctuations of the EDFA and thus improve the detecting precision. Moreover, this novel method enables us to use differential detection method for further reducing the ASE noise, and thus eliminating the baseline drift of ringdown signal. A magnetic field sensor was developed as a proof-of-concept demonstration. The experimental results demonstrate that the proposed sensor with a sensitivity of 0.01537 (1/km·Gs) was achieved. This is the highest magnetic field sensitivity compared to the time-domain active FLRD method. Due to the reduced ASE noise, the stability of the proposed sensing system was also greatly improved.

Research on the Performance of Multimode Optical Chaotic Secure Communication System With Multidimensional Keys and a Complex Entropy Source

In this paper, we design an optical chaotic secure communication system with multi-dimensional keys and a complex entropy source, which can allow secure communication working in different modes such as unicast, multicast, and broadcast. In the proposed scheme, amplified spontaneous emission (ASE) noise of the erbium-doped fiber amplifier (EDFA) with sufficient randomness is used as an entropy source to improve the security of the system. And by using the electro-optic delay feedback loops, the key spaces are introduced and the phase distortion is generated, then the data are masked in both phase and intensity fields. As a frequency-dependent group delay (FDGD) module, Gires-Tournois interferometer (G-T I) in the feedback loop can effectively hide the time delay signature (TDS) and achieve additional 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">36</sup> key spaces. The influence of different key mismatches on decryption function is numerically investigated, and the results indicate that the broadband nature of ASE noise makes the TDS a very sensitive encryption key, which increases the difficulty of illegal third parties stealing information. And with the help of the wavelength converter and wavelength division multiplexer, secure communication in various modes is successfully realized, which greatly improves the communication efficiency and is suitable for various security places.