KEYWORDS: Data modeling, Modeling, Education and training, Optical amplifiers, Optical networks, General packet radio service, Simulations, Signal attenuation, Photonics, Control systems
Optical networks are evolving toward ultrawide bandwidth and autonomous operation. In this scenario, it is crucial to accurately model and control optical power evolutions (OPEs) through optical amplifiers (OAs), as they directly affect the signal-to-noise ratio and fiber nonlinearities. However, a fundamental contradiction arises between the complex physical phenomena in optical transmission and the required precision in network control. Traditional theoretical methods underperform due to ideal assumptions, while data-driven approaches entail exorbitant costs associated with acquiring massive amounts of data to achieve the desired level of accuracy. In this work, we propose a Bayesian inference framework (BIF) to construct the digital twin of OAs and control OPE in a data-efficient manner. Only the informative data are collected to balance the exploration and exploitation of the data space, thus enabling efficient autonomous-driving optical networks (ADONs). Simulations and experiments demonstrate that the BIF can reduce the data size for modeling erbium-doped fiber amplifiers by 80% and Raman amplifiers by 60%. Within 30 iterations, the optimal controlling performance can be achieved to realize target signal/gain profiles in links with different types of OAs. The results show that the BIF paves the way to accurately model and control OPE for future ADONs.
Tracking and compensating polarization in real-time is a challenging task and the existing algorithms lack determinacy and interpretability. We demonstrate real-time polarization tracking based on a white-box digital twin modeling the entire polarization tracking system. By calculating with the Stokes vectors and Muller matrices, it is derived that the output power can be expressed by 9 terms consisting of retardances of the electrical polarization controller. We conduct experiments to test and compare the performances of the digital-twin- based algorithm with other algorithms. The experiment results show that the digital-twin-based real-time polarization tracking can ensure the recovery time is less than 0.8 ms in any case. In most cases, the necessary sample times to realize the polarization tracking can be cut down to 9. The adoption of digital twin allows the algorithm to skip the loop of perturbation, sampling, and adjusting over the real system, thereby significantly reducing the sample times and recovery time. The proposed method changes the situation in that existing algorithms are full of random factors and require numerous sample times during polarization tracking.
Chaotic optical communication has shown large potential as a hardware encryption method in the physical layer. As an important figure of merit, the bit rate–distance product of chaotic optical communication has been continually improved to 30 Gb/s × 340 km, but it is still far from the requirement for a deployed optical fiber communication system, which is beyond 100 Gb/s × 1000 km. A chaotic carrier can be considered as an analog signal and suffers from fiber channel impairments, limiting the transmission distance of high-speed chaotic optical communications. To break the limit, we propose and experimentally demonstrate a pilot-based digital signal processing scheme for coherent chaotic optical communication combined with deep-learning-based chaotic synchronization. Both transmission impairment recovery and chaotic synchronization are realized in the digital domain. The frequency offset of the lasers is accurately estimated and compensated by determining the location of the pilot tone in the frequency domain, and the equalization and phase noise compensation are jointly performed by the least mean square algorithm through the time domain pilot symbols. Using the proposed method, 100 Gb/s chaotically encrypted quadrature phase-shift keying (QPSK) signal over 800 km single-mode fiber (SMF) transmission is experimentally demonstrated. In order to enhance security, 40 Gb/s real-time chaotically encrypted QPSK signal over 800 km SMF transmission is realized by inserting pilot symbols and tone in a field-programmable gate array. This method provides a feasible approach to promote the practical application of chaotic optical communications and guarantees the high security of chaotic encryption.
A degenerated look-up table based perturbative nonlinearity compensation (DLUT-PNC) algorithm for probabilistically shaped 16QAM signals was proposed to compensate intra-channel fiber nonlinearity. However, this method adopts the standard 16 QAM signals without considering the influence of ASE noise to calculate the degenerated elements of table. Hence, the degenerated elements of the table are not strictly optimal. In this paper, a blind adaptive DLUT-PNC (BADLUT- PNC) method based on the gradient descent algorithm is proposed. We use the gradient descent algorithm to optimize the degenerated elements and then obtain the optimal degeneration scheme. In a single channel 70GBaud dual-polarization 16QAM transmission simulation with a 1200km link, the proposed scheme is investigated. The simulation result shows that the extra 0.15~0.45dB SNR improvements can be achieved by adopting our proposed BA-DLUT-PNC compared to the conventional DLUT-PNC method.
As the demand for broadband applications continues rising, low cost and high capacity PON system has attracted more attention to keep up with the increasing demand in the future access network. Recently, the IEEE 802.3 Ethernet Working Group has already sponsored the discussion of next generation Ethernet passive optical network (NG-EPON) to provide 25-Gb/s per wavelength. In order to upgrade current 10-Gb/s PON to realize the capacity of 100 Gb/s PON with 25 Gb/s per wavelength, a variety of experimental demonstrations have shown the feasibility of 25-Gb/s per wavelength using the modulation schemes of four-level pulse amplitude modulation (PAM-4), electrical duobinary (EDB), optical duobinary (ODB) or non-return-to-zero on-off-keying (NRZ-OOK) for high speed transmission. In order to achieve higher performance, these transmission schemes are always combined with the advanced digital signal processing (DSP) which increases the technical complexity and the cost as well. Most of the previous demonstration are based on the off-line processing, therefore requires more time for the practical deployment.
In this paper, we demonstrate the first field trial a real-time 100Gb/s TWDM-PON system with 4×25-Gb/s downstream and 4×10-Gb/s upstream transmission using 10G-class directly-modulated lasers (DMLs) and APD/PIN receivers. A single delay-interferometer (DI) is used to achieve frequency equalization as well as chirp management to increase the high frequency components of the system response and combat the chromatic dispersion (CD) during the fiber transmission. Note that there is no DSP applied for the whole system. Electrical clock/data recovery (CDR) chips are integrated on the main board for data generation, recovery and real-time bit error rate (BER) measurement. We obtained a power budget of 33 dB with 0-40km of standard single mode fiber based on NRZ-OOK modulation format for the downstream. The system stability is also verified using deployed 40-km fiber infrastructure over 67-hour real-time measurement.
We have proposed to use a directly modulated tunable fiber ring laser based on reflective semiconductor optical
amplifiers(RSOA) and tunable optical filter (TOF) as an upstream source in multi-wavelength shared(UMWS) time
division multiplexing-passive optical network (TDM-PON) configuration. Downstream signal is broadcasted in TDM
way while upstream signals are multiplexed in hybrid time/wavelength division multiplexed way, which upgrades the
upstream capacity greatly. Bidirectional transmission of downstream data at 10-Gb/s and upstream data at 1.25-Gb/s per
wavelength over 25-km single mode fiber (SMF) is demonstrated with a power penalty of ~0.5 dB at both ends. A stable
performance is observed for the upstream wavelength tuned from 1530 nm to 1595 nm.
A novel all-optical encryption/decryption method based on stimulated Brillouin scattering (SBS) effect in optical fiber is proposed for the first time. The operation principle is explained in detail and the encryption and decryption performance is experimentally evaluated. The encryption keys could be the SBS gain amplitude, bandwidth, central wavelength and spectral shape, which are configurable and flexibly controlled by the users. We experimentally demonstrate the SBS encryption/decryption process of a 10.86-Gb/s non-return-to-zero (NRZ) data by using both phase-modulated and current-dithered Brillouin pumps for proof-of-concept. Unlike the traditional optical encryption methods of chaotic communications and optical code-division-multiplexing access (OCDMA), the SBS based encryption/decryption technique can directly upgrade the current optical communication system to a secure communication system without changing the terminal transceivers, which is completely compatible with the current optical communication systems.
We propose and demonstrate a novel high-gain-efficiency long-wavelength band (L-band) erbium-doped fiber amplifier with a double-pass backward-pump configuration, in which the strong backward C-band amplified spontaneous emission is effectively utilized. The L-band gain is greatly enhanced in comparison with the copumped configuration. Without using any excessive components, the new configuration can provide the same gain as the conventional configuration, but only using 40% pump power. Meanwhile, the noise figure is also effectively improved under the low pump power.
We have demonstrated error-free operations of slow-light via stimulated Brillouin scattering (SBS) in optical fiber for
10-Gb/s signals with different modulation formats, including
non-return-to-zero (NRZ), phase-shaped binary
transmission (PSBT) and differential phase-shift-keying (DPSK). By directly modulating the pump laser diode (LD)
using current noise source, the SBS gain bandwidth and profile can be simply controlled by the peak-to-peak value and
power density distribution of the current noise. Super-Gaussian noise modulation of the Brillouin pump LD allows a
flat-top and sharp-edge SBS gain spectrum, which can reduce
slow-light induced distortion in case of 10-Gb/s NRZ and
PSBT signals. For the 10-Gb/s NRZ signal, the error-free slow-light operation has been achieved for the fist time and the
corresponding maximal delay-time with error-free operation is 35 ps. Then we propose the PSBT format to minimize
distortions resulting from SBS filtering effect and dispersion accompanied with slow light owing to its high spectral
efficiency and strong dispersion tolerance. The maximal delay of 51 ps with error-free operation has been achieved.
Furthermore, the DPSK format is directly demodulated through a Gaussian-shaped SBS gain, which is achieved using
Gaussian-noise modulation of the Brillouin pump. The maximal
error-free time delay after demodulation of a 10-Gb/s
DPSK signal is as high as 81.5 ps, which is the best demonstrated result for 10-Gb/s slow-light.
In this paper, a novel in-band optical spectra and filter shape monitoring technique is experimentally demonstrated. Based on swept coherent detection, the proposed technique simultaneously measures the signal and ASE spectra by adjusting the polarization states of the signal and local oscillator. In our experiment, a high resolution of 0.002 nm is achieved.
1+1 protection is usually used to implement fast failure recovery and provide high reliability to data connections. A typical scheme of 1+1 protection employs a primary working lightpath and a dedicated diversely-routed backup ligthpath to carry the same data, in which the same wavelengths are always used for the two lightpath, thus putting edge-disjoint restrictions on the wavelength routing. Because current standard requires <50-ms protection-switching time, a mechanical switches with several millisecond switching time can be used before the receiver for channel switching. However, with the transmission speed of single wavelength channel increasing to tens of Gb/s, a faster switching time is highly desired to reduce the amount of data loss. In this paper, we propose an out-of-band 1+1 protection scheme, which employs two different wavelengths for primary working lightpath and protection backup path, respectively. At the destination node, a fast tunable heterodyne-detection receiver is used to select the desired wavelength lightpath. The proposed fast tunable receiver significantly reduces the protection switching time between the two paths. To investigate the performance of the proposed protection scheme, a fast channel selection experiment is performed. Two optical wavelength channels were modulated simultaneously by a
Mach-Zehnder (MZ) external modulator with data rate 1.25Gb/s. The tunable heterodyne receiver switches between the working lightpath and protection lightpath to demonstrate the capability of 1+1 protection. A <0.8-ns switching time is obtained which demonstrates the potential of hitless protection switching, if the switching occurs at the transition of two neighboring '1's.
We proposed and demonstrated a new configuration of the low noise figure C+L- band erbium- doped fiber amplifier. In the configuration, a preamplifier is used to reduce the noise figure, and an improved double-pass configuration with a fiber Bragg grating was employed to enhance the L-band gain and while to reduce the noise figure. The experiment demonstrated that the noise figure in the new broad-band amplifier was improved by ~2 dB, and the gain was enhanced up to above 25dB over the region from 1525 to 1605nm.
A tunable, gain-clamped (GC) double-pass Erbium-doped fiber amplifier (EDFA) using only one fiber Bragg grating (FBG) has been demonstrated, which solves the problem existing the conventional GC-EDFA using two FBGs, in which the clamped-gain is very difficult to be tuned. In the new GC-EDFA, the lasing oscillation for clamping the gain is produced between a FBG and a fiber reflection mirror, and a variable optical attenuator (VOA) is used to change the loss of the laser, which is filtered solely from a narrowband filter for tuning the clamped-gain, however it does not change the signal power directly. Meanwhile, the double-pass configuration enhances efficiently the gain, therefore, compared with the single-pass configuration, the maximum possible input signal power for gain-clamping is greatly extended. Furthermore, the FBG can depress the strong backward amplification spontaneous emission in double-pass configuration, so it can reduce the noise figure a certain extent. Finally, a gain-tunable GC-EDFA with a wide dynamic input power range is demonstrated.
A new design of all-optical gain-clamped L-band double-pass (DP) erbium-doped fiber amplifier (EDFA) has been demonstrated, in which, the input port and the odd-channel output port of interleaver are connected with a DP configuration EDF through a circulator to form lasing ring cavity for clamping gain, and the even port is utilized to export the amplified signals. A low NF can be achieved because the lasing co-propagates with the signal, and the lasing is exported separately from the amplified signal thanks to interleaver. Meanwhile, the fiber Bragg grating incorporated in DP configuration suppresses the backward ASE generation, and therefore improves efficiently the gain and lowers the NF. In such a way, the clamped gain of 16.3dB with a variation below 0.2dB and the noise figure below 5dB is achieved on the new L-band gain-clamped EDFA.
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