With the diversified development for network service in terms of quality of service, bandwidth, and noise tolerance, variable-bandwidth gridless optical networks (V-GON) have become a promising technology for future networking. Unlike traditional elastic optical networks, which use orthogonal frequency division multiplexing for flexible allocation of subcarriers, V-GON adopts wave division multiplexing with variable modulation format and adjustable bandwidth, which can provide a more convenient way of data transmission. One of the key issues for V-GON is routing and spectrum allocation (RSA) due to the complexity of multi-channels. With complex modulation formats and different center wavelengths, an RSA algorithm needs to assign center frequencies, bandwidths, and modulation formats for each connection and also needs to consider the noise tolerance of the path. In this paper, we focus on optimizing routing, modulation format, and spectrum allocation by deep reinforcement learning to meet the demands of noise tolerance at different speeds. We proposed a reinforcement learning model to realize the availability forecast. The model can predict the feasibility of a pre-allocated optical spectrum. We conduct a numerical simulation to validate the performance. The results show that the proposed Graph Neural Network-Optical Path Availability Prediction algorithm can improve network efficiency, and utilization of spectral resources, and reduce the blocking ratio, which can support dynamic connectivity and interference reduction. In NSFNET network topology our proposed GNN-OPAP algorithm model reduces the loss by 95.88% compared to the DNN model and 64.23% compared to the LSTM model. In 4*mesh network topology, our proposed GNN-OPAP algorithm model reduces the loss by 16.14% compared to the DNN model and 76.33% to the LSTM model. This research provides new insights into the RSA problems in V-GON and provides a powerful reference for designing and optimizing future optical communication networks.
The excellent properties of the narrow linewidth, single longitudinal mode and constant frequency of the seed-injected solid-state single-frequency pulse laser make it suitable in the applications of the gravitational wave detection, doppler wind radar, and greenhouse gas flux measurement. FPGAs have been widely utilized in the laser electronic control systems due to its high integration and parallel processing capabilities. Based on the classical Ramp-Hold-Fire principle, we develop an injection locking system by using the modular FPGA architecture and the Verilog programming language. To demonstrate the program's viability, Vivado software is utilized for online simulation and debugging to guarantee the correctness of time conversion between different modules. The simulation results show a good time match between the master and slave lasers. The realization of seed injection locking is verified by detecting the increase of output laser energy, shortening pulse setup time and single longitudinal mode output pulse after injection. Finally, a 2 μm single frequency pulse laser is generated with a repetition rate 300 Hz and output power 4.5 mJ.
When a laser irradiates into the liquid medium, the medium absorbs the laser energy and induces sound source. As a new method to generate underwater sound wave, laser-acoustic has a variety of commercial and oceanographic applications on the information transmission between aerial and underwater platform, underwater target detection, marine environment measurement etc. due to its merits such as high acoustic intensity, spike pulse and wide frequency spectrum. According to different energy intensity of the laser pulse and the spatial and temporal distribution of energy interaction region, the mechanism of the laser interacting with water that generating sound are classified as thermoelastic, vaporization and optical breakdown mainly. Thermoelastic is an important mechanism of laser-acoustics. The characteristics of photoacoustic signal that induced by thermoelastic mechanism was summarized and analyzed comprehensively. According to different induce conditions, theoretical models of the photoacoustic signal induced by a δ pulse and a long pulse laser are summarized respectively, and its nature characteristic in the time domain and frequency domain were analyzed. Through simulation, the theoretical curve of the sound directivity was drawn. These studies will provide a reference for the practical application of laser-acoustics technology.
Acoustic transducers are traditionally used to generate underwater acoustical energy with the device physically immersed in water. Novel methods are required for communicating from an in-air platform or surface vessel to a submerged vessel. One possible noncontact downlink communication system involves the use of laser induced acoustic source. The most common mechanisms of opto-acoustic energy conversion are, by order of increasing laser energy density and efficiency, thermal expansion, surface evaporation and optical breakdown. The laser induced acoustic source inherently bears the obvious advantage of not requiring any physical transducer in the medium. At the same time, acoustic energy propagation is efficient in water, whereas optical energy propagate well in air, leading to a more efficiency opto-acoustic communication method. In this paper, an opto-acoustic underwater Communication system is described, aiming to study and analysis whether laser induced sound could achieve good performance for effective communication in practical application.
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