查看更多>>摘要：A method of spectrum estimation based on the genetic simulated annealing[GSA]algorithm is proposed,which is applied to retrieve the three-dimensional wind field of typhoon Nangka observed by our research group.Compared to the genetic algorithm[GA],the GSA algorithm not only extends the detection range and guarantees the accuracy of retrieval results but also demonstrates a faster retrieval speed.Experimental results indicate that both the GA and GSA algorithms can enhance the detection range by 35％more than the least squares method.However,the convergence speed of the GSA algorithm is 17 times faster than that of the GA,which is more beneficial for real-time data processing.
查看更多>>摘要：We propose a neural network equalization delta-sigma modulation[DSM]technique.After performing DSM on the multi-order quadrature amplitude modulation[QAM]orthogonal frequency division multiplexing[OFDM]signal at the transmitting end,neural network equalizer technology is used in the digital signal processing at receiving end.Applying this technology to a 4.6 km W-band millimeter wave system,it is possible to achieve a 1 Gbaud 8192-QAM OFDM signal transmission.The data rate reached 23.4 Gbit/s with the bit error rate at 3.8 × 10-2,lower than soft-decision forward-error correction threshold[4 × 10-2].
查看更多>>摘要：This Letter proposes a high-security modulation scheme for optical transmission systems.By using multi-constellation shaping and asymmetric encryption,the information security can be enhanced and quantum computer cracking can be effectively resisted.Three-dimensional[3D]carrier-less amplitude phase modulation is utilized to superposition and transmit 3D signals.Experimental verification is conducted using a seven-core weakly coupled fiber platform.The results demonstrate that the proposed scheme can effectively protect the system from any illegal attacker.
查看更多>>摘要：Random lasers are a type of lasers that lack typical resonator structures,offering benefits such as easy integration,low cost,and low spatial coherence.These features make them popular for speckle-free imaging and random number gen-eration.However,due to their high threshold and phase instability,the production of picosecond random lasers has still been a challenge.In this work,we have developed three dyes incorporating polymer optical fibers doped with various scat-tering nanoparticles to produce short-pulsed random fiber lasers.Notably,stable picosecond random laser emission lasting 600 ps is observed at a low pump energy of 50 μJ,indicating the gain-switching mechanism.Population inversion and gain undergo an abrupt surge as the intensity of the continuously pumped light nears the threshold level. When the intensity of the continuously pumped light reaches a specific value,the number of inversion populations in the"scattering cavity"surpasses the threshold rapidly.Simulation results based on a model that considers power-dependent gain saturation confirmed the above phenomenon.This research helps expand the understanding of the dynamics behind random medium-stimulated emission in random lasers and opens up possibilities for mode locking in these systems.
查看更多>>摘要：Increasing bandwidth requirements have posed significant challenges for traditional access networks.It is difficult for intensity modulation/direct detection to meet the power budget and flexibility requirements of the next-generation passive optical network[PON]at 100G and beyond considering the new requirements.This is driving researchers to develop novel optical access technologies.Low-cost,wide-coverage,and high-flexibility coherent PON is emerging as a strong contender in the competition.In this article,we will review technologies that reduce the complexity of coherent PON[CPON],enabling it to meet the commercial requirements.Also,advanced algorithms and architectures that can enhance system coverage and flexibility are also discussed.
查看更多>>摘要：The laser-induced damage detection images used in high-power laser facilities have a dark background,few textures with sparse and small-sized damage sites,and slight degradation caused by slight defocus and optical diffraction,which make the image superresolution[SR]reconstruction challenging.We propose a non-blind SR reconstruction method by using an exquisite mixing of high-,intermediate-,and low-frequency information at each stage of pixel reconstruction based on UNet.We simplify the channel attention mechanism and activation function to focus on the useful channels and keep the global information in the features.We pay more attention on the damage area in the loss function of our end-to-end deep neural network.For constructing a high-low resolution image pairs data set,we precisely measure the point spread function[PSF]of a low-resolution imaging system by using a Bernoulli calibration pattern;the influence of different distance and lateral position on PSFs is also considered.A high-resolution camera is used to acquire the ground-truth images,which is used to create a low-resolution image pairs data set by convolving with the measured PSFs.Trained on the data set,our network has achieved better results,which proves the effectiveness of our method.
查看更多>>摘要：Sensors based on optical resonators often have their measurement range limited by their cavity linewidth,particularly in the measurement of time-varying signals.This paper introduces a method for optical frequency shift detection using multi-ple harmonics to expand the dynamic range of sensors based on optical resonators.The proposed method expands the measurement range of optical frequency shift beyond the cavity linewidth while maintaining measurement accuracy.The theoretical derivation of this method is carried out based on the equation of motion for an optical resonator and the recur-sive relationship of the Bessel function.Experimental results show that the dynamic range is expanded t0 4 times greater than the conventional first harmonic method while still maintaining accuracy.Furthermore,we present an objective analy-sis of the correlation between the expansion factor of the method and the linewidth and free spectrum of the optical resonator.
查看更多>>摘要：We demonstrate single-mode microdisk lasers in the telecom band with ultralow thresholds on erbium-ytterbium co-doped thin-film lithium niobate[TFLN].The active microdisk was fabricated with high-Qfactors by photolithography-assisted che-momechanical etching.Thanks to the erbium-ytterbium co-doping providing high optical gain,the ultralow loss nanostruc-turing,and the excitation of high-Q coherent polygon modes,which suppresses multimode lasing and allows high spatial mode overlap between pump and lasing modes,single-mode laser emission operating at 1530 nm wavelength was observed with an ultralow threshold,under a 980-nm-band optical pump.The threshold was measured as low as 1 μW,which is one order of magnitude smaller than the best results previously reported in single-mode active TFLN microlasers.The conver-sion efficiency reaches 4.06 × 10-3,which is also the highest value reported in single-mode active TFLN microlasers.
查看更多>>摘要：All-fiber few-mode erbium-doped fiber amplifiers[FM-EDFAs]with isolation and wavelength division multiplexers[IWDMs]have been developed to enable flexible pumping in different directions.The FM-EDFA can achieve＞30 dB modal gain with＜0.3 dB differential modal gain[DMG].We experimentally simulate the DMG performance of a cascade FM-EDFA system using the equivalent spectrum method.The overall DMG reaches 1.84 dB after 10-stage amplification.We also build a recir-culating loop to simulate the system,and the developed FM-EDFA can support transmission up to 3270 km within a 2 dB overall DMG by optimizing the few-mode fiber length in the loop.
查看更多>>摘要：The 1.4-1.8 μm eye-safe lasers have been widely used in the fields of laser medicine and laser detection and ranging.The diamond Raman lasers are capable of delivering excellent characteristics,such as good beam quality concomitantly with high output power.The intra-cavity diamond Raman lasers have the advantages of compactness and low Raman thresholds compared to the external-cavity Raman lasers.However,to date,the intra-cavity diamond cascaded Raman lasers in the spectral region of the eye-safe laser have an output power of only a few hundred milliwatts.A1485 nm Nd∶YVO4/diamond intra-cavity cascaded Raman laser is reported in this paper.The mode matching and stability of the cavity were optimally designed by a V-shaped folded cavity,which yielded an average output power of up to 2.2 W at a pulse repetition frequency of 50 kHz with a diode to second-Stokes conversion efficiency of 8.1％.Meanwhile,the pulse width of the second-Stokes laser was drastically reduced from 60 ns of the fundamental laser to 1.1 ns,which resulted in a high peak power of 40 kW.The device also exhibited single longitudinal mode with a narrow spectral width of＜0.02 nm.
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