A forest fire smoke detection model combining convolutional neural network and vision transformer

Forest fires seriously jeopardize forestry resources and endanger people and property. The efficient identification of forest fire smoke, generated from inadequate combustion during the early stage of forest fires, is important for the rapid detection of early forest fires. By combining the Convolutional Neural Network (CNN) and the Lightweight Vision Transformer (Lightweight ViT), this paper proposes a novel forest fire smoke detection model: the SR-Net model that recognizes forest fire smoke from inadequate combustion with satellite remote sensing images. We collect 4,000 satellite remote sensing images, 2,000 each for clouds and forest fire smoke, from Himawari-8 satellite imagery located in forest areas of China and Australia, and the image data are used for training, testing, and validation of the model at a ratio of 3:1:1. Compared with existing models, the proposed SR-Net dominates in recognition accuracy (96.9%), strongly supporting its superiority over benchmark models: MobileNet (92.0%), GoogLeNet (92.0%), ResNet50 (84.0%), and AlexNet (76.0%). Model comparison results confirm the accuracy, computational efficiency, and generality of the SR-Net model in detecting forest fire smoke with high temporal resolution remote sensing images

All-optical format conversion-based flexible optical interconnection using nonlinear MZI with nested-pump assisted NOLM

An all-optical format conversion (AOFC) scheme of star-m-ary quadrature amplitude modulation (star-mQAM) based on a nonlinear Mach-Zehnder interferometer (MZI) with nested-pump assisted nonlinear optical loop mirror (nested-PA-NOLM) is proposed and numerically simulated. In this scheme, input multi-Gbps star-8QAM signals can be converted into three quadrature phase shift keying (QPSK) signals (namely QPSK-A, -B and -C) through the PA-NOLM under different input power of the signal and the pump. The nonlinear MZI is formed by two PA-NOLMs of the upper and the lower arms, the former and the latter 3-dB optical couplers (OCs), a directional variable optical attenuator (VOA) in the upper arm and a directional variable phase shifter (VPS) in the lower arm. A VOA and a VPS are used to adjust the power ratio (PR) and relative phase shift (RPS) between any two of QPSK-A, -B and -C. When any two adjusted signals in QPSK-A, -B and -C are coherently superposed, the aggregated star-8QAM signal can be extracted again. Furthermore, the proposed scheme can also be used to convert the 20 Gbps bipolar 4-ary pulse amplitude modulation (PAM4) signal into two 10 Gbps BPSK signals and a 20 Gbps QPSK signal. When the proposed scheme is combined with the phase-sensitive amplification (PSA), it can also be used to convert one 16QAM into two QPSK signals. The scheme performance is analyzed via constellation diagrams, power waveforms, the error vector magnitude (EVM) and the bit error rate (BER) of the optical signals. The scheme can not only be deployed in optical gateways to connect optical networks using different modulation formats, but also has a potential applied advantage in security information transmission between different optical networks

Optical Frequency Comb Generation Based on Optoelectronic Oscillator and Fabry-Perot Phase Modulator

We propose and demonstrate an optical pulse generator using optoelectronic oscillator (OEO) and Fabry-Perot phase modulator (FP-PM). A complete theoretical analysis is developed, and the advantages of the proposed system are also discussed. The optical frequency comb (OFC) is generated with an OEO loop to create broadband comb mode with low noise. It is theoretically proved that OFC pulses with a spectrum of 33 flat comb lines can be generated using an FP-PM. 25 GHz optical pulses with full-width-at-half-maximum (FWHM) less than 4 ps, signal-to-noise ratio (SNR) better than 40 dB. By changing the length of the fiber in OEO, the timing jitter is 100 fs in this system. The phase noise of the 25 GHz signal is −107.8 dBc/Hz at 10 kHz offset, which is measured when the fiber length is 230 m. The system is promising to attain high-quality electrical-optical (EO) comb with low timing jitter

Tunable terahertz all-dielectric linear-to-circular polarization conversion metasurface

Terahertz (THz) linear-to-circular (LTC) polarization conversion plays a crucial role in imaging and 6G wireless communication. This paper will give an account of a thermally tunable THz LTC polarization converter by using the active all-dielectric metasurface. It consists of zirconium oxide (ZrO2) microsphere resonators, active strontium titanate (STO) cladding, and flexible polyimide substrate. Through numerical simulation, the amplitude of the ellipticity of the proposed polarization converter at 0.265 THz is –1, indicating that perfect right-hand circular polarization (RHCP) wave is achieved. Meanwhile, the amplitude of the ellipticity is less than –0.8 between 0.247 and 0.278 THz (relative bandwidth is 12%). In addition, with the temperature changes of 180 K (from 200 to 380 K), the operating frequency of the converter can be tuned from 0.220 to 0.291 THz, a sensitivity about 39 GHz/100 K is achieved. Besides, the modulation depth of the ellipticity amplitude can achieve 92% at 0.220 THz, which demonstrates that the converter can output terahertz wave with different polarization states, and the device can be fabricated on a large scale. These perfect conversion performances show that the converter has potential applications in high-speed communication and imaging

All-Optical Regeneration and Format Conversion for 4APSK Signals Based on Nonlinear Effects in HNLF

An all-optical format conversion and regeneration scheme about 4-ary amplitude and phase shift keying (4APSK) signals is proposed and numerically simulated based on nonlinear effects in the high nonlinear fiber (HNLF). The input 4APSK signal is firstly converted into a regular quadrature phase shift keying (QPSK) signal by the nonlinear Mach-Zehnder interferometer (MZI) based on the self-phase modulation (SPM). Secondly, a degenerate phase-sensitive amplification (PSA) based on the four-wave mixing (FWM) is utilized to convert the regular-QPSK into two binary phase shift keying (BPSK) signals. The nonlinear MZI configuration is also used to compress the amplitude noise of BPSK. Thirdly, one phase shifter and one variable optical attenuator (VOA) are used to adjust the relative phase and power relationships of the two amplitude-regenerated BPSK signals. The regenerated 4APSK and converted QPSK signals can be generated in one 3-dB optical coupler through coherent addition of the two regenerated BPSK signals. The error-vector-magnitude (EVM) and the bit-error-rate (BER) are calculated and compared to evaluate the scheme performance. The proposed scheme can be applied as an optical regenerator or format convertor at the network gateway to increase the transmission distance or connect optical networks with different modulation formats

Fiber-optic parametric amplifier-based all-optical format conversion enabling optical networks interconnection with different modulation formats

A fiber-optic parametric amplifier (FOPA)-based all-optical format conversion (AOFC) scheme is proposed and numerically simulated to achieve optical networks interconnection with different modulation formats. In this scheme, the power transfer function (PTF) and the relative phase shift (RPS) functions between the input and output optical signals for the single-pump FOPA are derived and numerically analyzed. For the input 20 Gbps bipolar 4-ary pulse amplitude modulation (PAM4) signal, it can be converted into a BPSK signal (BPSK1) based on the power saturation characteristic of the PTF. By adjusting the input power of the input PAM4 signal, it can also be converted into a level-swapping PAM4 signal based on the single-pump FOPA. When the level-swapping PAM4 signal is sent into the single-pump FOPA with suitable power again, another BPSK signal (BPSK2) could also be generated. When the PAM4-to-BPSK format converter based on the single-pump FOPA is combined with the dual-pump FOPA (namely phase-sensitive amplifier, PSA), the 16-ary quadrature amplitude modulation (16QAM) signal can also be de-aggregated into four BPSK signals or two quadrature phase shift keying (QPSK) signals. The constellation diagrams, the power waveforms, the error vector magnitude (EVM) and the bit error rate (BER) of the relevant optical signals are measured to evaluate the scheme performance. The scheme can be deployed at the optical gateway to realize optical networks interconnection using different modulation formats

An All-Optical Microwave Frequency Divider with Tunable Division Factors Based on DP-DPMZM

Based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved. The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers before the photodetector to increase the conversion gain. Experiment results also demonstrate that the frequency division factors can be adjusted

An All-Optical Microwave Frequency Divider with Tunable Division Factors Based on DP-DPMZM

Based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM), an all-optical frequency divider is proposed and experimentally demonstrated. Two radio frequency (RF) signals are modulated on an optical carrier to work as a dual-beam master laser (ML). The optical signals of the ML are injected into a distributed feedback (DFB) laser to initiate the period-two (P2) state oscillation. By beating the output of the slave laser (SL) via circulator in a photodetector, a frequency divider with tunable factors can be achieved. The innovation of the scheme lies in having a simple structure and only requires optical devices, which is operated in wide RF frequency range without any electrical amplifiers before the photodetector to increase the conversion gain. Experiment results also demonstrate that the frequency division factors can be adjusted