In this work, we propose to utilize the artificial neural network (ANN) to realize the computing of the pulse performance of the linear cavity fiber laser. At the first, a four hidden layer ANN (called ANN1) is trained to judge whether a small noise pulse in the fiber cavity can evolve into a stable mode-locked pulse with different cavity parameters. ANN1 has an accuracy of 98.3% on the test data set and we use it to quickly calculate the pulse convergence region in the three-dimensional parameter space. Then, a three hidden layer ANN (called ANN2) is trained to calculate the output pulses shape of fiber laser, and its accuracy is verified. After that, based on ANN2 and genetic algorithm, we design a method to inverse deducing the laser parameters with known output pulse width. This algorithm has a small-time complexity. By repeating the genetic process, the accuracy of this algorithm will also be improved. The authors believe that the neural network model presented in this work is an efficient and universal means to study the dynamics of optical fibers and will have a great application prospect in future related work.
We use the full vector beams propagation method (VFE-BPM) to simulate the nonlinear propagation process of the cylindrical vector beams (CVBs). We have shown that the CVBs have poor transverse stability which causes which causes the breakup due to the ring-shaped beam field. Then, we use the approximate analytic theory to qualitative analyze the variations of the numerically calculated instability growth rates, which shows excellent agreement with the simulated results.
All-fiber wavelength-tunable fiber laser is a desirable light source architecture in many fields owing to their low cost, compactness and easy integration. However, most of them have independent filter elements and saturated absorption elements, which will undoubtedly increase the redundancy of laser. In this paper, we realize an all-fiber wavelength-tunable Ytterbium (Yb)-doped laser with the tunable central wavelength from 1023 nm to 1076 nm based on fiber loop mirror (FLM). The fiber loop (FLM) fused with two segments of polarization-maintaining fibers (PMF) acts as both a comb filter and a saturable absorber (SA). We believe that lasers with a simple structure and wide wavelength tuning range will have potential applications in sensing, communication, spectroscopy, and medicine.
KEYWORDS: Fiber lasers, Signal to noise ratio, Polarization, Linear polarizers, Telecommunications, Single mode fibers, Polarizers, Multiplexing, Multiplexers, Random lasers
We propose and experimentally demonstrate a Yb-doped random fiber laser with a controllable oscillating mode based on injection locking technology. An external signal light is used to realize the locking of the transverse mode. By simply adjusting the injected signal light power, random fiber laser can directly oscillate at the LP01 mode, hybrid mode, and LP11 mode, respectively. Besides, random lasing with a low threshold and high slope efficiency can be obtained.
A tunable passively mode-locked fiber laser with cylindrical vector beams (CVB) generation in a linear cavity was presented. The mode-locking mechanism is based on the nonlinear multimode interference effect of the graded-index multimode fiber (GIMF). The Sagnac loop mirror works as a filter. An ultra-broadband long-period fiber grating (UBLPFG) with a high conversion efficiency < 90% from 1004 nm to 1068 nm is used to covert fundamental mode to higher-order modes. The laser can achieve a continuously tunable wavelength range from 1032.344 nm to 1042.556 nm by changing the reflection spectrum of the Sagnac loop mirror thermally. When the laser operates at the central wavelength of 1042.556 nm, the output pulse trains have a period of 92.08 ns with pulse duration of 1.15 ns. The slope efficiency of the laser is about 4.73% with the mode-locking threshold of 167.7 mW. The purity of the radially and azimuthally polarized beams is measured to be higher than 93.8%.
Reducing the size of devices and the loss of waveguides are two significant research contents in integrated optics. Surface plasmon polariton (SPP) waveguides can break the diffraction limit and provide tight light confinement, however, they are subject to unavoidable high propagation loss due to the metallic ohmic loss. Traditional dielectric waveguides can propagate light with ultralow loss, but they are subject to the diffraction limit in each direction which will result in large mode size. In general, mode size and loss of waveguides are mutually restricted. Here, we proposed an all-dielectric nanowire waveguide which can confine light into nanoscale gap region and realize deep subwavelength mode confinement in two dimensions. A normalized mode area of 1.4×10-2 is achieved, which keeps on the same level with the plasmonic waveguides. The strong mode confinement is attributed to the discontinuity of the normal component of electric field at the interface of two materials. We determined the supported mode of the all-dielectric nanowire waveguide is quasi-TM mode by analyzing the electric vector distributions. The quasi-TM eigenmode is lossless in theory because of no metal components, which is consistent with our simulation results. The lossless propagation in theory is a significant breakthrough compared to the plasmonic waveguides. The all-dielectric nanowire waveguide realizes both subwavelength mode confinement and low-loss propagation simultaneously, conquers the trade-off between mode size and loss of waveguides in theory.
In this work, we combine the plasmonic material with high index dielectric to design a metasurface. With the dyadic Green function and coupled-dipole approach, a Huygens’ metasurface is obtained by two dimensional array of subwavelength Ag core-Si shell nanoparticles, the transmission efficiency is close to unity in a broadband spectrum, and the reflection is completely eliminated by spectrally overlapping the magnetic dipole resonance with the electric dipole resonance. The designed high transmitted Huygens’ metasurface can be applied to wavefront shaping and beam forming.
We have proposed and demonstrated the generation of high power, wide band square-wave pulse in a figure-8 Yb-doped mode-locked fiber laser. The fiber laser operates at 1083.65 nm with 3 dBbandwidth of 6.5 nm, which can emit nanosecond square pulses with a maximum average output power of 1.31 W and peak power 40 W, respectively. The bandwidth, to the best of our knowledge, is the widest output bandwidth in a square-wave pulse fiber laser operating at 1 μm band.
Single quantum dot-cavity system with a deep confinement potential quantum dot is detailedly investigated, with both s- and p-exciton incoherent pump. Through gradually increasing pump rate (about 10-4=ps ∼ 12=ps), the mean photon number shows a linear-dependence on pump power, the photon probability distribution, characterized by g(2)(0), transforms from antibunching to bunching through Poisson, and the spectra go from the doublet to a singlet, the linewidth shows clear reduction in the lasing region. If we increase pump rate further, the mean photon number decreases monotonically to zero, g(2)(0) reaches its maximum value 2, and all the electrons stack at upper lasing level, indicating thermal light generation. The results show, the deep QD-cavity system under s- and p-exciton pump can generate laser although it is not an ideal coherent light, and with only p-exciton pump considered, in spite of the coherent light generated, this pump method is unreasonable to simulate the experimental conditions for the negligible energy spacing between s-exciton and p-exciton.
We show theoretically that the upper and lower cutoff frequencies in a two-dimensional photonic crystal coupled-cavity waveguide (CCW) can be moved synchronously by changing two configuration parameters of the waveguide simultaneously. The CCW is formed in a two-dimensional photonic crystal (2-D PhC) consisting of a square array of dielectric rods in the air. Efficient methods have been demonstrated for moving the two cutoff frequencies in the same direction over equal distances up to 25.7% of the photonic band gap. The results can be applied to the design of integrated optical devides based on photonic crystal waveguides.
The general role of the surface plasmons in the transmission of
the metallic grating with narrow slits has been numerical
described using the finite difference time domain method.
Different parameters of grating have been used in the numerical
simulation. It is concluded that whether the transmission peak of
the SP resonance emerges or not does not depend on the SP
travelling on the grating surface. The grating depth and the width
of slit really give a dominant influence on the energy
transmission for the SP resonance.
The independent control of the upper and lower cutoff frequencies of the guided modes in coupled-cavity wavguides (CCWs) is investigated numerically. The CCWs are formed in a two-dimensional photonic crystal (2D PhC) consisting of a square array of dielectric rods in the air. The dielectric constant and radius of the rods in the perfect PhC is 11.56 and 0.18α, respectively, in which α is lattice constant. By using the plane wave expansion method (PWEM), the impact of two influencing factors on cutoff frequencies in CCWs is calculated systematically. Efficient methods have been demonstrated for tuning one cutoff frequency while keeping the other unchanged. The indepent control ranges of the upper and lower cutoff can be up to 67.85% and 68.57% of photonic band gap (PBG), respectively. The results can be applied to the design of PhC-based optical devices such as band filters and optical switches.
The optical reflector based on two-dimensional photonic crystal constructed by a square lattice of dielectric rods has already been reported in recent years, But the enormous difficulties to fabricate this structure are well-known, because the height of the rods must be finite in a real system so in this case no guided modes appears when air waveguides are created. On the contrary, there is not this inherent limitation for the photonic crystal waveguide made of air holes. In this paper, I will demonstrate an optical reflector based on photonic crystal,which constructed by air holes introduced into high index material. We design a monomode waveguide with even symmetry and discuss the characteristic of the reflector obtained by inserting several defects into the monomode waveguide in FDTD method.This kind of reflectors still have guided mode even if it possess finite thickness. This will make optical reflector based on two-dimensional photonic crystal nearer to practical application.
Multimode interference optical pulse power splitters for 1.053μm wavelength have been designed in this paper. The guided mode propagation analysis method is used to analyze the working principle of MMI power splitter. We designed the power splitters base on the analysis. Then finite difference beam propagation method (FDBPM) was used to analyze the splitting performance of the devices. At last, we analyzed the temporal performance of the device (such as pulse broaden) working for optical pulse input with the Finite Difference Time Domain (FDTD) method. The dispersion properties for ultra short 1.053μm optical pulses input were analyzed.
The interference of the surface plasmons polaritons (SPPs),
localized SPPs, has been numerical analyzed by 2D finite
difference time domain (FDTD) method. The near-field distributions
of the localized SPPs have been presented. It is found that the
quality of the output is not always good with strong interaction
of the SPPs in super-RENS. It is also found that the near-field
distribution and the output are almost changeless when the regions
of the dark stripes have been adjusted.
The factors that affect the properties of the filters in a two-dimensional photonic crystal (2-D PC) waveguide are investigated quantitatively. The waveguide is constructed by omitting one line rods in a perfect 2-D PhC composed of circular dielectric rods located at a square lattice. The 2-D PC filters (2-D PCF) are formed by adding some defect rods in the waveguide. The numerical calculation results show that the reflectivity and transmission of the filter are dependent on the size, dielectric constant and number of defect rods. Moreover, the transmission spectrum of a PCF is also obtained by using fast fourier transform (FFT) method and comb-like curve shape similar to that in the transmission spectrum of Fabry-Perot etalons is found in it .
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