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In this paper, we employ a symmetrical graded index multimode fiber-step index multimode fiber-graded index multimode fiber (GIMF-SIMF-GIMF) structure as artificial saturable absorber to achieve mode-locked operation in an Erbium-doped fiber laser. After optimizing the cavity length, pump power and orientation of polarization controller, noise-like pulse (NLP) is built in anomalous dispersion region experimentally. It is worth noting that except for the traditional NLP, a special NLP with unique features is obtained whose temporal and spectral properties are different from the known case on NLP reported before. According to the experimental results, we also acquire and compare properties of subpulse within NLP envelope with the change of pump power. Last but not least, harmonic of the peculiar NLP is found under appropriate cavity conditions.

A severe infectious disease characterized by nephritis, hepatitis and splenitis has attacked goslings around Shandong province in China since 2016. A novel chicken-origin avian orthoreovirus (ARV) was isolated with LMH cells from affected goslings named Reo/Goose/SDPY/1116/17 (SDPY-ARV) strain, and the infection was successfully reproduced experimentally. The ARV-SDPY full genome sequencing was conducted using Next-Generation Sequencing (NGS) technique on Illumina HiSeq platform. The complete genome of SDPY-ARV was 23,427 bp in length and consist of 10 dsRNA segments ranged from 1192 bp (S4) to 3958 bp (L1) which encoding 12 viral proteins. Genomic sequence analysis showed that the SDPY-ARV strain is in the same branch with broiler, pheasant-origin ARV isolates, and shares 51.8–96.2% of nucleotide identity of σC gene with them; while only 49.3–50.3% with waterfowl isolates. In addition, the occurrence of 10 segments genetic reassortment of SDPY strain is confirmed among the PA15511, the 1733 and the PA13649 strains from America. In conclusion, the causative agent of gosling hemorrhagic necrotic hepatitis and nephritis occurring in China is a novel chicken-origin goose orthoreovirus.

In 2017, an emerging disease outbreak with high mortality in goslings occurred in China. A novel goose astrovirus was isolated and identified as the causative agent of this disease. Genomic analysis revealed that this virus strain was significantly distinct from published astrovirus strains.

We propose and demonstrate a fiber sensor for simultaneous temperature and strain measurements. The proposed sensor is implemented by a cascaded-cavity Fabry–Perot (FP) fiber interferometer. The two cascaded FP cavities comprise a micro-air-cavity in a hollow-core tube fiber and a micro-silica-cavity in a standard single-mode fiber. To separate the interference spectrum of each FP cavity, the total spectrum is filtered in the frequency domain through band-pass filters, whose central frequencies were predesigned based on the relationship between the spatial frequency and free spectral range of each FP cavity. The different cross-sectional areas and thermal-optic coefficients of the two FP cavities confer different sensitivities to temperature and strain. Both parameters were measured simultaneously by tracking the wavelength shifts in the filtered interference spectra of the FP cavities. Moreover, the temperature–strain cross-sensitivity was compensated by solving a sensitivity-coefficient matrix equation for the two cavities, using the calibrated temperatures and strains. Other advantages of the proposed sensor are simple fabrication and an all-fiber structure. Owing to these properties, the proposed sensor is potentially applicable to real sensing applications.

Versatile structures of wavelength-dependent bound solitons are obtained based on nonlinear polarization rotation (NPR) mode-locked technology in an anomalous-dispersion fiber laser. After optimizing the intra-cavity birefringence and finely adjusting the operating wavelength of the laser, both the conventional soliton and loosely bound-state soliton pairs can be generated and switched under different operating wavelengths. With the evolution of bound state, the spectral interference fringes show significant changes and the temporal separation between bound solitons varies accordingly. Altering initial settings of laser parameters, wavelength-dependent multiple-soliton bound states are also found experimentally. Moreover, the formation and evolution mechanism of the bound states are explored and analyzed in this work.

The formation and evolution of dip-type spectral sidebands are numerically and experimentally researched in a soliton fiber ring laser passively mode locked by the nonlinear polarization rotation (NPR) technique. We provide a theoretical model that can predict the positions of dip-type sidebands, and point out that the formation of the dip-type sidebands is due to the local destructive interference effect between the soliton and dispersive waves induced by the periodic soliton perturbations in the laser cavity. The expression describing the position of dip-type sidebands is strictly deduced, which indicates that the positions of dip-type sidebands on the spectrum can be changed with the pulse width variation. The reliability of the theoretical model of dip-type sidebands is verified by experiments and simulations; both the experimental observations and numerical simulations can well confirm the theoretical predictions.

We report on the influence of the average nonlinear coefficient on noise-like pulse (NLP) in a figure-of-eight erbium-doped fiber laser. Since the nonlinear switching point of nonlinear amplifying loop mirror (NALM) shifts with distinct laser configurations, through changing the length of highly nonlinear fiber (HNLF) in NALM, properties of output pulse have been compared and analyzed. The spectral evolutions occur and the peak power of NLP presents a decline when the HNLF is lengthened in NALM. Also, the tuning range of the duration of NLP shows a difference based on the average nonlinear coefficient selected.

In order to improve the accuracy and expand the range of the phase-shifting algorithm application, a precise three-step phase retrieval algorithm suitable for the interferograms with less than one fringes numbers is proposed. The proposed method improves the accuracy, on the one hand because normalization and subtraction are introduced to reduce background intensity fluctuation, on the other hand because Lissajous ellipse fitting (LEF) method is introduced to reconstruct phase maps from the normalized and Gram-Schmidt (GS) orthonormalized maps. Because the approximation operations for cumulative sum aren’t used in the GS method, the proposed algorithm is suitable for not only interferograms that the fringes numbers are more than one but also interferograms that fringes numbers are less than one. Moreover, the proposed method can be applied to simple and complex patterns. Thus, the proposed algorithm has a wider range of applications. The proposed algorithm’s reliability and performance are confirmed by simulations and experiments.

We report on the generation of high-order solitons with order continuously adjustable in an erbium-doped fiber laser mode-locked by a graded index multimode fiber–step index multimode fiber–graded index multimode fiber (GIMF–SIMF–GIMF) saturable absorber (SA). The SA has advantages of high damage threshold, easy fabrication and low cost. The fundamental soliton to eleventh-order soliton were obtained by adjusting the pump power and PC. It was found that both increasing pump power and adjusting PC can affect the solitons splitting during experiment. The generation of high-order solitons is due to the peak power clamping effect of laser cavity and the pulse shaping effect of GIMF–SIMF–GIMF SA. Last but not least, this is the first time to adjust the order of solitons continuously from the first to eleventh in a fiber laser mode-locked by GIMF–SIMF–GIMF SA.

In this article, we numerically research the generation of Dissipative-Soliton-Resonance (DSR) pulse in anomalous dispersion regime based on spectral filtering effect. We find that a strong spectral filtering effect can limit the spectrum broadening and avoid the pulse breaking up in the high effective gain of the cavity, which leads to the formation of DSR pulse. Meanwhile, we also find that the peak power of DSR pulse increases with the saturation power, which is in line with the case in normal dispersion regime. As a comparison, the DSR pulse cannot be obtained in the absence of spectral filtering effect, which proves that the generation of DSR pulse needs strong spectral filtering effect in anomalous dispersion regime. We believe that our work can be served as a theoretically guideline to investigate the generation of DSR pulse in anomalous dispersion regime.

In this article, the peak-power expression of dissipative-soliton-resonance (DSR) pulse is derived, in a normal-dispersion fiber laser, by using the equation for the resonance curve and the relationship between the parameters of cubic–quintic complex Ginzburg–Landau (CGLQ) equation and the cavity parameters. According to the peak-power expression, the peak power of DSR pulses is inversely proportional to the average dispersion and the square of the gain bandwidth, is proportional to the square of the saturation power. That is to say, we can improve the peak power of DSR pulse in three ways: Firstly, increase the saturation power in the case of sinusoidal-saturable-absorber transmission curve; secondly, decrease the gain bandwidth properly; thirdly, decrease the average dispersion suitably. In addition, the further results of numerical simulations are obtained by using pulse-tracing technique, which are in good agreement with the theoretical derivation of peak power of DSR pulses. This means that our work can serve as a guideline to design high-peak-power DSR fiber laser.

Circular polarization shift-keying (CPolSK) modulation is crucial for optical communication in free space optical communication. In this paper, we propose a new optical communication system with multiple orbital angular momentum (OAM) modes for division multiplexing CPolSK modulation signals. A well-designed reference beam is employed to interfere with the CPolSK-OAM-division multiplexing (CPolSK-OAM-DM) signals for coherent detection. Then, the complex modulation signal is converted into intensity change directly detected by photo-detector. The communication performance can be further improved by subtracting the two interference beams detected. In numerical simulation, the demodulated bit error rate (BER) is 2.25 × 10−4 with the signal noise ratio (SNR) of 12-dB, and it can be reduced to 1.25 × 10−4 after difference operation. Through mapping the signals to both the initial phases and circular polarization states of the multiplexing channels, we construct the phase-CPolSK-OAM-DM system, the demodulated BER is 1.07 × 10−4 with the SNR of 15-dB. The results demonstrate that the CPolSK-OAM-DM modulation can effectively expand the communication capacity of the CPolSK system. The CPolSK-OAM-DM system has great potential in the field of high-speed broadband optical communications.

A phase retrieval method from three interferograms based on normalized vector is proposed to achieve high accuracy and less time computation. It needn’t pre-filtering for the interferograms, which reduces its complexity and shortens the processing time. The difference maps are used to filter out the background intensity after compensating the fluctuation. Then, the normalized vector is used to obtain tested phase distribution with high precision. It is suitable for simple and complex fringes. Moreover, the phase can be correctly extracted when the fluctuation of background intensity and modulation amplitude is existed. The reliability of the algorithm is verified with simulated and experimental data.

A multiwavelength erbium-doped fiber laser based on tunable comb spectral filter and intensity-dependent loss modulation is proposed and experimentally demonstrated. The laser allows fine and multifunctional tunable operations of channel-spacing, peak-location, spectral-range, and wavelength-number. More specifically, channel-spacing switch from 0.4 nm to 0.2 nm and peak-location adjustment within half of free spectrum range are obtained via controlling the tunable comb filter. The wavelength-number and the spectral-range of the lasing lines can be accurately controlled by intensity-dependent loss modulation in the laser cavity, enabled by a power-symmetric nonlinear optical loop mirror. In addition, fine control over the wavelength-number at fixed spectral-range is realized by simply adjusting the pump power. More important, the tunable operation process for every type of specific parameter is individual, without influences for other output parameters. Such features of this fiber laser make it useful and convenient for the practical application.

The outbreak of an infectious disease characterized by severe symptom of gout has set great threat to several major goose-producing regions in China since December 2016. The causative agent for the novel infection has been identified was a novel goose-origin astrovirus (GoAstV). Lack of effective detection methods indeed hinders further research, as well as prevention and control of GoAstV. Keep this in mind, a TaqMan-based one-step real-time quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) assay for rapid detection of GoAstV was developed. Primers and probe were targeting the capsid protein gene sequence (ORF2). The method is capable of detecting quite low number of targeting nucleic acid as low as 10 copies/μL. What's more, it is also of great specificity and repeatability for GoAstV detection. No cross-activity was found with other goose-origin viruses. The assay had excellent intra-assay and inter-assay repeatability with the coefficient of variation (CV) value from 0.48% to 0.99%. A total of 340 GoAstV specimens from different regions of China were used in this study to verify the feasibility and effectiveness of this method in clinical diagnosis. The results indicated that qRT-PCR is a highly sensitive, specific and repeatable method for quantitative detection of GoAstV, which can be used to detect this virus, thereby facilitating epidemiological investigations of gout in goslings.

Based on the quantum-behaved particle swarm optimization (QPSO) algorithm and the discrete layer peeling (DLP) approach, we propose a scheme to design the right-angled triangular spectrum fiber Bragg gratings (RTS-FBGs). In this method, for a target reflectivity spectrum, the DLP approach is used to generate an appropriate initial guess of the complex coupling coefficients, and the QPSO technique is applied to optimize the initial complex coupling coefficients. For the QPSO method, the whole complex solution space can be searched for the coupling coefficients. Using the proposed method, single- and multi-channel RTS-FBGs are designed. Simulation results demonstrate that the edge of the right-angled triangular spectrums designed by our method is quite linear and the shape of the spectrum is also very consistent with the target spectrum, in contrast to those obtained by existing method. The RTS-FBGs can find potential applications in wavelength interrogation in optical sensor system.

A tunable multiwavelength erbium-doped fiber laser is proposed and experimentally studied. The intensity-dependent loss (IDL) in a nonlinear optical loop mirror is utilized for stable multiwavelength lasing output. The accurate switch operation, i.e., the lasing lines emerge/disappear one by one at the longer wavelength side of the initial one, is achieved by adjusting the intra-cavity loss using a variable attenuator. The effect of the intra-cavity loss on the lasing characteristics is theoretically analyzed. Numerical results confirm the experiment measurements and suggest that both the IDL and the gain spectrum, which vary with the intra-cavity loss, lead to the observed tunable lasing behavior.

The covariance matrix method is a simple method for solving the Zernike polynomial with the higher fitting precision. In this paper, it was used to analyze the several optical wave fronts of the fine polished aluminum disk surface captured by a Twyman-Green interferometer system. We had found that the PV (peak-to-valley) and rms (root-mean-square) values of the wave front aberration changes with changing the Zernike term and the expressions for the several optical wave fronts with the different sampling dots were wrong. By analyzing the relations among the condition number of the coefficients matrix, the Zernike term, and the number of the sampling dots, it was indicated that the number of the sampling dots had only reduced the fluctuation the PV and the rms value while the Zernike term increases, but did not change the case that the expressions for the wave front aberration were wrong when the Zernike term is larger than 14, especially when the number of the sampling dots is less. Such an analysis will be valuable in solving the Zernike polynomial for the wave front aberration analysis by using the covariance matrix method in optical testing.

Based on the mutated adaptive quantum-behaved particle swarm optimization (MAQPSO) algorithm and the discrete layer peeling (DLP) algorithm, we propose a method to design triangular-spectrum fiber Bragg gratings (TS-FBGs). In this method, the DLP algorithm is used to generate an appropriate initial range of the index modulation, and the MAQPSO technique is applied to optimize the index modulation within this range. The quantum-behaved particle swarm optimization algorithm with mutation operation can improve the search performance of this algorithm. We purposely use a linear weighting factor for the fitness value function in view of the linear edge triangular-spectrum. This dramatically accelerates the convergence in the numerical implementation. Using the proposed method, a 0.2 nm bandwidth TS-FBG is designed and the performance is shown to be better than previously reported results in the literature. Then, a 2.5 nm bandwidth TS-FBG is reconstructed; it is indicated that a short grating length can be used to realize the TS-FBG with chirp-free structure so that complex phase modulation is avoided in fabrication. Finally, a triple-channel TS-FBG with sampled-free structure is successfully designed and optimized. We also present an analysis on the tolerance of the design method over possible fabrication error.

The deduction of Zernike coefficients is usually influenced by the finite number of sampling dots on interferogram and their inherited measurement errors. In this paper, a simplified Gram–Schmidt method for solving the Zernike polynomial with the higher fitting precision is presented and used to analyze the wave front aberrations for the circle interference fringe of the fine polished aluminum disk surface captured by a Twyman-Green interferometer system. We find the stability of the Zernike coefficients changes with changing the Zernike term, which has lead to the wrong expression for the wave front aberration. By analyzing the condition number of the coefficients matrix and the fitting precision of the method, it is indicated that the instability can be avoided when the Zernike term is lower than 14. Such an analysis will be valuable in solving the Zernike polynomial for the wave front aberration analysis in optical testing.