Abstract:Arrayed waveguide gratings (AWGs) are extensively employed in fiber Bragg grating (FBG) interrogation systems due to their compact size, lightweight nature, and excellent interrogation performance. The resolution and total measurement range of AWG-based FBG interrogation systems are constrained by the output properties of AWG. We proposed an AWG-based large dynamic range interrogation system. The temperature dependence of AWG is exploited to achieve continuous interrogation. The test results show that the interrogation system has a dynamic range of 28.67 nm, an interrogation accuracy better than 25 pm, and a wavelength resolution of 6 pm.

Abstract:In this paper, an actively Q-switched wavelength injection locking random fiber laser (RFL) based on random phase-shifted fiber Bragg grating (RPS-FBG) is proposed, and the performance of the laser is verified by experiments. Within the reflection bandwidth range of RPS-FBG, spanning from 1 549.2 nm to 1 549.9 nm, different laser modes with stable central wavelength and peak power can be selectively chosen by varying the injected light wavelength. The power fluctuation within 1 h is less than 0.1 dBm, and the central wavelength drift is less than 0.02 nm. When the pump power increases from 90 mW to 300 mW, the pulse width decreases from 3.2 μs to 1.5 μs, and the pulse repetition frequency is 20 kHz. The RFL can reach a stable locking state at the lowest pump power of 100 mW and the lowest injection power of 3 dBm. When the wavelength is locked, the output pulse is a single pulse. On the contrary, the unlocked output pulse is multi-pulse. The laser has the characteristics of high wavelength tunability in the reflection range of RPS-FBG and it can be an ideal light source in the fields of laser imaging and pulse coding.

Abstract:In this paper, a grapefruit microstructure fiber (GMF) temperature sensor coated with liquid crystal (LC) based on waist-enlarged taper is proposed and fabricated, and its temperature sensing characteristics are analyzed. The waist-enlarged taper is formed at the fusion point between single mode fiber (SMF) and GMF. The capillary glass tube is sleeved outside GMF, LC is filled into the capillary glass tube, and its two ends are finally sealed to form a sensor. The experimental results show that when the length of GMF is 2.5 cm, the temperature sensitivity of the sensor can reach up to 195.3 pm/°C in the range of 30—90 °C, and it has a good stability for reuse. Thereby, it can be used in biochemical, industrial production and other temperature detection areas.

Abstract:A passively Q-switched all-fiber laser is demonstrated using a 10-cm-long bismuth-doped fiber (BDF) as a saturable absorber (SA). The dual-wavelength operation was obtained due to the nonlinear effect inside the fabricated BDF, which has a high germanium content. Stable Q-switched pulses were obtained at the dual synchronous wavelengths of 1 530.1 nm and 1 531.1 nm. When the pump power is tuned from 105.3 mW to 191.0 mW, the repetition rate can be varied from 82.6 kMz to 117.6 kHz. The maximum pulse energy and average output power were 83.4 nJ and 9.8 mW, respectively while the minimum pulse width was 8.5 μs at the maximum pump power of 191.0 mW. Our results indicate that BDF could be a promising alternative optical modulator for pulsed fiber laser application.

Abstract:This article analyzes the transmission line characteristics of plasmonic hybrid metal insulator metal (HMIM) waveguide, circular ring resonator (CRR) based dual-band band-pass filters with two transmission poles in both pass-bands in the optical regime using coupled line feed. The transmission line characteristics of an HMIM waveguide, such as characteristic impedance (ZPV), effective refractive index (neff) and propagation length (Lspp), have been obtained by using full wave simulation. Using basic HMIM slot waveguide, a CRR with periodic loading of double- and triple-ring CRR is numerically analyzed. Two input ports have been used for excitation, which are located at the separation of 180° positions along the CRR, and are coupled with the ring by parallel coupled lines, producing the dual pass-bands with the synchronous excitation of two transmission poles. The proposed double-ring dual-band band-pass filter (DR-DB-BPF) offers 35 dB extinction ratio (ER), 299.69 nm free spectral range (FSR) and narrow band full width half maximum (FWHM) of 78.057—112.43 nm. The triple-ring DB-BPF (TR-DB-BPF) has 22.5 dB ER, FSR of 292.18 nm and FWHM of 42.751—59.58 nm. The proposed filters are very useful in the development of dual-band filters for electronic photonic integrated circuits (EPICs), as the optical signals are filtered at two wavelengths simultaneously.

Abstract:In order to improve the problems that the minimum hamming weight (MHW) of the polar codes of the traditional Gaussian approximation (GA) construction is small and its performance is not good enough, an improved channel construction algorithm of polar codes based on frozen bits is proposed by combining the construction of the Reed-Muller (RM) code to effectively increase the MHW and analyzing the correcting and checking functions of the frozen bits in the successive cancellation list (SCL) decoding. The construction algorithm selects the channel with the smaller row weight corresponding to the information channel in the channel construction stage, and some channels are set as the frozen channels under the proposed frozen channel setting principle. So the proposed construction algorithm not only eliminates the channels with the smaller row weight and optimizes the distance spectrum of polar codes, but also makes full use of the checking ability of the frozen bit in SCL decoding to improve the error correction performance of polar codes. The polar codes constructed by this algorithm are named as FRM-polar codes. The simulation results show that the proposed FRM-polar codes have a larger performance gain than the RM-polar codes and the polar codes constructed by GA under different code-lengths. In addition, the proposed construction algorithm has the same complexity as the construction algorithm of the RM-polar codes.

Abstract:In this paper, a photonic crystal fiber (PCF) with a dispersion-engineered and high nonlinear coefficient has been designed for supercontinuum generation (SCG) and frequency comb generation (FCG). The proposed PCF has a Si3N4 rod in the core. This rod provides more optical confinement in the core by increasing the refractive index of the core. This high confinement reduces the effective mode area of PCF and thus increases the nonlinear coefficient. The effective mod area and the nonlinear coefficient are obtained as 0.814 μm2 and 25 W-1m-1, respectively. By varying different parameters for dispersion engineering, a suitable dispersion profile for the structure has been obtained so that the proposed PCF has two zero dispersion wavelengths (ZDWs) at 900 nm and 1 590 nm. By injecting a pumping with power of 1 kW and duration of 50 fs at a wavelength of 1 555 nm to the designed PCF with a length of 4 mm, the output spectrum is broadened in the range from 800 nm to 3 500 nm. For FCG by the four-wave mixing (FWM) method, phase matching conditions must be provided, and for that, the pumped wavelength must be in the anomalous dispersion regime and near ZDW. As a result, two continuous wave lasers pumping at the wavelengths of 1 551 nm and 1 558 nm have been injected into the PCF and optical frequency combs (OFCs) with a pulse width of 1 nm and a free spectral range of 7 nm has been obtained.

Abstract:The origin of Angelica dahurica medicinal herbs varies, and their pharmacological effects also differ. In order to achieve rapid and accurate identification of the origin of Angelica dahurica medicinal herbs, this study utilizes laser induced breakdown spectroscopy (LIBS) technology combined with machine learning algorithms to identify the original source of Angelica dahurica. Sliced samples of Angelica dahurica were taken from four regions:Hebei, Henan, Zhejiang, and Sichuan. The spectral data from the sliced samples were used as features, and different algorithms including support vector machine (SVM), back propagation (BP) neural network, genetic algorithm-back propagation (GA-BP) neural network, particle swarm optimization-back propagation (PSO-BP) neural network, convolutional neural network (CNN), and CNN-SVM were employed to classify the origin of Angelica dahurica samples. The results show that the average prediction accuracy of the BP, GA-BP, and PSO-BP algorithms reached 89.64%, 89.66%, and 89.93%, respectively. The average prediction accuracy of the SVM, CNN, and CNN-SVM algorithms reached 89.92%, 90.32%, and 90.53%, respectively. The average prediction accuracy improved when the two algorithms were combined, and the CNN-SVM algorithm showed a 44% increase in the lowest prediction accuracy compared to the SVM algorithm. Overall, the combination of the CNN-SVM algorithm and LIBS technology demonstrated the best performance for identifying the origin of Angelica dahurica, a traditional Chinese medicinal herb, and can provide reference for the origin identification of medicinal materials.

Abstract:We have reported the characteristics of a Z-scan for the poly(azaneylylidene-acylene) (DAZA) polymer, as nonlinear medium with a large nonlinear phase shift using continuous-wave (CW) laser beam. It has been verified that the Fresnel diffraction model is applicable for analyses of Z-scan measurements with DAZA polymer at high laser power. It was found that Z-scan curves with peak-to-valley features appear as the applied light intensity increases in the case of a large nonlinear phase shift. The Z-scan experiments were carried out using a CW laser to verify the theoretical calculations in the case of a large nonlinear phase shift model. Our results show good agreements between the experimental data and the proposed theoretical models.

Abstract:This paper is devoted to introduce a novel four-dimensional memristor-involved system and its applications in image encryption and chaotic circuit. The typical dynamical behaviors of the memristor-involved system are explored, such as chaotic phase potraits, Lyapunov exponent spectrum (LES), bifurcation diagram (BD) and complexity analysis. Then a color image encryption algorithm is designed. In this algorithm, the sequences generated by the four-dimensional memristor-involved system are used in scrambling and diffusion algorithm for three channels. The algorithm analysis results based on key space, key sensitivity, information entropy, histogram distribution, correlation coefficients, data loss and noise attacks indicate that the proposed algorithm can improve the security of the color image encryption algorithm. Finally, the memristor-involved chaotic circuit is implemented by using some discrete components. The experimental results of hardware circuit are consistent with the Multisim simulation results and the numerical simulation results. The research results have certain universality and portability, and can provide technical support for the subsequent analysis of other nonlinear circuits and the application of chaotic secure communication.