Hu Liang

Accurate real-time monitoring of moisture and wear debris in lubricating oil is critical for ensuring the stable operation and extended service life of industrial machinery. This paper proposes a dual-parameter optical fiber sensor based on a tapered photonic crystal fiber (PCF) structure cascaded with a fiber Bragg grating (FBG). The sensor exploits the strong evanescent field interaction between the tapered PCF region and the lubricating oil. By monitoring the wavelength shifts of envelope 1 and interference dip 2 in the transmission spectrum, simultaneous detection of moisture (0-1%) and iron-based wear debris (0-100 μg‧mL^-1) is achieved. Experimental results demonstrate moisture sensitivity of 28.61 nm/% and wear debris sensitivity of 0.212 nm/(μg‧mL^-1), with dual-parameter decoupling relative errors below 5%. A cascaded FBG enables temperature compensation over the range of 40-65 °C, enhancing measurement reliability under varying thermal conditions. The proposed sensor features straightforward fabrication and robust anti-interference capability, offering an effective solution for multiparameter online monitoring of industrial lubricating oil.

The fiber Mamyshev oscillator (MO), as a high-performance fiber oscillator that delivers high-peak-power pulse, has been intensively investigated. However, one major difficulty in the MO is the self-starting capability, and rare efforts have been dedicated to unveil the real-time soliton dynamics of the all-fiber self-starting MO. Herein, we construct an all-fiber self-starting erbium-doped Mamyshev oscillator, and by utilizing time-stretching dispersive Fourier-transform (TS-DFT) technique, we reveal the distinct dynamical diversity of pulsating solitons. Firstly, the self-starting mode-locking process is studied, in which the evolution from noise to mode-locking state is found. Subsequently, a variety of soliton pulsation states are studied, such as invisible soliton pulsation, and even a chaotic pulsation state. More interestingly, we further investigate invisible soliton molecule pulsation and soliton explosion of soliton molecule. It is found that the occurrence of invisible pulsation is mainly due to self-phase modulation (SPM) effect which exists in nonlinear optical fiber systems. To the best of our knowledge, this is the first observation of invisible soliton molecule pulsation in an all-fiber erbium-doped MO. In addition, optical turbulence and harmonic mode-locking are also observed. We believe our work is of great significance to enrich the study of nonlinear physics in dissipative systems. These experimental observations will enrich the understanding of pulse dynamics in the fiber MO, which will have prospective applications including laser micromachining and frequency comb ranging fields.

In this paper, we propose an optical high-fidelity decryption technology for Visual Cryptography (VC) based on incoherent optical polarization exclusive NOR (XNOR) operation. The plaintext image is divided into two binary ciphertexts by the Random-Grid-based Visual Secret Sharing (RGVSS) algorithm. These ciphertexts are printed onto the polarizing films with orthogonal polarization. The P- and S-polarizing pixels in the polarizing films represent the “black” and “white” pixels of the ciphertexts, respectively. Due to the optical transmission property of polarizing film, the pixel in the decrypted image appears bright only when the stacked pixels for the two ciphertexts have the same polarizing orientation. High-fidelity image decryption is then achieved. The proposed technology has been successfully demonstrated through simulation and experimentation. Thanks to its advantages of no pixel expansion, incoherent illumination, being free of computer assistance, and flexibility of ciphertext carriers, this method provides a broad prospect for convenient, large-format, high-fidelity information recovery applications for VC.

Due to the ability of optical modulators to achieve rapid modulation of optical signals, meeting the demands of high-speed data transmission, modulators based on different novel nanomaterials have become one of the research hotspots over the past dacade. Recently, TiN/Ti₃C₂ heterojunction exhibits highly efficient thermo-optic performance and extremely strong stability. Therefore, we have demonstrated an all-optical modulator based on the principle of Michelson interference and the thermo-optic effect in this paper. The modulator employs a TiN/Ti₃C₂ heterojunction-coated microfiber (THM) and further demonstrates its ability to generate phase shifts through an ASE light source. The modulator, with a phase shift slope of 0.025π/mW, can also convert the phase shifts of signal light into amplitude modulation through Michelson interference. The fixed signal light wavelength is 1552.09 nm, and the modulation depth is stable at about 26.4 dB within a wavelength detuning range of −10 to 6 nm; The waveforms of signal light at modulation rates of 500 Hz, 1000 Hz, 2000 Hz, and 3000 Hz were tested, and a 3 dB modulation bandwidth of 2 kHz was measured. The all-optical modulator based on THM has the advantages of high efficiency and stability and has broad application prospects in the fields of all-optical signal processing and high-speed optical communication.

In this study, the organic dye methylene blue (MB) is used as the dopant to modify TiO _{2− x} to form TiO _{2− x} -MB, which can be utilized as a saturable absorber (SA) in mode-locked fiber lasers at 1.55 μm and 2.0 μm for generating ultrashort pulses.

The use of a quadrupolar-wound coil of conjoined-tube anti-resonant fiber (CTF) in an interferometric air-core fiber optic gyroscope (FOG) is proposed and demonstrated. The CTF coil has low transmission loss and high modal purity, resulting in a long-term bias stability of 0.016 deg/h for the integration time of 1000 s. Furthermore, when compared to a gyro operated with conventional polarization-maintaining fiber (PMF) coil of the same length and diameter, the conjoined-tube anti-resonant fiber optic gyroscope (CTFOG) has an 11.2-fold reduction in thermal sensitivity, rendering the CTF a promising technological approach to efficiently improve the thermal stability of FOG in the future.

A thin-diameter photonic crystal fiber (TDPCF) magnetic field sensor based on hole collapse and infiltration is proposed and demonstrated. Due to the controlled hole collapse in TDPCF, the interaction between the mode field distribution and the magnetic fluid (MF) is effectively strengthened, causing the direct absorption and scattering of magnetic nanoparticles to transmitted light. Consequently, the proposed sensor exhibits a magnetic field sensitivity of up to 0.099 dB/Oe within the range of 0 to 60 Oe. The TDPCF-based magnetic field sensor has several desirable merits such as high sensitivity, convenient integration, and good stability, which provides a promising candidate in environmental and industrial-related magnetic field monitoring applications.