Optical Fiber Technology最新文献

We present a nondestructive measurement based on filtered back projection (FBP) for the distribution of rare-earth dopant in optical fibers. Based on the approach, a measurement system is established, where the single-mode pumped laser illuminates the fiber under test from the side, generating multi-wavelength fluorescence through photoluminescence (PL). The distribution of rare-earth doped particles is proportional to the distribution of fluorescence intensity. The projection images are collected by the CCD camera at 90° relative to the excitation arm. According to the computed tomography (CT), the rotation of the optical fiber enables the experimental measurements of intensity information extracted from multi-angle projections. The rare-earth dopant distribution of the fiber is reconstructed by the improved filtered back projection algorithm, which improves the quality of the reconstructed result by incorporating total variation (TV) algorithm. To evaluate the proposed approach, rare-earth dopant distribution is compared with results measured by EPMA, exhibiting a correlation coefficient above 0.99, and the relationship between the dopant distribution and the refractive index is analyzed. Measurements on doped particle distributions at various wavelengths are conducted, and the fluorescence spectrum are constructed to further analyze the fluorescence characteristics of rare earth doped fiber. Measurement of RE dopant distribution will be useful for quality evaluation and optimization of partial active optical fibers.

We theoretically demonstrate the propagating performance of twin beams generated in a Sagnac fiber loop by developing a practical model of optical parametric loop mirror consisting of an optical coupler with adjustable splitting ratio, a nonlinear fiber, a dispersion element, and two tunable attenuators placed at different positions in the loop. Two situations of frequency degenerate and frequency non-degenerate four-waving mixing are considered and various of factors including dispersion conditions, internal losses in the loop, and splitting ratios of the coupler are investigated in detail. When the splitting ratio of the coupler is 1:1 and no loss is in the loop, both the frequency degenerate and non-degenerate twin beams can propagate from different ports completely by introducing proper dispersion, and switching between phase-sensitive and phase-insensitive amplification can be realized by changing the dispersion within the loop. In general, the propagation of signal and idler beams at the two output ports of the fiber loop are influenced by both the splitting ratio of the coupler and the internal loss within the loop. Adjusting the internal loss can partially compensate for the asymmetry of the splitting ratio of the coupler, facilitating spatial separation of the signal and idler beams. Our research is useful for the generation of twin beams using Sagnac fiber loop and the realization of switchable phase-sensitive amplifiers.

For the measurement of relative humidity, this study employed Surface Plasmon Resonance (SPR) technology, a sensor with a micro-conical fiber structure (sensing length is only 375 μm) was combined with Polyvinyl Alcohol (PVA) to create a humidity sensor that is highly sensitive, compact, dense, and exhibits good linearity. The humidity sensor is based on a gold film (thickness of about 40 nm) on the surface of the miniature fiber optic structure, and by applying PVA coating, the SPR humidity sensor shows resonance peaks in the transmission spectrum in ambient air, and as the number of layers of PVA coating (thickness) is added, the resonance peaks’ positions are red-shifted. The experimental findings demonstrated that this SPR humidity sensor’s sensitivity was 0.162 nm/%RH at an initial resonance wavelength of about 550 nm (one layer) and about 1.542 nm/%RH at an initial resonance wavelength of 656 nm (five layers) in the range of 46 %RH to 93 %RH. The wavelength and the relative humidity had a good linear connection. Temperature tests revealed the sensor has a −0.152 nm/°C temperature sensitivity between 20 °C and 50 °C and has a high linearity (0.999). Therefore, the sensor has potential applications in humidity measurement.

Machine learning plays a significant role in various fields. As a fundamental part of machine learning, matrix operations are one of the most important computational parts of neural networks. However, the advancement of Moore’s law is hindered by limitations in the number and size of transistors on electronic chips. Therefore, implementing an optical neural network (ONN) using photonic devices to accomplish matrix–vector multiplication (MVM) has attracted significant attention. Compared with traditional electronic neural networks, ONN exhibits faster computational speed, higher parallel input capability and greater energy efficiency. Nevertheless, crosstalk and signal loss are inevitable characteristics in optical signal transmission, which can degrade the performance of ONN. In this paper, we present analysis models and simulations to assess the effects of crosstalk and loss on optical computing systems. We have observed that the accuracy of ONN degrades when crosstalk and loss are present. In severe cases, ONN is unable to complete the classification task. To mitigate the interference of crosstalk, we have designed a novel double-layer structure to reduce the number of optical devices required for signal transmission and optimize the impact of crosstalk on ONN performance. For the identical classification task, the ONN based on a double-layer structure exhibits better interference immunity than the generic ONN, with a 10% performance improvement. In particular, performance is improved by 50% when only crosstalk is considered.

We demonstrated a new type of metal-oxide heterostructures, Gallium-Doped Zinc Oxide (Ga:ZnO) as a saturable absorber (SA) for the generation of a Q-switched laser operating in the 1.55 μm region. The Ga:ZnO was fabricated by a sonochemical approach and then it used the embedding method to combine it with polyvinyl alcohol (PVA) to form a thin film. The Ga:ZnO PVA film was effectively incorporated into a ring cavity to produce a Q-switched pulse laser. The Ga:ZnO PVA film has a modulation depth of ∼13 % with a saturation intensity of 0.09 MW/cm². The high pulse energy and maximum average output power of 315.76 nJ and 16.12 mW were achieved. The SA film has a repetition rate within a range of 25.94 to 51.05 kHz, while the pulse width decreased from 10.93 µs to 2.215 µs, respectively. This is the first time that Ga:ZnO PVA has been used in fiber laser applications.

We successfully investigate the generation of Q-switched pulses utilizing two distinct forms of silver nanoparticles (AgNPs): AgNPs thin film and AgNPs powder. Employing a green synthesis approach with AgNO3 and Oolong tea extract, AgNPs were fabricated as saturable absorbers (SAs) for Q-switching. The AgNPs thin film SA exhibited a remarkable repetition rate of 79.53 kHz, coupled with a pulse width of 2.38 µs and a pulse energy of 1.08 nJ. In contrast, AgNPs powder achieved a repetition rate of 40.53 kHz, a pulse width of 3.33 µs, and a pulse energy of 2.03 nJ. Notably, the AgNPs thin film demonstrated superior stability with a signal-to-noise ratio (SNR) of 55.07 dB compared to the powder’s SNR of 50.65 dB. These findings underscore the significant impact of the physical form of saturable absorbers on pulse characteristics, offering promising avenues for diverse applications in telecommunication, optical fiber sensors, and material processing. The novelty lies in comparing different physical forms of AgNPs as saturable absorbers, revealing distinct performance metrics and highlighting their potential for various technological applications.

The straightness perception of scraper conveyor is a technology that helps to achieve intelligent operation of coal mine working faces. However, there is a problem of accuracy degradation caused by sensor torsion based on fiber Bragg grating (FBG) shape sensing technology. This paper proposes an accuracy compensation method based on torsion angle, and verifies the effectiveness of accuracy compensation through simulation and experimental research. Experimental tests have shown that when the torsion angle of the sensing substrate is 10° and 20°, the end accuracy of the reconstructed curve after accuracy compensation is increased by 2.77% and 1.93% compared to before compensation, respectively. This study indicates that compensation based on the torsion angle can significantly improve the accuracy of two-dimensional (2D) curve reconstruction, and it has broad engineering application prospects in fields such as straightness perception of scraper conveyors and monitoring of underwater pipelines.

We demonstrate a fiber optic accelerometer for low frequency vibration detection in this paper. A slider moving along a guide rail is suspended over an optical fiber into which a fiber Bragg grating (FBG) is inscribed. When acceleration signal acts on our sensing structure, the slider will vibrate vertically under the constraint of the optical fiber, inducing the change of FBG axial strain and we can therefore establish the relationship between vibrational acceleration and wavelength shift. Laboratory measurements validate the effectiveness of the derived theoretical results that the sensor owns a low natural frequency of 9.5 Hz and a high sensitivity up to 926.29 pm/g from 0.5 to 9 Hz. The sensor structure also shows a good ability to resist lateral interference that the cross-sensitivity is calculated as 0.3%.

We have developed both theoretically and experimentally an all polarization-maintaining fiber-based master oscillator power amplifier (MOPA) system, which allows for amplifying the single-frequency continuous-wave (CW) fiber laser to >20 W without compromising the laser intensity noise (−110 dBc/Hz@ relaxation oscillation peak) at the specific wavelength of ∼1540 nm. The experimental results agree well with the simulated results. To the best of our knowledge, this is the first demonstration of a ∼1540-nm single-frequency all fiber laser and reaching such a high-power level. The amplified laser features a narrow linewidth of ∼1.4 kHz and a spectral side-mode-suppression ratio of >38 dB, even as the laser wavelength is tuned from 1538.216 nm to 1540.616 nm. It is believed to be the narrowest laser linewidth realized in the <1550-nm wavelength band of an Erbium-Ytterbium co-doped fiber MOPA system. The all polarization-maintaining configuration of the MOPA ensures the amplified laser linearly polarized with the polarization extinction ratio of >22 dB and power root mean square fluctuations of <0.2 %@1h. This high-performance single-frequency fiber laser is expected to be an ideal pump source in the spin-exchange relaxation-free (SERF)-based atomic sensors after second harmonic generation.

Arterial pulse wave monitoring has been recognized as an effective medical diagnostic tool for various cardiovascular diseases. To overcome the barriers in traditional, complex, and expensive detection configurations, new electronic and optical sensors have been developed with their unique advantages. Particularly, various configurations of fiber-optic sensors have been proposed. This paper demonstrates the use of a tapered optical fiber structure to create a sensitive sensor that can detect carotid arterial pulse waves on the skin surface. The demonstrated fiber sensor probe utilizes an in-line Mach-Zehnder interferometer configuration and liquid-gold film coating on the sensor tip to enhance its sensitivity and demonstrate its use by encapsulating the sensor with a flexible elastomer material for detecting arterial pulse waves with a simple testing configuration. Considering the simple fabrication and high sensitivity without a complex demodulation scheme, the proposed sensor has broad implementation in biomedical health monitoring systems.