We present a detailed investigation on higher order mode suppression due to differential gain in large mode area step index fiber amplifiers with confined Yb doping using spatially and spectrally ...resolved imaging (S 2 ). A novel active fiber with Yb doping confined to the central 30% of the core area is fabricated and its performance is directly compared to a fiber with a conventional homogeneously doped core with almost identical parameters. At high pump rates, S 2 and beam pointing stability measurements clearly demonstrate fundamental mode operation of the confined doping few mode fiber, even under imperfect launching conditions and environmental perturbations. In addition, we discuss the mode content as a function of gain in co-pumped fiber amplifiers with and without confined rare earth core doping using a power propagation model for fibers with similar parameters to those used in our experiments. Our simulation results as well as amplification experiments indicate the great potential of the confined doping concept for single mode high power operation.
Abstract
We report on a compact, highly sensitive all-fiber accelerometer suitable for low frequency and low amplitude vibration sensing. The sensing elements in the device are two short segments of ...strongly coupled asymmetric multicore fiber (MCF) fusion spliced at 180° with respect to each other. Such segments of MCF are sandwiched between standard single mode fibers. The reflection spectrum of the device exhibits a narrow spectrum whose height and position in wavelength changes when it is subjected to vibrations. The interrogation of the accelerometer was carried out by a spectrometer and a photodetector to measure simultaneously wavelength shift and light power variations. The device was subjected to a wide range of vibration frequencies, from 1 mHz to 30 Hz, and accelerations from 0.76 mg to 29.64 mg, and performed linearly, with a sensitivity of 2.213 nW/mg. Therefore, we believe the accelerometer reported here may represent an alternative to existing electronic and optical accelerometers, especially for low frequency and amplitude vibrations, thanks to its compactness, simplicity, cost-effectiveness, implementation easiness and high sensitivity.
We report on the use of a multi-core fibre (MCF) comprising strongly-coupled cores for accurate strain sensing. Our MCF is designed to mode match a standard single mode optical fibre. This allows us ...to fabricate simple MCF interferometers whose interrogation is carried out with light sources, detectors and fibre components readily available from the optical communications tool box. Our MCF interferometers were used for sensing strain. The sensor calibration was carried out in a high-fidelity aerospace test laboratory. In addition, a packaged MCF interferometer was transferred into field trials to validate its performance under deployment conditions, specifically the sensors were installed in a historical iron bridge. Our results suggest that the MCF strain sensors here proposed are likely to reach the readiness level to compete with other mature sensor technologies, hence to find commercial application. An important advantage of our MCF interferometers is their capability to operate at very high temperatures.
We demonstrate a deep-learning-based fiber imaging system that can transfer real-time artifact-free cell images through a meter-long Anderson localizing optical fiber. The cell samples are ...illuminated by an incoherent LED light source. A deep convolutional neural network is applied to the image reconstruction process. The network training uses data generated by a setup with straight fiber at room temperature (∼20 ° C) but can be utilized directly for high-fidelity reconstruction of cell images that are transported through fiber with a few degrees bend or fiber with segments heated up to 50°C. In addition, cell images located several millimeters away from the bare fiber end can be transported and recovered successfully without the assistance of distal optics. We provide evidence that the trained neural network is able to transfer its learning to recover images of cells featuring very different morphologies and classes that are never “seen” during the training process.
We propose and demonstrate a compact and simple vector bending sensor capable of distinguishing any direction and amplitude with high accuracy. The sensor consists of a short segment of asymmetric ...multicore fiber (MCF) fusion spliced to a standard single mode fiber. The reflection spectrum of such a structure shifts and shrinks in specific manners depending on the direction in which the MCF is bent. By monitoring simultaneously wavelength shift and light power variations, the amplitude and bend direction of the MCF can be unmistakably measured in any orientation, from 0° to 360°. The bending sensor proposed here is highly sensitive even for small bending angles (below 1°).
Sensitive optical experiments in fiber, including for applications in communications and quantum information, are limited by the noise generated when light scatters from thermally excited ...guided-acoustic phonons. Novel fibers, such as microstructured fibers, offer control over both optical and acoustic waveguide properties, which can be designed to mitigate optomechanical noise. Here, we investigate the optomechanical properties of microstructured anti-resonant hollow-core fibers and demonstrate their promise as a low-noise fiber platform. By developing an ultra-sensitive spectroscopy technique, a seven capillary anti-resonant hollow-core fiber is found to exhibit record low optomechanical coupling (<10−4 W−1 m−1), in agreement with comprehensive numerical calculations. The largest scattering occurs from a guided acoustic mode in the air confined in the core of the fiber. Acoustic resonances in the silica, due to minimal overlap with the optical mode in the core, scatter a hundred times less, resulting in negligible depolarization noise. The largest optomechanical interactions in anti-resonant hollow-core fibers are found to be at least three (five if evacuated) orders of magnitude weaker than those in conventional single-mode fibers, which makes this class of fibers a promising platform for low noise applications, including quantum information processing and optical communication.
We report the design of micro-bend-resistant low-differential-mode-group-delay (low-DMGD) few-mode fibers that support up to six mode groups (12 LP modes, 21 spatial modes) and that are adapted to ...multiple-input multiple-output mode-division-multiplexed transmissions. Compared to previous designs, the micro-bending sensitivity is reduced by more than a tenfold factor with acceptable impacts on attenuation, effective area, and DMGD for 2, 3, and 4 mode groups, but with some degradation for five and six mode groups. These fibers also exhibit low coupling between their mode groups, which is beneficial for DMGD compensation and multiple-input multiple-output processing. Based on these designs, we fabricate and characterize a 4-mode-group (6-LP-mode, 10-spatial-mode) fiber with a micro-bending sensitivity reduced by a factor up to 20 compared to previous realizations. This sensitivity is even lower than that of typical standard single-mode fibers, which should allow the deployment in most telecommunication networks without significant induced losses. A DMGD-compensated link with values ≤72 ps/km is also realized. Finally, we show that previous fibers with 5 and 6 mode groups already have low micro-bending sensitivities, which should prevent from using micro-bend-resistant designs which, in these cases, can degrade the attenuation, effective area and DMGD.
In this letter, we demonstrate how the soliton-plasma interaction initiates trapping of the generated dispersive waves (DWs) in an experimentally feasible tapered He-filled hollow-core anti-resonant ...fiber (HC-ARF). We show that the taper gradient strongly influences the pulse trapping dynamics and thus determines the intensity and blueshift of the trapped DW. This process leads to an efficient DW generation down to 100 nm with a 3.4-octave supercontinuum spanning 100-1150 nm (2.73 PHz) by tapering a 36-μm core HC-ARF to 18 μm under 19-bar He, pumped at 800 nm with 6-μJ pulse energy. The proposed fiber taper structure could be an alternative route to generate light in the extreme ultra-violet (EUV) spectral range using moderate gas pressure and relatively low pulse energy.
Fiber-optic imaging systems play a unique role in biomedical imaging and clinical practice due to their flexibilities of performing imaging deep into tissues and organs with minimized penetration ...damage. Their imaging performance is often limited by the waveguide mode properties of conventional optical fibers and the image reconstruction method, which restrains the enhancement of imaging quality, transport robustness, system size, and illumination compatibility. The emerging disordered Anderson localizing optical fibers circumvent these difficulties by their intriguing properties of the transverse Anderson localization of light, such as single-mode-like behavior, wavelength independence, and high mode density. To go beyond the performance limit of conventional system, there is a growing interest in integrating the disordered Anderson localizing optical fiber with deep learning algorithms. Novel imaging platforms based on this concept have been explored recently to make the best of Anderson localization fibers. Here, we review recent developments of Anderson localizing optical fibers and focus on the latest progress in deep-learning-based imaging applications using these fibers.
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