Currently, the power handling capability of optical fibers is primarily limited by glass damage thresholds and induced nonlinearities, including stimulated Brillouin scattering and stimulated Raman scattering. In order to mitigate unwanted nonlinear effects, a majority of high power delivery fibers have increased core sizes, which are generally used near the threshold of multimode operation. Under high power, thermal changes lead to transverse mode instabilities which degrade the overall beam quality. We have been investigating hollow core fibers based on the anti-resonant effect (ARHCF) due to their excellent guiding properties, such as low loss, large core sizes, wide transmission windows, and significantly increased optical nonlinearity and damage thresholds. Anti-resonant HCFs have significantly simpler designs compared to other microstructured fibers, namely photonic bandgap fibers, which leads to more flexibility and less complex fabrication. An ARHCF design was optimized in Comsol Multiphysics for single mode operation, low propagation loss, and low bending loss. The ARHCF was fabricated at the University of Central Florida. Initial testing has shown that power handling up to 170 W input, 0.7 GW/cm2 at the fiber facet is possible with no damage to the fiber.
Many applications rely on the ultra-precise timing of optical signals through fiber, such as fiber interferometers, large telescope arrays, in phase arrayed antennae, optical metrology, and precision navigation and tracking. Environmental changes, specifically those caused by temperature fluctuations, lead to variations in the propagation delay of optical signals and thereby decrease the accuracy of the system’s timing. The cause of these variations in delay is the change in the glass properties of the optical fiber with temperature. Both the refractive index of the glass and the length of the fiber are dependent on the ambient temperature. Traditional optical fiber suffers from a delay sensitivity of 39 ps/km/K. We are reducing the temperature sensitivity of the fiber delay through the application of a novel design of optical fiber, Anti-Resonant Hollow Core Fiber. The major improvement in the thermal sensitivity of this fiber comes from the fact that the light is guided in an air core, with very little overlap into the glass structure. This drastically reduces the impact that the thermally sensitive glass properties have on the propagation time of the optical signal. Additionally, hollow core fiber is inherently radiation insensitive, due to the light guidance in air, making it suitable for space applications.
Many applications rely on the ultra-precise timing of optical signals through fiber, such as fiber interferometers, large telescope arrays, in phase arrayed antennae, optical metrology, and precision navigation and tracking. Environmental changes, specifically those caused by temperature fluctuations, lead to variations in the propagation delay of optical signals and thereby decrease the accuracy of the system’s timing.
The cause of these variations in delay is the change in the glass properties of the optical fiber with temperature. Both the refractive index of the glass and the length of the fiber are dependent on the ambient temperature. Traditional optical fiber suffers from a delay sensitivity of 39 ps/km/K. We are reducing the temperature sensitivity of the fiber delay through the application of a novel design of optical fiber, Anti-Resonant Hollow Core Fiber. The major improvement in the thermal sensitivity of this fiber comes from the fact that the light is guided in an air core, with very little overlap into the glass structure. This drastically reduces the impact that the thermally sensitive glass properties have on the propagation time of the optical signal. Additionally, hollow core fiber is inherently radiation insensitive, due to the light guidance in air, making it suitable for space applications.
A simple, interferometric force sensor based on a multicore optical fiber (MCF) that operates in reflection mode is presented. The device consists of a short segment of MCF inserted at the distal end of a conventional single mode optical fiber (SMF). To demonstrate the concept we used a mechanical piece with grooves to press the MCF. In this way the external force on the MCF is converted in localized pressure on the fiber which causes attenuation losses to the interfering modes and makes the interference pattern to shrink. The changes experienced by the interference pattern can be easily monitored. The sensor here proposed is highly sensitive since it can resolve forces down to 0.01 N.
In this work, we demonstrate the use of particularly characterised multicore optical fibres (MCFs) to devise compact, compellingly simple, ultrasensitive interferometric sensors which are capable of sensing single or multiple physical parameters. Generally, our devices operate in reflection mode and consist of a few centimetres of MCF fusion spliced to standard single-mode optical fibre (SMF). The tools and instrumentation needed to fabricate our devices are a conventional fibre cleaver and a fusion splicing machine. We demonstrate a highly-sensitive bending sensor (inclinometer) with a MCF with three strongly coupled cores which is capable of distinguishing multiple bending or inclination orientations, and also a force sensor based on MCF with seven coupled cores. In both cases the devices are interrogated with a low-power LED and a miniature spectrum analyser. Bending or force on the MCF induces drastic changes of the supermodes, their excitation, and consequently, on the reflected spectrum (interference pattern).
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