We report on the multidimensional characterization of femtosecond pulse nonlinear dynamics in a tellurite glass graded-index multimode fiber. We observed novel multimode dynamics of a quasi-periodic ...pulse breathing which manifests as a recurrent spectral and temporal compression and elongation enabled by an input power change. This effect can be assigned to the power dependent modification of the distribution of excited modes, which in turn modifies the efficiency of involved nonlinear effects. Our results provide indirect evidence of periodic nonlinear mode coupling occurring in graded-index multimode fibers thanks to the modal four-wave-mixing phase-matched via Kerr-induced dynamic index grating.
We demonstrate birefringence enhancement in an optical fiber with artificial core anisotropy. A nanostructured fiber core in the form of a glass slab with layers of germanium-doped silica interleaved ...with the layers of fluorine-doped silica enabled an increase of the birefringence of 0.54×10 -4 without any stress zones. The experimental result confirms the numerical prediction of birefringence enhancement over previously presented fibers by increasing the refractive index contrast between the two core base glasses. Birefringence improvement has been achieved only by core material engineering and not by adding any stress zones or other approaches involving cladding shaping and core geometry design. The modification introduced to core had no impact on the guiding performance of the realized fiber, which remained perfectly matched to the SMF-28 standard in terms of its numerical aperture NA = 0.11 and the effective mode-field diameter MFD = 10.1 μm at the wavelength of 1550 nm.
Efficient collection of photoluminescence arising from spin dynamics of nitrogen vacancy (NV) centers in diamond is important for practical applications involving precise magnetic field or ...temperature mapping. These goals may be realized by the integration of nanodiamond particles with optical fibers and volumetric doping of the particles alongside the fiber core. That approach combines the advantages of robust axial fixation of NV diamonds with a direct spatial overlap of their fluorescence with the guided mode of the fiber. We developed a suspended core silicate glass fiber with 750 nm-diameter nanodiamonds located centrally in the 1.5 µm-core cross-section along its axis. The developed fiber probe was tested for its magnetic sensing performance in optically detected magnetic resonance measurements using a 24 cm-long fiber sample, with the NV excitation and fluorescence collection from the far ends of the sample and yielding optical readout contrast of 7% resulting in 0.5 µT·Hz
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magnetic field sensitivity, two orders of magnitude better than in earlier designs. Thanks to its improved fluorescence confinement, the developed probe could find application in magnetic sensing over extended fiber length, magnetic field mapping or gradiometry.
The power scaling of single mode fiber lasers and amplifiers, due to the wide area of applications, has been the subject of great interest for many years. Increasing the mode area seems to be the ...obvious way to scale up the output power level from the single emitter if you consider well-known limitations like nonlinear effects, material damage threshold or thermal lensing. The nanostructurization of the fiber core is a method to control precisely optical properties of the active fiber. This method allows to design and develop the fiber with the core of any arbitrary defined refractive index distribution, with precision not available with other known fiber technology. The nanostructurization also open up an opportunity to incorporate simultaneously various active and non-active glasses into the fiber core. Those advantages can be used to fabricate the new class of fibers for laser applications. Here we show ytterbium doped phosphate single-mode fiber with nanostructured core, which is the first proof-of-concept of active fiber with entirely nanostructured core area.
We report an experimental study on transmission of orbital angular momentum mode in antiresonant fibers generated with a dedicated all-fiber optical vortex phase mask. The vortex generator can ...convert Gaussian beam into vortex beams with topological charge l = 1. Generated vortex beam is directly butt-coupled into the antiresonant fiber and propagates over distance of 150 cm. The stability and sensitivity of the transmitted vortex beam on the external perturbations including bending, axial stress, and twisting is investigated. We demonstrate distortion-free vortex propagation for the axial stress force below 0.677 N, a bend radius greater than 10 cm.
We present first fiber Bragg grating (FBG) inscribed in polarization maintaining (PM) optical fiber with artificially anisotropic core achieved by an appropriate distribution of discrete ...germanium-doped areas in nanoscale. We proved that this FBG reveals unique properties. Its single-resonance spectral shape, strain and temperature sensitivities are similar to that for grating written in cylindrically symmetrical optical fiber, which indicates that it behaves as the grating fabricated in a non-PM fiber, whereas it is written in the fiber that preserves the orthogonal polarization components of the mode. Moreover, due to the relatively low birefringence of the fiber, the FBG is insensitive to the excited polarization state and twist, and only a negligible shift of the spectrum is noticeable with no changes in its shape. Thus, FBG inscribed in ZEBRA fiber is a kind of hybrid structure that can be used for all-fiber lasers that generate polarized wave, as well as for polarization fiber sensors and components with spectral insensitivity to random or intentional twist.
Fibre bundle (FB)-based endoscopes are indispensable in biology and medical science due to their minimally invasive nature. However, resolution and contrast for fluorescence imaging are limited due ...to characteristic features of the FBs, such as low numerical aperture (NA) and individual fibre core sizes. In this study, we improved the resolution and contrast of sample fluorescence images acquired using in-house fabricated high-NA FBs by utilising generative adversarial networks (GANs). In order to train our deep learning model, we built an FB-based multifocal structured illumination microscope (MSIM) based on a digital micromirror device (DMD) which improves the resolution and the contrast substantially compared to basic FB-based fluorescence microscopes. After network training, the GAN model, employing image-to-image translation techniques, effectively transformed wide-field images into high-resolution MSIM images without the need for any additional optical hardware. The results demonstrated that GAN-generated outputs significantly enhanced both contrast and resolution compared to the original wide-field images. These findings highlight the potential of GAN-based models trained using MSIM data to enhance resolution and contrast in wide-field imaging for fibre bundle-based fluorescence microscopy. Lay Description: Fibre bundle (FB) endoscopes are essential in biology and medicine but suffer from limited resolution and contrast for fluorescence imaging. Here we improved these limitations using high-NA FBs and generative adversarial networks (GANs). We trained a GAN model with data from an FB-based multifocal structured illumination microscope (MSIM) to enhance resolution and contrast without additional optical hardware. Results showed significant enhancement in contrast and resolution, showcasing the potential of GAN-based models for fibre bundle-based fluorescence microscopy.
We demonstrate the development of anti-resonant hollow core fibers functionalized with nanodiamonds and their application to ODMR-based and microwave-free magnetic field gradiometry. The diamond ...particles were uniformly deposited from a solvent suspension on the inner surfaces of two 50 cm long hollow-core fiber sensors. This enabled efficient excitation of the diamond fluorescence using 532 nm light, as well as collecting the nitrogen vacancy color center red fluorescence to the hollow fiber guided modes, which facilitated fully guided mode operation of each sensor with 400 nT/sqrt(Hz) sensitivity. Two fiber probes in a differential arrangement provided magnetic field gradient measurement with a 35 mT dynamic range without the presence of microwaves. Specific applications, like the control of magnetic switching in spintronics computing, could benefit from accurate and microwave-free readout modalities for mT-scale magnetic fields. The demonstrated hollow core fiber probes fulfill these requirements. They combine the robustness and the possibility of macroscopic separation between the scanned target and the readout location due to the guiding of the NV fluorescence, while maintaining a dynamic range that matches state-of-the-art single-crystal diamond-based sensors.
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•Demonstration of a 50 cm-long magnetically sensitive silica hollow core fibers with fluorescent diamonds in the air core.•Demonstration of 400 nT/sqrt(Hz) field sensitivity when the NV light is excited and collected from the fiber’s far ends.•35 mT dynamic range magnetic field gradiometry by employing a differential measurement with or without microwaves.•Room temperature diamond introduction into fiber compatible with concentration scaling or bio-functionalized diamonds.
We present the experimental verification of a new type of an active nanostructured fiber devoted to simultaneous laser emission at two wavelengths: 1040 nm and 1534 nm in the fundamental mode. The ...fiber core is formed with two types of nanorods made of a phosphate glass doped with either Yb 3+ or co-doped with Yb 3+ /Er 3+ ions, respectively. A distribution of the nanorods in the core allows to control relative gain and modal properties of the fiber at both wavelengths and to maintain the single mode performance with a high quality beam generated in a single fiber core. The double-cladding fiber structure allows efficient excitation with a single 975 nm diode pump laser. As a proof-of-concept we demonstrated an active fiber with 15 µm core diameter composed of 6649 nanorods with an individual diameter of 160 nm. The fiber was used in a laser setup. The laser operation was verified for simultaneous two-color laser generation at output power levels of 0.78 W and 0.42 W with slope efficiency of 23.0% and 9.8% at 1040 nm and 1534 nm, respectively.
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