In this study, a refractive-index guiding single-crystal fiber (SCF) with air–solid cladding was proposed and numerical simulation investigation was carried out. In general, refractive-index guided ...cladding was constructed through air-holes in the solid material. It resulted in the effective reduction in the number of guided-modes, and the single-mode and few-mode transmission could be realized. The influences of different materials with different refractive indices, cladding structure, and fabrication errors on the confinement loss and effective guided-mode number with the variation in wavelength from 2.5 to 3.2 µm were numerically investigated by the finite element method. Thus, the optimal design of the SCF was successfully obtained. This study may open a new avenue for the design of SCFs and their applications in the fiber lasers and sensors.
All-normal dispersion supercontinuum generation (SG) in a large hollow core photonic crystal fiber (PCF) infiltrated with carbon tetrachloride is studied experimentally. The PCF is optimized to have ...a flat normal dispersion in a broadband range (0.8–1.7 µm) varying from -150 to 0 ps/nm/km. The effective mode area at pump wavelength (λ=1030 nm) is as large as 42.2 µm2 and readily meets the requirements for an all-fiber supercontinuum system. Infiltration of the core with carbon tetrachloride ensures a high nonlinear coefficient of the fiber equal to 22 1/W/km. Using an off-the-shelf 1030 nm fiber laser with 400 fs and 25 nJ input pulses, we generated an all-normal supercontinuum in the 850–1250 nm wavelength range.
This research investigates the visible upconversion luminescence which is induced by multiphoton absorption of soft glass fiber defects. The study of this phenomenon has thus far been restricted to ...standard silica fibers. We observed the emission of green and cyan light as a consequence of fiber material ionization. We investigate both the commercial ZBLAN step index and in-house-made tellurite nanostructured graded-index fibers. For the latter, the analysis of the luminescence signal permits us to determine the core and cladding refractive index difference. Upconversion luminescence is a powerful tool for characterizing soft glass fibers and a promising platform for innovative photonic technologies and mid-IR applications.
We report on successful refractive index profiling of commercially available step-index and in-house made graded-index multimode specialty optical fibers by means of X-ray computed microtomography. ...Our results demonstrate that the latter is an advantageous technique for characterizing large core optical fibers, which allows for retrieving information about the refractive index at optical frequencies by exploiting the absorption coefficient of X-rays.
We report on near-infrared supercontinuum generation in a submeter-long single-mode, nanostructured core fiber. The fiber core is composed of few thousand pure silica and germanium-doped silica glass ...nanorods with diameter of 200 nm each. The nanorods’ distribution is calculated based on the Maxwell–Garnett effective medium approach to mimic effective parabolic refractive index distribution in the fiber core. The standard stack-and-draw method was used to scale down the fiber structure and obtain subwavelength nanorods in the core. Size and distribution of individual nanorods are essential to determine modal and dispersion properties of the fiber without assistance of air holes in the fiber cladding. We study supercontinuum generation performance in this nanostructured core fiber pumping with low-cost microchip laser operating at 1550 nm with 1 ns pulse length and pulse energy of 0.4 µJ. A modulation instability-driven supercontinuum is generated in the fiber, covering a wavelength span of 1400–2300 nm. Due to possibility of dispersion engineering and all-solid structure the nanostructured fibers offer new possibilities for development of low-cost all-fiber supercontinuum light sources for the near-infrared range and cascaded ultrabroadband supercontinuum all-fiber systems.
Development of photonic crystal fibers made of two or more types of glasses can be of considerable advantage in designing of specific properties of photonic crystal fibers. Replacing air holes with a ...medium with different refractive index provides an additional degree of freedom in fiber dispersion designing. Multi-component oxide glasses can be easily modified by changing the concentration of its ingredients, which in turn changes thermo-mechanical and optical properties of glass. In this paper, we discuss feasibility of joint thermal processing of two types of glasses for photonic crystal fiber drawing. Specifically, we optimize composition of our in-house synthesized high-alkaline borosilicate glass. A series of six- and seven-component glasses synthesized in
SiO
2
--B
2
O
3
--Al
2
O
3
--(BaO)--Li
2
O--Na
2
O--K
2
O
oxide system was examined in experiments of combining with commercial lead-silicate glasses F2 and SF6. Joint thermal processing was validated by demonstration of successfully drawn structures of all-solid glass photonic crystal fibers. Critical glass parameters for thermal process of preform fabrication and subsequent fiber drawing, such as thermal expansion coefficient, characteristic viscosity temperatures and crystallization susceptibility were measured, and matched to F2 and SF6 glasses by optimizing composition of borosilicate glasses.
Here, we provide experimental verification supporting the use of short-section imaging bundles for two-photon microscopy imaging of the mouse brain. The 8 mm long bundle is made of a pair of ...heavy-metal oxide glasses with a refractive index contrast of 0.38 to ensure a high numerical aperture NA = 1.15. The bundle is composed of 825 multimode cores, ordered in a hexagonal lattice with a pixel size of 14 μm and a total diameter of 914 μm. We demonstrate successful imaging through custom-made bundles with 14 μm resolution. As the input, we used a 910 nm Ti-sapphire laser with 140 fs pulse and a peak power of 9 × 10
W. The excitation beam and fluorescent image were transferred through the fiber imaging bundle. As test samples, we used 1 μm green fluorescent latex beads, ex vivo hippocampal neurons expressing green fluorescent protein and cortical neurons in vivo expressing the fluorescent reporter GCaMP6s or immediate early gene Fos fluorescent reporter. This system can be used for minimal-invasive in vivo imaging of the cerebral cortex, hippocampus, or deep brain areas as a part of a tabletop system or an implantable setup. It is a low-cost solution, easy to integrate and operate for high-throughput experiments.
In weakly coupled few mode fibers (FMFs), used in optical communication systems to increase data capacity, the difference between the effective refractive indices of successive spatial modes is a ...critical parameter. In this paper, we demonstrate that nanostructured FMFs composed of two different types of subwavelength glass rods can be used to effectively control the propagation properties of individual spatial modes. However, the design and optimization of such fibers proves challenging due to the large number of parameters associated with their free-form refractive index distribution. To address this problem, we use an optimization method based on generative inverse design networks (GIDNs) modified to account for the optical properties of weakly coupled FMFs. Our results show that a nanostructured FMF with a core containing multiple angularly modulated concentric rings can achieve differences between the effective refractive indices of 10 spatial modes exceeding 1.2 × 10−3, surpassing other forms of weakly coupled FMFs. Importantly, the parameters of the structure ensure the feasibility of fabricating the designed fibers. Compared to traditional FMF optimization using a deep neural network with a large, randomly generated data set, our method achieves comparable accuracy in predicting refractive index differences, while achieving better spatial mode separation with a six times smaller data set. By using our proposed approach, which could potentially be applied to the design of other types of optical fibers characterized by a large number of parameters, we can significantly reduce the number of training examples required and the time needed to achieve high-quality results.
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