•A new design of fast-response multi-segment hollow-core fiber gas cell for laser spectroscopy is demonstrated.•The setup utilizes 1.35-m-long hollow-core fiber segments arranged in series which are ...simultaneously filled with gas.•Direct absorption spectroscopy of methane at 1687 nm is used for setup characterization. Its pros and cons are discussed.•The pressure buildup and drawdown times are identified as a critical factor limiting the total response time the sensor.
Typically, hollow-core fiber (HCF)-based laser gas sensing systems use a single monolithic fiber as a gas cell. This results in a tradeoff between sensitivity which requires long optical fiber and sensor’s response time, that grows with the fiber length. Here we present a simple approach to solve this issue with new all-fiber modular gas cell design. The setup uses modified fiber mating sleeves to connect multiple HCFs in series, with optical loss of typically from 2 to 3 dB per connection. By injecting the sample gas at every second HCF-to-HCF connection, all HCF segments are filled simultaneously. We demonstrated the setups with two and four HCF segments, each with a length of 1.35 m. Laser absorption spectroscopy of methane near 1687 nm is used for setup characterization. Using the inlet pressure of 2 bar, the gas filling time is reduced over 13 times, from 77.9 s for a monolithic fiber, to only 5.9 s for the four-segment design (total HCF length of 5.4 m). With the pressure increased to 3 bar, the response time is further decreased to 3.6 s. Pressure buildup and drawdown times in the HCF were also examined.
We report development of ytterbium doped silica fiber with nanostructured core for laser applications. We study influence of non-continuous distributed Yb dopants on gain, beam quality, and fiber ...laser performance. The fiber core is composed of over 43 thousand nanorods with a central part doped with Yb. The diameter of each nanorod is 72 nm. With this method we obtained a flat refractive index profile with uniformity of 1.3 × 10
refractive index unit (RIU) despite the non-uniformity of 1.2 × 10
RIU in Yb doped preform rods used for the fiber development. We demonstrate a nanostructured core single-mode fiber laser with 61.8% of slope efficiency, and extremely low numerical aperture 0.027 of generated mode.
We present both a theoretical and an experimental study of a novel compact lensed fiber system utilizing a nanostructured GRIN lens. The lens can be integrated with an optical fiber, which ensures a ...unique and efficient focusing in any high index medium, such as a liquid. We use the effective medium approach to design lenses with arbitrary refractive index. To fabricate lenses, we utilize a discrete array of nano-sized rods made of two types of glasses, and apply a standard stack-and-draw fiber drawing technology. The fabricated nanostructured GRIN lenses have a parabolic refractive index profile with a diameter of a standard fiber, very short working distances (55 µm in the air) and a high numerical aperture (NA = 0.16). As a proof-of-concept of the new micro-lensed fiber system, we demonstrate an experiment on optical trapping of micrometer-sized glass beads. We also show that our method is compatible with optical fiber technology and allows for any shape of the refractive index distribution in 2D. Thanks to that a new functionality could be achieved by replacing the GRIN lens with an axicon lens, vortex type elements, micro-lenses arrays or diffraction elements.
•Three component lead-bismuth-gallium glasses have high susceptibility to crystallization.•Thermal stability of glass increased with SiO2 and GeO2 addition to its composition.•MidIR transmittance and ...nonlinearity decreased with growth of SiO2 concentration.•PbO–Bi2O3–Ga2O3 glasses with SiO2 and CdO additions are good material for PCF.•Stack-and-draw method of PCF fabrication was used with thermal stable glasses.
Three component PbO–Bi2O3–Ga2O3 glasses are characterized by high midIR transmittance, with a large susceptibility to crystallization. In this paper we investigate the increase in the thermal stability of these glasses by the addition of oxides such as GeO2, SiO2, Tl2O, CdO, Nb2O5. The resulting multicomponent glasses are well suited for the fabrication of microstructured fibers and micro-optical elements. The increased thermal stability of the modified multi-component glasses resulted in the IR absorption cut-off shifting to shorter wavelengths.
Abstract The development of bend‐induced effectively single‐mode fiber with a square cross‐section and flat top‐hat intensity distribution is reported using core topology nanostructuring dedicated to ...femtosecond laser ablation systems. The fiber's core comprises 5419 silica and germanium‐doped silica nanorods with a diameter of 430 nm each arranged into a hexagonal lattice. The distribution of the rods is calculated using in‐house developed code based on the Monte Carlo algorithm to obtain a target shape of mode and intensity distribution. As a proof‐of‐concept, a silica nanostructured fiber with a 24 µm core is developed and verified against the purity of mode guidance, bending, and guiding losses. It is shown that for a wavelength of 1030 nm, the fiber is effectively single‐mode with 96% mode purity when bending with a radius of 20 cm is applied. The fiber has a measured mode area of 360 µm 2 , numerical aperture of 0.03, and total losses of 0.07 dB m −1 .
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.
We present experimental results on fiber Bragg gratings inscription in nanostructured graded-index (nGRIN) and multi-step index (MSIN) optical fibers, both having non-uniform radial distribution of ...GeO
dopant in the fiber cores. In particular, the positive role of radial shaping the GeO
distribution in the fiber core on grating reflection efficiency is reported. We postulate that an appropriate spatial distribution of the germanium concentration that matches the fundamental mode profile improves grating spectral response due to more efficient grating-mode interaction, as compared with uniformly doped step-index optical fibers with the same overall doping level. Moreover, we show that radially shaped fibers exhibit moderately higher temperature responses than their step-index counterparts.
We report on efficient inscription of fiber Bragg gratings (FBGs) in a new type of single mode fiber with nanostructured core and with an effective parabolic graded index profile, using the standard ...phase mask method and a 248 nm pulsed laser. A nanostructured core allows to obtain high concentration of GeO
in subwavelength glass rods and simultaneously to maintain low average germanium dopant level of silica similarly to standard single mode fibers. We showed that in a nanostructured core fiber, a factor of 3 better efficiency in gratings inscription was achieved, although the fiber has 20% lower average concentration of GeO
with respect to SMF-28. In the nanostructured fiber we obtained a significant improvement in temperature sensitivity, while the strain sensitivity of FBG in nGRIN optical fiber is the same as in case of standard single-mode fiber (SMF-28). We have measured the strain sensitivity of 0.72 × 10
1/με (1.11 pm/με@1.53μm), and the temperature sensitivity is about 30% higher than for FBG in SMF-28 and equals to 10.2 × 10
1/K (15.6 pm/K@1.53μm).
We report on modeling, development, and optical characterization of fused silica photonic crystal fiber with germanium doped microinclusion placed in the middle of the core. The fiber is designed to ...efficiently couple and guide LP02 mode. It offers high optical density in the center region, large mode separation, low losses, and small dispersion with relatively flat profile for both LP01 and LP02 modes in 1-1.6 µm wavelength range. We demonstrate that by changing geometrical and material parameters of the inclusion partially independent tuning of propagation constants of individual modes is possible, what might be found is a variety of potential applications, e.g., in nonlinear optics. We also show that diffraction-limited propagation of LP02 mode in free space can be exploited in microscopy or lab-on-a-chip systems, where the proposed fiber can be used for light delivery.
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