Anton N. Kolyadin

Light transmission in negative curvature hollow core fiber in extremely high material loss region

In this paper we demonstrate the light transmission in a spectral range of 2.5 to 7.9 µm through a silica negative curvature hollow core fiber (NCHCF) with a cladding consisting of eight capillaries. A separation between the cladding capillaries was introduced to remove the additional resonances in the transmission bands. The measured optical loss at 3.39 µm was about 50 dB/km under a few modes waveguide regime.

Hollow-core revolver fibre with a double-capillary reflective cladding

We report the fabrication of the first hollow-core revolver fibre with a core diameter as small as 25 μm and an optical loss no higher than 75 dB km-1 at a wavelength of 1850 nm. The decrease in core diameter, with no significant increase in optical loss, is due to the use of double nested capillaries in the reflective cladding design. A number of technical problems pertaining to the fabrication of such fibres are resolved.

Photonic jets produced by microspheres integrated with hollow-core fibers for ultraprecise laser surgery

Recently it was proposed to use sharply focused optical beams produced by dielectric microspheres, also termed “photonic nanojets”, in contact laser surgery applications. The proposed designs were based on using multimodal beams and suffered from limited efficiency. In this work we developed single-mode designs of such devices providing higher efficiency and significantly smaller focal spot sizes compared to multimodal systems. The proposed single-mode systems include: i) diode-pumped Er:YAG laser source operating at the wavelength corresponding to the maximal water absorption peak in the tissue (λ = 2.94 μm), ii) low-loss hollow-core microstructured fiber delivery, and iii) high-index (n~1.8) focusing barium-titanate glass microsphere integrated with the fiber. By testing the system in air we demonstrated the focal spot diameters to be less than 4λ. Our numerical modeling shows a principal possibility to achieve diffraction-limited spot sizes on the order of λ/2. Due to the fact that the location of the photonic jet at the sphere surface is not strongly affected by the presence of fluid such systems can find applications in ultraprecise contact intraocular, brain or cellular microsurgeries.

Application of Negative Curvature Hollow-Core Fiber in an Optical Fiber Sensor Setup for Multiphoton Spectroscopy

In this paper, an application of negative curvature hollow core fiber (NCHCF) in an all-fiber, multiphoton fluorescence sensor setup is presented. The dispersion parameter (D) of this fiber does not exceed the value of 5 ps/nm × km across the optical spectrum of (680–750) nm, making it well suited for the purpose of multiphoton excitation of biological fluorophores. Employing 1.5 m of this fiber in a simple, all-fiber sensor setup allows us to perform multiphoton experiments without any dispersion compensation methods. Multiphoton excitation of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) with this fiber shows a 6- and 9-fold increase, respectively, in the total fluorescence signal collected when compared with the commercial solution in the form of a hollow-core photonic band gap fiber (HCPBF). To the author’s best knowledge, this is the first time an NCHCF was used in an optical-fiber sensor setup for multiphoton fluorescence experiments.

Negative curvature hollow core fibers for Raman lasing in the mid IR spectral range

In this paper we consider a problem of using negative curvature hollow-core fibers for creation of Raman lasers in the mid IR spectral range. New designs of this type of fibers with cladding formed by one layer of double nested capillaries are discussed and their optical properties are investigated numerically and experimentally. It will be shown that it is possible to reduce the Raman generation threshold by decreasing an effective mode area in such fibers using nested capillaries in the cladding.

The Design Optimization and Experimental Investigation of the 4.4 μm Raman Laser Basedon Hydrogen-filled Revolver Silica Fiber

Optical properties of hollow-core revolver fibers are numerically investigated depending on various parameters: the hollow-core diameter, the capillary wall thickness, the values of the minimum gap between the capillaries, the number of capillaries in the cladding and the type of glass (silica and chalcogenide). Preliminary, similar calculations are made for simple models of hollow-core fibers. Based on the obtained results, the optimal design of the revolver fiber for Raman laser frequency conversion (1560 nm to 4420 nm in H2) was determined. As a result, efficient ns-pulsed 4420 nm Raman laser based on H2-filled revolver silica fiber is realized. Quantum efficiency as high as 36 % is achieved and output average power as high as 250 mW is demonstrated.

1.56 μm Sub-microjoule femtosecond pulse delivery through low-loss microstructured revolver hollow-core fiber

Being capable of light localization in the large air-filled core, microstructured hollow-core fibers (HCF) are highly promising for a long-distance high-power ultra-short pulse (USP) delivery due to extremely low fiber nonlinearity. Among them negative-curvature revolver hollow-core fiber (RHCF) having a cladding formed with a single layer of non-touched cylindrical silica glass capillaries [1] is the most beneficial for high power USP delivery owing to its cost-effective fabrication technology (due to much more simple fiber design) in comparison with hypocycloid Kagome [2] or hexagonal-cladding [3] hollow-core photonic crystal fibers; very low group velocity dispersion (GVD) [4] and outstanding localization of the fundamental mode (more than 99.993%) [1], which means only ∼10−4 part of total optical power travelling inside silica glass elements of the fiber. In this work we develop and optimize high-power all-fiber USP MOPA source emitting femtosecond pulses with ∼1 MW peak power in the telecom spectral band near 1.56 μm and demonstrate long-distance high power pulse delivery through 11.7 m-long air-filled RHCF with attenuation of less than 30 dB/km and acceptable output beam quality (M2∼1.4).

Hollow Core Fibers with Single and Double Nested Capillaries Cladding and Fiber Based Raman Lasers

The revolver hollow core fibers of three different types were fabricated, including fibers with double nested capillaries in the cladding. Efficient hydrogen Raman lasers (1064 ⇒1907 nm) based on all of these fibers were demonstrated.