RU2834670C1 - Fibre-optic structure for pumping laser - Google Patents

Abstract

FIELD: electric elements; lasers.

SUBSTANCE: invention relates to fibre-optic continuous laser radiation generators. Optical fibre structure for pumping laser comprises cladding, active fibre doped with ytterbium ions, with possibility of generation of radiation in range of 1000-1028 nm, according to invention comprises active fibre with side pumping, consisting of an active fibre doped with ytterbium ions with a variable diameter and a passive fibre with a variable diameter, fibre Bragg gratings, fibre combiners, wavelength-stabilized pumping laser diodes, wherein doping of active fibre core with ytterbium ions makes 50-90 % of core diameter with concentration in range of 200-500 ppm.

EFFECT: elimination of waveguide modes of higher orders, optimization of temperature mode of laser operation and increase of threshold of mode instability effect.

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Description

Field of technology

The invention relates to fiber optic generators of continuous laser radiation and can be used in industrial enterprises.

One of the important requirements for modern laser systems, in particular for those used for further pumping of active media, is high efficiency of conversion of pump radiation power into radiation power at the required wavelength. In this case, better absorption of pump radiation and better conversion efficiency are achieved if the pump radiation has high brightness (high value of the optical beam quality). When using optical fiber doped with active ytterbium ions as a pumped active medium, high generation efficiency provides an acceptable level of heating of the active fiber, due to a low quantum defect (the difference in the pump radiation frequency and the laser generation frequency). When using a bulk crystal as a pumped active medium, for example, yttrium-aluminum garnet doped with ytterbium ions (Yb: YAG), which is usually pumped with radiation at a wavelength in the range of 940-970 nm, high generation efficiency can also be achieved by using pump radiation with a longer wavelength and with a higher brightness, which ensures a lower quantum defect. For an active medium doped with ytterbium ions, if the operating wavelength of laser generation is in the range of 1030 nm, then it is possible to use a source with a close wavelength as pumping, for example, in the range of 1010 nm, which ensures an acceptable quantum defect (in the region of 2%) and, accordingly, an acceptable operating temperature mode of the active medium. When pumping an active Yb: YAG crystal, in order to ensure a high quality value of the optical beam generated by the optical radiation element, a high quality value of the optical beam of the pump radiation (high brightness) is also necessary. Therefore, a highly efficient laser source of pump radiation with a generation wavelength in the range of 1000-1028 nm with a high-quality optical beam is necessary for the creation of modern multi-cascade laser systems [1, 2].

The level of development of fiber-optic laser technologies currently allows achieving output generation powers of the order of 0.9 kW at a wavelength of 1010 nm with a differential generation efficiency of 70%, and 0.75 kW at a wavelength of 1007 nm, with a differential generation efficiency of 64% [2]. To obtain such generation parameters, a special configuration of an all-fiber laser system is required, including special active fibers, diode pump modules, and a heat-removal system that prevents the occurrence of thermal effects, in particular, mode instability [3]. To prevent parasitic generation at wavelengths in the 1030 nm range, it is necessary to use fibers with a reduced concentration of ytterbium ions.

State of the art

A high-power, super-bright, low-noise pump source [4] is known from the prior art, made with one or more combined multimode seed sources, which produces a smooth light signal λp, preferably with a wavelength of 975 nm or any other desired wavelength in the range of 974-1030 nm. The multimode seed source can be made in the form of a fiber component or in the form of a multimode laser diode, and the output light signal can reach a power of several hundred watts.

The specified prototype does not provide elimination of higher order waveguide modes.

Disclosure of the essence of the invention

The objective of the invention is to improve the structural elements of the device.

The technical result of the invention consists in eliminating waveguide modes of higher orders, ensuring high quality of the optical beam of generated radiation. An additional technical result is an increase in the threshold of occurrence of the mode instability effect. The design of the invention also allows for optimal heat removal of excess thermal power.

The fiber-optic structure of the laser source contains wavelength-stabilized pumping laser diodes, an active fiber doped with ytterbium ions, providing laser generation in the range of 1000-1028 nm. The device is equipped with an active fiber with lateral pumping, which consists of an active fiber with a variable diameter, doped with ytterbium ions and a passive fiber (satellite) with a variable diameter. The device also contains fiber Bragg gratings and a fiber combiner.

Passive optical fibers, in a coating containing scattering microparticles (for example, hexagonal boron nitride), provide uniform scattering of residual optical power into the surrounding space (termination of residual optical radiation) from one of the fiber Bragg gratings, uniform scattering of the optical power of spontaneous luminescence, and uniform scattering of unabsorbed pump radiation.

The device shell consists of a metal alloy and allows for spiral laying of optical fibers with an optimal bending radius. The shell provides optimal heat removal from active and passive fibers, reducing the thermal load on optical fibers, which leads to an increase in the threshold for the occurrence of the mode instability effect.

The active fiber has a special doping profile with ytterbium ions, which leads to selective amplification of waveguide modes in the active fiber and helps improve the quality of the output optical beam, while the doping of the core with ytterbium ions is 50-90% of the core diameter with a concentration in the range of 200-500 ppm.

Wavelength-stabilized laser diodes are used as pump modules.

The fiber combiner allows the use of more than one laser diode to pump the active medium in different directions relative to the propagation of the generated radiation: in the opposite direction, in the same direction, and in two directions simultaneously.

Bragg gratings provide generation of radiation at the required wavelength in the range of 1000-1028 nm.

Implementation of the invention

Example #1

The pump combiner combines the radiation of several laser pump diodes to achieve the optical power required to pump the active fiber. The active fiber core is doped with ytterbium ions to 70% of the core diameter with a concentration of 200 ppm. The radiation from the diode pump source excites the active fiber ions in the ground state and initiates their transition to upper energy levels, thus creating a population inversion. A resonator formed by fiber Bragg gratings provides laser generation at a wavelength determined by the reflection wavelength of the gratings. The output fiber of the fiber unit is welded to another active element that needs to be pumped. As a result, the device generates radiation at the required wavelength of 1020 nm.

Example #2

The pump combiner combines the radiation of several laser pump diodes to achieve the optical power required to pump the active fiber. The active fiber core is doped with ytterbium ions to 90% of the core diameter with a concentration of 500 ppm. The radiation from the diode pump source excites the active fiber ions in the ground state and initiates their transition to upper energy levels, thus creating a population inversion. A resonator formed by fiber Bragg gratings provides laser generation at a wavelength determined by the reflection wavelength of the gratings. The output fiber of the fiber unit is welded to another active element that needs to be pumped. As a result, the device generates radiation at the required wavelength of 1010 nm.

Bibliography:

1) Dergachev A., Samartsev I., Gapontsev V. High-power, rare-earth-doped crystal amplifier based on ultra-low-quantum-defect pumping scheme Utilizing single or low-mode fiber lasers: patent. 11316319 USA. - 2022.

2) Platonov N. et al. High-efficient kW-level single-mode ytterbium fiber lasers in all-fiber format with diffraction-limited beam at wavelengths in 1000-1030 nm spectral range //Fiber Lasers XVII: Technology and Systems. - SPIE, 2020. - T. 11260. - C. 1126003.

3) Smith A.V., Smith J.J. Mode instability in high power fiber amplifiers //Optics express. -2011. - T. 19. - No. 11. - C. 10180-10192.

4) Gapontsev V., Samartsev I. HIGH-POWER FIBER PUMP SOURCE WITH HIGH-BRIGHT LOW-NOISE OUTPUT RADIATION IN THE WAVELENGTH RANGE OF 974-1030 nm. - 2016. RU 2591586.

Claims (1)

A fiber optic structure for a pump laser, comprising a cladding, an active fiber doped with ytterbium ions, with the ability to generate radiation in the range of 1000-1028 nm, characterized in that it contains an active fiber with lateral pumping, consisting of an active fiber doped with ytterbium ions, with a variable diameter and a passive fiber with a variable diameter, fiber Bragg gratings, fiber combiners, wavelength-stabilized pump laser diodes, wherein the doping of the active fiber core with ytterbium ions is 50-90% of the core diameter with a concentration in the range of 200-500 ppm.