RU2708902C1 - Device for switching modes of operation of fibre-optic laser and method for production thereof - Google Patents

Abstract

FIELD: optics.

SUBSTANCE: invention relates to optical elements for fibre lasers, in particular to saturable absorbers. Summary of the invention is a device for switching modes of operation of a fibre-optic laser based on a controlled saturable absorber of carbon nanotubes, consisting of a substrate on which an electrode is placed, counter electrode, polished to core portion of optical fibre, connected by direct contact with electrode made in form of film of carbon nanotubes, wherein the polished part of the fibre, the film and the counter electrode are electrically connected to each other through the ionic liquid, and said film is configured to change nonlinear absorption at the wavelength of the laser when the potential difference is applied to the electrode and the counter electrode. To create the device, a method is proposed, which includes the following operations: obtaining a film of single-layer carbon nanotubes grown by chemical vapour deposition on catalyst particles passing in a gas stream through a hot zone of the furnace and forming said nanotubes deposited on a filter installed at the outlet of the furnace, wherein change of synthesis parameters is selected to diameter of nanotubes, providing maximum absorption for a given thickness of film at wavelength of laser, fixing on substrate optical fibre, part of which is polished to core, pressing by a direct contact of a film of carbon nanotubes to a flat surface of the polished fibre, a reference electrode and a counter electrode are placed side by side on the substrate, a film of carbon nanotubes is coated on a flat surface of the polished fibre with a drop of ionic liquid, so that the film, the reference electrode and the counter electrode are bound by the ionic liquid.

EFFECT: technical result of invention implementation consists in improvement of stability and range of possible modes.

7 cl, 6 dwg

Description

Technical field

The invention relates to optical elements for fiber lasers, in particular to saturable absorbers.

State of the art

The patent of the Russian Federation No. 2485562, published on June 20, 2013, “A module of a saturable absorber based on a polymer composite with single-walled carbon nanotubes (options), is known in the art.” The document describes a saturable absorber module based on a polymer composite with single-walled (single-layer) carbon nanotubes on a single-mode optical fiber. The polymer composite contains a polymer mixed with single-walled carbon nanotubes, selected to absorb radiation with the required wavelength. The nanotube composite film is located on a surface polished along the same plane of the fiber sheath. The technical result consists in providing increased optical stability of the absorber.

The patent of the Russian Federation No. 2486647, published on June 27, 2013, “All-fiber laser with ultra-short pulse duration”, is known. The document describes an ultrashort fiber laser that contains a sequentially installed pump laser, a module for inputting pump laser radiation into a ytterbium-doped fiber, a splitter, a polarization controller, a device for providing self-starting and mode synchronization, designed as a film-absorbing absorber integrated into an optical fiber based on a polymer composite with single-walled carbon nanotubes. A part of a fiber laser containing ytterbium-doped fiber, an input module for pumping laser radiation into an active fiber, an insulator-polarizer, and a fiber splitter are made of single-mode fiber with polarization support. The saturable film absorber is located on the surface of the plane of the D-shaped polished sheath of a single-mode fiber, the plane of the D-shaped polished sheath of the fiber is set so that the polarization of the transmitted radiation lies in this plane. The technical result consists in providing the ability to maintain stable polarization at the output when generating ultrashort pulses at a wavelength of 1 μm.

Also known is U.S. Patent Application No. US 2013180650, published July 18, 2013, “Single-walled carbon nanotube saturable absorber production via multi-vacuum filtration method”, which provides a method for manufacturing a carbon nanotube saturable absorber by vacuum filtration.

The device described in the article “Active control of all-fiber graphene devices with electrical gating. Nature Communications ”from 2015 by Lee, E.J., Choi, S.Y., Jeong, H., Park, N.H., Yim, W., Kim, M.H. The saturable absorber device is a substrate on which a part of the D-shaped polished fiber sheath is fixed, and electrodes are also placed. In this case, a graphene film in the ionic liquid is pressed against the electrodes and the polished fiber sheath. The device allows you to effectively control the absorption in the fiber. The disadvantage is that graphene is a semimetal. As a result, it has a small enlightenment under the influence of light (modulation depth).

Semiconductor nanotubes have a structure significantly different from graphene - this is a semiconductor with a band gap of the order of 1 eV. This leads to a greater amount of enlightenment (modulation depth). A large modulation depth increases the stability of pulsed generation and the range of possible modes of pulsed generation.

The technical problem and the technical result

The technical problem to be solved by the claimed invention is directed is the development of a device for switching pulsed modes of an optical fiber laser and a method for its manufacture, which requires less technological operations.

The technical result of the invention coincides with the technical task, and also provides the creation of a device for switching modes of operation of an optical fiber laser with enhanced stability.

Decision

To achieve a technical result, a device is proposed for switching the operation of a fiber-optic laser based on a controlled saturable absorber of carbon nanotubes, consisting of a substrate on which an electrode is placed, a counter electrode, a part of the fiber polished to the core, connected by direct contact with the electrode, made in the form of a carbon film nanotubes, while the polished part of the fiber, the film and the counter electrode are electrically connected to each other through an ionic liquid, and The embedded film is made with the possibility of changing the nonlinear absorption at the laser wavelength upon application of the potential difference to the electrode and counter electrode.

The device can be designed in such a way that C2mim BF4, or DEME BF4, or C2mim PF6, or EMI BF4, or MEMP TFS with a working window from -2 V to 2 V is used as the ionic liquid. In this case, the device can include a reference electrode.

To achieve a technical result, a method for manufacturing a device for switching the operation modes of an optical fiber laser is proposed, including the following operations:

- get a film of single-layer (single-walled) carbon nanotubes grown by chemical vapor deposition on the catalyst particles flying in a gas stream through the hot zone of the furnace and forming the specified nanotubes deposited on the filter installed at the outlet of the furnace, and the diameter is selected by changing the synthesis parameters nanotubes providing maximum absorption for a given film thickness at a laser wavelength,

- fix the optical fiber on the substrate, part of which is polished to the core,

- press by direct contact the film of carbon nanotubes to the flat surface of the polished fiber,

- a reference electrode and a counter electrode are placed next to the substrate,

- cover a film of carbon nanotubes on a flat surface of a polished fiber with a drop of ionic liquid, so that the film, the reference electrode and the counter electrode are bound by the ionic liquid.

A special case of the method is the option in which all operations are carried out in an argon atmosphere and then the device for switching the laser operating modes is isolated from air.

Another special case of the method is the option in which a laser is used at a wavelength of 1560 nm, and the diameter of the nanotubes pressed against the fiber is from 1.3 nm to 1.4 nm.

Description of drawings

The figure 1 shows the propagation of the mode through a fiber polished to the core (D-shape in cross section or polished fiber), and also shows the TM and TE modes of the film. In this case, pos. 1 - polished fiber surface, pos. 2 - the core of the optical fiber, pos. 3 shell.

In FIG. 2-5 show the stages of creating a device for switching the operating modes of a fiber optic laser in a section. The following notation is introduced in the diagram. 4 - glass substrates, pos. 5 - a film of nanotubes, pos. 6 - ionic liquid, pos. 7 - reference electrode, pos. 8 - counter electrode.

In FIG. Figure 6 shows a possible diagram of the use of the device for switching the operating modes of an optical fiber laser. The following designations are introduced: pos. 14 - laser LED, pos. 15 - wavelength division multiplexer (WDM), pos. 9 - Erbium doped fiber (EDFA), pos. 10 - insulator (ISO 1550), pos. 11 - a device for switching modes of the fiber optic laser, pos. 12 - element for controlling the polarization, pos. 13 - a beam splitter that outputs laser radiation out through the fiber.

Detailed Solution Description

In the description of the present invention, the terms “includes” and “including” are interpreted as meaning “includes, inter alia,”. These terms are not intended to be construed as “consists of only”.

Unless defined separately, technical and scientific terms in this application have standard meanings generally accepted in the scientific and technical literature.

The present invention relates to the generation of pulses in fiber lasers using a saturable absorber on single-walled carbon nanotubes (SWCNTs) without polymer synthesized by aerosol synthesis. The advantages of the solution are a wide spectral range of operation, high energy, low cost, manufacturability.

The essence of the solution is a device for switching the operating modes of an optical fiber laser (Fig. 2-5), consisting of polished optical fiber (1, 2, 3) and a film of carbon nanotubes (5), connected to each other by direct contact without using a polymer matrix or surface -active substances, and placed in an ionic liquid (6), while this film of carbon nanotubes is made with the possibility of changing the absorption of light waves in a certain range when applying voltage to the electrodes (5, 7, 8).

Carbon nanotubes on the surface of a polished fiber (Fig. 1, item 1) interact with an evanescent wave and act as a saturable absorber. Absorption is controlled by applying voltage to carbon nanotubes (5) placed in an ionic liquid (6) and a counter electrode (8) made of a conductive material and placed in the same ionic liquid. Changing the absorption of carbon nanotubes at the working laser wavelength allows for controlled reproducible switching of the modes of pulsed generation of a fiber laser — mode synchronization and Q-switching.

The synthesis of nanotubes is carried out by chemical vapor deposition during the passage of a catalyst particle in a gas stream through the hot zone of the furnace. At the exit from the furnace, the nanotubes are collected on the filter, forming a uniform film. The film thickness is determined by the time of collection of nanotubes.

The film of nanotubes on the filter can be transferred onto any substrate by the dry transfer method. In this method, the film leans against the substrate and after a slight pressure passes from the filter to the substrate. This method can be scaled to mass production. In this case, the film consists of semiconductor and metal nanotubes with a semiconductor fraction of 2/3 or more. As ionic liquids, C2mim BF4, DEME BF4, C2mim PF6, EMI BF4, MEMP TFSI or any analogs can be used.

An important difference of the invention is another manufacturing technology, in which only one step is required, and not three, as is the case with graphene. Moreover, since graphene is a semimetal, it has low enlightenment under the influence of light (modulation depth). Using a mixture of carbon nanotubes: 2/3 of semiconductor, 1/3 metal, gives the following advantages. Semiconductor nanotubes have significantly different structures from graphene - this is a semiconductor with a band gap of the order of 1 eV. This leads to a greater amount of enlightenment (modulation depth). A large modulation depth increases the stability of pulsed generation and the range of possible modes of pulsed generation. The metal nanotubes in the mixture provide the speed of the saturable absorber.

In FIG. Figure 6 shows an example of using the device to switch the operating modes of an optical fiber laser (11). During the experiment, 10 m of erbium-doped fiber (9) was used, which was pumped using a BL976-PAG500 laser diode (14) at a wavelength of 980 nm, which was connected to the ring resonator through a wavelength division multiplexer (15). Through a beam splitter (13), 50% of the laser radiation was led out from the resonator; an insulator 10 (ISO 1550) was installed at the other end of the resonator. A device for monitoring the polarization of radiation (12) closes the ring resonator and connects to the multiplexer 15. The total length of the assembled laser is 20 m. The wavelength of the laser radiation emerging from the resonator is 1560 nm.

In the laser of FIG. 6, a device was used to switch the operating modes of an optical fiber laser (11), in which a saturable absorber on single-walled carbon nanotubes had nanotubes of a certain diameter. The film thickness of carbon nanotubes is calculated from the empirical formula

D = -417 log (T),

where D is the film thickness (diameter of the nanotubes), T is the transparency of the film at the laser wavelength. So, for the case of 40% transmittance, the film thickness of carbon nanotubes is 170 nm, and in the case of 60% transmittance, the thickness of the nanotubes should be 90 nm.

Although the invention has been described with reference to the disclosed embodiments, it should be apparent to those skilled in the art that the specific cases described in detail are for illustrative purposes only and should not be construed as limiting the scope of the invention in any way. It should be understood that various modifications are possible without departing from the gist of the present invention.

Claims (12)

1. A device for switching modes of operation of a fiber-optic laser based on a controlled saturable absorber of carbon nanotubes, consisting of a substrate on which an electrode is placed, a counter electrode, a part of the fiber polished to the core connected by direct contact with an electrode made in the form of a film of carbon nanotubes, this polished part of the fiber, the film and the counter electrode are electrically connected to each other through an ionic liquid and the specified film is made with the possibility of changing not ineynogo absorption at the wavelength of the laser at a potential difference to the electrode and counterelectrode. 2. The device according to p. 1, characterized in that it contains a reference electrode. 3. The device according to claim 1, characterized in that a potential difference from -2 V to 2 V is applied to the electrode and the counter electrode. 4. The device according to claim 1, characterized in that C2mim BF4, or DEME BF4, or C2mim PF6, or EMI BF4, or MEMP TFS is used as the ionic liquid. 5. A method of manufacturing a device for switching modes of a fiber optic laser, comprising the following operations: - get a film of single-walled carbon nanotubes grown by chemical vapor deposition on catalyst particles flying in a gas stream through the hot zone of the furnace and forming these nanotubes deposited on the filter installed at the outlet of the furnace, and the diameter of the nanotubes is selected by changing the synthesis parameters, providing maximum absorption for a given film thickness at a laser wavelength, - fix the optical fiber on the substrate, part of which is polished to the core, - press by direct contact the film of carbon nanotubes to the flat surface of the polished fiber, - a reference electrode and a counter electrode are placed next to the substrate, - cover a film of carbon nanotubes on a flat surface of a polished fiber with a drop of ionic liquid, so that the film, the reference electrode and the counter electrode are bound by the ionic liquid. 6. The method according to p. 5, characterized in that they carry out all operations in an argon atmosphere and then the device is isolated from air. 7. The method according to p. 5, characterized in that a laser is used at a wavelength of 1560 nm and the diameter of the nanotubes pressed against the fiber is from 1.3 nm to 1.4 nm.

Images