KR102337546B1 - Amplifier for fiber laser enabled by step-index large mode area fiber and ultrafast fiber laser comprising the same - Google Patents

Abstract

The present invention relates to an optical fiber amplifier using a step index large mode area fiber and an ultra-short pulse fiber laser device including the same, and more particularly, to achieve a high core pump absorption rate and at the same time By using an optical fiber that suppresses photo darkening, maintains excellent beam profile, and facilitates fusion between optical fibers in the ultra-short pulse laser amplification system, the length of the amplified optical fiber is less than 1 m It relates to an optical fiber optical amplifier capable of obtaining sufficient amplification effect while minimizing nonlinear effects in an amplification system by maintaining the

Description

Optical amplifier using stepped wide mode area optical fiber and ultra-short pulse fiber laser device including the same

The present invention relates to an optical amplifier using a step index large mode area fiber and an ultra-short pulse optical fiber laser device including the same, and more particularly, to achieve a high core pump absorption rate and optical By using an optical fiber that suppresses photo darkening, maintains an excellent beam profile, and facilitates fusion between optical fibers in the ultra-short pulse laser amplification system, the length of the amplified optical fiber is reduced to 1 m or less. It relates to an optical amplifier capable of obtaining a sufficient amplification effect while minimizing the nonlinear effect in the amplification system by maintaining it, and an ultrashort pulse fiber laser device including the same.

The ultra-short pulse laser is a laser that concentrates energy in a short instant of tens of picoseconds (ps) to tens of femtoseconds (fs), and the concentration of energy per hour is very high, so it is possible to process specimens that cannot be processed with conventional lasers. In addition, due to the physical phenomenon in which energy transfer is completed before thermal diffusion begins and a local ultra-high temperature is formed, it is not limited to a specific material, and clean processing is possible even in small processing sizes of micrometers (μm) or less, so display repair, semiconductor/solar Cell processing, ophthalmic procedures, marking and surface treatment, etc. are in the spotlight in the ultra-fine processing field.

These ultra-short pulse lasers can be classified into a crystal type and an optical fiber type according to the laser amplification medium. In general, the crystal type has the advantage of being able to form a narrow and clean pulse width due to less nonlinearity, but it is relatively vulnerable to changes in the surrounding environment. However, it is disadvantageous to heat dissipation, making it difficult to apply to high-output systems. On the other hand, in the case of an optical fiber-based ultrashort pulse laser that uses optical fiber as an amplification medium, the pulse shape is relatively poor due to the high-order dispersion and non-linear characteristics of the optical fiber, but the optical path is composed of optical fiber, so it is insensitive to environmental changes and stable. . In addition, due to the structural characteristics of the amplification medium, heat dissipation is easy and thus a relatively high average power can be secured. .

However, due to the small core area of the optical fiber and the long length of 1 m or more, the nonlinear phase shift cumulative value (B-integral) is relatively large, which results in distortion of the laser spectrum and low pulse quality. .

One of the methods to alleviate this problem is to reduce the length of the optical fiber required for amplification. To reduce the length of the amplification optical fiber, there is a method to increase the concentration of rare earth ions added to the optical fiber, but in ^{the case of Yb 3+} ions, the doping concentration As the value increases, the possibility of inter-ion clustering increases, which may adversely affect the long-term stability of the system. Also, as ^{the concentration of Yb 3+} ions increases, the numerical aperture (NA) increases, resulting in beam quality (beam). There is a disadvantage that quality(M ^{2 )) is lowered.}

Another solution is to increase the diameter of the core and reduce the cladding to core area ratio (CCAR) to increase the amplification efficiency, but in this case, micro-bending loss occurs. Higher-order mode may be more likely to occur.

On the other hand, among all-solid wide mode area optical fibers, there are research results that apply a pedestal layer around the core to lower the refractive index of the core. figures and if there is a difference since the harm the core mode into the cladding to leak or the pump is not locked in a cladding part in amplify and the discomfort which must be strictly managed, Yb ³⁺ to the core in order to overcome the above disadvantages and Although ^{an optical fiber type in which Al 3+} ions are added and Ge ions are doped into the clad has been proposed, the refractive index of the core is increased by adding ^{Yb 3+} and Al ^{3+ ions.} There is a disadvantage in that the manufacturing process becomes complicated during the heightening process.

Yb ^3+, with the core in a recent study of addition of Al ^3+, and P ⁵⁺ ions, such as (mol) to induce the generation AlPO4, and access to them by satisfying a high concentration of Yb ³⁺ and low index of refraction at the same time is also being done. However, for optical fibers used in ultra-short lasers, a numerical aperture lower than the refractive index lowered by AlPO4 generation is required.

On the other hand, briefly describing the prior art existing in the field to which the technology of the present invention pertains, first, US Patent Publication No. US 2011/0206341 A1 is a prior art optical fiber having Yb ions added thereto and having a low NA value and thus excellent beam characteristics. As a result, when an optical fiber medium is used to amplify an ultrashort pulse laser, the pulse distortion phenomenon due to the cumulative nonlinear phase shift (B-integral) is prominent, and the usual method taken to alleviate this is Yb ^{3 added to the core Increasing the concentration of +} increases the pump absorption rate of the optical fiber, but increasing the ^{concentration of Yb 3+} leads to an increase in the refractive index of the core, leading to photo darkening due to beam quality and cluster formation. may be increased, but in the prior art, Yb ³⁺ , Al ³⁺ and P ⁵⁺ ions are added to the core, the clad is located around the core, and the molar concentration ^{of Al 3+} and P ^{5+ ions in the core} The optical fiber is formed through the molarity inequality of Yb ³⁺ , Al ^{3+ ,} and P ⁵⁺ ions when the relationship is Al ³⁺ = P ⁵⁺ , Al ³⁺ > P ⁵⁺ and Al ³⁺ < P ^{5+ .} By selecting the concentration ratio of ^{Al 3+} and P ⁵⁺ ions added along with ^{Yb 3+ , the possibility of photoblackening even at high Yb 3+} concentration was reduced, and at the same time, the increase in the core refractive index was minimized to improve the beam quality ( A method for maintaining excellent beam quality) is presented, and FIG. 1 shows a change in refractive index according to a change in ^{the P 5+ content in this case.}

However, when the Yb Al:P composition is high, it is difficult to control the index profile and it is difficult to keep the background loss low. Also, the non-uniform distribution of ions distorts the refractive index distribution of the optical fiber core. include problems.

In addition, US Patent Publication No. 2013/0114129 A1 presents a fiber laser and amplifier in which an optical fiber to which Yb, an amplification medium, is added, is implemented using a photonic crystal fiber (PCF) structure, and a representative structure thereof is shown. 2 is shown.

In FIG. 2, in the cross section of a photonic crystal fiber for the development of a wide area mode optical fiber, 1 is an optical fiber, 2 is a core, 3 is a cladding, and 4 shows a medium having a different refractive index, but this is a complex structure. Due to this, it is difficult to fusion with other optical fibers, so there is a disadvantage in that there is a limitation in configuring an optical fiber amplifier.

Therefore, the quality of the laser beam (beam quality (M ² )) is excellent, the fusion between the optical fibers is easy, and the pump laser absorption rate of the optical fiber per unit length to minimize the nonlinear phase shift (B-integral) that accumulates through the optical fiber By constructing an optical fiber-based pulse laser amplification system using this high optical fiber and the same, the need to develop an optical amplifier with improved characteristics and an ultra-short pulse optical fiber laser device including the same is still in continuous demand.

US Patent Publication No. US 2011/0206341 A1 (published date: 2011.08.25) US Patent Publication No. US 2013/0114129 A1 (published date: 2013.05.09)

The present invention was created to solve the above problems, and in constructing an optical fiber-based pulse laser amplification system, a pump laser of an optical fiber per unit length in order to minimize the nonlinear phase shift (B-integral) accumulated through the optical fiber An object of the present invention is to provide an optical amplifier using an optical fiber having a high absorption rate and an ultrashort pulse fiber laser device including the same.

In addition, the present invention has a high pump laser absorption rate of the optical fiber per unit length in order to minimize the nonlinear phase shift (B-integral) accumulated through the optical fiber, and the quality of the laser beam (beam quality (M ² )) is excellent, and the optical fiber Another object of the present invention is to provide an optical fiber that is easily fusion-bonded.

The present invention provides an optical amplifier comprising a step index large mode area fiber.

In the optical amplifier according to the present invention, the stepped wide mode area optical fiber includes a core suitable for transmission and amplification of an optical signal and a cladding surrounding the core, The ytterbium (Yb) content is contained in an amount of 0.2 to 10 wt%, the aluminum (Al) content and the phosphorus (P) content are each contained in an amount of 0.5 to 25 wt%, and the clad is compared to the entire clad component, The germanium (Ge) content may be included in an amount of 1 to 40 wt%.

As an embodiment, the length of the optical fiber may be 1.5 m or less.

As an embodiment, the optical fiber may have a clad pump absorption rate of 10 dB/m or more.

In one embodiment, the ytterbium (Yb) content in the core is in the range of 0.3 to 8 wt%, the content of aluminum (Al) is in the range of 2 to 20 wt%, relative to the total core component, and the phosphorus (P) content is in the range of 2 to 20 wt%. The content may range from 5 to 25 wt %.

As an embodiment, the content of germanium (Ge) in the clad may be in the range of 2 to 30 wt% based on the total clad component.

As an embodiment, in the optical amplifier, at least one selected from a pump combiner and a pump light source may be optically connected to a stepped wide mode area optical fiber.

In one embodiment, each of the core and the clad of the optical fiber may be a silica matrix.

In one embodiment, the step-type wide mode area optical fiber is disposed by being wound in the air in a circular or elliptical shape with a diameter of 0.5 cm to 500 cm, or wound on the outer surface of a tube or tube having a cylindrical or polygonal cross-section or the optical amplifier. can be used for

The present invention may also provide an ultra-short pulse laser device including the optical amplifier according to the present invention, and using an ultra-short pulse within 100 ps to 10 fs based on the output pulse after compression.

The present invention also provides a method of manufacturing an optical fiber, comprising the steps of: a) forming a clad composed of a silica-germanium oxide layer by injecting a mixed gas of a Si precursor and a Ge precursor into a ceramic tube having a cavity formed therein; b) forming a phospho-silicate soot inside the clad by chemical vapor deposition and introducing ytterbium (Yb) and aluminum (Al) ions into the phospho-silicate soot through solution doping, forming an optical fiber preform in a shape in which a tube is wrapped around a surface; c) forming an optical fiber preform comprising a clad doped with germanium ions and a core doped with ytterbium (Yb), aluminum (Al) and phosphorus (P) inside the clad by removing the ceramic tube; And d) processing the optical fiber preform to extract the optical fiber; a clad doped with germanium ions and a core doped with ytterbium (Yb) aluminum (Al) and phosphorus (P) in the clad, including Provided is a method for manufacturing an optical fiber.

The present invention also provides an optical fiber obtained by the above-described manufacturing method and an optical amplifier comprising the optical fiber.

According to the present invention, the core of the optical fiber is doped with ytterbium (Yb), aluminum (Al), and phosphorus (P) components, respectively, and the clad is doped with germanium (Ge). The optical amplifier using a step index large mode area fiber achieves a high core pump absorption rate of 20 dB/m or more through the optical fiber, and at the same time suppresses the photo darkening phenomenon, Aperture) is maintained below 0.07 to have the advantage of excellently maintaining a beam profile.

In addition, according to the present invention, the core is doped with ytterbium (Yb), aluminum (Al) and phosphorus (P) ions, respectively, and the clad is doped with germanium (Ge) ions. In the case of using a step index large mode area fiber, the optical amplifier according to the present invention minimizes the nonlinear effect in the amplification system by maintaining the length of the amplifying optical fiber to 1.5 m or less, more preferably 1 m or less. At the same time, there is an advantage that sufficient amplification effect can be obtained.

In addition, since the transmission efficiency of the optical fiber according to the prior art is greatly reduced during the fusion process, it is essential to use an expensive fusion machine. It has the additional advantage of stably obtaining high permeation efficiency even when used.

1 is a diagram illustrating a change in refractive index of an optical fiber according to a change in ^{phosphorus (P5 +} ) content in an optical fiber according to the prior art.
2 is a diagram illustrating a cross-section of a photonic crystal fiber for the development of a large area optical fiber according to the prior art.
3 is a schematic diagram of a MOPA (Master Oscillator Power Amplifier) type high-power ultra-short pulse laser device using an optical fiber according to an embodiment of the present invention.
4 is a schematic diagram of an ultra-short pulse laser device in which the main amplification stage is composed of two stages based on a stepped wide mode area optical fiber according to the present invention.
5 is a graph showing a cross-sectional image 4a and a refractive index distribution 3b of an optical fiber drawing from a preform according to the present invention.
6 is a diagram showing an ion concentration distribution graph (4a) measured through Energy Dispersive X-ray Spectroscopy (EDS) of an optical fiber according to the present invention and a measured absorption rate (4b) of the optical fiber according to the present invention.
7 is a schematic diagram of the configuration of an amplifier for confirming the amplification characteristics of an optical fiber according to the present invention.
FIG. 8 is a graph showing experimental results on the amplification characteristics of the optical fiber according to FIG. 7 .

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of a cooling device for a fiber laser amplification module according to the present invention will be described in detail so that those of ordinary skill in the art can easily practice the present invention. .

In each drawing of the present invention, the size or dimensions of the structures are enlarged or reduced than the actual size for clarity of the present invention, and well-known components are omitted to reveal the characteristic configuration, so it is not limited to the drawings. .

In the detailed description of the principle of the preferred embodiment of the present invention, if it is determined that a detailed description of a related well-known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

The optical amplifier according to the present invention is an optical amplifier including a step index large mode area fiber, wherein the step index large mode area fiber surrounds the core and a core suitable for transmission and amplification of an optical signal. includes a clad, and the core of the optical fiber contains 0.2 to 10 wt% of ytterbium (Yb) compared to the entire core component, and an aluminum (Al) content and a phosphorus (P) content of 0.5 to 25 wt%, and the clad is characterized in that the germanium (Ge) content is included in an amount of 1 to 40 wt%, based on the total clad component.

On the other hand, as a more preferable example for each component doped into the core and the clad in the step-type large mode area optical fiber according to the present invention, in the case of the core, the ytterbium (Yb) content is 0.3 to 8 wt%, more preferably It may have a range of 1 to 7 wt%, the content of aluminum (Al) may be in the range of 2 to 20 wt%, more preferably 5 to 16 wt%, and the content of phosphorus (P) is 5 to 25 wt %, more preferably in the range of 8 to 23 wt %. In addition, the content of germanium in the clad may preferably range from 2 to 30 wt%, more preferably from 5 to 25, based on the total clad components.

Here, in the present invention, the content of each component in the core and/or clad represents the weight of the individual components (element) relative to the total weight of the composition constituting the core in the case of the core component, and also in the case of the clad component. Likewise, it refers to the weight occupied by individual components (elements) relative to the total weight of the composition constituting the clad. That is, the phosphorus (P) content in the range of 0.5 to 25 wt% means that the total mass of the phosphorus (P) element in the core present in ionic form, etc. is 0.5 to 15 wt% relative to the mass of the composition of the entire core. it means.

Such a laser device including an optical amplifier according to the present invention is possible, but is not limited thereto, to a laser device used in ultra-fine processing fields such as displays, semiconductor/solar cell processing, ophthalmic procedures, marking and surface treatment.

On the other hand, as described in the background art, when the length of the optical fiber becomes longer than 1 m, this causes the nonlinear phase shift accumulation value (B-integral) to be relatively large, which causes the laser spectrum to be distorted and the pulse quality (pulse quality). ) is lowered, and to reduce the length of the amplifying optical fiber, the degree of addition of ytterbium (Yb3+) ions added to the optical fiber must be increased. In this case, the numerical aperture (NA) of the optical fiber core increases and the beam In addition to the disadvantage of lowering the quality (beam quality (M ² )), the possibility of aggregation between ytterbium (Yb3+) ions increases, which may cause photodarkening.

Therefore, while conducting research on improvement of these problems, the present inventors found that Yb ³⁺ , Al ³⁺ , P ⁵⁺ ions are in the core of the optical fiber, and Ge ions are in a specific content in the clad. It has been found that the above problems can be solved when a step index large mode area fiber is manufactured and used as an amplification medium.

That is, in the present invention, in amplifying the output of a pulsed laser having a relatively low average output, ytterbium (Yb ³⁺ ), aluminum (Al ³⁺ ), phosphorus (P ^{5) in the core of the optical fiber as an amplification medium +} ) ions are added in a specific range, and germanium (Ge ⁴⁺ ) ions are added in a specific range to the clad of the optical fiber. Step index large mode area fiber ) is used in the amplifier.

The optical amplifier using an optical fiber according to the present invention can be used as an amplification system in a pulse laser device using an optical fiber. (seed) It is possible to amplify the output of the laser.

In general, an optical amplifier may include an optical fiber for amplification and a support for supporting the same. Here, a pump light source such as a pump laser diode (pump LD), a pump combiner, a Wavelength Division Multiplexor (WDM), It may include devices such as a pump combiner isolator mode stripper and a pump dump.

On the other hand, the optical fiber used therein to provide the optical amplifier according to the present invention may use a step index large mode area fiber (step index large mode area fiber). The stepped wide mode area optical fiber may have a clad absorption of 20 dB/m or more and a clad refractive index higher than that of silica.

Meanwhile, the step index large mode area fiber according to the present invention includes a central core suitable for transmission and amplification of an optical signal and a cladding surrounding the core.

Here, the core may have a cylindrical shape, and the clad may have a circular cylindrical shape to surround the core, but is not limited thereto. In addition, the optical fiber may amplify the power of the laser beam while transmitting the laser beam.

In order to manufacture such an optical fiber, in the present invention, an optical fiber preform is first manufactured, and the preform is processed through drawing or the like to extract the optical fiber.

Looking at this in more detail, the method of manufacturing an optical fiber according to the present invention comprises the steps of: a) forming a clad comprising a silica-germanium oxide layer by injecting a mixed gas of a Si precursor and a Ge precursor into a ceramic tube having a cavity formed therein; b) forming a phospho-silicate soot inside the clad by chemical vapor deposition and introducing ytterbium (Yb) and aluminum (Al) ions into the phospho-silicate soot through solution doping, forming an optical fiber preform in a shape in which a tube is wrapped around a surface; c) forming an optical fiber preform comprising a clad doped with germanium ions and a core doped with ytterbium (Yb), aluminum (Al) and phosphorus (P) inside the clad by removing the ceramic tube; and d) processing the optical fiber preform to extract the optical fiber; in this way, a clad doped with germanium ions and ytterbium (Yb) aluminum (Al) and phosphorus (P) in the clad ) to obtain an optical fiber composed of a doped core.

Hereinafter, the manufacturing method of the optical fiber will be concretely described in each step.

First, as a first step, in the step (a) of forming a clad consisting of a silica-germanium oxide layer in a ceramic tube having a cavity formed therein, the clad portion corresponding to the outside of the preform for manufacturing the optical fiber is placed inside the ceramic tube. It is a step of forming the inside of the cavity by chemical vapor deposition, etc. To this end, a ceramic tube removable in step c) is used, and a mixed gas of a Si precursor and a Ge precursor is respectively introduced into the ceramic tube to form _{a multi-layered GeO 2} -SiO _{2 layer.} At this time, it is possible to use the silica tube as the ceramic tube to be used, it is possible to use the GeCl ₄ SiCl ₄ as the Si precursor and a Ge precursor.

In this process, the deposition temperature in the range of 1000 ~ 1800 ℃ can be used, and since the tube can be closed due to the high temperature, a backward pressurizing system is applied. In addition, the temperature gradient formed during deposition is compensated by adjusting the gas flow rate and the temperature of the burner, so that the force of diffusion of molecules is balanced.

As a second step, ^{the step (b) of depositing ytterbium (Yb 3+} ), phosphorus (P ⁵⁺ ) and aluminum (Al ³⁺ ) ions on the core (step b) corresponds to the inside of the preform for manufacturing the optical fiber. This is the step of forming the core part. To this end, phospho-silicate soot (P ₂ O ₅ -SiO ₂ ) is formed on the inside of the clad by chemical vapor deposition, and the porosity is controlled through a pre-sintering step. and stabilize it. ^{Next, Yb 3+} , Al ³⁺ ions are supplied through solution doping technique, and after sintering the soot, the tube is closed and the ceramic tube such as the silica tube is Complete the optical fiber preform wrapped around the surface. _{In this process, POCl 3} is strongly injected ^{to supplement phosphorus (P 5+} ) ions that are evaporated due to high vapor pressure.

As a third step, step (c)) of forming an optical fiber preform by removing the ceramic tube outside the deposited clad is a ceramic tube doped with germanium ions, such as a silica tube, obtained in step b) above and deposited. Corresponding to the step of completing the optical fiber preform by removing the ceramic tube from the ceramic tube-optical fiber preform composite including a clad and a core doped with ytterbium (Yb), aluminum (Al) and phosphorus (P) inside the clad do.

Here, the ceramic tube outside the clad can be easily removed by HF etching and/or mechanical milling.

As a final step, in the step (d) of manufacturing the optical fiber by processing the optical fiber preform, the optical fiber can be manufactured by a drawing method from the preform, which is usually mounted on an optical fiber extraction facility, and the It can be taken out by melting the tip of the optical fiber preform. The drawn out optical fiber is coated with an ultraviolet curable resin or a thermosetting resin, and the resin is cured with ultraviolet rays or heat to form an outer sheath, and the outer sheath increases the mechanical strength of the optical fiber, thereby protecting the optical fiber from the external environment.

In this case, the preform may have a diameter of 5 to 20 mm and a length of 0.1 to 1 m, and the characteristics of the optical fiber, such as the size, composition ratio, and refractive index of the core/clad of the optical fiber, are already in the forming stage of the preform. is determined, and the step of drawing the optical fiber of step d) corresponds to the step of drawing out the optical fiber of the predetermined characteristic while controlling the temperature or speed so as to have uniform characteristics in the longitudinal direction.

Meanwhile, as the optical amplifier according to the present invention uses the optical fiber, one having a length of 1.5 m or less may be used, and preferably, an optical fiber having a length of 1 m or less may be used.

In addition, since the optical amplifier according to the present invention uses the optical fiber, the clad pump absorption rate may be 10 dB/m or more, and preferably, the clad pump absorption rate 20 dB/m or more may be used.

In addition, according to the manufacturing method of the optical fiber according to the present invention, preferably, the ytterbium (Yb) content in the core is in the range of 0.3 to 8 wt%, and the content of aluminum (Al) is 2 to 8 wt%, relative to the total core component. It is in the range of 20 wt%, and the content of phosphorus (P) can provide an optical fiber adjusted in the range of 5 to 25 wt%, and the content of germanium (Ge) in the clad is higher than the total clad component, An optical fiber in the range of 2 to 30 wt% may be provided, wherein the optical fiber may have a core and a clad of silica matrix, respectively.

On the other hand, in the optical amplifier according to the present invention, at least one selected from a pump combiner and a pump light source may be optically connected to a step-type wide mode area optical fiber, and preferably, a pump light source-pump combine You can connect by the order of optical fibers.

In addition, the step-type wide mode area optical fiber according to the present invention is disposed to be wound in the atmosphere in a circular or elliptical shape with a diameter of 0.5 cm to 500 cm, or wound around the outer surface of a tube or tube having a cylindrical or polygonal cross section. It can be used in an amplifier, and by selecting and applying an appropriate winding diameter, there is a relative difference in the loss of the fundamental mode and higher order mode of the optical fiber, and consequently the fundamental mode is dominant. Pulse output can be secured. When the winding diameter is more than 500 cm, the relative loss difference between modes is insignificantly small, and when the winding diameter is 0.5 cm or less, the loss suffered by the fundamental mode is also very large, so it is usually within 0.5 cm to 500 cm Select from and apply.

In addition, the present invention can provide an optical fiber obtained by the method for manufacturing an optical fiber, an optical amplifier including the optical fiber, and an ultrashort pulse laser device including the optical amplifier. In this case, the ultra-short pulse laser device may be a laser device using ultra-short pulses in the range of 100 ps to 10 fs based on the output pulse after compression.

3 is a schematic diagram of a high-power ultra-short pulse laser device of a MOPA (Master Oscillator Power Amplifier) type using an optical fiber according to an embodiment of the present invention. More specifically, the stable and low-output seed laser oscillated from the resonator (Oscillator, 1) is spread on the time axis so as to have a sufficiently low peak output while passing the optical stretcher (2) prior to amplification, If necessary, it passes through the pre-amplifier 3 and includes the optical fiber 7, the isolator 4, the pump light source 5 and the pump combiner 6 according to the present invention. amplifier) is prepared to have a high gain.

The laser that has passed through the pre-amplification stage 3 passes through the isolator 4 in the main amplification stage that blocks the propagation of light in the reverse direction, then passes through the pump combiner 6 and is incident on the optical fiber 7, and the pump light source (Laser diode, 5) is also incident on the optical fiber 7 through the pump combiner (6).

The amplified laser passing through the optical fiber 7 passes through the compressor 8 and is compressed into an ultra-short pulse laser in the range of 100 ps to 10 fs. There may be two or more pump light sources (pump LD, 5) connected to the pump combiner (6) depending on the pump output and the characteristics of the pump light source (pump LD) required here. Here, the stepped wide mode area optical fiber 7, which is the amplification medium of the main amplification stage, is wound with a diameter of 0.5 to 500 cm for the purpose of removing higher order modes except for the fundamental mode.

In addition, the ultra-short pulse laser device according to the present invention may be configured as a multi-stage in which a plurality of main-amplifiers are connected in series.

4 shows a system in which the main amplification stage based on a stepped wide mode area optical fiber according to the present invention consists of two stages, and between the main amplification stage and the main amplification stage, an isolator 4 and a higher-order mode stripper for removing the higher-order mode (Mode stripper, 9) may be located, and a higher-order mode canceller 9 may also be located at the end of the final amplification stage.

Hereinafter, physical properties of the optical fiber for laser according to the present invention, manufactured as described above, will be described in detail based on the drawings shown in FIGS. 5 to 8 .

5 is a diagram showing a cross-sectional image of an optical fiber drawn from a preform and a graph showing a refractive index distribution completed through the present invention.

The shape of the core and the clad of 20 um or less is clearly shown from a) of FIG. 5, and the core (ytterbium (Yb ³⁺ ), phosphorus (P ^{5) in the optical fiber manufactured according to the present invention from FIG. 5 b) +} ) and aluminum (Al ³⁺ ) ion-doped) and clad (germanium-doped) are shown. Through this, it can be confirmed that the refractive index of the clad is uniform and has a refractive index that is about 0.0017 higher than that of index-matching oil. can

In addition, the difference in refractive index between the core and the clad is about 0.0017, and a numerical aperture (NA) of 0.07 level can be expected. .

FIG. 6 a) is a graph of ion concentration distribution measured through Energy Dispersive X-ray Spectroscopy (EDS). The concentration in the core of the optical fiber is 0.4 mol% (4 wt. % Yb), Al2O3 is 4.4 mol% (11 wt% Al), and P2O5 is 4.8 mol% (17 wt% P), confirming the overall flat concentration distribution.

On the other hand, it is shown that germanium (Ge) ions in the clad have a content of about 20 wt% based on the silica matrix compared to the total clad components by refractive index measurement.

In addition, in the case of P2O5 in a) of FIG. 6, it can be seen that there is no dip in the center, which means that additional supply of P2O5 was effective during the preform manufacturing process. In addition, P2O5 has a slightly higher concentration value than Al2O3, and through this, the photoblackening phenomenon can be further reduced.

6b) is the measured absorption coefficient of the optical fiber manufactured according to the present invention, it can be confirmed that it has a high value of 22.3 dB/m at 976 nm.

7 is a schematic diagram of the configuration of an amplifier for confirming the amplification characteristics of the optical fiber according to the present invention. Both end surfaces of the optical fiber manufactured according to the embodiment are 4% reflective surfaces, and the optical fiber itself is configured to serve as a laser resonator; The pump and the laser are incident on the optical fiber through the lens or are collimated and emitted. The high-order mode was removed by bending the optical fiber with a diameter of 5 cm.

8 is a graph showing experimental results on the amplification characteristics of an optical fiber manufactured according to the embodiment using the amplifier according to FIG. 7 .

Here, if a pump light source (pump LD) that is not wavelength stabilized is used, the central wavelength of (pump LD) may flow to a different value during the amplification process, which may affect wavelength conversion efficiency. On the other hand, when a wavelength-stabilized pump light source (pump LD) is used, the conversion efficiency can be kept constant because the central wavelength is kept constant during the amplification process.

In this embodiment, a 2 m optical fiber was used when a pump light source (pump LD) with wavelength stabilization was used, and a 0.5 m optical fiber was used when a wavelength stabilized pump light source (pump LD) was used. When a wavelength stabilized pump light source (pump LD) with an average output of 71.5 W is used, the maximum output of the laser is 58.6 W, and the conversion efficiency reaches 80%. ^{The beam quality (M 2} )) at an output of 107 W is 1.29 to 1.39, and better results can be obtained by lowering the numerical aperture of the optical fiber by adjusting the germanium (Ge) concentration of the clad.

As described above, the present invention has been described with reference to the embodiments shown in the accompanying drawings, which are only exemplary, and various modifications and equivalent other embodiments are possible by those of ordinary skill in the art. will understand that Therefore, the technical protection scope of the present invention should be defined by the following claims.

1: Oscillator
2: Stretcher
3: Pre-amplifier
4: isolator
5: Pump light source (laser diode)
6: Pump combiner
7: optical fiber (stepped wide mode area optical fiber)
8: Compressor (Compressor)
9: Mod Stripper

Claims (12)

In an optical amplifier comprising a step index large mode area fiber,
The stepped large mode area optical fiber includes a core and a clad surrounding the core,
The core of the optical fiber contains 0.3 to 8 wt% of ytterbium (Yb) relative to the entire core component, and the content of aluminum (Al) is in the range of 2 to 20 wt%, and phosphorus (P) The content is included in 5 to 25 wt%,
The clad contains 5 to 25 wt% of germanium (Ge) compared to the total clad components,
The pump absorption rate of the clad is more than 10 dB/m,
Optical amplifier, characterized in that the NA (Numerical Aperture) of the optical fiber core is 0.07 or less.
According to claim 1,
The optical amplifier, characterized in that the length of the optical fiber is 1.5 m or less.
delete delete delete According to claim 1,
The optical amplifier is an optical amplifier, characterized in that at least one selected from a pump combiner and a pump light source is optically connected to a step-type wide mode area optical fiber.
According to claim 1,
The optical amplifier is an optical amplifier, characterized in that each of the core and the clad is a silica matrix.
According to claim 1,
The step-type wide mode area optical fiber is disposed by being wound in the air in a circular or elliptical shape within a diameter of 0.5 cm to 500 cm, or being wound around the outer surface of a tube or tube having a cylindrical or polygonal cross-section and used in an optical amplifier. an optical amplifier with
An ultra-short pulse laser device comprising the optical amplifier according to any one of claims 1, 2, and 6 to 8, and using an ultra-short pulse within 100 ps to 10 fs based on the output pulse after compression. .
a) forming a clad composed of a silica-germanium oxide layer by respectively introducing a mixed gas of a Si precursor and a Ge precursor into a ceramic tube having a cavity formed therein;
b) forming a phospho-silicate soot inside the clad by chemical vapor deposition and introducing ytterbium (Yb) and aluminum (Al) ions into the phospho-silicate soot through solution doping, forming an optical fiber preform in a shape in which a tube is wrapped around a surface;
c) forming an optical fiber preform comprising a clad doped with germanium ions and a core doped with ytterbium (Yb), aluminum (Al) and phosphorus (P) inside the clad by removing the ceramic tube; and
d) processing the optical fiber preform to extract the optical fiber; comprising a clad doped with germanium ions and a core doped with ytterbium (Yb), aluminum (Al) and phosphorus (P) inside the clad Manufacturing method of optical fiber
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