KR20210053092A - 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 ultrashort pulse optical fiber laser device including the same and, more particularly, to an optical fiber amplifier and an ultrashort pulse optical fiber laser device including the same which achieve a high core pump absorption rate and simultaneously suppress photo darkening phenomena, keep a beam profile excellent, and use an optical fiber which facilitates fusion between optical fibers in an ultrashort pulse laser amplification system to maintain the length of an amplification fiber to be 1 m or less, thereby minimizing non-linear effects in the amplification system and simultaneously obtaining a sufficient amplification effect.

Description

Optical amplifier using step-type wide mode area optical fiber and ultra-short pulse fiber laser device including the same {AMPLIFIER FOR FIBER LASER ENABLED BY STEP-INDEX LARGE MODE AREA FIBER AND ULTRAFAST FIBER LASER COMPRISING THE SAME}

The present invention relates to an optical amplifier using a step index large mode area fiber and an ultra-short pulsed fiber laser device including the same, and more particularly, to 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 an ultra-short pulse laser amplification system, the length of the amplified optical fiber is reduced to 1 m or less. The present invention relates to an optical amplifier capable of obtaining a sufficient amplification effect while minimizing a nonlinear effect in an amplification system by maintaining, and an ultrashort pulsed fiber laser device including the same.

The ultrashort pulse laser is a laser that concentrates energy in a short instant of tens of picoseconds (ps) to tens of femtoseconds (fs), and because the concentration of energy per hour is very high, 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 local ultra-high temperature is formed, it is not limited to specific materials, and clean processing is possible even in small processing sizes of micrometers (μm) or less. It is in the spotlight in the field of ultra-fine processing such as cell processing, ophthalmic procedures, marking and surface treatment.

These ultrashort pulse lasers can be classified into crystal type and 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 low nonlinearity, but is relatively vulnerable to changes in the surrounding environment. It is disadvantageous in heat dissipation and is difficult to apply to high-power systems. On the other hand, in the case of an optical fiber-based ultra-short pulse laser using optical fiber as an amplification medium, the shape of the pulse is relatively poor due to the high-order dispersion and nonlinear characteristics of the optical fiber, but the optical path is made of optical fiber, so it is insensitive to environmental changes and is stable. . In addition, due to the structural characteristics of the amplification medium, heat dissipation is easy, and thus relatively high average power can be secured, and the advantages of optical fiber-based ultrashort pulse lasers meet the needs of industrial fields requiring stability and productivity. .

However, due to the small core area of the optical fiber and the long length of 1 m or more, the nonlinear phase shift accumulation value (B-integral) is relatively large, which causes the laser spectrum to be distorted and the pulse quality to be lowered. .

One of the ways to alleviate this problem is to reduce the length of the optical fiber required for amplification. To reduce the length of the amplified optical fiber, there is a method of increasing the concentration of rare earth ions added to the optical fiber, but in ^{the case of Yb 3+} ions, the doping concentration The higher the value is, the higher the likelihood of the formation of inter-ion clusters increases, which may adversely affect the long-term stability of the system.In addition, as ^{the concentration of Yb 3+} ions increases, the numerical aperture (NA) increases and the beam quality (beam There is a disadvantage of lowering the quality(M ^{2 )).}

Another solution is to increase the amplification efficiency by increasing the diameter of the core and reducing the cladding to core area ratio (CCAR), but in this case, micro-bending loss occurs. Higher-order modes may increase the likelihood of occurrence.

On the other hand, among all-solid wide mode-area optical fibers, there are research results that have the effect of lowering the refractive index of the core by applying a pedestal layer around the core, but the size and shape of the pedestal are optimized. 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 An optical fiber type in which Al ³⁺ ions are added and Ge ions are doped to the clad has been proposed, but ^{the refractive index of the core is increased by the addition of Yb 3+} and Al ³⁺ ions, and the Ge ion concentration of the clad is increased to offset this effect. There is a disadvantage that the manufacturing process becomes difficult during the process of raising.

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 It is also being done. However, in the case of optical fibers used in ultrashort lasers, a lower numerical aperture is required than the refractive index lowered by AlPO4 generation.

On the other hand, briefly describing the prior art existing in the field to which the technology of the present invention belongs. First, U.S. Patent Laid-Open Publication US 2011/0206341 A1 is a conventional optical fiber with excellent beam characteristics due to the addition of Yb ions and low NA values. As a result, when the optical fiber medium is used to amplify the ultrashort pulse laser, the phenomenon of pulse distortion due to the accumulated nonlinear phase shift (B-integral) is remarkable, and the usual method taken to mitigate 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, resulting in the possibility of photo darkening due to beam quality and cluster formation. May increase, but in the prior art, Yb ³⁺ , Al ³⁺ and P ⁵⁺ ions are added to the core, a clad is located around the core, and the molar concentration ^{of Al 3+} and P ^{5+ ions in the core} In the case where the relationship is Al ³⁺ = P ⁵⁺ , Al ³⁺ > P ⁵⁺ and Al ³⁺ <P ⁵⁺ , the optical fiber is formed through the molar inequalities of Yb ³⁺ , Al ³⁺ and P ^{5+ ions.} was defined, the quality of the Al ^3+, and P ^5+, select ion concentration ratio and the lower the likelihood of developing the light darkening, even at high concentration Yb ^3+, and at the same time minimizing the increase in the refractive index of the core beam to be added, with Yb ³⁺ ( beam quality), and FIG. 1 shows the change in refractive index according to the change in ^{the P 5+ content in this case.}

However, if the composition of Yb Al:P is high, it is difficult to control the index profile and it is difficult to keep the background loss low, and the uneven distribution of ions distorts the refractive index distribution of the optical fiber core. Includes problems.

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

In the cross-section of the photonic crystal fiber for the development of a wide area mode optical fiber in FIG. 2, 1 is an optical fiber, 2 is a core, 3 is a cladding, and 4 is a medium having different refractive indices. Therefore, it is difficult to fusion with other optical fibers, and there is a disadvantage in that there are limitations in configuring the optical fiber amplifier.

Therefore, the laser beam quality (beam quality (M ² )) is excellent, the fusion between optical fibers is easy, and the pump laser absorption rate of the optical fiber per unit length is minimized to minimize the nonlinear phase shift (B-integral) accumulated through the optical fiber. By constructing an optical fiber-based pulse laser amplification system using the high optical fiber and the same, the need for development of an optical amplifier with improved characteristics and an ultra-short pulsed optical fiber laser device including the same is continuously required to this day.

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

The present invention was created to solve the above problem, in constructing an optical fiber-based pulse laser amplification system, in order to minimize the nonlinear phase shift (B-integral) accumulated through the optical fiber, the pump laser of the optical fiber per unit length An object of the present invention is to provide an optical amplifier using an optical fiber having a high absorption rate and an ultra-short pulsed 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 can be easily fused between.

The present invention provides an optical amplifier including 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 clad surrounding the core, and the core of the optical fiber includes a total core component, Ytterbium (Yb) content is included in 0.2 to 10 wt%, aluminum (Al) content and phosphorus (P) content are included in 0.5 to 25 wt%, respectively, and the clad is compared to the total 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 pump absorption rate of the clad of 10 dB/m or more.

As an example, compared to the total core component, the content of ytterbium (Yb) 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%, and The content can range from 5 to 25 wt%.

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

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

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

As an embodiment, the step-shaped wide mode optical fiber is arranged by being wound around the air in a circular or elliptical shape within a diameter of 0.5 cm to 500 cm, or wound around the outer surface of a cylindrical or polygonal tube or tube having a cross-section. 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 an output pulse after compression.

The present invention also provides a method of manufacturing an optical fiber, comprising the steps of: a) forming a clad made of a silica-germanium oxide layer by introducing a mixture gas of a Si precursor and a Ge precursor into a ceramic tube having a cavity formed therein; b) phospho-silicate soot is formed inside the clad by chemical vapor deposition, and ytterbium (Yb) and aluminum (Al) ions are introduced into the phospho-silicate soot through solution doping, and the ceramic Forming an optical fiber preform in which the tube surrounds the 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) in the clad by removing the ceramic tube; And d) processing the optical fiber preform to extract the optical fiber; including, a clad doped with germanium ions, and a core doped with ytterbium (Yb) aluminum (Al) and phosphorus (P) inside the clad. It provides a method of 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 an optical fiber is doped with ytterbium (Yb), aluminum (Al), and phosphorus (P), respectively, and the clad is doped with germanium (Ge). An 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, suppresses photo darkening, and reduces core NA (Numerical It has the advantage of maintaining an excellent beam profile by maintaining the aperture) below 0.07.

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, it has the advantage of obtaining a sufficient amplification effect.

In addition, since the transmission efficiency of the optical fiber according to the prior art is greatly reduced in the fusing process, it is essential to use an expensive fusing machine, and caution is required in the fusing process, and thus there is difficulty in mass production, but the optical fiber according to the present invention has a general fusing device. It has an additional advantage of stably obtaining high transmission efficiency even when used.

1 is a diagram showing 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 showing a cross-section of a photonic crystal fiber for developing a wide area optical fiber according to the prior art.
3 is a schematic diagram of a high-power ultra-short pulse laser device of a Master Oscillator Power Amplifier (MOPA) type using an optical fiber according to an embodiment of the present invention.
4 is a schematic diagram of an ultrashort pulse laser device in which the main amplification stage based on the stepped wide mode area optical fiber is configured in two stages according to the present invention.
5 is a diagram showing a graph showing a cross-sectional image 4a and a refractive index distribution 3b of an optical fiber obtained from a preform according to the present invention.
6 is a graph showing an ion concentration distribution graph (4a) measured through an 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.
7 is a schematic diagram of an amplifier for confirming the amplification characteristics of an optical fiber according to the present invention.
8 is a graph showing the experimental results for the amplification characteristics of the optical fiber according to FIG. 7.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of a cooling apparatus for an optical fiber laser amplification module according to the present invention will be described in detail so that those skilled in the art can easily implement the present invention. .

In each drawing of the present invention, the size or dimensions of the structures are shown to be enlarged or reduced than in actuality for the sake of clarity of the present invention, and the known configurations have been omitted so as to reveal a characteristic configuration, so the drawings are not limited thereto. .

In describing the principle of the preferred embodiment of the present invention in detail, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, a 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 includes a core suitable for transmission and amplification of an optical signal and surrounding the core. Contains a clad, and the core of the optical fiber contains a ytterbium (Yb) content of 0.2 to 10 wt% relative to the total core component, and an aluminum (Al) content and a phosphorus (P) content of 0.5, respectively. To 25 wt%, and the clad is characterized in that the content of germanium (Ge) is 1 to 40 wt% relative to the total clad component.

Meanwhile, as a more preferable example of each component doped to the core and clad in the stepped wide 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 have a range of 2 to 20 wt%, more preferably 5 to 16 wt%, and the content of phosphorus (P) is 5 to It may have a range of 25 wt%, more preferably 8 to 23 wt%. In addition, the content of germanium in the clad may preferably have a range of 2 to 30 wt%, more preferably 5 to 25, based on the total clad component.

Here, the content of each component in the core and/or clad in the present invention represents the weight occupied by the individual component (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 Similarly, it means representing the weight occupied by individual components (elements) relative to the total weight of the composition constituting the clad. That is, when the phosphorus (P) content is included in the range of 0.5 to 25 wt%, 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.

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

On the other hand, as described in the background art, when the length of the optical fiber becomes longer than 1 m, the nonlinear phase shift accumulation value (B-integral) is relatively large, resulting in distortion of the laser spectrum and pulse quality. ) Decreases, and in order to reduce the length of the amplified 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 Along with the disadvantage of lowering the quality (beam quality (M ² )), the possibility of clustering between ytterbium (Yb3+) ions increases, and photodarkening may occur.

Therefore, while researching on improvement of these problems, the inventors of the present invention have a ^{specific content of Yb 3+} , Al ³⁺ , P ⁵⁺ ions in the core of the optical fiber, and Ge ions in the clad. It has been found that the above problem can be solved when a step index large mode area fiber added in the range of 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 power, ytterbium (Yb ³⁺ ), aluminum (Al ³⁺ ), and phosphorus (P ^{5) are applied to the core of the optical fiber as an amplification medium. +} ) Ions are added in a specific range, and germanium (Ge ⁴⁺ ) ions are added to the clad of the optical fiber in a specific range. ) Is used for an 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, and a seed laser having a small output and a pump laser having a high power are simultaneously incident on an amplifying medium such as an amplifying optical fiber to be seeded. (seed) It can amplify the output of the laser.

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

Meanwhile, as an optical fiber used therein to provide the optical amplifier according to the present invention, a step index large mode area fiber may be used. The stepped wide mode area optical fiber may exhibit 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 core at a center 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 cylinder 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, according to the present invention, an optical fiber preform is first manufactured, and the optical fiber can be extracted by processing the preform through drawing or the like.

Looking at this in more detail, the method of manufacturing an optical fiber according to the present invention includes the steps of: a) forming a clad made of a silica-germanium oxide layer by introducing a mixture gas of a Si precursor and a Ge precursor into a ceramic tube having a cavity formed therein; b) phospho-silicate soot is formed inside the clad by chemical vapor deposition, and ytterbium (Yb) and aluminum (Al) ions are introduced into the phospho-silicate soot through solution doping, and the ceramic Forming an optical fiber preform in which the tube surrounds the 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) in the clad by removing the ceramic tube; And d) processing the optical fiber preform to extract the optical fiber; and a clad doped with germanium ions by this method, and ytterbium (Yb) aluminum (Al) and phosphorus (P) inside the clad. ), it is possible to obtain an optical fiber made of a doped core.

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

First, as a first step, the step (a) of forming a clad made of a silica-germanium oxide layer on a ceramic tube with a cavity formed therein (step (a)) is a cladding part corresponding to the outside of the preform for manufacturing an optical fiber into the ceramic tube. It is a step of forming by chemical vapor deposition on the inside of the pupil. For this, a ceramic tube that can be removed in step c) is used, and a mixed gas of a Si precursor and a Ge precursor is respectively added to 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, a deposition temperature in the range of 1000 ~ 1800 ℃ can be used, and because the tube can be closed due to 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 through which molecules are diffused is balanced.

As the second step, ^{the step (b) of depositing ytterbium (Yb 3+} ), phosphorus (P ⁵⁺ ), and aluminum (Al ³⁺ ) ions on the core) corresponds to the inside of the preform for manufacturing an optical fiber. This is the step of forming the core part. To this end, a phospho-silicate soot (P ₂ O ₅ -SiO ₂ ) is formed in the interior of the clad by chemical vapor deposition, and the porosity is controlled through a pre-sintering step. And stabilizes. ^{Next, Yb 3+} and Al ³⁺ ions are supplied through a solution doping technique, and finally, after sintering a soot, the tube is closed, and the ceramic tube such as the silica tube is removed. Complete the optical fiber preform in the form of wrapping the surface. _{In this process, POCl 3} is strongly injected ^{to replenish 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 performed by doping and depositing germanium ions in a ceramic tube such as a silica tube obtained in step b) above. Corresponds to the step of completing an optical fiber preform by removing the ceramic tube from a clad and a ceramic tube-optical fiber preform composite comprising 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 a method such as HF etching and/or mechanical milling.

As a final step, step (d)) of manufacturing an optical fiber by processing the optical fiber preform can manufacture an optical fiber by drawing from the preform, which is usually mounted on an optical fiber extraction facility, and the It can be pulled out by melting the end of the optical fiber preform. The drawn optical fiber is coated with an ultraviolet curable resin or a thermosetting resin, and the outer layer may be formed by curing the resin with ultraviolet or heat, and the outer layer may protect the optical fiber from the external environment by increasing the mechanical strength of the optical fiber.

At this time, the preform may be used with a diameter of 5 to 20 mm and a length of about 0.1 to 1 m, and the characteristics of the optical fiber such as the size and composition ratio of the core/clad of the optical fiber, and the refractive index are already in the formation step of the preform. It is determined, and the step of drawing the optical fiber of step d) corresponds to the step of controlling the temperature or speed and drawing the optical fiber of the predetermined characteristic so as to have uniform characteristics in the longitudinal direction.

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

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

In addition, according to the manufacturing method of the optical fiber according to the present invention, preferably, the content of ytterbium (Yb) in the core is in the range of 0.3 to 8 wt% relative to the total core component, and the content of aluminum (Al) is 2 to 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 compared to the total clad component, An optical fiber in the range of 2 to 30 wt% may be provided, and in this case, the core and clad of the optical fiber may each be a silica matrix.

Meanwhile, 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 stepped wide mode area optical fiber, and preferably, a pump light source-pump combine. It can be connected by the sequence of u-optical fibers.

In addition, the stepped wide mode area optical fiber according to the present invention is arranged to be wound in the atmosphere in a circular or elliptical shape within a diameter of 0.5 cm to 500 cm, or wound around the outer surface of a cylindrical or polygonal tube or tube to have an optical fiber. It can be used in an amplifier, and by selecting and applying an appropriate winding diameter, it makes a relative difference in the loss of the fundamental mode and higher order mode of the optical fiber, and as a result, the fundamental mode is dominant. The pulse output can be secured. When the winding diameter is 500 cm or more, the relative loss difference between modes is meaninglessly small, and when the winding diameter is 0.5 cm or less, the loss experienced 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 manufacturing method of the optical fiber, an optical amplifier including the optical fiber, and an ultrashort pulse laser device including the optical amplifier. In this case, the ultrashort pulse laser device may be a laser device using an ultrashort pulse in a range of 100 ps to 10 fs based on an output pulse after compression.

3 is a schematic diagram of a high-power ultra-short pulse laser device of a Master Oscillator Power Amplifier (MOPA) type using an optical fiber according to an embodiment of the present invention. More specifically, the stable and low-power seed laser oscillated from the resonator (1) passes through the stretcher (2) prior to amplification and spreads in the time axis to have a sufficiently low peak power, If necessary, the main amplification stage (Main-Amplifier) passes through the pre-amplifier (3) and includes an optical fiber (7), an isolator (4), a pump light source (5), and a pump combiner (6) according to the present invention. amplifier) 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, passes through a pump combiner 6, and enters the optical fiber 7, and is a pump light source. (Laser diode, 5) is also incident on the optical fiber 7 through the pump combiner (6).

The laser amplified while passing through the optical fiber 7 passes through the compressor 8 and is compressed into an ultrashort pulse laser in the range of 100 ps to 10 fs. In some cases, there are two or more pump light sources (pump LD) 5 connected to the pump combiner (6) depending on the required pump output and characteristics of the pump LD. Here, the stepped wide mode area optical fiber 7, which is the amplification medium of the main amplification end, 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 ultrashort pulse laser device according to the present invention may be configured in multiple stages by connecting a plurality of main-amplifiers in series.

In FIG. 4, a system in which the main amplification stage based on the stepped wide mode area optical fiber according to the present invention is composed of two stages, and between the main amplification stage and the main amplification stage, an isolator 4 and a high-order mode remover for removing a higher-order mode. 9) may be located, and a higher-order mode canceller 9 may be located at the end of the final amplification stage.

Hereinafter, the physical properties of the optical fiber for a 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 and a graph showing a refractive index distribution of an optical fiber obtained from a preform, completed through the present invention.

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

In addition, the difference in refractive index between the core and the clad is about 0.0017, which can expect a numerical aperture (NA) of 0.07 level, and the numerical aperture can be adjusted by adjusting the doping level of germanium (Ge) ions in the clad during the preform manufacturing process. .

6A is a graph of ion concentration distribution measured through Energy Dispersive X-ray Spectroscopy (EDS), wherein the concentration in the core in the optical fiber is based on a silica matrix, and Yb2O3 is 0.4 mol% (4 wt. % Yb), Al2O3 is 4.4 mol% (11 wt% Al), and P2O5 is 4.8 mol% (17 wt% P), and a flat concentration distribution as a whole can be confirmed.

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 relative to the total clad components by measuring the refractive index.

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

6B shows the measured absorption rate of the optical fiber manufactured according to the present invention, and it can be seen 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 an optical fiber according to the present invention, in which both ends of the optical fiber manufactured according to the above embodiment are 4% reflective surfaces, and the optical fiber itself is configured to serve as a laser resonator, The pump and laser are incident on the optical fiber through the lens or collimated and emitted. The optical fiber was subjected to bending at the level of 5 cm in diameter to eliminate higher-order modes.

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

Here, if a pump light source (pump LD) that is not wavelength stabilized is used, the center wavelength of (pump LD) may flow at a different value during the amplification process, which may affect wavelength conversion efficiency. On the other hand, if the wavelength-stabilized pump LD is used, the center wavelength is kept constant even during the amplification process, and thus the conversion efficiency can be obtained constant.

In the present embodiment, a 2 m optical fiber was used when a pump light source (pump LD) that was not wavelength stabilized was used, and a 0.5 m optical fiber was used when a pump light source (pump LD) that was wavelength stabilized was used. When a wavelength stabilized pump LD with 71.5 W average power is used, the maximum power 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, but this is only exemplary, and various modifications and other equivalent embodiments are possible from those of ordinary skill in the art. You will understand. Therefore, the technical protection scope of the present invention should be determined 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 (11)

In the optical amplifier comprising a step index large mode area fiber (step index large mode area fiber),
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 core of the optical fiber contains 0.2 to 10 wt% of ytterbium (Yb), and 0.5 to 25 wt% of aluminum (Al) and phosphorus (P), relative to the total core component. Become,
The clad is an optical amplifier, wherein the content of germanium (Ge) is 1 to 40 wt% relative to the total clad component.
The method of claim 1,
Optical amplifier, characterized in that the length of the optical fiber is less than 1.5 m.
The method of claim 1,
The optical amplifier, characterized in that the pump absorption rate of the clad is 10 dB/m or more.
The method of claim 1,
Compared to the total core component, the content of ytterbium (Yb) in the core is in the range of 0.3 to 8 wt%, and the content of aluminum (Al) is in the range of 2 to 20 wt%,
The optical amplifier, characterized in that the content of phosphorus (P) is in the range of 5 to 25 wt%.
The method of claim 1,
The optical amplifier, characterized in that the content of germanium (Ge) in the clad is in the range of 2 to 30 wt% relative to the total clad component.
The method of claim 1,
In the optical amplifier, at least one selected from a pump combiner and a pump light source is optically connected to a stepped wide mode area optical fiber.
The method of claim 1,
The optical amplifier of the optical fiber, characterized in that the core and the clad are each silica matrix.
The method of claim 1,
The stepped wide mode area optical fiber is used for an optical amplifier by being wound around the air in a circular or elliptical shape within a diameter of 0.5 cm to 500 cm, or by being wound around the outer surface of a cylindrical or polygonal tube or tube having a cross section. Optical amplifier.
An ultra-short pulse laser device comprising the optical amplifier according to any one of claims 1 to 8, and using ultra-short pulses within 100 ps to 10 fs based on output pulses after compression.
a) forming a clad made of a silica-germanium oxide layer by respectively introducing a mixture gas of a Si precursor and a Ge precursor into a ceramic tube having a cavity formed therein;
b) phospho-silicate soot is formed inside the clad by chemical vapor deposition, and ytterbium (Yb) and aluminum (Al) ions are introduced into the phosphosilicate soot through solution doping, and the ceramic Forming an optical fiber preform in which the tube surrounds the 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) in 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. Optical fiber manufacturing method
An optical fiber obtained by the manufacturing method according to claim 10, and an optical amplifier comprising the optical fiber.

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