KR20200048059A - Gain medium having selective doping concentration and optical amplifier including same - Google Patents

Abstract

The present invention relates to an optical amplification device, which comprises: an optical pumping unit for generating pump light; a gain medium unit for performing optical amplification of a seed beam through the pump light; and a light transmission unit which collects the pump light generated by the optical pumping unit and transfers the collected pump light to the gain medium unit. The gain medium unit includes a first segment including a focusing point, which is the point with the highest focusing rate of the pump light, and a second segment including a non-focusing point, which is the point with the lowest focusing rate of the pump light, wherein the doping rate of the first segment is higher than the doping rate of the second segment. The present invention selectively increases the doping concentration of a portion with high pump intensity or a portion with high laser mode distribution, thereby obtaining more amplified laser output intensity at the same pump intensity in comparison to the case in which the doping concentration is uniform in the gain medium.

Description

GAIN MEDIUM HAVING SELECTIVE DOPING CONCENTRATION AND OPTICAL AMPLIFIER INCLUDING SAME}

The present invention relates to a gain medium and an optical amplifying device including the same, and more particularly, to a gain medium in which doping is subdivided and to an optical amplifying device comprising the same.

Laser devices are effectively used throughout the industry, including manufacturing processes, and are widely used in the field of medical devices that serve to precisely incise skin or selectively ablate parts of body tissue during surgical operations.

In general, the laser means amplification of light by a stimulated emission phenomenon, and the laser amplification device is a gain medium capable of amplifying light, a resonator capable of trapping light, and a gain medium. The pumping part that gives energy to the body is essential. Here, the resonator may be composed of a reflector and an output mirror, which are disposed on both sides of the gain medium.

Since the gain medium is excited by the pumping energy and can amplify the incoming seed beam, it is widely used for amplification of lasers or light. At this time, pumping is required for density inversion in the gain medium. Amplification of light is achieved through.

Here, optical pumping is one of various methods of applying pumping energy, and refers to an action of optically injecting excitation energy into a gain medium, and electrons inside the gain medium are excited by light pumping action and seeded by induced emission. Amplify the beam.

Lasers can be classified into various types of lasers, such as gas lasers, liquid lasers, solid-state lasers, and semiconductor lasers, depending on the type of gain medium. Here, a solid state material such as glass or crystal is used as a gain medium, and a laser device doped with rare earth ions such as neodymium, chromium, erbium, thulium, and ytterbium is particularly used in a solid state laser device. laser device), and the solid laser device has an advantage of being relatively efficient and compact.

However, when the solid-state laser device is configured as a high power laser for increasing the power of the laser, there is a problem in that considerable heat is generated in the gain medium in the light pumping process. This is a problem that only a part of the pumped light contributes to laser oscillation or amplification, and the rest is present in the gain medium as heat, which causes uneven heat distribution in the gain medium, degrades the laser beam quality and further improves the gain. It can cause mechanical defects such as cracking and damage of the medium.

In order to solve the heat problem, a thin disk shape in which the heat dissipation area is widened by configuring the medium in a thin thickness, a slab form using a thin plate-like structure having a large volume to area ratio as the medium, and an optical fiber (Fiber) The shape and the like have been presented, but the thin disc and slab shape has the disadvantage that the structure is very complex, such as requiring precise alignment, and the fiber shape has a thin core and requires high energy light to be converged in a narrow space. effect).

Therefore, recently, as a form of a high power laser, a single crystal fiber (SCF) form in which various advantages are appropriately compromised has been attracting attention. SCF is a rod made of monocrystalline material.

In the conventional SCF, the doping concentration of the laser gain medium is evenly distributed throughout the gain medium. In this case, there is a problem that efficient amplification cannot be achieved because the spatial overlap of the seed beam and the pump light is not considered at all. That is, when pump absorption due to doping occurs in a region where the overlap of the seed beam mode and the pump mode is low, the pump light absorption is not used for laser oscillation and amplification, but is lost as spontaneous emission and heat, so that the amplification efficiency decreases. do.

In order to solve the above problems, an object of the present invention is to provide an optical amplification device in which laser oscillation efficiency is significantly improved through a gain medium selectively doped with a portion having high spatial overlap between the laser mode and the pump mode.

In order to solve the above technical problem, the present invention discloses an optical amplification device, condensing an optical pumping unit for generating pump light, a gain medium unit for amplifying the seed beam through the pump light, and the pump light generated by the optical pumping unit Thus, including a light transmission unit for transmitting to the gain medium portion, the gain medium portion is the first segment containing the focus point of the highest point of focus of the pump light and the non-focus point of the point of the lowest focus rate of the pump light It includes a second segment included, it characterized in that the doping rate of the first segment is formed higher than the doping rate of the second segment.

In addition, the first segment is centered around the focusing point, a first intermediate point which is an intermediate point between the focusing point and a non-focusing point adjacent to one direction of the focusing point, and a ratio adjacent to the other direction of the focusing point and the focusing point. It is characterized in that it is an area formed below the distance between the second intermediate point, which is the intermediate point of the focusing point.

In addition, the first segment is characterized in that the area formed of 6.5 to 8.5 mm.

In addition, the second segment is characterized by being an undoped region.

In addition, the gain medium portion is characterized in that the single crystal fiber (Single Crystal Fiber, SCF) type.

In addition, the gain medium is characterized in that it has a cylindrical rod shape (cylindrical rod) having a circular or polygonal cross section.

In addition, the present invention is another embodiment of the optical amplification device, the optical amplification device is a light pumping unit for generating a pump light by starting, a gain medium portion for amplifying the seed beam through the pump light, and the pump light generated by the pump light source unit Including a light transmission unit for condensing and transmitting the gain medium, the gain medium unit includes a first segment including a region having the highest light distribution of the seed beam and a second portion including a region having the lowest light distribution of the seed beam. Including a segment, the doping rate of the first segment is characterized in that it is formed higher than the doping rate of the second segment.

In addition, the first segment is characterized in that the area corresponding to the optical path of the seed beam.

In addition, the doping rate is gradually lowered from the first segment toward the second segment.

In addition, the first segment is characterized in that it is a cylindrical region formed less than 1/2 of the radius of the gain medium portion based on the center point in the axial direction of the gain medium portion.

According to embodiments of the present invention The effects of the optical amplifying device are as follows.

According to the present invention, by selectively increasing the doping concentration of a portion having a high pump intensity or a portion having a high laser mode distribution, compared with the case where the doping concentration is uniform in the gain medium, amplified laser output intensity can be obtained at the same pump intensity .

In addition, it is possible to improve the efficiency of laser oscillation by lowering efficient light pumping and reabsorption of the amplified beam.

However, the gain medium having the selective doping concentration according to the embodiments of the present invention and the effects that the optical amplifying device including the same can achieve are not limited to those mentioned above, and other effects not mentioned are described below From this will be clearly understood by those of ordinary skill in the art.

The accompanying drawings, which are included as part of the detailed description to aid understanding of the present invention, provide embodiments of the present invention and describe the technical spirit of the present invention together with the detailed description.
1 shows a configuration diagram of an optical amplifying device 1000 according to the present invention.
Figure 2 shows a gain medium 400 according to an embodiment of the present invention.
3 is a cross-sectional view of the gain medium portion 400 shown in FIG. 2 in A-A 'direction.
FIG. 4 specifically illustrates the first segment 410A of the gain medium 400 of FIG. 2.
5 is a cross-sectional view of each gain medium portion in which uniform doping or selective doping is performed as an embodiment of the present invention.
FIG. 6 is a graph showing the value of the amplification output versus the pumping output of each gain medium section (Case 1 to 4) shown in FIG.
7 (a) and 7 (b) are graphs showing the amplification factor (Gain) compared to the pumping output of the gain medium portion doped under various conditions.
8 is a graph showing the absorbance value of the pump light compared to the pumping output of the gain medium doped under various conditions.
9 shows a gain medium unit 400 according to another embodiment of the present invention.
10 is a cross-sectional view of the gain medium portion 400 shown in FIG. 9 in A-A 'direction.
11 is a graph showing the doping concentration according to the radius r in the gain medium part 400 shown in FIG. 9.

Terms or words used in the present specification and claims should not be interpreted as being limited to ordinary or lexical meanings, and the inventor may appropriately define the concept of terms in order to explain his or her invention in the best way. Based on the principle that it can be, it should be interpreted as meanings and concepts consistent with the technical spirit of the present invention. Therefore, the configuration shown in the embodiments and drawings described in this specification is only one of the most preferred embodiments of the present invention, and does not represent all of the technical spirit of the present invention, and can replace them at the time of application. It should be understood that there may be various equivalents and variations. Hereinafter, a gain medium having a selective doping concentration according to an embodiment of the present invention and an optical amplifying device including the same will be described in detail with reference to the accompanying drawings.

1 shows a configuration diagram of an optical amplifying device 1000 according to the present invention.

The optical amplifying apparatus 1000 according to the present invention includes an initial laser beam to be amplified, that is, a seed beam generator 100 that generates a seed beam, an optical pumping unit 200 that generates pump light, and an incident pump light It includes a light transmission unit 300 for condensing the pump light generated in the gain medium unit 400 and the light pumping unit 200 where light amplification of the seed beam is performed through the light medium 300 and condensing the pump light.

The seed beam generator 100 generates laser light, and transmits light generated from the seed beam generator 100 to the gain medium 400.

The light pumping unit 200 generates pump light and causes the generated pump light to enter the gain medium 400. Due to this, the amount of energy stored in the gain medium unit 400 increases, and the density inversion of the medium occurs, so that the seed beam is optically amplified. Here, the light pumping unit 200 may be a laser diode array in which a plurality of laser diodes LD are mounted, and collimation may be performed by a micro lens or the like.

The gain medium part 400 amplifies the seed beam irradiated to the gain medium part 400 by using the energy obtained through the pump light, and ultimately emits an amplified laser. As an example, the gain medium 400 may have a cylindrical pillar shape having a diameter of approximately 1 to 2 mm or less.

The light transmission unit 300 may be an optical device that collects the pump light generated by the light pumping unit 200 and transmits it to the gain medium unit. As an embodiment, a collimating lens and a focusing lens may be used to collect (or focus) light generated by the light pumping unit 200 and irradiate the gain medium unit 400. .

The present invention is to increase the laser oscillation efficiency through the gain medium unit 400 which increases the doping rate of the overlap of the seed beam and the pump light incident on the gain medium unit 400, that is, the spatial overlap of the laser mode and the pump mode is high. It is aimed at. Hereinafter, the gain medium 400 according to the present invention will be described in detail with reference to FIGS. 2 to 4.

Figure 2 shows a gain medium 400 according to an embodiment of the present invention.

Referring to FIG. 2, the gain medium 400 according to the present invention includes a first segment 410A including a focus point 412A, which is a point having the highest focus rate of the pump light, and a point at which the focus rate of the pump light is lowest. And a second segment 410B including a phosphorus non-focusing point 412B, wherein a doping rate of the first segment 410A is higher than that of the second segment 410B.

In order to increase the amplification efficiency of the laser, the pump energy absorbed by the gain medium 400 should contribute only to the amplification of the laser mode as much as possible. That is, when the pump energy absorption is high in the space where the laser mode is distributed, the laser efficiency may be maximized.

To this end, the present invention selectively increases the doping rate (or doping concentration) where the pump light generated from the light pumping unit 200 in the gain medium 400 is focused (or is segmented) or the laser mode The doping concentration is increased only in the distributed space so that most of the absorbed pump energy can contribute to laser amplification.

Particularly, in the case of a gain medium such as a single crystal fiber (SCF) used as the gain medium of the present invention, the reabsorption rate of the amplified beam can be reduced, and in a region where the doping concentration is low, heat conductivity is relatively high and heat dissipation Efficiency can also be increased. Here, the SCF gain medium may be a cylindrical rod having a circular or polygonal cross section.

The first segment 410A is a region in which the focusing point 412A, which is the point where the focusing rate of the pump light is the highest, is included and the doping rate is formed high. Here, 'focused' means that incident pump light is gathered in one place, and 'point' means a specific area including dots.

The second segment 410B is a region in which the doping rate is low because the non-focusing point 412B, which is the point where the focusing rate of the pump light is the lowest, is included. Here, 'non-focusing' means that the incident pump light is the most dispersed, that is, the most diffused, and 'point' means a specific area including dots. The detailed configuration of the gain medium 400 will be described with reference to FIGS. 3 and 4.

FIG. 3 shows a cross section in the A-A 'direction of the gain medium part 400 shown in FIG. 2, and FIG. 4 specifically shows a first segment 410A of the gain medium part 400 of FIG. 2 Did.

Referring to FIG. 4, the first segment 410A of the gain medium 400 according to the present invention is an intermediate point between the focusing point and a non-focusing point adjacent to one direction of the focusing point, centering on the focusing point. It is characterized in that it is an area formed below a distance between the first intermediate point and the second intermediate point which is the intermediate point of the non-focusing point adjacent to the other direction of the focusing point and the focusing point.

Since the focusing point 412A, which is the highest focusing rate of the incident pump light, and the non-focusing point 412B, which is the lowest focusing rate, appear alternately, the focusing point 412A has a non-focusing point adjacent to both sides. (412B) is formed. The first segment 410A is a first intermediate point, which is an intermediate point of a non-connecting point 412B, and a second intermediate point, which is an intermediate point between the other non-connecting point 412B, around the focusing point 412A. It may be formed of a region (ie, L / 2 + L / 2), or may be formed below a distance between the first intermediate point and the second intermediate point.

The focusing point 412A and the non-focusing point 412B may be formed in various positions and numbers in the gain medium 400 according to a pump condition in which pump light of the light pumping unit 200 is incident. Specifically, it may vary according to the angle (Numerical Aperture, NA), the radius of the gain medium, the length of the gain medium, and the refractive index of the gain medium. As an embodiment, the first segment 410A may be formed at 8.3 mm under the condition of NA 0.11 of the pump light, radius of the gain medium of 0.5 mm, and refractive index of the gain medium of 1.82.

In the first segment 410A, a doped host material may be used at a certain concentration (for example, 1 to 5%), and in one embodiment, rare earths such as tolium (Tm) or ytterbium (Yb) may be used. A doped yttrium-aluminum-garnet (YAG) may be used, and the second segment 410B may be a host material doped at a concentration lower than that of the first segment 410A. When the second segment 410B is undoped, an undoped host material may be used, and in this case, it may be an undoped YAG.

5 is a cross-sectional view of each gain medium portion in which uniform doping or selective doping is performed as an embodiment of the present invention. In order to confirm the efficiency of the gain medium having a selective doping concentration, the NA of the pump light is 0.11, the radius of the pump light is 200 μm, the radius of the gain medium is 0.5 mm, the refractive index of the gain medium is 1.82, and the length of the gain medium is computed under the condition of 30 mm. Compared.

Case 1 and Case 3 are uniformly doped the entire gain medium at a concentration of 1% or 2%, and Case 2 and Case 4 are the first segment containing the focus point, which is the point where the focus rate of the pump light is highest in the gain medium. The region corresponding to is uniformly doped at a concentration of 1% or 2%, and the region corresponding to the second segment including the non-focusing point, which is the point where the focus rate of the pump light is the lowest, is non-doped. In Case 2 and Case 4, it can be seen that the first segment region in the gain medium is formed to be about 7.5 mm. At this time, the distance L between the focusing point where the focusing rate of the pump light is the highest point and the non-focusing point which is the point where the focusing rate of the pump light is the lowest is 8.3 mm, but in order to easily compare the effects with Case 1 and Case 3 The first segment region was set to 7.5 mm so that the total doping concentration in the gain medium of Case 1 and Case 4 was the same.

FIG. 6 is a graph showing the value of the amplification output compared to the pumping output of each gain medium section (Case 1 to 4) shown in FIG. 5.

In the graph of FIG. 6, 1p and 2p mean the doping concentrations of 1% and 2%, and 1pseg and 2pseg mean that the concentration of 1% or 2% is selectively doped, and 50W is the initial seed beam. It means that the output is 50 W.

Comparing Case 1 and Case 4, it can be seen that the amplified output is the same where the pumping output is 0. This is because the total doping concentration of the uniformly doped gain medium of 1% and the selective selective doping of 2% is the same, so that when the pumping output is 0, the absorption rate of the seed beam is the same. However, it can be seen that as the pumping output gradually increases, a significant difference occurs in the amplified output.

Through this, it can be seen that even when the doping is performed at the same concentration, when the region where the pump light is focused is selectively doped, the amplification output becomes larger.

Also, comparing Case 3 and Case 4, it can be seen that the amplified output is lower in Case 3 where the pumping output is 0. This result is because the 2% uniformly doped gain medium has a higher total doping concentration than the 2% selective doping gain medium (approximately twice), which is higher where the seed beam absorption is higher in the higher doping concentration. Because it happens. In case 4, it can be seen that the amplification output according to the pumping output is higher or almost similar within a certain range of the pumping output, although the total doping concentration is only about half as compared to case 3.

That is, when the region where the pump light is focused is selectively doped, it means that the same amplification output can be exhibited at half the concentration when the whole is uniformly doped within a certain range of the pumping output.

7 (a) and 7 (b) are graphs showing the amplification factor (Gain) compared to the pumping output of the gain medium portion doped under various conditions.

7A, the total doping concentration of the 1% uniformly doped gain medium 1p and the 2% selective doping gain medium 2pseg is the same as described above.

When comparing 1p10W and 2pseg10W, it can be seen that the amplification rate is remarkably large when the doping is selectively performed despite the same doping total concentration. This is the same when comparing 1p50W and 2pseg50W, and 1p100W and 2pseg100W.

7 (b), the total doping concentration is about 2 times higher than that of the 2% uniformly doped gain medium (2 pseg) in which the 2% uniformly doped gain medium (2p) is selectively doped.

When comparing 2pseg10W and 2p10W, it can be seen that although the total doping concentration is only about half, the amplification output according to the pumping output is higher or almost similar in a certain range. This is the same when comparing 2pseg50W and 2p50W, and 2pseg100W and 2p100W.

In conclusion, as compared with the case where the doping concentration of the entire gain medium is maintained and the doping concentration is selectively increased only at the portion where the pump is focused, the output intensity of the doped granular amplification medium is uniformly doped. As a result, the former always has a high amplification rate. I could confirm.

8 is a graph showing the absorbed pump power value of the pump light compared to the pumping output of the gain medium doped under various conditions.

When comparing 1p10W and 2pseg10W in FIG. 8 (a), it can be confirmed that both have the same total doping concentration, and thus the absorption rate of the pump light is almost the same. Considering these results together with FIGS. 6 and 7, it can be seen that although the absorption rate of the pump light is the same, the amplification rate of the gain medium in which selective doping is performed is remarkably high. This is the same when comparing 1p50W, 2pseg50W of FIG. 8 (b), 1p100W, 2pseg100W of FIG. 8 (c).

9 shows a gain medium part 400 according to another embodiment of the present invention, and FIG. 10 shows a cross section in the A-A 'direction of the gain medium part 400 shown in FIG. 9, and 11 is a graph showing the doping concentration according to the radius r in the gain medium 400 shown in FIG. 9.

The gain medium 400 according to another embodiment of the present invention includes a first segment 420A including an area having the highest light distribution of the seed beam and a second area including an area having the lowest light distribution of the seed beam. Including the segment 420B, the doping rate of the first segment 420A is formed to be higher than the doping rate of the second segment 420B.

The first segment 420A includes a seed beam, that is, a region having the highest spatial overlap with laser mode. Here, the first segment 420A may be an area corresponding to (or corresponding to) the optical path of the seed beam. The portion of the gain medium 400 having the highest spatial overlap with the laser mode is the central portion in the axial direction. Therefore, the cylindrical region corresponding to the predetermined radius r may be the first segment 420A based on the central point in the axial direction. In one embodiment, r may be less than 1/2 of the gain medium radius. This is because it is advantageous that the seed beam radius is less than 1/2 of the radius of the gain medium in order to enter the gain medium while maintaining the beam quality without diffraction influence. As a specific example, when the gain medium radius is 500 μm, the size of the seed beam incident on the gain medium is preferably 200 μm or less.

The second segment 420B is an area in which a doping concentration is lower than that of the first segment 420A, and may be an undoped area as an embodiment. On the other hand, without doping the second segment 420B, it is also possible to gradually dopantly lower the concentration from the first segment 420A toward the second segment 420B.

FIG. 11 is a graph showing the doping concentration according to the radius r in the gain medium part 400 shown in FIG. 9, and FIG. 11 (a) is a form in which the concentration continuously decreases toward the outer side from the central axis (ex ) Exponential reduction, doping with a Gaussian distribution), and (b) of FIG. 11 maintains the same concentration up to a certain distance and dopes the rest. 11 (c) is a form in which the concentration is doped so as to decrease stepwise. The above doping forms have the highest doping concentration in the axial center portion with the highest spatial overlap with the laser mode.

When selectively doping a place having high overlap with the laser mode as described above, improved amplification output may be exhibited when the whole is uniformly doped at the same concentration.

Although the exemplary embodiments of the present invention have been described in detail above, those skilled in the art to which the present invention pertains will understand that various modifications are possible within the limits without departing from the scope of the present invention. . Therefore, the scope of rights of the present invention should not be limited to the described embodiments, but should be determined not only by the claims to be described later, but also by the claims and equivalents.

1000: optical amplification device
100: seed beam generator
200: optical pumping unit
300: light transmitting unit
400: gain medium
410A, 420A: first segment
412A: Focusing point
410B, 420B: second segment
412B: Non-focused point

Claims (11)

An optical pumping unit generating pump light;
A gain medium unit for amplifying the seed beam through the pump light; And
A light transmission unit that collects pump light generated by the light pumping unit and transfers the light to the gain medium unit;
Including, the gain medium portion includes a first segment including a focusing point, which is the point with the highest focusing rate of the pump light, and a second segment including a non-focusing point, which is the point where the focusing rate of the pump light is lowest, The optical amplification device, characterized in that the doping rate of the first segment is formed higher than the doping rate of the second segment.
According to claim 1,
The first segment
Centering on the focusing point,
The distance between the focusing point and the first intermediate point, which is the intermediate point of the non-focusing point adjacent to one direction of the focusing point, and the second intermediate point, which is the intermediate point of the focusing point and the non-focusing point adjacent to the other direction of the focusing point. An optical amplifying device characterized in that it is a region formed below.
According to claim 2,
The first segment is an optical amplifying device, characterized in that the area formed of 6.5 to 8.5 mm.
According to claim 1,
And the second segment is an undoped region.
According to claim 1,
The gain medium portion is a single crystal optical fiber (Single Crystal Fiber, SCF) type optical amplification device.
According to claim 1,
The gain medium is an optical amplification device, characterized in that the cylindrical rod (cylindrical rod) having a circular or polygonal cross-section.
An optical pumping unit generating pump light;
A gain medium unit for amplifying the seed beam through the pump light; And
A light transmission unit that collects the pump light generated by the pump light source unit and transfers it to the gain medium;
Including, the gain medium portion includes a first segment including a region having the highest light distribution of the seed beam and a second segment including a region having the lowest light distribution of the seed beam, the first segment The doping rate of the optical amplification device, characterized in that formed higher than the doping rate of the second segment.
The method of claim 7,
The first segment is an optical amplifying device, characterized in that the area corresponding to the optical path of the seed beam.
The method of claim 7,
And the second segment is an undoped region.
The method of claim 7,
The optical amplifying device, characterized in that the doping rate is gradually lowered from the first segment to the second segment.
The method of claim 7,
The first segment is a light amplifying device, characterized in that the cylindrical region formed by less than 1/2 of the radius of the gain medium portion based on the center point in the axial direction of the gain medium portion.

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