JP5259923B2 - Optical amplification module and laser light source - Google Patents

Optical amplification module and laser light source Download PDF

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JP5259923B2
JP5259923B2 JP2006012998A JP2006012998A JP5259923B2 JP 5259923 B2 JP5259923 B2 JP 5259923B2 JP 2006012998 A JP2006012998 A JP 2006012998A JP 2006012998 A JP2006012998 A JP 2006012998A JP 5259923 B2 JP5259923 B2 JP 5259923B2
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optical amplification
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JP2007194501A (en
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忍 玉置
素貴 角井
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Megaopto Co Ltd
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本発明は、被増幅光を光増幅媒体において光増幅する光増幅モジュール、および、このような光増幅モジュールを備えるレーザ光源に関するものである。   The present invention relates to an optical amplification module that optically amplifies light to be amplified in an optical amplification medium, and a laser light source including such an optical amplification module.

現在、レーザ光を用いた加工技術が注目されており、加工用や医療用など各分野においてレーザ光源の需要が高まっている。各種のレーザ光源の中で特に注目されているレーザ光源として、ファイバレーザ光源が挙げられる。このファイバレーザ光源は、ＹｂやＥｒやＴｍなどの各種希土類元素を添加された光ファイバを光増幅媒体として備え、この光増幅媒体に励起光を供給して被増幅光を光増幅したり、共振器構造によりレーザ発振させたりすることができる。ファイバレーザ光源の利点として、レーザ光が光ファイバ内で閉じ込められていることから扱いが容易である点、熱放射性が良いことから大規模な冷却設備を必要とすることがない点、などが挙げられる。
CLEO/Europe Conference’05, No.CP2-2-THU, 2005 Currently, processing technology using laser light is attracting attention, and demand for laser light sources is increasing in various fields such as processing and medical use. A fiber laser light source is mentioned as a laser light source which attracts special attention among various laser light sources. This fiber laser light source includes an optical fiber to which various rare earth elements such as Yb, Er, and Tm are added as an optical amplifying medium, supplies pumping light to the optical amplifying medium, and optically amplifies the amplified light, or resonates. The laser structure can be used to oscillate the laser. Advantages of the fiber laser light source include that it is easy to handle because the laser light is confined in the optical fiber, and that it does not require a large-scale cooling facility because of its good thermal radiation. It is done.
CLEO / Europe Conference'05, No.CP2-2-THU, 2005

しかし、高パワーの光が光ファイバ内で発生することにより、光ファイバ内の添加物や不純物にダメージを与え、光ファイバ自体の損失が増加してしまう現象が発生してしまう。これは、フォトダークニングと呼ばれる現象であり、反転分布率が高い状態の光増幅媒体内の希土類元素が高出力な光によってダメージを受けてしまうためである。特に希土類添加濃度が高いファイバでは発生しやすい。   However, when high-power light is generated in the optical fiber, a phenomenon occurs in which the additives and impurities in the optical fiber are damaged and the loss of the optical fiber itself increases. This is a phenomenon called photodarkening, because the rare earth element in the optical amplifying medium having a high inversion distribution rate is damaged by high-power light. In particular, it is likely to occur in fibers with a high rare earth addition concentration.

本発明は、上記問題点を解消する為になされたものであり、フォトダークニングの発現を抑圧することができる光増幅モジュールおよびレーザ光源を提供することを目的とする。   The present invention has been made to solve the above-described problems, and an object thereof is to provide an optical amplification module and a laser light source capable of suppressing the occurrence of photodarkening.

本発明に係るレーザ光源は、被増幅光を出射する被増幅用光源と、被増幅光を入力して、被増幅光を増幅して出力する光増幅モジュールとを有する。光増幅モジュールは、(1) 希土類元素Ｙｂを光導波領域に添加され、被増幅光を入力する第１光増幅媒体と、(2) 第１光増幅媒体と接続され、第１光増幅媒体のＹｂ元素濃度より高い濃度のＹｂ元素を光導波領域に添加された第２光増幅媒体と、(3) 第１光増幅媒体に励起光を出力し、その結果第１光増幅媒体から励起光を第２光増幅媒体に伝搬させる励起部とを備え、第１光増幅媒体および第２光増幅媒体は、被増幅光をシングルモード伝搬させるコアと、励起光をマルチモード伝搬させる内側クラッドと、内側クラッドを取り囲む外側クラッドとを含み、Ｙｂ元素の添加濃度が２０００wt.ppm以上７５００wt.ppm以下であり、第１光増幅媒体中での反転分布率が４０％以上であり、被増幅光を第１光増幅媒体および第２光増幅媒体において光増幅し、１０６４ｎｍ波長の光を出射することを特徴とする。
A laser light source according to the present invention includes a light source for amplification that emits light to be amplified, and an optical amplification module that inputs the light to be amplified, amplifies the light to be amplified, and outputs the amplified light. The optical amplification module includes: (1) a rare earth element Yb added to the optical waveguide region and a first optical amplification medium for inputting the amplified light; and (2) a first optical amplification medium connected to the first optical amplification medium. A second optical amplifying medium in which a Yb element having a concentration higher than the Yb element concentration is added to the optical waveguide region; and (3) outputting excitation light to the first optical amplifying medium, and as a result, exciting light from the first optical amplifying medium. An excitation unit for propagating to the second optical amplification medium, and the first optical amplification medium and the second optical amplification medium have a core for propagating the amplified light in a single mode, an inner cladding for propagating the excitation light in a multimode, and an inner side The Yb element addition concentration is 2000 wt.ppm or more and 7500 wt.ppm or less , the inversion distribution rate in the first optical amplifying medium is 40% or more, Optical amplification in optical amplification medium and second optical amplification medium , Characterized in that it emits light of a 1064nm wavelength.

本発明に係る光増幅モジュールでは、励起部で出力された励起光は、初めに第１光増幅媒体に伝搬され、続いて第２光増幅媒体に伝搬される。そして、入力された被増幅光は、第１光増幅媒体および第２光増幅媒体において光増幅され、その光増幅された光が出力される。初めに励起光が伝搬する第１光増幅媒体では、伝搬する励起光のパワーが比較的大きいものの、Ｙｂ元素濃度が比較的低い。一方、続いて励起光が伝搬する第２光増幅媒体では、Ｙｂ元素濃度が比較的高いものの、伝搬する励起光のパワーが比較的小さくなる。したがって、第１光増幅媒体および第２光増幅媒体の何れにおいても、フォトダークニングの発現が抑制され、高い利得で被増幅光が光増幅され得る。
In the optical amplification module according to the present invention, the excitation light output from the excitation unit is first propagated to the first optical amplification medium, and then propagated to the second optical amplification medium. The inputted amplified light is optically amplified in the first optical amplification medium and the second optical amplification medium, and the optically amplified light is output. In the first optical amplifying medium through which pumping light first propagates, the power of the propagating pumping light is relatively large, but the Yb element concentration is relatively low. On the other hand, in the second optical amplifying medium through which the excitation light subsequently propagates, although the Yb element concentration is relatively high, the power of the propagating excitation light is relatively small. Therefore, in both the first optical amplification medium and the second optical amplification medium, the occurrence of photodarkening is suppressed, and the amplified light can be optically amplified with a high gain.

本発明に係るレーザ光源は、第１光増幅媒体のＹｂ元素濃度が第２光増幅媒体のＹｂ元素濃度の半分以下であるのが好適である。第１光増幅媒体の吸収条長積が第２光増幅媒体の吸収条長積の６０％以上であるのが好適である。第２光増幅媒体の励起光入射端領域での反転分布率が４０％未満であるのが好適である。また、第１光増幅媒体および第２光増幅媒体は、Ｙｂ元素以外の３価の正イオンを光導波領域に添加されているのが好適である。これらの場合には、フォトダークニングの発現が更に効果的に抑制され得る。
Laser light source according to the present invention, Yb element concentration of the first optical amplifying medium is preferably not more than half of Yb element concentration of the second optical amplifying medium. It is preferable that the absorption length product of the first optical amplification medium is 60% or more of the absorption length product of the second optical amplification medium. The inversion distribution ratio in the excitation light incident end region of the second optical amplification medium is preferably less than 40%. In the first optical amplification medium and the second optical amplification medium, it is preferable that trivalent positive ions other than the Yb element are added to the optical waveguide region. In these cases, the occurrence of photodarkening can be more effectively suppressed.

本発明に係るレーザ光源は、被増幅光を出力する被増幅光用光源を有し、被増幅光を第１光増幅媒体に出力する上記の本発明に係る光増幅モジュールとを備えることを特徴とする。このレーザ光源では、被増幅光用光源から出力された被増幅光は光増幅モジュールにおいて光増幅され、その光増幅された光が出力される。   A laser light source according to the present invention includes a light source for amplified light that outputs amplified light, and includes the optical amplification module according to the present invention that outputs the amplified light to a first optical amplification medium. And In this laser light source, the amplified light output from the light source for amplified light is optically amplified in the optical amplification module, and the optically amplified light is output.

本発明によれば、フォトダークニングの発現を抑圧することができる。   According to the present invention, the occurrence of photodarkening can be suppressed.

以下、添付図面を参照して、本発明を実施するための最良の形態を詳細に説明する。なお、図面の説明において同一の要素には同一の符号を付し、重複する説明を省略する。   The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

図１は、本実施形態に係るレーザ光源１の構成図である。この図に示される本実施形態のレーザ光源１は、被増幅光用光源１０および光増幅モジュール２０を備える。このレーザ光源１では、被増幅光用光源１０から出力された被増幅光は光増幅モジュール２０において光増幅され、その光増幅された光が出力される。   FIG. 1 is a configuration diagram of a laser light source 1 according to the present embodiment. The laser light source 1 of this embodiment shown in this figure includes a light source for amplified light 10 and an optical amplification module 20. In the laser light source 1, the light to be amplified output from the light source for amplified light 10 is optically amplified in the optical amplification module 20, and the light amplified light is output.

光増幅モジュール２０は、第１光増幅媒体２１、第２光増幅媒体２２および励起部２３を備える。第１光増幅媒体２１および第２光増幅媒体２２それぞれは、希土類元素を光導波領域に添加された光導波路であり、好適には希土類元素としてのＹｂ元素をコア領域に添加された光ファイバである。第１光増幅媒体２１および第２光増幅媒体２２は、各々の一端が互いに光学的に接続され、好適には融着接続されている。第１光増幅媒体２１の希土類元素濃度より第２光増幅媒体２２の希土類元素濃度が高い。   The optical amplification module 20 includes a first optical amplification medium 21, a second optical amplification medium 22, and an excitation unit 23. Each of the first optical amplification medium 21 and the second optical amplification medium 22 is an optical waveguide in which a rare earth element is added to the optical waveguide region, and preferably an optical fiber in which a Yb element as a rare earth element is added to the core region. is there. One end of each of the first optical amplification medium 21 and the second optical amplification medium 22 is optically connected to each other, and preferably fusion-connected. The rare earth element concentration of the second optical amplification medium 22 is higher than the rare earth element concentration of the first optical amplification medium 21.

励起部２３は、励起光源２４および光カプラ２５を含む。励起光源２４は、第１光増幅媒体２１および第２光増幅媒体２２それぞれに添加された希土類元素を励起し得る波長の励起光を出力するものであり、好適にはレーザダイオードを含む。光カプラ２５は、励起光源２４から出力された励起光を入力して、その励起光を第１光増幅媒体２１へ出力する。   The excitation unit 23 includes an excitation light source 24 and an optical coupler 25. The excitation light source 24 outputs excitation light having a wavelength capable of exciting the rare earth element added to each of the first optical amplification medium 21 and the second optical amplification medium 22, and preferably includes a laser diode. The optical coupler 25 receives the excitation light output from the excitation light source 24 and outputs the excitation light to the first optical amplification medium 21.

この光増幅モジュール２０では、励起光源２４から出力された励起光は、光カプラ２５を経て、第１光増幅媒体２１および第２光増幅媒体２２の順に伝搬する。被増幅光用光源１０から出力された被増幅光は光増幅モジュール２０に入力され、その被増幅光は光カプラ２５を経た後に第１光増幅媒体２１および第２光増幅媒体２２において光増幅さる。そして、この光増幅された光が光増幅モジュール２０から出力される。   In the optical amplification module 20, the excitation light output from the excitation light source 24 propagates in the order of the first optical amplification medium 21 and the second optical amplification medium 22 through the optical coupler 25. The amplified light output from the light source for amplified light 10 is input to the optical amplification module 20, and the amplified light is optically amplified in the first optical amplification medium 21 and the second optical amplification medium 22 after passing through the optical coupler 25. . The light amplified light is output from the light amplification module 20.

このように、本実施形態では、励起部２３で出力された励起光は、初めに第１光増幅媒体２１に伝搬され、続いて第２光増幅媒体２２に伝搬される。初めに励起光が伝搬する第１光増幅媒体２１では、伝搬する励起光のパワーが比較的大きいものの、希土類元素濃度が比較的低い。一方、続いて励起光が伝搬する第２光増幅媒体２２では、希土類元素濃度が比較的高いものの、伝搬する励起光のパワーが比較的小さくなる。したがって、第１光増幅媒体２１および第２光増幅媒体２２の何れにおいても、フォトダークニングの発現が抑制され、高い利得で被増幅光が光増幅され得る。   Thus, in the present embodiment, the excitation light output from the excitation unit 23 is first propagated to the first optical amplification medium 21 and then propagated to the second optical amplification medium 22. In the first optical amplifying medium 21 where the pumping light first propagates, the power of the pumping light propagating is relatively large, but the rare earth element concentration is relatively low. On the other hand, in the second optical amplifying medium 22 through which the excitation light subsequently propagates, although the rare earth element concentration is relatively high, the power of the propagated excitation light is relatively small. Therefore, in any of the first optical amplifying medium 21 and the second optical amplifying medium 22, the occurrence of photodarkening is suppressed, and the amplified light can be optically amplified with a high gain.

第１光増幅媒体２１中での反転分布率が４０％以上であり、第１光増幅媒体２１の希土類元素濃度が第２光増幅媒体２２の希土類元素濃度の半分以下であるのが好適である。第１光増幅媒体２１の吸収条長積が第２光増幅媒体２２の吸収条長積の６０％以上であるのが好適である。第２光増幅媒体２２の励起光入射端領域での反転分布率が４０％未満であるのが好適である。また、第１光増幅媒体２１および第２光増幅媒体２２それぞれは、希土類元素以外の３価の正イオン（例えばＡｌ３＋）を光導波領域に添加されているのが好適である。これらの場合には、フォトダークニングの発現が更に効果的に抑制され得る。 The inversion distribution ratio in the first optical amplification medium 21 is preferably 40% or more, and the rare earth element concentration of the first optical amplification medium 21 is preferably less than half of the rare earth element concentration of the second optical amplification medium 22. . The absorption length product of the first optical amplification medium 21 is preferably 60% or more of the absorption length product of the second optical amplification medium 22. The inversion distribution ratio in the excitation light incident end region of the second optical amplification medium 22 is preferably less than 40%. Each of the first optical amplifying medium 21 and the second optical amplifying medium 22 is preferably added with trivalent positive ions (for example, Al 3+ ) other than rare earth elements in the optical waveguide region. In these cases, the occurrence of photodarkening can be more effectively suppressed.

図２は、第１光増幅媒体２１および第２光増幅媒体２２それぞれの断面および屈折率プロファイルを示す図である。同図（ａ）は断面を示し、同図（ｂ）は径方向の屈折率プロファイルを示す。この図に示されるように、第１光増幅媒体２１および第２光増幅媒体２２それぞれは、希土類元素を添加され被増幅光をシングルモード伝搬させるコア２０１と、励起光をマルチモード伝搬させる内側クラッド２０２と、この内側クラッド２０２を取り囲む外側クラッド２０３とを含むのが好適である。また、第１光増幅媒体２１および第２光増幅媒体２２それぞれの希土類元素濃度が２０００wt.ppm以上であるのが好適である。これらの場合には、フォトダークニングの発現が抑制され、更に高い利得で被増幅光が光増幅され得る。   FIG. 2 is a diagram showing cross sections and refractive index profiles of the first optical amplifying medium 21 and the second optical amplifying medium 22, respectively. FIG. 4A shows a cross section, and FIG. 4B shows a refractive index profile in the radial direction. As shown in this figure, each of the first optical amplifying medium 21 and the second optical amplifying medium 22 includes a core 201 that adds a rare earth element and propagates light to be amplified in a single mode, and an inner cladding that propagates pump light in a multimode. Preferably, 202 and an outer cladding 203 surrounding the inner cladding 202 are included. Further, the rare earth element concentration of each of the first optical amplifying medium 21 and the second optical amplifying medium 22 is preferably 2000 wt.ppm or more. In these cases, the occurrence of photodarkening is suppressed, and the amplified light can be optically amplified with a higher gain.

図３は、比較例のレーザ光源９の構成図である。この図に示される比較例のレーザ光源９は、被増幅光用光源１０および光増幅モジュール２０Ａを備える。このレーザ光源９では、被増幅光用光源１０から出力された被増幅光は光増幅モジュール２０Ａにおいて光増幅され、その光増幅された光が出力される。この比較例の光増幅モジュール２０Ａは、本実施形態に係る光増幅モジュール２０中の第１光増幅媒体２１を除いた構成である。   FIG. 3 is a configuration diagram of the laser light source 9 of the comparative example. The laser light source 9 of the comparative example shown in this figure includes an amplified light source 10 and an optical amplification module 20A. In the laser light source 9, the amplified light output from the amplified light source 10 is optically amplified by the optical amplification module 20A, and the optically amplified light is output. The optical amplification module 20A of this comparative example has a configuration excluding the first optical amplification medium 21 in the optical amplification module 20 according to this embodiment.

以下では、比較例のレーザ光源９と対比しつつ、本実施形態に係るレーザ光源１の作用効果について更に説明する。第１光増幅媒体２１および第２光増幅媒体２２それぞれは、図２に示されるような構成の光ファイバであって、希土類元素としてＹｂ元素がコア２０１に添加されている。励起光の波長は９１５ｎｍであり、被増幅光の波長は１０６４ｎｍである。第２光増幅媒体２２のＹｂ元素濃度は１５０００wt.ppmである。   Below, the effect of the laser light source 1 which concerns on this embodiment is further demonstrated, contrasting with the laser light source 9 of a comparative example. Each of the first optical amplifying medium 21 and the second optical amplifying medium 22 is an optical fiber configured as shown in FIG. 2, and a Yb element is added to the core 201 as a rare earth element. The wavelength of the excitation light is 915 nm, and the wavelength of the amplified light is 1064 nm. The Yb element concentration of the second optical amplifying medium 22 is 15000 wt.ppm.

図４は、比較例のレーザ光源９に含まれる光増幅媒体２２における反転分布率の長手方向分布を示す図である。横軸は、光カプラ２５からの励起光伝搬距離を表している。この図に示されるように、光増幅媒体２２において、励起光入射端に近いほど、反転分布率が高く、増幅度も大きい。それ故、フォトダークニングが発現し易い。   FIG. 4 is a diagram illustrating the longitudinal distribution of the inversion distribution rate in the optical amplifying medium 22 included in the laser light source 9 of the comparative example. The horizontal axis represents the pumping light propagation distance from the optical coupler 25. As shown in this figure, in the optical amplifying medium 22, the closer to the excitation light incident end, the higher the inversion distribution ratio and the larger the amplification degree. Therefore, photodarkening tends to occur.

図５は、本実施形態に係るレーザ光源１に含まれる第１光増幅媒体２１および第２光増幅媒体２２における反転分布率の長手方向分布を示す図である。横軸は、光カプラ２５からの励起光伝搬距離を表している。ここでは、上記比較例の場合と同じ出力パワーとなるように励起光パワーを一定とした。上記比較例の場合と同じ吸収条長積となるように、第１光増幅媒体２１の希土類添加濃度および長さＬ１を調整するとともに、第２光増幅媒体２２の長さＬ２を調整した。この図に示されるように、例えば、第１光増幅媒体２１の希土類イオン濃度を第２光増幅媒体２２の希土類イオン濃度の半分（つまり、第１光増幅媒体２１の希土類イオン濃度を７５００wt.ppm）とし、第２光増幅媒体２２の長さＬ２を５〜６ｍとすると、第２光増幅媒体２２の励起光入射端での反転分布率は、約４０〜５０％となり、十分に低くなっていることがわかる。したがって、フォトダークニングの発現が抑制され得る。   FIG. 5 is a diagram showing the longitudinal distribution of the inversion distribution ratio in the first optical amplification medium 21 and the second optical amplification medium 22 included in the laser light source 1 according to the present embodiment. The horizontal axis represents the pumping light propagation distance from the optical coupler 25. Here, the pumping light power was made constant so that the same output power as in the comparative example was obtained. The rare earth addition concentration and the length L1 of the first optical amplifying medium 21 were adjusted, and the length L2 of the second optical amplifying medium 22 was adjusted so as to have the same absorption length product as in the comparative example. As shown in this figure, for example, the rare earth ion concentration of the first optical amplification medium 21 is half of the rare earth ion concentration of the second optical amplification medium 22 (that is, the rare earth ion concentration of the first optical amplification medium 21 is 7500 wt. Ppm). ) And the length L2 of the second optical amplifying medium 22 is 5 to 6 m, the inversion distribution rate at the excitation light incident end of the second optical amplifying medium 22 is about 40 to 50%, which is sufficiently low. I understand that. Therefore, the occurrence of photodarkening can be suppressed.

また、励起光波長を９７４ｎｍとし、上記と同じ励起光パワーとし、上記と同じ出力パワーとなるように、第１光増幅媒体２１の長さＬ１および第２光増幅媒体２２の長さＬ２を調整した。第１光増幅媒体２１を用いること無く、濃度が大きい第２光増幅媒体２２を全て使った場合、第２光増幅媒体２２の長さＬ２は約６ｍで十分であることを確認した。これは、Ｙｂ元素が添加された光増幅媒体において、波長９７４ｎｍの方が波長９１５ｎｍに比べ吸収係数が大きく、長さが短くて澄むからである。   Further, the length L1 of the first optical amplifying medium 21 and the length L2 of the second optical amplifying medium 22 are adjusted so that the pumping light wavelength is 974 nm, the same pumping light power as above, and the same output power as above. did. It was confirmed that when the second optical amplification medium 22 having a high concentration was used without using the first optical amplification medium 21, a length L2 of the second optical amplification medium 22 was about 6 m. This is because, in the optical amplifying medium to which the Yb element is added, the wavelength 974 nm has a larger absorption coefficient than the wavelength 915 nm, and is shorter and clearer.

図６は、本実施形態に係るレーザ光源１に含まれる第１光増幅媒体２１および第２光増幅媒体２２における反転分布率の長手方向分布を示す図である。ここでは、励起光波長を９７４ｎｍとし、濃度の小さい第１光増幅媒体２１を用い、第２光増幅媒体２２の長さＬ２を３.５ｍとして、第１光増幅媒体２１および第２光増幅媒体２２のトータルの吸収条長積を調整した。その結果、第２光増幅媒体２２の励起光入射端での反転分布率は、約４０％となり、十分に低くなることがわかる。フォトダークニングの発現を抑圧するためには、波長９７４ｎｍの励起光を用いた方が、反転分布率を小さくでき、抑圧法として有効である。   FIG. 6 is a diagram showing the longitudinal distribution of the inversion distribution ratio in the first optical amplification medium 21 and the second optical amplification medium 22 included in the laser light source 1 according to the present embodiment. Here, the pumping light wavelength is 974 nm, the first optical amplifying medium 21 having a low concentration is used, the length L2 of the second optical amplifying medium 22 is 3.5 m, and the first optical amplifying medium 21 and the second optical amplifying medium are used. The total absorbent strip length product of 22 was adjusted. As a result, the inversion distribution ratio at the excitation light incident end of the second optical amplifying medium 22 is about 40%, which is sufficiently low. In order to suppress the occurrence of photodarkening, the use of excitation light having a wavelength of 974 nm can reduce the inversion distribution ratio and is effective as a suppression method.

本実施形態に係るレーザ光源１または光増幅モジュール２０において、第１光増幅媒体２１の濃度が薄いことは、光増幅媒体２１，２２の全体の長さが長くなってしまうことと同義であり、その故、光増幅媒体２１，２２において非線形シフト量が大きくなってしまう。図７は、本実施形態に係るレーザ光源１において第２光増幅媒体２２の長さＬ２と非線形シフト量との関係を示す図である。励起光波長が９７４ｎｍであって、第２光増幅媒体２２の長さＬ２が３.５ｍである場合、非線形シフト量は、比較例の構成（図３）の非線形シフト量に対して約１ｄＢ以下に抑圧され得る。この値は、第１光増幅媒体２１と第２光増幅媒体２２との間の融着部の損失ばらつきや、第２光増幅媒体２２から出力端までの間の損失ばらつきの範囲内と判断できるため、第１光増幅媒体２１を用いることに因り増加する非線形シフト量は問題にならない。   In the laser light source 1 or the optical amplification module 20 according to the present embodiment, a low concentration of the first optical amplification medium 21 is synonymous with an increase in the overall length of the optical amplification media 21 and 22. Therefore, the nonlinear shift amount becomes large in the optical amplification media 21 and 22. FIG. 7 is a diagram showing the relationship between the length L2 of the second optical amplifying medium 22 and the nonlinear shift amount in the laser light source 1 according to the present embodiment. When the pumping light wavelength is 974 nm and the length L2 of the second optical amplifying medium 22 is 3.5 m, the nonlinear shift amount is about 1 dB or less with respect to the nonlinear shift amount of the configuration of the comparative example (FIG. 3). Can be suppressed. This value can be determined to be within the range of the loss variation of the fused portion between the first optical amplification medium 21 and the second optical amplification medium 22 and the loss variation between the second optical amplification medium 22 and the output end. Therefore, the amount of nonlinear shift that increases due to the use of the first optical amplifying medium 21 does not matter.

本発明は、上記実施形態に限定されるものではなく、種々の変形が可能である。上記実施形態では、被増幅光の伝搬方向と同じ方向に励起光を伝搬させる前方向励起であったが、被増幅光の伝搬方向と逆の方向に励起光を伝搬させる後方向励起であってもよい。   The present invention is not limited to the above embodiment, and various modifications can be made. In the above embodiment, the forward pumping is used to propagate the pumping light in the same direction as the propagation direction of the amplified light, but the backward pumping is used to propagate the pumping light in the direction opposite to the propagation direction of the amplified light. Also good.

本実施形態に係るレーザ光源１の構成図である。It is a block diagram of the laser light source 1 which concerns on this embodiment. 第１光増幅媒体２１および第２光増幅媒体２２それぞれの断面および屈折率プロファイルを示す図である。It is a figure which shows the cross section and refractive index profile of each of the 1st optical amplification medium 21 and the 2nd optical amplification medium 22. 比較例のレーザ光源９の構成図である。It is a block diagram of the laser light source 9 of a comparative example. 比較例のレーザ光源９に含まれる増幅媒体２２における反転分布率の長手方向分布を示す図である。It is a figure which shows the longitudinal direction distribution of the inversion distribution rate in the amplification medium 22 contained in the laser light source 9 of a comparative example. 本実施形態に係るレーザ光源１に含まれる第１光増幅媒体２１および第２光増幅媒体２２における反転分布率の長手方向分布を示す図である。It is a figure which shows the longitudinal direction distribution of the inversion distribution rate in the 1st optical amplification medium 21 and the 2nd optical amplification medium 22 which are included in the laser light source 1 which concerns on this embodiment. 本実施形態に係るレーザ光源１に含まれる第１光増幅媒体２１および第２光増幅媒体２２における反転分布率の長手方向分布を示す図である。It is a figure which shows the longitudinal direction distribution of the inversion distribution rate in the 1st optical amplification medium 21 and the 2nd optical amplification medium 22 which are included in the laser light source 1 which concerns on this embodiment. 本実施形態に係るレーザ光源１において第２光増幅媒体２２の長さＬ２と非線形シフト量との関係を示す図である。It is a figure which shows the relationship between the length L2 of the 2nd optical amplification medium 22, and the nonlinear shift amount in the laser light source 1 which concerns on this embodiment.

符号の説明Explanation of symbols

１…レーザ光源、１０…被増幅光用光源、２０…光増幅モジュール、２１…第１光増幅媒体、２２…第２光増幅媒体、２３…励起部、２４…励起光源、２５…光カプラ。   DESCRIPTION OF SYMBOLS 1 ... Laser light source, 10 ... Light source for to-be-amplified light, 20 ... Optical amplification module, 21 ... 1st optical amplification medium, 22 ... 2nd optical amplification medium, 23 ... Excitation part, 24 ... Excitation light source, 25 ... Optical coupler.

Claims (5)

被増幅光を出射する被増幅用光源と、
前記被増幅光を入力して、前記被増幅光を増幅して出力する光増幅モジュールとを有し、
前記光増幅モジュールは、
希土類元素Ｙｂを光導波領域に添加され、前記被増幅光を入力する第１光増幅媒体と、
前記第１光増幅媒体と接続され、前記第１光増幅媒体のＹｂ元素濃度より高い濃度のＹｂ元素を光導波領域に添加された第２光増幅媒体と、
前記第１光増幅媒体に励起光を出力し、その結果前記第１光増幅媒体から励起光を前記第２光増幅媒体に伝搬させる励起部と
を備え、
前記第１光増幅媒体および前記第２光増幅媒体は、被増幅光をシングルモード伝搬させるコアと、励起光をマルチモード伝搬させる内側クラッドと、前記内側クラッドを取り囲む外側クラッドとを含み、前記Ｙｂ元素の添加濃度が２０００wt.ppm以上７５００wt.ppm以下であり、
前記第１光増幅媒体中での反転分布率が４０％以上であり、
前記被増幅光を前記第１光増幅媒体および前記第２光増幅媒体において光増幅し、１０６４ｎｍ波長の光を出射する
ことを特徴とするレーザ光源。 A light source for amplification that emits light to be amplified;
An optical amplification module that inputs the amplified light and amplifies and outputs the amplified light;
The optical amplification module includes:
A rare earth element Yb added to the optical waveguide region, and a first optical amplification medium for inputting the amplified light;
A second optical amplifying medium connected to the first optical amplifying medium, wherein a Yb element having a concentration higher than the Yb element concentration of the first optical amplifying medium is added to the optical waveguide region;
An excitation unit that outputs excitation light to the first optical amplification medium and, as a result, propagates excitation light from the first optical amplification medium to the second optical amplification medium;
The first optical amplifying medium and the second optical amplifying medium include a core that propagates light to be amplified in a single mode, an inner cladding that propagates pumping light in a multimode, and an outer cladding that surrounds the inner cladding, and the Yb The additive concentration of the element is 2000 wt.ppm or more and 7500 wt.ppm or less ,
The inversion distribution ratio in the first optical amplification medium is 40% or more;
The laser light source, wherein the light to be amplified is optically amplified in the first optical amplification medium and the second optical amplification medium, and light having a wavelength of 1064 nm is emitted. 前記第１光増幅媒体のＹｂ元素濃度が前記第２光増幅媒体のＹｂ元素濃度の半分以下であることを特徴とする請求項１記載のレーザ光源。 The laser light source according to claim 1, wherein the Yb element density before Symbol first optical amplifying medium, characterized in that less than half of Yb element concentration of the second optical amplifying medium. 前記第１光増幅媒体の吸収条長積が前記第２光増幅媒体の吸収条長積の６０％以上であることを特徴とする請求項１記載のレーザ光源。   2. The laser light source according to claim 1, wherein an absorption length product of the first optical amplification medium is 60% or more of an absorption length product of the second optical amplification medium. 前記第２光増幅媒体の励起光入射端領域での反転分布率が４０％未満であることを特徴とする請求項１記載のレーザ光源。   2. The laser light source according to claim 1, wherein an inversion distribution ratio in an excitation light incident end region of the second optical amplification medium is less than 40%. 前記第１光増幅媒体および前記第２光増幅媒体は、Ｙｂ元素以外の３価の正イオンが光導波領域に添加されていることを特徴とする請求項１記載のレーザ光源。
2. The laser light source according to claim 1, wherein trivalent positive ions other than Yb element are added to the optical waveguide region in the first optical amplification medium and the second optical amplification medium.
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