JP2005148223A - Optical waveguide and optical energy transmitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide or the like in which spatially incoherent light beams are converged into regions having small diameters. <P>SOLUTION: An optical waveguide 10 has an axis 11 which is extended from a first tip 110 to a second tip 120 in a linear or curved manner. The cross section, which is vertical to the axis 11 of the optical waveguide 10, includes a circular first region that includes the axis 11 and has an average refractive index N<SB>1</SB>, a ring shaped second region that surrounds the first region and has an average refractive index N<SB>2</SB>and a ring shaped third region that surrounds the second region and has an average refractive index N<SB>3</SB>. The number of the waveguide modes of the light beams which are guided in the core regions along the axis 11 is equal to or greater than 100 and a relationship equation of S<SB>2</SB>/S<SB>1</SB>≤0.5 is satisfied, wherein S<SB>1</SB>is the cross-sectional area of the core region at the first tip 110 and S<SB>2</SB>is the cross-sectional area of the core region at the second tip 120. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical energy transmission device capable of condensing light in a small-diameter region, and an optical waveguide preferably used for guiding light in such an optical energy transmission device.

For example, the laser diode array disclosed in Patent Document 1 has a plurality of laser diodes arranged in an array, and can achieve high luminance.
US Pat. No. 5,764,675

  In the laser diode array as described above, by using the lens, the light output from each laser diode can be condensed in different small diameter regions. However, no means has been found for condensing the light output from all the laser diodes in a common small diameter region. Further, a means for condensing not only the light output from the laser diode array but also spatially incoherent light in a small diameter region has not been found.

  Note that spatially coherent light refers to light having a complete correlation between the phases of light at different positions in a plane perpendicular to the propagation direction of the light. Spatial incoherent light refers to light that is not spatially coherent. The light output from the laser diode array is spatially incoherent because there is no correlation between the phases of the light output from the individual laser diodes.

  The present invention has been made to solve the above problems, and an object thereof is to provide an optical waveguide and an optical energy transmission device capable of condensing spatially incoherent light in a small-diameter region. To do.

An optical waveguide according to the present invention has an axis extending from a first end to a second end, and a cross section perpendicular to the axis at an arbitrary position along the axis includes an axis and has an average refractive index at least at one optical wavelength. A core region having an N _core and a cladding region surrounding the core region and having an average refractive index N _clad lower than the average refractive index N _core, and light guided to the core region along the axis at the first end When the cross-sectional area of the core region at the first end is S ₁ and the cross-sectional area of the core region at the second end is S ₂ , “S ₂ / S ₁ ≦ 0. 5 ”is satisfied. In this optical waveguide, since the number of guided modes is large, light can be coupled to the guided mode with high efficiency regardless of the quality of the beam quality, and light is input to the first end to input the second end. Can output light, thereby improving the light intensity at the second end.

In the optical waveguide according to the present invention, when the profile volume of the core region at the first end is Ω ₁ and the profile volume of the core region at the second end is Ω ₂ at the optical wavelength, “S ₂ / S ₁ It is preferable that the relational expression <Ω ₂ / Ω ₁ ”is satisfied. In this case, since the number of waveguide modes per unit area in the cross section perpendicular to the optical axis of the optical waveguide can be increased from the first end to the second end, the light intensity can be increased.

An optical waveguide according to the present invention is the above-mentioned optical wavelength cross-section perpendicular to the axis at an arbitrary position along the axis, surrounds the first region having an average refractive index N ₁ comprises a shaft, the first region A second region having an average refractive index N ₂ and a third region surrounding the second region and having an average refractive index N ₃ , and the average refractive indexes N ₁ , N ₂ , and N ₃ are “N ₂ ² − It is preferable that the relational expression of “N ₃ ² > N ₁ ² −N ₂ ² > 0” is satisfied. In this case, since “N ₁ > N ₂ > N ₃ ”, the first region can guide light as a core region at the first end, and the first region and the second region can be guided at the second end. The region can guide light as a core region. In addition, since “N ₂ ² −N ₃ ² > N ₁ ² −N ₂ ² ”, the waveguide mode per unit area in the cross section perpendicular to the optical axis of the optical waveguide from the first end to the second end. Therefore, the light intensity can be increased. The area _{S 1} of the first region in the first end is at 25 mm ² or more, the sum _{S 2} of the first and second regions each area in the second end is suitable to be 4 mm ² or less, In this case, since the core diameter at the first end is large, it is easy to couple a large-diameter light source, and since the core diameter at the second end is small, a high-intensity light output can be obtained.

An optical waveguide according to the present invention is the above-mentioned optical wavelength cross-section perpendicular to the axis at an arbitrary position along the axis, surrounds the first region having an average refractive index N ₁ comprises a shaft, the first region A second region having an average refractive index N ₂ , and the second region is surrounded by a surrounding medium having an average refractive index N ₃ at the second end, and the average refractive indexes N ₁ , N ₂ , and N ₃ are “ It is preferable that the relational expression “N ₂ ² −N ₃ ² > N ₁ ² −N ₂ ² > 0” is satisfied. In this case, since “N ₁ > N ₂ > N ₃ ”, the first region can guide light as a core region at the first end, and the first region and the second region can be guided at the second end. The region can guide light as a core region. In addition, since “N ₂ ² −N ₃ ² > N ₁ ² −N ₂ ² ”, the waveguide mode per unit area in the cross section perpendicular to the optical axis of the optical waveguide from the first end to the second end. Therefore, the light intensity can be increased. Further, the area S ₁ of the first region at the first end is 25 mm ² or more, the sum S ₂ of the areas of the first region and the second region at the second end is 4 mm ² or less, and the surrounding medium is gas. In this case, since the core diameter at the first end is large, it is easy to couple a large-diameter light source, and since the core diameter at the second end is small, a high-intensity light output is possible. Can be obtained.

  An optical energy transmission device according to the present invention includes the optical waveguide according to the present invention described above and a light source that outputs light having the light wavelength, and the light output from the light source is a core region at the first end of the optical waveguide. It is characterized by being coupled to. In addition, it is preferable that the light output from the light source is spatially incoherent. In this optical energy transmission device, light output from the light source is input to the first end of the optical waveguide, transmitted through the optical waveguide, and output from the second end of the optical waveguide to the outside. At this time, at the second end, since the cross-sectional area of the core region is smaller than that of the first end and the number of guided modes per unit area is large, a high-intensity light output can be obtained compared to the case of the light source alone. .

  In the optical waveguide according to the present invention, at the optical wavelength, a plurality of guided modes of light guided to the core region at the first end includes a first mode group and a second mode group. When the number of guided modes belonging to the first mode group at one end is L and the number of guided modes of light guided to the core region at the second end is N, “N / L ≧ 1 / 2 ”and the optical coupling between an arbitrary guided mode belonging to the second mode group at the first end and an arbitrary guided mode of light guided to the core region at the second end. Is substantially negligible. In this optical waveguide, the waveguide mode at the first end coupled to the waveguide mode at the second end is selectively excited at the first end, so that the second light intensity higher than the light intensity at the first end is obtained. Can be obtained at the edge.

  An optical energy transmission device according to the present invention includes the above-described optical waveguide according to the present invention and a light source that outputs light having the above-described light wavelength, and light output from the light source is a first light at a first end of the optical waveguide. It is characterized by being coupled to a waveguide mode belonging to a mode group. In addition, it is preferable that the light output from the light source is spatially incoherent. In this optical energy transmission device, the light output from the light source is input to the first end of the optical waveguide, is coupled to the waveguide mode belonging to the first mode group with high efficiency, is transmitted through the optical waveguide, Output from the second end of the waveguide to the outside. At this time, light having a power substantially equal to the power of the light input to the first end is obtained at the second end, and the cross-sectional area of the core region is smaller at the second end than at the first end. Compared with the case, a high-intensity light output can be obtained.

An optical waveguide according to the present invention, in the above-mentioned light wavelength, the cross section perpendicular to the axis at an arbitrary position along the axis, a first region having a mean refractive index N _1, the average refractive index and surrounding the first region A second region having N ₂ and a third region surrounding the second region and having an average refractive index N ₃ , wherein the average refractive indexes N ₁ , N ₂ , and N ₃ are “N ₁ > N ₂ > N _It is preferable that an optical amplification section along the axis is satisfied and the first region is made of glass containing a rare earth element that absorbs light having the above-described light wavelength. In this case, since “N ₁ > N ₂ > N ₃ ”, the first region and the second region can guide light as the core region at the first end, and the first region is the core at the second end. Light can be guided as a region. Furthermore, since there is an optical amplification section in which the rare earth element is contained in the first region, the rare earth element is excited and excited by coupling the optical power to the core region at the first end and propagating to the optical amplification section. The light propagating through the first region can be amplified by the rare earth element, and the amplified light can be guided to the core region at the second end. As a result, the optical power coupled to the core region at the first end can be efficiently transmitted to the core region at the second end, and the area of the core region at the second end is “S ₂ / Since S ₁ ≦ 10 ⁻⁴ ”is small, a high-intensity light output can be obtained at the second end.

  In the optical waveguide according to the present invention, it is preferable that the rare earth element is any one or a plurality selected from Yb, Nd, Er, Bi, and Pr, and thereby the wavelength from the visible band to the near infrared. The light in the region can be absorbed efficiently.

  The optical waveguide according to the present invention preferably includes an optical feedback means for returning the light propagated through the first region of the optical amplification section to the first region of the optical amplification section. This makes it possible to resonate light passing through the first region of the optical amplification section and efficiently extract optical power from the excited rare earth element.

An optical waveguide according to the present invention, the sum _{S 1} of the first region and the second region of each area of the first end is at 25 mm ² or more, the area _{S 2} of the first region in the second end 0.001 mm ² or less It is preferable that In this case, since the core diameter at the first end is large, it is easy to couple a large-diameter light source, and since the core diameter at the second end is small, a high-intensity light output can be obtained.

  In the optical waveguide according to the present invention, it is preferable that the first region at the second end substantially guides a single spatial mode at the light emission wavelength at which the rare earth element emits light. In this case, a spatially coherent light output can be obtained at the second end, and light collection by a lens or the like is facilitated.

  An optical energy transmission device according to the present invention includes the above-described optical waveguide according to the present invention and a light source that outputs light having the above-described light wavelength, and the light output from the light source is in the core region at the first end of the optical waveguide. It is characterized by being combined. It is preferable to further include an optical feedback means for returning the light propagated through the first region of the optical amplification section of the optical waveguide to the first region of the optical amplification section. The light output from the light source is preferably spatially incoherent. In this optical energy transmission device, the light output from the light source is input to the first end of the optical waveguide and excites the rare earth element in the optical amplification section. The excited rare earth element amplifies light output from the second end to the outside. At this time, the energy absorbed by the rare earth element can be efficiently extracted outside by resonating the light passing through the optical amplification section by the optical feedback means. As a result, the light energy input to the core region at the first end can be efficiently transmitted to the core region at the second end, and the area of the core region at the second end is smaller than that at the first end. High intensity light output can be obtained as compared with the case of a single device.

  According to the present invention, spatially incoherent light can be collected in a small diameter region.

  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.

(First embodiment of optical waveguide)
First, a first embodiment of an optical waveguide according to the present invention will be described. FIG. 1 is an explanatory diagram of an optical waveguide 10 according to the first embodiment. 2A shows the configuration of the optical waveguide 10, FIG. 2B shows the refractive index profile at the first end 110 of the optical waveguide 10, and FIG. 1C shows the second end 120 of the optical waveguide 10. FIG. A refractive index profile is shown.

As shown in FIG. 2A, the optical waveguide 10 has an axis 11 extending linearly or curvedly from the first end 110 to the second end 120. At an arbitrary position along the axis 11, the cross section of the optical waveguide 10 perpendicular to the axis 11 includes a circular first region that includes the axis 11 and has an average refractive index N ₁ , and surrounds the first region and has an average refraction. including a second region of the annular having rate N _2, and a third region of the annular having an average refractive index N ₃ surrounds the second region.

  The third region may be coated with a coating medium such as polymer, carbon, and metal. Thereby, generation | occurrence | production and growth of the damage of the side surface of the optical waveguide 10 which cause a fracture | rupture are suppressed.

These average refractive indexes N ₁ , N ₂ , and N ₃ satisfy the relationship represented by the following formula (1) as shown in FIGS. More preferably, the relationship expressed by the following formula (2) is also satisfied.

なお、Ｍ種類の媒質からなる領域の平均屈折率ｎ_ａｖｇは、これらＭ種類の媒質のうちの第ｍの媒質の屈折率をｎ[m]とし、第ｍの媒質の体積をｆ[m]としたときに、下記(3)式で表される。１種類の媒質からなる領域の平均屈折率は、その媒質の屈折率と等しい。

The average refractive index n _avg of the region composed of M types of media is such that the refractive index of the mth medium among these M types of media is n [m], and the volume of the mth medium is f [m]. Is expressed by the following equation (3). The average refractive index of a region composed of one type of medium is equal to the refractive index of the medium.

第１端１１０における第１領域１１１，第２領域１１２および第３領域１１３を含む断面構造と、第１位置１３０における第１領域１３１，第２領域１３２および第３領域１３３を含む断面構造とは、互いに等しい。軸１１に沿った第１端１１０と第１位置１３０との間の部分では、軸１１に垂直な断面の構造および寸法は、軸１１に沿って一様である。

A cross-sectional structure including the first region 111, the second region 112, and the third region 113 at the first end 110, and a cross-sectional structure including the first region 131, the second region 132, and the third region 133 at the first position 130. Are equal to each other. In the portion between the first end 110 and the first position 130 along the axis 11, the structure and dimensions of the cross section perpendicular to the axis 11 are uniform along the axis 11.

  The cross-sectional structure including the first region 121, the second region 122, and the third region 123 at the second end 120, and the cross-sectional structure including the first region 141, the second region 142, and the third region 143 at the second position 140 Are equal to each other. Even in the portion between the second end 120 and the second position 140 along the axis 11, the structure and dimensions of the cross section perpendicular to the axis 11 are uniform along the axis 11.

  A cross-sectional structure including the first region 131, the second region 132, and the third region 133 at the first position 130, and a cross-sectional structure including the second region 141, the second region 142, and the third region 143 at the second position 140. Are similar to each other. In the taper portion 150 between the first position 130 and the second end 140 along the axis 11, the outer diameter of the third region continuously changes along the axis 11, and a cross section perpendicular to the axis 11. The structure of is also changing continuously.

The outer diameter of the third region 113 at the first end 110 (ie, the outer diameter of the third region 133 at the first position 130) is the outer diameter of the third region 123 at the second end 120 (ie, at the second position 140). Larger than the outer diameter of the third region 143. The outer diameter of the first region and _{D 1,} the outer diameter of the second region and _{D 2,} when the outer diameter of the third region and _{D 3,} along the axis 11, the ratio _(D 1 / _{D 2)} is constant And the ratio (D ₂ / D ₃ ) is also constant. Also, along the axis 11, the average refractive index N ₁ of the first region is constant, the average refractive index of the second region N ₂ is also constant, a third region average refractive index N ₃ also constant.

In a section between the first end 110 and the first position 130 along the axis 11, at the wavelength of 850 nm, the first region acts as a core region, and both the second region and the third region act as cladding regions. Thus, the light is confined in the first region and guided. At the first end 110, the average refractive index N _core of the core region is higher than the average refractive index N _clad of the cladding region.

In the section between the second end 120 along the axis 11 and the second position 140, both the first region and the second region act as a core region and the third region acts as a cladding region at a wavelength of 850 nm. Thus, the light is confined and guided in both the first region and the second region. Also at the second end 120, the average refractive index N _core of the _core region is higher than the average refractive index N _clad of the cladding region.

The optical waveguide 10 has 100 or more waveguide modes of light guided to the core region along the axis 11 at the first end 110 and the second end 120 and a position between them at a wavelength of 850 nm. Further, the cross-sectional area of the core region in the first end 110 a (cross-sectional area of the first region) and S _1, the cross-sectional area of the core region in the second end 120 (the sum of the first and second regions respectively of the cross-sectional area) the When S _2, satisfy the relationship of these S ₁ and S ₂ are expressed by the following equation (4).

また、波長８５０ｎｍにおいて、第１端１１０におけるコア領域のプロファイル体積をΩ_１とし、第２端１２０におけるコア領域のプロファイル体積をΩ_２としたときに、Ｓ_１，Ｓ_２，Ω_１およびΩ_２が下記(5)式で表される関係を満たす。

Further, when the profile volume of the core region at the first end 110 is Ω ₁ and the profile volume of the core region at the second end 120 is Ω ₂ at a wavelength of 850 nm, S ₁ , S ₂ , Ω ₁ and Ω ₂ Satisfies the relationship expressed by the following equation (5).

なお、コア領域のプロファイル体積Ωは以下のように定義される。光導波路の断面内の径方向の屈折率プロファイルがコア領域でｎ(r)と表され、このコア領域を包囲するクラッド領域の屈折率がｎ_cladであるとする。ただし、ｒは、コア領域の中心を原点とする径方向座標であり、コア領域は「０≦ｒ≦ρ」の範囲に相当する。屈折率ｎ_０の媒質から空間的にインコヒーレントな光が光導波路の一端に結合するとする。このとき、光導波路のコア領域に閉じ込められて導波する光のパワーＰ_ｂｒは下記(6)式で表される。この(6)式中に現われるプロファイル体積Ωは下記(7)式で表される。これらの式から判るように、光導波路が伝送することができる光のパワーは、コア領域のプロファイル体積に比例する。

The profile volume Ω of the core region is defined as follows. It is assumed that the refractive index profile in the radial direction in the cross section of the optical waveguide is expressed as n (r) in the core region, and the refractive index of the cladding region surrounding the core region is n _clad . Here, r is a radial coordinate with the center of the core region as the origin, and the core region corresponds to a range of “0 ≦ r ≦ ρ”. It is assumed that spatially incoherent light is coupled to one end of the optical waveguide from a medium having a refractive index n ₀ . At this time, the power P _br of light guided and confined in the core region of the optical waveguide is expressed by the following equation (6). The profile volume Ω appearing in the equation (6) is expressed by the following equation (7). As can be seen from these equations, the power of light that can be transmitted by the optical waveguide is proportional to the profile volume of the core region.

この光導波路１０では、第１端１１０におけるコア領域（第１領域１１１）に導波される導波モードから、第２端１２０におけるコア領域（第１領域１２１，第２領域１２２）に導波される導波モードへの結合は、テーパ部１５０により実現される。したがって、外部から第１端１１０のコア領域に光が結合されると、光強度が向上した光が第２端１２０において得られる。

In the optical waveguide 10, the light is guided from the waveguide mode guided to the core region (first region 111) at the first end 110 to the core region (first region 121, second region 122) at the second end 120. The coupling to the guided mode is realized by the tapered portion 150. Therefore, when light is coupled to the core region of the first end 110 from the outside, light with improved light intensity is obtained at the second end 120.

Preferably, the area (area of the first region) _{S 1} of the core region at the first end 110 is at 25 mm ² or more, the sum of the respective areas an area (first region and second region of the core region in the second end 120 ) S ₂ is 4 mm ² or less.

More preferable numerical examples are as follows. The outer diameter of the first region and _{D 1,} the outer diameter of the second region and _{D 2,} the outer diameter of the third region is taken as _{D 3,} the ratio _(D 1 / _{D 2)} is at 0.4 The ratio (D ₂ / D ₃ ) is 0.8. Outer diameter _{D 3} of the third region 113 at the first end 110 is 36 mm, the outer diameter _{D 3} of the third region 123 at the second end 120 is 1.2 mm. The value of “N ₂ ² −N ₃ ² ” is 0.992, and the value of “N ₁ ² −N ₂ ² ” is 0.007. At this time, the area S ₁ of the core region at the first end 110 is 104 mm ² , the area S ₂ of the core region at the second end 120 is 0.73 mm ² , and the ratio (S ₂ / S ₁ ) is 0.7. 007.

The V parameter of the optical waveguide 10 at the wavelength of 850 nm is 3562 at the first end 110 and 3533 at the second end 120. Therefore, the number of guided modes is 6.3 × 10 ⁶ at the first end 110 and 6.2 × 10 ⁶ at the second end 120. By this way guided mode number is 100 or more (preferably 10 ⁵ or more), the optical waveguide 10 can be guided a spatially incoherent light.

When the refractive index of the core region is N _core , the refractive index of the cladding region is N _clad , and the core radius is ρ, the number M of the waveguide modes at the wavelength λ of the optical waveguide is expressed by (8) It is expressed by a formula. The V parameter appearing in the equation (8) is expressed by the following equation (9). Note that equation (8) holds when r is sufficiently larger than the value 1.

また、第１端１１０におけるコア領域のプロファイル体積Ω_１は０.７３ｍｍ^２であり、第２端１２０におけるコア領域のプロファイル体積Ω_２は０.７２ｍｍ^２であり、比（Ω_２／Ω_１）は０.９９と大きい。このように比（Ω_２／Ω_１）が大きいことにより、生じ得る光損失を小さく抑えることができる。

Further, the profile volume Ω ₁ of the core region at the first end 110 is 0.73 mm ² , and the profile volume Ω ₂ of the core region at the second end 120 is 0.72 mm ² , and the ratio (Ω ₂ / Ω ₁ ) Is as large as 0.99. As described above, since the ratio (Ω ₂ / Ω ₁ ) is large, the possible optical loss can be reduced.

  FIG. 2 is a cross-sectional view of the optical waveguide 10 according to the first embodiment. This figure shows a cross-sectional structure at an arbitrary position along the axis 11 of the optical waveguide 10, and shows a first region 101, a second region 102, and a third region 103 in the cross section. The circular first region 101 is made of silica glass, and the annular second region 102 surrounding the first region 101 is also made of silica glass. The annular third region 103 surrounds the second region 102.

The refractive index difference between the first region 101 and the second region 102 is such that a refractive index increasing agent (for example, GeO ₂ ) or a refractive index decreasing agent (for example, F) is added to the first region 101 or the second region 102. This is realized. The refractive index difference between the second region 102 and the third region 103 is also realized by adding a refractive index increasing agent or a refractive index decreasing agent to the second region 102 or the third region 103.

Further, as shown in FIG. 2, in the third region 103, a plurality of voids in which a medium (gas or vacuum) having a refractive index of about 1 is contained in silica glass having a refractive index of about 1.45. By arranging the holes 104, it is preferable that the effective refractive index of the third region 103 is reduced, thereby realizing a refractive index difference between the second region 102 and the third region 103. In a region where a plurality of holes are densely arranged in a solid medium, the effective refractive index of the region is approximated by an average refractive index. In order to set the value of “N ₂ ² −N ₃ ² ” to 0.992 as described above, the area ratio of the holes 104 in the silica glass in the third region 103 may be set to about 0.9.

  The plurality of holes 104 need only exist in the radial direction so as to surround the second region 102 and may not exist over the entire third region 103. This is because light is confined in the inside of the hole 104 having a predetermined thickness in the radial direction, and the structure outside the layer does not affect the waveguide characteristics.

(Second embodiment of optical waveguide)
Next, a second embodiment of the optical waveguide according to the present invention will be described. FIG. 3 is an explanatory diagram of the optical waveguide 20 according to the second embodiment. 2A shows the configuration of the optical waveguide 20, FIG. 2B shows the refractive index profile at the first end 210 of the optical waveguide 20, and FIG. 1C shows the second end 220 of the optical waveguide 20. FIG. A refractive index profile is shown.

As shown in FIG. 2A, the optical waveguide 20 has a shaft 21 extending linearly or curvedly from the first end 210 to the second end 220. At an arbitrary position along the axis 21, the cross section of the optical waveguide 20 perpendicular to the axis 21 has a circular first region including the axis 21 and having an average refractive index N ₁ , and surrounds the first region and has an average refraction. and a second region of the annular having rate N _2. Further, in the section 251 between the second end 220 and a second position 240, the second region is surrounded by enclosing medium 243 with an average refractive index _{N 3.} The surrounding medium 243 is, for example, gas or polymer. These average refractive indexes N ₁ , N ₂ , and N ₃ satisfy the relationship expressed by the above formula (1) as shown in FIGS. More preferably, the relationship expressed by the above formula (2) is also satisfied.

  The cross-sectional structure including the first region 211 and the second region 212 at the first end 210 and the cross-sectional structure including the first region 231 and the second region 232 at the first position 230 are equal to each other. In the portion between the first end 210 along the axis 21 and the first position 230, the structure and dimensions of the cross section perpendicular to the axis 21 are uniform along the axis 21.

  The cross-sectional structure including the first region 221 and the second region 222 at the second end 220 and the cross-sectional structure including the first region 241 and the second region 242 at the second position 240 are equal to each other. Even in the portion between the second end 220 and the second position 240 along the axis 21, the structure and dimensions of the cross section perpendicular to the axis 21 are uniform along the axis 21.

  The cross-sectional structure including the first region 231 and the second region 232 at the first position 230 and the cross-sectional structure including the second region 241 and the second region 242 at the second position 240 are similar to each other. In the tapered portion 250 between the first position 230 and the second end 240 along the axis 21, the outer diameter of the second region continuously changes along the axis 21, and a cross section perpendicular to the axis 21. The structure of is also changing continuously.

The outer diameter of the second region 212 at the first end 210 (ie, the outer diameter of the second region 232 at the first position 230) is the outer diameter of the second region 222 at the second end 220 (ie, at the second position 240). Larger than the outer diameter of the second region 242). When the outer diameter of the first region is D ₁ and the outer diameter of the second region is D ₂ , the ratio (D ₁ / D ₂ ) is constant along the axis 21. Also, along the axis 21, the average refractive index N ₁ of the first region is constant, the average refractive index N ₂ is also constant second region.

In a section between the first end 210 along the axis 21 and the first position 230, at a wavelength of 850 nm, the first region acts as a core region, the second region acts as a cladding region, and the light is first It is confined in the region and guided. At the first end 210, the average refractive index N _core of the core region is higher than the average refractive index N _clad of the cladding region.

In the section between the second end 220 and the second position 240 along the axis 21, both the first region and the second region act as a core region and the surrounding medium 240 acts as a cladding region at a wavelength of 850 nm. Thus, the light is confined and guided in both the first region and the second region. Also at the second end 220, the average refractive index N _core of the _core region is higher than the average refractive index N _clad of the cladding region.

The optical waveguide 20 has 100 or more waveguide modes of light guided to the core region along the axis 21 at a wavelength of 850 nm. Further, the cross-sectional area of the core region in the first end 210 (cross-sectional area of the first region) and S _1, the cross-sectional area of the core region in the second end 220 (the sum of the first and second regions respectively of the cross-sectional area) the When S _2, satisfy the relationship of these S ₁ and S ₂ are expressed by the above equation (4).

In addition, when the profile volume of the core region at the first end 210 is Ω ₁ and the profile volume of the core region at the second end 220 is Ω ₂ at a wavelength of 850 nm, S ₁ , S ₂ , Ω ₁ and Ω ₂ Satisfies the relationship expressed by the above equation (5).

  In this optical waveguide 20, the waveguide mode guided to the core region (first region 211) at the first end 210 is guided to the core region (first region 221, second region 222) at the second end 220. The coupling to the guided mode is realized by the tapered portion 250. Therefore, when light is coupled to the core region of the first end 210 from the outside, light with improved light intensity is obtained at the second end 220.

Preferably, the area (area of the first region) _{S 1} of the core region at the first end 210 is at 25 mm ² or more, the sum of the respective areas an area (first region and second region of the core region in the second end 220 ) S ₂ is 4 mm ² or less. Preferably, the surrounding medium 243 is a gas such as N ₂ or air and has a refractive index N ₃ of about 1.

More preferable numerical examples are as follows. The ratio (D ₁ / D ₂ ) between the outer diameter D ₁ of the first region and the outer diameter D ₂ of the second region is 0.3. Outer diameter _{D 2} of the second region 212 at the first end 210 is 36 mm, the outer diameter _{D 2} of the second region 222 at the second end 220 is 1 mm. The value of “N ₂ ² −N ₃ ² ” is 1.1025, and the value of “N ₁ ² −N ₂ ² ” is 0.01. At this time, the area S ₁ of the core region at the first end 210 is 92 mm ² , the area S ₂ of the core region at the second end 220 is 0.79 mm ² , and the ratio (S ₂ / S ₁ ) is 0.7. 009.

The V parameter of the optical waveguide 20 at the wavelength of 850 nm is 3991 at the first end 210 and 3880 at the second end 220. Accordingly, the number of guided modes is 7.9 × 10 ⁶ at the first end 210 and 7.5 × 10 ⁶ at the second end 220. By this way guided mode number is 100 or more (preferably 10 ⁵ or more), the optical waveguide 20 can be guided a spatially incoherent light.

In addition, the profile volume Ω ₁ of the core region at the first end 210 is 0.92 mm ² , and the profile volume Ω ₂ of the core region at the second end 220 is 0.87 mm ² , and the ratio (Ω ₂ / Ω ₁ ) Is as large as 0.95. As described above, since the ratio (Ω ₂ / Ω ₁ ) is large, the possible optical loss can be reduced.

  FIG. 4 is a cross-sectional view of the optical waveguide 20 according to the second embodiment. This figure shows a cross-sectional structure at an arbitrary position in a section 251 between the second end 220 and the second position 240 along the axis 21 of the optical waveguide 20. Two regions 202 and the surrounding medium 243 are shown. The circular first region 201 is made of silica glass, and the annular second region 202 surrounding the first region 201 is also made of silica glass. The surrounding medium 243 surrounds the second region 202.

The refractive index difference between the first region 201 and the second region 202 is realized by adding a refractive index increasing agent or a refractive index decreasing agent to the first region 201 or the second region 202. Further, in order to set the value of “N ₂ ² −N ₃ ² ” to 1.102 as described above, the surrounding medium 243 may be air or an inert gas having a refractive index of about 1.

(Third embodiment of optical waveguide)
Next, a third embodiment of the optical waveguide according to the present invention will be described. FIG. 5 is an explanatory diagram of the optical waveguide 30 according to the third embodiment.

As shown in this figure, the optical waveguide 30 has an axis 31 extending linearly or curvedly from the first end 310 to the second end 320. At an arbitrary position along the axis 31, the cross section of the optical waveguide 30 perpendicular to the axis 31 has a circular first region that includes the axis 31 and has an average refractive index N ₁ , and surrounds the first region and has an average refraction. and a second region of the annular having rate N _2. Further, as in the case of the first embodiment, the second region may be surrounded by a third region having an average refractive index N ₃ , or, as in the case of the second embodiment, the second end. in 320 the section between the second position 340, the second region is surrounded by enclosing medium having an average refractive index N _3. These average refractive indexes N ₁ , N ₂ , and N ₃ satisfy the relationship represented by the above formula (1). More preferably, the relationship expressed by the above formula (2) is also satisfied.

  The cross-sectional structure including the first region 311 and the second region 312 at the first end 310 and the cross-sectional structure including the first region and the second region at the first position 330 are equal to each other. In the portion between the first end 310 and the first position 330 along the axis 31, the structure and dimensions of the cross section perpendicular to the axis 31 are uniform along the axis 31.

  The cross-sectional structure including the first region 321 and the second region 322 at the second end 320 and the cross-sectional structure including the first region and the second region at the second position 340 are equal to each other. Even in the portion between the second end 320 and the second position 340 along the axis 31, the structure and dimensions of the cross section perpendicular to the axis 31 are uniform along the axis 31.

  The cross-sectional structure including the first region and the second region at the first position 330 and the cross-sectional structure including the first region and the second region at the second position 340 are similar to each other. In the tapered portion 230 between the first position 330 and the second end 340 along the axis 31, the outer diameter of the second region continuously changes along the axis 31, and a cross section perpendicular to the axis 31. The structure of is also changing continuously.

The outer diameter of the second region 312 at the first end 310 (ie, the outer diameter of the second region at the first position 330) is the outer diameter of the second region 322 at the second end 320 (ie, the second diameter at the second position 340). Larger than the outer diameter of the two regions). When the outer diameter of the first region is D ₁ and the outer diameter of the second region is D ₂ , the ratio (D ₁ / D ₂ ) is constant along the axis 31. Also, along the axis 31, the average refractive index N ₁ of the first region is constant, the average refractive index N ₂ is also constant second region.

In the section between the first end 310 and the first position 330 along the axis 31, at a wavelength of 850 nm, the first region acts as a core region, the second region acts as a cladding region, and the light is first It is confined in the region and guided. At the first end 310, the average refractive index N _core of the core region is higher than the average refractive index N _clad of the cladding region.

Even in the section between the second end 320 along the axis 31 and the second position 340, at a wavelength of 850 nm, the first region acts as a core region, the second region acts as a cladding region, and the light is first It is confined in the region and guided. However, when the third region or the surrounding medium is provided, both the first region and the second region act as the core region, the third medium or the surrounding medium acts as the cladding region, and the light is in the first region. And confined in both the second region and the second region. Also at the second end 320, the average refractive index N _core of the _core region is higher than the average refractive index N _clad of the cladding region.

The optical waveguide 30 has 100 or more waveguide modes of light guided to the core region along the axis 31 at a wavelength of 850 nm. Further, the cross-sectional area of the core region in the first end 310 a (cross-sectional area of the first region) and S _1, the cross-sectional area of the core region in the second end 320 (the sum of the first and second regions respectively of the cross-sectional area) the When S _2, satisfy the relationship of these S ₁ and S ₂ are expressed by the above equation (4).

  In the optical waveguide 30, coupling from the waveguide mode guided to the core region at the first end 310 to the waveguide mode guided to the core region at the second end 320 is realized by the tapered portion 350. . Therefore, when light is coupled to the core region of the first end 310 from the outside, light with improved light intensity is obtained at the second end 320.

FIG. 6 is an explanatory diagram of the waveguide mode of the optical waveguide 30 according to the third embodiment. The number of guided modes in the first end 310 of the optical waveguide 30 is M, representing the electric field distribution of the waveguide mode of the m of the M guided mode and g _m. Further, the number of guided modes in the second end 320 of the optical waveguide 30 is N, representing the electric field distribution of the waveguide mode of the first n of the N waveguide mode and h _n. However, M is an integer of 2 or more, N is a positive integer smaller than M, m is an integer of 1 to M, and n is an integer of 1 to N.

When these electric field distributions are used, the electric field E _{1 of} light guided to the first end 310 and the electric field E _{2 of} light guided to the second end 320 are developed by the following equation (10). The

また、第１端３１０に導波される光のパワーＰ_１、および、第２端３２０に導波される光のパワーＰ_２それぞれは、下記(11)式で表される。ただし、各導波モードｇ_ｍ，ｈ_ｎは、互いに直交しており、絶対値の二乗の断面内の積分が値１となるように規格化されているものとする。

Further, the power P _{1 of} light guided to the first end 310 and the power P _{2 of} light guided to the second end 320 are expressed by the following equation (11). However, it is assumed that the waveguide modes g _m and h _n are orthogonal to each other and are standardized so that the integral in the cross section of the square of the absolute value becomes the value 1.

第１端３１０での導波モードｇ_ｍと第２端３２０での導波モードｈ_ｎとはテーパ部３５０において互いに結合しており、その結合は下記(12)式で表される。係数ｔ_ｎ,ｍは、テーパ部３５０などの光導波路構造によって決まる。

The waveguide mode g _m at the first end 310 and the waveguide mode h _n at the second end 320 are coupled to each other at the tapered portion 350, and the coupling is expressed by the following equation (12). The coefficient t _{n, m} is determined by the optical waveguide structure such as the tapered portion 350.

好ましくは、第１端３１０でのＭ個の導波モードは、第１群に属するＬ個の導波モードｇ_１〜ｇ_Ｌと、第２群に属する(Ｍ−Ｌ)個の導波モードｇ_Ｌ＋１〜ｇ_Ｍとに区分される。そして、第１端３１０における第２モード群に属する任意の導波モードと、第２端３２０における任意の導波モードとの間で、光結合が実質的に無視できる。すなわち、好適には下記(13)式を満たす。

Preferably, the M waveguide modes at the first end 310 include _L waveguide modes g _{1 to} g L belonging to the first group and (ML) waveguide modes belonging to the second group. It is divided into g _{L + 1 to} g _M. Then, optical coupling can be substantially ignored between an arbitrary guided mode belonging to the second mode group at the first end 310 and an arbitrary guided mode at the second end 320. That is, the following expression (13) is preferably satisfied.

このとき、上記(12)式は、下記(14)式で近似され得る。

At this time, the above equation (12) can be approximated by the following equation (14).

ここで、任意のｋ（ただし、１≦ｋ≦Ｎ）について下記(15)式で表される光電界を第１端３１０に入射した場合を考える。＊は複素共役を表す。

Here, consider a case where an optical electric field represented by the following equation (15) is incident on the first end 310 for an arbitrary k (where 1 ≦ k ≦ N). * Represents a complex conjugate.

このとき、第１端３１０に導波される光のパワーＰ_１、および、第２端３２０に導波される光のパワーＰ_２それぞれは、下記(16)式で表される。

At this time, the power P _{1 of} the light guided to the first end 310 and the power P _{2 of the} light guided to the second end 320 are expressed by the following equation (16).

しかし、本実施形態に係る光導波路３０は増幅作用を有しないので、Ｐ_２はＰ_１以下であるから、下記(17)式が成り立つ。

However, since the optical waveguide 30 according to the present embodiment does not have an amplifying function, P ₂ is equal to or less than P ₁ , and therefore the following equation (17) holds.

外部から光導波路３０の第１端３１０に光を結合して、第１モード群に属するＬ個の導波モードｇ_１〜ｇ_Ｌを選択的に励振した場合には、下記(18)式が成り立ち、さらに下記(19)式が成り立つ。

By coupling light into the first end 310 of the optical waveguide 30 from the outside, when selectively excited the L of the waveguide mode g ₁ to g _L belonging to the first mode group, the following equation (18) The following equation (19) holds.

したがって、第１端３１０における第１モード群に属する導波モードの数Ｌ、第２端３２０における導波モードの数Ｎ、第１端３１０に導波される光のパワーＰ_１、および、第２端３２０に導波される光のパワーＰ_２それぞれの間には、下記(20)式が成り立つ。

Therefore, the number L of guided modes belonging to the first mode group at the first end 310, the number N of guided modes at the second end 320, the power P _{1 of} light guided to the first end 310, and the first The following equation (20) is established between each power P _{2 of the} light guided to the two ends 320.

高い効率で光を伝送するためには、比（Ｎ／Ｌ）が大きいことが必要であり、特に下記(21)式が成り立つのが好ましい。

In order to transmit light with high efficiency, the ratio (N / L) needs to be large, and it is particularly preferable that the following equation (21) holds.

例えば、下記(22)式が成り立つように光導波路３０を構成することにより、下記(23)式で表されるような高効率を実現することができる。

For example, by configuring the optical waveguide 30 so that the following expression (22) is established, high efficiency represented by the following expression (23) can be realized.

（光エネルギ伝送装置の第１実施形態）
次に、本発明に係る光エネルギ伝送装置の第１実施形態について説明する。図７は、本実施形態に係る光エネルギ伝送装置１の構成図である。光エネルギ伝送装置１は、上述した第１実施形態に係る光導波路１０に加えて、光源８０および波面調整素子９０を備える。

(First Embodiment of Optical Energy Transmission Device)
Next, a first embodiment of the optical energy transmission device according to the present invention will be described. FIG. 7 is a configuration diagram of the optical energy transmission device 1 according to the present embodiment. The optical energy transmission device 1 includes a light source 80 and a wavefront adjusting element 90 in addition to the optical waveguide 10 according to the first embodiment described above.

The light source 80 outputs light A having a wavelength of 850 nm.
The number of the guided mode of light guided in the core region of the optical waveguide 10 is 100 or more (preferably 10 ⁵ or higher). The light source 80 may be a laser light source that oscillates in a single transverse mode, a multi-mode laser light source that oscillates in a plurality of transverse modes and outputs spatially incoherent light, Further, an LD stack in which laser diodes are two-dimensionally arranged may be used.

  The wavefront adjusting element 90 receives the light A output from the light source 80 and outputs the light B with the divergence angle and the beam diameter adjusted. The wavefront adjusting element 90 includes, for example, a lens array, a diffractive optical element, and a curved mirror.

  The optical waveguide 10 inputs the light B output from the wavefront adjusting element 90 to the first end 110, guides the light to the core region, and outputs the light C from the second end 120 to the outside.

  In this optical energy transmission device 1, the light output from the light source 80 is input to the first end 110 of the optical waveguide 10 after the divergence angle and the beam diameter are adjusted by the wavefront adjusting element 90. The light is guided by the core region and output from the second end 120 of the optical waveguide 10 to the outside. As a result, the light is collected in a small-diameter region, and light with improved light intensity is obtained at the second end 120.

  In particular, when a multimode laser light source or an LD stack is used as the light source 80, high power light can be generated from the light source 80, and this high power light is output from the second end 120 of the optical waveguide 10. Therefore, it is suitable for applications such as processing.

  Further, since the optical waveguide 10 is according to the above-described embodiment, the light output from the multimode laser light source or the LD stack is condensed to a small diameter, and high intensity is obtained at the second end 120 of the optical waveguide 10. Can get the light.

  In the case where the optical waveguide 20 is used instead of the optical waveguide 10, similar actions and effects can be obtained. In addition, although it is easy to realize a laser diode with high output power at a wavelength of 850 nm, the wavelength is not necessarily limited thereto, and other laser diodes such as 405 nm, 980 nm, and 1450 nm, rare earth-doped fiber lasers and solids It may be 1000-1100 nm at which the laser operates. When the optical waveguide 30 is used instead of the optical waveguide 10, the light output from the light source 80 and passed through the wavelength conversion element 90 is converted into a waveguide mode belonging to the first mode group at the first end of the optical waveguide 30. By combining with high efficiency, the same effect can be obtained.

(Fourth Embodiment of Optical Waveguide)
Next, a fourth embodiment of the optical waveguide according to the present invention will be described. FIG. 8 is an explanatory diagram of an optical waveguide 40 according to the fourth embodiment. 2A shows the configuration of the optical waveguide 40, FIG. 2B shows the refractive index profile at the first end 410 of the optical waveguide 40, and FIG. 2C shows the second end 420 of the optical waveguide 40. FIG. A refractive index profile is shown.

As shown in FIG. 2A, the optical waveguide 40 has an axis 41 extending linearly or curvedly from the first end 410 to the second end 420. At any position along the axis 41, the cross section of the vertical waveguide 40 to the shaft 41, a circular first region having an average refractive index N ₁ includes a shaft 41, surrounded by average refractive the first region including a second region of the annular having rate N _2, and a third region of the annular having an average refractive index N ₃ surrounds the second region.

These average refractive indexes N ₁ , N ₂ , and N ₃ satisfy the relationship expressed by the above formula (1) as shown in FIGS. More preferably, the relationship expressed by the above formula (2) is also satisfied.

  A cross-sectional structure including the first region 411, the second region 412 and the third region 413 at the first end 410, and a cross-sectional structure including the first region 431, the second region 432 and the third region 433 at the first position 430. Are equal to each other. In the portion between the first end 410 and the second position 430 along the axis 41, the structure and dimensions of the cross section perpendicular to the axis 41 are uniform along the axis 41.

  A cross-sectional structure including the first region 421, the second region 422, and the third region 423 at the second end 420, and a cross-sectional structure including the first region 441, the second region 442, and the third region 443 at the second position 440. Are equal to each other. Even in the portion between the second end 420 along the axis 41 and the second position 440, the structure and dimensions of the cross section perpendicular to the axis 41 are uniform along the axis 41.

  A cross-sectional structure including the first region 431, the second region 432, and the third region 433 at the first position 430, and a cross-sectional structure including the first region 441, the second region 442, and the third region 443 at the second position 440. Are similar to each other. In the tapered portion 450 between the first position 430 and the second position 440 along the axis 41, the outer diameter of the third region continuously changes along the axis 41, and a cross section perpendicular to the axis 41. The structure of is also changing continuously.

  A reflecting mirror 460 is provided at the second position 440, and an optical amplification section 470 is formed between the second position 440 and the second end 420. The reflecting mirror 460 transmits light having a wavelength of 915 nm and reflects light having a wavelength of 1120 nm. Such a reflecting mirror 460 can be realized by a fiber grating in which the average refractive index of the first region is periodically modulated in the axial direction. In addition, the end surface of the second end 420 is in contact with gas, and part of the light that reaches the second end 420 through the first region is returned to the first region by Fresnel reflection, and the other part is output to the outside. The In the optical amplification section 470, the first region is constituted by silica glass to which Yb is added. In portions other than the optical amplification section 470, Yb is not added.

The outer diameter of the third region 413 at the first end 410 (ie, the outer diameter of the third region 433 at the first position 430) is the outer diameter of the third region 423 at the second end 420 (ie, at the second position 440). Larger than the outer diameter of the third region 443. The outer diameter of the first region and _{D 1,} the outer diameter of the second region and _{D 2,} when the outer diameter of the third region and _{D 3,} along the axis 41, the ratio _(D 1 / _{D 2)} is constant And the ratio (D ₂ / D ₃ ) is also constant. In addition to the reflection mirror 460, along the axis 41, the average refractive index N ₁ of the first region, the average refractive index N ₂ of the second region, and the average refractive index N ₃ of the third region are uniform. It is. However, in the optical amplification section 470 Yb is added with the other portions, the average refractive index N ₁ of the first region is not necessarily equal.

In the section between the first end 410 and the first position 430 along the axis 41, both the first region and the second region act as a core region, and the third region acts as a cladding at a wavelength of 915 nm. The light is confined and guided in the first region and the second region. At the first end 410, the average refractive index N _core of the core region is higher than the average refractive index N _clad of the cladding region.

In the section between the second end 420 and the second position 440 along the axis 41, the first region acts as a core region, and both the second region and the third region act as cladding at a wavelength of 1120 nm. Thus, the light is confined in the first region and guided. At the second end 420, the average refractive index N _core of the core region is higher than the average refractive index N _clad of the cladding region.

The optical waveguide 40 has 100 or more waveguide modes of light guided to the core region along the axis 41 at the first end 410 at a wavelength of 915 nm. Further, the cross-sectional area of the core region in the first end 410 (the sum of the first and second regions respectively of the cross-sectional area) and S _1, the cross-sectional area of the core region in the second end 420 (the cross-sectional area of the first region) the When S _2, satisfy the relationship of these S ₁ and S ₂ are expressed by the above equation (4).

  In this optical waveguide 40, the waveguide mode guided to the core region (first region 411, second region 412) at the first end 410 is changed by the tapered portion 450 to the first region 441 and the first region 440 at the second position 440. 2 coupled to region 442. Light having a wavelength of 915 nm coupled to the first region 441 and the second region 442 at the second position 440 is absorbed by the rare earth element in the light amplification section 470 and then emitted as light having a wavelength of 1120 nm. The emitted light induces further emission, and the optical power absorbed by the rare earth element is extracted as light having a wavelength of 1120 nm. Furthermore, since the first region of the optical amplification section 470 is in the optical resonator constituted by the second end 420 where the Fresnel reflection occurs and the reflecting mirror 460, laser oscillation occurs at a wavelength of 1120 nm, and part of the oscillated light Is taken out from the second end 420 to the outside. Thereby, the extraction efficiency of optical power from rare earth elements can be improved.

Preferably, the area of the core region at the first end 410 (the sum of the areas of the first region and the second region) S ₁ is 25 mm ² or more, and the area of the core region at the second end 420 (the area of the first region) ) S ₂ is 0.001 mm ² or less.

More preferable numerical examples are as follows. The outer diameter of the first region and _{D 1,} the outer diameter of the second region and _{D 2,} the outer diameter of the third region is taken as _{D 3,} the ratio _(D 1 / _{D 2)} is 0.16 the ratio _(D 2 / D ₃₎ is 0.5. Outer diameter _{D 3} of the third region 413 at the first end 410 is 12 mm, the outer diameter _{D 3} of the third region in the second end 420 is 125 [mu] m. The value of “N ₂ ² −N ₃ ² ” is 0.21, and the value of “N ₁ ² −N ₂ ² ” is 0.007. At this time, the area S ₁ of the core region at the first end 410 is 28 mm ² , the area S ₂ of the core region at the second end 420 is 0.000079 mm ² , and the ratio (S ₂ / S ₁ ) is 2. 8 × 10 ⁻⁶ .

At the first end 410, the V parameter of the optical waveguide 40 at the wavelength of 915 nm is 9440, and the number of waveguide modes is 4.5 × 10 ⁷ . By this way guided mode number is 100 or more (preferably 10 ⁵ or more), the optical waveguide 40 inputs a spatially incoherent light in the core region of the first end 410 waveguide can do.

  On the other hand, at the second end 420, the V parameter of the optical waveguide 40 at the wavelength of 1120 nm is 2.3. Since “V <2.405”, single mode operation is realized at the second end 420. As a result, light with a uniform wavefront is obtained as an output from the second end 420, which is suitable for further condensing with a lens or the like.

  FIG. 9 is a cross-sectional view of an optical waveguide 40 according to the fourth embodiment. This figure shows a cross-sectional structure in the optical amplification section 470 of the optical waveguide 40, and shows a first region 401, a second region 402, and a third region 403 in the cross section. The cross-sectional structure in other portions is substantially the same except that no rare earth element is added to the first region 401. The circular first region 401 is made of silica glass, and in particular, a rare earth element Yb is added. The annular second region 402 surrounding the first region 401 is also made of silica glass. The annular third region 403 is made of a polymer and surrounds the second region 402.

The refractive index difference between the first region 401 and the second region 402 is partly realized by the rare earth element added to the first region 401 in the optical amplification section 470. It is also realized by adding a refractive index increasing agent (for example, GeO ₂ ) or a refractive index decreasing agent (for example, F) to the two regions 402. The refractive index difference between the second region 402 and the third region 403 is realized by the refractive index difference between the silica glass and the polymer.

  Note that the third region 403 may be made of silica glass having holes, similarly to the optical waveguide of the first embodiment. Further, it is preferable that the center of the first region 401 is different from the center of the second region 402, or the outer periphery of the second region 402 is non-circular, and the incident optical power is absorbed by the rare earth element. Efficiency can be increased. Moreover, it is also preferable to use not only Yb but also Nd, Er, Bi, Pr and a plurality of these as the rare earth element, thereby selecting an excitation wavelength and an amplification wavelength over a wide range of 500 nm to 1600 nm. be able to.

(Second Embodiment of Optical Energy Transmission Device)
Next, a second embodiment of the optical energy transmission device according to the present invention will be described. FIG. 10 is a configuration diagram of the optical energy transmission device 4 according to the present embodiment. The optical energy transmission device 4 includes a light source 80 and a wavefront adjusting element 90 in addition to the optical waveguide 40 according to the fourth embodiment described above.

Light source 80 outputs light A of wavelength 915 nm, the number of the guided mode in this case light guided in the core region of the optical waveguide 40 is 100 or more (preferably 10 ⁵ or higher).

  As in the first embodiment of the optical energy transmission device, the light source 80 can be a single transverse mode laser light source, a laser light source that oscillates in a plurality of transverse modes, or an LD stack. The wavefront adjusting element 90 includes a lens array, a diffractive optical element, and a curved mirror, and adjusts the divergence angle and beam diameter of the light A and outputs it as the light B.

  The optical waveguide 40 inputs the light B output from the wavefront adjusting element 90 to the first end 410, guides the light to the core region, and once the light is absorbed by the rare earth element, the second light is emitted. Light C is output from the end 420 to the outside.

  In this optical energy transmission device 4, the light output from the light source 80 is input to the first end 410 of the optical waveguide 40 after the divergence angle and the beam diameter are adjusted by the wavefront adjusting element 90. After being guided by the core region, it is absorbed by the rare earth element added to the optical waveguide 40. The rare earth element that has absorbed the light again emits light, which is output from the second end 420 of the optical waveguide 40 to the outside. As a result, light having a smaller beam diameter than the input light can be obtained as an output from the second end 420, and light with improved light intensity can be obtained.

  In particular, a multi-mode laser light source or an LD stack is used as the light source 80, so that high power light can be input to the optical waveguide 40 and extracted from the second end 420 with a reduced beam diameter. It is suitable for applications such as processing.

It is explanatory drawing of the optical waveguide 10 which concerns on 1st Embodiment. It is sectional drawing of the optical waveguide 10 which concerns on 1st Embodiment. It is explanatory drawing of the optical waveguide 20 which concerns on 2nd Embodiment. It is sectional drawing of the optical waveguide 20 which concerns on 2nd Embodiment. It is explanatory drawing of the optical waveguide 30 which concerns on 3rd Embodiment. It is explanatory drawing of the waveguide mode of the optical waveguide 30 which concerns on 3rd Embodiment. It is a lineblock diagram of optical energy transmission device 1 concerning this embodiment. It is explanatory drawing of the optical waveguide 40 which concerns on 4th Embodiment. It is sectional drawing of the optical waveguide 40 which concerns on 4th Embodiment. It is a block diagram of the 2nd optical energy transmission apparatus 4 which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,4 ... Optical energy transmission apparatus, 10 ... Optical waveguide, 11 ... Axis, 110 ... 1st end, 111 ... 1st area | region, 112 ... 2nd area | region, 113 ... 3rd area | region, 120 ... 2nd end, 121 ... 1st area, 122 ... 2nd area, 123 ... 3rd area, 130 ... 1st position, 131 ... 1st area, 132 ... 2nd area, 133 ... 3rd area, 140 ... 2nd position, 141 ... 1st Region 142, second region 143, third region 150, tapered portion, 20 optical waveguide, 21 axis, 210 first end, 211 first region, 212 second region, 220 second Edge, 221 ... first region, 222 ... second region, 230 ... first position, 231 ... first region, 232 ... second region, 240 ... second position, 241 ... first region, 242 ... second region, 243 ... Surrounding medium, 250 ... Tapered portion, 30 ... Optical waveguide, 31 ... Shaft, 310 ... No. End, 311 ... 1st area, 312 ... 2nd area, 320 ... 2nd end, 321 ... 1st area, 322 ... 2nd area, 330 ... 1st position, 340 ... 2nd position, 350 ... taper part, 40 ... optical waveguide, 41 ... axis, 410 ... first end, 411 ... first region, 412 ... second region, 413 ... third region, 420 ... second end, 421 ... first region, 422 ... second region, 423 ... third region, 430 ... first position, 431 ... first region, 432 ... second region, 433 ... third region, 440 ... second position, 441 ... first region, 442 ... second region, 443 ... 3rd area | region, 450 ... taper part, 460 ... reflective mirror, 470 ... light amplification area, 80 ... light source, 90 ... wavefront adjustment element.

Claims (19)

Having an axis extending from the first end to the second end;
A cross section perpendicular to the axis at any position along the axis at at least one optical wavelength, the core region including the axis and having an average refractive index N _core , and surrounding the core region, the average refractive index N a cladding region having an average refractive index N _clad lower than that of the _core , and having 100 or more waveguide modes of light guided to the core region along the axis at the first end,
When the cross-sectional area of the core region at the first end is S ₁ and the cross-sectional area of the core region at the second end is S ₂ , the relational expression “S ₂ / S ₁ ≦ 0.5” is established. Fulfill,
An optical waveguide characterized by that. When the profile volume of the core region at the first end is Ω ₁ and the profile volume of the core region at the second end is Ω ₂ at the optical wavelength, “S ₂ / S ₁ <Ω ₂ / Ω ₁ The optical waveguide according to claim 1, wherein the relational expression is satisfied. In the light wavelength, a cross section perpendicular to the axis at an arbitrary position along the axis, a first region having a mean refractive index N ₁ includes the shaft, the average refractive index N ₂ and surrounding the first region And a third region surrounding the second region and having an average refractive index N ₃ , and the average refractive indexes N ₁ , N ₂ , and N ₃ are “N ₂ ² −N ₃ ² > N”. The optical waveguide according to claim 2, wherein the relational expression ₁ ² −N ₂ ² > 0 ”is satisfied. The area S ₁ of the first region at the first end is 25 mm ² or more, and the sum S ₂ of the areas of the first region and the second region at the second end is 4 mm ² or less. The optical waveguide according to claim 3. In the light wavelength, a cross section perpendicular to the axis at an arbitrary position along the axis, a first region having a mean refractive index N ₁ includes the shaft, the average refractive index N ₂ and surrounding the first region The second region is surrounded by a surrounding medium having an average refractive index N ₃ at the second end, and the average refractive indexes N ₁ , N ₂ , and N ₃ are “N ₂ ² ”. The optical waveguide according to claim 2, wherein a relational expression of “−N ₃ ² > N ₁ ² −N ₂ ² > 0” is satisfied. The area S ₁ of the first region at the first end is 25 mm ² or more, the sum S ₂ of the areas of the first region and the second region at the second end is 4 mm ² or less, and the surrounding medium is gas The optical waveguide according to claim 5, wherein: An optical waveguide according to claim 2, and a light source that outputs light having the light wavelength,
The light output from the light source is coupled to the core region of the first end of the optical waveguide;
An optical energy transmission device.   8. The optical energy transmission device according to claim 7, wherein the light output from the light source is spatially incoherent. In the optical wavelength, a plurality of waveguide modes of light guided to the core region at the first end includes a first mode group and a second mode group,
At the optical wavelength, the number of guided modes belonging to the first mode group at the first end is L, and the number of guided modes of light guided to the core region at the second end is N. Sometimes, the relational expression “N / L ≧ 1/2” is satisfied,
Optical coupling is substantially between an arbitrary guided mode belonging to the second mode group at the first end and an arbitrary guided mode of light guided to the core region at the second end. Can be ignored,
The optical waveguide according to claim 1. An optical waveguide according to claim 9, and a light source that outputs light of the light wavelength,
Light output from the light source is coupled to a waveguide mode belonging to the first mode group at the first end of the optical waveguide;
An optical energy transmission device.   The optical energy transmission device according to claim 10, wherein the light output from the light source is spatially incoherent. In the light wavelength, a cross section perpendicular to the axis at an arbitrary position along the axis, a first region having a mean refractive index N _1, second with an average refractive index N ₂ and surrounding the first region And a third region surrounding the second region and having an average refractive index N _3, and the relational expression that the average refractive indexes N ₁ , N ₂ , and N ₃ are “N ₁ > N ₂ > N ₃ ” Meet,
There is an optical amplification section along the axis, and in the optical amplification section, the first region is made of glass containing a rare earth element that absorbs light of the optical wavelength.
The optical waveguide according to claim 1.   13. The optical waveguide according to claim 12, wherein the rare earth element is any one or more selected from Yb, Nd, Er, Bi, and Pr.   13. The optical waveguide according to claim 12, further comprising optical feedback means for returning the light propagated through the first region of the optical amplification section to the first region of the optical amplification section. The sum _{S 1} of the first region and the second region each area of the first end is not less 25 mm ² or more, the second area _{S 2} of the first region is at an end is 0.001 mm ² or less, characterized in that The optical waveguide according to claim 12.   The optical waveguide according to claim 15, wherein the first region at the second end substantially guides a single spatial mode at a light emission wavelength at which the rare earth element emits light. An optical waveguide according to claim 12, and a light source that outputs light of the optical wavelength,
The light output from the light source is coupled to the core region of the first end of the optical waveguide;
An optical energy transmission device.   18. The optical energy transmission device according to claim 17, further comprising optical feedback means for returning the light propagated through the first region of the optical amplification section of the optical waveguide to the first region of the optical amplification section. The optical energy transmission device according to claim 17, wherein the light output from the light source is spatially incoherent.

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