JP2009123883A - Optical amplifier and optical oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier and an optical oscillator that can uniformalize distribution in the excitation density on a core layer of a double-clad type planar optical waveguide. <P>SOLUTION: The optical amplifier has a double-clad type planar optical waveguide 10a, an excited light input means 20 to input excited light 100 to the planar optical waveguide 10a, and a signal light input means 30 to input signal light 110 to the planar optical waveguide 10a. For the planar optical waveguide 10a, a sum of the thickness in the lamination direction of a lower first cladding layer 12a and an upper first cladding layer 14a is decreased gradually toward a positive direction of X axis. The refractive index of the first cladding layer 12a and the upper first cladding layer 14a is smaller than that of a core layer 13, and the refractive index of a lower second cladding layer 11a is smaller than that of the lower first cladding layer 12a, while the refractive index of an upper second cladding layer 15a is smaller than that of the upper first cladding layer 14a. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical amplifier and an optical oscillator using a double-clad planar optical waveguide.

  2. Description of the Related Art Conventionally, optical amplifiers and optical oscillators using planar optical waveguides that use double-clad planar optical waveguides are known (see, for example, Patent Document 1 and Patent Document 2).

US Patent Application Publication No. 2003/0138021 US Pat. No. 6,785,304

  When excitation light is input to the conventional double-clad planar optical waveguide as described above, the thickness of the core layer and the first cladding layer of the double-clad planar optical waveguide is constant. Thus, the absorption coefficient of the excitation light by the double clad planar optical waveguide becomes constant, and the transmission power of the excitation light decreases exponentially according to the optical path length of the excitation light. Therefore, the amount of excitation light absorbed decreases as the optical path length of the excitation light increases. As a result, in the core layer of the planar optical waveguide, the pumping density distribution is non-uniform with respect to the traveling direction of the pumping light, and a large pumping power is required locally. Therefore, there is a problem that the excitation power necessary for the increase.

  In addition, non-uniformity in the distribution of excitation density in the core layer of the planar optical waveguide also causes non-uniformity in the heat distribution generated at each position of the core layer of the planar optical waveguide, and distortion and distortion in the planar optical waveguide. There was a problem that cracking occurred.

  Furthermore, when the signal light is input from a direction that is not parallel to the pump light in the optical amplifier, a non-uniform pump density distribution occurs in the beam cross-sectional direction of the signal light. As a result, there is a problem that the beam quality of the signal output light deteriorates.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical amplifier and an optical oscillator capable of uniformizing the excitation density distribution in the core layer of a double-clad planar optical waveguide. To get.

  An optical amplifier according to the present invention includes a double-clad planar optical waveguide, excitation light input means for inputting excitation light to the double-clad planar optical waveguide, and signal light for inputting signal light to the double-clad planar optical waveguide An optical amplifier provided with an input means, wherein the double clad planar optical waveguide has a lower second cladding layer, a lower first cladding layer, a core layer, an upper first cladding layer, and an upper second cladding layer in order. The first boundary surface between the lower first cladding layer and the core layer is a plane, and the second boundary surface between the core layer and the upper first cladding layer is the first boundary surface. A first end surface perpendicular to the first boundary surface; a second end surface parallel to the first end surface; and a second end surface perpendicular to the first boundary surface and the first end surface. 3 end faces and parallel to the third end face 4, and the sum of the thicknesses of the lower first cladding layer and the upper first cladding layer in the stacking direction is from the first end surface to the first end surface with respect to the direction perpendicular to the first end surface. The thickness in the stacking direction of the lower first cladding layer and the thickness in the stacking direction of the upper first cladding layer are smaller than the direction perpendicular to the third end surface. The refractive index of the lower first cladding layer and the upper first cladding layer is smaller than the refractive index of the core layer, and the refractive index of the lower second cladding layer is lower than that of the lower first cladding layer. The refractive index of the upper second cladding layer is smaller than the refractive index of the upper first cladding layer, and the excitation light input means is configured to excite the core layer. Is emitted toward the first end face, The excitation light is input from one end face to the lower first cladding layer, the core layer, and the upper first cladding layer, and the signal light input means outputs the signal light to be amplified by the core layer. The light is emitted toward any one of the first, second, third, and fourth end faces, and the signal light is input from the one end face to the core layer.

  In the optical amplifier according to the present invention, the distribution of the excitation density in the core layer of the double clad planar optical waveguide can be made uniform. Thereby, since a locally large excitation power is not required, the required gain can be achieved with a minimum excitation power. In addition, there is an effect that distortion and cracking of the planar optical waveguide caused by the nonuniformity of the heat distribution in the planar optical waveguide due to the nonuniformity of the excitation density in the core layer can be reduced. Furthermore, even when the signal light is input from a direction not parallel to the excitation light, the distribution of the excitation density in the beam cross-sectional direction of the signal light is made uniform, so that the amplification factor of the signal light is the same at each position in the beam stage surface. As a result, the beam quality of the signal output light is improved.

Embodiment 1 FIG.
An optical amplifier according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a perspective view showing a configuration of an optical amplifier according to Embodiment 1 of the present invention. In the following, in each figure, the same reference numerals indicate the same or corresponding parts.

  In FIG. 1, the optical amplifier according to the first embodiment of the present invention is provided with a double clad planar optical waveguide 10a, a pumping light input means 20, and a signal light input means 30. The arrows indicate the traveling directions of the excitation light 100 and the signal light 110.

  A semiconductor laser can be used as the excitation light input means 20. As the excitation light input means 20, any configuration may be used as long as it has a function of inputting the excitation light 100 to the double clad planar optical waveguide 10a.

  As the signal light input means 30, a configuration in which a semiconductor laser is condensed by a condenser lens can be used. As the signal light input means 30, any configuration may be used as long as it has a function of inputting the signal light 110 to the double clad planar optical waveguide 10a.

  The double clad planar optical waveguide 10a includes, from below, a lower second cladding layer 11a, a lower first cladding layer 12a, a core layer 13, an upper first cladding layer 14a, and an upper second cladding layer 15a. It is composed of

  The optical amplifier according to Embodiment 1 of the present invention uses a double-clad planar optical waveguide 10a. In this double-clad planar optical waveguide 10a, the optical path of the excitation light 100 with respect to the traveling direction of the excitation light 100 Since the sum of the thicknesses of the lower first cladding layer 12a and the upper first cladding layer 14a is gradually reduced as the length increases, the distribution of excitation density in the core layer 13 of the double-clad planar optical waveguide 10a Can be made uniform.

  Next, the operation of the optical amplifier according to the first embodiment will be described with reference to the drawings.

  First, in FIG. 1, the traveling direction of the pumping light 100 is the positive direction of the X axis, the traveling direction of the signal light 110 is the positive direction of the Z axis, and is orthogonal to the X axis and the Z axis. The direction toward the layer 14a is the positive direction of the Y axis.

  The excitation light 100 generated by the excitation light input means 20 travels in the positive direction of the X axis and is input to the double clad planar optical waveguide 10a. The signal light 110 generated by the signal light input means 30 travels in the positive direction of the Z axis and is input to the double clad planar optical waveguide 10a.

  FIG. 2 is a diagram showing a state of signal light propagation in the double-clad planar optical waveguide of the optical amplifier according to the first embodiment of the present invention.

  As shown in FIG. 2, in the double clad planar optical waveguide 10 a, the refractive index of the lower first clad layer 12 a and the upper first clad layer 14 a is set so that the signal light 110 can propagate through the core layer 13. Is set to a value smaller than the refractive index.

  In the first embodiment, the case where the refractive indexes of the lower first cladding layer 12a and the upper first cladding layer 14a are the same will be described. However, as long as the signal light 110 can propagate through the core layer 13, The refractive indexes of the lower first cladding layer 12a and the upper first cladding layer 14a may be different.

  FIG. 3 is a diagram showing a state of propagation of excitation light in the double-clad planar optical waveguide of the optical amplifier according to Embodiment 1 of the present invention.

  As shown in FIG. 3, in the double clad planar optical waveguide 10a, the excitation light 100 can be propagated through the lower first cladding layer 12a, the core layer 13 and the upper first cladding layer 14a. The refractive index is set to a value smaller than the refractive index of the lower first cladding layer 12a, and the refractive index of the upper second cladding layer 15a is set to a value smaller than the refractive index of the upper first cladding layer 14a. ing.

  In the first embodiment, the case where the lower second cladding layer 11a and the upper second cladding layer 15a have the same refractive index will be described. However, the excitation light 100 is emitted from the lower first cladding layer 12a, the core layer 13, and the upper second cladding layer 15a. The refractive index of the lower second cladding layer 11a may be different from that of the upper second cladding layer 15a as long as it can propagate through the first cladding layer 14a.

  The material of the core layer 13 of the double clad planar optical waveguide 10 a is a laser medium for absorbing the excitation light 100 and amplifying the signal light 110. Thus, the excitation light 100 is absorbed when the excitation light 100 propagates through the core layer 13, and the signal light 110 is amplified when the signal light 110 propagates through the core layer 13.

Here, as shown in FIG. 3, the excitation light 100 propagates through the lower first cladding layer 12a, the core layer 13, and the upper first cladding layer 14a, but the excitation light 100 is absorbed by the core layer 13 and is The first cladding layer 12a and the upper first cladding layer 14a are not absorbed. The absorption coefficient α (X) [1 / m] of the excitation light 100 by the double cladding type planar optical waveguide 10a and the absorption of the excitation light 100 by the core layer 13 when the X coordinate of the double cladding type planar optical waveguide 10a is X. The relationship with the coefficient α ₀ [1 / m] is that the thickness D _core [μm] of the core layer 13 at the position where the X coordinate is X, the lower first cladding layer 12a, the core layer 13, and the upper first cladding layer 14a. _Is expressed by the following formula (1) using the sum of the thicknesses D _total (X) [μm].

α (X) = α ₀ · D _core / D _total (X) Equation (1)

Here, the absorption amount of the excitation light 100 by the core layer 13 in the minute section where the X coordinate is X to X + ΔX and in the minute section where the X coordinate is X + ΔX to X + 2 · ΔX will be considered. It is assumed that D _total (X) is constant in a minute section where the X coordinate is X to X + ΔX.

Let P _f (X) [W] be the power of the pumping light 100 that travels in the positive direction of the X axis at the position where the X coordinate is X. At this time, the amount of absorption P _abs (X) [W / m] of the excitation light 100 by the core layer 13 per unit length in a minute section where the X coordinate is X to X + ΔX is expressed by the following equation (2). .

P _abs (X) = P _f (X) · {1-exp (−α (X) · ΔX)} / ΔX
Formula (2)

On the other hand, the amount of absorption P _abs (X + ΔX) [W / m] of the excitation light 100 by the core layer 13 per unit length in the minute interval of X coordinates X + ΔX to X + 2 · ΔX is expressed by the following equation (3). The

P _abs (X + ΔX) = P _f (X) · exp (−α (X) · ΔX) · {1-exp (−α (X + ΔX) · ΔX)} / ΔX
Formula (3)

The distribution of the excitation density in the core layer 13 of the double clad planar optical waveguide 10a is made uniform when P _abs (X) = P _abs (X + ΔX). At this time, the absorption coefficient α (X) of the excitation light 100 by the double-clad planar optical waveguide 10a in the minute section where the X coordinate is X to X + ΔX and the double-clad type plane in the minute section of the X coordinate X + ΔX to X + 2 · ΔX. The relationship with the absorption coefficient α (X + ΔX) of the excitation light 100 by the optical waveguide 10a is expressed by the following equation (4).

  α (X + ΔX) = − 1 / ΔX · ln {2-exp (α (X) · ΔX)} Equation (4)

At this time, the relationship between D _total (X) when the X coordinate is X to X + ΔX and D _total (X + ΔX) when the X coordinate is X + ΔX to X + 2 · ΔX is expressed by the following equation (5).

D _total (X + ΔX) = D _total (X) · α (X) / α (X + ΔX) (5)

  In the first embodiment, the core layer 13 is configured such that the sum of the thicknesses of the lower first cladding layer 12a and the upper first cladding layer 14a of the double-clad planar optical waveguide 10a satisfies Expression (5). The excitation density distribution in can be made uniform. That is, in the first embodiment, in the double clad planar optical waveguide 10a, the thickness of the first cladding layers 12a and 14a is reduced as the X coordinate is increased, so that the excitation light is increased as the X coordinate is increased. The absorption coefficient α (X) of 100 can be increased, and as a result, the excitation density distribution in the core layer 13 of the planar optical waveguide can be made uniform.

However, at this time, by reducing the thickness of the first cladding layers 12a and 14a as the X coordinate increases, the first cladding layers 12a and 14a It is necessary to set a difference in refractive index between the second cladding layers 11a and 15a. For example, consider a case where the length in the X-axis direction of the double-clad planar optical waveguide 10a is L and the position where the excitation light 100 is input to the double-clad planar optical waveguide 10a is the position where the X coordinate is 0. This is the case where the beam diameter of the excitation light 100 is equal to D _total (0) at the position where the X coordinate of the double clad planar optical waveguide 10a is 0, the numerical aperture of the excitation light 100 is NA _beam , and the double clad planar optical waveguide When the allowable numerical aperture derived from the refractive index difference between the refractive index n ₁ of the first cladding layer and the refractive index n ₂ of the second cladding layer of the waveguide 10 a is NA _wg = √ (n ₁ ² −n ₂ ² ) The allowable numerical aperture NA _wg needs to satisfy the following formula (6).

NA _wg > NA _beam · D _total (0) / D _total (L) Equation (6)

For example, consider the case where the material of the core layer 13 of the double clad planar optical waveguide 10a is glass doped with Yb ions. The thickness D _core in the Y-axis direction of the core layer 13 of the double clad planar optical waveguide 10a is 20 μm, and the thicknesses of the lower first cladding layer 12a, the core layer 13 and the upper first cladding layer 14a at a position where the X coordinate is 0. Let us consider a case where the sum D _total (0) is 220 μm, the length in the X-axis direction of the double clad planar optical waveguide 10a is 2 cm, and the length in the Z-axis direction is 3 cm.

Further, the input power of the pumping light 100 to the double clad planar optical waveguide 10a is 1 W, the wavelength of the pumping light 100 is 940 nm, the wavelength of the signal light 110 is 1030 nm, and the absorption cross section of Yb ions with respect to 940 nm is 2 Consider a case where the wavelength contained in the core layer 13 of the .26 × 10 ⁻²⁵ m ² and the double-clad planar optical waveguide 10 a is such that the ion density of Yb ions is 1.5 × 10 ²⁷ ions / m ³ . At this time, the absorption sectional area of the excitation light 100 by the core layer 13 of the double clad planar optical waveguide 10a is 339 / m.

FIG. 4 is a diagram illustrating a calculation result of the sum D _total (X) [μm] of the thicknesses of the lower first cladding layer 12a, the core layer 13, and the upper first cladding layer 14a. FIG. 5 is a diagram illustrating a calculation result of the absorption amount P _abs (X) [W / m] of the excitation light 100 by the core layer 13 per unit length.

4 and 5, the solid line is the case of the double clad planar optical waveguide 10a according to the first embodiment. The broken line is a case of a double clad planar optical waveguide in which the thickness of the first clad layer is constant, and is shown as a reference for comparison. As shown in FIG. 5, in the case of the double clad planar optical waveguide 10a according to the first embodiment, the absorption amount of the excitation light 100 by the core layer 13 with respect to the traveling direction of the excitation light 100 is 31 regardless of the X coordinate. It becomes a constant value of [W / m]. As a result, the excitation density in the core layer 13 becomes a constant value of 5.1 × 10 ⁷ [W / m ³ ], and the distribution of the excitation density is made uniform.

Here, a case where the beam diameter of the excitation light 100 is 220 μm and the numerical aperture of the excitation light 100 is 0.1 is considered. From the above calculation results, D _total (X) is 220 μm when the X coordinate is 0, and 84 μm when the X coordinate is 2 cm. Therefore, from Equation (6), the allowable numerical aperture NA _wg derived from the refractive index difference between the refractive index n ₁ of the first cladding layer and the refractive index n ₂ of the second cladding layer of the double-clad planar optical waveguide 10a is It is necessary that NA _wg > 0.26.

Further, here, the case bottom thickness of the first cladding layer _{12a D lclad (X) [μm} ] and the thickness _{D Uclad} the upper first cladding layer 14a (X) [μm] are equal. Consider a case where the core layer 13 has a vertically symmetrical shape as a center.

Figure 6 is a diagram showing the thickness _{D Lclad} the lower first clad layer 12a (X), the calculation results of the thickness _{D Uclad} the upper first cladding layer 14a (X) [μm].

  As described above, when the lower first cladding layer 12a and the upper first cladding layer 14a have a vertically symmetrical shape with the core layer 13 as the center, the thermal expansion of the lower first cladding layer 12a and the upper first cladding layer 14a occurs. Since they occur uniformly, the thermal stress from the lower first cladding layer 12a and the upper first cladding layer 14a to the core layer 13 is balanced, and the effect of reducing distortion and cracking due to the thermal stress is achieved.

  Here, the case where the lower first cladding layer 12a and the upper first cladding layer 14a have a vertically symmetrical shape with the core layer 13 as the center is shown, but the lower first cladding layer 12a and the upper first cladding layer 14a are shown. May not have a vertically symmetrical shape around the core layer 13.

  As described above, in the optical amplifier using the double clad planar optical waveguide 10a according to the first embodiment, the distribution of the excitation density in the core layer 13 of the double clad planar optical waveguide 10a can be made uniform. . As a result, since a locally large pumping power is not required, the required gain can be achieved with a minimum pumping power in the optical amplifier. In addition, there is an effect of reducing the distortion and cracking of the planar optical waveguide caused by the nonuniformity of the heat distribution in the planar optical waveguide due to the nonuniformity of the excitation density in the core layer 13. Furthermore, even when the signal light 110 is input from a direction that is not parallel to the pumping light 100 in the optical amplifier, the distribution of the pumping density in the beam cross-sectional direction of the signal light 110 is made uniform, so that the amplification factor of the signal light 110 becomes the beam stage. As a result, the beam quality of the signal output light is improved.

Embodiment 2. FIG.
An optical amplifier according to Embodiment 2 of the present invention will be described with reference to FIGS. FIG. 7 is a perspective view showing a configuration of an optical amplifier according to Embodiment 2 of the present invention. In addition, the overlapping description is abbreviate | omitted about the part which is the same as that of FIG. 1, or an equivalent part.

  In FIG. 7, the optical amplifier according to the second embodiment of the present invention is provided with a double-clad planar optical waveguide 10b, pumping light input means 20, and signal light input means 30.

  The double-clad planar optical waveguide 10b includes a lower second cladding layer 11b, a lower first cladding layer 12b, a core layer 13, an upper first cladding layer 14b, an upper second cladding layer 15b, and excitation light. The reflection means 16 is comprised.

  In the optical amplifier according to Embodiment 2 of the present invention, in the double-clad planar optical waveguide 10b, as the optical path length of the pumping light 100 becomes longer than the traveling direction of the pumping light 100, the lower first cladding layer 12b and the upper Since the sum of the thicknesses of the first cladding layer 14b is gradually reduced, the excitation density distribution in the core layer 13 of the double cladding type planar optical waveguide 10b can be made uniform, and the excitation light 100 Since the light is reflected by the excitation light reflecting means 16, the absorption efficiency of the excitation light 100 by the core layer 13 can be increased.

  Next, the operation of the optical amplifier according to the second embodiment will be described with reference to the drawings.

  Since the basic operation of the optical amplifier according to the second embodiment is the same as that of the optical amplifier according to the first embodiment, a duplicate description is omitted. Here, the operation related to the excitation light reflecting means 16 will be described.

  The excitation light 100 generated by the excitation light input means 20 travels in the positive direction of the X axis and is input to the double clad planar optical waveguide 10b. The excitation light 100 input to the double clad planar optical waveguide 10 b and propagated through the lower first cladding layer 12 b, the core layer 13, and the upper first cladding layer 14 b is reflected by the excitation light reflecting means 16.

The power of the pumping light 100 traveling in the positive direction of the X axis at the position where the X coordinate is X is P _f (X) [W], and the power of the pumping light 100 traveling in the negative direction of the X axis is P _b ( X) Let [W]. At this time, the amount of absorption P _abs (X) [W / m] of the excitation light 100 by the core layer 13 per unit length in a minute section where the X coordinate is X to X + ΔX is expressed by the following equation (7). .

P _abs (X) = P _f (X) · {1−exp (−α (X) · ΔX)} / ΔX + P _b (X) · {exp (α (X) · ΔX) −1} / ΔX
Formula (7)

On the other hand, the amount of absorption P _abs (X + ΔX) [W / m] of the excitation light 100 by the core layer 13 per unit length in a minute section of the X coordinate X + ΔX to X + 2 · ΔX is expressed by the following equation (8). The

P _abs (X + ΔX) = P _f (X) · exp (−α (X) · ΔX) · {1-exp (−α (X + ΔX) · ΔX)} / ΔX + P _b (X) · exp (α (X) .DELTA.X). {Exp (.alpha. (X + .DELTA.X) .DELTA.X) -1} /. DELTA.X
Formula (8)

The distribution of the excitation density in the core layer 13 of the double clad planar optical waveguide 10b is made uniform when P _abs (X) = P _abs (X + ΔX). D _total (X) satisfying this relationship can be obtained by calculation.

  For example, consider a case where the calculation conditions are the same as those described in the first embodiment.

FIG. 8 is a diagram illustrating a calculation result of the sum D _total (X) [μm] of the thicknesses of the lower first cladding layer 12b, the core layer 13, and the upper first cladding layer 14b. FIG. 9 is a diagram illustrating a calculation result of the absorption amount P _abs (X) [W / m] of the excitation light 100 by the core layer 13 per unit length.

8 and 9, the solid line represents the case of the double clad planar optical waveguide 10b according to the second embodiment. The broken line is a case of a double clad planar optical waveguide in which the thickness of the first clad layer is constant, and is shown as a reference for comparison. As shown in FIG. 9, in the case of the double clad planar optical waveguide 10b according to the second embodiment, the absorption amount of the excitation light 100 by the core layer 13 with respect to the traveling direction of the excitation light 100 is 38 regardless of the X coordinate. It becomes a constant value of [W / m]. As a result, the excitation density in the core layer 13 becomes a constant value of 6.4 × 10 ⁷ [W / m ³ ], and the distribution of the excitation density is made uniform.

In the second embodiment, the absorption efficiency of the excitation light 100 by the core layer 13 can be increased by reflecting the excitation light 100 by the excitation light reflecting means 16. Under the calculation conditions described above, the absorption amount P _abs (X) of the excitation light 100 by the core layer 13 per unit length was 31 [W / m] in the first embodiment. In the second embodiment, it is 38 [W / m], and the absorption efficiency of the excitation light 100 by the core layer 13 is larger than that in the first embodiment.

Here, a case where the beam diameter of the excitation light 100 is 220 μm and the numerical aperture of the excitation light 100 is 0.1 is considered. From the above calculation results, D _total (X) is 220 μm when the X coordinate is 0, and 173 μm when the X coordinate is 2 cm. Therefore, from Equation (6), the allowable numerical aperture NA _wg derived from the refractive index difference between the refractive index n ₁ of the first cladding layer and the refractive index n ₂ of the second cladding layer of the double-clad planar optical waveguide 10a is It is necessary that NA _wg > 0.13.

Under the calculation conditions described above, the allowable numerical aperture NA _wg required for the double-clad planar optical waveguide is 0.26 in the first embodiment, but is 0.13 in the second embodiment. Therefore, the allowable numerical aperture required for the double-clad planar optical waveguide is smaller than in the case of the first embodiment. As a result, when a double-clad type planar optical waveguide is manufactured with a certain allowable numerical aperture, the second embodiment squeezes the excitation light 100 into the second cladding layer as compared with the first embodiment. The effect that can be reduced.

Further, here, the thickness _{D Lclad} the lower first clad layer 12b (X) [μm], consider the case where the thickness _{D Uclad} first upper cladding layer 14b (X) [μm] are equal. Consider a case where the core layer 13 has a vertically symmetrical shape as a center.

Figure 10 is a diagram showing the thickness _{D Lclad} the lower first clad layer 12b (X), the calculation results of the thickness _{D Uclad} first upper cladding layer 14b (X) [μm].

  As described above, when the lower first cladding layer 12b and the upper first cladding layer 14b have symmetrical shapes with the core layer 13 as the center, the thermal expansion of the lower first cladding layer 12b and the upper first cladding layer 14b is caused. Since they occur uniformly, the thermal stress from the lower first cladding layer 12b and the upper first cladding layer 14b to the core layer 13 is balanced, and the effect of reducing distortion and cracking due to the thermal stress is achieved.

  Here, the case where the lower first cladding layer 12b and the upper first cladding layer 14b are vertically symmetrical about the core layer 13 is shown, but the lower first cladding layer 12b and the upper first cladding layer 14b are shown. May not have a vertically symmetrical shape around the core layer 13.

  As described above, in the optical amplifier using the double clad planar optical waveguide 10b according to the second embodiment, the optical amplifier using the double clad planar optical waveguide 10a according to the first embodiment is used. In addition, there is an effect that the absorption efficiency of the excitation light 100 by the core layer 13 can be increased.

Embodiment 3 FIG.
An optical amplifier according to Embodiment 3 of the present invention will be described with reference to FIGS. FIG. 11 is a perspective view showing a configuration of an optical amplifier according to Embodiment 3 of the present invention. In addition, the overlapping description is abbreviate | omitted about the part which is the same as that of FIG. 1, or an equivalent part.

  In FIG. 11, an optical amplifier according to Embodiment 3 of the present invention includes a double-clad planar optical waveguide 10c, pumping light input means (first pumping light input means) 20, and pumping light input means (second pump). Excitation light input means) 21 and signal light input means 30 are provided. The arrows indicate the traveling directions of the excitation light 100 and 101 and the signal light 110.

  The double-clad planar optical waveguide 10c includes a lower second cladding layer 11c, a lower first cladding layer 12c, a core layer 13, an upper first cladding layer 14c, and an upper second cladding layer 15c. ing.

  In the optical amplifier according to the third embodiment, in the double-clad planar optical waveguide 10c, the lower first cladding layer is intermediate between the two end faces through which the pumping light 100, 101 passes with respect to the traveling direction of the pumping light 100, 101. Since the sum of the thicknesses of 12c and the upper first clad layer 14c is minimized, the distribution of the excitation density in the core layer 13 of the double clad planar optical waveguide 10c can be made uniform, and the double clad Since the excitation lights 100 and 101 are input from both sides of the mold plane optical waveguide 10c, the excitation density in the core layer 13 can be increased.

  Next, the operation of the optical amplifier according to the third embodiment will be described with reference to the drawings.

  Since the basic operation of the optical amplifier according to the third embodiment is the same as that of the optical amplifier according to the first embodiment, a duplicate description is omitted. Here, operations related to the excitation light input means 20 and 21 will be described.

  The excitation light 100 generated by the excitation light input means 20 travels in the positive direction of the X axis and is input to the double clad planar optical waveguide 10c. On the other hand, the excitation light 101 generated by the excitation light input means 21 travels in the negative direction of the X axis and is input to the double clad planar optical waveguide 10c. The signal light 110 generated by the signal light input means 30 travels in the positive direction of the Z axis and is input to the double clad planar optical waveguide 10c.

At the position where the X coordinate is X, the power of the pumping light 100 traveling in the positive direction of the X axis is P _f (X) [W / m], and the power of the pumping light 101 traveling in the negative direction of the X axis is P _b (X) [W / m]. At this time, the absorption amount P _abs (X) [W / m] of the excitation light by the core layer 13 per unit length in the minute section where the X coordinate is X to X + ΔX is expressed by the above-described formula (7).

In addition, the absorption amount P _abs (X + ΔX) [W / m] of the excitation light by the core layer 13 per unit length in the minute section where the X coordinate is X + ΔX to X + 2 · ΔX is expressed by the above equation (8). The

The distribution of the excitation density is made uniform in the core layer 13 of the double clad planar optical waveguide 10c when P _abs (X) = P _abs (X + ΔX). D _total (X) satisfying this relationship can be obtained by calculation.

  For example, consider a case where the calculation conditions are the same as those described in the first embodiment. However, in the third embodiment, a case is considered in which the input powers of the excitation light 100 and the excitation light 101 to the double-clad planar optical waveguide 10c are both 1W.

FIG. 12 is a diagram illustrating a calculation result of the sum D _total (X) [μm] of the thicknesses of the lower first cladding layer 12c, the core layer 13, and the upper first cladding layer 14c. FIG. 13 is a diagram illustrating a calculation result of the absorption amount P _abs (X) [W / m] of excitation light by the core layer 13 per unit length.

12 and 13, the solid line is the case of the double clad planar optical waveguide 10c according to the third embodiment. The broken line is a case of a double clad planar optical waveguide in which the thickness of the first clad layer is constant, and is shown as a reference for comparison. As shown in FIG. 13, in the case of the double clad planar optical waveguide 10c according to the third embodiment, the absorption amount of the excitation light by the core layer 13 with respect to the traveling direction of the excitation light 100 and 101 is independent of the X coordinate. It becomes a constant value of 47 [W / m]. As a result, the excitation density in the core layer 13 becomes a constant value of 7.9 × 10 ⁷ [W / m ³ ], and the distribution of the excitation density is made uniform.

In the third embodiment, the excitation density in the core layer 13 can be increased by inputting the excitation lights 100 and 101 from both the positive and negative sides in the X-axis direction of the double clad planar optical waveguide 10c. Under the calculation conditions described above, the absorption amount P _abs (X) of the excitation light by the core layer 13 per unit length is 31 [W / m] and 38 [W / m] in the first and second embodiments, respectively. However, in this third embodiment, it is 47 [W / m], and the amount of absorption of excitation light by the core layer 13 is larger than in the first and second embodiments.

Here, a case is considered where the beam diameters of the excitation light 100 and 101 are 220 μm and the numerical aperture of the excitation light 100 and 101 is 0.1. From the above calculation results, D _total (X) is 220 μm when the X coordinate is 0, and 209 μm when the X coordinate is 1 cm. Therefore, from Equation (6), the allowable numerical aperture NA _wg derived from the refractive index difference between the refractive index n ₁ of the first cladding layer and the refractive index n ₂ of the second cladding layer of the double-clad planar optical waveguide 10 c is It is necessary that NA _wg > 0.11.

Under the calculation conditions described above, the allowable numerical aperture NA _wg required for the double-clad planar optical waveguide was 0.26 and 0.13 in the first and second embodiments, respectively. 3 is 0.11, and the allowable numerical aperture required for the double-clad planar optical waveguide is smaller than those in the first and second embodiments. As a result, when a double-clad type planar optical waveguide is manufactured with a certain allowable numerical aperture, the second clad layer of the excitation light 100 and 101 is more in the third embodiment than in the first and second embodiments. There is an effect that can reduce the squeezing out.

Further, here, the thickness _{D Lclad} the lower first clad layer 12c (X) [μm], consider the case where the thickness _{D Uclad} the upper first cladding layer 14c (X) [μm] are equal. Consider a case where the core layer 13 has a vertically symmetrical shape as a center.

Figure 14 is a diagram showing the thickness _{D Lclad} the lower first clad layer 12c (X), the calculation results of the thickness _{D Uclad} the upper first cladding layer 14c (X) [μm].

  As described above, when the lower first cladding layer 12c and the upper first cladding layer 14c have vertically symmetrical shapes around the core layer 13, the thermal expansion of the lower first cladding layer 12c and the upper first cladding layer 14c is caused. Since they occur uniformly, the thermal stress from the lower first cladding layer 12c and the upper first cladding layer 14c to the core layer 13 is balanced, and the effect of reducing distortion and cracking due to the thermal stress is achieved.

  Here, the case where the lower first cladding layer 12c and the upper first cladding layer 14c have a vertically symmetrical shape with the core layer 13 as the center is shown, but the lower first cladding layer 12c and the upper first cladding layer 14c are shown. May not have a vertically symmetrical shape around the core layer 13.

  As described above, the optical amplifier according to the third embodiment has an effect that the excitation density in the core layer 13 can be increased as compared with the optical amplifiers according to the first and second embodiments.

Embodiment 4 FIG.
An optical amplifier according to Embodiment 4 of the present invention will be described with reference to FIGS. FIG. 15 is a perspective view showing a first configuration of the optical amplifier according to Embodiment 4 of the present invention. 15 to 17, the same or corresponding parts as those in FIGS. 1, 7, and 11 are not described.

  In FIG. 15, a double clad planar optical waveguide 10d includes a lower second cladding layer 11d, a lower first cladding layer 12d, a core layer 13, an upper first cladding layer 14d, and an upper second cladding layer 15d. It is configured.

  FIG. 16 is a perspective view showing a second configuration of the optical amplifier according to Embodiment 4 of the present invention.

  In FIG. 16, a double clad planar optical waveguide 10e includes a lower second cladding layer 11e, a lower first cladding layer 12e, a core layer 13, an upper first cladding layer 14e, and an upper second cladding layer 15e. And excitation light reflecting means 16.

  Further, FIG. 17 is a perspective view showing a third configuration of the optical amplifier according to Embodiment 4 of the present invention.

  In FIG. 17, a double clad planar optical waveguide 10f includes a lower second cladding layer 11f, a lower first cladding layer 12f, a core layer 13, an upper first cladding layer 14f, and an upper second cladding layer 15f. It is configured.

  In the optical amplifier according to the fourth embodiment, in the double-clad planar optical waveguides 10d to 10f, the pumping light is transmitted with respect to at least one of the two orthogonal axes within the boundary surface between the core layer 13 and the first cladding layer. As the process proceeds, one of the first cladding layers on both the upper and lower sides of the core layer 13 is made thinner, and the thickness of the other first cladding layer is kept constant. Thus, the excitation density distribution in the core layer 13 of the planar optical waveguide can be made uniform.

    Next, the operation of the optical amplifier according to the fourth embodiment will be described with reference to the drawings.

  Since the basic operation of the optical amplifier according to the fourth embodiment is the same as that of the optical amplifier according to the first to third embodiments, a duplicate description is omitted. Here, as an example, a comparison is made using FIG. 1 and FIG.

  The fourth embodiment is characterized in that the thickness of the lower first cladding layer 12d of the double-clad planar optical waveguide 10d is constant. In the fourth embodiment, the sum of the thicknesses of the lower first cladding layer 12d and the upper first cladding layer 14d is the thickness of the lower first cladding layer 12a and the upper first cladding layer 14a in the first embodiment. To be equal to the sum of At this time, the fourth embodiment has an effect that the excitation density distribution in the core layer 13 of the planar optical waveguide can be made uniform, as in the first embodiment.

  Further, when the lower second cladding layer 11d and the lower first cladding layer 12d are polished or the lower second cladding layer 11d and the lower first cladding layer 12d are joined in the process of manufacturing the planar optical waveguide, The fact that the boundary surface between the two cladding layers 11d and the lower first cladding layer 12d is a flat surface that is not inclined makes the production of the planar optical waveguide technically easy and inexpensive.

  As described above, in the fourth embodiment, unlike the first embodiment described above, it is not necessary to reduce the thickness of both the lower first cladding layer 12d and the upper first cladding layer 14d. Since only the clad layer 14d needs to be thinned, the production of the planar optical waveguide is technically easy, and the cost is reduced.

  As described above, in the first to fourth embodiments, the case where the signal light 110 is input from the direction orthogonal to the traveling direction of the pumping light 100 and 101 has been described. It is not limited. For example, in the first embodiment, the signal light 110 may be input from a direction parallel to the traveling direction of the excitation light 100.

Embodiment 5 FIG.
An optical oscillator according to Embodiment 5 of the present invention will be described with reference to FIG. FIG. 18 is a perspective view showing a configuration of an optical oscillator according to the fifth embodiment of the present invention.

  18, the optical oscillator according to the fifth embodiment of the present invention is provided with a double-clad planar optical waveguide 10a, excitation light input means 20, a total reflection mirror 40, and a partial reflection mirror 41. The arrow indicates the traveling direction of the excitation light 100.

  The double clad planar optical waveguide 10a includes, from below, a lower second cladding layer 11a, a lower first cladding layer 12a, a core layer 13, an upper first cladding layer 14a, and an upper second cladding layer 15a. It is composed of

  As described above, in the first to fourth embodiments, the case of the optical amplifier has been described. However, in the fifth embodiment, the signal light is not input and used as a laser light oscillator.

  This can be realized, for example, by adding a total reflection mirror 40 and a partial reflection mirror 41 to both ends of the double clad planar optical waveguide 10a without using the signal light input means 30, as shown in FIG. It is.

  As described above, the double-clad planar optical waveguide is useful for application to optical amplifiers and laser light oscillators, but the application is not limited thereto.

  In the first to fifth embodiments described above, the double-clad planar optical waveguide has been described with respect to a rectangular parallelepiped shape. A shape is also conceivable.

1 is a perspective view showing the configuration of an optical amplifier according to Embodiment 1 of the present invention. It is a figure which shows the mode of the propagation | transmission of the signal light in the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows the mode of propagation | transmission of the excitation light in the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows the change of the X-axis direction of the sum of the thickness of the lower 1st clad layer of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 1 of this invention, a core layer, and an upper 1st clad layer. It is a figure which shows the change of the X-axis direction of the absorption amount of the excitation light by the core layer per unit length of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 1 of this invention. It is a figure which shows the change of the X-axis direction of the thickness of the lower 1st cladding layer of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 1 of this invention, and the thickness of an upper 1st cladding layer. It is a perspective view which shows the structure of the optical amplifier which concerns on Embodiment 2 of this invention. It is a figure which shows the change of the X-axis direction of the sum of the thickness of the lower 1st cladding layer of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 2 of this invention, a core layer, and an upper 1st cladding layer. It is a figure which shows the change of the X-axis direction of the absorption amount of the excitation light by the core layer per unit length of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 2 of this invention. It is a figure which shows the change of the X-axis direction of the thickness of the lower 1st cladding layer of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 2 of this invention, and the thickness of an upper 1st cladding layer. It is a perspective view which shows the structure of the optical amplifier which concerns on Embodiment 3 of this invention. It is a figure which shows the change of the X-axis direction of the sum of the thickness of the lower 1st cladding layer of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 3 of this invention, a core layer, and an upper 1st cladding layer. It is a figure which shows the change of the X-axis direction of the absorption amount of the excitation light by the core layer per unit length of the double clad type | mold planar optical waveguide of the optical amplifier which concerns on Embodiment 3 of this invention. It is a figure which shows the change of the X-axis direction of the thickness of the lower 1st cladding layer of the double clad type planar optical waveguide of the optical amplifier which concerns on Embodiment 3 of this invention, and the thickness of an upper 1st cladding layer. It is a perspective view which shows the 1st structure of the optical amplifier which concerns on Embodiment 4 of this invention. It is a perspective view which shows the 2nd structure of the optical amplifier which concerns on Embodiment 4 of this invention. It is a perspective view which shows the 3rd structure of the optical amplifier which concerns on Embodiment 4 of this invention. It is a perspective view which shows the structure of the optical oscillator based on Embodiment 5 of this invention.

Explanation of symbols

  10a double-clad planar optical waveguide, 10b double-clad planar optical waveguide, 10c double-clad planar optical waveguide, 10e double-clad planar optical waveguide, 10f double-clad planar optical waveguide, 11a, 11b, 11c, 11d, 11e, 11f Lower second cladding layer, 12a, 12b, 12c, 12d, 12e, 12f Lower first cladding layer, 13 Core layer, 14a, 14b, 14c, 14d, 14e, 14f Upper first Cladding layer, 15a, 15b, 15c, 15d, 15e, 15f Upper second cladding layer, 16 Excitation light reflection means, 20 Excitation light input means, 21 Excitation light input means, 30 Signal light input means, 40 Total reflection mirror, 41 Partial reflector.

Claims (10)

A double-clad planar optical waveguide;
Excitation light input means for inputting excitation light to the double clad planar optical waveguide;
An optical amplifier comprising signal light input means for inputting signal light to the double clad planar optical waveguide,
The double clad planar optical waveguide is
A lower second cladding layer, a lower first cladding layer, a core layer, an upper first cladding layer, and an upper second cladding layer are sequentially stacked;
A first boundary surface of the lower first cladding layer and the core layer is a plane;
A second boundary surface of the core layer and the upper first cladding layer is a plane parallel to the first boundary surface;
A first end surface perpendicular to the first boundary surface; a second end surface parallel to the first end surface; a third end surface perpendicular to the first boundary surface and the first end surface; and Having a fourth end face parallel to the third end face;
The sum of the thicknesses of the lower first cladding layer and the upper first cladding layer in the stacking direction is directed from the first end surface to the second end surface with respect to a direction perpendicular to the first end surface. Gradually getting smaller,
The thickness in the stacking direction of the lower first cladding layer and the thickness in the stacking direction of the upper first cladding layer are constant with respect to the direction perpendicular to the third end face;
The refractive index of the lower first cladding layer and the upper first cladding layer is smaller than the refractive index of the core layer,
A refractive index of the lower second cladding layer is smaller than a refractive index of the lower first cladding layer, and a refractive index of the upper second cladding layer is smaller than a refractive index of the upper first cladding layer;
The excitation light input means emits the excitation light for exciting the core layer toward the first end face, and the lower first cladding layer, the core layer, and the upper second end face from the first end face. The excitation light is input to one cladding layer,
The signal light input means emits the signal light to be amplified by the core layer toward one end face of the first, second, third, or fourth end face, and An optical amplifier, wherein the signal light is input from one end face to the core layer. The optical amplifier according to claim 1, wherein the double-clad planar optical waveguide has excitation light reflecting means for reflecting the excitation light on the second end face. A double-clad planar optical waveguide;
First and second excitation light input means for inputting first and second excitation lights to the double clad planar optical waveguide, respectively;
An optical amplifier comprising signal light input means for inputting signal light to the double clad planar optical waveguide,
The double clad planar optical waveguide is
A lower second cladding layer, a lower first cladding layer, a core layer, an upper first cladding layer, and an upper second cladding layer are sequentially stacked;
A first boundary surface of the lower first cladding layer and the core layer is a plane;
A second boundary surface of the core layer and the upper first cladding layer is a plane parallel to the first boundary surface;
A first end surface perpendicular to the first boundary surface; a second end surface parallel to the first end surface; a third end surface perpendicular to the first boundary surface and the first end surface; and Having a fourth end face parallel to the third end face;
The sum of the thicknesses of the lower first cladding layer and the upper first cladding layer in the stacking direction is an intermediate point between the first end surface and the second end surface with respect to a direction perpendicular to the first end surface. Becomes a minimum, gradually decreases from the first end surface toward the intermediate point, and gradually decreases from the second end surface toward the intermediate point,
The thickness in the stacking direction of the lower first cladding layer and the thickness in the stacking direction of the upper first cladding layer are constant with respect to the direction perpendicular to the third end face;
The refractive index of the lower first cladding layer and the upper first cladding layer is smaller than the refractive index of the core layer,
A refractive index of the lower second cladding layer is smaller than a refractive index of the lower first cladding layer, and a refractive index of the upper second cladding layer is smaller than a refractive index of the upper first cladding layer;
The first excitation light input means emits the first excitation light for exciting the core layer toward the first end surface, and the lower first cladding layer, Inputting the first excitation light to the core layer and the upper first cladding layer;
The second excitation light input means emits the second excitation light for exciting the core layer toward the second end surface, and the lower first cladding layer, the second end surface, The second excitation light is input to the core layer and the upper first cladding layer,
The signal light input means emits the signal light to be amplified by the core layer toward one end face of the first, second, third, or fourth end face, and An optical amplifier, wherein the signal light is input from one end face to the core layer. 4. The optical amplifier according to claim 1, wherein the lower first cladding layer and the upper first cladding layer have a vertically symmetrical shape about the core layer. 5. 4. The optical amplifier according to claim 1, wherein the thickness of the lower first cladding layer in a stacking direction is constant with respect to a direction perpendicular to the first end face. A double-clad planar optical waveguide;
An optical oscillator comprising excitation light input means for inputting excitation light to the double-clad type planar optical waveguide,
The double clad planar optical waveguide is
A lower second cladding layer, a lower first cladding layer, a core layer, an upper first cladding layer, and an upper second cladding layer are sequentially stacked;
A first boundary surface of the lower first cladding layer and the core layer is a plane;
A second boundary surface of the core layer and the upper first cladding layer is a plane parallel to the first boundary surface;
A first end surface perpendicular to the first boundary surface; a second end surface parallel to the first end surface; a third end surface perpendicular to the first boundary surface and the first end surface; and Having a fourth end face parallel to the third end face;
The sum of the thicknesses of the lower first cladding layer and the upper first cladding layer in the stacking direction is directed from the first end surface to the second end surface with respect to a direction perpendicular to the first end surface. Gradually getting smaller,
The thickness in the stacking direction of the lower first cladding layer and the thickness in the stacking direction of the upper first cladding layer are constant with respect to the direction perpendicular to the third end face;
A refractive index of the lower second cladding layer is smaller than a refractive index of the lower first cladding layer, and a refractive index of the upper second cladding layer is smaller than a refractive index of the upper first cladding layer;
The excitation light input means emits the excitation light for exciting the core layer toward the first end face, and the lower first cladding layer, the core layer, and the upper second end face from the first end face. An optical oscillator, wherein the pumping light is input to one cladding layer. The optical oscillator according to claim 6, wherein the double clad planar optical waveguide has excitation light reflecting means for reflecting the excitation light on the second end face. A double-clad planar optical waveguide;
An optical oscillator comprising first and second pumping light input means for inputting first and second pumping lights to the double-clad planar optical waveguide, respectively;
The double clad planar optical waveguide is
A lower second cladding layer, a lower first cladding layer, a core layer, an upper first cladding layer, and an upper second cladding layer are sequentially stacked;
A first boundary surface of the lower first cladding layer and the core layer is a plane;
A second boundary surface of the core layer and the upper first cladding layer is a plane parallel to the first boundary surface;
A first end surface perpendicular to the first boundary surface; a second end surface parallel to the first end surface; a third end surface perpendicular to the first boundary surface and the first end surface; and Having a fourth end face parallel to the third end face;
The sum of the thicknesses of the lower first cladding layer and the upper first cladding layer in the stacking direction is an intermediate point between the first end surface and the second end surface with respect to a direction perpendicular to the first end surface. Becomes a minimum, gradually decreases from the first end surface toward the intermediate point, and gradually decreases from the second end surface toward the intermediate point,
The thickness in the stacking direction of the lower first cladding layer and the thickness in the stacking direction of the upper first cladding layer are constant with respect to the direction perpendicular to the third end face;
A refractive index of the lower second cladding layer is smaller than a refractive index of the lower first cladding layer, and a refractive index of the upper second cladding layer is smaller than a refractive index of the upper first cladding layer;
The first excitation light input means emits the first excitation light for exciting the core layer toward the first end surface, and the lower first cladding layer, Inputting the first excitation light to the core layer and the upper first cladding layer;
The second excitation light input means emits the second excitation light for exciting the core layer toward the second end surface, and the lower first cladding layer, the second end surface, The optical oscillator, wherein the second pumping light is input to the core layer and the upper first cladding layer. 9. The optical oscillator according to claim 6, wherein the lower first cladding layer and the upper first cladding layer have a vertically symmetrical shape about the core layer. The optical oscillator according to claim 6, 7 or 8, wherein the thickness of the lower first cladding layer in the stacking direction is constant with respect to a direction perpendicular to the first end face.

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