Fiber laser device, production method for fiber laser device, and setting method
A fiber laser device includes: an amplifying fiber; a delivery fiber in which laser light that has been outputted from the amplifying fiber is guided; and a Raman filter that reflects part of Raman scattered light that is generated by stimulated Raman scattering caused to the laser light.
1. A fiber laser device comprising:
an amplifying fiber;
a delivery fiber in which laser light that has been outputted from the amplifying fiber is guided; and
a Raman filter that reflects part of Raman scattered light that is generated by stimulated Raman scattering caused to the laser light, wherein
the Raman filter satisfies inequality (a)
10
2
×
g
1
×
L
1
-
am
10
+
10
2
×
g
1
×
L
1
+
2
×
g
2
×
L
2
-
2
×
at
-
ar
10
<
10
2
×
g
1
×
L
1
+
2
×
g
2
×
L
2
-
ar
10
(
a
)
where:
L 1 represents a length of a light path from a first end to the Raman filter, wherein the first end is one of ends of the amplifying fiber and is disposed on an opposite side to the delivery fiber;
g 1 represents gain that the Raman scattered light receives per unit length in the light path;
L 2 represents a length of a light path from the Raman filter to a second end that is one of ends of the delivery fiber and is disposed on an opposite side to the amplifying fiber;
g 2 represents gain that the Raman scattered light receives per unit length in the light path;
am represents a reflection attenuation of the Raman filter;
at represents a transmission attenuation of the Raman filter; and
ar represents a reflection attenuation of a workpiece that is processable-by the fiber laser device.
2. The fiber laser device according to claim 1 , wherein the Raman filter further satisfies inequality (d)
2∫ L1 L1+L2 g ( P ( z )) dz−ar−am <0 (d)
where:
P(z) represents power of the laser light at a point at which a light path length from the first end to the delivery fiber, wherein the point is z; and
g(P(z)) represents gain that the Raman scattered light receives per unit length at the point.
3. The fiber laser device according to claim 2 , further comprising:
a fiber Bragg grating disposed to a third end that is one of ends of the amplifying fiber and is disposed on a delivery fiber side, wherein
the P(z) is given by equality (f) with use of r′ oc that is defined by equality (e)
r
oc
′
=
10
×
log
10
(
10
r
oc
10
+
10
2
t
oc
+
ar
10
)
(
e
)
P
(
z
)
=
P
×
(
10
r
oc
′
20
×
L
0
×
(
L
0
-
z
)
+
10
r
oc
′
20
×
L
0
×
(
L
0
+
z
)
)
(
f
)
where:
L 0 represents a length of the amplifying fiber;
r oc represents a reflection attenuation of the fiber Bragg grating;
t oc is a transmission attenuation of the fiber Bragg grating; and
P is power of the laser light outputted from the amplifying fiber via the fiber Bragg grating.
4. The fiber laser device according to claim 1 , further comprising:
a plurality of amplifying fibers that comprises the amplifying fiber; and
a combiner that combines the laser light that has been outputted from each of the plurality of amplifying fibers, wherein
the delivery fiber comprises:
delivery fibers in each of which the laser light that has been outputted from a corresponding one of the plurality of amplifying fibers is guided to the combiner; and
a delivery fiber in which the laser light that has been combined by the combiner is guided.
5. A method of producing a fiber laser device that comprises: an amplifying fiber; a delivery fiber in which laser light that has been outputted from the amplifying fiber is guided; and a Raman filter that reflects part of Raman scattered light that is generated by stimulated Raman scattering caused to the laser light, the method comprising:
providing the Raman filter that satisfies inequality (a)
10
2
×
g
1
×
L
1
-
am
10
+
10
2
×
g
1
×
L
1
+
2
×
g
2
×
L
2
-
2
×
at
-
ar
10
<
10
2
×
g
1
×
L
1
+
2
×
g
2
×
L
2
-
ar
10
(
a
)
where:
L 1 represents a length of a light path from a first end to the Raman filter, wherein the first end is one of ends of the amplifying fiber and is disposed on an opposite side to the delivery fiber;
g 1 represents gain that the Raman scattered light receives per unit length in the light path;
L 2 represents a length of a light path from the Raman filter to a second end that is one of ends of the delivery fiber and is disposed on an opposite side to the amplifying fiber;
g 2 represents gain that the Raman scattered light receives per unit length in the light path;
am represents a reflection attenuation of the Raman filter;
at represents a transmission attenuation of the Raman filter; and
ar represents a reflection attenuation of a workpiece that is processable by the fiber laser device.
6. A method of setting, in a fiber laser device, a reflection attenuation ar of a workpiece that is processable by the fiber laser device, the fiber laser device comprising: an amplifying fiber; and a delivery fiber in which laser light is guided, wherein the laser light has been outputted from the amplifying fiber, the method comprising:
setting the reflection attenuation ar to satisfy inequality (a)
10
2
×
g
1
×
L
1
-
am
10
+
10
2
×
g
1
×
L
1
+
2
×
g
2
×
L
2
-
2
×
at
-
ar
10
<
10
2
×
g
1
×
L
1
+
2
×
g
2
×
L
2
-
ar
10
(
a
)
where:
L 1 represents a length of a light path from a first end to the Raman filter, wherein the first end is one of ends of the amplifying fiber and is disposed on an opposite side to the delivery fiber;
g 1 represents gain that Raman scattered light receives per unit length in the light path;
L 2 represents a length of a light path from the Raman filter to a second end that is one of ends of the delivery fiber and is disposed on an opposite side to the amplifying fiber;
g 2 represents gain that the Raman scattered light receives per unit length in the light path;
am represents a reflection attenuation of the Raman filter;
at represents a transmission attenuation of the Raman filter; and
ar represents the reflection attenuation of the workpiece that is processable by the fiber laser device.