Coherent light generators – Optical fiber laser
Reexamination Certificate
1999-07-01
2002-05-07
Scott, Jr., Leon (Department: 2881)
Coherent light generators
Optical fiber laser
C372S700000, C372S027000, C372S102000, C372S064000, C372S012000, C372S020000, C372S026000, C372S028000, C372S031000, C372S032000
Reexamination Certificate
active
06385215
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a laser oscillation method and device for emitting laser beam with multiple wavelengths using optical fiber as a gain medium, and relates to a laser scalpel using such a laser oscillation device.
BACKGROUND OF THE INVENTION
Currently, laser oscillation devices to emit laser beam have been used for various apparatuses. For example, a laser scalpel equipped with a gas laser tube as a laser oscillation device is also put to practical use. While other than the gas laser tube a semiconductor laser is widely used as a laser oscillation device, typical laser oscillation devices emit a single wavelength of laser beam.
However, for the laser scalpel it is requested that laser beam with multiple wavelengths can be emitted according to various uses. As a laser oscillation device to comply with this request, there is a fiber laser. In this fiber laser, an optical fiber that laser ion is doped functions as a gain medium, and laser beam with multiple wavelengths can be emitted by cascade oscillation.
FIG. 1
shows the entire structure of fiber laser. Referring to
FIG. 1
, the fiber laser as a conventional laser oscillation device is explained below. In a fiber laser
1
illustrated herein, reflection elements
3
,
4
each are disposed at both sides of an optical fiber
2
as the gain medium, and a light emitting element
5
as excitation emission means opposes to one reflection element
3
.
The optical fiber
2
is of glass fiber, into the core of which given laser ion is doped. The light emitting element
5
is, for example, composed of LD (laser diode) whose emission makes laser ion of the optical fiber
2
excite to generate one laser beam including multiple wavelength components.
The one reflection element
3
to which the light emission
5
opposes is, for example, composed of a dichroic mirror, which efficiently transmits light beam with excitation wavelength generated by the light emitting element
5
but efficiently reflects light beam with oscillation wavelength resonated by the optical fiber
2
. The other reflection element
4
is, for example, composed of a half mirror (semitransparent mirror), which reflects and transmits laser beam excited by the optical fiber
2
according to its intensity.
In the fiber laser
1
described above, when emission of the light emitting element
5
is led through the reflection element
3
to the optical fiber
2
, laser ion of the optical fiber
2
is excited to generate laser beam with multiple wavelengths. The laser beam is resonated between a pair of the reflection elements
3
and
4
, emitted outside from the reflection element
4
at a given intensity.
Since laser beam thus emitted has multiple wavelength components, they are available to various apparatuses that need this property. However, the intensity ratio of multiple wavelengths in laser beam may not be in a desired condition. In this case, the intensity of a specific wavelength component needs to be reduced.
For example, as shown in
FIG. 1
, by using an optical filter
6
that gives a specific transmissivity to a specific wavelength, the intensity ratio of multiple wavelengths in laser beam eat be corrected into a desired condition. Further, by selecting one of optical filters
6
with various properties, the intensity ratio of multiple wavelengths in laser beam can be varied arbitrarily.
Also, like a fiber laser
11
in
FIG. 2
laser beam can be reflected in different directions for each of multiple wavelengths by a wavelength dispersion element
12
such as a diffraction grating and a prism, and its intensity can be separately modulated by multiple optical filters
13
,
14
.
As described above, the fiber lasers
1
,
11
can emit laser beam with multiple wavelengths, and the intensity ratio of multiple wavelengths can be brought into a desired condition. However, in case of the first fiber laser
1
, for laser beam with three or more wavelengths, it is difficult to bring the intensity ratio into a desired condition. Also, it is difficult to change the intensity of a specific wavelength component in a continuous and dynamic a manner.
In case of the second fiber laser
11
, even for laser beam with three or more wavelengths, the intensity ratio can be brought into a desired condition. However, it is still difficult to change the intensity of a specific wavelength component in a continuous and dynamic manner. Further, since it is difficult to multiplex multiple laser beams separated for respective wavelengths into one beam, it is not suitable for an apparatus having such a requirement.
Further, both the first and second fiber lasers
1
,
11
resonate laser beam generated at the optical fiber
2
while reflecting it by the reflection elements
3
,
4
on both sides. In this laser resonance, an optimum reflection factor has to be differentiated to each of the multiple wavelengths. However, in the fiber lasers
1
,
11
, multiple wavelength components of one laser beam are reflected uniformly by one reflection element
3
or
4
at each side of the optical fiber
2
. Therefore, the operation of laser resonance cannot reach the optimum condition.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a laser oscillation method that one laser beam including multiple wavelengths can be generated in the optimum condition and the intensity of multiple wavelengths can be modulated separately.
It is a further object of the invention to provide a laser oscillation device that one laser beam including multiple wavelengths can be generated in the optimum condition and the intensity of multiple wavelengths can be modulated separately.
It is a still further object of the invention to provide a laser scalpel using such a laser oscillation device.
According to the invention, a laser oscillation method for generating one laser beam including multiple wavelength components by locating reflection means for reflecting laser beam at both ends of an optical fiber where laser ion in doped and by exciting the laser ion in the optical fiber by light emitted from an excitation emission means, comprises the step of:
separating laser beam emitted from at least one end of the optical fiber into beams with multiple wavelengths; and
reflecting separately the beams with multiple wavelengths by the reflection means.
According to another aspect of the invention, a laser oscillation device for generating one laser beam including multiple wavelength components by locating reflection means for reflecting laser beam at both ends of an optical fiber where laser ion is doped and by exciting the laser ion in the optical fiber by light emitted from an excitation emission means, comprises:
a separation optical means that is located at least at one end of the optical fiber and separates laser beam into beams with multiple wavelengths:
wherein the beams with multiple wavelengths separated by the separation optical means are reflected separately by the reflection means.
According to another aspect of the invention, a laser oscillation device, comprises:
an optical fiber where laser ion is doped;
an excitation emission means that generates one laser beam including multiple wavelength components by exciting the laser ion in the optical fiber by light emission;
a total reflection means that is located at one end of the optical fiber and reflects uniformly laser beam with multiple wavelengths;
a separation optical means that is located at another end of the optical fiber and separates laser beam into beams with multiple wavelengths; and
a plurality of partial reflection means that reflect separately laser beams with multiple wavelengths separated by the separation optical means.
According to another aspect of the invention, a laser oscillation device, comprises:
an optical fiber where laser ion is doped;
an excitation emission means that generates one laser beam including multiple wavelength components by exciting the laser ion in the optical fiber by light emission;
a pair of separation optical means that are located individually at both ends of the op
Jr. Leon Scott
NEC Corporation
Young & Thompson
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