Laser oscillator

A laser oscillator of the present invention comprises: a semiconductor laser module; a first optical fiber for propagating a laser beam from the semiconductor laser module; and a first prism including a first input surface fusion-bonded to the first optical fiber and receiving the laser beam having been input from the first optical fiber, a first reflection surface for reflecting the laser beam having been input from the first input surface and for transmitting a stimulated Raman scattered beam, and a first output surface for outputting the laser beam having been reflected on the first reflection surface.

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2018-089131, filed on 7 May 2018, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a laser oscillator.

Related Art

In some cases, a laser oscillator has been used for cutting or welding a metallic material or a plastic material. A laser output from the laser oscillator may exceed 1 kW. The laser beam output from the laser oscillator may include a laser beam originally intended, and a stimulated Raman scattered beam having a different waveform from the originally intended laser beam. The inclusion of the stimulated Raman scattered beam reduces output of a laser beam, so that suppressing the stimulated Raman scattered beam is required. For this reason, a reflector at a fiber laser has been given a coating for reflecting the originally intended laser beam and a coating for transmitting the stimulated Raman scattered beam.

Patent document 1 is presented as a document relating to a light source device for attenuating the foregoing stimulated Raman scattered beam. Patent document 1 discloses a light source device in which an optical part having an insertion loss spectrum for attenuating a stimulated Raman scattered beam and for transmitting an excitation beam or an amplified beam is arranged on a propagation path for the stimulated Raman scattered beam.

Patent document 2 is presented as a document relating to an optical system given a coating for reflecting a laser beam and a coating for transmitting a stimulated Raman scattered beam. Patent document 2 discloses a gas component measuring device having a first concave mirror for reflecting a laser beam and for transmitting a stimulated Raman scattered beam.

SUMMARY OF THE INVENTION

However, adding a new optical part for suppressing a stimulated Raman scattered beam complicates a device configuration.

Thus, the present invention is intended to provide a laser oscillator capable of suppressing a stimulated Raman scattered beam while suppressing complication of a configuration.

(1) The present invention relates to a laser oscillator (laser oscillator100,200,300,400described later, for example) comprising: a semiconductor laser module (semiconductor laser module10described later, for example); a first optical fiber (first optical fiber40described later, for example) for propagating a laser beam from the semiconductor laser module; and a first prism (first prism50,150described later, for example) including a first input surface (first input surface51described later, for example) fusion-bonded to the first optical fiber and receiving the laser beam having been input from the first optical fiber, a first reflection surface (first reflection surface52,152described later, for example) for reflecting the laser beam having been input from the first input surface and for transmitting a stimulated Raman scattered beam, and a first output surface (first output surface53described later, for example) for outputting the laser beam having been reflected on the first reflection surface.

(2) The laser oscillator described in (1) may comprise: an optical system (fiber coupler60described later, for example) for propagating the laser beam having been output from the first prism; a second prism (second prism70,170described later, for example) including a second input surface (second input surface71described later, for example) for receiving the laser beam having been propagated through the optical system, a second reflection surface (second reflection surface72,172described later, for example) for reflecting the laser beam having been input from the second input surface and for transmitting a stimulated Raman scattered beam, and a second output surface (second output surface73described later, for example) for outputting the laser beam having been reflected on the second reflection surface; and a second optical fiber (second optical fiber80described later, for example) to which the second output surface is fusion-bonded and used for propagating the laser beam. The first prism and the second prism may be attachable to and detachable from the optical system.

(3) In the laser oscillator described in (2), the optical system may include two housings (coupler housings66,67described later, for example) having swivel configurations rotatable about a predetermined central axis (central axis X described later, for example), the first prism may be held by one of the two housings, and the second prism may be held by the other of the two housings.

(4) The laser oscillator described in any one of (1) to (3) may comprise: a detector (detector55described later, for example) arranged to face the first reflection surface of the first prism and detecting the intensity of the laser beam having been transmitted through the first reflection surface; a current supply unit (current supply unit95described later, for example) that supplies the semiconductor laser module with an excitation current; a changeover unit (switch units111to115described later, for example) capable of making a change between supplying the excitation current and not supplying the excitation current from the current supply unit to the semiconductor laser module; and a control unit (control unit90described later, for example). If the intensity of the beam detected by the detector exceeds a set value, the control unit may control the changeover unit to make a change to not supplying the excitation current to the semiconductor layer module, thereby stopping emission of a laser beam.

(5) In the laser oscillator (laser oscillator400described later, for example) described in (2) or (3), the first reflection surface (first reflection surface152described later, for example) may be configured as a first curved surface for reflecting the laser beam from the first optical fiber as parallel beams, and the second reflection surface (second reflection surface172described later, for example) may be configured as a second curved surface for reflecting the parallel beams of the laser beam from the first reflection surface and for focusing and coupling the reflected beams in the second optical fiber.

The laser oscillator provided by the present invention is capable of suppressing a stimulated Raman scattered beam while suppressing complication of a configuration.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described below by referring to the drawings. The present invention can be embodied in many different modes, and should not be limited to the contents of exemplary embodiments described below. After an element is described by referring to any of the drawings, an element comparable to the already-described element will be given the same sign in the description and the drawings, and the description of the comparable element will be omitted, where appropriate.

First Embodiment

[Overall Configuration of Laser Oscillator]

A laser oscillator according to a first embodiment of the present invention will be described by referring to the drawings.FIG. 1is a schematic configuration view showing the laser oscillator according to the first embodiment of the present invention.FIG. 2Ais a sectional view schematically showing a part of the configuration of the laser oscillator according to the first embodiment of the present invention. As shown inFIGS. 1 and 2A, a laser oscillator100according to the first embodiment includes a laser output unit1, a module driver110, a first optical fiber40, and a first prism50(seeFIG. 2A).

The laser output unit1is a unit that outputs a laser beam. The laser output unit1includes multiple (in the illustration of the drawing, five) semiconductor laser modules10(11,12,13,14,15), an in-module optical fiber20(21,22,23,24,25), and a resonator or a combiner30(resonator31, combiner32).

The semiconductor laser module10(11,12,13,14,15) includes a housing2, a semiconductor laser element3, and a lens4. The semiconductor laser element3emits a laser beam. The lens4refracts and focuses a laser beam from the semiconductor laser element3. The housing2houses the semiconductor laser element3and the lens4.

The semiconductor laser module10(11,12,13,14,15) forms a semiconductor laser module group including a mixture of semiconductor laser modules of different rated outputs. As a specific example, the semiconductor laser module group includes a mixture of a semiconductor laser module of 50 W and a semiconductor laser module of 100 W. While a laser output from a laser oscillator can be controlled only in units of 100 W using only the semiconductor laser module of 100 W, providing the semiconductor laser module of 50 W further like in this case allows control of a laser output in units of 50 W. By providing a semiconductor laser module of 10 W or less in the semiconductor laser module group, it becomes possible to control a laser output more finely. A laser output can also be controlled by controlling a current in the semiconductor laser module.

The in-module optical fiber20(21,22,23,24,25) is derived from the housing2. The in-module optical fiber20(21,22,23,24,25) is for propagating a laser beam from the semiconductor laser module10(11,12,13,14,15), and for supplying the laser beam to the resonator or combiner30(resonator31, combiner32).

In the presence of the resonator31, a laser beam from the semiconductor laser module10(11,12,13,14,15) is used as an excitation beam for the resonator31. In the presence of only the combiner32, laser beams from the multiple semiconductor laser modules11,12,13,14, and15are focused by the combiner32and used. Both the resonator31and the combiner32may be provided. By employing any of these methods, the laser oscillator100outputs a laser beam through the first optical fiber40for output.

The first optical fiber40is for propagating (passing, guiding) a laser beam from the laser output unit1including the semiconductor laser module10(11,12,13,14,15).

The module driver110is a part that drives the multiple semiconductor laser modules10(11,12,13,14,15) individually.

The module driver110applies two control modes as follows selectively to each of the multiple semiconductor laser modules10(11,12,13,14,15) and executes the applied mode: a rated drive mode of driving the semiconductor laser module so as to produce a rated output (turning on a corresponding switch unit); and a stop mode of not driving the semiconductor laser module (turning off a corresponding switch unit). More specifically, the semiconductor laser module10(11,12,13,14,15) is to be placed only in one of the two states, an output OFF state and a rated output ON state. The module driver110includes a current supply unit95as a power supply, a switch unit111, a switch unit112, a switch unit113, a switch unit114, and a switch unit115, a control signal generation unit116, and a control unit90.

The current supply unit95is a unit that supplies the semiconductor laser element3of the semiconductor laser module10(11,12,13,14,15) with an excitation current.

Each of the switch units111,112,113,114, and115as a changeover unit is a unit interposed in a circuit for supplying an excitation current from the current supply unit95to a corresponding one of the semiconductor laser modules11,12,13,14, and15. Each of the switch units111,112,113,114, and115is a unit capable of making a change between supplying an excitation current and not supplying the excitation current from the current supply unit95to a corresponding one of the semiconductor laser modules11,12,13,14, and15.

The control signal generation unit116is a unit that generates a control signal SC1, a control signal SC2, a control signal SC3, a control signal SC4, and a control signal SC5for controlling corresponding ones of the switch units111,112,113,114, and115.

The control unit90controls drive of the switch units111,112,113,114, and115, and the control signal generation unit116.

The first prism50includes a first input surface51, a first reflection surface52, and a first output surface53. The first input surface51is a surface for receiving an input laser beam. The first input surface51is fixed to the first optical fiber40by being fusion-bonded to the first optical fiber40. The first reflection surface52is a surface for reflecting the laser beam having been input from the first input surface51and for transmitting a stimulated Raman scattered beam. In the first embodiment, the first reflection surface52is formed by being given multiple coatings. The first output surface53is a surface for outputting the laser beam having been reflected on the first reflection surface52.

Supplemental explanation of the first reflection surface52will be given below. A stimulated Raman scattered beam (SRS beam) to be transmitted through the first reflection surface52is one type of scattered beam of a laser beam and is more likely to occur with increase in the intensity of the laser beam. The occurrence of the stimulated Raman scattered beam causes a problem that output of an originally intended laser beam is reduced. The stimulated Raman scattered beam becomes more intensified as it is propagated through an optical fiber, so that it is removed on the first reflection surface52. After the laser beam is reflected on the first reflection surface52, the component of the stimulated Raman scattered beam in the laser beam is reduced once. This prevents the stimulated Raman scattered beam from become more intensified during subsequent propagation of the stimulated Raman scattered beam.

Assuming that a laser beam has a wavelength of 1070 nm, a stimulated Raman scattered beam has a wavelength of 1120 nm. The first reflection surface52desirably causes reflection of 99.0% or more of the beam having a wavelength of 1070 nm, and desirably causes transmission of 97.0% or more of the beam having a wavelength of 1120 nm. The first reflection surface52is required to cause reflection of at least 98.0% or more of the beam having a wavelength of 1070 nm, and to cause transmission of 95.0% or more of the beam having a wavelength of 1120 nm.

The first reflection surface52causes transmission of a component having a wavelength except a wavelength of ±25 nm of that of a laser beam. The oscillation wavelength of the laser beam has a distribution of from about 5 nm to about 10 nm. Thus, by designing the first reflection surface52so as to achieve a reflectivity of 99.0% or more in a range of ±15 nm of the wavelength of the laser beam and to cause transmission of 97.0% or more of a beam having a wavelength except a wavelength of ±25 nm of that of the laser beam, it becomes possible to reduce a stimulated Raman scattered beam while suppressing loss of the laser beam.

As shown inFIG. 2A, the laser oscillator100includes a detector55in addition to the laser output unit1, the first optical fiber40, and the first prism50described above. The detector55is arranged to face the first reflection surface52of the first prism50. The detector55detects the intensity of a laser beam having been transmitted through the first reflection surface52. The detector55is configured using a photodiode, for example, capable of detecting the wavelength of a stimulated Raman scattered beam.

If the intensity of a stimulated Raman scattered beam detected by the detector55exceeds a set value, the control unit90controls the switch units111,112,113,114, and115to make a change to not supplying an excitation current to the semiconductor laser element3of the semiconductor layer module10(11,12,13,14,15), thereby stopping emission of a laser beam.

The following describes how a laser beam travels. The laser beam is output from the laser output unit1as indicated by an arrow L1, propagated through the first optical fiber40, and then input to the interior of the first prism50in a spreading manner as indicated by an arrow L2and an arrow L3. A stimulated Raman scattered beam is transmitted through the first reflection surface52as indicated by an arrow L100and then released to the outside. The laser beam is reflected in a spreading manner on the first reflection surface52as indicated by an arrow L4and an arrow L5, and then output through the first output surface53.

The laser oscillator of the first embodiment achieves the following effect, for example. The laser oscillator100of the first embodiment includes: the semiconductor laser module10(11,12,13,14,15); the first optical fiber40for propagating a laser beam from the semiconductor laser module10(11,12,13,14,15); and the first prism50including the first input surface51fusion-bonded to the first optical fiber40and receiving the laser beam having been input from the first optical fiber40, the first reflection surface52for reflecting the laser beam having been input from the first input surface51and for transmitting a stimulated Raman scattered beam, and the first output surface53for outputting the laser beam having been reflected on the first reflection surface52.

Thus, the laser oscillator100provided by the first embodiment is capable of suppressing a stimulated Raman scattered beam while suppressing complication of a configuration. This eventually achieves maintenance or increase of a laser output from the laser oscillator100.

The laser oscillator100of the first embodiment includes: the detector55arranged to face the first reflection surface52of the first prism50and detecting the intensity of the laser beam having been transmitted through the first reflection surface52; the current supply unit95that supplies the semiconductor laser module10(11,12,13,14,15) with an excitation current; the switch units111to115each being capable of making a change between supplying the excitation current and not supplying the excitation current from the current supply unit95to the semiconductor laser module10(11,12,13,14,15); and the control unit90. If the intensity of the beam detected by the detector55exceeds a set value, the control unit90controls the switch units111to115to make the change to not supplying the excitation current to the semiconductor layer module10(11,12,13,14,15), thereby stopping emission of a laser beam. A laser output can be controlled by controlling a current in the semiconductor laser module. Thus, the laser output can also be controlled by providing the current supply unit95with a current control function.

As a result of the control by the control unit90, a stimulated Raman scattered beam is prevented from being guided at a high intensity in the laser oscillator100to reduce the occurrence of damage of the laser oscillator100.

FIG. 2Bis a sectional view schematically showing a part of the configuration of a laser oscillator600according to a first comparative example. The laser oscillator600includes the laser output unit1, the first optical fiber40, and a quartz block601. The first optical fiber40is fusion-bonded to the quartz block601. The first optical fiber40of this configuration is attached to the laser output unit1. The following describes how a laser beam travels in the first comparative example. The laser beam is output from the laser output unit1as indicated by an arrow L1, propagated through the first optical fiber40, and then input to the interior of the quartz block601in a spreading manner as indicated by an arrow L31and an arrow L32. Then, the laser beam is output to the outside.

The laser beam is not emitted through a terminal surface of the first optical fiber40but is emitted through an end surface of the quartz block601in order to spread the laser beam in the quartz block601to reduce the intensity of the laser beam, and then emit the laser beam to the outside. Heat due to dirt or a nonreflective coating is easily generated at a boundary surface for emitting the laser beam to the outside. Thus, reducing the intensity of the laser beam is effective in preventing burning. The configuration of the first comparative example does not include a surface for transmitting a stimulated Raman scattered beam and guiding the stimulated Raman scattered beam to the outside, such as the first reflection surface52of the first prism50described above. Hence, the stimulated Raman scattered beam is to be emitted as it is from the quartz block601. This is not preferable as it causes the risk of reduction of output from the laser oscillator600.

Second Embodiment

FIG. 3Ais a sectional view schematically showing a part of the configuration of a laser oscillator200according to a second embodiment of the present invention. As shown inFIG. 3A, the laser oscillator200includes a fiber coupler60as an optical system, a second prism70, and a second optical fiber80, in addition to the first optical fiber40and the first prism50. The configuration of the laser oscillator200is similar in other respects to that of the first embodiment.

Thus, the description in the first embodiment is also applied herein and such a configuration of the laser oscillator200will not be described below.

The fiber coupler60is for propagating a beam having been output from the first prism50. The fiber coupler60is used for facilitating attachment and detachment of an optical fiber to and from the laser oscillator200. The fiber coupler60includes a coupler housing61, and a lens62and a lens63arranged in the coupler housing61.

The second prism70includes a second input surface71, a second reflection surface72, and a second output surface73. The second input surface71is a surface for receiving a laser beam having been propagated through the fiber coupler60. The second reflection surface72is a surface for reflecting the laser beam having been input from the second input surface71and for transmitting a stimulated Raman scattered beam. In the second embodiment, the second reflection surface72is formed by being given multiple coatings. The second reflection surface72is formed in the similar way to the first reflection surface52. The second output surface73is a surface for outputting the laser beam having been reflected on the second reflection surface72. The second prism70is attachable to and detachable from the fiber coupler60. The first prism50is also attachable to and detachable from the fiber coupler60.

The second optical fiber80is fusion-bonded to the second output surface73. The second optical fiber80is for propagating the laser beam having been transmitted through the fiber coupler60.

The following describes how a laser beam travels in the second embodiment. The laser beam is output from the laser output unit1as indicated by an arrow L1, propagated through the first optical fiber40, and then input to the interior of the first prism50in a spreading manner as indicated by an arrow L2and an arrow L3. A stimulated Raman scattered beam is transmitted through the first reflection surface52as indicated by an arrow L100and then released to the outside. The laser beam is reflected in a spreading manner on the first reflection surface52as indicated by an arrow L4and an arrow L5, and then output through the first output surface53.

As indicated by an arrow L6and an arrow L7, the laser beam becomes parallel beams at the lens62of the fiber coupler60. Then, the parallel beams are focused by the lens63of the fiber coupler60as indicated by an arrow L8and an arrow L9, and then input to the second prism70through the second input surface71. A stimulated Raman scattered beam is transmitted through the second reflection surface72as indicated by an arrow L200and then released to the outside. The laser beams are reflected on the second reflection surface72as indicated by an arrow L10and an arrow L11. Then, the reflected beams are focused in the second optical fiber80and propagated through the second optical fiber80.

The laser oscillator of the second embodiment achieves the following effect, for example. The laser oscillator200of the second embodiment includes: the fiber coupler60for propagating a laser beam having been output from the first prism50; the second prism70including the second input surface71for receiving the laser beam having been propagated through the fiber coupler60, the second reflection surface72for reflecting the laser beam having been input from the second input surface71and for transmitting a stimulated Raman scattered beam, and the second output surface73for outputting the laser beam having been reflected on the second reflection surface72; and the second optical fiber80to which the second output surface73is fusion-bonded and used for propagating the laser beam. The first prism50and the second prism70are configured to be attachable to and detachable from the fiber coupler60.

As described above, the laser oscillator200of the second embodiment uses two prisms, the first prism50and the second prism70to reduce a stimulated Raman scattered beam, compared to the laser oscillator100of the first embodiment.

FIG. 3Bis a sectional view schematically showing a part of the configuration of a laser oscillator700according to a second comparative example. The laser oscillator700includes the first optical fiber40, a first quartz block701, the fiber coupler60, a second quartz block702, and the second optical fiber80. The following describes how a laser beam travels in the second comparative example. The laser beam is output from the laser output unit1as indicated by an arrow L1, propagated through the first optical fiber40, and then input to the interior of the quartz block701in a spreading manner as indicated by an arrow L31and an arrow L32. As indicated by an arrow L33and an arrow L34, the laser beam becomes parallel beams at the lens62of the fiber coupler60. While the parallel beams are focused by the lens63of the fiber coupler60as indicated by an arrow L35and an arrow L36, the parallel beams are input to the second quartz block702. Then, as indicated by an arrow L37, the resultant laser beam is propagated through the second optical fiber80.

The quartz blocks701and702can be inserted into and removed from the fiber coupler60. This produces an advantage that the quartz blocks701and702can be inserted and removed easily for change of the first optical fiber40and the second optical fiber80. The configuration of the second comparative example does not include a surface for transmitting a stimulated Raman scattered beam and guiding the stimulated Raman scattered beam to the outside, such as the first reflection surface52of the first prism50and the second reflection surface72of the second prism70. This is not preferable in terms of the probability that the stimulated Raman scattered beam will be coupled as it is to the second optical fiber80.

Third Embodiment

FIG. 4is a sectional view schematically showing the configuration of a laser oscillator300according to a third embodiment of the present invention. The laser oscillator300of the third embodiment differs from the laser oscillator200of the second embodiment in that the first prism50and the second prism70are held by the fiber coupler60having a swivel configuration. The configuration of the laser oscillator300is similar in other respects to that of the second embodiment. Thus, the description in the second embodiment is also applied herein and such a configuration of the laser oscillator300will not be described below.

The fiber coupler60of the laser oscillator300includes a coupler housing66, a coupler housing67, the lens62, and the lens63. The coupler housing66and the coupler housing67as two housings have swivel configurations with which one of the housings can rotate about a predetermined central axis X relative to the other. The first prism50is attached to the coupler housing66so as to be detachable from the coupler housing66. The lens62is arranged in the coupler housing66. The second prism70is attached to the coupler housing67so as to be detachable from the coupler housing67. The lens63is arranged in the coupler housing67.

Thus, the first prism50, the coupler housing66, and the lens62rotate integrally about the central axis X of the fiber coupler60. The second prism70, the coupler housing67, and the lens63rotate integrally about the central axis X of the fiber coupler60. The first prism50is held by the coupler housing66as one of the two housings. The second prism70is held by the coupler housing67as the other of the two housings.

The laser oscillator of the third embodiment achieves the following effect, for example. In the laser oscillator300of the third embodiment, the fiber coupler60includes the two coupler housings66and67having swivel configurations rotatable about the predetermined central axis X. The first prism50is held by the coupler housing66as one of the two coupler housings66and67. The second prism70is held by the coupler housing67as the other of the two coupler housings66and67.

Thus, the first prism50and the coupler housing66can rotate relative to the coupler housing67, and the second prism70and the coupler housing67can rotate relative to the coupler housing66. This allows the first optical fiber40fusion-bonded to the first prism50to rotate relative to the coupler housing67, and allows the second optical fiber80fusion-bonded to the second prism70to rotate relative to the coupler housing66.

By the presence of the first prism50, a direction in which the first optical fiber40extends and the optical axis direction of the fiber coupler60are arranged at an angle of 90°. This allows a manufacturer to arrange the first optical fiber40in an intended direction so as to rotate the first optical fiber40about the optical axis of the fiber coupler60. By the presence of the second prism70, a direction in which the second optical fiber80extends and the optical axis direction of the fiber coupler60are arranged at an angle of 90°. This allows the manufacturer to arrange the second optical fiber80in an intended direction so as to rotate the second optical fiber80about the optical axis of the fiber coupler60. As the first optical fiber40and the second optical fiber80can rotate freely, twists of the first optical fiber40and the second optical fiber80are suppressed.

Fourth Embodiment

FIG. 5is a sectional view schematically showing a part of the configuration of a laser oscillator400according to a fourth embodiment of the present invention. The laser oscillator400of the fourth embodiment differs from the laser oscillator200of the second embodiment and the laser oscillator300of the third embodiment in that the first prism50and the second prism70are replaced by a first prism150and a second prism170. The configuration of the laser oscillator400is similar in other respects to those of the second embodiment and the third embodiment. Thus, the descriptions in the second embodiment and the third embodiment are also applied herein and such a configuration of the laser oscillator400will not be described below.

The first prism150includes a first reflection surface152. The first reflection surface152is configured as a first curved surface for reflecting a laser beam from the first optical fiber40as parallel beams. The second prism170includes a second reflection surface172. The second reflection surface172is configured as a second curved surface for reflecting the parallel beams of the laser beam from the first reflection surface152and for focusing and coupling the reflected beams in the second optical fiber80. A lens is not arranged in the fiber coupler60.

The following describes how a laser beam travels in the fourth embodiment. The laser beam is output from the laser output unit1as indicated by an arrow L1, propagated through the first optical fiber40, and then input to the interior of the first prism50in a spreading manner as indicated by an arrow L2and an arrow L3. A stimulated Raman scattered beam is transmitted through the first reflection surface152as indicated by an arrow L100and then released to the outside. The laser beam is reflected on the first reflection surface152as indicated by an arrow L21and an arrow L22. Then, resultant parallel beams are output through the first output surface53. The reflection surface152is a curved surface for converting the spread laser beam to parallel beams. Thus, after reflection on the reflection surface152, the laser beam becomes parallel beams.

The parallel beams of the laser beam pass through the fiber coupler60as they are as indicated by the arrows L21and L22, and then input to the second prism170. A stimulated Raman scattered beam is transmitted through the second reflection surface172as indicated by an arrow L200and then released to the outside. The laser beams are reflected on the second reflection surface172as indicated by an arrow L23and an arrow L24. Then, the reflected beams are focused in the second optical fiber80and propagated through the second optical fiber80. The reflection surface172is a curved surface allowing focusing of the laser beam as the parallel beams so as to couple the parallel beams in the second optical fiber80. Thus, after reflection on the reflection surface172, the laser beams are coupled in the second optical fiber80.

The laser oscillator of the fourth embodiment achieves the following effect, for example. In the laser oscillator400of the fourth embodiment, the first reflection surface152is configured as the first curved surface for reflecting a laser beam from the first optical fiber40as parallel beams. The second reflection surface172is configured as the second curved surface for reflecting the parallel beams of the laser beam from the first reflection surface152and for focusing and coupling the reflected beams in the second optical fiber80.

Thus, the laser beam as the parallel beams passes through the fiber coupler60. As the laser beam passing through the fiber coupler60is in the form of the parallel beams, a lens is not required in the fiber coupler60. Making a lens unnecessary makes it possible to prevent a stimulated Raman scattered beam from being amplified further due to reflection of the stimulated Raman scattered beam on a surface of a lens and return of the stimulated Raman scattered beam toward a resonator.

The embodiments of the present invention have been described above. In each the first to fourth embodiments, the laser oscillator includes the control unit. However, this configuration is not restrictive. The control unit may be provided separately from the laser oscillator.

In the first to fourth embodiments, the first reflection surface52, the second reflection surface72, the first reflection surface152, and the second reflection surface172are formed by being given coatings. However, this configuration is not restrictive. Each of these reflection surfaces may be formed by a diffraction grating (grating).

In the first embodiment, the control unit90is configured in such a manner that, if the intensity of a beam detected by the detector55exceeds the set value, the control unit90controls the switch units111to115to make a change to not supplying an excitation current to the semiconductor laser module10(11,12,13,14,15), thereby stopping emission of a laser beam. However, this configuration is not restrictive. More specifically, the control unit90may be configured to control any of the switch units111to115partially to make a change to not supplying an excitation current to any of the semiconductor laser modules10(11,12,13,14,15), thereby reducing emission of a laser beam.

EXPLANATION OF REFERENCE NUMERALS