Light source device

A light source device includes: a plurality of laser sources; a plurality of collimating parts, each configured to collimate the light beam emitted from a corresponding one of the laser sources; a combining grating configured to diffract, at an identical diffraction angle, light beams that have passed through the collimating parts and are incident on the combining grating at different incident angles, to combine the diffracted light beams; and a plurality of plane transmission gratings, wherein each of the plane transmission gratings is disposed in an optical path between a corresponding one of the collimating parts and the combining grating, and wherein each of the plane transmission gratings is adjustable so as to allow selection of a wavelength of the light beam incident on the combining grating.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No. 2018-061647, filed on Mar. 28, 2018, the contents of which are hereby incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a light source device that applies wavelength beam combining (WBC) to emit high-output laser light.

2. Description of Related Art

Demand for light source devices to emit high-output laser light has increased in various fields including laser processing such as laser soldering. One example of light source devices to emit high-output laser light is a wavelength beam combining device (hereinafter referred to as a “WBC device”). U.S. Pat. No. 6,192,062 describes an example of a WBC device. The WBC device described in U.S. Pat. No. 6,192,062 includes: a light source unit, such as a laser diode (LD) bar, in which a plurality of laser sources (for example, LDs) are arranged and each of the laser sources are configured to emit light with a predetermined gain spectral bandwidth; a collimating lens that collimates laser beams emitted from the laser sources; a condenser lens that condenses the laser beams passing through the collimating lens; a grating on which the laser beams condensed by the condenser lens is incident; and a partially reflecting mirror that is disposed in an optical path of diffracted beams diffracted by the grating. The partially reflecting mirror and each of the plurality of laser sources form an external cavity, and lights resonated in external cavities are each transmitted through partially reflecting mirrors and are combined.

SUMMARY OF THE INVENTION

In the WBC device, portions of the diffracted beams from the grating are reflected by the partially reflecting mirror and are returned back into the laser source. However, the light source device with the above structure has a great external cavity length between the laser source and the partially reflecting mirror. In one example, the external cavity length is approximately 1 meter. With a great external cavity length, even a slight deviation in position of an optical element constituting the external cavity due to vibration causes a great deviation of the light beam. This may result in a failure of external resonance, and thus the WBC device may not work.

One object of the present invention is to provide a light source device in which the external cavity length can be shortened.

A light source device according to one embodiment of the present invention includes: a plurality of laser sources each configured to emit light having a peak wavelength in a range of 350 nm to 550 nm with a predetermined gain bandwidth; collimating parts each configured to collimate light emitted from a corresponding one of the laser sources into a substantially parallel light; a combining grating configured to diffract, at an identical diffraction angle, lights that have passed through the collimating part and are incident on the combining grating at different incident angles, to combine the diffracted lights; and plane transmission gratings each disposed in an optical path between a corresponding one of the collimating parts and the combining grating, each of the plane transmission gratings is adjustable so as to allow selection of a wavelength of the light incident on the combining grating. Each of the plane transmission gratings is configured to diffract a portion of light emitted from a corresponding one of the laser sources back to the corresponding one of the laser sources, to cause external resonance between the corresponding one of the laser sources and each of the plane transmission gratings.

A light source device according to another embodiment of the present invention includes: a plurality of laser sources each configured to emit light having a peak wavelength in a range of 350 nm to 550 nm with a predetermined gain bandwidth; collimating parts each configured to collimate the light emitted from a corresponding one of the laser sources into a substantially parallel light; a combining grating configured to diffract, at an identical diffraction angle, lights that have passed through the collimating part and are incident on the combining grating at a different incident angle to combine the diffracted light; and volume holographic gratings each disposed in an optical path between a corresponding one of the laser sources and the combining grating, each of the volume holographic gratings determines a wavelength of the light incident on the combining grating. Each of the volume holographic gratings is configured to diffract a portion of the light emitted from a corresponding one of the laser sources back to the laser source, to cause external resonance between the corresponding one of the laser sources and each of the volume holographic gratings.

A light source device according to yet another embodiment of the present invention includes: a plurality of laser sources each configured to emit light having a peak wavelength in a range of 350 nm to 550 nm with a predetermined gain bandwidth; collimating parts each configured to collimate an incident light into a substantially parallel light; a combining grating configured to diffract, at an identical diffraction angle, lights each having passed through a corresponding one of the collimating parts and incident on the combining grating at different incident angles, to combine the diffracted light; and fiber Bragg gratings each disposed in an optical path between a corresponding one of the laser sources and a corresponding one of the collimating parts, each of the fiber Bragg gratings determines a wavelength of a light incident on the combining grating. Each of the fiber Bragg gratings is configured to diffract a portion of the light emitted from a corresponding one of the laser sources back to the corresponding laser source, to cause external resonance between the corresponding one of the laser sources and each of the fiber Bragg gratings.

According to certain embodiments, a light source device having a short external cavity length can be provided.

Problems, configurations, and effects other than the above will become apparent from the following description of certain embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

First Embodiment

FIG. 1is a schematic view of a light source device according to a first embodiment of the present invention. A light source device10of the present embodiment includes a plurality of external cavity modules100and a combining grating110. Each of the external cavity modules100includes a laser source102, a collimating part104, a plane transmission grating106, and a stage108. In each external cavity module100, the laser source102, the collimating part104, and the plane transmission grating106are disposed at the same stage108, so that the external cavity module100can be moved integrally. In this case, the laser source102is preferably disposed in contact with the stage108to allow the laser source102to be cooled by cooling the stage108.

An x axis, a y axis, and a z axis, which are orthogonal to one another, are shown inFIG. 1for the convenience of description. InFIG. 1, light beams are schematically represented in dashed lines and denoted as light beams120. Each of the light beams120shown in dashed lines is emitted from the laser source102, passes through the collimating part104and the plane transmission grating106, and then enters the combining grating110. Although a light beam has a divergence angle or a width, only the optical axis of the beam is shown in dashed lines inFIG. 1for the convenience of description.

All of the light beams120have their optical axes on a single x-z plane.

The laser source102may be a laser diode (hereinafter referred to as “LD”) configured to emit light having a peak wavelength in a range of 350 nm to 550 nm with a predetermined gain bandwidth. For example, the laser source102may be an LD including a nitride semiconductor configured to emit light having a center wavelength of 410 nm with a gain bandwidth Δλ of 20 nm. In this case, the wavelength of light emitted from the laser source102is in a range of 400 nm to 420 nm.

When the LD serving as the laser source102has a front side from which light is emitted and a rear side opposite to the front side, it is preferable that the front side is provided with an antireflective coating to have a reflectance reduced to nearly 0%, for example, approximately in a range of 0.1% to 2.0%. The rear mirror preferably has a reflectance of nearly 100%, for example, 85% to 99.9%. Because the LD to emit light having a wavelength in a range of 350 nm to 550 nm tends to be deteriorated in the air, the laser source102is preferably hermetically sealed. For example, an LD in a can-type package may be used for the laser source102. Using the can-type package for the laser source102allows for further having an effect of cooling and an effect of electrostatic and electromagnetic shielding.

Each collimating part104is configured to collimate individual light emitted from a corresponding one of the laser sources102into substantially parallel light. Each collimating part104may be, for example, a collimating lens disposed opposing a corresponding one of the laser sources102. Each collimating part104corresponding to a corresponding one of the laser sources102may be a single lens or a plurality of lenses in combination.

Each plane transmission grating106is disposed in an optical path between the collimating part104and the combining grating110of the same external cavity module100. Each plane transmission grating106is configured to diffract a portion of light emitted from the laser source102of the same external cavity module100back to the laser source102, to cause external resonance between the laser source102and the corresponding plane transmission grating106. In more detail, the external resonance occurs between the rear side of the LD that serves as the laser source102and the plane transmission grating106. That is, a combination of the laser source102, the collimating part104, and the plane transmission grating106forms a single external cavity. The cavity length of the external cavity is defined by the distance between the laser source102and the plane transmission grating106. The external cavity may have a Littrow configuration. The “Littrow configuration” refers to a configuration that allows light to be diffracted at the same angle as an incident angle and the diffracted light being reflected is fed back to the laser diode along the same route as the incident light.

The plane transmission grating106having grating grooves is disposed such that the orientation of the grating grooves is parallel to the y axis as shown inFIG. 1. The plane transmission grating106has a rotation axis parallel to the y axis and is disposed on the stage108so as to be rotated about the rotation axis with respect to the stage108. When the plane transmission grating106is rotated about the rotation axis, the incident angle at which the light emitted from the laser source102enters the plane transmission grating106changes, so that the wavelength of light resonating in a corresponding external cavity may be selected. Accordingly, the plane transmission grating determines the wavelength of light passing through the plane transmission grating106and incident on the combining grating110. That is, the plane transmission grating106serves as a wavelength selecting element for the external cavity. Rotation of the plane transmission grating106may be controlled by a known driving unit in the art, such as a stepper motor.

As shown inFIG. 1, the light passing through the plane transmission grating106of the external cavity module100enters the combining grating110at a different incident angle. InFIG. 1, the light beam120is shown in the dashed line extending from the plane transmission grating106to the combining grating110.

For the convenience of description, the light beam120is also referred to as the light emitted from the external cavity module100in the present specification. The incident angle of each light beam120entering the combining grating110is defined by the mounting angle of a corresponding external cavity in which the external resonance occurs. More specifically, the incident angle of each light beam120can be set and adjusted by selecting the position and the angle of a corresponding one of the external cavity modules100relative to the combining grating110. For example, the angle of the external cavity module100as a whole can be adjusted by rotating the stage108, so that the incident angle of the light entering the combining grating110can be adjusted. Such an adjustment can be performed by a known device in the art, such as a stepper motor.

The combining grating110has grating grooves and is disposed such that the orientation of the grating grooves is parallel to the y axis shown inFIG. 1. The combining grating110is configured to diffract the light beams120, each of which passes through the collimating part104and the plane transmission grating106of a corresponding external cavity module100and which enter the combining grating110at different incident angles, toward the same diffraction angle to combine the light beam120so as to form a combined beam130. The combined beam130has an optical axis on the x-z plane, on which the optical axes of the light beams120are also located. Next, diffracting of the combining grating110will be described with reference toFIG. 2.

FIG. 2is a schematic view illustrating the incident angle of the light entering the combining grating110and the diffraction angle of the diffracted light. InFIG. 2, a solid line N-N indicates a normal of the combining grating110. Assuming the light beam120enters the combining grating110at an incident angle of a and the diffracted beam (the combined beam130) is diffracted by the combining grating110at a diffraction angle of β, the relationship expressed in Formula (1) is satisfied.
sin α+sin β=N·m·λ,Formula (1)

In Formula (1), a indicates the incident angle, β indicates the diffraction angle, N indicates the number of grooves in the combining grating per 1 mm, m indicates an order of diffraction, and λ indicates the wavelength of the light beam.

For example, provided that each of the laser sources102is configured to emit a laser beam with a center wavelength of 410 nm and a wavelength in range of 400 nm to 420 nm and the combining grating has 2,222 grooves per 1 mm, a first order diffraction occurs such that, when each of the light beams having wavelengths shown in Table 1 enters the combining grating at the corresponding incident angle α, the light beams are diffracted at the same diffraction angle β, so as to form the combined beam.

That is, with the plane transmission grating106, a wavelength of a light emitted from each of the external cavity modules100is selected to be a corresponding one of 400.53 nm, 405.30 nm, 410.00 nm, 414.63 nm, or 419.19 nm, which are in the column of the wavelength “λ” in Table 1.

Then, the position of the external cavity module100is adjusted such that light enters the combining grating110at the corresponding incident angle shown in the column of the incident angle “α” in Table 1, namely, 43.32 degrees, 44.16 degrees, 45.00 degrees, 45.84 degrees, or 46.68 degrees. Accordingly, the lights emitted from the external cavity modules100are diffracted by the combining grating110at the same diffraction angle of 11.77 degrees, so that the high-output combined beam130is formed.

FIG. 1illustrates an example in which a reflection grating is used for the combining grating110; however, a transmission grating may be used for the combining grating110. The transmission grating absorbs less light compared with the reflection grating, and thus is less easily damaged. With the reflection grating, only a zero-order reflecting light and a first-order diffracted light is obtained, which allows the stray light to be reduced.

In the present embodiment, the external cavity is formed between the laser source102and the plane transmission grating106in each external cavity module100, so that a single longitudinal mode oscillation at the selected wavelength is obtained. The length of the external cavity is defined by a distance between the laser source102and the plane transmission grating106. Reduction in the distance between the laser source102and the plane transmission grating106increases a tolerance of deviation of the position of optical elements that constitute the external cavity is, which enables the light source device10to have a high vibration resistance. For example, along with increase in output of a light source device, a water-cooling system is required for the light source device; however, the operation of the external cavity may become unstable due to the pulsation of cooling water. Also, an external cavity with a long cavity length requires precise adjustment during initial assembly, which leads to the difficulty in the assembly. According to the present embodiment, such a high precision adjustment is not required during initial assembly, so that the light source device can be easily assembled.

Second Embodiment

FIG. 3is a schematic view of a light source device according to a second embodiment of the present invention. A light source device20in the present embodiment is a modification of the light source device10. In the present embodiment, members, portions, components, and elements having the same functions as the first embodiment are denoted by the same reference numerals as those in the first embodiment, and duplicative description thereof may be omitted.

The light source device20includes a plurality of laser sources102as in the light source device10. Each of the laser sources102includes a collimating part104and a plane transmission grating106. The plane transmission grating106is configured to diffract a portion of light emitted from the corresponding laser source102back to the laser source102to cause external resonance between the laser source102and the plane transmission grating106. That is, the laser source102, the collimating part104, and the plane transmission grating106form an external cavity.

The light source device20is different from the light source device10mainly in the aspects described below. A deflector-condenser lens210is disposed in an optical path between the external cavities and a combining grating110. Light beams120, which pass through the plane transmission gratings106and are emitted from the external cavities, propagate in the z direction as shown inFIG. 3, in parallel to one another until the light beams120reach the deflector-condenser lens210. The incident angles of the light beams120incident on the combining grating110are defined by the deflector-condenser lens210. That is, with the deflector-condenser lens210, the light beams120emitted from the external cavities are incident on the combining grating110at appropriate incident angles. The light beams that have entered the combining grating110are then diffracted at the same diffraction angle and are combined by the combining grating110.

The laser sources102are preferably hermetically sealed as in the first embodiment. For example, an LD in a can-type package may be used for the laser sources102. Each laser source102, a corresponding one of collimating parts104, and a corresponding one of plane transmission gratings106may be provided at the same stage to form a module, as in the first embodiment. Additionally, in the present embodiment, the plurality of the laser sources102are arranged parallel to the x-axis direction shown inFIG. 3, so that all of the laser sources102may be disposed on the same stage. In this case, a lens array corresponding to the arrangement of the laser sources102may be used for the collimating part104. Also, an LD bar in which a plurality of LDs are arranged on the same semiconductor substrate may be used for the plurality of the laser sources102. In the present embodiment, as in the first embodiment, a cavity length of the external cavity is reduced, which enables the light source device20to have a high vibration resistance. Further, according to the present embodiment, the light source device20can be easily assembled.

Third Embodiment

FIG. 4is a schematic view of a light source device according to a third embodiment of the present invention. A light source device30in the present embodiment is a modification of the light source device20in the second embodiment. In the present embodiment, members, portions, components, and elements having the same functions as those in the second embodiment are denoted by the same reference numerals as the second embodiment, and duplicative description thereof may be omitted.

The light source device30is different from the light source device20mainly in that prisms310are used instead of a deflector-condenser lens210. As shown inFIG. 4, five external cavities are provided in the light source device30, and prisms310are disposed each corresponding to a corresponding one of external cavities other than the external cavity at the center. The incident angle of light beam120emitted from the external cavity and entering a combining grating110is defined by the prism310disposed in the optical path between the external cavity and the combining grating110. That is, with the prisms310, corresponding ones of the light beams120each emitted from a corresponding one of the external cavities are incident on the combining grating110at appropriate incident angles. An orientation of the optical path of the light beam120emitted from the central external cavity of the plurality of external cavities is not needed to be changed until reaching the combining grating110, and thus the prism310is not disposed on the optical path of the light beam120emitted from the central external cavity. The light beams incident on the combining grating110at respective incident angles are then diffracted at the same diffraction angle to be combined by the combining grating110.

In the present embodiment, each single prism310is provided with respect to a corresponding one of external cavities except the central external cavity, so that, if an alignment error or the like of the external cavity occurs, a position of the corresponding prism can be individually adjusted to correct an incident position on the combining grating110. For example, in the case in which a position of a single external cavity is slightly deviated from a predetermined position along the x axis, without correction, the light beam120emitted from the external cavity at the deviated position is incident on the combining grating at a different incident angle. This increases a beam parameter product (BPP) of the combined beam130, which is formed by diffraction and combination on the combining grating110, resulting in deterioration of quality of the combined beam130. When such a deviation in position occurs, by adjusting the position of the corresponding prism310along the z axis, the incident position of the light beam120refracted by the prism310incident on the combining grating110can be adjusted while maintaining the incident angle.

Thus, the deviation of the incident position of the light beam120can be corrected.

Fourth Embodiment

FIG. 5is a schematic view of a light source device according to a fourth embodiment of the present invention. A light source device40in the present embodiment is a modification of the light source device20in the second embodiment. In the present embodiment, members, portions, components, and elements having the same functions as those in the second embodiment are denoted by the same reference numerals as those in the second embodiment, and the duplicative description thereof may be omitted.

The light source device40is different from the light source device20mainly in that a condenser lens402, a diaphragm404, and a collimating lens406are further disposed in this order in an optical path between an external cavity and a combining grating110. The condenser lens402, the diaphragm404, and the collimating lens406form an afocal optical system. In the present embodiment, more specifically, the afocal optical system is disposed between a plane transmission grating106and a deflector-condenser lens210. In order to describe the effects of the afocal optical system, each light beam120is indicated by a beam having a width inFIG. 5. InFIG. 5, f1indicates a focal length of a collimating part104, f2indicates a focal length of the deflector-condenser lens210, and f3indicates focal lengths of the condenser lens402and the collimating lens406.

As shown inFIG. 5, the collimating part104is disposed spaced apart from a laser source102at a distance of f1, the plane transmission grating106is disposed spaced apart from the collimating part104at a distance of f1, the deflector-condenser lens210is disposed spaced apart from the plane transmission grating106at a distance of f2, and the combining grating110is disposed spaced apart from the deflector-condenser lens210at a distance of f2. The afocal optical system that includes the condenser lens402and other optical elements is disposed within the front focal length f2of the deflector-condenser lens210.

The light emitted from the laser source102has a divergence angle within a certain range. The collimating part104collimates the light emitted from the laser source102into a substantially parallel light. In order to perform such collimation, a distance along the z axis between the laser source102and the collimating part104needs to be precisely controlled. As described above, in the case in which the laser source102includes the LD configured to emit light having a peak wavelength in a range of 350 nm to 550 nm with a predetermined gain bandwidth, the laser source102is preferably hermetically sealed. In view of this, the collimating part104can be provided by, for example, with the use of a can-type package, joining a lens to be the collimating part104to the can-type package, in which precise control of the distance between the collimating part104and the laser source102is difficult. Thus, the deviation of position of the collimating part104may cause the light beam120after passing through the collimating part104to be in an undesirable condition.

The afocal optical system disposed between the collimating part104and the deflector-condenser lens210can correct the condition of the light beam120that has passed through the collimating part104. That is, even the undesirable condition of the light beam120that has passed through the collimating part104can be converted to the desirable condition by the afocal optical system. Accordingly, a combined beam130with a higher quality can be obtained. In other words, the afocal optical system can increase the tolerance of the deviation of position of the collimating part104.

In the afocal optical system, the light beam120is once condensed at the rear focal point by the condenser lens402. The diaphragm404is disposed at the rear focal point. The diaphragm404blocks a portion of light that is not well focused by the condenser lens402, which increases the quality of the light beam120that passes through the afocal optical system. Thus, the combined beam130with a higher quality and a low BPP can be obtained. Instead of the diaphragm404, a pinhole may be employed.

Fifth Embodiment

FIG. 6is a schematic view of a light source device according to a fifth embodiment of the present invention. A light source device50in the present embodiment is a modification of the light source device20in the second embodiment. In the present embodiment, members, portions, components, and elements having the same functions as those in the second embodiment are denoted by the same reference numerals as those in the second embodiment, and duplicative description thereof may be omitted.

The light source device50is different from the light source device20mainly in that a volume holographic grating506is used instead of the plane transmission grating106as a wavelength determining element. For the convenience of description, the “volume holographic grating” is also referred to as “VHG” in the present specification. The VHG506is disposed in an optical path between a laser source102and a combining grating110. More specifically, the VHG506is disposed in the optical path between a collimating part104and a deflector-condenser lens210. The VHG506is configured to diffract a portion of light emitted from the laser source102back to the laser source102to cause external resonance between the laser source102and the VHG506. That is, a combination of the laser source102, the collimating part104, and the VHG506forms a single external cavity. The cavity length of the external cavity is defined by the distance between the laser source102and the VHG506.

The VHG506is configured to diffract only light with the designed wavelength. Accordingly, the wavelength of light that resonates in an external cavity and the wavelength of light that passes through the VHG506and that is incident on the combining grating110are determined by the VHG506, to be the designed wavelength of the VHG506. Light beams120each emitted from a corresponding one of the external cavities pass through the deflector-condenser lens210and are incident on the combining grating110at different incident angles. As described above, in order to allow all of the lights incident on the combining grating110to be diffracted at the same diffraction angle, each light beam120emitted from a corresponding one of the external cavities needs to have a wavelength corresponding to a corresponding incident angle (refer to Table 1). Thus, the external cavity is provided with VHG506having the required designed wavelength. According to the present embodiment, as in the first to fourth embodiments, a cavity length of the external cavity can be reduced, which allows for increasing vibration resistance of the light source device50. Also, a high precision adjustment is not required during initial assembly, so that the light source device can be easily assembled.

Sixth Embodiment

FIG. 7is a schematic view of a light source device according to a sixth embodiment of the present invention. A light source device60in the present embodiment is a modification of the light source device50in the fifth embodiment. In the present embodiment, members, portions, components, and elements having the same functions as those in the fifth embodiment are denoted by the same reference numerals as those in the fifth embodiment, and duplicative description thereof may be omitted.

The light source device60is different from the light source device50mainly in that a VHG506is disposed between a laser source102and a collimating part104. According to the present embodiment, as in the first to sixth embodiments, a cavity length of the external cavity can be reduced, which allows for increasing vibration resistance of the light source device60. Further, the distance between the VHG506and the laser source102is shorter than that in the light source device50, which allows for increasing the tolerance of angular deviation of the laser source102on the x-z plane.

Seventh Embodiment

FIG. 8is a schematic view of a light source device according to a seventh embodiment of the present invention. A light source device70in the present embodiment is a modification of the light source device60in the sixth embodiment. In the present embodiment, members, portions, components, and elements having the same functions as those in the sixth embodiment are denoted by the same reference numerals as those in the sixth embodiment, and duplicative description thereof may be omitted. InFIG. 8, a light beam120is shown as a beam having a width for the convenience of description.

The light source device70is different from the light source device60mainly in that a fiber Bragg grating706is used instead of the volume holographic grating506as the wavelength determining element. For the convenience of description, the “fiber Bragg grating” is also referred to as a “FBG” in the present specification. The FBG706is disposed in an optical path between a laser source102and a collimating part104. A condenser lens702is disposed between the laser source102and the FBG706.

The light emitted from the laser source102is condensed by the condenser lens702and enters the FBG706. A portion of light emitted from the laser source102is diffracted by the FBG706back to the laser source102, and thus external resonance occurs between the laser source102and the FBG706. That is, a combination of the laser source102, the condenser lens702, and the FBG706forms a single external cavity. The cavity length of the external cavity is defined by the distance between the laser source102and the FBG706.

The FBG706diffracts only the light having the Bragg wavelength corresponding to a grating period of the FBG706, and thus the wavelength of light that resonates in the external cavity and the wavelength of light that passes through the FBG706and that enters a combining grating110are determined by the FBG706, to be the Bragg wavelength of the FBG706. The light beam120emitted from the external cavity passes through a deflector-condenser lens210and is incident on the combining grating110at a different incident angle. As described above, in order to allow all of the lights incident on the combining grating110to be diffracted at the same diffraction angle, each light beam120emitted from corresponding one of the external cavities needs to have a wavelength corresponding to a corresponding one of the incident angles (refer to Table 1). Thus, each external cavity is provided with the FBG706having the required Bragg wavelength. According to the present embodiment, as in the first to sixth embodiments, a cavity length of each external cavity can be reduced, which allows for increasing vibration resistance of the light source device70. Also, a high precision adjustment is not required during initial assembly, so that the light source device can be easily assembled.

While certain embodiments of the present invention have been described above, it should be understood that the technical scope of the present invention is not limited to the description of those embodiments. Some of the configurations in the described embodiments may be replaced by other configurations, or may be modified. An embodiment based on such changes and modifications may be encompassed in the technical scope of the present invention as clearly indicated in the descriptions of claims. For example, the embodiments described above are described in detail to facilitate understanding of the present invention.

However, the present invention is not necessarily limited to the configurations that include all of the structures and steps described in the embodiments described above.

A portion of a structure of a certain embodiment may be replaced with or added to a structure of another embodiment. For example, the afocal optical system in the light source device40shown inFIG. 5according to the fourth embodiment including the condenser lens402, the diaphragm404, and the collimating lens406may also be employed in the other embodiments. For example, the afocal optical system may be disposed between each of the external cavity modules100and the combining grating110in the light source device10shown inFIG. 1. In the light source device30shown inFIG. 4, the afocal optical system may be disposed between each of external cavities except for the external cavity at the center of the plurality of external cavities and the prism310, and the afocal optical system may also be disposed between the external cavity at the center and the combining grating110. The afocal optical system may be disposed between each of the external cavities and the deflector-condenser lens210in the light source device50shown inFIG. 6. Also, the afocal optical system may be disposed between each of the collimating parts104and the deflector-condenser lens210in the light source device60shown inFIG. 7. Furthermore, the afocal optical system may be disposed between each of the collimating parts104and the deflector-condenser lens210in the light source device70shown inFIG. 8.

Moreover, as in the external cavity modules100in the light source device10, the laser source102, the collimating part104, and the VHG506in each of the external cavities of the light source device50may be formed as a module. Then, in the case in which the light beams120each emitted from a corresponding one of the external cavities are incident on the combining grating110without using the deflector-condenser lens210, the incident angle of each of the light beams120on the combining grating110can be selected and adjusted by selecting the mounting angle of each of the modules that includes the corresponding external cavity. The laser source102, the VHG506, and the collimating part104in the external cavity of the light source device60may be formed as a module. Then, in the case in which the light beams120each emitted from a corresponding one of the external cavities are incident on the combining grating110without using the deflector-condenser lens210, the incident angle of each of the light beams120on the combining grating110can be selected and adjusted by selecting the mounting angle of each of the modules that includes the corresponding external cavity. The laser source102, the condenser lens702, the FBG706, and the corresponding collimating part104in each external cavity of the light source device70may be formed as a module. Then, in the case in which the light beams120each emitted from a corresponding one of the external cavities are incident on the combining grating110without using the deflector-condenser lens210, the incident angle of each of the light beams120on the combining grating110can be selected and adjusted by selecting the mounting angle of each of the modules that includes the corresponding external cavity.

In the light source devices50,60, and70, prisms310shown inFIG. 4may be used instead of the deflector-condenser lens210. With such a configuration, if an alignment error or the like of the external cavities occurs, adjustment of corresponding one or more of prism allows individual correction.