JP2012042819A - Laser diode module and laser source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the decrease of power density of emission light from a rectangle fiber in a laser diode module hermetically sealed, by using a rectangle fiber excellent in optical coupling with laser diode.SOLUTION: The laser diode module includes an end face light emission type laser diode 4, an optical fiber 1 having an end portion 6 connected optically with the laser diode 4 and a package 9 for housing and hermetically sealing the laser diode 4 and the end portion 6 of the optical fiber. In the module, the optical fiber 1 has a rectangle core 2 having a cross-sectional shape with long sides and short sides and a clad 3 formed around the core 2. The short side dimension A is equal to or less than 1/2 of the long side dimension B and the number of modes which can be propagated to the direction of the short sides of the core 2 is two or more. The short side dimension A is equal to or less than 30 μm and the maximum dimension C of the clad 3 in the direction along the short sides of the core 2 is at least three times as long as the short side dimension A of the core 2.

Description

  The present invention relates to a laser diode module and a laser light source.

  Conventionally, as a semiconductor laser, an edge-emitting laser diode in which light is emitted from a side end surface of a semiconductor multilayer film laminated on a substrate, or a surface-emitting laser diode in which light is emitted perpendicular to the surface of the substrate Etc. are known. An edge-emitting laser diode generally has a rectangular end face as an emission face (emitter).

A semiconductor laser is widely used as a light source for optical fiber communication or as an excitation light source for exciting an amplification medium (optical pumping) in a laser light source such as a solid-state laser. As an amplifying medium for a solid-state laser, for example, a medium such as a YAG crystal or a silica-based optical fiber is doped with a rare earth element (Nd, Yb, Er, etc.). This type of solid-state laser is used in various devices for processing, medical use, sensing (measurement), military use, and the like. Particularly in the case of processing equipment, a laser light source having high power and power density (power per unit cross-sectional area) is required in order to improve efficiency in applications such as cutting, drilling, welding, and welding.
When using a semiconductor laser as an optical fiber communication light source as well as an excitation light source for a laser light source, an optical fiber is used as an optical transmission path for allowing light emitted from the semiconductor laser to enter the amplification medium. . In order to realize long-distance transmission of optical fiber communication and a laser light source with high power and high power density, it is necessary to make the laser light incident on the optical fiber from the semiconductor laser with high power density.

In Patent Document 1, the end of an optical fiber is tapered so that the output light of a semiconductor laser having a square active layer end face can be efficiently coupled to the optical fiber without using a conventional lens system such as a cylindrical lens. In addition, a connection structure is described in which the tapered tip is formed so that the radius of curvature in the active layer thickness direction is smaller than the radius of curvature in the active layer width direction and is opposed to the end face of the active layer.
In Patent Document 2, in order to suppress deterioration of characteristics of a semiconductor laser due to oxidation, the semiconductor laser is housed in a package that blocks outside air, and an optical fiber that guides laser light from the semiconductor laser to the outside is provided on the wall of the package. A laser module is described which is structured to be soldered to a hole and to keep the penetration portion airtight.
In Patent Document 3, when organic impurities (flux, epoxy, etc.) are deposited on the light emitting portion of a high power laser, the power of the emitted light is absorbed in the deposit and heat is generated, causing a laser failure. The use of chemical components that absorb organic impurities is described in an enclosed hermetic container.

Further, a rectangular fiber having a rectangular core cross-sectional shape is known as an optical fiber for allowing the laser light from the edge-emitting laser diode to enter.
In Patent Document 4, a microlens made of one optical fiber is disposed between a laser diode bar in which a plurality of light emitting units are arranged in the width direction and a plurality of rectangular fibers coupled to each light emitting unit. The structure is described.
In Patent Document 5, as in Patent Document 4, a light source in which a plurality of light emitting units are aligned and input ends of a plurality of rectangular fibers are coupled, and an output end of each rectangular fiber is stacked in a cross-sectional direction. The structure is described.
Patent Document 6 includes a laser bar having a plurality of light emitting points arranged in an array and an optical fiber arranged in an array so as to face the light emitting points, and an incident portion of the optical fiber is a cylindrical portion. A structure formed in a lens shape is described.

Further, the following invention is known as a configuration for gathering inputs from a plurality of laser diodes into one output.
Patent Document 7 discloses an optical coupling including a laser diode subsystem having two or more laser diodes or an array, and a plurality of optical waveguides whose core cross-sectional shape matches the cross-sectional shape of the beam emitted from the laser diode and functions as an input port. And a means for transmitting the output of the optical coupling subsystem. The optical coupling subsystem collects laser light input to a plurality of optical waveguides into one output, and the cross-sectional shape of the output is an input guide. A laser system is described which consists of a superposition of waveguides and which can maintain the initial input power density even at the output.
Patent Document 8 discloses a solid-state laser including a light source having a plurality of light-emitting portions, one optical fiber waveguide, and optical means for coupling light from an emission end of the optical fiber waveguide to an active medium of the solid-state laser. In the optical excitation system, the incident end of the optical fiber has an elongated cross-sectional core, vertical and horizontal numerical apertures corresponding to the light emitting portions, and vertical and horizontal directions that can guide light emitted from the plurality of light emitting portions of the light source to the maximum. A structure having a lateral extent is described.
Patent Document 9 discloses a clad amplification fiber having a predetermined length, a plurality of excitation light sources, a plurality of multimode fibers for coupling each light source to the clad of the clad amplification fiber, and one core coupled to the core of the clad amplification fiber. To avoid excessive losses in a device consisting of a single mode fiber, where multiple multimode fibers and a single mode fiber are focused and the cross-sectional area is tapered toward the cladding amplification fiber, The ratio of the numerical aperture NAoutput of the clad amplification fiber that is the output and the numerical aperture NAinput of the multimode fiber that is the input is the ratio of the sum ΣAi of the cross-sectional areas of the plurality of multimode fibers to the minimum cross-sectional area A ′ of the tapered portion. On the other hand, NAoutput should be increased so that (NAoutput / NAinput) ² ≧ ΣAi / A ′. And are described.

JP-A 63-163806 Japanese Patent No. 2970635 Japanese Patent No. 3522214 US Pat. No. 5,127,068 US Pat. No. 5,268,978 JP 2008-203598 A US Pat. No. 5,668,903 U.S. Pat. No. 4,818,062 US Pat. No. 5,864,644

The rectangular fibers of Patent Documents 4 to 6 are effective as a technique for condensing light from a plurality of LDs without reducing the power density of light from a laser diode (LD). However, in order to prevent the deterioration of the LD, the hermetic sealing as described in Patent Documents 2 to 3 is not described. For example, in paragraphs 0027 to 0028 of Patent Document 6, a storage groove having a size slightly larger than the size of the optical fiber is formed on the upper surface of the holding member using a material such as glass by machining, and the storage is performed. It is described that an optical fiber is inserted into the groove and fixed.
However, according to the study of the present inventor, it has been found that when a conventional rectangular fiber is used for a laser diode module and hermetically sealed, the power density of light emitted from the rectangular fiber is reduced.
In addition, in the conventional rectangular fiber, the long side direction of the cross-sectional shape of the core is usually matched with the long side direction of the light emitting part in accordance with the shape of the light emitting part of the LD. At this time, if the short side dimension of the cross-sectional shape of the core is too large compared to the short side dimension of the light emitting portion, the light power density may be lowered.

  The present invention has been made in view of the above circumstances, and uses a rectangular fiber excellent in optical coupling with a laser diode, and is capable of suppressing a reduction in power density of light emitted from the rectangular fiber. It is an object to provide a stopped laser diode module.

  In order to solve the above-mentioned problems, the present invention provides an end-emitting laser diode, an optical fiber having a tip optically connected to the laser diode, and the laser diode and the tip of the optical fiber inside. A laser diode module that is housed in a hermetically sealed package, the optical fiber having a rectangular cross-sectional shape having a long side and a short side, and a clad formed around the core The core has a short side dimension that is 1/2 or less of the long side dimension, and the number of modes that can propagate in the short side direction of the core is two or more, The laser diode has a short side dimension of 30 μm or less, and a maximum dimension of the clad in a direction along the short side of the core is three times or more the dimension of the short side of the core. To provide a joule.

It is preferable that the tip portion of the optical fiber has the lens shape.
It is preferable that a cylindrical lens is disposed between the tip portion of the optical fiber and the light emitting portion of the laser diode.
Also, the present invention receives a plurality of the laser diode modules and outputs of the plurality of laser diodes of the plurality of laser diode modules through the optical fiber of each laser diode module, and provides one light guide. A laser light source is provided that includes an optical coupling system that is incident on an optical fiber.

According to the present invention, in a laser diode module using a core having a rectangular cross section, the power density of light can be maintained without the dimension in the short side direction of the core being too large.
Further, in a laser diode module hermetically sealed using an optical fiber having a rectangular core excellent in optical coupling with a laser diode, the optical fiber can be used even if there is a dimensional change in the sealing material used for hermetic sealing. It is possible to suppress a decrease in the power density of light emitted from the optical fiber due to the influence of the side pressure on the core.

1 is a perspective view showing a first embodiment of a laser diode module of the present invention. (A) is sectional drawing in alignment with the longitudinal direction of an optical fiber which shows an example of the optical coupling structure of a laser diode and the front-end | tip part of an optical fiber, (b) is an example of a cross section perpendicular | vertical to the longitudinal direction of an optical fiber. FIG. It is a graph which shows typically an example of the relation between the outgoing angle of a laser diode, and a far field pattern (FFP). (A) is sectional drawing which shows an example of the cross section of an optical fiber whose cross-sectional shape is circular, (b) is sectional drawing which shows an example of the cross section of an optical fiber whose cross-sectional shape is elliptical, c) is a cross-sectional view showing an example of a cross section of an optical fiber having a rectangular cross-sectional shape. It is a perspective view which shows 2nd Embodiment of the laser diode module of this invention. It is a perspective view showing an example of a laser light source using a plurality of laser diode modules of the present invention. It is a perspective view which shows an example of the optical coupling system which consists of a some lens. It is sectional drawing of the optical coupling system shown in FIG. It is a perspective view which shows an example of the optical coupling system which consists of an optical waveguide board | substrate which has a some core. FIG. 10 is a cross-sectional view of the optical coupling system shown in FIG. 9. It is a perspective view which shows an example of the optical coupling system which consists of a some optical fiber. It is sectional drawing of the optical coupling system shown in FIG. It is a graph which shows an example of the relationship between the short side dimension (A) of a core, coupling efficiency, and optical power density. It is a graph which shows an example of the change of the emitted light numerical aperture (NA) by the ratio (C / A) of the maximum dimension (C) of the clad in the direction along the short side of a core, and the short side dimension (A) of a core. .

The present invention will be described below based on preferred embodiments with reference to the drawings.
FIG. 1 shows a first embodiment of a laser diode module of the present invention. The laser diode module 10 includes a laser diode 4, an optical fiber 1 having a tip 6 optically connected to the laser diode 4, and a package 9 that accommodates the laser diode 4 and the tip 6 of the optical fiber 1 therein. Is provided.

  As the laser diode 4, an edge-emitting laser diode is used. As shown in FIG. 2A, the active layer is exposed to the end face of the laser diode 4 by cleavage, for example, and a light emitting portion 4a that emits laser light is formed. Although the dimension of the light emitting part 4a is not particularly limited, for example, the height direction of the light emitting part 4a (the thickness direction of the active layer, the vertical direction in FIG. 2A) is about 1 μm and the width direction (see FIG. In 2 (a), the direction perpendicular to the paper surface is 50 to 100 μm. The light emitting unit 4a has a plurality of modes capable of propagating in the width direction, and is multimode in the width direction.

  As shown in FIG. 2, the optical fiber 1 has a core 2 extending along the central axis and a clad 3 formed around the core 2. The refractive index of the core 2 is higher than the refractive index of the cladding 3. The material of the core 2 and the clad 3 is not particularly limited, and can be appropriately selected from light-transmitting materials such as quartz glass, multicomponent glass, and plastic that are conventionally used for optical fibers.

The distal end portion 6 of the optical fiber 1 is positioned so that the end surface of the core 2 faces the light emitting portion 4 a of the laser diode 4. Since the configuration for holding the tip portion 6 of the optical fiber 1 is not particularly limited, the illustration is omitted in FIG. 2A. For example, as shown in FIG. The tip portion 6 of the optical fiber 1 can be supported by using solder 8 or the like for fixing the optical fiber 1 to the fiber mount 15.
Further, the laser diode 4 can be held on the mount 5, for example. In order to prevent the laser diode 4 from being overheated, the mount 5 is preferably provided with a heat sink or a cooling element (not shown). The laser diode 4 emits light by a drive current supplied from the outside of the package 9 via the lead wire 14, and the conductor 14 and the wire 12 on the mount 5 electrically connect the lead wire 14 and the laser diode 4. It is connected to the.

  The package 9 is a container for hermetically sealing the laser diode 4 and the distal end portion 6 of the optical fiber 1 and can be constituted by a combination of a case and a cap, for example. In the drawing, the inside of the package 9 is shown, so that the upper surface and the front surface of the hand are opened, but the entire surface needs to be covered for hermetic sealing. Further, the optical fiber 1 is inserted into a hole opened in the side wall of the package 9. Further, as shown in FIG. 2A, a sealing material 11 such as an adhesive or solder is filled between the outer peripheral surface of the optical fiber 1 and the hole of the package 9, and the optical fiber 1 is attached to the package 9. It is fixed.

  In the case of this embodiment, it is preferable that the front-end | tip part 6 of the optical fiber 1 becomes a taper shape toward the light emission part 4a, and the end surface of the core 2 is processed into a cylindrical lens shape. Alternatively, the cylindrical lens 7 can be disposed between the light emitting portion of the laser diode 4 and the tip portion of the optical fiber 1 as in the second embodiment shown in FIG. When the cylindrical lens 7 is provided, the distal end portion of the optical fiber 1 does not need to be processed into a lens shape, and may have a shape having an end surface perpendicular to the longitudinal direction of the optical fiber 1.

  In the case of the laser diode module 10 of the present embodiment, the shape of the core 2 of the optical fiber 1 is rectangular in the cross section perpendicular to the longitudinal direction of the optical fiber 1 as shown in the cross-sectional view of FIG. The cross-sectional shape of the core 2 is such that the dimension B corresponding to the width direction of the light emitting part 4a is the dimension A corresponding to the height direction of the light emitting part 4a in a state where the end face of the core 2 faces the light emitting part 4a of the laser diode 4. A longer shape is preferable for efficient optical coupling with the light emitting portion 4a having a width larger than the height. In the case of this embodiment, the cross-sectional shape of the core 2 is a rectangle having a short side and a long side. The short side of the dimension A corresponds to the height direction of the light emitting part 4a of the light emitting part 4a, and the long side of the dimension B corresponds to the width direction of the light emitting part 4a. In the present specification, “the short side and the long side of the rectangle that is the cross-sectional shape of the core 2” may be simply referred to as “the short side and the long side of the core 2”.

The laser light emitted from the light emitting unit 4a is emitted while spreading with a certain spread angle in the width direction and the height direction. The numerical aperture NA of the emitted light is the refractive index of the medium to which the light is emitted (in FIG. 2, the medium is a gas such as air, and in this case, the refractive index n of the medium can be approximated by approximately 1.0). If the divergence angle is 2θ (the outgoing angle corresponding to one side of the central axis is θ), NA = n × sin θ. The numerical aperture of the edge emitting laser diode 4 is generally about 0.1 to 0.4, and the numerical aperture tends to be larger in the height direction than in the width direction of the light emitting portion 4a.
The numerical aperture NA of the optical fiber, _{n 1} the refractive index of the core 2, and the refractive index of the cladding 3 and _{n 2,} the maximum theoretical _NA, is represented by ^{_{(n 1 2 -n 2 2)}} 1/2 The In general, light in an optical fiber propagates within the NA of the optical fiber.
The emission NA from the laser diode is about 0.1 in the horizontal direction and about 0.4 in the vertical direction. For this reason, by processing the distal end portion 6 of the optical fiber 1 into a cylindrical lens shape in the horizontal direction, or by arranging a cylindrical lens 7 at the distal end portion 6, the vertical NA is reduced to about 0.1. The light can be incident on the optical fiber 1 with high coupling efficiency.

  As described above, the height of the light emitting unit 4a is usually extremely small, and the height of the light emitting unit 4a is increased in consideration of the size of the beam spreading while reaching the end surface of the core 2 from the end surface of the light emitting unit 4a. The short side dimension A of the core 2 necessary for making the spreading laser beam incident on the optical fiber 1 with sufficiently high coupling efficiency is small. In order to suppress a decrease in the power density of light propagating through the optical fiber 1, the cross-sectional area of the core 2 is preferably small, and the short side dimension A of the core 2 is ½ or less of the long side dimension B of the core 2. It is preferable that Furthermore, it is preferable that the short side dimension A of the core 2 is 30 μm or less. It is sufficient for the long side dimension B of the core 2 to be slightly wider than the width of the light emitting portion 4a, for example, about 60 to 200 μm.

  FIG. 3 schematically shows an example of the relationship between the emission angle of the laser diode 4 and the far field pattern (FFP) of the optical fiber 1. As shown in FIG. 3, the distribution of the emission angles that can be coupled in the higher-order mode is wider than that in the fundamental mode. That is, the light coupled from the laser diode 4 to the higher-order mode of the optical fiber 1 with a larger emission angle has a large emission angle (that is, the NA of the emitted light is large) when emitted from the optical fiber 1, and the light. The power density of the outgoing light from the fiber 1 tends to decrease.

The optical fiber 1 tends to increase the number of modes that can be propagated as the short side dimension A and the long side dimension B of the core 2 are large. For example, if the short side dimension A is about 30 μm, there are about 10 modes that can propagate in the short side direction of the core 2.
Most of the laser light emitted from the laser diode 4 with a small NA enters the optical fiber 1 with a small NA and is coupled to the fundamental mode, but a part of the laser light that cannot be coupled to the fundamental mode due to misalignment is: The light enters the optical fiber 1 with a larger NA and is coupled to a higher order mode.

  Conversely, when there is only one mode that can propagate in the short side direction of the core 2 (that is, in the case of a single mode), it is impossible to couple to the higher order mode, The proportion of light that can be coupled also decreases, and the coupling efficiency decreases. That is, if most of the light coupled to the optical fiber 1 is coupled to the fundamental mode, propagation with a high power density can be realized. For this reason, the lower limit of the short side dimension A of the core 2 is preferably defined so that the number of modes that can propagate in the direction of the short side of the core 2 is 2 or more.

However, even if the light is coupled to the fundamental mode of the optical fiber 1 with a small NA, if there is a perturbation to the optical fiber 1 such as bending with a small side pressure or a radius of curvature r with respect to the optical fiber 1, some May be mode-converted from the basic mode to the higher-order mode. When mode conversion to a higher order mode occurs, the NA of propagating light increases, so the NA when emitted from the optical fiber 1 also increases, and the power density of the emitted light decreases. That is, as clarified by the above-mentioned investigation by the present inventor, the reason why the power density of the emitted light is reduced when the conventional rectangular fiber is used in the hermetic sealing module is the core sandwiched between the fiber fixing portions. This is thought to be due to the fact that very large stress was generated.
Therefore, in order to suppress the mode conversion to the higher-order mode, it is necessary to have a structure in which stress generated when the optical fiber 1 is fixed to the side wall of the package 9 is not easily applied to the core 2.

  The stress at the time of fixing the optical fiber is mainly caused by a dimensional change when the sealing material 11 used for fixing the optical fiber 1 to the package 9 is solidified. For example, when the sealing material 11 is solder, it is supplied between the optical fiber 1 and the package 9 in a state of being melted and heated, and stress is generated in the optical fiber 1 by contracting with cooling. Even when the sealing material 11 is an adhesive, a stress is generated in the optical fiber 1 by causing a dimensional change (shrinkage or expansion) with curing.

  In general, stress is proportional to strain. In the case of the normal optical fiber 1, it can be assumed that the proportionality constant (elastic modulus, Young's modulus, etc.) is not significantly different between the core 2 and the clad 3. The clad 3 contracts (or expands) almost evenly. In this case, the ratio between the dimensional change of the core 2 and the dimensional change of the clad 3 is substantially equal to the ratio of the dimensions of the core 2 and the clad 3. That is, as the dimension of the clad 3 is larger than the dimension of the core 2, the strain applied to the core 2 due to the dimensional change of the sealing material 11 decreases and the strain applied to the clad 3 increases.

Further, as described above, in the case of the optical fiber 1 in which the short side dimension A of the core 2 is small, the influence of the stress on the propagation mode becomes more important in the short side direction of the core 2. For this reason, in the optical fiber 1, as shown in FIG. 4, the maximum dimension C of the cladding 3 in the direction along the short side of the core 2 is preferably three times or more the short side dimension A of the core 2. If the ratio (C / A) between the dimension C of the clad 3 and the short side dimension A of the core 2 is 3 times or more, the strain applied to the core 2 is 1/3 or less of the dimensional change of the sealing material 11. The mode conversion from the basic mode to the higher order mode can be effectively suppressed.
The outer peripheral shape of the clad 3 may be circular as shown in FIG. 4 (a), may be elliptical as shown in FIG. 4 (b), or may be rectangular as shown in FIG. 4 (c).
Note that all of the rectangular fibers described in Patent Documents 4 to 6 described above do not satisfy the requirements of the present invention because the clad is thin. For this reason, it is presumed that the influence of stress on the core is large at the time of fixing.

  As a method for suppressing the stress on the core 2 against the side pressure from the surroundings, a buffer layer having a flexible buffering action, such as a resin coating or a foam, is provided around the cladding 3, and the optical fiber 1 It is also conceivable for the buffer layer to absorb dimensional changes that occur around it. However, since the resin coating or foam transmits gas, a buffer layer cannot be provided between the sealing material 11 and the optical fiber 1 when the laser diode 4 is hermetically sealed. That is, since the portion where the cladding 3 of the optical fiber 1 is exposed needs to be fixed to the package 9 for hermetic sealing, the dimensions of the cladding 3 are required to suppress the stress applied to the core 2 without a buffer layer. A method of increasing the ratio (C / A) between C and the short side dimension A of the core 2 is effective.

  As described above, the laser diode module 10 of the present embodiment can prevent foreign matter from entering by hermetic sealing, suppress failure of the laser diode, and has high coupling efficiency from the laser diode 4 to the optical fiber 1. A decrease in power density can be suppressed. For this reason, it can be suitably used as a laser light source, particularly as an excitation light source for a solid-state laser.

  In order to construct a high-power and high-power-density laser light source, as shown in FIG. 6, light emitted from a plurality of laser diodes 4 can be coupled to a single light guide optical fiber 21 and output. It is preferable to make it. The light guide optical fiber 21 includes a core 22 and a clad 23 formed around the core 22. The cross-sectional shape of the core 22 is not particularly limited, and may be a circular shape, a rectangular shape, or any other desired shape.

  The laser light source shown in FIG. 6 receives a plurality of laser diode modules 10 and outputs of the plurality of laser diodes 4 included in the plurality of laser diode modules 10 through the optical fiber 1 of each laser diode module 10. And an optical coupling system 20 to be incident on the light guiding optical fiber 21. The optical coupling system 20 can also be hermetically sealed in the package 19. The method of fixing the optical fiber 1 to the package 19 can be the same as the method of fixing the optical fiber 1 to the package 9 of the laser diode module 10.

  6, the existence of the optical coupling system 20 is schematically shown. Specifically, for example, as shown in FIGS. 7 to 8, the optical coupling system 30 in which a plurality of lenses 31, 32, 33 are combined, FIG. 9 to 10, an optical coupling system 40 using an optical waveguide substrate 43 having a plurality of cores 41 in a clad 42, and an optical coupling system in which a plurality of optical fibers 51 are focused as shown in FIGS. 50 or the like.

  In the optical coupling system 30 shown in FIGS. 7 to 8, the lenses 31, 32, and 33 are cylindrical lenses having a cylindrical lens surface. The plurality of optical fibers 1 are arranged in a line along the short side direction of the core 2. That is, when the longitudinal direction of the optical fiber 1 is the X direction and the direction in which the plurality of optical fibers 1 are parallel is the Y direction, the short side direction of the core 2 is directed to the Y direction, and the long side direction of the core 2 is The direction is perpendicular to both the X direction and the Y direction, that is, the Z direction. In FIG. 8A, the left and right are in the X direction, and the top and bottom are in the Z direction. In FIG. 8B, the left and right are the X direction and the top and the bottom are the Y direction.

The lens 31 is a columnar lens provided for each of the emission ends of the plurality of optical fibers 1 arranged in parallel, and spreads in the Y direction as shown in FIG. It has a function of collimating the light output from.
The lens 32 has a function of condensing the light collimated by each lens 31 in the Y direction toward the core 22 of the light guide optical fiber 21.
The lens 33 has a function of collecting light in the Z direction.
As shown in FIG. 8B, the dimensions of the lens 32 and the lens 33 along the Y direction are large so that the entire output from the plurality of optical fibers 1 can be received by each one of the lenses 32 and 33. It has spread.
As shown in FIG. 7, the region 24 in which the shape of the core 2 of each optical fiber 1 is projected onto the incident-side end face of the light guiding optical fiber 21 via the optical coupling system 30 is within the range of the circular core 22. It is preferably included. In this case, in FIG. 8A, the range S of the region 24 along the Z direction is smaller than the diameter φ of the core 22.

The optical coupling system 40 shown in FIGS. 9 to 10 includes an optical waveguide substrate 43 in which a plurality of cores 41 are formed in a clad 42. Each core 41 optically couples between the exit end of the optical fiber 1 and the end face on the incident side of the light guide optical fiber 21.
As a method for producing the optical waveguide substrate 43, for example, in order from the substrate side, a portion of the clad 42 below the core 41, a portion of the core 41 and the clad 42 having the same height as the core 41, and a core 41 of the clad 42 The method of laminating the upper part is mentioned. The shape of the core 41 along the plane of the substrate can be patterned by, for example, photolithography.

An optical coupling system 50 shown in FIGS. 11 to 12 includes a plurality of optical fibers 51 in which a core 52 and a clad 53 have a rectangular cross section. Each optical fiber 51 optically couples between the output end of the optical fiber 1 and the end face on the incident side of the light guide optical fiber 21.
Since the optical fiber 51 has excellent flexibility in the short side direction of the core 52, it is possible to easily wire a plurality of optical fibers 51 so as to be laminated at a position facing the incident side end face of the light guiding optical fiber 21.

  Hereinafter, the present invention will be specifically described with reference to examples.

(Test results on the short side dimension A of the core)
As an example of the optical fiber 1 having the cross-sectional shape shown in FIG. 2B, the material of the core 2 and the cladding 3 is made of silica glass, and an appropriate refractive index difference is provided between the core 2 and the cladding 3. A rectangular core circular clad fiber in which the short side dimension A is 6 μm, 12 μm, 18 μm, 24 μm, 30 μm or 50 μm, the long side dimension B of the core 2 is 75 μm, and the clad 3 is a circular shape with a diameter of 125 μm. Samples A to F were manufactured, in which each fiber tip was processed into a wedge-shaped lens, and an LD chip with an emitter width of 70 μm was arranged at the tip so as to allow optical coupling. For each sample, the light emitted from the LD chip at an output of 8 W was coupled to a rectangular core circular clad fiber, and the fiber incident power (W) was measured. Further, the coupling efficiency (%) was calculated from the ratio between the fiber incident power and the LD chip output, and the optical power density (mW / μm ² ) was calculated from the ratio between the fiber incident power and the core area. The results are shown in Table 1. FIG. 13 shows the relationship between the coupling density and the optical power density with respect to the short side dimension A of the core 2. The shorter the short side dimension A of the core 2 was, the higher the optical power density was. However, the coupling efficiency (%) was remarkably low when the short side dimension A was 6 μm.

For each sample, the number of modes that can propagate in the short side direction of the core 2 was measured by mode analysis. As a result, when the short side dimension A is 12 to 50 μm, the number of modes that can propagate in the short side direction is 2 In contrast to the above (multimode), when the short side dimension A is 6 μm, the number of modes that can propagate in the short side direction is 1 (single mode).
According to this test result, if the number of modes capable of propagating in the short side direction of the core 2 is 2 or more and the short side dimension A is 30 μm or less, the coupling efficiency and the optical power density are high, which is preferable. I understand.

(Test results for C / A dimensional ratio of clad / core)
As shown in FIG. 4, optical fiber samples 1 to 5 whose clad shape is circular (see FIG. 4 (a)), elliptical (see FIG. 4 (b)) or rectangular (see FIG. 4 (c)). Produced.
In the sample 1, the clad shape is rectangular, the short side dimension A of the core 2 is 25 μm, the long side dimension B of the core 2 is 105 μm, the maximum dimension C of the clad 3 in the direction along the short side of the core 2 is 45 μm, The maximum dimension D of the clad 3 in the direction along the long side of the core 2 is 125 μm, and the value of the ratio C / A is 1.8.
In the sample 2, the clad shape is rectangular, the short side dimension A of the core 2 is 25 μm, the long side dimension B of the core 2 is 105 μm, and the maximum dimension C of the clad 3 in the direction along the short side of the core 2 is 62. The maximum dimension D of the cladding 3 in the direction along the long side of the core 2 is 125 μm, and the value of the ratio C / A is 2.5.

In the sample 3, the clad shape is elliptical, the short side dimension A of the core 2 is 25 μm, the long side dimension B of the core 2 is 105 μm, and the maximum dimension C of the clad 3 in the direction along the short side of the core 2 is 50 μm. The maximum dimension D of the clad 3 in the direction along the long side of the core 2 is 125 μm, and the value of the ratio C / A is 2.
In the sample 4, the clad shape is elliptical, the short side dimension A of the core 2 is 25 μm, the long side dimension B of the core 2 is 105 μm, and the maximum dimension C of the clad 3 in the direction along the short side of the core 2 is 75 μm. The maximum dimension D of the clad 3 in the direction along the long side of the core 2 is 125 μm, and the value of the ratio C / A is 3.
Sample 5 has a circular clad shape, the core 2 has a short side dimension A of 25 μm, the core 2 has a long side dimension B of 105 μm, a cladding outer diameter (dimension C and dimension D) of 125 μm, and a ratio C / A. Is 5.
Table 2 summarizes the structural parameters of Samples 1-5. In each optical fiber, the refractive index and the like of the core 2 and the clad 3 were adjusted so that the numerical aperture (NA) in the short side direction of the core 2 was about 0.23.

  For samples 1 to 5, laser diode modules were produced. As the laser diode, an LD chip having a light emitting portion (emitter) width of 70 μm and a numerical aperture (NA) in the height direction of the emitter of about 0.4 was used, and light was emitted at an output of 8 W. In the optical fiber, the tip portion facing the LD chip was processed into a lens shape as shown in FIG.

There were three types of the sealing material 11: no sealing material (no fixing), adhesive, and solder.
When the optical fiber was fixed to the package with an adhesive or solder, the laser diode could be hermetically sealed, but when the optical fiber was not fixed to the package, there was a gap and the laser diode was hermetically sealed. I couldn't.

For each of the laser diode modules described above, the numerical aperture NA (emitted light NA) in the core short side direction of light emitted through the core 2 of the optical fiber 1 was measured. FIG. 14 shows a graph summarizing the results as the relationship between the dimensional ratio C / A and the emitted light NA. In FIG. 14, the NA (fiber NA) of each optical fiber is indicated by a dotted line.
As shown in FIG. 14, in the case of no fixation, the emitted light NA showed a constant value of about 0.1 regardless of the value of the dimensional ratio C / A. This is presumably because most of the light can be coupled to the fundamental mode of the optical fiber with a small NA when it enters the optical fiber from the laser diode, and propagates through the optical fiber with a small NA. However, since hermetic sealing is not achieved, there is a risk of failure due to foreign matter entering the package.
When the optical fiber is fixed with an adhesive or solder, the package can be hermetically sealed, but when the dimensional ratio C / A is smaller than 3, the emitted light NA increases. This is because a side pressure is applied to the optical fiber 1 due to the dimensional change of the sealing material 11 and stress is applied to the core 2, so that mode conversion from the fundamental mode to the higher order mode occurs in the optical fiber, and the NA of the propagating light is light. This is considered to be due to expansion within the range of the NA of the fiber (maximum of about 0.23).

  According to this test result, when the dimensional ratio C / A is 3 or more, the intrusion of foreign matter can be prevented by hermetic sealing, and the optical fiber can be used even if there is a dimensional change in the sealing material used for hermetic sealing. Thus, it is possible to realize a laser diode module capable of suppressing the influence of the side pressure on the core and propagating the optical fiber 1 while maintaining a small NA.

(Laser light source fabrication example 1)
As shown in FIGS. 7-8, the laser light source provided with the optical coupling system 30 which consists of the cylindrical lenses 31-33 was produced.
As the optical fiber 1, a core 2 having a short side dimension A of 25 μm, a core 2 having a long side dimension B of 75 μm, and a numerical aperture of 0.15 was used. As the laser diode, an LD chip having a light emitting portion (emitter) width of 70 μm was used, and light was emitted at an output of 8 W.
As the light guide optical fiber 21, a core 22 having a diameter φ of 125 μm, a numerical aperture of 0.15, and a non-reflective coated end face on the incident side was used.
As the lenses 31 to 33, lenses whose surfaces were non-reflective coated were used.
As a result, a laser light source with high power and high power density could be produced.

(Laser light source fabrication example 2)
9-10, the laser light source provided with the optical coupling system 40 which consists of the optical-waveguide board | substrate 43 which has the some core 41 in the clad 42 was produced.
As the optical fiber 1, a core 2 having a short side dimension A of 25 μm, a core 2 having a long side dimension B of 75 μm, and a numerical aperture of 0.15 was used. As the laser diode, an LD chip having a light emitting portion (emitter) width of 70 μm was used, and light was emitted at an output of 8 W.
In the optical waveguide substrate 43, the cross-sectional shape of the core 41 is a rectangle having a short side of 25 μm × long side of 75 μm, the numerical aperture NA is 0.15, and the pitch of the three cores 41 is equal to the cladding diameter of the optical fiber 1. It was set to 125 μm which is about the same. In addition, the core 41 and the clad 42 of the optical waveguide substrate 43 were used with non-reflective coating on the input and output side end faces.
As the light guide optical fiber 21, a core 22 having a diameter φ of 125 μm, a numerical aperture of 0.15, and a non-reflective coated end face on the incident side was used.
The end face on the output side of the optical fiber 1 and the end face on the input side of the core 41 were optically coupled by butt coupling. Similarly, the end face on the emission side of the core 41 and the end face on the input side of the light guiding optical fiber 21 were also optically coupled by butt coupling.
As a result, a laser light source with high power and high power density could be produced.

(Laser light source production example 3)
As shown in FIGS. 11-12, the laser light source provided with the optical coupling system 50 from the some rectangular fiber 51 was produced.
As the optical fiber 1, a core 2 having a short side dimension A of 25 μm, a core 2 having a long side dimension B of 75 μm, and a numerical aperture of 0.15 was used. As the laser diode, an LD chip having a light emitting portion (emitter) width of 70 μm was used, and light was emitted at an output of 8 W.
As the optical fiber 51, a clad 53 having a rectangular shape with a short side of 50 μm × long side dimension of 110 μm, a numerical aperture NA of 0.15, and a non-reflective coating on the input side and output side end faces was used.
As the light guide optical fiber 21, a core 22 having a diameter φ of 200 μm and a numerical aperture of 0.15 was used.
The end face on the output side of the optical fiber 1 and the end face on the input side of the rectangular fiber 51 were optically coupled by butt coupling. Similarly, the end face on the output side of the rectangular fiber 51 and the end face on the input side of the light guiding optical fiber 21 were also optically coupled by butt coupling.
As a result, a laser light source with high power and high power density could be produced.

A: core short side dimension, B: core long side dimension, C: maximum cladding dimension in the direction along the core short side, D: maximum cladding dimension in the direction along the core long side, 1 ... Optical fiber, 2 ... core, 3 ... cladding, 4 ... laser diode, 6 ... tip of optical fiber, 7 ... cylindrical lens, 9 ... package, 10 ... laser diode module, 11 ... sealing material, 20, 30, 40 , 50... Optical coupling system, 21.

Claims (4)

An edge-emitting laser diode; an optical fiber having a tip optically connected to the laser diode; and a package that hermetically seals the laser diode and the tip of the optical fiber. A laser diode module comprising:
The optical fiber has a core whose cross-sectional shape is a rectangle having a long side and a short side, and a clad formed around the core, and the core has a dimension of the short side of the long side. Less than half of the dimension, the number of modes propagating in the direction of the short side of the core is two or more, the dimension of the short side is 30 μm or less, and along the short side of the core The laser diode module according to claim 1, wherein a maximum dimension of the clad in a direction is at least three times a dimension of the short side of the core.   The laser diode module according to claim 1, wherein the tip of the optical fiber has the lens shape.   2. The laser diode module according to claim 1, wherein a cylindrical lens is disposed between the tip portion of the optical fiber and a light emitting portion of the laser diode.   A plurality of the laser diode modules according to any one of claims 1 to 3, and outputs of the plurality of laser diodes of the plurality of laser diode modules are received via the optical fibers of the respective laser diode modules, A laser light source comprising: an optical coupling system that is incident on a single light guiding optical fiber.

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