JP2001111153A - Optical coupling system - Google Patents

Abstract

(57) Abstract: In a semiconductor laser module that couples light emitted from a semiconductor laser to a single mode optical fiber, high output is achieved by efficiently converting light coupled as cladding mode light to a propagation mode. To achieve high reliability. A single mode optical fiber includes a core, a first cladding formed around the core and having a lower refractive index than the core, and a refractive index formed around the first cladding and smaller than the first cladding. A diffraction grating is provided on the optical path of the single mode optical fiber, the diffraction grating being configured by an outer peripheral layer having a refractive index and converting the laser light coupled as cladding mode light into propagation mode light propagating in the same direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention typically relates to a semiconductor laser module or an optical coupling system, and more particularly to an improvement in a semiconductor laser module or an optical coupling system capable of operating at a high optical output.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers have been used in large quantities as signal light sources and optical fiber amplifier excitation light sources in optical communications. In optical communications, semiconductor lasers are used as signal light sources and excitation light sources, and a group of components for optically coupling the laser light from the semiconductor laser to a single-mode optical fiber is packaged as a device. In many cases, these components are referred to as semiconductor laser modules, and the term of the optical coupling system is used as a general term including the case where the components do not have a unitary external shape.

FIG. 6 shows an example of the structure of such a semiconductor laser module. In the figure, a Peltier module 42 is fixed in a package 11, and a substrate 16 on which the semiconductor laser element 13, the thermistor 14, and the lens 15 are further fixed is fixed on the Peltier module 42. Further, a ferrule 20 into which the single mode optical fiber 17 is inserted and fixed is fixed to the through hole 11c on the side wall of the package 11.

In this semiconductor laser module, the laser light emitted from the semiconductor laser
After being collected by the optical fiber 5, the single mode optical fiber 17
Of the single mode optical fiber 1
Wave 7 is guided through and used for a desired application.

When an electric current is applied to drive the semiconductor laser device 13, the temperature of the semiconductor laser device 13 rises due to heat generation. This temperature rise causes a change in the oscillation wavelength and optical output of the semiconductor laser device. Therefore, the temperature of the semiconductor laser element is measured by the thermistor 14 fixed in the vicinity of the semiconductor laser element, and the temperature of the semiconductor laser element is kept constant by adjusting the current flowing through the Peltier module 12 using the measured value. This stabilizes its characteristics.

[0006]

By the way, in recent years, as the multiplexing of signal light wavelengths in optical communication progresses, an optical fiber amplifier can amplify a large number of signal lights at the same time. Operation is required. For this reason, a semiconductor laser module of 1480 nm or 980 nm band used as an excitation light source of an optical fiber amplifier must be capable of operating at a high optical output of 200 mW or more.
As for No. 3, those having an optical output radiated from the end face of 300 mW or more have come to be used.

[0007] The semiconductor laser module is a device in which the laser light emitted from the semiconductor laser element 13 is optically coupled to the single mode optical fiber 17 as described above. Here, the single mode optical output (hereinafter, referred to as “fiber end output” (Pf) in the present specification) emitted from the end of the single mode optical fiber 17 on the side opposite to the semiconductor laser element 13 side, and the semiconductor laser element 13. Is referred to as a coupling efficiency (hereinafter, referred to as “element output” (Po) in the present specification), and the value of the coupling efficiency is usually about 70%. .

[0008] Of the element output, about 70% of the light contributing to the fiber end output is the core 1 of the single mode optical fiber.
7a, but does not contribute to the fiber end power.
0% of the light is the end 17 of the single mode optical fiber 17 on the semiconductor laser element side, except for the one lost by reflection.
At the time of incidence on d, a cladding mode is induced in the cladding 17b of the single mode optical fiber 17, and while propagating in the optical fiber 17, a part thereof is gradually lost to the outside and is lost.

FIG. 7 shows experimental data obtained by cutting the optical fiber of the semiconductor laser module little by little and examining how the magnitude of the light output radiated from the fiber end changes. In the figure, the horizontal axis represents the length measured from the end 17d of the optical fiber on the semiconductor laser element side, and the vertical axis represents the light output (fiber end output) emitted from the end face of the optical fiber opposite to the semiconductor laser. . From FIG.
As the distance from 7d increases, the fiber end output decreases, because light coupled to the optical fiber as a cladding mode at the fiber end face 17d escapes outside the cladding as it propagates.

The semiconductor laser module used here has a semiconductor laser element that emits 298 mW of light at the end face, and has a distance of 150 c from the fiber end face 17d.
The optical fiber output at m is 201 mW. That is, in this case, about 97 mW of light is coupled as cladding mode light and is lost outside the optical fiber.

Further, according to FIG. 1, at a position separated from the ferrule end face by about 30 cm or more, the fiber end output does not depend on the length of the fiber. This means that of the light emitted from the semiconductor laser device, the fiber end face 1
The light coupled to the optical fiber in the cladding mode at 7d means that the light is emitted outside the cladding within a distance of about 30 cm from the fiber end face 17d. In particular, it can be seen that the rate of change is large in a region within 5 cm from the fiber end face 17d, and most of the cladding mode light is lost in this portion.

Next, FIG. 8A is a sectional structural view of a ferrule 20 into which an end portion 17d of the optical fiber 17 is inserted and fixed, and FIG. 8B is a view showing the structure of the optical fiber 17. (C) is a diagram showing a refractive index distribution of the optical fiber 17.

In FIG. 8A, a ferrule 20 has through holes 20a and 20b communicating with each other at both ends, and a capillary 22 made of zirconia (ZrO2) is fitted into the through hole 20a. The optical fiber 17 has a nylon tube 21 whose UV coating 17c at the tip is removed.
Is inserted into the ferrule 20 through the through hole 20b of the ferrule 20, and the portion from which the UV coating 17c at the tip is removed is inserted into the through hole 22a of the zirconia capillary 22, and the inside of the through holes 20b and 22a Thus, the ferrule 20 and the capillary 22 are fixed together with the nylon tube 21 with an adhesive 23.

Although the length of such a ferrule can be variously designed, a typical numerical value used for a semiconductor laser module is 9 mm to 20 mm.

In FIGS. 2B and 2C, the refractive index of the cladding layer 17b is set lower than that of the core 17a. Around the clad layer 17b, there is a coating layer 17c made of an ultraviolet curable resin (hereinafter, may be simply abbreviated as UV resin), but the refraction of the coating layer 17c in an optical fiber used in the field of optical communication. The rate is usually to allow the cladding mode light to escape as much as possible,
It is designed to be higher than the refractive index of the cladding layer 17b as shown in FIG.

When the laser light emitted from the semiconductor laser device 13 enters the optical fiber whose end is inserted and fixed in the ferrule 20 as described above, the light coupled in the cladding mode on the fiber end face 17d is converted into the fiber end 17d. Is radiated to the outside of the cladding layer 17b and is lost. Therefore, such laser light cannot be effectively used as pump light of the optical fiber amplifier.

The light radiated to the outside of the cladding layer 17b inside the ferrule 20 is caused by the adhesive 23, the nylon tube 21 and the ferrule 2 around the optical fiber.
Since it is absorbed by 0 and converted into heat, a local temperature rise occurs inside the ferrule. Such a phenomenon occurs more remarkably when the output power of the semiconductor laser device 13 used in the semiconductor laser module increases and the intensity of the radiated light of the cladding mode light inside the ferrule 20 increases.

As described above, when a local temperature rise occurs,
The optical fiber breaks due to the difference in the coefficient of thermal expansion between the quartz glass constituting the optical fiber 17 and the surrounding members. In addition, since the adhesive 23 and the nylon tube 21 are deteriorated due to the rise in temperature, there is a problem that the adhesive strength of the fiber and the nylon tube inside the ferrule is reduced. As described above, in the conventional semiconductor laser module, there is a problem that the reliability cannot be secured because the output of the cladding mode light also increases with the increase in the output of the semiconductor laser element.

SUMMARY OF THE INVENTION The present invention has been made to solve a problem which becomes conspicuous when the above-mentioned conventional semiconductor laser device is increased in output, and an object thereof is to use a semiconductor laser module or an optical coupling system. In addition to providing a more reliable semiconductor laser module or optical coupling system by preventing the emission of clad mode light from the optical fiber, the effective use of clad mode light by taking measures to convert the clad mode light to propagation mode light It is to plan.

[0020]

Means for Solving the Problems In order to achieve the above object, the present invention has the following structure to solve the problems. That is, the present invention provides a semiconductor laser device, a single-mode optical fiber for receiving light emitted from the semiconductor laser device, and an optical fiber interposed between the semiconductor laser device and the single-mode optical fiber and emitted from the semiconductor laser device. An optical coupling system having an optical coupling means for optically coupling the laser light to the single mode optical fiber, wherein the single mode optical fiber,
A core, a first cladding formed around the core and having a lower refractive index than the core, and a peripheral layer formed around the first cladding and having a lower refractive index than the first cladding; An optical coupling system comprising a diffraction grating that converts the laser light coupled as mode light into propagation mode light propagating in the same direction.
Here, the outer peripheral layer can be formed as a second clad layer having a smaller refractive index than the first clad layer, or can be formed as a coating layer having a smaller refractive index than the first clad layer. It is possible.

According to the optical coupling system having such a configuration, the leakage of the cladding mode light excited in the cladding layer to the outside of the cladding layer is reduced, and more of the cladding mode light is converted into the propagation mode light by the diffraction grating. be able to. For this reason, it is possible to reduce the displacement tolerance of the single mode optical fiber, and it is possible to easily assemble the optical coupling system with a high yield.

The present invention further has the following aspects (second to sixth inventions). That is, the second invention receives a semiconductor laser device and light emitted from the semiconductor laser device. Semiconductor having a single mode optical fiber and an optical coupling means interposed between the semiconductor laser element and the single mode optical fiber for optically coupling a laser beam emitted from the semiconductor laser element to the single mode optical fiber A laser module, wherein the single-mode optical fiber has a core, a first clad formed around the core and having a smaller refractive index than the core, and a first clad formed around the first clad. Having a coating layer having a small refractive index, and propagating the laser light coupled as cladding mode light in the same direction. A semiconductor laser module characterized by having a diffraction grating to convert the light.

In the second aspect of the present invention, the refractive index of the coating layer around the first cladding layer is smaller than that of the first cladding layer. The cladding mode light not coupled to the core as a propagation mode does not escape to the outside of the first cladding layer, is confined inside the first cladding layer and propagates, and is converted into propagation mode light by the diffraction grating during this time. Therefore, the clad mode light can be effectively used, and a local temperature rise inside the ferrule is suppressed, so that a more reliable semiconductor laser module can be obtained.

According to a third aspect of the present invention, there is provided a semiconductor laser device, a single mode optical fiber for receiving light emitted from the semiconductor laser device, and an optical fiber interposed between the semiconductor laser device and the single mode optical fiber. A semiconductor laser module having optical coupling means for optically coupling a laser beam emitted from the semiconductor laser element to the single mode optical fiber, wherein the single mode optical fiber is formed around a core and a core. A first clad layer having a refractive index smaller than the core, and a double clad fiber formed around the first clad layer and having a second clad layer having a smaller refractive index than the first clad layer And converts the laser light coupled as cladding mode light into propagation mode light propagating in the same direction. And a means for solving the problems with the configuration having the diffraction grating.

According to the third aspect of the present invention, since the refractive index of the second clad layer around the first clad layer is formed smaller than the refractive index of the first clad layer, As in the first invention, the cladding mode light not coupled to the core of the single mode optical fiber as a propagation mode is confined inside the first cladding layer and propagates without escaping to the outside of the first cladding layer, During this time, the semiconductor laser module is converted to a propagation mode by the diffraction grating, so that the clad mode can be effectively used and a local temperature rise inside the ferrule is prevented, so that a more reliable semiconductor laser module Is obtained.

According to a fourth aspect of the present invention, in addition to the configuration of the first or second aspect, the single-mode optical fibers on which the laser light from the semiconductor laser element is incident have different orders. Means for solving the problem is a configuration having a plurality of diffraction gratings for converting a plurality of cladding mode lights into propagation mode lights propagating in the same direction.

According to the fourth aspect of the present invention, since the single mode optical fiber has a plurality of diffraction gratings for converting a plurality of cladding mode lights having different orders into propagation mode lights propagating in the same direction, a plurality of diffraction gratings are provided. In each of the diffraction gratings, the cladding mode light of the order corresponding to the period is converted into the propagation mode light, so that a higher output propagation mode light can be obtained.

According to a fifth aspect of the present invention, in addition to the configuration of any one of the first to fourth aspects, the diffraction grating is configured so that the laser light from the semiconductor laser element is incident on the single mode optical fiber. The configuration formed at a position within 5 cm from the end is a means for solving the problem.

According to the fifth aspect of the present invention, since the cladding mode light is more efficiently converted into the propagation mode light, a higher output propagation mode light can be obtained.

According to a sixth aspect of the present invention, in addition to the configuration of any one of the first to fourth aspects, the end of the single mode optical fiber on the side where the laser light from the semiconductor laser element is incident is provided. This is a means for solving the problem by a configuration protected by a ferrule, wherein at least one of the diffraction gratings is located in the ferrule.

According to the sixth aspect of the present invention, since the diffraction grating is formed inside the ferrule into which the end of the single mode optical fiber into which the laser beam from the semiconductor laser element is incident is inserted and fixed. In addition, the cladding mode light is more efficiently converted into propagation mode light, and a high-power propagation mode light is obtained.

In the single mode optical fiber according to the present invention, a diffraction grating for converting a cladding mode light into a propagation mode light propagating in the same direction is formed from an end face of the fiber which receives the light emitted from the semiconductor laser device. In the portion, a core, a first cladding layer formed around the core and having a smaller refractive index than the core, and a refractive index smaller than the first cladding layer formed around the first cladding layer. It is important to have a configuration having a coating layer having a single-mode optical fiber other than this portion. The single-mode optical fiber comprises a core and a cladding layer having a lower refractive index than the core and a core formed around the core. Or a single-mode light having a cladding layer or coating layer having a refractive index higher than that of the cladding layer formed on the outer periphery thereof. Aiba) can be used to connect the like fusion splicing.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a semiconductor laser module using an optical coupling system according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross sectional view showing the structure of a semiconductor laser module according to the present invention. As shown in the figure, the semiconductor laser module of the present embodiment is
The semiconductor laser element 13 is fixed to the substrate 16, and the substrate 16 is fixed on the Peltier module 42 fixed on the bottom plate 11 a of the package 11 by soldering.
A ferrule 20 into which the single mode optical fiber 17 is inserted and fixed is fixed to the side wall 11c of the package 11,
The light from the semiconductor laser element 13 condensed by the lens 15 fixed on the substrate 16 is arranged to be coupled. Input end 17 of single mode optical fiber 17
A diffraction grating 51 is formed near d.

The semiconductor laser device 13 used in the semiconductor laser module of the present invention is a high-power semiconductor laser device that oscillates in single transverse mode. As such a semiconductor laser device, for example, a device having an active layer having a GaInAsP strained multiple quantum well structure formed on an InP substrate and having a 1480 nm band is used, and a resonator having a front end surface and a rear end surface thereof is used. 300mW by optimizing the length and reflectivity of the front and rear end faces
Continuous operation at a high light output exceeding the above.

FIG. 2 shows the structure and the refractive index profile of the single mode optical fiber 17 used in the first embodiment of the semiconductor laser module according to the present invention. That is, as shown in FIG. 2A, the single-mode optical fiber includes a core 17a, a cladding layer 17b1, and a UV resin coating layer 17c, and the refractive index of the UV resin coating layer 17c is as shown in FIG. Cladding layer 17
It is designed to be lower than the refractive index of b1. Such a difference in refractive index can be made desired by appropriately changing the UV resin material by a known method, or by adjusting the refractive index of the cladding layer 17b1.

As shown in FIG. 8A, the tip of the single mode optical fiber 17 is inserted through the through-hole 20b of the ferrule 20 in a state where the UV coating 17c of the tip is removed and inserted into the nylon tube 21. Is inserted into the through hole 22a of the capillary 22 made of zirconia, where the UV coating 17c at the tip is removed.
The adhesive 2 is attached to the ferrule 20 and the capillary 22 together with the nylon tube 21 inside the through holes 20b and 22a.
It is fixed at 3.

The length of the ferrule 20 is 12 mm
Is used.

As is well known, when a Ge-doped quartz glass is irradiated with ultraviolet light of a predetermined wavelength,
It is formed utilizing the fact that the refractive index increases according to the intensity of the irradiated ultraviolet light. That is, Ge is doped into the core 17a of the single mode optical fiber 17 and ultraviolet light is irradiated from the outside so that interference fringes are formed in the optical axis direction of the single mode optical fiber. Diffraction grating 51 having refractive index according to distribution
Are formed on the core 17a. As an element having such an effect, in addition to Ge, for example, Ce (cerium), T
a (tantalum), Be (beryllium) and the like are known.

The period of the diffraction grating is set to a value such that the clad mode light is converted into the propagation mode. That is, when converting the m-order cladding mode light into the propagation mode light by the diffraction grating 51 among the cladding mode lights, if the propagation constant of the propagation mode is β0 and the propagation constant of the m-order cladding mode light is βm. The period Δm of the diffraction grating may be designed to satisfy the following equation. β0−βm = 2πΛm (1)

In the semiconductor laser module having such a configuration, light emitted from the semiconductor laser element 13 is condensed by a lens and enters the single mode optical fiber 17. Of the incident light, the light coupled to the core 17a is:
The light propagates in the core 17a as a fundamental mode. On the other hand, light not coupled to the core 17a excites a cladding mode in the cladding layer 17b1. The cladding mode light excited here is composed of a plurality of propagation modes,
The refractive index of the first cladding layer 17b1 is the UV coating layer 17c
Is propagated while repeating reflection at the interface between the first cladding layer 17b1 and the UV coating layer 17c without leaking to the outside of the first cladding layer 17b1. When the clad mode light reaches the region where the diffraction grating 51 is formed, m of the clad mode light satisfying the expression (1) is satisfied.
The next cladding mode light is converted by the diffraction grating 51 into propagation mode light propagating in the same direction, and propagates through the single mode optical fiber 17.

Therefore, even in the case of a semiconductor laser module in which the intensity of light coupled as a cladding mode is extremely high, it is possible to effectively use the cladding mode light, and to produce a semiconductor laser module having a higher output than before. In addition, since a local temperature rise inside the ferrule is suppressed, a more reliable semiconductor laser module is provided.

FIG. 3 shows a structure and a refractive index profile of a single mode optical fiber 17 used in a second embodiment of the semiconductor laser module according to the present invention. That is, as shown in FIG. 9A, a single mode optical fiber 17 used in the second embodiment is used.
Is a double clad fiber having a core 17a, a first clad layer 17b1 and a second clad layer 17b2 formed around the first clad layer 17b1, and as shown in FIG. Second cladding layer 17b
The refractive index of 2 is designed to be lower than the refractive index of the first cladding layer 17b1. Such a refractive index difference can be set to a desired value by appropriately adjusting the type or amount of the dopant doped into the first cladding layer 17b1 and the second cladding layer 17b2.

The tip of the double clad fiber 17 is
As in the first embodiment, as shown in FIG. 8A, the UV coating 17c at the tip is removed and the nylon tube 21 is removed.
Is inserted into the ferrule 20 through the through hole 20b of the ferrule 20, and the portion from which the UV coating 17c at the tip is removed is inserted into the through hole 22a of the zirconia capillary 22, and the inside of the through holes 20b and 22a Thus, the ferrule 20 and the capillary 22 are fixed together with the nylon tube 21 with an adhesive 23.

In the semiconductor laser module of the second embodiment having such a configuration, the lens 1
Of the light that has entered the single mode optical fiber 17 via the optical fiber 5, the light coupled to the core 17a propagates inside the core 17a as a fundamental mode. On the other hand, light not coupled to the core 17a excites a cladding mode in the first cladding layer 17b1. The clad mode light to be excited here is composed of a plurality of propagation modes, and the first clad layer has a refractive index larger than that of the second clad layer 17b2. Cladding layer 1
7b1 without leaking to the first cladding layer 17
The light propagates while repeating reflection at the interface between b1 and the second cladding layer 17b2. When the cladding mode light reaches the region where the diffraction grating 51 is formed, the m-th order cladding mode light that satisfies the expression (1) among the cladding mode light is propagated in the same direction by the diffraction grating 51. The light is converted into mode light and propagates through the single mode optical fiber 17.

In the second embodiment, a double clad fiber is used as the single mode optical fiber 17, so that the cladding mode is also obtained at the portion of the single mode optical fiber 17 where the UV coating is located inside the ferrule 20. There is no radiation to the outside. Therefore, compared with the first embodiment, it is possible to more effectively prevent the cladding mode radiation, and this is converted into the propagation mode light by the diffraction grating 51, so that a higher output semiconductor laser module can be manufactured. As much as possible, a local temperature rise inside the ferrule is almost completely prevented, so that a more reliable semiconductor laser module is provided.

In the first and second embodiments, as the diffraction grating for converting cladding mode light into propagation mode light, a plurality of diffraction gratings for converting cladding mode light of a plurality of different orders into propagation mode light are used. The single mode optical fiber 17 can be formed.

That is, in the above-described first and second embodiments, near the end of the single mode optical fiber 17 on the side of the semiconductor laser element 13, m described in relation to the expression (1) is used.
In addition to the diffraction grating 51 for converting the next cladding mode light into the propagation mode light, a diffraction grating 52 for converting the n-th (n ≠ m) cladding mode light into the propagation mode light is formed (FIG. 4).
The period Δn of the diffraction grating 52 is such that the propagation constant of the propagation mode is β0 and the propagation constant of the n-th order cladding mode light is β.
Assuming that n, the design should satisfy the following equation. β0−βn = 2πΛn (2)

As described above, by forming a plurality of diffraction gratings for converting a plurality of orders of cladding mode light into propagation mode light, respectively, a plurality of diffraction gratings can be propagated as cladding mode light as compared with the case where a single diffraction grating is used. It is possible to convert more of the light to the propagation mode, and the effect of the present invention becomes more remarkable.

As described with reference to FIG. 7, most of the clad mode light is radiated to the outside in a portion within 5 cm from the end face 17d of the single mode optical fiber and is easily lost. It is preferable that the diffraction grating to be converted is formed in this portion.

Further, if the diffraction grating is formed at a portion of the single mode optical fiber 17 located in the ferrule 20, the effect of the present invention described above becomes more remarkable because the diffraction grating is closer to the fiber end face 17d. The layout of the diffraction grating is also convenient (FIG. 5). In this case, when a plurality of diffraction gratings are used, at least one diffraction grating may be located inside the ferrule 20.

Further, not only the core but also the clad 17
If a diffraction grating is also formed in b1, conversion from the cladding mode to the propagation mode occurs more efficiently.

As described above, the present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiments, and various modifications are possible based on the spirit of the present invention. Is not excluded from the scope of the present invention. In particular, in the above embodiment, the coupling optical system including one lens is shown as the optical coupling means for coupling the light emitted from the semiconductor laser element to the single mode optical fiber. Various known optical coupling means can be applied, such as a single lens or a single mode optical fiber whose tip is processed into a lens shape.

Although the above embodiment discloses an example in which the present invention is applied to obtain a particularly high optical fiber output, the present invention is not limited to such an application.
That is, even if the semiconductor laser element does not have a high end face light output described in this specification, the conversion from the cladding mode to the propagation mode can be performed according to the present invention. It is possible to use it.

In the embodiments of the present invention, the semiconductor laser module having the Peltier module has been described. However, it can be said that the present invention can be applied to a semiconductor laser module having no Peltier module, in particular, a coaxial semiconductor laser module. Not even.

Further, the optical coupling system used in the above-described semiconductor laser module according to the present invention can be effectively applied also as a means for relaxing the tolerance of the alignment of the single mode optical fiber. In other words, even if the single-mode optical fiber is fixed at a position slightly shifted from the position at which the maximum coupling efficiency is obtained due to imperfect alignment of the single-mode optical fiber, the inside of the cladding layer is determined based on the position shift. The excited cladding mode light propagates without leaking to the outside of the cladding layer, and is converted into propagation mode light by the diffraction grating. For this reason, the decrease in the coupling efficiency due to the misalignment of the single-mode optical fiber can be suppressed to be lower than that of the conventional semiconductor laser module, and the semiconductor laser module can be easily assembled with a high yield. .

[0057]

As described above, according to the optical coupling system of the present invention, of the light incident on the single mode optical fiber 17 from the semiconductor laser device, the light propagating as clad mode light is converted into the single mode optical fiber. Since the light propagates while being confined inside the cladding layer and is converted into propagation mode light propagating in the same direction by the diffraction grating, even in an optical coupling system in which the intensity of light coupled as the cladding mode is extremely large, Cladding mode light can be used effectively, making it possible to produce an optical coupling system with a higher output than before, and to suppress a local temperature rise inside the ferrule, so that a more reliable optical coupling system Is provided.

According to the second aspect of the present invention, since the coating layer having a smaller refractive index than the cladding layer is formed around the cladding layer of the single-mode optical fiber, the light propagating as the cladding mode light is transmitted to the single mode optical fiber. Since the light propagates while being confined inside the cladding layer of the fiber and is converted into propagation mode light propagating in the same direction by the diffraction grating, it is possible to effectively use the cladding mode light, and a higher output than before is obtained. Since a semiconductor laser module can be manufactured and a local temperature rise inside the ferrule is suppressed, a semiconductor laser module with higher reliability is provided.

According to the third aspect of the present invention, since the double clad fiber is used as the single mode optical fiber, the clad mode is not changed even in the portion where the UV coating located inside the ferrule of the single mode optical fiber is removed. It is possible to prevent cladding mode radiation more efficiently without being radiated to, and since this is converted to propagation mode light by the diffraction grating, a higher output semiconductor laser module can be manufactured,
Since a local temperature rise inside the ferrule is prevented, a more reliable semiconductor laser module is provided.

Further, in the fourth invention, since a plurality of diffraction gratings for converting the multi-order cladding mode light into the propagation mode light are formed, the cladding is more complicated than when a single diffraction grating is used. It is possible to convert more of the light propagating as mode light to the propagation mode, and to provide a semiconductor laser module with higher output.

Further, in the fifth invention, since the diffraction grating is formed in a portion within 5 cm from the end face of the single mode optical fiber, the cladding mode light can be more efficiently converted to the propagation mode light.

Further, in the sixth aspect, since the diffraction grating is located in the ferrule and protected, not only can the cladding mode light be more efficiently converted into the propagation mode light, but also the diffraction grating There is an effect that it is convenient in handling.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a structural example of a semiconductor laser module according to the present invention.

FIG. 2 is a diagram showing a cross-sectional structure diagram (a) and a refractive index profile (b) of a single mode optical fiber used for the semiconductor laser module according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a cross-sectional structure diagram (a) and a refractive index profile (b) of a single mode optical fiber used for a semiconductor laser module according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating another structural example of the semiconductor laser module according to the present invention.

FIG. 5 is a diagram illustrating an example of a cross-sectional structure of a ferrule according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating a structural example of a conventional semiconductor laser module.

FIG. 7 is experimental data showing the relationship between the distance from the end (17d) of the optical fiber on the semiconductor laser element side and the magnitude of light output radiated from the fiber end in a conventional semiconductor laser module.

FIG. 8 is a diagram showing an example of a cross-sectional structure of a ferrule in a conventional semiconductor laser module.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Package 42 Peltier module 13 Semiconductor laser element 14 Thermistor 15 Lens 16 Substrate 17 Optical fiber 20 Ferrule 50 Heat sink 51, 52 Diffraction grating

Claims (1)

[Claims] A semiconductor laser device; a single-mode optical fiber for receiving light emitted from the semiconductor laser device; and a light-emitting device provided between the semiconductor laser device and the single-mode optical fiber. An optical coupling system having an optical coupling means for optically coupling the laser light to the single mode optical fiber, wherein the single mode optical fiber is formed around the core and has a smaller refractive index than the core. Having a peripheral layer formed around the first cladding and having a smaller refractive index than the first cladding,
An optical coupling system comprising a diffraction grating that converts the laser light coupled as cladding mode light into propagation mode light propagating in the same direction.