JP2001051166A - Semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser module of higher reliability, capable of being operated with high optical output. SOLUTION: This semiconductor laser module has a semiconductor laser element 13, a single mode optical fiber 17 for receiving the light emitted from the semiconductor laser element 13, and an optical coupling means 15 mounted between the semiconductor laser element 13 and the single mode optical fiber 17 for optically coupling the laser beam with the single mode optical fiber 17, and the single mode optical fiber 17 has a core 17a, a first clad 17b formed around the core 17a and having the refraction factor smaller than that of the core, and a coating layer 17c formed around the first clad 17b and having the refraction factor smaller than that of the first clad 17b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser module, and more particularly to a semiconductor laser module capable of operating at a high light output.

[0002]

2. Description of the Related Art In recent years, semiconductor lasers have been used in large quantities in the field of optical communications as light sources for signals or excitation light sources for optical fiber amplifiers. When a semiconductor laser is used as a signal light source or an excitation light source for optical communication, it is often used as a semiconductor laser module that is a device that optically couples laser light from the semiconductor laser to an optical fiber.

FIG. 5 shows an example of the structure of such a conventional semiconductor laser module 40. As shown in FIG. In the figure, reference numeral 11 denotes a package in which a Peltier module 12 is fixed. On the Peltier module 42, the fixed substrate 16 to which the semiconductor laser element 13, the thermistor 14, and the lens 15 are fixed is fixed. A ferrule 20 is fixed to the through hole 11c of the side wall 11b of the package 11, and a single mode optical fiber 47 is inserted and fixed to the optical fiber insertion hole in the ferrule 20.

In the semiconductor laser module 40, the laser light emitted from the semiconductor laser
After being condensed by the single mode optical fiber 47, the light is incident on the end face of the single mode optical fiber 77.
It is guided inside and used for a desired application.

When a current is applied to drive the semiconductor laser element 13 of the semiconductor laser module 40, the semiconductor laser element 1 generates heat due to the heat generated by the semiconductor laser element 13 itself.
3, the temperature rise causes a change in the oscillation wavelength and light output of the semiconductor laser device 13.

For this reason, the semiconductor laser device 13 is fixed by a thermistor 14 fixed near the semiconductor laser device 13.
The temperature of the semiconductor laser element 13 is kept constant by adjusting the current flowing through the Peltier module 12 using the measured value, thereby stabilizing the characteristics.

[0007]

By the way, in recent years, as the multiplexing of signal light wavelengths in optical communication has progressed, a large number of signal lights can be simultaneously amplified in an optical fiber amplifier. Output operation has been required.

For this reason, a 1480 nm or 980 nm band semiconductor laser module used as an excitation light source for an optical fiber amplifier must be capable of operating at a high light output of 200 mW or more. Light emitting devices having a light output of 300 mW or more have been used.

The semiconductor laser module is a device for optically coupling the laser light emitted from the semiconductor laser element 13 to the single mode optical fiber 47 as described above. Here, a single mode optical output radiated from an end of the single mode optical fiber 47 opposite to the semiconductor laser element 13 side (hereinafter, this optical output is referred to as “fiber end output” (Pf) in the present specification); The ratio of the light output radiated from the front end face 13a of the semiconductor laser device 13 (hereinafter, this light output is referred to as “device output” (Po) in this specification) is called the coupling efficiency. Is usually about 70%.

[0010] Of the above element output (Po), about 70% of the light that contributes to the fiber end output (Pf) propagates in the core of the single mode optical fiber 47, but contributes to the fiber end output (Pf). Approximately 30% of the light that is not reflected by the single mode optical fiber 4 on the side of the semiconductor laser
7, the cladding mode is induced in the cladding of the single mode optical fiber 47 when entering the end 47d of
While propagating in the optical fiber 47, a part thereof is lost by being gradually radiated to the outside.

FIG. 6 shows data obtained by cutting the single mode optical fiber 47 of the semiconductor laser module 40 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 47d 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 element 13. It is.

FIG. 1 shows that the fiber end output decreases as the distance from the fiber end face 47d increases. This is considered to be because light coupled to the optical fiber in the cladding mode at the fiber end face 47d escapes outside the cladding as it propagates.

The semiconductor laser module 40 used here has the semiconductor laser element 13 which emits 298 mW of end face optical power, and the optical fiber output at a distance of 150 cm from the fiber end face 47d is 201 mW.

As a result, 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 apart from the end face of the ferrule 20 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 element 13, the fiber end face 4
The light coupled to the optical fiber 47 in the cladding mode at 7d means that the light is emitted out of the cladding within 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 47d, and most of the cladding mode light is lost in this portion.

FIG. 7 is an explanatory view showing the cross-sectional structure of the ferrule 20 into which the end 47d of the single mode optical fiber 47 is inserted and fixed. FIG. 8A is an explanatory view showing the structure of the optical fiber 47. FIG. 7B is an explanatory diagram showing a refractive index distribution of the optical fiber 47.

In FIG. 7, the ferrule 20 has through holes 20a and 20b communicating with each other at both ends. A capillary 22 made of zirconia (ZrO ₂ ) is fitted in the through hole 20a. The single mode optical fiber 47 is inserted into the ferrule 20 through the through hole 20b of the ferrule 20 in a state where the UV coating 47c at the distal end has been removed and inserted into the nylon tube 21.
The portion from which the V coating 47c has been removed is inserted into the through hole 22a of the zirconia capillary 22. In this state, the tip of the single mode optical fiber 47 is fixed to the ferrule 20 and the capillary 22 with the adhesive 23 together with the nylon tube 21 inside the through-hole 22a and the through-hole 20b.

Although the length of the ferrule 20 may be variously designed, a typical numerical value used for the semiconductor laser module 40 is 9 mm to 20 mm.

In FIGS. 8A and 8B, the refractive index of the cladding layer 47b is set lower than that of the core 47a. A coating layer 47c made of an ultraviolet curable resin (hereinafter, simply referred to as a UV resin) is provided around the cladding layer 47b, and the refractive index of the coating layer 47c in an optical fiber used in the field of optical communication is usually In order to allow the cladding mode light to escape to the outside as much as possible,
Is designed to be higher than the refractive index of the cladding layer 47b.

When the laser light emitted from the semiconductor laser element 13 enters the single mode optical fiber 47 whose end is inserted and fixed in the ferrule 20 as described above, the light coupled as the cladding mode on the fiber end face 47d is converted into a fiber. In the vicinity of the end 47d, the cladding layer 4
It is radiated outside 7b and is lost. Therefore, such laser light cannot be effectively used as pump light of the optical fiber amplifier.

On the other hand, the light radiated to the outside of the cladding layer 47b inside the ferrule 20 is
Is absorbed by the adhesive 23, the nylon tube 21 and the ferrule 20 and converted into heat. As a result, a local temperature rise occurs inside the ferrule 20.

Such a phenomenon occurs more remarkably when the semiconductor laser device 13 used in the semiconductor laser module 40 has a higher output and the intensity of the cladding mode light emitted inside the ferrule 20 increases.

When such a local temperature rise occurs,
The optical fiber 47 may be broken due to a difference in the coefficient of thermal expansion between the quartz glass constituting the optical fiber 47 and the surrounding members. In addition, the adhesive 2
3 and the nylon tube 21 deteriorate, the optical fiber 47 and the nylon tube 2 inside the ferrule 20 are removed.
In this case, a problem occurs that the adhesive strength of No. 1 decreases.

As described above, the conventional semiconductor laser module has a problem that the reliability cannot be secured because the output of the cladding mode light is also increased 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 of the present invention is to provide an optical fiber used in a semiconductor laser module. It is an object of the present invention to provide a more reliable semiconductor laser module capable of operating at a high optical output by preventing cladding mode radiation.

[0027]

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 first invention provides a semiconductor laser device, a single-mode optical fiber for receiving light emitted from the semiconductor laser device, and the semiconductor laser device 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 a laser element to the single mode optical fiber, wherein the single mode optical fiber is formed around a core and the core. Means for solving the problem include a first clad having a smaller refractive index and a coating layer formed around the first clad and having a smaller refractive index than the first clad.

According to the first aspect of the present invention, since the refractive index of the coating layer around the first cladding layer is smaller than the refractive index of the first cladding layer, the single mode optical fiber Since the cladding mode light not coupled to the core portion as the propagation mode does not escape to the outside of the first cladding layer and is confined inside the first cladding layer and propagates, the local temperature inside the ferrule Since the rise is suppressed, a more reliable semiconductor laser module can be obtained.

According to a second 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 interposition between the semiconductor laser device and the single-mode optical fiber. A semiconductor laser module having optical coupling means for optically coupling laser light emitted from the semiconductor laser element to the single mode optical fiber, wherein the single mode optical fiber is formed around a core and the core. A double clad fiber comprising a first clad having a smaller refractive index than the core and a second clad formed around the first clad and having a smaller refractive index than the first clad. It is a means to solve the problem with.

According to the second aspect of the present invention, the refractive index of the second cladding layer around the first cladding layer is smaller than the refractive index of the first cladding layer. Since the clad mode light not coupled to the core of the single mode optical fiber as a propagation mode does not escape to the outside of the first cladding layer and is confined inside the first cladding layer and propagates, local light inside the ferrule is generated. Therefore, a semiconductor laser module having higher reliability can be obtained.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the description of the present embodiment, the same reference numerals are given to the same parts as those in the conventional example, and the overlapping description will be omitted.

(First Embodiment) FIG. 1 shows a first embodiment of a semiconductor laser module according to the present invention. The semiconductor laser module 10 shown in FIG.
The semiconductor laser device 13 is fixed to a substrate 16, and the substrate 16 is fixed on the Peltier module 12 fixed on the bottom plate 11 a of the package 11 by soldering.

On the side wall 11b of the package 11, a ferrule 20 into which a single mode optical fiber 17 is inserted and fixed is provided.
Are fixed, and arranged so that light from the semiconductor laser element 13 condensed by the lens 15 fixed on the substrate 16 is coupled.

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 a transverse single mode. As such a semiconductor laser device 13, for example, a device having an active layer having a GaInAsP strained multiple quantum well structure formed on an InP substrate and having a band of 1480 nm is used. The semiconductor laser device 13 is capable of continuous operation with a high light output exceeding 300 mW by optimizing the length of the resonator including the front end face and the rear end face and the reflectivity of the front end face and the rear end face.

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 10 according to the present invention. The single mode optical fiber 17 has a core 17a and a cladding layer 17b1 as shown in FIG.
And the UV resin coating layer 17c, and the refractive index of the UV resin coating layer 17c is set lower than the refractive index of the cladding layer 17b1 as shown in FIG.

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. 3, the single mode optical fiber 17 is inserted into the ferrule 20 through the through hole 20b of the ferrule 20 in a state where the UV coating 17c at the distal end is removed and inserted into the nylon tube 21. U
The portion from which the V coating 17c has been removed is inserted into the through hole 22a of the zirconia capillary 22. In this state, the tip of the single mode optical fiber 17 is fixed to the ferrule 20 and the capillary 22 with the adhesive 23 together with the nylon tube 21 inside the through hole 22a and the through hole 20b.

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

The semiconductor laser module 10 having the above configuration
Then, the light emitted from the semiconductor laser element 13 is condensed by the 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 clad mode light to be excited here is composed of a plurality of propagation modes. Since the refractive index of the first clad layer 17b1 is made larger than the refractive index of the UV coating layer 17c, the first The first clad layer 17b1 and the UV coating layer 1 are not leaked to the outside of the clad layer 17b1.
The light propagates while being repeatedly reflected at the interface with 7c.

For this reason, even in the case of a semiconductor laser module in which the intensity of light coupled as a cladding mode is extremely high, a local temperature rise inside the ferrule is suppressed, so that a semiconductor laser module with higher reliability can be realized. Provided.

FIG. 4 shows a structure and a refractive index profile of a single mode optical fiber 27 used in a second embodiment of the semiconductor laser module according to the present invention.

That is, as shown in FIG. 7A, the single mode optical fiber 27 used in the second embodiment is composed of a core 27a, a first cladding layer 27b1 and a first cladding layer 27b1. This is a double-clad fiber having a second clad layer 27b2 formed around the periphery. As shown in FIG. 3B, the second clad layer 27
The refractive index of b2 is set lower than the refractive index of the first cladding layer 27b1.

Such a difference in the refractive index can be set to a desired value by appropriately adjusting the kind or amount of the dopant to be doped into the first cladding layer 27b1 and the second cladding layer 27b2.

The tip of the double clad fiber 27 is
As in the first embodiment, as shown in FIG.
The V coating 27c is removed and inserted into the ferrule 20 through the through-hole 20b of the ferrule 20 while being inserted into the nylon tube 21.
a and fixed to the ferrule 20 and the capillary 22 together with the nylon tube 21 with the adhesive 23 inside the through holes 20a and 22b.

In the semiconductor laser module according to the second embodiment having such a configuration, the lens 1
Of the light that has entered the single mode optical fiber 27 via the optical fiber 5, the light coupled to the core 27a propagates inside the core 27a as a fundamental mode.

On the other hand, light not coupled to the core 27a excites a cladding mode in the first cladding layer 27b1. The cladding mode light to be excited here is composed of a plurality of propagation modes, and the first cladding layer has a refractive index larger than that of the second cladding layer 27b2. The light propagates while repeating reflection at the interface between the first clad layer 27b1 and the second clad layer 27b2 without leaking to the outside of the clad layer 27b1.

In the second embodiment, since the double clad fiber is used as the single mode optical fiber 27, the cladding is also removed at the portion of the single mode optical fiber 27 where the UV coating 27c located inside the ferrule 20 is removed. The mode is not radiated to the outside.

Therefore, compared with the first embodiment, it is possible to more effectively prevent the radiation of the cladding mode, and the local temperature rise inside the ferrule is almost completely prevented. A semiconductor laser module having a high degree is provided.

As described above, the present invention has been described in detail based on the embodiments. However, the present invention is not limited to only 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. In addition, various known optical coupling means, such as one composed of two lenses and one in which the tip of a single mode optical fiber is processed into a lens shape, can be applied.

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, a semiconductor laser module having higher reliability can be provided by suppressing the temperature rise of the ferrule even for a semiconductor laser element having a normal end face optical output.

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.

[0054]

As described above, according to the first aspect of the present invention, of the light incident on the single mode optical fiber 17 from the semiconductor laser device, the light propagating as the cladding mode light is transmitted by the single mode optical fiber. The semiconductor laser module propagates while being confined inside the cladding layer and suppresses a local rise in temperature inside the ferrule, so that a semiconductor laser module capable of operating with a highly reliable optical output can be obtained.

Further, according to the second aspect of the present invention, since the double clad fiber is used as the single mode optical fiber, the cladding mode is also formed in the portion of the single mode optical fiber where the UV coating is located inside the ferrule. It is possible to prevent clad mode radiation more efficiently without being radiated to the outside, and to prevent a local temperature rise inside the ferrule, so that operation with more reliable light output is possible. Is a semiconductor laser module that can be used.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a first embodiment of a semiconductor laser module according to the present invention.

FIG. 2A is an explanatory view showing a cross section of a single mode optical fiber used for a semiconductor laser module according to a first embodiment of the present invention, and FIG. 2B is an explanatory view showing a refractive index profile thereof.

FIG. 3 is an explanatory view showing an example of a cross section of a ferrule of the semiconductor laser module according to the present invention.

FIG. 4A is an explanatory diagram showing a cross section of a single mode optical fiber used for a semiconductor laser module according to a second embodiment of the present invention, and FIG. 4B is an explanatory diagram showing a refractive index profile thereof.

FIG. 5 is an explanatory view showing a structural example of a conventional semiconductor laser module.

FIG. 6 is an explanatory view showing the relationship between the distance from the end of the optical fiber on the semiconductor laser element side and the magnitude of light output radiated from the end of the optical fiber in a conventional semiconductor laser module.

FIG. 7 is an explanatory view showing an example of a cross section of a ferrule of a conventional semiconductor laser module.

FIG. 8A is an explanatory view showing a cross section of a single mode optical fiber used in a conventional semiconductor laser module,
(B) is an explanatory view showing the refractive index profile.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Semiconductor laser module 11 Package 12 Peltier module 13 Semiconductor laser element 14 Thermistor 15 Lens 16 Fixed substrate 17 Single mode optical fiber 17a Core 17b Cladding layer 17c UV coating 20 Ferrule 27 Single mode optical fiber 27a Core 27b1 First cladding layer 27b2 First Second clad layer 27c UV coating

Claims (2)

[Claims] 1. A semiconductor laser element, a single mode optical fiber for receiving light emitted from the semiconductor laser element, and an optical fiber interposed between the semiconductor laser element and the single mode optical fiber and emitted from the semiconductor laser element. A semiconductor laser module having optical coupling means for optically coupling the laser light to the single mode optical fiber, 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 having a coating layer formed around the first clad and having a smaller refractive index than the first clad. Semiconductor laser module. 2. 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. A semiconductor laser module 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 a core and has a smaller refractive index than the core. And a second clad fiber formed around the first clad and having a lower refractive index than the first clad. .