JPH1152196A - Laser diode module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to efficiency propagate the laser beam emitted from a light emitting element to the output end of an optical fiber by forming a surface having a normal of an angle meeting the ratio of a spot size with respect to the optical axis direction of a core on a core end face which receives and propagates the laser beam of a different spot size. SOLUTION: The end face of the optical fiber 20 is diagonally treated such that the aspect ratio at this end face attains the aspect ratio smaller than the aspect ratio of a laser diode 10. The end face side of the optical fiber 20 is diagonally cut with the axial line of the laser beam in such a manner, by which an asymmetrical shape is given to the laser beam in a horizontal direction and a perpendicular direction. The aspect ratio is thus approximated to the aspect ratio of the laser diode 10 by applying the asymmetricalness of the beam shape. The propagation loss generated in a working step is made smaller than in the case the aspect ratio is so changed that the shape of the core at the light receiving end of the laser diode 10 is made analogous with the shape at the output end of the laser diode 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology of a laser diode module that can efficiently supply laser beams emitted from a light emitting element and having mutually different spot sizes in two orthogonal directions to an optical fiber.

[0002]

2. Description of the Related Art The horizontal spot size of laser light in a light emitting element is ω _LX , the vertical spot size is ω _LY ,
When the horizontal spot size of the laser beam in the optical fiber is ω _FX and the vertical spot size is ω _FY , the coupling optical system between the light emitting element and the optical fiber is coupled at an optimal magnification. In this case, when the laser light from the light emitting element is supplied to the optical fiber, a coupling loss expressed by equation (1) occurs between the two.

[0003]

(Equation 1)

Here, A _L is the ratio of the horizontal spot size to the vertical spot size of the light emitting element (ω _LX /
ω _LY ) and A _F are parameters indicating the ratio (ω _FX / ω _FY ) between the horizontal spot size and the vertical spot size of the optical fiber, respectively. Give an explanation.

When the aspect ratio is 1, the beam shape is circular because the horizontal spot size is equal to the vertical spot size, and when the aspect ratio is other than 1, the beam shape is elliptical. , A parameter indicating the ellipticity of the beam.

[0006] At present, laser diodes that emit laser light in the 1.3 and 1.55 micron wavelength bands used in ordinary optical fiber communication, and erbium-doped fibers (erbium) used in optical fiber amplifiers are used.
Wavelength for Exciting Doped Fiber
The aspect ratio of a laser diode that emits laser light in the 48-micron band is approximately 1.1 to 1.2, which is an almost circular beam. Therefore, when these laser diodes are combined with an optical fiber having an aspect ratio of 1, According to Equation (1), the coupling loss is 0.1 dB or less at the maximum according to the equation (1), and a good coupling having no practical problem can be obtained.

However, in the case of a laser diode that emits a laser beam having a pumping wavelength of 0.98 micron, which is advantageous for reducing the noise and increasing the efficiency of the amplifier using the erbium-doped fiber, the laser beam has an aspect ratio. Since the laser diode and the erbium-doped fiber amplifier are coupled by using a circular beam optical fiber having an aspect ratio of 1 because the beam is a flat elliptical beam having a diameter of 2 to 3, according to the equation (1), 0. A coupling loss of 5 to 1.2 decibels occurs, and laser light in the 0.98 micron band emitted by the laser diode cannot be efficiently supplied to the erbium-doped fiber.

In order to solve such a problem, there has been proposed a coupling optical system of a light emitting module shown in FIG. 5 described in JP-A-6-180404. In FIG. 5, 1
01 is a quartz single mode fiber, 102 is a core,
Reference numeral 103 denotes a cladding, 108 denotes a light emitting element having a large aspect ratio, 109 denotes a spherical lens, and 121 denotes a local portion at one end of the core 102 of the optical fiber 101, which has a large aspect ratio. 181 denotes a core end face adjusted to the aspect ratio of the light emitting element 108.
This is the light emitting surface.

The coupling optical system of the light emitting module shown in FIG. 5 supplies outgoing light having a large aspect ratio emitted from the light emitting element 108 to a core end face 121 of an optical fiber having a large aspect ratio via a spherical lens 109. Things.

That is, the size and shape of the light emitted from the light emitting element 108 are enlarged using the spherical lens 109 so as to match the size and shape of the core end face 121 of the optical fiber. The shape is gently adjusted inside the core 102 to the shape of the circular cross section of the core 102.

Here, FIG. 6 shows the results obtained by using Equation (1) to determine the coupling loss with respect to the aspect ratio _AF of the optical fiber, for example, assuming that the aspect ratio of the light emitting element is A _L = 3.
As shown in FIG. 6, the coupling loss is large when the difference between the aspect ratio A _L of the light emitting element and the aspect ratio A _F of the optical fiber is large, and is small when the difference is small.

In order to reduce the coupling loss, the coupling optical system shown in FIG. 5 reduces the difference between the aspect ratio A _L of the light emitting element and the aspect ratio A _F of the optical fiber.

[0013]

The configuration of the above-described conventional coupling optical system is such that the cross-sectional shape of the core of the optical fiber is made similar to the cross-sectional shape of the beam from the light-emitting element, so that the light-emitting element and the optical fiber can be separated. Can theoretically be zero, but in order to make the cross-sectional shape of the core of the optical fiber similar to the cross-sectional shape of the beam from the light emitting element, the optical fiber
Is realized by forcibly heating from outside and changing the cross-sectional shape according to the thermal change of the molecular state in the core,
In practice, it is difficult to obtain an ideal cross-sectional shape due to differences in products, etc., and the optical output extracted from the output end of the optical fiber after this processing is the same as that in the core caused by this thermal processing. Excessive loss, that is, a problem of deterioration due to propagation loss occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and there is provided a laser diode module capable of efficiently transmitting a laser beam supplied from a laser diode as a light emitting element to an output end of an optical fiber. The purpose is to gain.

It is a further object of the present invention to obtain a laser diode module in which the light output and the wavelength of laser light supplied from a laser diode as a light emitting element are stable.

[0016]

A laser diode module according to the present invention comprises: a laser diode for outputting laser light having a spot size different in a first direction and a second direction orthogonal to the first direction; An optical fiber having a core for receiving and propagating light and having a surface having a normal to an end face of the core at an angle corresponding to a spot size ratio with respect to the optical axis direction of the core.

[0017] Further, there is provided a laser diode for outputting laser light having a different spot size in a first direction and a second direction orthogonal to the first direction, and an optical fiber having a core for receiving and propagating the laser light. The end face of the core is defined as a surface having a normal line perpendicular to the optical axis direction of the core, and the spot size ratio on this surface is determined by the spot size ratio on the surface perpendicular to the optical axis direction. It consists of an optical fiber whose size ratio is close to that of the optical fiber.

Further, a lens is provided between the laser diode and the optical fiber.

The lens has a function of making the spot size ratio of the laser beam close to 1.

Further, the end face of the lens is provided with an optical coating that has low reflection near the oscillation center wavelength of the laser diode.

Further, an optical isolator is provided between the laser diode and the optical fiber.

Further, a filter for transmitting laser light of a specific wavelength band is provided in the core of the optical fiber.

Further, the core end face is provided with an optical coating which has low reflection near the oscillation center wavelength of the laser diode.

The optical fiber is obtained by locally increasing the sectional area of the core on the core end face side.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 is an explanatory diagram of a laser diode module according to a first embodiment, and FIG. 1A is a perspective view from the top of the laser diode module, and optical coupling in a direction horizontal to a so-called active layer of the laser diode. The state is shown. FIG. 1B is a perspective view from the side of the laser diode module, showing an optical coupling state in a direction perpendicular to the active layer of the laser diode.

In FIG. 1, reference numeral 10 denotes a laser diode as a light emitting element having a large aspect ratio and a horizontal spot size different from a vertical spot size, and 11 denotes a light emitting surface of the laser diode 10.
Reference numeral 20 denotes a light-receiving surface by cutting the end face obliquely with respect to the axis of the laser beam so that the aspect ratio differs only on the end face side that receives the emitted light of the laser diode 10 and the aspect ratio approaches the aspect ratio of the laser diode 10. , An optical fiber core 21, and a cladding 22 of the optical fiber 20.

The optical fiber 20 shown in FIG. 1 is processed as in the above-described conventional example so that the aspect ratio on the end face side for receiving the light emitted from the laser diode 10 is substantially equal to the aspect ratio of the laser diode 10. Instead, the end face is first processed so that the aspect ratio at the end face is smaller than the aspect ratio of the laser diode 10 (the light receiving surface is formed obliquely to the laser beam axis). Prepare first.

Then, the end face side of the optical fiber 20 is cut obliquely to the laser beam axis, that is, by giving the cut core cross section an asymmetric shape in the horizontal and vertical directions. , The asymmetry of the beam shape in the vertical and horizontal directions to give an aspect ratio of the laser diode 10
To the aspect ratio.

Therefore, according to the first embodiment, in the above-described diagonal cutting of the end face and the polishing of the cut face, since the heating processing is not performed as in the above-described conventional example, the excess loss is hardly generated. Instead of changing the aspect ratio so that the shape of the core at the light receiving end of the optical fiber 20 is similar to the shape of the light emitting end of the laser diode 10 as in the conventional example, the laser diode module described above has an aspect ratio Therefore, it is possible to reduce the propagation loss of the optical fiber 20 that occurs during the processing step of increasing the optical power.

That is, it is possible to obtain a laser diode module that can efficiently transmit the laser light supplied from the laser diode 10 to the output end of the optical fiber 20.

Further, as shown in FIG.
Is cut obliquely with respect to the laser beam axis, so that the laser light reflected on the light receiving end surface of the optical fiber 20 hardly returns directly to the laser diode 10. The oscillation state stabilizes. That is, the influence of the interference of the reflected light on the outgoing light is eliminated.

In other words, the light output of the laser light supplied from the laser diode 10 is stable, and the oscillation wavelength of the laser light is also stable (the oscillation characteristics of the laser diode are stable).
Laser diode module can be obtained.

The optical fiber 20 may have a tip (light receiving end) processed into an elliptical sphere. Since the aspect ratio can be made closer to the aspect ratio of the laser diode 10 by making the shapes in the horizontal direction and the vertical direction asymmetric, the optical output of the light emitted from the laser diode 10 can be efficiently supplied to the optical fiber 20.

The direction in which the end face of the optical fiber 20 is cut obliquely to the laser beam axis is not limited to the first embodiment but is limited to the direction shown in the figure. Instead, cutting may be performed in other directions according to individual cases.

Embodiment 2 FIG. 2 is an explanatory diagram of the laser diode module according to the second embodiment, and shows an optical coupling state in which a bullet surface parallel to a so-called active layer of the laser diode is seen through from above. In FIG. 2, as a new configuration with respect to the conventional example and the embodiment, reference numeral 30 denotes a connection between the laser diode 10 and the optical fiber 20 so that good coupling (highly efficient coupling) between the laser diode 10 and the optical fiber 20 is obtained. It is an optical lens provided between them.

In the laser diode module shown in FIG. 2, the size and shape of the light emitted from the laser diode 10 are enlarged using an optical lens 30 to match the size and shape of the core at the light receiving end of the optical fiber 20. Thus, the optical system can be assembled such that the coupling magnification between the laser diode 10 and the optical fiber 20 is optimized.

Therefore, according to the second embodiment, it is possible to obtain a laser diode module that can efficiently transmit the laser light supplied from the laser diode 10 to the output end of the optical fiber 20.

In FIG. 2, one optical lens 10 is used, but a plurality of optical lenses may be used according to the magnification. By providing a plurality of optical lenses, the beam profile of the laser diode 10 and the beam profile of the optical fiber can be matched, so that the coupling loss between the laser diode 10 and the optical fiber can be reduced.

Embodiment 3 The optical lens 30 shown in the second embodiment (FIG. 2) adjusts the aspect ratio of the laser diode 10 so as to approach the aspect ratio of the end face of the optical fiber when receiving the light emitted from the laser diode 10 and refracting it. A lens having a function of reducing the size may be used.

Therefore, according to the third embodiment, it is possible to use such a lens in this case without cutting the optical fiber 20 to make the aspect ratio sufficiently large as in the above-described embodiment. By adjusting the aspect ratio of the laser beam, the light emitted from the laser diode 10 can be efficiently coupled. That is, the laser diode 10 can be coupled with the laser diode 10 without using the optical fiber 20 having a large aspect ratio and a large propagation loss. Highly efficient coupling with the optical fiber 20 is obtained, the processing time for increasing the aspect ratio of the optical fiber 20 can be reduced, and the propagation loss of the optical fiber, which is slightly generated by the processing, can be reduced.

Accordingly, it is possible to obtain a laser diode module capable of efficiently transmitting the laser light supplied from the laser diode 10 to the output end of the optical fiber 20.

Embodiment 4 Further, a so-called optical coating that has low reflection in the vicinity of the oscillation center wavelength of the laser light of the laser diode 10 may be applied to the end face of the optical lens 30 shown in the second embodiment (FIG. 2) and 3 (FIG. 3). .

Therefore, according to the fourth embodiment, the light emitted from the laser diode 10 can enter and exit the optical lens 30 with low loss.
The reflection loss generated at the end face of the optical fiber 20 can be reduced, and the laser light supplied from the laser diode 10 can be efficiently transmitted to the optical fiber 20.
Can be obtained.

Embodiment 5 FIG. FIG. 3 is an explanatory diagram of the laser diode module according to the fifth embodiment.
In the meantime, as a new configuration with respect to the conventional example and the embodiment, 40 is provided between the optical fiber 20 and the optical lens 30, and the transmission loss is small only in the direction from the laser diode 10 to the optical fiber 20, and vice versa. An optical isolator having a large transmission loss in the direction.

The laser diode module shown in FIG.
Since it is possible to make it difficult for the reflected light generated at the end face of 0 and the reflected light generated at the output end of the optical fiber 20 to re-enter the laser diode 10, the laser diode 10 can stably oscillate. As a result, a laser diode module having a stable optical output and a stable oscillation wavelength (stable oscillation characteristics) can be obtained.

Since the other optical system has the same configuration as that of the above-described embodiment, the laser light from the laser diode 10 can be efficiently propagated to the output end of the optical fiber.

Embodiment 6 FIG. FIG. 4 is an explanatory diagram of the laser diode module according to the sixth embodiment, and shows an optical coupling state when a surface parallel to a so-called active layer of the laser diode is viewed from above. In FIG. 4, a so-called fiber grating 50 is provided near the output end of the core 22 and has a partially reduced refractive index of light of the core 22 as a new configuration with respect to the conventional example and the embodiment. .

For example, the fiber grating 50 is
GeO ₂ having a property that the molecular state changes and the refractive index of light is reduced when irradiated with ultraviolet rays is added in advance to the core 22 of the single mode fiber in the fiber manufacturing stage, and laser light is applied to the core 22. By applying a plurality of masks intermittently at certain intervals in the direction of travel of the core and further irradiating the core 22 with ultraviolet light, the core 22 is configured so that portions having a large refractive index of light and portions having a small refractive index are alternately repeated according to the masking. 22 is formed.

In general, in a laser diode module used in an erbium-doped fiber and having an oscillation wavelength of 0.98 micron band, the oscillation wavelength is fixed, for example, in the vicinity of the 0.978 micron band in order to increase the gain of the erbium-doped fiber. Is required.

Therefore, as described above, the fiber grating 50 intermittently forms a plurality of portions having a small refractive index in the core 22 at a certain interval, so that only the light of a certain specific wavelength is formed. Can have a high transmittance and a low transmittance for light of other wavelengths.

Accordingly, in the fiber grating 50 shown in FIG. 4, for example, the refractive index of the light to be reduced so that the transmittance is high for the laser light in the 0.978 micron band and the transmittance is low for the other wavelengths. The optimum pump laser diode module in which the erbium-doped fiber transmits the laser light of the specific wavelength can be obtained by adjusting and determining.

Therefore, according to the sixth embodiment, it is possible to obtain a laser diode module in which the light output and the wavelength of the laser light supplied from the laser diode 10 are stable.

Since the structure shown in FIG. 4 is obtained by simply adding the fiber grating 50 to the structure shown in the second embodiment (FIG. 2), the elevated structure shown in the second embodiment (FIG. 2) can be used. That is, it goes without saying that the laser light supplied from the laser diode 10 can be efficiently propagated to the output end of the optical fiber.

Embodiment 7 FIG. In each of the above embodiments, the end face of the optical fiber 20 is provided with the laser diode 1.
An optical coating that has low reflection near the oscillation center wavelength of the laser light of 0 may be applied.

In this case, the light emitted from the laser diode 10 can be made to enter the optical fiber 20 with low loss, so that the laser light supplied from the laser diode 10 can be efficiently propagated to the output end of the optical fiber 20. it can.

In particular, if such an optical coating is applied in the above-described sixth embodiment (FIG. 4), a laser diode module in which the light output and wavelength of the laser light supplied from the laser diode 10 are stable can be obtained. Can also.

Embodiment 8 FIG. In each of the embodiments described above, the optical fiber 20 has an asymmetric heat distribution with respect to two axes orthogonal to the cross section of the single mode fiber.
GeO ₂ having the property that the molecular state changes and the refractive index of the light decreases when irradiated with ultraviolet rays is added to the core 21 in advance in the fiber manufacturing stage, and the core 21 is asymmetrically formed with respect to the two axes. Heat-treated so as to be diffused into may be used.

Therefore, according to the eighth embodiment, in addition to the effects of each of the above-described embodiments, since single-mode fibers are generally produced in large quantities, they can be obtained at low cost, and can be obtained at low cost. You can get a module.

Embodiment 9 In each of the above-described embodiments, the optical fiber 20 may be obtained by subjecting a local portion of a polarization maintaining fiber described in Japanese Patent Application Laid-Open No. Hei 6-180404 to a heating process.

Since the polarization maintaining fiber is provided with a refractive index portion serving as a stress applying portion at a position symmetrical on both sides of the core 21 in order to fix the polarization plane of the light beam propagating through the optical fiber, ultraviolet rays are irradiated. Thus, the speed at which GeO ₂ diffuses differs between an axial direction parallel to the polarized light and an axial direction perpendicular thereto, and an optical fiber having an aspect ratio larger than 1 can be easily obtained. As a result, a laser diode module can be easily manufactured.

[0061]

According to the present invention, it is possible to obtain a laser diode module capable of efficiently transmitting a laser beam supplied from a laser diode as a light emitting element to an output end of an optical fiber.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a laser diode module according to a first embodiment.

FIG. 2 is an explanatory diagram of a laser diode module according to a second embodiment.

FIG. 3 is an explanatory diagram of a laser diode module according to a fifth embodiment.

FIG. 4 is an explanatory diagram of a laser diode module according to a sixth embodiment.

FIG. 5 is an explanatory diagram of a coupling optical system of a conventional light emitting module.

FIG. 6 is a diagram showing the relationship between the aspect ratio of the optical fiber and the coupling loss when the aspect ratio of the laser diode is set to 3;

[Explanation of symbols]

Reference Signs List 10 laser diode, 11 laser diode light emitting surface, 20 optical fiber, 21 core, 22 clad, 30 lens, 40 optical isolator, 50 fiber grating.

Claims (9)

[Claims] 1. A laser diode that outputs a laser beam having a spot size different from a first direction and a spot size in a second direction orthogonal to the first direction, and a core that receives and propagates the laser beam. A laser diode module comprising: an optical fiber having an end surface having a surface having a normal to an angle corresponding to the spot size ratio with respect to the optical axis direction of the core. 2. A laser diode which outputs laser light having a spot size different from each other in a first direction and a second direction orthogonal to the first direction, and an optical fiber having a core for receiving and propagating the laser light. The end face of the core is a surface having a normal in a direction intersecting with the optical axis direction of the core, and the ratio of the spot size on this surface is the ratio of the spot size on a surface perpendicular to the optical axis direction. A laser diode module comprising an optical fiber having a ratio closer to the spot size of the laser light. 3. The laser diode module according to claim 1, wherein a lens is provided between the laser diode and the optical fiber. 4. The laser diode module according to claim 3, wherein the lens has a function of making the spot size ratio of the laser light close to 1. 5. The laser diode module according to claim 3, wherein the end face of the lens is coated with an optical coating that exhibits low reflection near the oscillation center wavelength of the laser diode. 6. The laser diode module according to claim 1, wherein an optical isolator is provided between the laser diode and the optical fiber. 7. The laser diode module according to claim 1, wherein a filter that transmits laser light in a specific wavelength band is provided in a core of the optical fiber. 8. The laser diode module according to claim 1, wherein an optical coating having low reflection near the oscillation center wavelength of the laser diode is applied to an end face of the core. 9. The laser diode module according to claim 1, wherein the optical fiber has a locally enlarged cross-sectional area of the core on the core end face side.