JP2000284133A - Optical fiber and semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently couple the laser light from a semiconductor laser with an optical fiber, to stabilize the wavelength, to obtain superior mass-productivity, and to obtain the optical fiber which is adaptive to high luminance. SOLUTION: The optical fiber 1, formed of a core 2 and a clad 3 covering the periphery of the core, is characterized by that the core diameter of the incidence end is larger than that of the projection end and smoothly decreases from the incidence end 11 to the projection end by being equal to that of the projection end and the tip part 12 of the incidence end is wedgelike having curvature in the length-direction section of the optical fiber and linear in the section orthogonal to the mentioned section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber for receiving and transmitting laser light from a semiconductor laser, and to a semiconductor laser module in which the optical fiber and a semiconductor laser are integrated into a case.

[0002]

2. Description of the Related Art In recent years, with the development of the optical communication field, a semiconductor laser module for communication and a semiconductor laser module for exciting an EDFA (Er-doped fiber amplifier) are required to have high output and high brightness. In the conventional semiconductor laser module, a single mode semiconductor laser has been used, but a performance limit due to an insufficient semiconductor laser output is becoming apparent. Therefore, a semiconductor laser module using a multi-mode, high-output semiconductor laser is being developed, and an EDF using a double clad optical fiber is being developed.
A and others have been put to practical use.

In a conventional single mode semiconductor laser module, a ball lens alone or a combination of a ball lens and a GRIN lens is often used as an optical system for coupling a laser beam and an optical fiber. In the system, the magnification in the direction parallel to the active layer is equal to the magnification in the vertical direction. The reason for using such an optical system is that in a single-mode semiconductor laser, the size ωp in the direction parallel to the active layer in the light emitting region (corresponding to the size obtained by adding light exudation to the stripe width) and the active layer in the light emitting region The ratio to the vertical size ωv (corresponding to the size of the active layer thickness plus the amount of light erosion added) is about 10: 1, and is parallel to the vertical spreading angle θv of the active layer. This is because there is little difference from the divergence angle θp in the direction and the symmetry between the parallel direction and the vertical direction of the laser beam is good. On the other hand, in a high-power multimode semiconductor laser, the ratio of the light emitting region in the direction parallel to the active layer to the light emitting region in the vertical direction reaches several tens to one to several hundreds of ones. Spread angle θv
Greatly differs from the spread angle θp in the parallel direction (θv>
> Θp). For this reason, it is difficult to efficiently introduce laser light into an optical fiber having a light entrance opening (for example, circular) with good symmetry in the rotationally symmetric optical system as described above.

As one of the countermeasures, there is a method in which a cylindrical lens is used as a coupling optical system instead of a ball lens, and a divergence angle θv in a direction perpendicular to the active layer is adjusted. According to this method, the optical fiber can be directly coupled to the optical fiber, but the core diameter of the optical fiber that can be coupled is limited to a diameter equal to or larger than ωp.
This is because, since θp is not adjusted, the diameter of the laser light reaching the incident end of the optical fiber is larger than ωp. In the future, semiconductor lasers
p tends to be large, and if the output is increased, the luminance (energy density) is not improved.

Therefore, the laser beam is narrowed down in combination with another optical system, and coupled to an optical fiber having a core diameter smaller than the size ωp of the emission area in the direction parallel to the active layer of the semiconductor laser to achieve higher brightness. Can be considered.

[0006]

However, in the above method, it is essential to align one or more optical systems in order to couple the semiconductor laser and the optical fiber. Therefore, the manufacturing process becomes complicated, the mass productivity is low, the reproducibility is hardly obtained, and the cost increases. In addition, the emission state of the semiconductor laser is disturbed by the return light from the interface of one or more optical components, and a composite resonator is formed by an external resonator formed between the end face of the semiconductor laser and the interface of the optical component. The serious problem of wavelength splitting occurs. This is difficult to prevent even if an antireflection film (AR) is applied to the optical component.

The details will be described below. Generally, the oscillation wavelength of a semiconductor laser is almost determined only by the gain, and ± 2 nm near the peak wavelength of the gain (about 4 nm in total).
Oscillates in the range of Here, when the laser light reflected at the interface outside the semiconductor laser returns to the semiconductor laser as return light, a new resonator (external resonator) is formed between the emission surface of the semiconductor laser and the external interface. In this case, since the resonator of the semiconductor laser and the external resonator share an interface, a composite resonator is formed. As a result, the oscillation wavelength of the semiconductor laser is determined by the composite resonator. That is, the oscillation wavelength splits or flies. The width of wavelength splitting or wavelength jump depends on the FSR of the external resonator formed at the interface between the semiconductor laser end face and the optical components.
Greatly depends on When the FSR of the external resonator is within the range of the gain of the semiconductor laser, the width of the FSR (4 nm
Wavelength splitting or wavelength jumping. This results in noise in optical communication. Where FSR is
It is defined as:

FSR = λ ² / (2nL) λ is the wavelength, n is the refractive index, and L is the length of the resonator. As described above, according to the above-described method, not only is it difficult to align one or more optical components, but also to cope with high luminance, a plurality of optical components must be used, and an external resonator must be used. The problem of wavelength splitting due to the formation emerges, and the inherent wavelength unity of the semiconductor laser is lost.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical fiber which can efficiently couple laser light from a semiconductor laser to an optical fiber, has a stable wavelength, is excellent in mass productivity, and can cope with high brightness. The purpose is to provide an integrated semiconductor laser module.

[0010]

SUMMARY OF THE INVENTION The present invention relates to an optical fiber comprising a core and a cladding covering the periphery of the core, wherein the diameter of the core at the input end is larger than the core diameter at the output end, and the direction from the input end to the output end. The core diameter decreases smoothly until the core diameter becomes equal to the core diameter of the emission end, and in one section in the longitudinal direction of the optical fiber, the curvature of the tip of the incidence end is the curvature of the incidence end in the section perpendicular to the one section. The optical fiber is smaller than the curvature of the tip. In the present invention, it is preferable that the shape of the incident end in the one section is a wedge shape having a curvature at the tip, and that the tip of the incidence end has a curved shape in a section perpendicular to the one section.

According to the present invention, in an optical fiber comprising a core and a clad surrounding the core, the core diameter at the input end is larger than the core diameter at the output end, and the core diameter is increased from the input end to the output end. It gradually decreases until it becomes equal to the core diameter of the end, and the cross-sectional shape of the incident end in the one cross section is a wedge shape having a curvature at the tip, and in the cross section perpendicular to the one cross section, the cross section of the incident end is An optical fiber having a linear shape.

Further, the present invention is a semiconductor laser module comprising a semiconductor laser chip and an optical fiber for receiving a laser beam from the semiconductor laser chip at an incident end, wherein the optical fiber is the above-mentioned optical fiber.

[0013] These inventions will be described. The laser beam emitted from the high-power multi-mode semiconductor laser has a different vertical divergence angle θv and a different parallel divergence angle θp when focusing on the divergence angle (θv >> θp). The ratio of the light emitting region to the light emitting region in the vertical direction reaches several tens to one to several hundred to one. Therefore, according to the present invention, by using the optical fiber, the vertical divergence angle θv is adjusted to a divergence angle equal to or smaller than the NA of the optical fiber by the lens effect due to the tip having the above shape, and is parallel to the active layer. The size of the light emitting area in the direction ωp
It is possible to efficiently obtain high-brightness (high energy density) laser light from a fiber with a core diameter smaller than ωp at the output end by receiving light with the same or larger core diameter at the input end. Become.

In particular, regarding the formation of the external resonator, the external reflection surface of the semiconductor laser can be minimized only by the incident surface of the optical fiber, and the distance between the semiconductor laser end surface and the optical fiber incident surface is several μm to Since it can be made close to about 100 μm, the FSR does not become 4 nm or less. In particular, if the interval is set to several μm to 50 μm, F
SR becomes 7 to 8 nm or more, which is out of the range of the gain of the semiconductor laser. Therefore, wavelength splitting caused by the end face of the optical fiber cannot occur.

FIG. 1 is a schematic view of an optical fiber according to the present invention.
Shown in FIG. 1A is a side view, and FIG. 1B is a plan view.
The optical fiber 1 is composed of a core 2 having a circular cross section and a cladding 3 surrounding the core. Optical fiber input end 1
1 is machined to an angle α, and its tip 12 is cylindrical. That is, as shown in FIG. 1 (a), the tip of the optical fiber has a wedge shape having a curvature as shown in FIG. 1 (a), and the tip of the optical fiber has a straight line as shown in FIG. 1 (b). It is in shape. The core diameter at the entrance end 11 is larger than the core diameter at the exit end, and there is a tapered portion 13 whose diameter gradually decreases in the direction from the entrance end to the exit end (not shown). There is a tail portion 14 where the core diameter is constant up to the emission end at a point where the diameter becomes equal to the diameter. The core diameter at the entrance end is
When the cross section of the optical fiber is circular, the maximum core diameter rm may be set as long as the cross section perpendicular to the length direction of the optical fiber is circular.

Here, as an example of the dimensions of each part of the optical fiber, the core diameter at the incident end 11 is 100 μm, and the diameter of the cladding 3 is 110 μm. Tail part 1
4, the diameter of the core 2 is 50 μm,
Is 60 μm, the length of the tapered portion 13 is 2.5 m, and the length of the tail portion 14 is 7.5 m. The angle α in one section of the incident end 11 is 60 °, and the radius of curvature of the tip 12 is 20 μm. NA can be set to 0.22. In the cross section shown in FIG. 1 (b), the incident end is straight, but may be a convex curve.

Next, FIG. 2 shows a schematic view of a semiconductor laser module according to the present invention. FIG. 2A is a side view, and FIG.
Is a plan view. A mount 6 for a semiconductor laser chip is arranged on a table 8, and the semiconductor laser chip 4
Is fixedly mounted. The optical fiber 1 is fixed to a table 8 by a support jig 7. In order to inject a current into the semiconductor laser chip, the semiconductor laser chip and an external connection terminal (not shown) are wire-bonded (not shown). In FIG. 2A, the bus bar of the cylindrical portion at the tip 12 of the optical fiber 1 and the active layer 5 of the semiconductor laser chip 4 are arranged in parallel. The semiconductor laser light 9 emitted from the semiconductor laser chip 4 reaches the cylindrically processed tip portion 12 of the optical fiber 1 at a divergence angle θv in the direction perpendicular to the active layer.
Is narrowed down by the lens effect of the distal end portion 12 so as to be equal to or smaller than the NA of the optical fiber 1 and is incident.

On the other hand, in FIG. 2B, the semiconductor laser light 9 emitted from the emission surface 10 of the semiconductor laser chip 4 is
At the divergence angle θp in the direction parallel to the active layer, the optical fiber 1 reaches the cylindrically processed distal end portion 12, and θ
Since p is smaller than the NA of the optical fiber 1, the laser beam is incident as it is, and while passing through the tapered portion, the semiconductor laser light is concentrated and emitted from the emission end (not shown) having a small core diameter with high brightness (high energy density). .

The structure and type of the semiconductor laser 4 can be appropriately selected. For example, International Publication W0093 / 16
513 comprising a carrier block layer described in 513
There is a semiconductor laser having a (Decoupled Confinemnt Heterostructure) structure. In such a semiconductor laser,
For example, θv (FWHM) = 33 °, θp (1 / e ² ) = 9 °,
A stripe width of 100 μm can be used. In order to obtain high output and high brightness, a lateral multi-mode semiconductor laser is preferable.

In this case, the tip 12 of the optical fiber 1
If the distance between the emission surface 10 of the semiconductor laser 5 and the tip 12 of the optical fiber 1 is 10 to 35 μm, θv after passing through the cylindrical curved surface does not exceed the NA of the optical fiber 1, and Oscillation wavelength of 980n
In the case of m, the FSR is 14 to 48 nm, so that wavelength splitting does not occur.

[0021]

According to the present invention, the wavelength is stable with high luminance,
In addition, a semiconductor laser module which is easy in optical adjustment and excellent in mass productivity and an optical fiber constituting the semiconductor laser module can be obtained.

[Brief description of the drawings]

FIG. 1 illustrates an optical fiber according to the present invention.

FIG. 2 is a diagram showing a semiconductor laser module according to the present invention.

[Explanation of symbols]

1 ··· Optical fiber, 2 ··· Core, 3 ··
・ Clad, 4 ・ ・ Semiconductor laser chip, 5 ・ ・
Active layer, 6... Mount, 7... Support jig,
8 ··· Table, 9 ··· Laser light 10 ··· Outgoing surface, 11 ··· Incoming end, 12
..Tip, 13 ..Taper, 14 ..Tail

Claims (4)

[Claims] 1. An optical fiber comprising a core and a cladding covering the periphery of the core, wherein the core diameter at the input end is larger than the core diameter at the output end, and the core diameter increases from the input end to the output end. The diameter gradually decreases until it becomes equal to the diameter, and in one section in the longitudinal direction of the optical fiber, the curvature of the tip of the incidence end is smaller than the curvature of the tip of the incidence end in a section perpendicular to the one section. And optical fiber. 2. A cross-sectional shape of the incident end in the one section is a wedge shape having a curvature at a front end thereof, and a cross-sectional shape of the front end of the incident end is curved in a cross section perpendicular to the one cross section. The optical fiber according to claim 1, wherein 3. An optical fiber comprising a core and a clad covering the periphery of the core, wherein the core diameter at the input end is larger than the core diameter at the output end, and the core diameter increases from the input end to the output end. The diameter gradually decreases until it becomes equal to the diameter, and in one cross section, the cross-sectional shape of the incident end is a wedge shape having a curvature at the tip, and in the cross section perpendicular to the one cross section, the cross-sectional shape of the incident end is linear. An optical fiber characterized by being in a shape. 4. A semiconductor laser module comprising: a semiconductor laser chip; and an optical fiber that receives laser light from the semiconductor laser chip at an incident end, wherein the optical fiber is the optical fiber according to claim 1. A semiconductor laser module characterized by the above-mentioned.