JP2000171665A - Ld module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LD module which makes it possible to decrease the reflected light to a laser diode side at the incident end face of an optical fiber and to obtain high optical coupling efficiency in spite of a change in environment temperature. SOLUTION: A first lens 4 and a second lens 5 are disposed between the laser diode 2 and the incident end face 3A of the optical fiber 3. The incident end face 3A of the optical fiber 3 is inclined in a specific direction in such a manner that the orthogonal projection of the normal of the incident end face 3A exists within a range of ±30 deg. on the basis of the major axis of the near field pattern of the laser diode 2 on the exit end face of the laser diode 2. The central axis of the first lens 4 aligns to the optical axis of the laser diode 2 and the central axis of the second lens 5 is apart in a direction along with the major axis of the near field pattern with respect to the central axis of the first lens 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LD module, and more particularly to an LD module, which can reduce reflected laser light to a laser diode side at an incident end face of an optical fiber, and has a high optical coupling efficiency regardless of a change in environmental temperature. It relates to the obtained LD module.

[0002]

2. Description of the Related Art A laser diode module (hereinafter referred to as L)
Abbreviated as D module. ) Is constituted by an optical coupling between a laser diode and an optical fiber, and is widely used as a signal light source or an excitation light source in an optical communication system or an optical measurement system. As such an LD module, for example, an LD arranged in series as shown in FIG.
Modules are known.

FIG. 5 is a diagram showing the arrangement of components of a conventional LD module arranged in series. L in the series arrangement shown in FIG.
The D module is a module in which optical lenses (D) and (E) are disposed on the optical path between the laser diode (A) and the incident end face (C) of the optical fiber (B). ) Is formed as a plane perpendicular to the optical axis of the optical fiber (B). And this LD
In the module, to obtain the maximum optical coupling efficiency,
A laser diode (A), optical lenses (D) and (E), and an optical fiber (B) are arranged in series on the same optical axis.

In the above-mentioned LD module, the incident end face (C) of the optical fiber (B) is formed as a plane perpendicular to the optical axis, so that the incident light path and the reflected light path of the laser light from the laser diode (A). And approximately match. Therefore,
A part of the laser light incident from the laser diode (A) to the incident end face (C) of the optical fiber (B) is reflected at the incident end face (C) toward the laser diode (A), and the reflected light causes the laser diode There is a problem that (A) is adversely affected. Accordingly, an LD module having an offset arrangement improved so as to reduce reflected light has been proposed (see Japanese Patent Application Laid-Open No. 5-232356).

FIG. 6 is a diagram showing the arrangement of components of a conventional offset-disposed LD module. The LD module having the offset arrangement shown in FIG.
A module in which optical lenses (D) and (E) are disposed on the optical path between the optical fiber (B) and the incident end face (C) of the optical fiber (B). The optical fiber (B) is inclined in a predetermined direction with respect to a virtual plane perpendicular to the optical axis of the optical fiber (B). In this LD module, in order to obtain the maximum optical coupling efficiency, the optical lens (D) is arranged with its central axis coinciding with the optical axis of the laser diode (A), and the optical lens (E) is Are arranged in a so-called offset state, the center axis of which is separated from the center axis of the optical lens (D).

[0006]

By the way, even in an LD module assembled so as to obtain the maximum optical coupling efficiency, when the environmental temperature to be used is greatly changed,
Laser diode (A), optical lens (D), (E), optical fiber (B) due to thermal expansion and contraction of module
, The optical coupling efficiency decreases. In particular, in an LD module in which the central axes of the optical lenses (D) and (E) are offset from each other, the optical coupling efficiency is significantly reduced.

[0007] Therefore, there is a demand for an LD module that can reduce reflected light from the incident end face of an optical fiber to the laser diode side and that can obtain high optical coupling efficiency regardless of changes in environmental temperature.

[0008]

The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, the laser light from the laser diode usually has a near-field pattern (N
FP) is an elliptical shape, so that the incident end face of the optical fiber is inclined in a predetermined direction with respect to an imaginary plane perpendicular to the optical axis so that the reflected light to the laser diode side can be reduced. Also in the module, the inclination direction is set to the near field pattern (NF
P) It has been found that, if it is set along the long axis direction, it is possible to suppress a decrease in optical coupling efficiency due to a change in environmental temperature, and thus completed the present invention.

That is, the gist of the present invention is an LD module in which an optical lens is disposed on an optical path between a laser diode and an incident end face of an optical fiber, wherein the incident end face of the optical fiber is connected to an optical axis. The laser diode is tilted in a predetermined direction with respect to the virtual plane, and the tilt direction is ± 3 on the emission end face of the laser diode with reference to the long axis of the near field pattern (NFP) of the laser diode.
The LD module is characterized in that an orthogonal projection of a normal line of the incident end face is set in a range of 0 °.

Further, according to the present invention, a first lens disposed on the laser diode side and a second lens disposed on the optical fiber side are provided.
A central axis of the first lens coincides with an optical axis of the laser diode, and a central axis of the second lens is a long axis of the near-field pattern with respect to a central axis of the first lens. The LD module is characterized by being separated in the direction along the LD module.

In the LD module of the present invention, a part of the laser light incident from the laser diode is reflected on the incident end face of the optical fiber. At this time, since the incident end face of the optical fiber is inclined with respect to a virtual plane perpendicular to the optical axis, the laser light is reflected in a direction different from the incident optical path. Further, the structure in which the inclination direction of the incident end face of the optical fiber is set to a specific direction, even when the LD module is thermally expanded or contracted,
A change in the amount of laser light incident on the incident end face of the optical fiber is reduced.

Further, the structure in which the inclination direction of the incident end face of the optical fiber is set in a specific direction, and the central axes of the first lens and the second lens are separated in the specific direction, is that the center of the first lens and the second lens is Even when the distance between the axes changes due to thermal expansion or thermal contraction of the LD module, a change in the amount of laser light incident on the incident end face of the optical fiber is further reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an LD module according to the present invention will be described with reference to the drawings. FIG. 1 shows an LD according to the present invention.
FIG. 2 is a diagram illustrating an arrangement of components of a module. FIG. 2 is an explanatory view of the inclination direction of the incident end face of the optical fiber. FIG. 3 is a graph showing the relationship between the ambient temperature and the light output in the LD module as one embodiment. FIG. 4 is a graph showing the relationship between the ambient temperature and the light output in an LD module as a comparative example.

As shown by reference numeral (1) in FIG. 1, the LD module of the present invention has an optical lens as an optical lens on an optical path between a laser diode (2) and an incident end face (3A) of an optical fiber (3). This is a module provided with a first lens (4) and a second lens (5). The incident end face (3A) of the optical fiber (3) is inclined in a predetermined direction with respect to a virtual plane perpendicular to the optical axis. The inclination direction of the incident end face (3A) is
As shown in FIG. 2, on the emission end face of the laser diode (2), the incidence end face is within a range of ± 30 °, preferably ± 15 ° with respect to the long axis of the near field pattern (NFP) of the laser diode (2). The orthographic projection (indicated by the arrow in the figure) of the normal line of (3A) is set so as to be located.

The center axis of the first lens (4) arranged on the side of the laser diode (2) coincides with the optical axis of the laser diode (2), and is arranged on the side of the optical fiber (3). The central axis of the second lens (5) coincides with the optical axis of the optical fiber (3). The center axis of the second lens (5) is in relation to the center axis of the first lens (4).
They are separated by 10 μm or more, preferably 50 μm or more in the direction along the long axis of the near-field pattern (NFP).
The separation distance is 1,000 μm or less, more preferably 5 μm or less.
It is about 00 μm or less. That is, the two central axes are separated from each other such that a straight line orthogonal to both the central axes is located within a range of ± 30 ° with respect to the long axis of the near field pattern (NFP).

The laser diode (2) is sealed together with a gas for preventing oxidation, for example, in a package (not shown) provided with a light-transmitting window glass, and has high life reliability. The near field pattern (NFP) of the laser diode (2) has an aspect ratio of 1.2 to 1.2.
It has an elliptical shape of about 5, and the oscillation center wavelength of the emitted laser light is, for example, 900 to 1,000 nm, preferably 98 to 1,000 nm.
It is around 0 nm.

The optical fiber (3) has a diameter of about 125 μm and is held at the center of a cylindrical ferrule holder via a fiber ferrule (not shown). This optical fiber (3) may be a polarization plane preserving fiber called a so-called PANDA fiber or a single mode optical fiber.

The first lens (4) is a convex lens for aligning the laser light emitted from the laser diode (2) at a predetermined divergence angle into parallel rays. The second lens (5) is a convex lens that collects the parallel light beams aligned by the first lens (4) and forms an optical image of the laser beam on the incident end face (3A) of the optical fiber (3). is there. And
The first lens (4) and the second lens (5) are positioned in the optical path direction and in two axial directions on a plane orthogonal to the optical path, and are respectively held in cylindrical lens holders (not shown).

The LD module (1) of the present invention is assembled and adjusted so as to obtain the maximum optical coupling rate. That is, the normal projection (indicated by an arrow in the drawing) of the normal to the incident end face (3A) of the optical fiber (3) is substantially along the long axis of the near-field pattern (NFP) of the laser diode (2), and The central axis of the second lens (5) is relative to the central axis of the first lens (4).
The assembly is adjusted using a dedicated assembling apparatus (not shown) so as to be spaced apart by about 10 to 1,000 μm in the direction along the long axis of the near field pattern (NFP).

In the assembling adjustment, the optical coupling efficiency is measured based on a detection value of the light intensity of a laser beam transmitted through the optical fiber (3), which is received by a photodiode.
Then, in a state where the maximum optical coupling efficiency is obtained, a package (not shown) of the laser diode (2), a lens holder (not shown), and a ferrule holder (not shown).
And are joined by laser welding.

The LD module (1) of the present invention is used as a signal light source or an excitation light source in, for example, an optical communication system or an optical measurement system. In this LD module (1), the input end face (3
Since A) is inclined with respect to the virtual plane perpendicular to the optical axis, a part of the laser light incident from the laser diode (2) on the incident end face (3A) of the optical fiber (3) is incident on the incident end face (3A) ), The reflected light is reflected in a direction different from the incident light path. Therefore, according to the LD module (1) of the present invention, the incident end face (3A) of the optical fiber (3).
The reflected light traveling from the side toward the laser diode (2) can be greatly reduced.

The incident end face (3) of the optical fiber (3)
The orthogonal projection of the normal line of A) (indicated by an arrow in the figure) is substantially along the long axis of the near field pattern (NFP) of the laser diode (2), and the center axis of the second lens (5) is the first axis. The assembly is adjusted so as to be separated from the center axis of the lens (4) by about 10 to 1,000 μm in a direction along the orthogonal projection of the normal. Therefore, the first lens (4) and the second lens (5) are caused by thermal expansion or thermal contraction of the LD module (1).
Even when the distance between the center axes of the optical fibers changes, it is possible to reduce the change in the amount of laser light incident on the incident end face (3A) of the optical fiber (3). That is, according to the LD module (1) of the present invention, high optical coupling efficiency can be obtained irrespective of a change in environmental temperature.

[0023]

[Example 1] An LD module (1) having the structure shown in FIG. 1 was manufactured. In the LD module (1), the long axis of the near-field pattern (NFP) coincides with the normal projection of the normal line of the incident end face (3A) of the optical fiber (3) on the exit end face of the laser diode (2). Was. The central axes of the first lens (4) and the second lens (5) were separated by about 350 to 400 μm in the direction along the long axis of the near field pattern (NFP). Then, for this LD module (1), the environmental temperature is set to -10 to 5
Change in 5 ° C increments in the range of 0 ° C,
The relationship between the ambient temperature and the light output when the PC was driven was determined (see FIG. 3). The light output was obtained by measuring the output of the laser light emitted from the optical fiber (3) using a photodiode.

As a result, in the LD module (1), as shown in FIG. 3, the fluctuation range of the optical output at -10 to 25 ° C. is within 0.3 dB, and the fluctuation range at 25 to 50 ° C. is 0. .8 dB. And the fluctuation range at -10 to 50 ° C was about 1.1 dB. That is, in the LD module (1), a high temperature stability in which the fluctuation range of the optical output at −10 to 25 ° C. was within 0.3 dB was obtained.

COMPARATIVE EXAMPLE 1 The short axis of the near-field pattern (NFP) and the normal projection of the normal line of the incident end face (3A) of the optical fiber (3) were matched on the exit end face of the laser diode (2). Except for this point, an LD module similar to that of Example 1 was manufactured as a comparative example. Then, for the manufactured LD module, the relationship between the ambient temperature and the light output was obtained under the same conditions as in Example 1 (see FIG. 4).

As a result, in the LD module, as shown in FIG. 4, the fluctuation range of the optical output at -10 to 25 ° C. is about 1.5 dB, and the fluctuation range at 25 to 50 ° C. is 0.8 dB. It became about. Then, the fluctuation width at −10 to 50 ° C. was about 2.3 dB. That is, -10
The fluctuation range of the optical output at about 50 ° C. is about 2.3 dB,
The fluctuation range at −10 to 25 ° C. is also about 1.5 dB,
It has been found that the optical coupling efficiency varies greatly depending on the environmental temperature.

[0027]

As described above, according to the LD module of the present invention, since the incident end face of the optical fiber is inclined with respect to the virtual plane perpendicular to the optical axis, the laser light incident from the laser diode When a part of the light is reflected by the incident end face of the optical fiber, the reflected light is reflected in a direction different from the incident optical path. Therefore, it is possible to reduce the light reflected on the laser diode side at the incident end face of the optical fiber. Further, since the inclination direction of the incident end face of the optical fiber is set to a specific direction, even when the LD module thermally expands or contracts, it is possible to reduce the change in the amount of laser light incident on the incident end face of the optical fiber. As a result, high optical coupling efficiency can be obtained irrespective of changes in the environmental temperature.

Further, when the inclination direction of the incident end face of the optical fiber is set to a specific direction, and the central axes of the first lens and the second lens are separated in the specific direction, the first lens and the second lens Even when the distance between the center axes of the lenses changes due to thermal expansion or thermal contraction of the LD module, the change in the amount of laser light incident on the incident end face of the optical fiber can be further reduced, and the change in the ambient temperature can be reduced. Even higher optical coupling efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is an arrangement configuration diagram of components of an LD module according to the present invention.

FIG. 2 is an explanatory diagram of a tilt direction of an incident end face of an optical fiber.

FIG. 3 is a graph showing a relationship between an ambient temperature and a light output in an LD module as one embodiment.

FIG. 4 is a graph showing a relationship between an ambient temperature and an optical output in an LD module as a comparative example.

FIG. 5 is an arrangement diagram of components of a conventional LD module arranged in series.

FIG. 6 is a layout diagram of components of a conventional LD module having an offset layout.

[Explanation of symbols]

 1: LD module 2: Laser diode 3: Optical fiber 3A: Incident end face 4: First lens 5: Second lens

Claims (2)

[Claims] 1. An LD module having an optical lens disposed on an optical path between a laser diode and an incident end face of an optical fiber, wherein the incident end face of the optical fiber is positioned with respect to a virtual plane perpendicular to the optical axis. Is inclined in a predetermined direction, and the inclination direction is on the emission end face of the laser diode.
L is set so that the orthogonal projection of the normal to the incident end face is located within a range of ± 30 ° with respect to the long axis of the near field pattern of the laser diode.
D module. 2. An optical lens comprising: a first lens disposed on a laser diode side; and a second lens disposed on an optical fiber side, wherein a center axis of the first lens is aligned with an optical axis of the laser diode. 2. The LD module according to claim 1, wherein a center axis of the second lens is separated from a center axis of the first lens in a direction along a long axis of the near-field pattern.