JPH09331099A - Surface emitting laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface emitting laser improving light utility efficiency of an emitting light to various type optical system in the laser in which a horizontal resonator laser and a rising mirror corresponding to the end face of its laser diode are monolithically integrated. SOLUTION: When a line erected in a direction toward a reflected beam of a laser beam emitted in parallel with the lengthwise direction of an active layer 12 of a laser diode LD at a rising mirror from a mirror image point O' to the rising mirror M of a laser emitting point O of the diode LD is used as an optical axis (direction Z) and a line for connecting an upper edge A2 of the end face of the diode at the laser emitting direction side to an intersection Z1 of the line parallel to the lengthwise direction of the layer 23 of the diode and the mirror M is used as an aperture line AP, a distance between the intersection Z1 between the axis Z and the line AP and the point O' is set less than 5μm or less. A1 and A2 are disposed symmetrical to the axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting laser having a reflection raising mirror, typically a monolithically integrated reflection raising mirror.

[0002]

2. Description of the Related Art For example, there is known a surface emitting laser in which a laser diode and a rising mirror constituting a horizontal cavity laser as shown in FIG. 7 are monolithically integrated. This surface emitting laser is provided, for example, on a GaAs substrate 10 so that a laser diode LD and a photodiode PD face each other, and a common electrode 4 is provided on the lower surface of the substrate 10.
1 is provided. In the laser diode LD, for example, a first clad layer 11 made of AlGaAs of the same conductivity type as the substrate 10, an active layer 12 made of GaAs, and a second clad layer 13 of a conductivity type different from the first clad layer 11 are sequentially laminated, Further, the electrode 42 is provided on the second cladding layer 13. Laser light is emitted from the end surface of the active layer of the laser diode LD, and the end surface of the active layer is the light emission point O.

The end surface of the photodiode PD facing the laser diode LD is a reflecting mirror M having an inclination of 45 ° with respect to the surface of the substrate 10. The photodiode PD is, for example, an n-type Ga of the same conductivity type as the substrate 10.
The first semiconductor layer 21 made of As and the first semiconductor layer 2
A second semiconductor layer 22 made of p-type GaAs having a conductivity type different from 1 is sequentially stacked, and an electrode 43 is further provided on the second semiconductor layer 22.

In such a surface emitting laser, the laser light emitted from the end face O of the horizontal resonator formed between the both end faces of the laser diode LD is raised and reflected by the mirror so that the laser light is directed in the direction perpendicular to the substrate surface. Configured to point to.

[0005]

In the surface emitting laser in which the raising mirror M is monolithically integrated, the far field pattern (FFP) in the laser active layer thickness direction (θ⊥) is likely to be disturbed. This is because the numerical aperture of the raising mirror is generally smaller than the original radiation angle in the thickness direction of the active layer. This is because there is light or the like that is reflected by the laser end face again after being reflected and changes its propagation direction, and these interfere with light that is reflected and propagated as usual.

FFP in the laser active layer thickness direction (θ⊥)
An example of the measurement result is shown in FIG. Main lobe from center 9
Deviated, with a fringe pattern on the other side. Such FFP causes a big problem in application. That is, in various optical systems using this surface-emitting laser, it is necessary to take measures such as shifting the optical axis of the optical system or avoiding the fringe portion, resulting in a decrease in light utilization efficiency.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a surface emitting laser capable of improving the light utilization efficiency of emitted light for various optical systems.

[0008]

In order to achieve the above object, the present invention provides a surface emitting laser having a horizontal resonator laser and a rising mirror corresponding to the end face of the laser diode, and a laser emitting point of the laser diode. The laser beam emitted from the mirror image point on the rising mirror is parallel to the length direction of the active layer of the laser diode. When the upper edge of the end face on the side and a line that passes through the upper edge and is parallel to the length direction of the active layer of the laser diode and the intersection of the rising mirror are the opening lines, Provided is a surface emitting laser characterized in that a distance between an intersection with an aperture line and the mirror image point is set to 5 μm or less.

In this case, it is preferable that the upper edge of the laser diode and the upper edge of the raising mirror are arranged so as to be substantially symmetrical to each other with respect to the optical axis. The surface-emitting laser of the present invention defines a distance from the mirror image point to the aperture line, so that the F-mode laser with good single peak and symmetry can be obtained.
FP is obtained. The full width at half maximum (twice the angle at which the intensity of FFP becomes 1/2) is also narrowed, which makes it possible to improve the light utilization efficiency.

Further, by arranging the upper edge of the laser diode and the upper edge of the rising mirror at positions substantially symmetrical to each other with respect to the optical axis, the center of the FFP coincides with the optical axis. In particular, alignment is facilitated and light utilization efficiency is improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be specifically described below, but the present invention is not limited to the following embodiments. The surface emitting laser of the present invention is, for example, a surface emitting laser in which a horizontal resonator laser and a raising mirror corresponding to the end face of the laser diode are monolithically integrated, and specifically, the conventional surface emitting laser shown in FIG. Are defined so that the FFP is the best.

FIG. 1 is a schematic enlarged view showing the vicinity of the emitting side end face of a laser diode (LD) and a rising mirror M of a surface emitting laser according to one embodiment of the present invention. The structure of LD is
Similar to the above, for example, AlGaA of the same conductivity type as the substrate 10
The first clad layer 11 made of s, the active layer 12 made of GaAs, and the second clad layer 13 having a conductivity type different from that of the first clad layer 13 may be sequentially laminated, and other configurations may be used. , Is not particularly limited. Further, the portion having the rising mirror M as the wall surface is shown in FIG.
In this case, for example, the first semiconductor layer 21 made of n-type GaAs having the same conductivity type as the substrate 10 and the p-type GaAs having a conductivity type different from that of the first semiconductor layer 21 can be used. And a second semiconductor layer 22 made of, for example, an electrode 42 on the second semiconductor layer 22.
However, the present invention is not limited to this.

In the LD according to this embodiment, the center of the active layer 12 in the thickness direction is substantially at the center of the height of the end face of the LD,
Therefore, when the distance between the light emitting point O (center in the thickness direction) and the lower edge L of the LD emission end face F is a, the lower edge L of the LD end face F is defined.
To the upper edge A2 (the height of the end face) is approximately 2a.

On the other hand, standing up facing the horizontal cavity laser
The direction of the length of the active layer 12 from the lower edge L of the LD
It stands up at an angle of 45 ° to the parallel line of the direction,
The light is emitted from the light emitting point O of the LD in parallel with the length direction of the active layer 12.
The emitted laser light is reflected in the direction perpendicular to the length direction of the active layer 12.
Shoot. Mirror image of the LD's emission point O
The coordinate origin is set at the point O ', and the coordinates of this mirror image point O'
(0, 0), passing through the mirror image point O ′, and the length of the active layer 12
The line parallel to the X-direction, passing through the mirror image point O ',
The laser light emitted parallel to the length direction is reflected in the direction of reflection.
The axis (Z direction). In the present embodiment, the light emitting point
When the coordinates of O are (a, a), the upper edge A of the end face of the LD is
₂The coordinates of are (a, 2a). Also a launch mirror
Top edge A of₁Is flush with the top of the LD,
The upper edge A of the rising mirror₁The coordinates of (-a, 2
a). Upper edge A of the rising mirror₁And LD end face
Top edge A ₂The line connecting the and is defined as the opening line AP, and the opening line AP
The intersection with the optical axis is Z₁And

In the surface emitting laser of this embodiment, the distance C between Z ₁ and the light emitting point, in other words, the height of the LD end face is 5 μm or less, preferably about 0.5 to 3 μm. Further, assuming that the height of the active layer is a, the height of the upper edge of the end face of the LD is approximately 2a, and the height of the upper edge A ₁ of the rising mirror is approximately 2a. Accordingly, in the present embodiment, the upper edge A ₂ of the upper edge A ₁ and LD end surface of the rising mirror, symmetrically located with respect to the optical axis, aperture line AP and the optical axis is perpendicular to the aperture line AP Is bisected along the optical axis.

Next, the effect of using the surface emitting laser with the structural parameters thus defined will be described. FIG. 8 is an enlarged view of the LD end surface of the surface emitting laser and the vicinity of the rising mirror, as in FIG. In this figure, the reflection of the laser light emitted from the laser emission point O on the 45 ° mirror is such that the mirror image point O ′ is an apparent emission point, and the upper edge A _{1 of the} rising mirror and the upper edge of the laser emission end surface of the laser diode are reflected. The edge A ₂ serves as an opening. Similar to FIG. 1, a laser beam emitted through the mirror image point O ′ and parallel to the length direction of the active layer in the X direction and through the mirror image point O ′ and parallel to the length direction of the active layer is reflected. The direction is the optical axis (Z direction). The origin of coordinates is set to (0, 0) at the mirror image point O ′, the coordinates of the light emitting point O is (a, a), the coordinates of the upper edge A ₂ of the LD end face is (a, c), and the upper end of the rising mirror. The coordinates of the edge A ₁ are (a-c-d, c + d). Where d is LD
As the upper edge A _2, a distance between the upper edge A ₁ of mirror up to the longitudinal direction and parallel lines active layer (an opening line AP as in FIG. 1).

In FIG. 8, there is light (vignetting light) which is reflected by a 45 ° mirror as shown by a ray K and then re-reflected at the end face of the laser diode, which causes an apparent emission point to be O ″.
(2a, 0), and the upper edge A _{1 of the} rising mirror and the upper edge A ₂ of the laser emitting end face of the laser diode are used as openings. Further, there is light (clear light) such as the light ray N that does not hit the 45 ° mirror and passes through as it is.

In this case, according to the wave optics theory, it is necessary to consider diffraction by the aperture and interference with vignetting light and clear light. Here, in general, the light N is weak in intensity and far away from the center of the FFP, so that it is ignored, and only the light propagating normally in reflection and the vignetting light are considered, and the influence of diffraction and interference thereof is examined.

FIG. 2 shows the FFP calculated by using the distance c from the mirror image point O'to the aperture line AP as a parameter in the case of the original laser angle θ⊥ = 33 °. However, as shown in FIG. 1, c = 2a and d = 0. From FIG. 2, as shown in FIG. 2C, when c = 5 μm, the FFP center is dented, bimodal, and the peak width is wide. As shown in (B), c = 4μ
At m, it is unimodal. As shown in (A), c = 3 μm
In, an FFP having a single peak and good symmetry is obtained, and the peak width is narrow. From this, if the original value of θ⊥ changes, the desired value of c also changes. However, in the case of a realistic θ⊥ of about 30 degrees, c should be less than 5 μm, preferably 3 μm or less. I know it's good. The lower limit is determined from a practical point of view, but is about 0.5 μm. Also,
When c = 3 μm, the full width at half maximum θ⊥ of FFP is about 20 °, which is a major feature that it is narrower than θ⊥ = 33 ° of the original laser. It is possible to improve the light utilization efficiency by utilizing this.

Next, the improvement of the light utilization efficiency by narrowing the width of the FFP will be specifically described. If θ⊥ = 33 °,
Usually, the light utilization efficiency of condensing with a lens of NA = 0.09 is about 29%. In the surface emitting laser with a rising mirror, if the distance c from the mirror image point to the aperture line is 3 μm, θ⊥ can be about 20 degrees as described above.
Thereby, the light utilization efficiency can be improved up to about 35%. In general, it is difficult to reduce θ⊥ of the laser itself to 20 °, so that the structural parameters of the laser / standing-up mirror are, for example, c = 2a = 3 μm and d = 0 as shown in FIG. It is very useful in practice that such a narrow θ⊥ can be easily realized by the structure.

By setting the distance c from the mirror image point O ′ to the aperture line AP to be 5 μm or less, the FFP in the θ⊥ direction can be made unimodal and the FFP can be narrowed. In addition, the coincidence between the optical axis and the center of the FFP is important in various applications, especially in terms of ease of alignment. FIG. 3 shows the FFP when the height a of the active layer and the distance c from the mirror image point O ′ to the opening line AP are used as parameters. In this case, d = 0.
(A) is a = 2 μm and c = 4 μm, and (B) is a =
In the case of 1.3 μm and c = 2.6 μm, (C) shows a = 1.
When 3 μm and c = 4 μm, (D) is a = 1 μm and c =
This is the case of 4 μm. (A) and (B) shows a case where the active layer is resides in the middle of the end face, and the upper edge A ₂ of mirror up to the upper edge A ₂ of LD are located symmetrically with respect to the optical axis. (C) and (D) shows a case where the active layer 12 is shifted from the center of the end face, when the upper edge A ₂ of mirror up to the upper edge A ₂ of the LD is asymmetrical with respect to the optical axis Is.

As is apparent from FIG. 3, (C) and (D)
And, the center of the FFP and the optical axis are both deviated. On the other hand, in (A) and (B), the optical axis coincides with the center of the FFP. Thus, A ₁ and A ₂ are as symmetrical as possible with respect to the optical axis, that is, c≈2 as shown in FIG.
It is understood that it is preferable to configure the surface emitting laser so that a and d≈0. Even if c = 2a, FF
It is recognized that the symmetry of P is better as c is shorter (see (B)).

In FIG. 1, the lower edge of the rising mirror is in contact with the lower edge L of the LD, but in reality, due to manufacturing restrictions, the lower edge of the rising mirror and the lower edge L of the LD are in contact with each other. May be distant from. Also in this case, the above structural parameters are valid. That is, as shown in FIG. 4, when the lower edge ML of the rising mirror M and the lower edge L of the LD are separated from each other, the coordinate origin of the mirror image point O ′ of the light emitting point O is taken as the coordinate of the light emitting point O. Is (a, a), the coordinates of the upper edge of the LD are (a, 2a), and the coordinates of the upper edge of the raising mirror are (-a, a), which is the same as in FIG.

Next, a method of manufacturing the surface emitting laser according to the present invention will be described with reference to FIGS. First, for example, n-type (1
00) A laser diode is formed on a GaAs substrate having a crystal plane as a main surface. For this purpose, for example, as shown in FIG. 5A, for example, AlGaAs of the same conductivity type as the substrate 10 is used.
A first clad layer 11 made of GaAs, an active layer 12 made of GaAs, and a second clad layer 13 of a conductivity type different from that of the first clad layer are sequentially formed by metal organic CVD or the like. In this case, the thicknesses of the first cladding layer 11 and the second cladding layer 13 are made equal to each other as much as possible, and the active layer is formed of these cladding layers 1.
It is formed so as to be located between 1 and 13. Further, the total thickness of the LD constituted by these is 5 μm or less, preferably 3 μm or less.

Next, as shown in FIG. 5 (b), of these laminated bodies, the portion that remains as the semiconductor laser and forms the reflection mirror is removed by etching by reactive ion etching or the like. As a result, the end face F of the semiconductor laser is formed. Then, as shown in FIG. 5C, a protective film 30 such as a silicon oxide film or a silicon nitride film for covering and protecting the semiconductor laser remaining on the substrate 10 is formed by CVD or the like.

Next, the formation of a slope for forming a rising mirror and the formation of a photodiode are started. Figure 6
As shown in (d), the first semiconductor layer 21 of, for example, n-type GaAs is epitaxially grown on the substrate not covered with the mask layer. Further, as shown in FIG. 6E, a p-type second semiconductor layer 22 is epitaxially grown on the first semiconductor layer 21. In this case, since the crystal having the (100) plane orientation is used as the substrate, the crystal grows at an angle of 45 ° with respect to the substrate surface, and a crystal plane having an inclined surface of 45 ° can be formed. In the present invention, it is preferable that the growth height at this time is aligned with the LD height.

After that, the mask layer 30 is removed, the electrodes 42 and 43 are formed on the LD and the photodiode, respectively, and the common electrode 41 is formed on the back side of the substrate to obtain a surface emitting laser as shown in FIG. It can be manufactured. The surface-emitting laser thus obtained has a narrow full width at half maximum of the FFP, is excellent in symmetry, and can emit laser light whose center coincides with the optical axis of the FFP in a direction perpendicular to the substrate surface.

In the above description, the angle of the rising mirror with respect to the substrate surface is 45 °, but the angle is not limited to this, and an example in which the laser diode and the rising mirror are monolithically integrated is described. However, it can also be applied to a hybrid integrated surface emitting laser,
Other various modifications can be made without departing from the scope of the present invention.

[0029]

The surface-emitting laser of the present invention has a good far-field pattern in the active layer thickness direction (θ⊥) of the surface-emitting laser with a rising mirror, and its full width at half maximum is effectively narrow, resulting in light utilization efficiency. Can be improved.

[Brief description of drawings]

FIG. 1 is an enlarged view of an emission side end face of a laser diode of a surface emitting laser of the present invention and a portion of a rising mirror.

2A and 2B are graphs showing far-field patterns each having a parameter of a distance c between an intersection of an aperture line and an optical axis and a mirror image point.

3A to 3D are graphs showing far-field patterns with the distance c between the intersection of the opening line and the optical axis and the mirror image point and the height a of the active layer as parameters. is there.

FIG. 4 is an enlarged view of a portion of a rising mirror and a light emitting side end surface of a laser diode of a surface emitting laser when a lower edge of the rising mirror and a lower edge of the laser diode are separated from each other.

5A to 5C are cross-sectional views showing a manufacturing process of a surface emitting laser.

6 (d) and 6 (e) are cross-sectional views showing the manufacturing process following FIG.

FIG. 7 is a schematic sectional view showing the structure of a surface emitting laser.

FIG. 8 is an enlarged view of an emission side end surface of a laser diode of a conventional surface emitting laser and a portion of a rising mirror.

FIG. 9 is a graph showing a far field pattern of a conventional surface emitting laser.

[Explanation of symbols]

A ₁ ... Upper edge of rising mirror, A ₂ ... Upper edge of end surface of laser diode, AP ... Aperture line, LD ... Laser diode, O ... Emission point, O '... Mirror image point, M ... Standing mirror, 11 ... First clad layer, 12 ... Active layer, 13 ... Second
Clad layer

Claims (2)

[Claims] 1. A surface emitting laser having a horizontal cavity laser and a rising mirror corresponding to an end face of the laser diode, wherein a length of an active layer of the laser diode from a mirror image point of the laser emitting point of the laser diode to the rising mirror. The laser beam emitted parallel to the vertical direction is set as the optical axis which is a line that stands in the direction of the reflected light from the rising mirror, and passes through the upper edge of the end face of the laser diode on the laser emission direction side, and through the upper edge. When the line connecting the line parallel to the length direction of the active layer of the diode and the intersection of the rising mirror is defined as an opening line, the distance between the intersection of the optical axis and the opening line and the mirror image point is 5 μm.
A surface emitting laser characterized by having a length of less than m. 2. The surface emitting laser according to claim 1, wherein the upper edge of the laser diode and the upper edge of the raising mirror are arranged so as to be substantially symmetrical to each other with respect to the optical axis.