JPH0810778B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser, in particular, its waveguides are interconnected to each other on the inner side of the optical end face thereof, and a plurality of semiconductor lasers are provided from the connecting portion toward both optical end faces. The present invention relates to an array type semiconductor laser in which stripe-shaped branched waveguides are arranged.

[Outline of Invention]

The present invention relates to a semiconductor laser having a waveguide which is interconnected to each other, for example, at the center inside the optical end face, and in which a plurality of striped branch waveguides are arranged from the connecting portion toward both optical end faces, respectively. The branch waveguide is widened from each optical end face toward the coupling part to strengthen the coupling of each branch waveguide and narrow the half width of the far field pattern (hereinafter referred to as FFP), and in some cases, FFP is a single peak. The semiconductor laser can be easily and surely obtained.

[Conventional technology]

As a conventional high-power semiconductor laser, a so-called array type structure having a configuration in which a plurality of stripe-shaped waveguides (1) are arranged in parallel with each other at a narrow interval d as shown in the pattern diagram of the waveguide in FIG. There is something to take.

However, in the case of such a configuration, when the number of stripes is N, there is an N-1) th mode (first-order mode) in which the phase of the light propagation between the laser oscillation parts, that is, the waveguides in each stripe is shifted by 180 °. There is a problem that the full width at half maximum of the FFP is widened because the gain is easier to obtain than the 0th-order mode with a phase difference of 0 °, and the FFP becomes a double peak as shown in Fig. 6.

In contrast, for example, U.S. Pat. No. 4,255,717 and Electronics Letters
ers) 13 March 1986 Vol.22 No, 6 In the semiconductor lasers disclosed on pages 293 to 294, the waveguide pattern is schematically shown in FIG. (2), from which a plurality of branch waveguides (3) are respectively arranged toward both optical end faces (3a) and (3b) with a required narrow spacing d. in this case,
It is said that the 0th-order mode in which the phase difference of the propagation of light between adjacent ones is 0 ° is easily established by connecting the resonators with respect to each branch waveguide (3). Although the FFP in the semiconductor laser having such a structure has a single peak as shown in FIG. 8, its half-value width tends to be large.

[Problems to be solved by the invention]

The present invention provides an array-type semiconductor laser described above, that is, a semiconductor laser capable of reliably obtaining a single-peak FFP, if necessary, in a narrower half-value width of the FFP in the multi-light-emission type semiconductor laser. Is.

That is, in the present invention, the reason why the full width at half maximum of the semiconductor laser shown in FIG. 7 is large is that the optical coupling of each branch waveguide (3) is not sufficiently performed in the central coupling portion (2). It is intended to solve the problems described above based on the fact that the phase locking operation may not be performed.

[Means for solving problems]

In the present invention, as shown in the enlarged pattern diagram of the waveguide in FIG. 1, the waveguide (11) is connected to both optical fibers from a connecting portion (12) provided in the center inside both optical end faces. End face (11
A plurality of striped branch waveguides (13) are arranged in parallel toward a) and (11b), and particularly, the branch waveguides (13) are connected from the respective optical end faces (11a) and (11b) to a connecting portion. It has a structure in which the width is smoothly and continuously widened toward (12), and further, each branch on the optical end facet (11a) side is connected to the connecting part (12) side end and each optical end facet (11b) side branch. The end portion of the waveguide on the side of the coupling portion (12) is arranged so as to be spaced apart from each other while maintaining a predetermined distance L ₂ in the waveguide length direction.

[Action]

As described above, in the present invention, an array type semiconductor structure having a multi-light emitting structure provided with a plurality of branch waveguides (13) is adopted, and each branch waveguide (13)
By making the width wider toward the connecting part (12), the mutual coupling of light in the central connecting part (12) is surely achieved so that the phase locking is assured, and thereby the half width of the FFP is narrowed. Is made.

〔Example〕

An example of the semiconductor laser according to the present invention will be described in detail with reference to FIGS. 2 and 3. In this example, the structure is a gain guide type structure, and the waveguide (11) has the pattern described in FIG. FIG. 2 is an enlarged schematic plan view in which a part of the semiconductor laser according to the present invention is cut away.
FIG. 3 is an enlarged schematic sectional view taken along line AA of FIG.

In the illustrated example, on a n-type semiconductor substrate, for example, a GaAs semiconductor substrate (21), an n-type semiconductor layer of the same conductivity type as the first clad layer (22) made of GaAlAs and an active layer made of GaAs, for example, are used. The layer (23), the second clad layer (24) made of a p-type conductivity type different from that of the first clad layer (22), eg, GaAlAs, and the p-type conductivity type of the same, for example, GaAs. The cap layer (25) and the cap layer (25) are sequentially formed by a well-known technique such as MOCVD (Metal-Organic Chemical Vapor Deposition) or MBE (Molecular Beam Epitaxy), and the cap layer (25) is selectively exposed to, for example, protons or By ion-implanting boron, the current confinement means consisting of the high resistance current interruption region (26) is formed.
In the current cutoff region (26), for example, a current path (30) having a corresponding pattern is formed so that the waveguide (11) having the pattern shown in FIG. 1 can be formed in the active layer (23). As a result, the waveguide (11) shown in FIG. 1 is formed in an inverted pattern. Reference numerals (27) and (28) denote electrodes deposited on the cap layer (25) and the back surface of the substrate (21).

When a forward voltage is applied between the electrodes (27) and (28) in such a configuration, the current is cut off at the portion where the current cutoff region (26) is provided, and the current cutoff region (26)
By selectively forming a current path (30) in a portion where no gate is provided, a gain guide type waveguide (11), that is, an optical resonator having the pattern shown in FIG. 1 is formed in the active layer (23). It

The waveguide (11) has a striped branch waveguide (13) extending from the connecting portion (12) toward both optical end faces (11a) and (11b) as shown in FIG. The width Ws at each light end facet (11a) and (11b) and each light end facet (11
The distance Ds between the intervals a) and (11b) may be Ws = Ds = 4 μm, and the pitch Ps may be selected to be 8 μm. The length L ₁ of each branch waveguide (13) is, for example, 110 μm, and the connecting portion (12)
The length L ₂ can be selected to be 30 μm, for example. Further, in the illustrated example, when the branch waveguide (13) of the one side method and the branch waveguide (13) of the other side with respect to the central coupling portion (12) are displaced by a half pitch, one branch waveguide This is a case where the number Nb of the other branching waveguide (13) is selected as (Na-1) when the number of (13) is Na. Then, in each branch waveguide (13), side faces that are gradually wider from the optical end faces (11a) and (11b) toward the central connecting part (12), for example, adjacent side faces on the central connecting part (12) side, respectively. To be coincident, the gap between the adjacent branch waveguides (13) can be formed to have, for example, an isosceles triangle, but each side of the triangle of the gap, that is, both sides of each branch waveguide (13). Is not limited to a straight line, but may have a curved shape.

In the above example, the high resistance current interruption region (2
6) is provided, and the waveguide (1
1) is generated in the active layer, the n-type impurity is selectively ion-implanted or diffused to the depth reaching the cap layer (25) and the clad layer (24) as the current blocking region (26). Then, various gain guide type configurations can be adopted such as forming a current blocking region by a pn junction.

The semiconductor laser according to the present invention may have not only a gain guide type structure but also a refractive index guide type structure, for example. An example of this case will be described with reference to FIG. In FIG. 4, the portions corresponding to those in FIG. 3 are designated by the same reference numerals and the duplicate description is omitted, but in this case, the light from the active layer (23) is absorbed in the second cladding layer (24). And, in some cases, also has a current interruption effect, for example n
A light guide region of a refractive index guide type can be formed in the active layer (23) by providing a light absorption region (29) of a mold. That is, even in this case, the pattern of the light absorption layer (29) is
For example, it is formed in a pattern that is the reverse of the waveguide pattern described in FIG. 1, and the waveguide is formed immediately below the light absorption layer (29).

Further, in the waveguide described in FIG. 1, there is a case where one and the other branch waveguides (13) sandwiching the coupling portion (12) are displaced from each other by a half pitch. It is also possible to have a structure in which both branch waveguides are arranged in a straight line with the same number.

Further, the invention is not limited to the gain guide type semiconductor laser or the refractive index guide type semiconductor laser shown in FIGS. 3 and 4, but a semiconductor laser having various gain guide type or refractive index guide type or a guide type structure by a combination thereof. The present invention can be applied to.

Further, a semiconductor laser having a conductivity type opposite to the conductivity type of each part shown in FIGS. 3 and 4 can be used.

〔The invention's effect〕

As described above, the present invention has a multi-light emitting type high power semiconductor laser structure in which a plurality of branch waveguides (13) are arranged. By making each branch waveguide (13) wider toward the connecting portion (12), the coupling between the branch paths is strengthened, which strengthens the optical electric field distribution of the 0th mode and at the same time ensures phase locking. The full width at half maximum of the FFP will be narrowed depending on what was done. Further, as described in FIG. 1, when the branched waveguides on both sides of the connecting portion (12) are shifted by a half pitch, the 0th mode is apt to occur and a semiconductor laser showing a single-peak FFP is surely constructed. be able to.

[Brief description of drawings]

FIG. 1 is a schematic pattern diagram of a waveguide of an example of a semiconductor laser according to the present invention, FIG. 2 is an enlarged plan view of a partially cutaway example of a semiconductor laser according to the present invention, and FIG. -A
FIG. 4 is an enlarged cross-sectional view of the semiconductor laser according to the present invention, FIG. 5 is a waveguide pattern diagram of a conventional array-type semiconductor laser, and FIG. 6 is a far-field pattern diagram thereof. FIG. 7 is a pattern diagram of a waveguide of a conventional semiconductor laser, and FIG. 8 is a far field pattern diagram thereof. Reference numeral (11) is a waveguide, (12) is a connecting portion, and (13) is a branching waveguide.

Claims (1)

[Claims] 1. A plurality of striped branch waveguides are arranged from a connecting portion provided at an intermediate portion of the waveguide toward a first optical end surface and a second optical end surface facing each other, respectively. The branch waveguide is widened toward the connecting portion, and the end portion on the connecting portion side of the branch waveguide on the first optical end face side and the branch waveguide on the second optical end face side, Characterized by strengthening the optical coupling between the branch waveguides and maintaining the spacing for securing the phase locking in the waveguide length direction so that they are spaced from each other, and narrowing the half-width of the far-filled pattern. And a semiconductor laser.