JPH0525192B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to transverse mode control of a phase-locked integrated laser.

[Conventional technology]

Figure 3 is an example of Applied Physics Letters.
Volume 46, pp. 136-138 (Appl.Phys.Lett.vol.16pp.136-
138) is a cross-sectional view of the conventional integrated semiconductor laser shown in Figure 1, where 1 is an n ⁺ -InP substrate and 2 is a 2
- Inp lower cladding layer, 3 is InGaAsP active layer, 4 is p-InP upper cladding layer with three striped grooves, 5 is p-InGaAsP buried layer with forbidden band width between active layer 3 and InP. layer, 6 is a p-side electrode,
7 is an n-side electrode, 8 is a striped groove embedded part,
Reference numeral 9 denotes a waveguide region formed in a portion of the active layer 3 directly below the buried trench portion 8 .

Next, the operation will be explained. positive to the p-side electrode 6;
When a negative voltage is applied to the n-side electrode 7, holes are injected into the active layer 3 from the upper cladding layer 4 and electrons are injected from the lower cladding layer 2, and both are injected into the active layer 3 by the barrier of the double heterostructure. trapped and radiatively recombines. The generated light is confined near the waveguide region 9 by the refractive index distribution formed in the vertical and horizontal directions of the pn junction.

Here, when the three stripes are adjacent to each other within about 10 μm, the three lasers are not independent but optically coupled, and as a result, maintain a constant phase relationship at the same wavelength, resulting in so-called phase-locked oscillation. When multiple waveguides are coupled in this way, even if each waveguide alone propagates only the fundamental mode, the eigenmode (array mode) of the composite waveguide is the number of waveguides. only exists. Figure 4a,
b shows the electric field distribution and light intensity distribution of the triple waveguide, respectively. In the figure, ν is the number of the array mode, and ν=1 is the basic array mode. An integrated laser can oscillate in any of these three modes if the gain for each mode is equal.

[Problem that the invention seeks to solve]

Conventional integrated lasers can oscillate in three array modes because the current flows approximately uniformly across the complex waveguide region, so that the modal gain for each array mode is approximately equal. When oscillating in a high-order array mode, the far-field pattern becomes bimodal and the output beam angle becomes wide, making the output angle in the array direction (parallel to the pn junction) extremely narrow. There was a problem that the original characteristics of the laser could not be brought out.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain an integrated semiconductor laser that can oscillate in a fundamental array mode and can reduce operating current.

[Means for solving problems]

In the integrated semiconductor laser according to the present invention, a stripe-shaped separating portion having a width narrower than the width of the composite waveguide region and extending along the stripe direction of the waveguide region is located at a position opposite to the central portion of the composite waveguide region. The current blocking layer limits the current injected into the composite waveguide region, and the gain distribution in the plane perpendicular to the stripes is high in the central part of the composite waveguide region. It has a chevron-shaped shape that is sufficiently low on both sides.

[Effect]

In this invention, the current injected into the composite waveguide region is limited by the current blocking layer, and the gain distribution in the plane perpendicular to the stripes is high in the center of the composite waveguide region and sufficiently low on both sides. Because it has a mountain-shaped shape, the gain of high-order array modes that have peaks of light intensity distribution at both ends of the composite waveguide region is limited, and the light intensity distribution is reduced at the center of the composite waveguide region. Since the mode gain of the fundamental array mode having a large peak is the largest among the plurality of array modes, oscillation in the fundamental array mode can be realized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, 21 consists of p ⁺ -InP,
This is a current blocking layer having a centerline in the center of the array and striped separation portions 22 having a width narrower than the width of the entire array. Further, numerals 1 to 9 indicate parts equivalent to those of the conventional example shown in FIG.

Next, the operation will be explained.

The operations from voltage application, carrier injection into the active layer, light emission and waveguide in the active layer to phase synchronized oscillation are the same as in the conventional example. In this embodiment, the pn junction between the n-InP lower cladding layer 2 and the p ⁺ -InP current blocking layer 21 is reverse biased, so that current flows only through the isolation portion 22. That is, the current is confined near the center of the array. By appropriately selecting the width of the separation portion 22 and the thickness of the lower cladding layer, the lateral current distribution and therefore the gain distribution in the active layer 3 can be formed into a mountain shape as shown in FIG. As a result, the gain of the high-order array mode, which has a peak in the optical intensity distribution at both ends of the composite waveguide region, is limited, and the fundamental array mode, which has a large peak in the optical intensity distribution at the center of the composite waveguide region, is limited in gain. The basic mode is selected as the array mode because the mode gain is the largest among the plurality of array modes. Therefore, with this device, the transverse mode can be controlled to the fundamental mode, and a high-power semiconductor laser with a narrow output beam can be obtained.

In the above embodiment, a triple integrated semiconductor laser has been described, but the same effect can be obtained even in the case of four or more, if the gain distribution is close to the envelope of the light intensity distribution of the fundamental array mode. play.

In addition, in the above embodiment, the cladding layer and the active layer are
Although we have explained the case of InP and InGaAsP, Al _x Ga _1-x As crystal (0<x<
1) may be used to form the same structure.

〔Effect of the invention〕

As described above, according to the present invention, the gain distribution in the plane perpendicular to the stripes has a peak that is high at the center of the composite waveguide region and sufficiently low on both sides so that the mode gain for the fundamental array mode is maximized. Since it is configured to have a mold shape, the transverse mode can be controlled to the fundamental mode, and a high-power integrated semiconductor laser with a narrow output beam can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional front view showing an integrated semiconductor laser according to an embodiment of the present invention, FIG. 2 is a cross-sectional front view showing the gain distribution of the device of the above embodiment, and FIG. 3 is a cross-sectional front view showing a conventional integrated semiconductor laser. 4 are diagrams showing the electric field distribution and light intensity distribution in the array mode of the above embodiment device and the conventional device. 9... Waveguide region, 21... Current blocking layer, 22... Separation part. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. In a phase-locked integrated semiconductor laser having a composite waveguide region in which a plurality of striped waveguide regions are formed adjacent to each other, a semiconductor laser having a width narrower than the width of the composite waveguide region is provided. An integrated semiconductor laser comprising: a current blocking layer in which a stripe-shaped separating portion along the stripe direction of the waveguide region is provided at a position facing a central portion of the composite waveguide region.