JP2846668B2 - Broad area laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having an emission width of several tens to several hundreds μm and used for optical information processing, laser processing, and the like.

2. Description of the Related Art As the application field of the semiconductor laser expands, a demand for higher output of the semiconductor laser has been increasing in recent years. Currently, a semiconductor laser array and a broad area laser are known as those capable of obtaining a watt-class optical output.

Here, in the former, a large number of waveguides are arranged side by side by shortening the distance between the waveguides, laser light is coupled between adjacent waveguides, and the position of all the waveguides is synchronized to increase the output. It is intended. However, such a configuration has a problem that the far-field pattern is bimodal in many cases, and the manufacturing process is complicated.

On the other hand, the latter takes a wide waveguide width of several tens to several hundred μm,
Higher output is achieved by increasing the light emitting area of the laser emitting end face. Because of this simple structure,
There is an advantage that the manufacturing process can be simplified as compared with the former. However, since the oscillation transverse mode is multi-mode or filament oscillation, there is a problem that light cannot be focused on a small spot. For this reason, applications have been limited to use for energy sources and the like.

In order to control the oscillation lateral mode of the broad area laser (to make it a fundamental mode), a proposal has been made to provide a high-reflection portion at the center of the front end face (RTM-88-25, Report of the Laser Society of Japan RTM-88-25).

Problems to be Solved by the Invention However, such a structure has a problem that fine processing is required on the end face, so that the structure is difficult and lacks mass productivity.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a broad area laser capable of controlling an oscillation transverse mode and having excellent mass productivity.

Means for Solving the Problems In order to achieve the above object, the present invention provides a first region, a first region and a second region in which the equivalent refractive index decreases stepwise from the center toward both sides within the current injection width of the waveguide. A broad area laser in which a second region and a third region are sequentially formed, wherein a thickness of the cladding layer in the second region is larger than a thickness of the cladding layer in the third region;
An optical guide layer having a larger equivalent refractive index in the second region than the third region, a larger refractive index than the cladding layer in the second region, and a narrower width than the current injection width. By providing the first region, the equivalent refractive index of the first region is made larger than that of the second region.

The present invention also provides a broad area laser in which a cladding layer is formed on an active layer of a waveguide, wherein a current is applied to the active layer at a position approximately 0.4 to 0.7 μm above the cladding layer except for the center of the waveguide. A semiconductor layer having a conductive type capable of being injected and having a large absorption coefficient with respect to an oscillation wavelength is formed.

Operation Since the conventional broad area laser has no refractive index difference in the direction parallel to the pn junction in the waveguide, it oscillates in a number of transverse modes in addition to the fundamental transverse mode as shown in FIG. Either multi-mode oscillation or filament-shaped oscillation is caused by slight unevenness in composition or film thickness.

However, if the equivalent refractive index decreases stepwise from the center of the waveguide toward both ends as in the first invention, even if the current injection width is, for example, several tens to several hundreds μm, As shown in FIG. 2, the generated light is more likely to collect at the center of the waveguide, and it is possible to prevent filament oscillation. Further, it is possible to suppress an increase in the thickness of the semiconductor layer such as the cladding layer.

According to the second aspect, oscillation in the fundamental transverse mode is likely to occur for the following reason.

That is, the m-order transverse mode gain is generally expressed by the following equation (1), but as shown in FIG. 1, the light intensity of the higher-order mode has a large peak in a region closer to the end than the center of the waveguide. ing.

I _m (y): light intensity distribution in the active layer in the horizontal direction to the junction (m-order mode) g (y): gain distribution in the active layer in the horizontal direction to the junction If a semiconductor layer having a large absorption coefficient with respect to the oscillation wavelength is provided at a portion at a predetermined distance from the active layer at the end of the waveguide, a part of light generated in a region near both ends in the waveguide is provided. Absorbed by the semiconductor material. Therefore, as shown in FIG. 3, since the gain is suppressed in these regions, the mode gain of the higher-order mode is smaller than that of the fundamental mode, and oscillation in the fundamental transverse mode is more likely to occur.

As in the third aspect of the present invention, when the carrier injection amount in the central portion of the waveguide is larger than that in the other regions, the current inflow into the central portion of the waveguide is increased, and oscillation is easily performed. Further, at this time, as shown in FIG. 4, there is a peak of the light intensity of the fundamental transverse mode at the center of the waveguide. Therefore, according to the third aspect of the present invention, the state in which the fundamental transverse mode oscillates most easily is obtained.

Embodiment An embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 1, a 2.0 μm-thick n-type Ga _0.58 Al
_0.42 As clad layer [Se-doped, n = 5 × 10 ¹⁸ c
m ⁻³ ] 2 and an active layer (non-doped) 3 made of Ga _0.94 Al _0.06 As having a thickness of 0.08 μm, and a p-type Ga _0.58 Al having a thickness of 0.2 μm
_0.42 As cladding layer [Zn-doped, p = 2 × 10 ¹⁸ c
m ^-3 ] 4 are formed in order. An optical guide layer [Zn-doped, p = 2 × 10 ¹⁸ cm ⁻³ ] 5 made of p-type Ga _0.70 Al _0.35 As is formed on a part of the clad layer 4. On the cladding layer 4, p-type Ga _0.58 Al
_0.42 As cladding layer [Zn-doped, p = 2 × 10 ¹⁸ c
m ^-3 ] 6 is provided. This clad layer 6 has a thickness (t ₂ = 2.0 μm) at the center (near the light guide layer 5) in the figure.
Is formed to be larger than the thickness (t ₁ = 0.4 μm) at the end in the figure. 0.5 μm thick on the cladding layer 6
m-type cap layer made of p-type GaAs [Zn-doped, p = 5 × 10
¹⁸ cm ⁻³ ] 7, and an insulating layer 8 made of SiO ₂ is provided in a portion other than the current injection portion in the cap layer 7. A front electrode 9 is provided on the surface of the insulating layer 8 and the cap layer 7 on which the insulating layer 8 is not provided, and a back electrode 10 is formed on the back surface of the substrate 1.

In the cladding layer 6 and the cap layer 7, a portion corresponding to the light guide layer 5 is formed with a Zn diffusion region 11 in which the carrier concentration is increased by Zn diffusion, and the Zn diffusion region 11 has a depth of 0.5 to 0.5. It is configured to be 0.7 μm.

In the above embodiment, the current injection width (SiO ₂ layer 8
Width) W ₁ of the portion not provided it is set to 150 [mu] m, and the width of a portion cladding layer 6 is raised (the width of the absorption loss is small area) W ₂ is 90 [mu] m, the width of the portion corresponding to the light guide layer 5 W ₃ is set to 25μm.

Further, as the epitaxial crystal growth method of the example, a thin-film MO-CVD method and an MBE method with good uniformity were used, and in addition, a device was manufactured by using a photolithography technique.

Here, according to the present embodiment, the equivalent refractive index is the region C (the thin portion of the cladding layer 6) <the region B (the portion where the light guiding layer 5 is not included in the thick portion of the cladding layer 6) <the region A (the light guiding layer). 5). As described above, if the equivalent refractive index decreases stepwise from the center of the waveguide toward both ends, the generated light is more likely to be collected at the center of the waveguide, and filament oscillation can be prevented.

In the region C, light generated in the active layer 3 slightly absorbs into the cap layer 7 and is absorbed. Here, the thickness t ₁ of the cladding layer 6 provided below the cap layer 7, in the above embodiment is of a 0.4μm but no more light absorption of t ₁ at small to the region C to oscillate increases This causes an increase in the threshold value and a decrease in the external differential quantum effect. on the other hand,
When t ₁ is larger than 0.7 μm, the light does not reach the cap layer 7, and the light does not substantially differ from the region B. Therefore, t ₁
The thickness is preferably 0.4 μm or more and 0.7 μm or less.

Further, although light confinement in the active layer is poor in the region A, the provision of the Zn diffusion region 11 can prevent a decrease in gain in the region A and can create a high carrier injection state. This facilitates oscillation in the region A where the peak of the basic transverse mode exists, and thus facilitates oscillation of the basic transverse mode in the broad area laser.

The thickness of the light guide layer 5 is desirably 0.4 μm in consideration of the refractive index difference between the regions A and B, the cutoff condition of the higher-order mode in the vertical and transverse modes, and the like.

Further, in the present embodiment, a GaAlAs-based DH laser has been described as an example, but the present invention is not limited to this, and an InGaAlP-based, InGa
Semiconductor laser of other materials such as AsP system, quantum well structure, SCH
It can be applied to a semiconductor laser having a structure.

Effects of the Invention As described above, according to the present invention, it is possible to obtain an optical output of several hundred to several thousand mW, and it is possible to control the transverse mode. Therefore, a high-power laser beam can be converged on one point by a lens or the like, so that it is possible to apply to a wide range of fields such as micromachining using a laser and optical information processing.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a broad area laser according to an embodiment of the present invention, and FIG. 2 is a pn of the broad area laser according to the present invention.
FIG. 3 is a graph showing the distribution of the refractive index in the horizontal direction with the junction; FIG. 3 is a graph showing the distribution of the absorption loss and the gain of the laser of the present invention;
FIG. 4 is a graph showing a transverse mode distribution of a conventional broad area laser. 1 ... substrate, 2 ... cladding layer, 3 ... active layer, 4 ...
Clad layer, 5: light guide layer, 6: clad layer, 7
…… Cap layer, 8 …… Insulating layer, 9,10 …… Electrode, 11…
Zn diffusion region.

Claims (2)

(57) [Claims] A first region, a second region, and a third region are formed in order so that an equivalent refractive index decreases stepwise from a central portion toward both sides within a current injection width of a waveguide. An equivalent refractive index of the second region rather than the third region by making the thickness of the cladding layer of the second region thicker than the cladding layer of the third region. And providing a light guide layer having a refractive index larger than that of the cladding layer in the second region and narrower than the current injection width in the first region, so that the first region has a smaller refractive index than the second region. A broad area laser, wherein an equivalent refractive index of the first region is increased. 2. A broad area laser in which a cladding layer is formed on an active layer of a waveguide, wherein the cladding layer except for a central portion of the waveguide has a thickness of about 0.4 to less than 0.4%.
A broad-area laser, wherein a semiconductor layer having a conductivity type capable of injecting current into the active layer and having a large absorption coefficient with respect to an oscillation wavelength is formed at a position 0.7 μm above.