JP2742100B2 - Mask semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mask semiconductor laser used for a point light source of a magneto-optical memory, for example.

2. Description of the Related Art An example of a conventional mask semiconductor will be described.
An opaque light-shielding mask layer is formed on the light emitting end face of the semiconductor laser by vapor deposition, sputtering, or the like. By using an etching (dry, wet) technique or a heating and evaporating technique by light emission of the semiconductor laser itself, a part of the mask layer is removed or made optically transparent to form an opening for light emission. Is provided.

And by having such a configuration, the output beam emitted from the semiconductor laser is passed through an opening formed in a part of the mask layer to form an output beam having a small diameter of about the wavelength or less, Thus, recording and reproduction of high-density information are performed.

Problems to be Solved by the Invention In the mask semiconductor laser as described above, the outgoing beam emitted from the semiconductor laser generally has an elliptical cross-sectional shape, and the size of the opening provided in the mask layer is reduced. By restricting, a small outgoing beam of about the wavelength or less is obtained. However, in this case, due to the wave nature of light, the power of light passing through an opening having a diameter equal to or less than the wavelength becomes extremely weak, and the light source does not have sufficient light quantity. Even if it is made small, it is not possible to obtain a minute spot with effective power.

Means for Solving the Problems Therefore, in order to solve such a problem, the present invention provides a light-shielding mask layer formed on a light-emitting end face of a semiconductor laser, and a light-emitting mask layer is formed on a part of the mask layer. In the mask semiconductor laser provided with the opening, the major axis of the opening in the direction parallel to the active layer of the semiconductor laser is shorter than the minor axis of the elliptical emission beam emitted from the semiconductor laser, and It was formed to have a length equal to or longer than the wavelength of the output beam.

Action By this, the ellipticity of the emitted beam emitted from the semiconductor laser is improved and the beam shape becomes more circular,
In addition, since the beam diameter is smaller than the conventional beam diameter, spatial coherence can be improved, and sufficient light output can be obtained because the major axis of the aperture is about the wavelength of the output beam or longer.

Embodiment An embodiment of the present invention will be described with reference to FIG. A light-shielding mask layer 2 is formed on the light-emitting end face 1a of the semiconductor laser 1, and a light-emitting opening 3 is formed in a part of the mask layer 2.
Is provided. The semiconductor laser 1 in this opening 3
The major axis in the direction A parallel to the active layer of the semiconductor laser 1
Shorter than the minor axis of the elliptical outgoing beam emitted from
Moreover, it is formed to have a length equal to or longer than the wavelength of the emitted beam.

Therefore, the reason why the major axis of the opening 3 is set to the above-described length will be described in order below. First, a beam shaping method will be described. FIG. 2A shows the light emitting end face 1a.
3 shows the shape of the opening 3 as viewed from the side. The beam indicated by the broken line indicates the emitted beam 4 when the mask layer 2 is not formed, and at this time, the beam has a long elliptical shape. In order to improve the elliptic ratio (major axis / minor axis) of the beam shape so as to approach 1 as much as possible, the shape of the opening 3 is made circular as shown in FIG. You only have to block it. FIG. 2 (b) shows the shape of the output beam 4 when passing through the circular opening 3.
Shown in

Next, FIG. 3A shows an example in which the shape of the opening 3 formed in the mask layer 2 is elliptical. Usually, since the beam diameter in the thickness direction of the active layer of the semiconductor laser 1 is smaller than the beam diameter in the direction parallel to the active layer, even if the diameter of the circular opening 3 as described above is simply increased, In this case, the output beam 4 does not become circular. Therefore, by changing the elliptic ratio in a state where the minor axis of the outgoing beam 4 shown by the broken line and the minor axis of the elliptical opening 3 are almost matched, the outgoing beam as shown in FIG. 4 can be controlled. However, in this case, the minor axis of the elliptical opening 3 is slightly longer than the wavelength of the output beam 4. Thus, by forming the opening 3 having a wavelength larger than the wavelength, the shape of the opening 3 and the shape of the output beam 4 become substantially equal.

Next, FIG. 4A shows an example in which the major axis of the opening 3 is about the wavelength of the output beam 4 and the minor axis is shorter than the wavelength. When the short diameter of the opening 3 is equal to or smaller than the wavelength, the output beam 4 passing through the opening 3 does not become smaller in proportion to the shape of the opening 3 as shown in FIG. A circular beam whose diameter is about the wavelength is obtained. Even when the major axis of the opening 3 is smaller than the wavelength, the shape of the output beam 4 is a circular beam having a diameter of about the wavelength, and is not affected by the aperture shape.

However, when the major axis of the opening 3 becomes shorter than the wavelength, the intensity of the output light sharply decreases, the power transmittance decreases, and sufficient power for the semiconductor laser 1 cannot be obtained. Usually, since the oscillation mode of the semiconductor laser 1 is the TE mode, the direction of oscillation of the electric field is the direction A parallel to the active layer. Therefore, if the length in the direction A, that is, the major axis direction of the elliptical opening 3 is approximately the wavelength, a sufficient light intensity can be obtained even if the minor axis direction is shorter than the wavelength.

Therefore, for the reason described above, the major axis of the opening 3 in the direction parallel to the active layer of the semiconductor laser 1 is
The length of the output beam 4 is shorter than the minor axis of the elliptical output beam 4 and longer than the wavelength of the output beam 4.

Hereinafter, specific examples will be sequentially described. FIG. 5A shows a far field pattern of the conventional semiconductor laser, and FIG. 5B shows a far field pattern of the mask semiconductor laser of this embodiment. In the conventional semiconductor laser, the spread angle in the vertical direction B is much larger than the spread angle in the direction A (horizontal direction) parallel to the active layer. On the other hand, the spread angles of the mask semiconductor lasers are almost the same, which indicates that the output beam 4 is substantially circular. In this case, the opening diameter of the mask semiconductor laser is 0.8 μm.
It has an elliptical shape of about mx 0.45 µm.

Next, FIG. 6 shows the relationship between the opening diameter of the mask semiconductor laser and the ratio of the active layer having the full width at half maximum of the far field pattern in the two directions of the vertical direction B and the horizontal direction A. However, the oscillation wavelength is λ = 0.78 μm, and the shape of the opening 3 is an oblong shape long in the horizontal direction A. Further, the ratio of the spread angle measured in the full width at half maximum of the far field pattern between the horizontal direction A and the vertical direction B is calculated as the elliptic ratio B / A of the far field pattern.
And At this time, in FIG. 6, if the major axis (pinhole diameter) in the horizontal direction A is larger than the wavelength λ, FIG.
From the relationship (b), the elliptic ratio becomes 1 as the major axis increases.
However, the elliptic ratio becomes a value close to 1 below the wavelength λ. On the other hand, in the case of the conventional semiconductor laser, the elliptic ratio is about 3. As a result, the ellipticity of the far-field pattern is almost the same as that of the near-field pattern due to Fraunhofer diffraction.
Since it corresponds to the reciprocal of the elliptic ratio of 1a, it can be seen that the emitted beam 4 becomes circular when the diameter of the emitted beam 4 is about the wavelength or less. The minor diameters of the openings 3 are all smaller than or equal to the wavelength.

Next, FIG. 7 shows the relationship between the optical output when a current of 85 mA flows through the mask semiconductor laser and the major axis (lateral axis) of the opening 3. It can be seen that the laser light output after passing through the opening 3 has a sufficiently large value when the major axis of the opening 3 is larger than the wavelength λ, but the light output becomes smaller when the wavelength is smaller than the wavelength.

Therefore, as can be understood from the specific examples described above, in order to make the elliptic ratio of the outgoing beam 4 close to 1 and obtain a sufficient light output, the major axis of the opening 3 should be larger than the minor axis of the outgoing beam 4. The object can be achieved by making the length of the output beam 4 shorter and longer than the wavelength of the output beam 4.

As a method of manufacturing the mask semiconductor laser, a mask material that is opaque to the wavelength of the light source is formed on the end face of the semiconductor laser 1 by a method such as vapor deposition, coating, sputtering, or CVD. The opening 3 is formed in a part of the substrate by etching (dry, wet) by photolithography, heating and evaporating by condensing the laser beam from the outside, or heating and evaporating by light emission of the semiconductor laser itself. It can be manufactured by the following. Therefore, the opening 3 in this embodiment can be obtained by controlling the manufacturing conditions by such a method.

The present invention provides a mask semiconductor laser in which a light-shielding mask layer is formed on a light-emitting end face of a semiconductor laser and an opening for light emission is provided in a part of the mask layer. Is formed so that the major axis in the direction parallel to the active layer is shorter than the minor axis of the elliptical emission beam emitted from the semiconductor laser and is longer than the wavelength of the emission beam. The ellipticity of the emitted beam is improved and a more circular beam shape can be obtained. In addition, since the beam diameter is smaller than the conventional beam diameter, the spatial coherence can be further improved, and the long diameter of the aperture can be improved. Is about the wavelength of the output beam and longer than that, so that a sufficient light output can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIGS. 2 to 4 are explanatory views for explaining the basic principle of the structure of the present invention, and FIG. 5 is a conventional semiconductor laser and mask semiconductor laser. Waveform diagram showing the comparison of the far field pattern with
FIG. 6 is a characteristic diagram showing how the far-field pattern elliptic ratio changes with respect to the major axis of the opening, and FIG. 7 is a characteristic diagram showing how the optical output varies with the major axis of the opening. DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser, 1a ... Light emitting end face, 2 ... Mask layer, 3 ... Opening, 4 ... Outgoing beam, A ... Direction parallel to active layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ning Ide 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Masato Hariya 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. (72) Inventor Hiroshi Kobayashi 3-15-15 Hanakoganei, Kodaira-shi, Tokyo (72) Inventor Haruhiko Machida 4-107-7 Nakaochiai, Shinjuku-ku, Tokyo (56) References -785 (JP, A)

Claims (1)

(57) [Claims] 1. A mask semiconductor laser in which a light-shielding mask layer is formed on a light-emitting end face of a semiconductor laser and an opening for light emission is provided in a part of the mask layer. The major axis in the direction parallel to the active layer is
A mask semiconductor laser, wherein the mask semiconductor laser is formed so as to be shorter than a minor axis of an elliptical emission beam emitted from the semiconductor laser and to have a length equal to or longer than a wavelength of the emission beam.