JP2672710B2 - Optical amplifier and optical integrated circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical amplifier used for optical information processing, optical communication and the like, and an optical integrated circuit thereof.

2. Description of the Related Art As an optical amplifier performance, an optical amplifier having a short element length and a large amplification gain has been recently demanded. As a conventional example, there is a method of increasing the gain by using a zigzag waveguide as shown in FIG. That is, the input light is repeatedly reflected at the end face and is amplified,
A large gain can be obtained with a short element length. In this case, the incident angle of the laser light traveling in the waveguide with respect to the end face is larger than the critical angle so that the laser light is totally reflected at the bent portion.

SUMMARY OF THE INVENTION However, in such an optical amplifier, the output light is
Only one final spot is available. With GaAlAs-based materials that are often used as optical amplifiers, the optical output is limited by the optical density at the end face.Therefore, even if the number of zigzag waveguides is increased in the conventional configuration, the light output above the destruction level No output is available. Also, in the backward direction of the element,
Since no output light is emitted, it is also impossible to extract monitor light.

Means for Solving the Problems In view of the above drawbacks, the optical amplifier of the present invention is configured such that the incident angle of the laser light traveling in the waveguide with respect to the end face is smaller than the critical angle.

FIG. 1 shows the principle of the optical amplifier of the present invention. That is, in this optical amplifier, laser light traveling in the waveguide is output from a plurality of end faces.

Action With the above configuration, the laser light traveling in the waveguide is not totally reflected at the end face. Therefore, from the front side, the light output can be extracted from a plurality of spots, so that a higher output can be obtained as compared with the conventional one. Further, since the light output can be taken out from the rear side, it is possible to obtain the monitor light.

Embodiment FIG. 2 shows a structural diagram of an optical amplifier in an embodiment of the present invention. The above figure is a top view and is shown by broken lines so that the internal zigzag stripe portion can be seen. The following figure is a front view seen from the output side. p-GaAs substrate 1,
There is an n-GaAs current blocking layer 2 having a stripe portion 7 reaching the substrate 1 in a zigzag shape, and p-
GaAlAs clad layer 3, GaAlAs layer 4, n-GaAlAs layer clad layer
5, n-GaAs contact layer 6 is formed.

The current is injected only into the stripe portion 7, and optical amplification occurs in the active layer 4 above it. As shown in the above figure, the stripe portion is formed in a zigzag shape, and when laser light is input to one stripe portion on the input side, optical amplification occurs along this path, and a plurality of stripes on the output side are generated. The amplified light output is extracted from the stripe. Each stripe width is 6 μm
It is. Since this optical amplification is traveling wave type amplification, all the light from each stripe has the same phase, and from the output end,
A single mode light output is obtained. The angle formed by each zigzag stripe with the end face is an angle at which light in the stripe does not undergo total internal reflection at the end face, that is, a critical angle of 17 ° or less. In this embodiment, the angle is 5 °.

In this case, the outgoing beam direction is inclined by 15 ° from the front of the outgoing end according to Snell's law. Further, in FIG. 2, only the end face of one stripe on the input side is formed so as to be orthogonal to the stripe so that it is easy to input, but at an angle at which the input light does not totally reflect at the input end,
It does not matter as long as the input light enters the stripe parallel to the stripe.

FIG. 3 shows a diagram in which an optical amplifier according to an embodiment of the present invention is formed on the same substrate as a semiconductor laser. A semiconductor laser is formed on the same substrate on the input side of the optical amplifier shown in FIG. Since each stripe is formed on the same substrate by the photolithography technique, the positions and angles of the output end of the semiconductor laser and the input end of the optical amplifier can be accurately controlled, and it is not necessary to assemble and align them individually. The separation groove 8 electrically separates the semiconductor laser and the optical amplifier, and each element can be independently driven. Therefore, the wavelength is controlled by the current flowing through the optical amplifier and the optical output by the current flowing through the semiconductor laser. be able to.

Further, the stripe width of the semiconductor laser and the optical amplifier is narrow enough to maintain a single transverse mode, 6 μm, and
Since the optical amplifier performs traveling wave type amplification, the optical output from the optical amplifier is also single mode light.

With the above configuration, a light source with high output in a single transverse mode
Obtained with one chip.

FIG. 4 shows a process of manufacturing an optical integrated device including an optical amplifier and a semiconductor laser in one embodiment of the present invention. As shown in FIG. 4 (a), n-GaAs2 is crystal-grown on the p-GaAs substrate 1, and a photolithography technique is used to grow it.
A zigzag stripe to be a current injection portion is formed by etching as shown in FIG. On top of that, a double hetero pn junction is formed into a fourth layer by liquid phase epitaxy.
After being formed as shown in FIG. 4C, the separation groove 8 reaching the substrate 1 is formed by etching again using the photolithography technique (FIG. 4D). This etching is performed so that the end faces of the semiconductor laser and the optical amplifier are perpendicular to the substrate face at the double hetero pn junction. Finally,
Again, the electrodes are formed on the semiconductor laser section and the optical amplifier section by using the photolithography technique, and the electrodes are also formed on the substrate side.

In this embodiment, the number of stripes in the emission part of the optical amplifier is three, but any number may be used.

FIG. 5 shows the input / output characteristics of the optical amplifier of the present invention. This is the result when a constant current is supplied to the optical amplifier and the input of the semiconductor laser is changed. The element length of the optical amplifier
Even when it was as short as 200 μm, the output was over 200 mW, and linear characteristics were obtained with respect to the input. It can be seen that a high output is obtained as compared with the case of the conventional amplifier (FIG. 8). A horizontal far-field image and a longitudinal mode characteristic are
Shown in Figs. It can be seen that oscillation is in a single transverse mode and vertical mode. The output beam direction from the optical amplifier is output at an angle according to Snell's law with respect to the output end, and this angle is determined by the positional relationship between the zigzag stripe and the output end, the shape, and the refractive index. Can be controlled. In the case of this embodiment, since θ = 5 ° (FIG. 2), the direction of the outgoing beam has an inclination of 16 ° with respect to the outgoing end.

EFFECTS OF THE INVENTION According to the present invention, an optical amplifier with a short element length and high output can be realized, and with the optical integrated circuit of the present invention, a single transverse mode high output laser beam can be obtained with one chip. Becomes

[Brief description of the drawings]

FIG. 1 is a principle diagram of an optical amplifier of the present invention, FIG. 2 is a structural diagram of an optical amplifier of one embodiment of the present invention, and FIG. 3 is an optical amplifier of one embodiment of the present invention on the same substrate as a semiconductor laser. FIG. 4 is a view showing the manufacturing process of the embodiment, FIG.
FIG. 6 is an input / output characteristic diagram, FIG. 6 is a far field image diagram, FIG. 7 is a diagram showing longitudinal mode characteristic, and FIG. 8 is a principle (schematic) diagram of a conventional optical amplifier. 1 ... p-GaAs substrate, 2 ... n-GaAs layer, 3 ... p-Ga
AlAs layer, 4 ... GaAlAs active layer, 5 ... n-GaAlAs layer, 6
... n-GaAs layer, 7 ... stripe portion, 8 ... separation groove.

Claims (2)

(57) [Claims] 1. A waveguide having an end face perpendicular to the active layer, and having a waveguide bent at least once at the end face,
An optical amplifier characterized in that an incident angle of the laser light traveling in the waveguide with respect to the end face is smaller than a critical angle. 2. An optical integrated circuit in which the optical amplifier according to claim 1 is formed on the same substrate as a semiconductor laser.