JPH0964458A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser which can reduce the loss of injected energy as compared with that in conventional cases and which obtains a high optical output by small electric power. SOLUTION: An active part 2 which is composed of a semiconductor and which has the light amplification action and a phase shift part 3 in which light- emitting energy is coupled to only an optical mode in a prescribed direction are arranged inside a photonic crystal 1 which is provided with a refractive- index periodic structure on the order of the wavelength of light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser which can be used as a light source for various devices such as an optical integrated circuit.

[0002]

2. Description of the Related Art Conventionally, semiconductor lasers using semiconductors such as GaAs have been actively developed. This semiconductor laser has features such as spectral purity, high efficiency, easy modulation and easy handling, and can be used as an optical integrated circuit and other light sources.

In such a conventional semiconductor laser, as shown in FIG. 6 where the vertical axis represents light output and the horizontal axis represents injection current,
When the injection current exceeds a certain threshold, a laser beam is emitted in a predetermined direction as shown in FIG.
As shown in (1), spontaneous emission light is emitted in an unspecified direction.

[0004]

As described above, in the conventional semiconductor laser, an energy loss occurs due to the spontaneous emission light. In addition, in order to obtain a light output in a predetermined direction, an injection current equal to or more than a threshold value is required. For example, when a large number of light sources are required in a large-scale optical integrated circuit or the like, there is a problem that power for operation increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides a semiconductor laser capable of reducing injection energy loss and obtaining a high optical output with a small amount of electric power as compared with the related art. It is something to offer.

[0006]

According to the first aspect of the present invention,
In a photonic crystal having a refractive index periodic structure in the order of the wavelength of light, an active portion made of a semiconductor and having a light amplifying action, and a phase shift portion for coupling emission energy only to an optical mode in a predetermined direction are arranged. It is characterized by the following.

According to a second aspect of the present invention, in the semiconductor laser according to the first aspect, the photonic crystal has a repetitive structure in which a high refractive index medium and a low refractive index medium are regularly arranged three-dimensionally. Features.

According to a third aspect of the present invention, in the semiconductor laser according to the first or second aspect, the phase shift portion is arranged in a plane at substantially the center of the photonic crystal. .

According to a fourth aspect of the present invention, in the semiconductor laser according to any one of the first to third aspects, the active portion is disposed substantially at the center of the phase shift portion. In the semiconductor laser of the present invention having the above-described configuration, the active portion and the phase shift portion are provided in the photonic crystal having a structure in which light is reflected in all directions and is not emitted to the outside, so that the spontaneous emission light from the active portion is also reduced. Like the laser light, the light can be emitted in a predetermined direction specified by the phase shift unit. As a result, the loss of the injection energy can be reduced, and the threshold value can be substantially lowered, so that a high optical output can be obtained with a small amount of power.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a semiconductor laser according to the present invention. The upper part shows the entire sectional structure, and the lower part shows an enlarged part of the sectional structure. . In the figure, reference numeral 1 denotes a photonic crystal having a periodic structure of the refractive index on the order of the wavelength of light. In the photonic crystal 1, an active portion 2 made of a semiconductor and having an optical amplifying action is provided with an optical mode in a predetermined direction. Only the phase shift unit 3 for coupling the emission energy is provided.

The photonic crystal 1 is made of, for example, GaAs
(N1 = 3.6) and a low refractive medium 1b such as air (n2 = 1) or glass, for example, which are three-dimensionally arranged in the order of the wavelength of light (for example,
N layers are arranged so as to have a constant periodic structure (１ ／ wavelength).

In the example shown in FIG. 1, the phase shift portion 3 is formed in a plane at substantially the center of the photonic crystal 1 and has an optical width of light so as to form a λ resonator. Is set so as to be substantially the same as the wavelength. The active section 2 is disposed substantially in the center of the phase shift section 3 in a planar shape. The active portion 2 is made of, for example, InGaAs.
And the like.

FIG. 2 shows the relationship between the band gap of a photonic crystal having a diamond crystal structure and the normalized frequency. As shown in the figure, the photonic crystal has a structure in which light of a specific frequency is not emitted to the outside at all.

FIG. 3 shows a simplified two-dimensional crystal of a triangular periodic structure in which a rod of a low refractive medium (air or glass) is arranged in a high refractive medium (GaAs). A schematic diagram of the mode density (TE mode) as a result of analyzing a structure in which a λ resonator is disposed between the two layers and a light emitting layer having a light emission wavelength of 1.0 μm is disposed in the center thereof is shown.
The hatched region in the figure indicates a region with a high mode density indicating the degree of light coupling to the outside, and the region without a hatched line indicated as the photonic band gap indicates a region with a low mode density, that is, the outside. An area where no light is emitted is shown. Since the phase shift portion acting as a resonator is provided, an oscillation mode appears strongly in the photonic band gap.

Therefore, by selecting the light emission frequency of the active portion 2, as shown in FIG. 4 in which the vertical axis represents the light output and the horizontal axis represents the injection current, even in the region where the injection current is extremely small, FIG. As described above, in the semiconductor laser (photonic crystal structure laser) of the present invention, spontaneous emission light can be emitted in a predetermined direction similarly to the laser light.

Thus, the loss of the injection energy emitted as spontaneous emission light can be reduced, the threshold value can be substantially lowered, and a high light output can be obtained with a small power.

In the example described above, the phase shift unit 3
Has been described in the form of a single plane disposed substantially at the center of the photonic crystal 1. However, the position, shape and number of the phase shift units 3 are not limited to this example, but are disposed eccentrically. It can be deformed, for example, into a curved shape, or provided with a plurality.

Various modifications can be made to the material and structure of the photonic crystal 1, and similarly, various modifications can be made to the material and structure of the active part 2.

[0020]

As described above, according to the semiconductor laser of the present invention, the loss of the injection energy can be reduced, and a high optical output can be obtained with a small amount of power, as compared with the prior art.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a band gap of a photonic crystal and a normalized frequency.

FIG. 3 is a diagram schematically showing a mode density in the embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between light output and injection current in the embodiment of the present invention.

FIG. 5 is a diagram illustrating a state of light output according to the embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between a light output and an injection current in a conventional technique.

FIG. 7 is a diagram for explaining a state of light output in the related art.

[Explanation of symbols]

 1 Photonic crystal 1a High refraction medium 1b Low refraction medium 2 Active part 3 Phase shift part

Claims (4)

[Claims] 1. A photonic crystal having a periodic structure of a refractive index on the order of the wavelength of light within an active portion made of a semiconductor and having an effect of amplifying light, and a phase shift portion coupling light emission energy only to an optical mode in a predetermined direction. And a semiconductor laser. 2. The semiconductor laser according to claim 1, wherein the photonic crystal has a repeating structure in which a high-refractive-index medium and a low-refractive-index medium are regularly arranged three-dimensionally. 3. The semiconductor laser according to claim 1, wherein the phase shift portion is provided in a plane at substantially the center of the photonic crystal. 4. The semiconductor laser according to claim 1, wherein said active portion is disposed substantially at a center of said phase shift portion.