Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-03-13
2003-11-18
Lee, Eddie (Department: 2815)
Coherent light generators
Particular active media
Semiconductor
C372S050121, C372S096000
Reexamination Certificate
active
06650672
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a semiconductor laser element and a method for producing the semiconductor laser element. More particularly, the present invention relates to a semiconductor laser element suitable for a light source of an optical communication and a light source of an optical disc, and relates to a method for producing the semiconductor laser element.
(2) Description of Related Art
Typically, conventional semiconductor laser element is composed of a p-type electrode, an n-type electrode, a p-type light waveguide, an n-type light waveguide, and an active layer.
The p-type electrode, n-type electrode, p-type light waveguide, n-type light waveguide are disposed in the vicinity of the active layer, and are made of different materials from the active layer. With such a construction, light generated in the active layer is confined in the semiconductor laser element, a reduced emission is generated in the active layer, and laser light is generated. There is also known a semiconductor laser element that amplifies light with a certain wavelength, using Fabry-Perot resonator in which a cleavage plane is used as a resonator.
It is desired however that the conventional semiconductor laser elements have a low-threshold-current characteristic to be under improved control when they are used as light sources for light communications or optical discs.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a semiconductor laser element having an excellent light confinement effect and a low-threshold-current characteristic, and a method for producing the semiconductor laser element.
Recently, an artificially created dielectric constant three-dimensional periodic structure has received attention. This structure controls the movement of electromagnetic waves so as to move like electrons in crystals. This artificially created structure is called three-dimensional photonic crystal. The electromagnetic band that is caused by this structure and is equivalent to a band of light is called a photonic band.
The reason why the photonic band structure is receiving attention is that the structure may create a laser light whose output or wavelength does not change much with the change of temperature since it has a very low threshold value (theoretically it has no threshold value) and can perfectly control photons in space, which has been impossible for conventional techniques. Also, the photonic band structure is superior in electricity-light energy exchange efficiency since it controls emitted light in all directions in space. In other words, the photonic band structure may provide a low-power-consumption laser. It is thought that especially, a three-dimensional photonic band structure having the dielectric constant three-dimensional periodic structure provides the above effect at the maximum.
FIG. 14
shows an example of the three-dimensional photonic crystal structure (disclosed in the Japanese Laid-Open Patent Application No. 10-335758).
The three-dimensional photonic crystal structure shown in
FIG. 14
is made by periodically stacking layers of two or more kinds of materials which each periodically have pits and projections. For example, Si and SiO2 are used as the materials for the layers
1401
and
1402
, and are referred to as A
1401
and B
1402
, respectively. With such a three-dimensional structure, the propagation of light having a certain wavelength is cut and confined in the crystal structure due to the difference between the refractive indexes of light of the materials A
1401
and B
1402
. However, it is substantially impossible to achieve a semiconductor laser element by forming an active layer inside the above three-dimensional photonic crystal structure. Also, even if the active layer is formed inside the structure, it is difficult to form a waveguide for obtaining light.
In consideration of the above problems, the inventors of the present invention conceived a semiconductor laser element that uses the excellent light confinement effect of the three-dimensional photonic crystal structure by forming inside the three-dimensional photonic crystal structure an active unit that generates laser beams after receiving power, the three-dimensional photonic crystal structure being made of a stack of a plurality of refractive index changing layers in which a refractive index of light periodically changes in a certain direction.
The above object is fulfilled by a semiconductor laser element comprising: a three-dimensional photonic crystal structure which has a light confining effect and includes alternating first and second refractive index changing layers, wherein refractive index of light periodically changes in a first direction in each first refractive index changing layer and periodically changes in a second direction in each second refractive index changing layer; and an active unit which is disposed in a portion having a predetermined refractive index inside the three-dimensional photonic crystal structure, and generates a laser beam in response to reception of electric power.
With the above construction, it is possible to achieve a semiconductor laser element that has an excellent effect of confining the light generated in the active layer and a low-threshold-current characteristic since it uses the light confinement effect of the three-dimensional photonic crystal structure. Also, the three-dimensional photonic crystal structure of the present invention uses, instead of the conventional honeycomb-layer stack structure, first refractive index changing layers and second refractive index changing layers which are alternately stacked, where the refractive index of light periodically changes in a first direction in the first refractive index changing layers, and changes in a second direction in the second refractive index changing layers. This enables the active layer to be formed during the layer stacking process, achieving a semiconductor laser element using the three-dimensional photonic crystal structure.
In the above semiconductor laser element, the active unit may be disposed substantially at a center of the three-dimensional photonic crystal structure.
With the above construction, the active unit is disposed at the center of the three-dimensional photonic crystal structure. This enhances the light confinement effect and decreases the threshold of the electric current.
The above semiconductor laser element may further comprise a light waveguide which extends horizontally from an end of the active unit to at least a vicinity of an end of the three-dimensional photonic crystal structure.
In the above semiconductor laser element, each first refractive index changing layer may be composed of a plurality of optically refractive stripes arranged parallel to each other with a predetermined pitch so that refractive index of light periodically changes in the first direction, each second refractive index changing layer is composed of a plurality of optically refractive stripes arranged parallel to each other with substantially the same pitch as the predetermined pitch so that refractive index of light periodically changes in the second direction, phase of period of the plurality of optically refractive stripes constituting one refractive index changing layer is different from a phase of period of the plurality of optically refractive stripes constituting adjacent refractive index changing layer, and a laser emitting stripe that includes the active unit is disposed in place of one optically refractive stripe.
In the above semiconductor laser element, the active unit may be disposed substantially at a center of the laser emitting stripe in the direction of length, and two portions ranging from both ends of the active unit to both ends of the laser emitting stripe are a p-type light waveguide and an n-type light waveguide, respectively, the p-type and n-type light waveguides each doubling as a carrier conduction path.
The above semiconductor laser element may further comprise: a p-type carrier conducti
Ishino Masato
Kito Masahiro
Lee Eddie
Matsushita Electric - Industrial Co., Ltd.
Nguyen Joseph
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