Semiconductor laser device

Details Semiconductor laser device Semiconductor laser device

1998-09-30

2001-09-04

Leung, Quyen P. (Department: 2881)

Coherent light generators

Particular active media

Semiconductor

C372S096000

Reexamination Certificate

active

06285699

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distributed feedback semiconductor laser device.
2. Description of the Related Art
Conventionally semiconductor lasers have been widely used as a light source for optical recording apparatuses, optical communications and pumping solid state lasers. Among the semiconductor lasers, the DFB (distributed feedback) type are provided with cyclic bumps and dips within an optical guide in the semiconductor laser to form a diffraction grating, whereby the wavelength is stabilized using a light feedback effect due to the diffraction grating. Because such a DFB laser oscillates in a stable single mode, no longitudinal mode hopping phenomenon caused with a change in temperature will occur and thus a mode hopping noise which is observed in a general Fabry-Perot semiconductor laser will not be generated. Therefore, the DFB laser is especially excellent as a light source of which a low high-frequency noise level is required. Furthermore, the DFB laser has such excellent features that changes in oscillation wavelength with changes in temperature are small and that the oscillation wavelength can be selected by varying a cycle of the diffraction grating, and accordingly it is suitable for light sources for optical communications or for pumping solid state lasers.
FIGS. 6
is a view showing an example of a conventional semiconductor laser device of DFB laser type.
FIG. 6A
is a general perspective view and
FIG. 6B
is a partial perspective view showing a shape of a diffraction grating. A semiconductor laser device of DFB laser type is described in Japanese Unexamined Patent Publication JP-A 60-66484(1985), in which are sequentially formed an n-type(hereinafter, denoted by ‘n-’) Al
0.40
Ga
0.60
As cladding layer
103
, a non-doped Al
0.10
Ga
0.90
As active layer
104
, a p-type(hereinafter, denoted by ‘p-’) Al
0.25
Ga
0.75
As optical guide layer
105
, an n-GaAs current blocking layer
106
having a stripe-like window, a p-Al
0.40
Ga
0.60
As cladding layer
107
and p-GaAs contact layer
108
on an n-GaAs substrate
102
, and electrodes
101
,
109
are respectively formed on the bottom face of the substrate
102
and the top surface of the contact layer
108
.
As shown in
FIG. 6B
, diffraction gratings
112
,
113
composed of cyclic bumps and dips are formed in a region
111
which is the bottom of the stripe-like window in the top face of the optical guide layer
105
, and on the top surface of the current blocking layer
106
, respectively. The cladding layer
107
is formed on the diffraction gratings
112
,
113
so as to be embeded in the stripe-like window.
In a conventional semiconductor laser device of DFB laser type as shown in
FIGS. 6A and 6B
, electric current is injected into the active layer
104
through the stripe-like window of the current blocking layer
106
. For this end, also in a bottom region, i.e. a current injection region of the stripe-like window of the optical guide layer
105
is formed a diffraction grating.
In processes for forming the diffraction grating such as etching, however, crystalline surfaces are exposed to the atmosphere, and as a result the substrate surface suffers oxidation, which causes many crystal defects. Therefore, in the structure as shown in
FIGS. 6A and 6B
, the crystal defects concentrate in the vicinity of right above the active layer
104
, which forms a portion of poor crystal property.
In such a semiconductor laser, existing crystal defects trigger a further increasing tendency towards crystal defects during the operation, resulting in remarkable loss of life of the semiconductor laser. Furthermore, an increase in internal loss in the laser oscillator occurs and causes a problem of increase in oscillation threshold current or decrease in efficiency.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a semiconductor laser device having a low oscillation threshold current, high oscillation efficiency, high reliability, long life time and stabilized oscillation wavelength.
The invention provides a self-aligned structure semiconductor laser device comprising:
an active layer;
a pair of cladding layers respectively formed on both faces of the active layer, the cladding layers having a band gap wider than that of the active layer; and
a current blocking layer having a stripe-like window embedded in one of the cladding layers,
wherein a diffraction grating for controlling an oscillation wavelength is formed on an interface of the current blocking layer or between the interface and the active layer excluding the stripe-like window.
According to the invention, a carrier is injected upon applying the voltage to the semiconductor laser, and the carrier is blocked by the current blocking layer in passing through the cladding layers. Consequently, the carrier passes through regions where the current blocking layer is not formed, i.e. only through the stripe-like grooves. The carrier injected into the active layer recombines to emit light, and as the injection current level is increased, induced emission starts and finally laser oscillation occurs. Part of the laser light is distributed into the bottom of the current blocking layer and is then guided.
At the bottom of the current blocking layer is formed a diffraction grating for stabilization of oscillation wavelength. Such types of diffraction gratings may be used that a) cyclic bumps and dips are formed at either or both of the lower and upper interfaces of the current blocking layer, b) a grating layer is formed between the active layer side interface of the current blocking layer and the active layer.
A cycle &Lgr; of the cyclic bumps and dips formed in the lower region of the current blocking layer, or a cycle &Lgr; of changes in width of the grating layer are set so as to meet the following equation (1).
&Lgr;=
m·&lgr;
0
/(2
·nr
)  (1)
wherein m is an integer of 1 or more (1, 2, 3, . . . ), nr is a refractive index of the optical guide path and &lgr; is an oscillation wavelength. When this grating condition is satisfied, light having the wavelength &lgr; is selected, so that a single mode oscillation can be realized.
Moreover, in the invention, since the diffraction grating is formed over the region excluding the stripe-like window and no diffraction grating is formed in the current injection region through which the current passes, there is no occurrence of crystal defects in this current injection region. Therefore, there is little possibility of problems of increase in oscillation threshold current and decrease in oscillation efficiency. Furthermore, it is possible to suppress the decrease in reliability due to growing of the crystal defects.
The invention provides a self-aligned structure semiconductor laser device comprising:
an active layer;
an optical guide layer formed on one face or a pair of optical guide layers on both faces of the active layer, respectively, the optical guide layer(s) having a band gap wider than that of the active layer;
a pair of cladding layers formed so as to sandwich the active layer and the optical guide layer(s) therebetween, the cladding layers having a band gap wider than that of the optical guide layer; and
a current blocking layer having a stripe-like window embedded in at least one of the cladding layers;
wherein a diffraction grating for controlling an oscillation wavelength is formed on an interface of the current blocking layer or between the interface and the active layer excluding the stripe-like window.
According to the invention, since the optical guide layer is disposed on either or both of the faces of the active layer, the light generated in the active layer is guided by the optical guide layer. Consequently, concentration of the light in the active layer can be avoided and a high-power and long life-time laser is realized.
Furthermore, in the invention the diffraction grating is formed over the region excluding the stripe-like window and there exists no diffraction grating in the current injection region, crystal defe

Affiliated with

Also associated with

Rating

Semiconductor laser device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Semiconductor laser device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2456728