Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-07-21
2001-08-21
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
Reexamination Certificate
active
06278720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a high power semiconductor laser, and more particularly to a high power semiconductor laser of a ridge waveguide (RWG) structure having an increased catastrophic optical damage (COD) level, and to method of fabricating a semiconductor laser device of a ridge waveguide structure.
2. Description of the Prior Art
A semiconductor laser having a wavelength of 0.98 &mgr;m has been used to amplify signal through an optical fiber as a source of light of the erbium doped fiber amplifier (EDFA). The larger the optical power of 0.98 &mgr;m semiconductor laser, the more the optical amplification rate of the EDFA is increased. Accordingly, the fabrication of 0.98 &mgr;m semiconductor laser having a high optical power has been interested.
But, when the optical power of a semiconductor laser increases, the durability of a semiconductor laser is limited, the main cause being local heating due to optical absorption in the output facets that can result in catastrophic optical damage (COD).
To solve the above-mention problems, a bent-waveguide nonabsorbing mirror (NAM) structure, an exponential-shaped flared stripe structure, or an ion-implantation into the output facets are proposed.
The conventional method of fabricating a semiconductor laser of a ridge waveguide (RWG) structure having a wavelength of 0.98 &mgr;m will be explained with reference of
FIG. 7
to
11
.
FIG. 7
is a cross-sectional view of RWG semiconductor laser of RWG structure according to a conventional method.
One of the conventional methods will now be described with FIG.
7
.
First, as shown in
FIG. 7
, a GaInAsP graded layer
102
, a GaInP cladding layer
103
, a GaInAsP graded layer
104
, a GaInAs/GaInAsP active layer
105
, a GaInAsP graded layer
106
, a GaInP cladding layer
107
, a GaInAsP graded layer
108
, and a GaAs ohm contact layer
109
are grown by metal organic vapor phase epitaxy(MOVPE), in this order, on the GaAs substrate
101
.
Next, a silicon nitride film and a photoresist are successively deposited on the grown substrate, and a photoresist is patterned to form a ridge composed of 2 to 3 &mgr;m width and 20 &mgr;m channel width by conventional photolithographic and selective etching steps. After removing the photoresist, a GaAs ohm contact layer
109
, a GaInAsP graded layer
108
, and a GaInP cladding layer
107
are selectively removed by wet etching using the silicon nitride film as a mask.
After removing the silicon nitride film used as a mask, a silicon nitride film
110
is deposited on the entire surface, and open the contact windows using photolithograpy and etching technique of the top surface of the ridge. Sequentially, the first p side electrode and the second p side electrode
111
of approximately 2 to 3 &mgr;m thickness by using Au platting process are successively formed. The GaAs substrate grinds to be remain a thickness of approximately 100 &mgr;m, and a n side electrode
112
is formed on the rear surface of the GaAs substrate
101
.
In operation, when a forward bias voltage is applied across the substrate and the ohmic contact layer, current flows into the active layer through the ridge and carriers are confined in the active layer, resulting in carrier recombinations that produce laser light, The laser light by optical gain is generated in the active layer having 2 to 3 &mgr;m width and 600 to 1000 &mgr;m length in the lower portion of the ridge. The laser light generated by optical gain like this is injected in the vicinity of the active layer by a difference in refractive index of each layer along in the longitudinal direction of the active layer and a difference in effective refractive index of the lower portion and its expected portion of the ridge along in the horizontal direction of the active layer.
Accordingly, the active layer shape composed of the resonator of RWG semiconductor laser is combined by mixing gain-guiding wave and refractive index-duiding, The active layer of a stick shape of a rectangle has some enlarged shape along in the horizontal direction, that is, the length come under a resonator length of RWG semiconductor laser, and the width of a rectangle is some larger than the ridge width.
In case of operating a conventional RWG semiconductor laser like this in accordance with high injection current, the higher optical power density is formed at the output facets, and the active layer absorbe a part of the optical power. Accordingly, the output facet that can result in catastrophic optical damage (COD) is abruptly destructed by the local heating due to optical absorption.
Another conventional method illustrated in
FIGS. 8 and 9
is adapted to solve the destruction problem of the output facet due to COD.
FIGS. 8 and 9
are cross-sectional view showing a RWG semiconductor laser of the bent-waveguide nonabsorbing mirror (NAM) structure proposed to rise the COD level.
As shown in
FIG. 8
, first, a GaAs substrate
113
with exact [100] orientation is formed a 1 &mgr;m-deep channel for laser stripe parallel to [01-1] by wet etching. And a n type AlGaAs cladding layer
114
, a single-quantum-well graded-refractive-index separae-confinement heterostructure (SQW-GRINSCH) layer
115
, and a p type AlGaAs cladding layer
116
are then grown on the nonplanar substrate by molecular beam epitaxy (MBE). Next, after depositing a silicon nitride film and a photoresist on the grown substrate, the ridge of 3.5 &mgr;m width and 1.25 &mgr;m depth by dry etching using the silicon nitride film as a mask is formed.
Subsequently, after removing the a silicon nitride film used as a mask, a silicon nitride film
117
is deposited on the entire of the ridge, and a p side electrode
118
is then formed. The output facet trench of 6 &mgr;m depth is formed by chemical assisted ion-beam etching (CAIBE). After coating with Al2O3 layers in the output facets, a n side electrode
119
is then formed. This structure restrains the optical absorption so that the laser optical power is seceded from active layer of the output facet region, since the laser resonator is moved to the longitudinal direction at the output facet region. In case NAM region of this structure, the laser light generated from the active layer is coupled with AlGaAs cladding layer that has a high band gap and is not generated an optical absorption. Accordingly, a size of the beam patterns is getting bigger, and the temperature of the output facets is getting lower.
Other conventional method illustrated in
FIG. 10
is adapted to reduce the COD generating in the output facets of the RWG structure due to the high optical power density. Generally, when the active layer is narrow, the kink is decreased. But, the degradation characteristics of the output facets is increased by increasing the optical power density.
FIG. 10
is a stripe structure for semiconductor laser with exponential-shaped flared stripe.
As shown in
FIG. 10
, the stripe width is wider at the front to reduce the optical power density. It is narrower at the rear facet to achieve stable lateral-mode operation. These two regions are connected by an exponential-shaped flared stripe
120
that produces a smooth mode-transition due to the electrical field along the cavity taking an exponential form. The optical power density is decreased by enlarging an optical power distribution proceeding along the resonator since the end portion of the active layer makes an exponential-shaped flared stripe. In case of this structure, the optical power level
121
caused by a COD is enlarged at the front facet A still conventional method illustrated in
FIG. 11
is adapted to rise the COD level by ion-implanting a dopant impurity in vicinity of the optical power facets.
FIG. 11
is a cross-sectional view showing a conventional semiconductor laser of a window structure.
First, as shown in
FIG. 7
, a n type AlGaAs cladding layer
123
, a AlGaAs/AlGaAs quantum well layer
124
, a p type AlGaAs first cladding layer
125
, a p type AlGaAs etching stop layer
126
, a p type AlGaAs sec
Jang Dong Hoon
Lee Jung Kee
Park Chul Soon
Park Kyung Hyun
Davie James W.
Electronics and Telecommunications Research Institute
Jacobson & Holman PLLC
LandOfFree
High power semiconductor lasers with ridge waveguide structure does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High power semiconductor lasers with ridge waveguide structure, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High power semiconductor lasers with ridge waveguide structure will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2464341