Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-07-17
2004-03-09
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C385S014000
Reexamination Certificate
active
06704337
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wavelength-variable semiconductor laser, which is used in the fields of optical communication and optical information processing (e.g., optical disks, displays, and the like); an optical integrated device structured by such a wavelength-variable semiconductor laser and an optical waveguide device; and a method for producing the same. More particularly, the present intention relates to the structure of an integrated short-wavelength light source structured by a semiconductor laser chip, including the above-mentioned wavelength-variable semiconductor laser, and an optical waveguide type wavelength converting device; and a method for producing the same.
2. Description of the Related Art
In the field of optical communication, the development of a small and low-cost optical module in which a semiconductor laser, an electronic element, an optical fiber, and the like are hybrid-integrated on a quartz type light wave circuit platform has been highly valued.
The important factor to be considered in connection the above is to fix each element with high positional accuracy so as to minimize transfer loss as much as possible. For such a purpose, a surface mounting type optical module which directly couples a semiconductor laser with a single-mode fiber using a Si substrate with a V-shaped groove has been realized (e.g., 1997 National Convention of the Institute of Electronics, Information, and Communication Engineers of Japan, C-3-63). According to such a technique, markers are formed on a Si substrate and a semiconductor laser element, and a center of the V-shaped groove and a light-emitting point of the semiconductor laser element are detected by the image recognition of the markers so as to perform positioning adjustment (positional alignment) with high accuracy. With such a structure, mounting deviation can be suppressed to about ±0.61 &mgr;m in an x-direction, and to about ±1 &mgr;m in a z-direction.
In the field of optical information processing, a small short-wavelength light source is demanded in order to realize a higher-density optical disk and a high definition display. Techniques for realizing a short-wavelength includes a second harmonic-wave generation (hereinafter, referred to as “SHG”) method which uses a semiconductor laser and an optical waveguide type wavelength converting device employing a quasi-phase-matching (hereinafter, referred to as “QPM”) method (for example, see Yamamoto et al., Optics Letters, Vol. 16, No. 15, p. 1156, 1991).
FIG. 1
is a view showing a general structure of a blue light source using an optical waveguide type wavelength converting device.
According to the structure shown in
FIG. 1
, a wavelength-variable semiconductor laser
110
having a distributed Bragg reflection (hereinafter, referred to as “DBR”) region is used as a semiconductor laser
110
. Hereinafter, the wavelength-variable semiconductor laser having the DBR region is referred to as a “DBR semiconductor laser” or a “DBR laser”.
The DBR semiconductor laser
110
is, for example, a 100 mW class AlGaAs type DBR semiconductor laser of a 0.85 &mgr;m band. The DBR semiconductor laser
110
includes an active layer region
112
and a DBR region
111
. By varying a current injected into the DBR region
111
, it is possible to vary an oscillation wavelength.
On the other hand, an optical waveguide type wavelength converting device
116
, which serves as a wavelength converting element, includes an optical waveguide
115
formed in a X-cut MgO-doped LiNbO
3
substrate
113
and periodic domain-inverted regions
114
. The semiconductor laser
110
and the wavelength converting device
116
are fixed onto submounts
117
and
118
, respectively, in a junction-up manner.
Laser beams obtained from an outputting end surface of the DBR semiconductor laser
110
are directly coupled with the optical waveguide
115
of the optical waveguide type wavelength converting device
116
. Specifically, by adjusting the positional relationship between the DBR semiconductor laser
110
and the optical waveguide type wavelength converting device
116
on the submounts
117
and
118
, laser beams of about 60 mW are coupled with the optical waveguide
115
of the wavelength converting device
116
for the laser output of about 100 mW from the semiconductor laser
110
. Moreover, by controlling an amount of the current injected into the DBR region
111
of the DBR semiconductor laser
110
, the oscillation wavelength thereof is fixed within the allowable range of the phase matching wavelength in the optical waveguide type wavelength converting device
116
. With such a structure, at present, it is possible to obtain blue light with a wavelength of 425 nm at the output of about 10 mW.
FIG. 2
is a view showing a general structure of a blue light source using a domain-inverted type waveguide device.
A DBR semiconductor laser
221
(i.e., a 100 mW class AlGaAs type DBR semiconductor laser of a 0.85 &mgr;m band) includes a DBR region
228
for fixing an oscillation wavelength. Within the DBR region
228
, an internal heater (not shown) is provided so as to vary an oscillation wavelength. On the other hand, a domain-inverted type waveguide device
224
serving as a wavelength converting element includes an optical waveguide
226
formed in a X-cut MgO-doped LiNbO
3
substrate
225
and periodic domain-inverted regions
227
.
A laser beam
229
, which is output from the semiconductor laser
221
and is collimated by a collimator lens
222
(numerical aperture NA=0.5), is converged onto an end surface of the optical waveguide
226
in the domain-inverted type waveguide device
224
by a focusing lens
223
(NA=0.5). The laser beam
229
is then coupled with the optical waveguide
226
having the domain-inverted regions
227
. Specifically, for a laser output of about 100 mW, it is possible to allow a laser beam of about 70 mW to be coupled with the optical waveguide
226
. With such a structure, the oscillation wavelength thereof is fixed within the allowable range of the phase matching wavelength in the domain-inverted type waveguide device
224
by controlling an amount of the current injected into the DBR region
228
of the DBR semiconductor laser
221
.
The blue light output thereby obtained increases in proportional to the square value of the output of the laser beam coupled with the optical waveguide
226
. Therefore, coupling efficiency is a critical factor in order to obtain blue light with a high output.
In the case of the surface mounting type optical module which directly couples a semiconductor laser with a single-mode fiber, in order to couple a semiconductor laser beam into the optical fiber at a high efficiency, it is necessary to have positional adjustment (alignment) accuracy in the order of a submicron with respect to an x-direction and a y-direction which are parallel to the cross-section of the optical fiber and in the order of several microns with respect to a z-direction along the optical axis of the optical fiber. In such a case, the optical fiber is typically fixed with high accuracy by using a V-shaped groove. In addition, the semiconductor laser chip has been conventionally positioned with high accuracy with respect to an x-direction, which is parallel to the surface of the mounting substrate within the cross-section of the optical fiber, and a z-direction along the optical axis of the optical fiber. However, as to the positioning of the semiconductor laser chip with respect to a y-direction, which is parallel to the surface of the mounting substrate within the cross-section of the optical fiber, it is generally difficult to perform positioning (alignment) adjustment and fixation with the accuracy of a submicron or less due to the existence of a solder layer for fixation.
On the other hand, in the short-wavelength light source structured by a semiconductor laser and an optical waveguide type wavelength converting device (i.e., an optical waveguide device), the lens coupling ty
Kitaoka Yasuo
Mizuuchi Kiminori
Yamamoto Kazuhisa
Ip Paul
Nguyen Phillip
RatnerPrestia
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