Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2001-02-15
2003-09-23
Ip, Paul (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C385S065000, C385S073000, C385S083000
Reexamination Certificate
active
06625188
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device used in the optical communication field and, in particular, to a semiconductor device provided with a high-NA (numerical aperture) lens in conformity with high-speed/large-capacitance optical communications.
2. Description of the Related Art
As shown in
FIG. 7
, in a conventional semiconductor device
50
, an optical coupling construction is adopted in which light
52
radiated from the end surface of a light emitting element
11
is condensed on an end surface of an optical fiber
14
by using a ball lens
53
.
In this semiconductor device
50
, a silicon (Si) substrate
55
shown in
FIGS. 8A through 8C
is used.
In the silicon substrate
55
, there is formed in the upper surface portion
55
a
thereof a V-shaped groove
55
b
having a substantially V-shaped (trapezoidal) sectional configuration. This V-shaped groove
55
b
is formed by performing anisotropic etching on the surface of the silicon substrate
55
by using a resist mask formed by photolithography.
And, in the silicon substrate
55
, the edge portion connected to the upper surface portion
55
a
of the V-shaped groove
55
b
exhibited inclined surfaces
55
e
,
55
f
and
55
g
having peculiar inclination angles due to the silicon crystal structure (&thgr;1, &thgr;2 and &thgr;3, which are all 54.7 degrees).
And, in the silicon substrate
55
of the optical semiconductor device
50
shown in
FIG. 8
, the positioning of the light emitting element
11
is effected in the upper surface portion
55
a
near the V-shaped groove
55
b
, the positioning of the ball lens
53
being effected in the V-shaped groove
55
b
, the optical axes of the light emitting element
11
and the ball lens
53
coinciding with each other.
However, in the field of optical communications, there is an ever-increasing demand for increasing the communication speed and decreasing the optical coupling loss between the optical semiconductor device
50
constituting the optical coupling of the light emitting element
11
and the optical fiber
14
. The optical coupling loss greatly influences the speed of the optical communication and may thus be an obstruction to high-speed optical communication.
In view of this, the present applicant has proposed use of an aspheric lens to decrease the optical coupling loss, instead of the ball lens
53
.
As shown in
FIGS. 9A and 9B
, in the optical semiconductor device
60
, instead of the conventional ball lens
53
, an aspheric lens
63
is mounted and fixed in the V-shaped groove
55
b
of the silicon substrate
55
.
As shown in
FIG. 10
, this aspheric lens
63
consists of a limited type lens of an optical glass and comprises a lens main body
63
a
provided with both-side convex aspheric surfaces, and an edge portion
63
b
in the peripheral edge of the lens main body
63
a
, the outer diameter (&phgr;) being 1.0 mm, the lens thickness (tc) being 0.81 mm, the optical length (L=L
1
+tc+L
2
) being 3.56 mm, the focal distance (L
2
) being approximately 2 mm, NA (numerical aperture) being 0.45, the magnification (m) being
3
. Further, the distance (L
1
) from the object point to the apex of the lens surface being 0.3 mm.
Here, the NA can be generally expressed by the following equation.
NA=n
sin &thgr;
where &thgr; is the angle made by the ray having maximum opening of the rays emitted from the object point in the axis and the optical axis; and n is the refractive index of the medium where the object point exists. Thus, the larger the NA, the higher the resolution, making it possible to enhance the efficiency in optical coupling. Further, by making the lens in an aspheric configuration, it is possible to restrain the influence of the aberration.
In this way, in the optical semiconductor device
60
having the aspheric lens whose NA is 0.45, the output light
52
radiated from the end surface of the light emitting element
11
passes the aspheric lens
63
as shown in
FIG. 9
, and focuses on the end surface of the optical fiber
14
(See FIG.
7
). This improvement decreases the loss in optical coupling as compared with the ball lens
53
.
Incidentally, in this optical semiconductor device
60
, to cope with the increase in speed and capacitance of optical communication and to utilize the characteristics of the aspheric lens to the utmost, it is necessary to further enhance the NA of the lens and reduce the WD (working distance=L
1
), which is the distance from the light emitting element
11
to the aspheric lens.
In the proposed optical semiconductor device
70
shown in
FIG. 12
, an aspheric lens
23
having high NA and short WD is mounted on a silicon substrate
55
.
As shown in
FIG. 11
, the aspheric lens
23
consists of an infinite-type lens of optical glass and comprises a lens main body
23
a
provided with double convex aspheric surfaces and an edge portion
23
b
in the periphery of the lens main body
23
a
, the outer diameter (&phgr;) being 1.0 mm, the lens thickness (tc) being 0.81 mm, the focal distance (L
2
) being infinite, the NA (numerical aperture) being 0.60.
Generally speaking, in an aspheric lens, there is a strict demand for accuracy in optical axis matching as the NA increases. In this aspheric lens
23
, the light output from one side becomes parallel rays, so that the optical axis matching can be conducted relatively easily.
However, as shown in
FIG. 12
, when the aspheric lens
23
having high NA is mounted as it is in the V-shaped groove
55
b
of the conventional silicon substrate
55
and fixed therein, a portion (H) is generated that interferes with the inclined surface
55
g
of the V-shaped groove
55
b.
Thus, there is a problem that the high NA aspheric lens
23
which utilizes the characteristics of an aspheric lens to the utmost and which has short WD cannot be mounted on the silicon substrate
55
.
Further, as shown in
FIG. 13
, focusing attention on the outer diameter of the aspheric lens
23
, it might be possible to prevent the generation of the above-mentioned portion H by reducing the outer diameter (&phgr;). However, from the viewpoint of the intention of maintaining high NA, it is necessary to further reduce the WD. As a result, the size of the aspheric lens
23
is only reduced in geometrical similarity, and, as the size of the lens is reduced, the WD is further shortened, making it impossible to prevent the generation of the portion (H) interfering with the inclined surface
55
c.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical semiconductor device of high NA having improved optical communication efficiency that increases the speed and capacitance in optical communication and allows mounting of a short WD lens.
As first means for solving at least one of the above problems, an optical semiconductor device is provided that comprises a semiconductor substrate having on one side an etched and substantially V-shaped first groove portion formed by etching, an optical element having an optical axis in the direction of the first groove portion and mounted to the one side, and a lens mounted in the first groove portion. The first groove portion comprises first and second opposing inclined surfaces and a third inclined surface perpendicular to the first and second inclined surfaces. A second groove portion is formed in the substrate and extends in a direction perpendicular to the direction of the first groove portion. The second groove portion includes the first, second and third inclined surfaces. The lens is mounted to the first and second inclined surfaces and has a part thereof protruding in the second groove portion. The optical element optically communicates through the lens.
Further, in the optical semiconductor device the second groove portion may be formed as a recess extending across the substrate.
Further, in the optical semiconductor device an edge portion of the lens may abut the side wall of the second groove portion.
A second means for solving at least one of the above
Kikuchi Kimihiro
Ono Miki
Alps Electric Co. ,Ltd.
Ip Paul
Menefee James
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