Optical: systems and elements – Optical amplifier
Reexamination Certificate
2001-03-14
2002-10-15
Tarcza, Thomas H. (Department: 3663)
Optical: systems and elements
Optical amplifier
C385S146000
Reexamination Certificate
active
06466361
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a converging device, light source module, a laser device and an optical signal amplifier. More particularly, the present invention relates to a converging device for converging light having a high aspect ratio emitted from a semiconductor array laser to a small spot, and a light source module, a laser device and an optical signal amplifier using such converging device.
2. Description of the Related Art
In the field of optical communications, optical measurement and laser processing, a semiconductor array laser such as laser diode bar (hereinafter, referred to as LD bar) in which a plurality of laser diodes are horizontally aligned is used as a laser device or a pumping source for the laser device. A light emitting surface of the LD bar has a long horizontal axis of approximately 10 mm in a direction of alignment of the laser diodes and a short vertical axis of approximately 1 &mgr;m in a thickness direction of the light emitting surface. Thus, a spot of the light emitted from such a light emitting surface has an elliptic shape having a high aspect ratio. When such a light is converged by a normal optical system, the light can be sufficiently converged in the vertical direction, however, the light can only be converged within at most, several millimeters in the horizontal direction.
Therefore, various devices have been developed for converging a light having a large aspect ratio emitted from the LD bar or the like to a small spot having substantially the same length in both directions. Such devices include a fiber coupling system, a two-mirror system and a triangle duct.
In the fiber coupling system, as shown in
FIG. 40
, the light is input to ends of a plurality of optical fibers
42
which are aligned horizontally adjacent the light emitting surface
40
of the LD bar. Other ends of the fibers
42
are bundled in a round shape to obtain round spot of light therefrom. In this system, however, as the light emitting surface of the converged light is formed by the end surfaces of the bundled fibers, a converging ratio is limited.
In the two-mirror system, as shown in
FIGS. 41 and 42
, the light is input between the two mirrors
50
,
52
which are arranged in a parallel alignment from an upper diagonal upper direction to a lower diagonal direction. The mirrors
50
,
52
have reflective surface
50
a,
50
b
which face each other. The light input is reflected repeatedly between the reflective surface
50
a,
52
a
so that the light is shifted both horizontally and vertically. The mirrors
50
,
52
face toward each other and are horizontally and vertically space from each other. The light beam (
1
) passes above the mirror
52
to be emitted and the light beams (
2
)-(
5
) are reflected between the reflective surfaces
50
a,
52
a
one to four times and output to be vertically beneath the light beam (
1
). The light beams (
1
)-(
5
) are converted from a horizontal alignment to a vertical alignment in the above manner. Thus, the spot of light is converged to 1/5 in horizontal direction. In this system, however, as a plurality of optical devices are used, alignment of the devices is complex, the cost and time for production and alignment is high and reliability of convergence is low.
In the triangle duct system, as shown in
FIG. 43
, a duct portion
12
having an equilateral triangle shape, which is made from a thin plate, is prepared. The light to be converged is input from an incident surface
12
a,
which is a surface at the base of the triangle extending in the thickness direction of the duct portion
12
. The light is totally reflected in the reflective surfaces
12
b,
which is a surface at equal side extending in the thickness direction, to be transmitted toward a vertex of the triangle so as to be converged. The converged light is emitted to an optical fiber
27
provided at the vertex of the duct portion
12
. According to the system, as the structure of the device is simple, the time and cost for production and alignment may be decreased, and the reliability for converging the light beams can be improved.
However, in the above triangle duct
12
, as reflection of the light in the reflective surface
12
b
is repeated, an incident angle of the light in the reflective surface
12
b
decreases. As a result, when the light is intended to be converged to the smaller spot, the incident angle of the light in the reflective surface
12
b
cannot be maintained within a critical angle of a total reflection. Therefore, according to the above-configured duct, the maximum convergence of the light can only be in the range of 1/3-1/5.
FIG. 44
shows a result of a ray-tracing, in which four parallel light beams at 3 mm pitch are input in an equilateral triangle duct made of a silica glass having a thickness of 100 &mgr;m, a vertical angle of 10°, and a width of the incident surface of 12 mm. The light introduced from the incident surface
12
a
is transmitted toward the vertex of the duct portion
12
by being reflected in the reflective surfaces
12
b.
As the reflection is repeated, the incident angle of the light in the reflective surface
12
b
decreases. Adjacent the vertex of the duct portion
12
, the incidental angle of the light cannot be maintained within the critical angle of the total reflection and the light is leaked outside the duct portion
12
. As a result, converged light with a small spot cannot be obtained from the vertex of the duct portion
12
.
In order to solve the above problem, as shown in
FIG. 45
, a convex surface may be formed in the incident surface
12
a
of the duct portion
12
for refracting the light toward the vertex of the duct portion
12
in order to reduce the number of reflections in the reflective surface
12
b.
In such a duct, since both edges of the incident surface
12
a
cannot be placed closely to the light emitting surface of the LD bar
16
, the light is leaked from both of the edges to lower a coupling efficiency.
Therefore, there is a demand for a converging device for converging the light to the smaller spot by utilizing the advantages of the triangle duct.
It is an object of the present invention to provide converging device which can efficiently converge a light having a high aspect ratio to a smaller spot with a simple structure. It is another object of the present invention to provide a light source module, a laser device and an optical signal amplifier using such a converging device.
SUMMARY OF THE INVENTION
In order to achieve the above object, there is provided a converging device comprising a converging portion for converging a light, said converging portion having an incident surface in which a light to be converged is introduced, a tip portion provided in an opposite side of said incident surface in a direction of transmission of said light and a reflective surface for reflecting said light introduced from said incident surface so that said light is transmitted toward said tip portion, and a guide portion provided in said reflective surface along a direction from said incident surface to said tip portion, wherein said light transmitted in said converging portion is introduced to said guide portion and said introduced light in said guide portion is reflected so that said light is transmitted toward one end of said guide portion in a tip portion side, said light transmitted in said guide portion toward said converging portion is transmitted by maintaining a condition of substantially total reflection with respect to said reflective surface of said converging portion, and said converged light is emitted from at least one of said tip portion and said one end of said guide portion.
In the above converging device, the light introduced to the converging device from the incident surface is transmitted toward the tip portion to be converged by being reflected in the reflective surface. The converged light is finally emitted from the tip portion or the end of the guide portion. According the above converging device, since the light transmitted
Sekiguchi Hiroshi
Yamaura Hitoshi
Hoya Corporation
Sommer Andrew R.
Tarcza Thomas H.
Woodard Emhardt Naughton Moriarty & McNett
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