Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-09-02
2002-02-12
Ham, Seungsook (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S239000
Reexamination Certificate
active
06346701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photodetection method and photodetection device and photodetection/light emission device that are utilized for example in a photodetection unit for optical communication using infra-red rays.
2. Description of the Related Art
Photodetection devices of this type are provided at the fiber tip part in information communication devices using for example optical fibers and are constituted by a combination of a single lens and a photodetection element. A conventional known photodetection devices are illustrated in FIGS.
11
(
a
), (
b
), (
c
), (
d
) and (
e
). In these Figures,
1
is a photodetection element, and
2
is a condenser lens arranged in front of it; condenser lens
2
is usually integrated with a photodetection element package (constituted by transparent resin in which a photodetection element
1
is molded).
As shown in FIGS.
11
(
a
), (
b
) and (
c
), the shape of the condenser lens may be flat, semi-cylindrical, or cylindrical but, if no modification is made to this, suffers from the defect that it easily admits external optical interference such as light from fluorescent lamps or incandescent lamps arriving at the optical input face and constitutes a source of photodetector noise, because of its wide half-value angle of about ±60°.
In order to deal with this drawback the following proposals have been made:
(1) to restrict the half-value angle to to ±30° or ±15° by suitably modifying the lens shape of the semi-cylindrical or hemispherical lens;
(2) as shown in FIG.
11
(
d
), to provide an external interference exclusion section
3
connected to both sides or one side of semi-cylindrical condenser lens
2
(see Japanese Utility Model Number 2561800): or
(3) as shown in FIG.
11
(
e
), to cover the parts other than the central part of condenser lens
2
with a screening element
4
(Laid-open Japanese patent publication H. 8-330608, Japanese patent number 2651756).
However, the above proposals (
1
) to (
3
) had the following drawbacks.
In the case of (1), since the photodetection e.m.f. is not fixed within the half-value angle, although there is a large photodetection e.m.f. in respect of light from directly in front, as the photodetection angle is increased, the photodetection e.m.f. gradually falls. Consequently, as shown in FIGS.
12
(A) and (B), the photodetection angular efficiency is poor when it is below 50%. FIG.
12
(A) shows characteristic in the case of suitably modifying the shape of the cylindrical lens shown in FIG.
11
(
c
), and FIG.
12
(B) shows characteristic in the case of suitably modifying the shape of the semi-cylindrical lens shown in FIG.
11
(
b
).
In the case of (2), the presence of the interference exclusion section
3
renders the shape complicated and restricts the possibilities for miniaturization.
In the case of (3). Only a very small portion of the incoming light reaches photodetection element
1
, so the photodetection e.m.f. is very weak. Also, since the screening effect in regard to interfering light that gets in from the apertures of screening element
4
is poor there is a limit to the extent to which the effect of optical interference can be excluded. Also, since a screening element must be provided separately from condenser lens
2
, manufacturing costs are high.
Further, in the cases of (2) and (3), the designs are such that incoming light from directly in front converges onto the photodetection surface of photodetection element
1
so when the optical intensity arriving at this point is high there is a risk of the output of this point of convergence becoming saturated. Also, since the output of the areas to which convergence does not take placed is normally practically zero, if the angle of photodetection changes, causing the point of convergence to shift, the reaction time is prolonged, with the risk that response to signal changes may be delayed. Furthermore, since the photodetection e.m.f. is unstable at angles where the light is converging onto a contaminated or defective portion of photodetection element
1
, the output tends to be easily affected by photodetection angle. Also, since photodetection element
1
is arranged at the position of the focal point, a large distance is required between the surface of condenser lens
2
and photodetection element
1
, which limits possibilities for miniaturizing the device.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of the present invention is to provide a photodetection method and photodetection device and photodetection/light emission device wherein there is no possibility of optical interference being picked up, which has a stable photodetection e.m.f. in a prescribed region, and which has high photodetection angular efficiency.
The following are means for resolving the above-mentioned issues.
A first aspect of the present invention is a method of photodetection, wherein photodetection is performed with a condenser lens positioned in front of a photodetection element, in which: as said condenser lens, a non-spherical lens is employed that concentrates at a single point without spherical aberration light that is input from the optic axis direction of this lens; and by positioning said photodetection element such that the photodetection surface of said photodetection element is further towards the lens than the point of convergence of said condenser lens, it is arranged that light that has passed through said condenser lens is photodetected over most of the photodetection surface of said photodetection element and that said photodetection element is positioned in a position where it can photodetect all of light that is incident inclined at a prescribed angle with respect to the optic axis of said condenser lens.
A second aspect of the present invention is a photodetection device, wherein photodetection is performed with a condenser lens positioned in front of a photodetection element, in which: as said condenser lens, a non-spherical lens is employed that concentrates at a single point without spherical aberration light that is input from the optic axis direction of this lens; and by positioning said photodetection element such that the photodetection surface of said photodetection element is further towards the lens than the point of convergence of said condenser lens, it is arranged that light that has passed through said condenser lens is photodetected over most of the photodetection surface of said photodetection element and that said photodetection element is positioned in a position where it can photodetect all of light that is incident inclined at a prescribed angle with respect to the optic axis of said condenser lens.
A third aspect of the present invention is a is photodetection device, according to aspect
2
, wherein said photodetection element is positioned in the position closest to said condenser lens in the range in which it can photodetect all of light incident at a prescribed angle with respect to said condenser lens.
A fourth aspect of the present invention is a photodetection device, according to aspect
2
, wherein the shape of the curved surface of the non-spherical surface of said non-spherical lens is a shape expressed by the following expression:
f
(
x
)=(1
/R
)·[
x
2
/[1+{1
+A ·
(
x/R
)
2
}
1/2
]]+Bx
4
+Cx
6
+Dx
8
+Ex
10
where R is the radius of curvature, x is the distance from the center of the lens, A, B, C, D and E are coefficients of the non-spherical surface, and f(x) is the lens shape when the distance is x.
A fifth aspect of the present invention is a photodetection device, according to aspect
4
, wherein R=1.67793 and A=−0.66229.
A sixth aspect of the present invention is a Photodetection device, according to aspect
4
, wherein R 1.72732 and A=−0.28636.
A seventh aspect of the present invention is a Photodetection device, according to aspect
2
, wherein the 95% photodetection e.m.f. range is within ±30
Dowa Mining Co. Ltd.
Ham Seungsook
Oliff & Berridg,e PLC
Spears Eric
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