Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-05-22
2002-12-24
Epps, Georgia (Department: 2873)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S014000, C385S094000
Reexamination Certificate
active
06497517
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-receiving module which receives light signals in optical fiber transmissions. In particular, the invention achieves an improvement of inexpensive resin-molded package elements, and it is therefore an object of the invention to provide a resin-molded package having a structure by which the light receiving part is protected from external noise.
2. Prior Art
In a light-receiving module of a prior art, a receiving photodiode (PD module: as shown in
FIG. 1
) was housed and shielded in an expensive metallic casing.
A description is given of a light-receiving module of a prior art. In a PD module
15
in
FIG. 1
, a PD chip
17
is fixed at the middle of the upper surface of a metallic disk stem
16
. A metallic cap
18
is fixed on the stem
16
. A metallic cylindrical lens holder
19
is welded to the stem
16
so that it encloses a cap
18
. Also, a conical type ferrule holder
20
is fixed on the lens holder
19
.
A metallic ferrule
22
is fixed at the tip end of an optical fiber
21
. The ferrule
22
is inserted into a top hole of the ferrule holder
20
, and fixed therein. The tip ends of the optical fiber and ferrule are polished to be slant so that no reflected returning light enters an LD.
The PD module
15
is accommodated in a metallic casing consisting of a metallic stem
16
, metallic lens holder
19
and metallic ferrule holder
20
. The light receiving part is likely to be influenced by peripheral noise since the impedance thereof is high and the signal current thereof is small. However, since the light receiving part is covered by a metallic can, it is possible to be electrically shielded from peripheral noise.
An amplification circuit which amplifies the light current connects the PD module. This is also accommodated in a metallic casing and is designed to be resistant to noise.
FIG. 2
shows an example of such a light receiving circuit. A wiring pattern is depicted on an epoxy circuit substrate
30
. The lead pins of the PD
15
housed in a metallic can in
FIG. 1
is inserted into a wiring pattern
32
of the substrate
30
and soldered therein. An amplification circuit
31
connected the wiring pattern
32
is also an element covered by a metallic casing. The metallic casing is connected to a ground terminal on the circuit substrate. A wire
33
extending from an amplification circuit
31
enclosed by a metallic casing is connected to an output circuit and a power source.
Since, in the light receiving part, the signal current is low and the amplification is high, the light receiving part is apt to receive noise. As regards the prior art light-receiving module, the PD module, drive circuit, and amplification circuit are individually housed in separate casings. Therefore, even though the light-receiving module receives light in an external surrounding where noise exists, there is almost no influence where external noise reaches and is mixed with weak receiving signals.
Where the PD module in
FIG. 1
is used, there is no invasion of external noise into the PD (light receiving part) circuit. However, there are a considerable number of elements and parts. It is necessary for wires to be printed on a printed substrate
30
. The amplification circuit
31
enclosed by a metallic casing is soldered thereto, and a pin of the PD module housed in a metallic can in
FIG. 1
is further soldered thereto. As described above, amplification circuit elements housed in independent metallic cans are required, and printed substrates are also required. That is, the number of components is increased, thereby causing an increase in the production cost.
There are still further problems even in the module in
FIG. 1
, one of which is that the stem face and the optical fiber direction are vertical, and the other of which is that of light propagating in space over a considerable distance in a package. Therefore, a lens
26
is also required. The PD module is large-sized, and the light-receiving module in which an amplification part is incorporated will become large-sized as shown in FIG.
2
. The size of the light-receiving module will inevitably increase.
Further, since expensive metallic packages are used for PD and circuits such as an amplification circuit, production cost is increased. Insofar that an expensive and large-sized light-receiving module is used, light transmission cannot extend to general household use. It is essential that light-receiving modules are small-sized and inexpensive in order to allow extensive use of light transmission to include general household use. If individual components are housed in expensive metallic packages, low cost construction is difficult. Further, in view of making them small-sized, it is preferable that the PD and amplifier (AMP) are not separate from each other.
SUMMARY OF THE INVENTION
Recently, an attempt has been made to achieve a small-sized and inexpensive product by mounting a waveguide (or optical fiber), PD chip and AMP chip on one substrate. A PD and amplifier are mounted on one substrate, and light is caused to propagate in parallel on the substrate. Since a waveguide or an optical fiber, and a PD and an amplifier are mounted on a planar substrate, this is called “planar mounting”. The example is illustrated in
FIG. 3
(Plan view) and
FIG. 4
(Cross-sectional view). A light waveguide
44
is formed on an Si bench
42
, and a PD
47
is placed on the termination end, and an amplifier (AMP)
48
chip is provided on the same substrate
42
.
The termination end of an optical fiber
49
is connected to the end of the light waveguide
44
. Light propagating through the optical fiber
49
is input from the light waveguide
44
to the waveguide-type light-receiving layer of the PD
47
. That is, the light is converted to photocurrents. The photocurrents are immediately amplified by the amplifier
48
. Since light signals of the PD are directly amplified beforehand without routing in any unnecessary wiring, the light signals have high resistance against noise.
Since the waveguide or optical fiber, PD and amplifier are placed on one substrate, the optical receiving module can be small-sized and lightweight. Since the chips themselves are small, they can be disposed adjacent to each other, whereby the elements can be made further small-sized. The number of packages (casings) is also reduced one, and the cost thereof can be decreased. If a ceramic package is employed with a reduced number of packages, the hermeticity can be improved. However, the cost is not reduced. One of the most inexpensive packages is a commonly available resin mold. Therefore, it is highly advantageous to employ a resin mold package in order to reduce the production cost.
In such a pattern where the receiving signal light of the PD is intense (that is, a short-range transmission), it will cause almost no problem. However, as the receiving signals become weak due to long-range transmission, the problem of noise occurs. If only a resin mold is employed, there is no shielding effect against external noise. Since the input impedance is high with a high amplification ratio noise is likely to be detected despite the light receiving part consisting of a PD and an amplifier. That is, the light receiving part is of a structure that is liable to be affected by noise, and sufficient reception cannot be obtained with respect to weak signals since noise is not shielded. It is therefore an object of the invention to provide an inexpensive and small-sized light-receiving module which resolves such problems, and protect the light receiving part thereof from external noise.
A light-receiving module according to the invention has an optical fiber or a light waveguide, a light receiving element PD and an amplifier (AMP), wherein the light receiving part is covered by a conductive material having openings through which resin can pass, for example, a metallic plate, metallic meshed member, metallic porous plate having a plurality of pores, and the light receiving part, metallic meshed member an
Kuhara Yoshiki
Nakanishi Hiromi
Epps Georgia
Harrington Alicia M
Smith , Gambrell & Russell, LLP
Sumitomo Electric Industries Ltd.
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