Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-07-31
2001-08-28
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06282000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical transmitting and receiving module for coupling a light emitting device and a light receiving device with an optical fiber through which a plurality of transmitting light beams and receiving light beams having different wavelengths are transferred.
2. Description of the Related Art
FIG. 5
is a cross section of a conventional optical transmitting and receiving module. As shown in the figure, the casing of this optical transmitting and receiving module can be roughly divided into four blocks, a center block
1
, a laser diode (LD) block
2
, a photodiode (PD) block
3
, and a fiber block
4
. Inside the center block
1
, an optical demultiplexing filter
5
is mounted. A laser diode (LD)
6
serving as a light emitting device and a lens holder
8
for holding a lens
7
are mounted in the LD block
2
. A photodiode (PD)
9
serving as a light receiving device and a lens holder
11
for holding a lens
10
are mounted in the PD block
3
. An optical fiber
12
and a lens holder
14
for holding a lens
13
are mounted in the fiber block
4
.
A transmitting light beam having a wavelength &lgr;
1
emitted from the LD
6
is made parallel by the lens
7
in the LD block
2
, passes through the optical demultiplexing filter
5
in the center block
1
, is collected by the lens
13
in the fiber block
4
, enters an end face of the optical fiber
12
, and is transmitted through the optical fiber
12
. On the other hand, a receiving light beam having a wavelength &lgr;
2
transmitted through the optical fiber
12
is diffused at the end face of the optical fiber
12
, is made parallel by the lens
13
in the fiber block
4
, is reflected from the optical demultiplexing filter
5
, is collected by the lens
10
in the PD block
3
, and is received by the PD
9
.
In the above-described conventional optical transmitting and receiving module, ideally, the optical demultiplexing filter
5
has an optical demultiplexing characteristic in which only a transmitting light beam having the wavelength &lgr;
1
emitted from the LD
6
is passed. Since a part of the transmitting light beam having the wavelength &lgr;
1
is actually reflected, the reflected light beam is irregularly reflected at inside walls of the center block
1
, passes through the optical demultiplexing filter
5
, and undesirably enters the light receiving surface of the PD
9
. When the transmitting light beam is detected by the PD
9
in this way, the S/N ratio of a receiving signal deteriorates.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an optical transmitting and receiving module which prevents a transmitting light beam emitted from a light-emitting device and reflected from an optical demultiplexing filter from being undesirably incident on the light-receiving surface of a light-receiving device after passing through the optical demultiplexing filter.
The foregoing object is achieved according to the present invention through the provision of an optical transmitting and receiving module provided with returning-light preventing means for preventing light from returning to a light-receiving device, wherein, in one casing block, a light-emitting device for emitting a transmitting light beam, a first lens for collimating the transmitting light beam emitted from the light-emitting device, an optical demultiplexing filter for passing the light beam collimated by the first lens, and a second lens for collecting the light passing through the optical demultiplexing filter at an end face of an optical fiber are coaxially disposed; a third lens for collecting a receiving light beam emitted from the end face of the optical fiber, collimated by the second lens, and reflected from the optical demultiplexing filter, and a light-receiving device for receiving the light collected by the third lens are disposed; a cover for covering the front space of a mounting surface for mounting the optical demultiplexing filter is placed on the casing block; and the cover is provided with returning-light preventing means for preventing the transmitting light beam reflected from the optical demultiplexing filter from reaching the light-receiving device after passing through the optical demultiplexing filter.
When the optical transmitting and receiving module is formed as described above, in the transmitting light beam having the wavelength &lgr;
1
emitted from the light-emitting device, since the reflected light reflected from the optical demultiplexing filter advances in a direction changed by the returning-light preventing means of the cover, it hardly occurs that the transmitting light beam having the wavelength &lgr;
1
is undesirably incident on the light-receiving surface of the light-receiving device, and the S/N ratio of a receiving signal is increased.
In the optical transmitting and receiving module, a tongue piece formed by cutting and folding a part of the cover may serve as the returning-light preventing means.
The tongue piece, formed by cutting and folding a part of the cover, can be easily manufactured by pressing a metal plate. In addition, it is expected that a returning-light preventing effect is positively obtained by adjusting the angle at which the tongue piece is folded.
As the returning-light preventing means, an unreflecting, absorbing material may be used. For example, an unreflecting, absorbing material is attached inside the cover and the material absorbs a transmitting light beam having the wavelength &lgr;
1
reflected from the optical demultiplexing filter. Alternatively, an uneven surface may be used. An uneven surface is formed inside the cover, and a transmitting light beam having the wavelength &lgr;
1
reflected from the optical demultiplexing filter is irregularly reflected from the uneven surface so that the reflected light does not return to the optical demultiplexing filter.
In the optical transmitting and receiving module, a label for securing the cover may be wound around the casing block so as to seal a hole formed in the cover by the tongue piece.
When the label for securing the cover is wound around the casing block so as to seal the hole formed around the tongue piece, the label also serves as cover securing means and a dust-proof effect of the cover is improved.
The receiving light reflected from the optical demultiplexing filter can be received by the light-receiving device by collecting it with the third lens. When the receiving light reflected from the optical demultiplexing filter is led to the third lens through a reflecting member in order to place the light-emitting device and the light-receiving device on the same plane in the casing block, the optical transmitting and receiving module can be easily mounted on a printed circuit board.
The casing block may be formed by cutting a metal material. It can be formed with a metal die such as a die-cast.
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Hattori Atsunori
Kikuchi Kimihiro
Kyoya Shoichi
Someno Yoshihiro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Pascal Leslie
Singh Dalzid
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