Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-04-22
2003-11-18
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06650450
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light transmitting and receiving device and, in particular, to the one suitable for performing two-way optical communication by transmitting and receiving light beams in the outdoor atmosphere as a transmission medium.
2. Description of the Related Art
A variety of light transmitting and receiving devices for transmitting and receiving optical beams through the outdoor atmosphere as a transmission medium have been proposed.
In the optical communication system disclosed in Japanese Patent Laid-Open No. 5-134207, two identically constructed optical communication devices installed facing each other with a distance allowed therebetween perform two-way optical communication.
FIG. 24
shows a major portion of one conventional optical communication device. This optical communication device comprises light projecting means having a light emitting device
101
for generating a signal light and a positive-powered projection lens
102
, light receiving means having a light receiving device
103
for receiving a signal light and a positive-powered light receiving lens
104
, a polarizing beam splitter
105
which reflects a projected light beam while receiving a received light beam, and a beam expander
106
which expands a projected light beam LA while converging a received light beam LB. The beam expander
106
has a negative-powered lens unit
107
and a positive-powered lens unit
108
.
The polarizing beam splitter
105
is located where the optical axes of the light projection lens
102
and the light receiving lens
104
intersect each other, and the beam expander
106
is arranged to the transmission side of the polarizing beam splitter
105
for the projected light beam.
A laser diode is used for the light emitting device
101
for generating the signal light, and the polarizing beam splitter
105
is a rectangularly parallelopipedal or cubic polarizing beam splitter having a beam splitting surface
105
a
of a deposited dielectric multilayer which reflects most of the s-polarized light beam while transmitting most of the p-polarized light beam.
To achieve efficient light transmission and reception using the polarizing beam splitter
105
, a light beam LB received from an opposing light transmitting and receiving device B (not shown) is designed to be p-polarized when a transmitted light LA from the light transmitting and receiving device A shown in
FIG. 24
is s-polarized.
The s-polarized light beam of the light beam emitted from the light emitting device
101
for generating the signal light becomes a substantially parallel light beam, is mostly reflected by the beam splitting surface
105
a
of the polarizing beam splitter
105
, and is transmitted as the transmitted light beam LA from the light transmitting and receiving device A to the light transmitting and receiving device B.
The (p-polarized) light beam projected by the light transmitting and receiving device B is incident on the light transmitting and receiving device A as the received light beam LB, and is mostly transmitted through the beam splitting surface
105
a
of the polarizing beam splitter
105
, and reaches the light receiving device
103
for detecting the signal light.
Two-way optical communication is performed for light transmission and reception in this way in the above system.
In the optical communication device constructed as shown in
FIG. 24
, the light beam projected from the light projection lens
102
is substantially vertically incident, in the form of a substantially parallel light beam, on a transmission and reception surface
109
of the polarizing beam splitter
105
. For this reason, a light beam
110
reflected from the transmission and reception surface
109
, out of the projected light beam, is introduced in whole (i.e., in its entirety) in an effective light receiving surface of the light receiving device
103
as noise light.
This noise light is now referred to as a first noise light. As shown in
FIG. 25
, the light beam
112
transmitted through the beam splitting surface
105
a
reaches and is reflected by a surface
111
shown as a top surface, is reflected from the beam splitting surface
109
a
, travels to the light receiving lens
104
, and is introduced in whole in the effective light receiving surface of the light receiving device
103
for signal light detection as noise light. This noise light is here referred to as a second noise light.
The first and second noise light rays are the cause for a so-called cross-talk, and degrade the accuracy of optical communication. To cope with the second noise light, the surface
111
is conventionally subjected to antireflection process by grinding and then applying a black coating thereon. To cope with the first noise light, the only available antireflection process is applying an antireflection coating onto the transmission and reception surface
109
. The antireflection coating cannot reduce reflectance to zero and cross-talk still persists.
Simply tilting the polarizing beam splitter
105
of the conventional structure cannot improve the situation in which two noise light rays return to the light receiving lens
104
. If an attempt is made to tilt only the transmission and reception surface
109
of the polarizing beam splitter
105
, the optical axis of projection and the optical axis of reception fail to intersect each other at a right angle, and in such a case, particular consideration needs to be given to the design of a lens barrel, requiring a complex component design.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a light transmitting and receiving device for use as an optical communication device for accurate optical communication in which at least first noise light or second noise light is efficiently prevented from entering a light receiving element by setting up the appropriate form of a polarizing beam splitter through which transmission and reception of beams are performed for two-way optical communication.
Accordingly, in one aspect, the light transmitting and receiving device of this invention, through the polarizing beam splitter of a transparent body including a beam splitting surface therewithin, projects a light beam from light projecting means in a predetermined direction and receives a light beam in the predetermined direction at light receiving means, wherein the polarizing beam splitter is designed such that a light beam reflected from one of the surfaces constituting the polarizing beam splitter, out of the light beam from the light projecting means, is introduced into the light receiving means via the beam splitting surface at an inclination with respect to the optical axis of the light receiving means.
More particularly, the light transmitting and receiving device of the present invention preferably comprises a light projecting unit having an optical axis of projection, a light receiving unit having an optical axis of reception, and an optical member, disposed where the optical axis of projection intersects the optical axis of reception, including therewithin a light beam splitter which reflects one of the light beam of the light projecting unit and the light beam of the light receiving unit while transmitting therethrough the other of the light beam of the light projecting unit and the light beam of the light receiving unit, and having a transmission surface from which the light beam of the light projecting unit is transmitted and a surface opposing the transmission surface, wherein the transmission surface and the opposing surface are mutually in parallel and are inclined to the principal ray of the transmitted light beam from the transmission surface.
In the light transmitting and receiving device, the light projecting unit preferably comprises a light source for emitting a polarized light beam, and the beam splitter is a polarizing beam splitter.
Preferably, the optical axis of projection and the optical axis of reception are perpendicular to each other.
Preferably, the optical member has a
Orino Kanjo
Oshima Shigeru
Canon Kabushiki Kaisha
Pascal Leslie
Singh Dalzid
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