Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-07-19
2002-05-07
Chan, Jason (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06384944
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical communication apparatus, and more specifically to an integral transmitter-receiver optical communication apparatus which is commonly used for both transmitting and receiving signals in the form of a laser beam modulated in accordance with an information signal.
2. Description of the Related Art
FIG. 5
shows an integral transmitter-receiver optical communication apparatus as an example to which the present invention is applicable. This optical communication apparatus includes a telescopic optical system
10
, a light beam deflecting device
20
and a transmitter-receiver unit
30
. The telescopic optical system
10
is used for both projecting and receiving a laser beam modulated by the information signal. In this illustrated example, the telescopic optical system
10
is constructed as a reflecting telescope. The light beam deflecting device
20
is positioned between the telescopic optical system
10
and the transmitter-receiver unit
30
to adjust the direction of the receiving light which enters the transmitter-receiver unit
30
through the telescopic optical system
10
and also the direction of the transmitting light which is emitted from the transmitter-receiver unit
30
to the telescopic optical system
10
.
The transmitter-receiver unit
30
is provided with a semiconductor laser source
32
which emits a laser beam modulated by the modulator
31
in accordance with a transmission information signal. The semiconductor laser source
32
is constructed to emit the modulated laser beam so that S-polarized light thereof is reflected. The transmitter-receiver unit
30
is further provided with a polarization beam splitter (PBS)
33
on which the linearly polarized light emitted from the semiconductor laser source
32
is incident. The polarization beam splitter
33
reflects S-polarized light while allowing P-polarized light to pass therethrough. The S-polarized light that is reflected by the polarization beam splitter
33
is incident on the light beam deflecting device
20
via a &lgr;/4 retardation plate
34
. The transmitter-receiver unit
30
is further provided, on a transmission light path of the polarization beam splitter
33
, with a beam splitter
35
in order to receive the light signal transmitted from a complementing optical transmitter, which is positioned opposite to the optical communication apparatus. A light receiving element
36
and a position detecting sensor
37
, each of which receives a modulated laser beam, are respectively positioned on two separate light paths split by the beam splitter
35
. Accordingly, the light emitted by the aforementioned complementing optical transmitter to be received by the telescopic optical system
10
is turned into P-polarized light through the &lgr;/4 retardation plate
34
. Subsequently, the P-polarized light passes through the polarization beam splitter
33
and then enters the beam splitter
35
to be split into two separate light beams so that the two separate light beams are incident on the light receiving element
36
and the position detecting sensor
37
, respectively. A signal processing circuit
38
is connected to the light receiving element
36
to read out the information conveyed by the light received by the light receiving element
36
.
The integral transmitter-receiver optical communication apparatus having the aforementioned structure is generally positioned opposite to the semiconductor laser beam of a complementing optical communication apparatus having an identical structure, wherein the transmission range of the laser beam emitted by the semiconductor laser beam
32
overlaps the transmission range of the semiconductor laser beam emitted by the complementing optical communication apparatus, so that the laser beam modulated by the modulator
31
can be received by the light receiving element
36
in each of the mutually complementing optical communication apparatuses.
In each of the mutually complementing optical communication apparatuses, the light beam deflecting device
20
maintains the parallelism of the transmitting laser beam which is incident thereon to be deflected outwards through the telescopic optical system
10
, and also the parallelism of the received laser beam (which is emitted by the complementing optical communication apparatus) to be incident on the light beam deflecting device
20
. The light beam deflecting device
20
can include a rotatable deflection mirror which can be driven about two axes (X and Y axes) which are orthogonal to each other. A rotational portion of the rotatable deflection mirror is coupled to an electromagnetic driver which includes coils and permanent magnets. This electromagnetic driver is driven in accordance with signals output from the position detecting sensor
37
. The position detecting sensor
37
detects the variation in the position of the receiving light which enters the transmitter-receiver unit
30
to output a drive command signal to the electromagnetic driver through a controller
21
and an X/Y driver
22
to rotate the deflection mirror
20
about the X-axis and the Y-axis thereof, so that the receiving light enters the transmitter-receiver unit
30
at an appropriate position. The position of the deflection mirror
20
continues to be detected by the position detecting sensor
37
in a feed-back operation so that the parallelism of both the light transmitted by the transmitter and the light received by the receiver are maintained.
In the conceptual structure of the integral transmitter-receiver optical communication apparatus shown in
FIG. 5
, crosstalk does not occur, in theory, between the transmitting laser beam emitted from the semiconductor laser source
32
and the received laser beam incident upon the light receiving element
36
and the position detecting sensor
37
. However, in practice, there is a possibility of such crosstalk occurring due to the polarization beam splitter
33
not being able to perfectly polarize the incident light (in fact, it is practically impossible to provide a polarization beam splitter having a polarization beam splitting thin layer therein through which the incident light is perfectly polarized, and hence, the occurrence of a small percentage of infiltrating (stray) light cannot be prevented), and/or due to the polarization beam splitter
33
and the beam splitter
35
being positioned very closely to each other.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide an integral transmitter-receiver optical communication apparatus, wherein the occurrence of a crosstalk between the transmitting light and the receiving light can be prevented. A more specific object of the present invention is to provide an integral transmitter-receiver optical communication apparatus wherein the transmitting light can be prevented from entering the side of the receiver, in the case where a polarization beam splitter and a beam splitter (i.e., a polarization beam splitting plane and a beam splitting plane) are positioned adjacent to each other.
To achieve the above-mentioned objects, according to the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a transmitter-receiver device which includes: a transmitter having a laser source for emitting a laser beam modulated in accordance with a transmission information signal, a receiver having a position detecting sensor and a light receiving element which receive a complementing modulated laser beam transmitted from a complementing transmitter, and a beam splitting device for splitting the modulated laser beam and the complementing modulated laser beam which are incident thereon as two separate laser beams; a telescopic optical system for transmitting the modulated laser beam emitted by the laser source and for receiving the complementing modulated laser beam transmitted from the complementing transmitter; and a light beam deflecting device positioned between the telescopic optical s
Gotoh Tatsuo
Kojima Yoichi
Takayama Homu
Wakamiya Shunichiro
Yamagata Masakazu
Asahi Seimitsu Kabushiki Kaisha
Chan Jason
Greenblum & Bernstein P.L.C.
Phan Hanh
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