Abstract:
Disclosed is 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 system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor.

Description:
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 λ/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 λ/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 system and the transmitter-receiver device, wherein the light beam deflecting device is controlled in accordance with a signal output from the position detecting sensor. The beam splitting device includes: in order from the light beam deflecting device side, a polarization beam splitting plane which allows a first linearly polarized laser beam of the modulated laser beam emitted from the laser source to pass therethrough to proceed towards the light beam deflecting device, and reflects a second linearly polarized laser beam of the complementing modulated laser beam transmitted from the complementing transmitter, the second linearly polarized laser beam having a phase different from a phase of the first linearly polarized laser beam by 90 degrees; and a beam splitting plane for splitting the second linearly polarized laser beam reflected by the polarization beam splitting plane into two separate laser beams to be respectively received by the position detecting sensor and the light receiving element. The modulated laser beam emitted from the laser source has a non-circular shape of intensity distribution, a first length in a θ-parallel direction of a cross section taken along a plane perpendicular to the modulated laser beam being shorter than a second length in a θ-perpendicular direction of the cross section, the first length and the second length extending perpendicularly to each other; and wherein the orientation of the laser source is determined so that the θ-parallel direction becomes substantially parallel to an optical axis extending from the polarization beam splitting plane to the beam splitting plane. 
     Preferably, the polarization beam splitting plane and the beam splitting plane are respectively formed on first and second planes of a common prism which are orthogonal to each other. 
     Preferably, an afocal optical system positioned between the light beam deflecting device and the transmitter-receiver device is also provided. 
     Preferably, the transmitter-receiver device includes a λ/4 retardation plate positioned between the afocal optical system and the polarization beam splitting plane. 
     Preferably, the light beam deflecting device includes an adjustable deflection mirror that is driven in accordance with the signal output from the position detecting sensor. 
     Preferably, the transmitter-receiver device includes a band-pass filter between the beam splitting plane and the light receiving element. 
     Preferably, the transmitter-receiver device includes a band-pass filter between the beam splitting plane and the position detecting sensor. 
     Preferably, the polarization beam splitting plane and the beam splitting plane are formed on the prism apart from each other by a predetermined distance. 
     Preferably, a casing is further provided in which the prism having the polarization beam splitting plane and the beam splitting plane is supported, the casing being provided with a light interceptive wall positioned around a boarder between the polarization beam splitting plane and the beam splitting plane. 
     Preferably, a casing in which the prism having the polarization beam splitting plane and the beam splitting plane is supported, the casing being provided, on a light path of the polarization beam splitting plane, with an opening for allowing light which is emitted from the semiconductor laser source to be reflected by the polarization beam splitting plane to exit the casing. 
     According to another aspect of the present invention, there is provided an integral transmitter-receiver optical communication apparatus, including: a laser source for emitting a laser beam modulated by transmission information signal; a telescopic optical system for transmitting the modulated laser beam and for receiving a complementing modulated laser beam transmitted from a complementing transmitter; a position detecting sensor; a light receiving element; a polarization beam splitting plane positioned between the laser source and the telescopic optical system; an adjustable deflection mirror positioned between the telescopic optical system and the polarization beam splitting plane and driven in accordance with a signal output from the position detecting sensor; and a beam splitting plane positioned adjacent to the polarization beam splitting plane for splitting a laser beam reflected by the polarization beam splitting plane into two separate laser beams to be respectively received by the light receiving element and the position detecting sensor. The polarization beam splitting plane allows a first linearly polarized laser beam of the modulated laser beam emitted from the laser source to pass therethrough to proceed towards the deflecting mirror, and reflects a second linearly polarized laser beam of the complementing modulated laser beam transmitted from the complementing transmitter, the second linearly polarized laser beam having a phase different from a phase of the first linearly polarized laser beam by 90 degrees. The beam splitting plane splits the second linearly polarized laser beam reflected by the polarization beam splitting plane into two separate laser beams to be respectively received by the light receiving element and the position detecting sensor. The modulated laser beam emitted from the laser source has a non-circular shape of intensity distribution, a first length in the θ-parallel direction of a cross section taken along a plane perpendicular to the modulated laser beam being shorter than a second length in the θ-perpendicular direction of the cross section, the first length and the second length extending perpendicularly to each other. The orientation of the laser source is determined so that the θ-parallel direction becomes substantially parallel to an optical axis extending from the polarization beam splitting plane to the beam splitting plane. 
     The present disclosure relates to subject matter contained in Japanese Patent Application Nos. 10-204551 (filed on Jul. 21, 1998) and 11-81376 (filed on Mar. 25, 1999) which are expressly incorporated herein by reference in their entireties. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be discussed below in detail with reference to the accompanying drawings in which: 
     FIG. 1 is a perspective view of the fundamental elements of the first embodiment of the transmitter-receiver unit of an integral transmitter-receiver optical communication apparatus to which the present invention is applied; 
     FIG. 2 is a cross sectional view of the fundamental elements of the first embodiment of the transmitter-receiver unit shown in FIG. 1; 
     FIG. 3 is a cross sectional view of the fundamental elements of the second embodiment of the transmitter-receiver unit of an integral transmitter-receiver optical communication apparatus to which the present invention is applied; 
     FIG. 4 is a cross sectional view of fundamental elements of the third embodiment of the transmitter-receiver unit of an integral transmitter-receiver optical communication apparatus to which the present invention is applied; and 
     FIG. 5 is a schematic illustration showing an example of a conventional integral transmitter-receiver optical communication apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show the fundamental elements of the first embodiment of a transmitter-receiver unit (transmitter-receiver device)  30  of an integral transmitter-receiver optical communication apparatus to which the present invention is applied. In FIGS. 1 and 2, members or elements similar to those shown in FIG. 5 have the same reference designators. As shown in FIG. 2, the first embodiment of the optical communication apparatus is provided between the deflection mirror  20  and the transmitter-receiver unit  30  with a second afocal optical system  40 . The second afocal optical system  40  includes a first lens group  40 A having a positive power and a second lens group  40 B having a negative power, in this order from the deflection mirror  20  side in a direction toward the transmitter-receiver unit  30 . The second afocal optical system  40  is an optical system of zero convergent power, whose focal points are infinitely distant, so that the light beam which exits from the second afocal optical system  40  remains as a substantially parallel beam if the light beam which enters the second afocal optical system  40  is a parallel beam. However, the beam diameter of the light beam incident on the second afocal optical system is reduced therethrough in the direction from the object side to the transmitter-receiver unit  30  side. The reduction ratio of the diameter (magnification) of the telescopic optical system (i.e., the first afocal optical system)  10  can be set to a ratio of approximately one to four (four times), while the reduction ratio of the diameter (magnification) of the second afocal optical system  40  can be set to a ratio of approximately one to two (two times). 
     The transmitter-receiver unit  30  is provided with a beam splitting unit (beam splitting device)  15  which includes a central prism  60  and a couple of auxiliary prisms  70  and  80 . Each of the central prism  60  and the couple of auxiliary prisms  70  and  80  is a right-angle prism. The central prism  60  includes two adhesive surfaces  61  and  62 , which are angled relative to each other by a right angle (90 degrees). Each of the two adhesive surfaces  61  and  62  is angled relative to an optical axis  40 X of the second afocal optical system  40  by 45 degrees. The auxiliary prism  70  includes an adhesive surface  71  which is attached to the adhesive surface  61  by an adhesive. The auxiliary prism  70  further includes incident/exit surfaces  72  and  73  which are angled relative to each other by a right angle, while each of the incident/exit surfaces  72  and  73  is angled relative to the adhesive surface  71  by 45 degrees. Likewise, the auxiliary prism  80  includes an adhesive surface  81  which is attached to the adhesive surface  62  by an adhesive. The auxiliary prism  80  further includes incident/exit surfaces  82  and  83  which are angled relative to each other by a right angle, while each of the incident/exit surfaces  82  and  83  is angled relative to the adhesive surface  81  by 45 degrees. In the illustrated embodiment shown in FIG. 2, the central prism  60  is provided with flat surfaces  63  and  64  which extend parallel to an optical axis O. Each of the flat surfaces  63  and  64  is angled relative to each of the adhesive surfaces  61  and  62  by 45 degrees. The flat surface  63 , which is narrower than the flat surface  64 , separates the adhesive surface  61  apart from the adhesive surface  62  in the direction of the optical axis  36 X of the light receiving element  36  by a distance “A” shown in FIG.  2 . 
     A polarization beam splitting thin layer is interposed between the adhesive surface  61  of the central prism  60  and the adhesive surface  71  of the auxiliary prism  70  to form a polarization beam splitting plane PBS therebetween. Likewise, a beam splitting thin layer is interposed between the adhesive surface  62  of the central prism  60  and the adhesive surface  81  of the auxiliary prism  80  to form the beam splitting plane BS therebetween. The polarization beam splitting plane PBS is angled relative to the optical axis  40 X of the second afocal optical system  40  and the optical axis  32 X of the semiconductor laser source  32  by 45 degrees. The beam splitting plane BS is angled relative to the optical axis  40 X of the second afocal optical system  40  and the optical axis  37 X of the position detecting sensor  37  by 45 degrees. The optical axis  32 X of the light receiving element  32  is coincident with the optical axis  40 X of the second afocal optical system  40 . 
     As shown in FIG. 2, a collimator lens  51  for collimating the laser beam emitted from the semiconductor laser source  32  is positioned on the optical axis  32 X of the semiconductor laser source  32 . A condenser lens  52  for focusing the received parallel beam on the light receiving element  36  and a band-pass filter  54  are positioned on the optical axis  36 X of the light receiving element  36 . A condenser lens  53  for focusing the received parallel beam on the light receiving element  37  and a band-pass filter  55  are positioned on the optical axis  37 X of the position detecting sensor  37 . The incident surfaces  72  and  73  of the auxiliary prism  70  extend perpendicular to the optical axis  36 X and the optical axis  32 X, respectively, while the incident surfaces  82  and  83  of the auxiliary prism  80  extend perpendicular to the optical axis  37 X and the optical axis  36 X, respectively. The locations of the light receiving element  36  and the position detecting sensor  37  can be exchanged. It should be noted that the cemented auxiliary prisms  70  and  80  are supported by a casing  90  therein by a supporting member which is not shown in either FIG. 1 or  2 . In addition, it should be noted that the lenses  51 ,  52  and  53 , and the filters  54  and  55  have been omitted in FIG.  1 . 
     A laser beam emitted from the semiconductor laser source  32  is incident on the incident surface  73  of the auxiliary prism  70 , which is positioned within the transmitter-receiver unit  30 . As shown schematically in FIG. 1, the laser beam emitted from the semiconductor laser source  32  has a linear or elliptic shaped intensity distribution, rather than a circular-shaped intensity distribution. Namely, in a cross section taken along a plane which is perpendicular to the laser beam emitted from the semiconductor laser source  32 , the length θH (shorter-axis direction) in a direction parallel (θ-parallel) to the optical axis  36 X is shorter than the length θV (longer-axis direction) in a direction perpendicular (θ-perpendicular) to the optical axis  36 X. The θ-parallel direction of length θH is the direction of the linear polarization. The orientation of the semiconductor laser source  32  is determined by rotating the semiconductor laser source  32  about the optical axis  32 X so that the θ-parallel direction of length θH becomes substantially parallel to the optical axis extending from the polarization beam splitting plane PBS to the beam splitting plane BS. Various conditions of the polarization beam splitting plane PBS, formed between the adhesive surface  61  of the central prism  60  and the adhesive surface  71  of the auxiliary prism  70 , are determined so that the polarization beam splitting plane PBS becomes a plane which reflects S-polarized light while allowing P-polarized light to pass therethrough. Namely, the polarization beam splitting plane allows the linearly polarized laser beam emitted from the semiconductor laser beam  32  (positioned as described above) to pass through the polarization beam splitting plane PBS while reflecting a linearly polarized laser beam whose phase is different from the linearly polarized laser beam emitted from the semiconductor laser beam  32  by 90 degrees. The λ/4 retardation plate  34  is provided for changing the P-polarize d light received from the complementing optical communication apparatus into S-polarized light by rotating the plane of polarization of the incident laser beam by 90 degrees. 
     The integral transmitter-receiver optical communication apparatus having the above mentioned structure is utilized in a manner similar to a conventional integral transmitter-receiver optical communication apparatus. Namely, the present embodiment of the optical communication apparatus is utilized by being positioned approximately 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 laser beam emitted by the semiconductor laser beam of the complementing optical communication apparatus, so that the laser beam modulated by the modulator  31  is received by the light receiving element  36  in both of the mutually complementing optical communication apparatuses. In this case, the possibility of the laser beam emitted from the semiconductor laser source  32  to be incident on the polarization beam splitting plane PBS may partly enter the side of the beam splitting plane BS is small because the θ-parallel direction of length θH of the incident laser beam extends substantially parallel to the optical axis which extends from the polarization beam splitting plane PBS to the beam splitting plane BS. Accordingly, as shown in FIG. 1, the possibility of crosstalk occurring becomes less, since the distance B between the incident laser beam and the boarder of the polarization beam splitting plane PBS and the beam splitting plane BS becomes large. This is apparent when comparing a case where the θ-perpendicular direction of length θV is oriented to extend substantially parallel to the optical axis which extends from the polarization beam splitting plane PBS to the beam splitting plane BS. Subsequently, the P-polarized light which is passed through the polarization beam splitting plane PBS is projected outwardly through the second afocal optical system  40 , the deflection mirror  20  and the telescopic optical system  10 , in that order. The laser beam emitted from the opposite optical communication apparatus is changed into S-polarized laser beam through the λ/4 retardation plate  34  to be then reflected by the polarization beam splitting plane PBS. Thereafter the laser beam reflected by the polarization beam splitting plane PBS is split into two beams to be respectively received by the position detecting sensor  37  and the light receiving element  36 . 
     Furthermore, in the illustrated embodiment shown in FIG. 2, the central prism  60  is provided with the flat surface  63  which separates the adhesive surfaces  61  and  62  apart from each other in the direction of the optical axis  36 X of the light receiving element  36 , which reduces the possibility of the laser beam (emitted from the semiconductor laser source  32  to pass through the polarization beam splitting plane PBS) partly proceeding as infiltrating light towards the beam splitting plane BS to enter the position detecting sensor  37  and/or the light receiving element  36 . Consequently, the occurrence of a crosstalk due to such infiltrating light can also be prevented. 
     FIG. 3 shows fundamental elements of the second embodiment of the transmitter-receiver unit  30  which corresponds to that shown in FIG. 2, wherein the occurrence of a crosstalk due to the infiltrating light is prevented, while FIG. 4 shows fundamental elements of the third embodiment of the transmitter-receiver unit  30  which corresponds to that shown in FIG. 2, wherein the occurrence of a crosstalk due to the infiltrating light is prevented. In FIG. 3, the casing  90  is provided, on a light path of the polarization beam splitting plane PBS, with an opening  91  for positively allowing the light which is emitted from the semiconductor laser source  32  to be reflected by the polarization beam splitting plane PBS to exit the casing  90 . In FIG. 4, the light which is emitted from the semiconductor laser source  32  to pass through the polarization beam splitting plane PBS is prevented from reaching either the position detecting sensor  37  or the light receiving element  36  by means of providing the casing  90  with a light interceptive wall  92  positioned around a boarder between the polarization beam splitting plane PBS and the beam splitting plane BS. The structures of the second and third embodiments are identical to that of the first embodiment except for the added opening  91  or the added wall  92 , so that other members or elements in the second and third embodiments which are similar to those in the first embodiment are designated by the same reference numerals and therefore will not be herein discussed. The second and third embodiments can be combined; namely, the casing  90  can be provided with both the opening  91  and the wall  92 . Furthermore, the orientation of the semiconductor laser source  32  and the set-up thereof in the first embodiment can be used together with the mechanical structures shown in FIGS. 2 through 4. 
     According to the above description, an integral transmitter-receiver optical communication apparatus has been provided, wherein the occurrence of a crosstalk between the transmitting light and the receiving light can be substantially prevented. 
     Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.