Abstract:
An optical space transmission apparatus which performs a first communication, in which a light beam propagating through a space is used, with a remote apparatus includes a communication section and an identification section. Here, the communication section performs a second communication, which is different from the first communication, with a plurality of remote apparatuses and the identification section identifies the remote apparatus, which performs the first communication, from among the plurality of remote apparatuses by performing the second communication.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an optical space transmission apparatus which communicates from a communication apparatus installed at one point with communication apparatuses installed at a plurality of points using an optical signal which propagates through the air. 
   2. Description of the Related Art 
   Using  FIG. 6 , an overview of a conventional optical space communication system will be explained. Here,  FIG. 6  is a schematic view of the conventional optical space communication system (Japanese Patent Laid-Open No. 2000-224112 (European Patent No. 1054520B1: European equivalent to the Japanese Patent)) and as shown in this schematic view, the optical space communication system is constructed by an optical space transmission apparatus  60  and remote apparatuses  61   a  to  61   c.    
   An optical signal radiated from a light source  62  of the optical space transmission apparatus  60  is changed to a substantially parallel light beam  64  which is spread a little when passing through an optical system  63 , this light beam  64  is reflected on a movable mirror  65  and transmitted to the respective remote apparatuses  61   a  to  61   c.    
   Furthermore, the movable mirror  65  is driven according to a preset sequence and angle, and when a transmission to the remote apparatus  61   a  is completed, then the movable mirror  65  directs the light beam to the remote apparatus  61   b , and when a transmission to the remote apparatus  61   b  is completed, then the movable mirror  65  directs the light beam to the remote apparatus  61   c  and transmits the light beam to the remote apparatus  61   c . In this way, by scanning the remote apparatuses sequentially and performing communications, communications are established between a communication apparatus installed at one point and communication apparatuses installed at a plurality of points. 
   This scanning is performed at a high speed and the users of the respective remote apparatuses need not be aware of a waiting time when receiving signals. Moreover, an optical signal is free of restrictions on the frequency band as in the case of radio waves, and can thereby transmit information at a high speed and communicate a sufficient volume of information even through intermittent transmissions using sequential scanning. 
   Moreover, in the above described Japanese Patent, it is proposed that a center apparatus scans respective remote apparatuses using a mirror, is provided with a light source and an optical detector to perform bidirectional communications with the remote apparatuses. 
   Furthermore, for reasons of safety of eyes, to prevent degradation of the communication quality of optical radio waves generated due to attenuation of light beams caused by weather conditions such as rain and snow under conditions in which the output levels of light beams are limited, it is necessary to narrow the diameters of light beams and correctly direct the light beams to the remote apparatuses. As a method of realizing this, in the Japanese Patent Laid-Open No. 2000-224112, it is proposed about a function in which five photodiodes are arrayed and the directions of light beams based on the outputs of the respective photodiodes are corrected. 
   Moreover, a method of calculating the directions of the remote apparatuses by projecting the light beams sent from the remote apparatuses onto an optical position detection element is also widely known as a method of correcting the directions of light beams. 
   However, for the method of changing the angle of the mirror according to a preset sequence and angle and sequentially scanning all the remote apparatuses, communication channels are also established with remote apparatuses not requiring communications. For this reason, when many remote apparatuses are scanned, the mirror is also driven to irradiate light beams to remote apparatuses not requiring communications, wasting the time to decide that communications are not necessary, unable to allocate sufficient communication times to remote apparatuses requiring communications. Furthermore, the method of using an array of five photodiodes to correctly direct light beams to remote apparatuses and finding exact directions of the remote apparatuses based on the outputs of the respective photodiodes and the optical position detection elements, etc., is adopted, but when the power of a remote apparatus is OFF, the center apparatus cannot identify the remote apparatus and wastes time until the center apparatus searches the remote apparatus and decides consequently that a communication therewith is not possible, unable to realize efficient optical space communications between one point and multi points. 
   Moreover, even when the power of the remote apparatus is ON, a processing time for correctly directing light beams to remote apparatuses not requiring communications is wasted, unable to realize efficient optical space communications between one point and multi points. 
   SUMMARY OF THE INVENTION 
   One aspect of the optical space transmission apparatus of the present invention performs a first communication, in which a light beam propagating through a space is used, with a remote apparatus and includes a communication section and an identification section. Here, the communication section performs a second communication, which is different from the first communication, with a plurality of remote apparatuses and the identification section identifies the remote apparatus, which performs the first communication, from among the plurality of remote apparatuses by performing the second communication. 
   One aspect of the optical space communication system of the present invention includes the optical space transmission apparatus and the plurality of remote apparatuses. 
   The features of the optical space transmission apparatus and the optical space communication system of the present invention will become more apparent from the following detailed description of a preferred embodiment of the invention with reference to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram of an optical space communication system according to Embodiments 1 to 3; 
       FIG. 2  is a front view of the light-receiving surface of an optical position detection element; 
       FIG. 3  is a flow chart showing a control procedure executed in a center apparatus according to Embodiment 1; 
       FIG. 4  is a flow chart showing a control procedure executed in a center apparatus according to Embodiment 2; 
       FIG. 5  is a flow chart showing a control procedure executed in a center apparatus according to Embodiment 3; and 
       FIG. 6  is a schematic block diagram of an optical space communication system according to a conventional example. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be explained below. 
   Embodiment 1 
     FIG. 1  is a schematic diagram of an optical space communication system according to an embodiment of the present invention. In  FIG. 1 , reference numeral  10  denotes a center apparatus (an optical space transmission apparatus) and  11   a ,  11   b ,  11   c  denote remote apparatuses. Here, when the respective remote apparatuses  11   a  to  11   c  need to communicate with the center apparatus  10 , the remote apparatuses requests the center apparatus  10  for communications using a low-speed channel  13  (e.g., telephone line, radio channel, another optical channel). 
   The center apparatus  10  scans the remote apparatuses which have requested communications through the low-speed channel  13  using a light beam  12  and sequentially performs bidirectional communications with the remote apparatuses. Here, if a telephone line is used as the low-speed channel  13 , it is possible to use an existing communication line and thereby reduce costs. 
   When a communication with one remote apparatus is completed, a movable mirror  104  is driven to switch a scan to the next remote apparatus which has requested a communication through the low-speed channel  13 . 
   The center apparatus  10  is provided with a light-emitting element  101  (e.g., semiconductor laser) and a transmission light emitted from this light-emitting element  101  is sent to the remote apparatuses  11   a  to  11   c . The transmission light emitted from the light-emitting element  101  is deflected and the deflection direction is set to the direction horizontal to the surface of the sheet. 
   Furthermore, the transmission light is reflected by the polarization beam splitter  102  toward a transmission/reception lens  103 , passes through the transmission/reception lens  103  and is changed to a substantially parallel light beam which is spread a little. This light beam enters a movable mirror  104  (reflective member) and is sent to a desired remote apparatus by changing the angle of the movable mirror  104 . 
   On the other hand, the received light sent from the remote apparatuses  11   a  to  11   c  follows a reverse path on the same optical axis as that of the transmission optical signal of the center apparatus  10 , is reflected on the movable mirror  104 , then passes through the transmission/reception lens  103  and enters the polarization beam splitter  102 . Here, since the polarization direction of the received light from the remote apparatuses  11   a  to  11   c  is set to the direction perpendicular to the polarization direction of the transmission light (the polarization direction is a direction perpendicular to the surface of the sheet), the received light passes through the polarization beam splitter  102  as is and enters a beam splitter  105 . 
   Most of the received light passes through the beam splitter  105 , enters a light-receiving element  106  for detection of an optical signal and is detected as a communication signal, while a part of the light is reflected by the beam splitter  105  and enters an optical position detection element  107 . 
   Next, the structure of the optical position detection element  107  will be explained using  FIG. 2 . Here,  FIG. 2  is a front view of the light-receiving surface of the optical position detection element  107  and shows a spot formed on this light-receiving surface together. 
   The optical position detection element  107  is a photodiode divided into four portions  21   a  to  21   d  and is designed to output signals according to a light intensity distribution of a light spot  22  formed on the light-receiving surface from these photodiodes  21   a  to  21   d.    
   As shown in  FIG. 2 , the light spot  22  is formed on a peripheral area slightly away from the central area of the photodiodes  21   a  to  21   d  in the condition before a correction of the optical axis shift which will be described later. 
   The light incident upon the photodiode  107  is photoelectrically converted, and then transmitted to a control circuit  109  where the output voltages from the photodiodes  21   a  to  21   d  are compared and an optical axis shift correction information is thereby generated. 
   Then, the control circuit  109  generates a drive signal for driving the movable mirror  104  based on this optical axis shift correction information and sends this information to a drive circuit  110 . This causes the movable mirror  104  to be driven to shift the light spot  22  positioned in the peripheral area of the photodiodes  21   a  to  21   d  to the central area so that the output voltages output from the photodiodes  21   a  to  21   d  become substantially equal. As a result, the shift on the optical axis between the transmission light and the received light is corrected and an automatic tracking is performed so that the transmission light sequentially scans the remote apparatuses. 
   A communication request from a first remote apparatus (e.g., the remote apparatus  11   a ) sent through the low-speed channel  13  is received by a communication unit  108  and the information thereof is sent to the control circuit  109  (an identification section). When the communication with the first remote apparatus is completed, the control circuit  109  drives the movable mirror  104  so that the light beam  12  is directed to a second remote apparatus (e.g., the remote apparatus  11   b ) which has sent the next communication request through the communication unit  108 . 
   In the above embodiment, the movable mirror  104  is driven so as to communicate transmission light in order in which communication requests are sent, but it is also possible to switch the movable mirror  104  in order in which the remote apparatuses  11   a  to  11   d  are registered, in descending order of priority given to the communication requests, in ascending order of distances to the center apparatus  10  or in order combining these orders. 
     FIG. 3  shows a control flow at the center apparatus  10  according to this embodiment of the present invention. In the process in S 302 , the first remote apparatus is determined and in the process in S 303 , an initial direction adjustment is made to the remote apparatus determined in S 302 . The initial direction adjustment at the time of installation, etc., is made by manually driving the movable mirror  104  for the respective remote apparatuses. Furthermore, it is also possible to adopt a method of automatically calculating the direction of the remote apparatus by calculating a position coordinate information on the center apparatus and the remote apparatus using GPS, etc. 
   When the angle of the movable mirror  104  is moved and the optical signal from the user can be received to a certain degree, an automatic tracking functions, and therefore it is possible to accurately direct the light beam to the remote apparatus. 
   In the process in S 304 , the angle information on the movable mirror  104  at that time is written in a memory in the control circuit  109 . When the initial direction settings for all the remote apparatuses  11   a  to  11   d  are not completed in the process in S 305 , the next remote apparatus is determined in the process in S 306 , and S 303  and S 304  are repeated until the initial direction settings for all the remote apparatuses  11   a  to  11   d  are completed. 
   When the initial direction settings for all the remote apparatuses  11   a  to  11   d  are completed, it is decided in the process in S 307  whether there is any remote apparatus which has sent a communication request and S 307  is repeated until a remote apparatus which has sent a communication request appears. When a remote apparatus which has sent a communication request is found in the process in S 307 , the remote apparatus is determined in the process in S 308  in any one of order in which the remote apparatuses  11   a  to  11   d  are registered, order of communication requests, descending order of priority given to the communication requests, ascending order of distances to the center apparatus  10  or order combining these orders. 
   Then, in the process in S 309 , the movable mirror  104  is driven in the direction of the remote apparatus determined in the process in S 308  and when an optical communication with the remote apparatus is established, the communication is started in the process in S 310 . Here, the remote apparatus directs a light beam to the center apparatus. A loop is executed until the communication is completed in the process in S 311  and when the communication is completed, the process goes back to S 307  and repeats steps in S 307  to S 311 . 
   Embodiment 2 
     FIG. 4  shows a processing flow of searching a remote apparatus which has sent a communication request in the center apparatus  10  of this embodiment using a low-speed channel  13 . 
   First, in S 402 , a remote apparatus for which it is checked to see whether there is any communication request or not is determined and the remote apparatus is registered. Then, in S 403 , it is checked to see whether there is any communication request or not from the remote apparatus determined in the process in S 402  and a reply from this remote apparatus is waited. When no reply is received from the remote apparatus in S 404 , the processes in S 404  and S 405  are repeated until the waiting times out in S 405 . When there is a reply from the remote apparatus in S 404 , the process moves to the process in S 406  and when the reply from the remote apparatus is a communication request, the process moves to S 407 . 
   In S 407 , it is decided whether the remote apparatus which has sent a communication request is registered as the remote apparatus which has sent a communication request or not, and if the remote apparatus is not registered yet, the remote apparatus is registered as the remote apparatus which has sent a communication request in the process in S 408  and the process goes back to S 411 . When the remote apparatus is already registered, the process go back to S 411  as is. 
   When the reply from the remote apparatus is not a communication request in the process in S 406 , the process moves to S 409  and checks to see whether the remote apparatus is already registered as the remote apparatus which has sent a communication request or not. When the remote apparatus is registered as the remote apparatus which has sent a communication request, the registration is deleted in the process in S 410  and when the remote apparatus is not registered, the process moves to the process in S 411  as is. The next remote apparatus to be checked is determined in the process in S 411  and the process goes back to S 403  and repeats the above described flow. 
   Embodiment 3 
     FIG. 5  shows a processing flow of spontaneously sending a communication request from the remote apparatuses  11   a  to  11   d . In the process in S 502 , the center apparatus  10  waits a communication request and the communication request cancellation request from the remote apparatuses. Upon receiving the request from the remote apparatus in the process in S 503 , the process moves to the process in S 504  and if the request is a communication request, the remote apparatus is registered as the remote apparatus which has sent a communication request in the process in S 505 . When the request is the communication request cancellation request in the process in S 504 , this remote apparatus is deleted from the registration of remote apparatuses which have sent communication requests in the process in S 506 . Then, the process moves to the process in S 502  and repeats the above described flow thereafter. 
   Embodiments 1 to 3 above have assumed that the number of remote apparatuses is four but it goes without saying that the number of remote apparatuses can be three or less or five or more. 
   According to the embodiments above, it is possible to communicate with only the remote apparatuses requiring communications and thereby efficiently communicate with a plurality of remote apparatuses. Furthermore, it is possible to remove remote apparatuses not requiring communications from those to be scanned and thereby secure more communication times for remote apparatuses requiring communications. 
   While preferred embodiments have been described, it is to be understood that modification and variation of the present invention may be made without departing from the scope of the following claims. 
   “This application claims priority from Japanese Patent Application No. 2003-413892 filed on Dec. 11, 2003, which is hereby incorporated by reference herein.”