Abstract:
The invention provides an optical communication apparatus to communicate a data signal. The optical communication apparatus is capable of firmly carrying out optical communication using an optical transmission media. The optical transmission media may be connected between a first optical communication apparatus and a second optical communication apparatus. Upon a detector detecting an incoincidence between an electric signal outputted from a light receiving element and a test signal, a controller may control a parameter of a light emitting power control signal to increase an intensity of an optical signal outputted from a light emitting element. Upon the detector detecting a coincidence therebetween, the controller may set a current value of a parameter of the light emitting power control signal as a parameter upon a selector selecting the data signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical communication apparatus. 
     2. Description of the Related Art 
     FIG. 8 is a block diagram for explaining an example of the constitution of a conventional optical communication apparatus. There is a diode (hereinafter, abbreviated as LD)  1  which converts an electric signal into laser beam having a corresponding intensity and transmits the laser beam to outside via an optical fiber, not illustrated. An LD driving unit  2  drives LD  1  in accordance with transmission data (Tx. Data) inputted via a signal line  3  and an output signal  7  from APC (Auto Power Control)  5 . A portion of the laser beam emitted from LD  1  is incident on a photodiode  4  and the photodiode  4  converts the incident laser beam into an electric signal. 
     APC  5  controls the LD driving unit  2  in accordance with the electric signal outputted from the photodiode  4  and a reference amplitude (Tx. Ref) of a transmission signal inputted from a signal line  6  such that the intensity of the laser beam emitted from LD  1  becomes a predetermined amplitude. Laser beam transmitted via an optical fiber, not illustrated, is incident on a photodiode  8  and the photodiode  8  converts the laser beam into a corresponding electric signal. An amplifying unit  9  amplifies the electric signal outputted from the photodiode  8  by a predetermined gain and outputs the electric signal to an inner portion of the optical communication apparatus as reception data (Rx. Data) via a signal line  10 . 
     The transmission data is supplied to the LD driving unit  2  via the signal line  3 . The LD driving unit  2  drives LD  1  to emit laser beam in accordance with the transmission data and the output signal  7  from APC  5 . The laser beam emitted from LD  1  is transmitted to other party of communication, not illustrated, via an optical fiber, not illustrated. 
     The portion of the laser beam emitted from LD  1  is incident on the photodiode  4  and accordingly, an electric signal in correspondence with the intensity of the laser beam emitted from LD  1  is inputted to APC  5 . APC  5  compares the electric signal outputted from the photodiode  4  with the reference amplitude (Tx. Ref) of the transmission signal inputted from the signal line  6  and controls the LD driving unit  2  such that both maintain a predetermined relationship (for example, such that both are equal to each other). As a result, the intensity of the laser beam emitted from LD  1  always becomes a predetermined amplitude. 
     Further, the laser beam transmitted via an optical fiber, not illustrated, is photoelectrically converted into the corresponding electric signal by the photodiode  8 , amplified by the amplifying unit  9  by a predetermined gain and thereafter is outputted to the inner portion of the optical communication apparatus as reception data via the signal line  10 . 
     According to the above-described conventional optical communication apparatus, the intensity of the transmitted laser beam is always set to be a predetermined amplitude. It is general that the intensity of the laser beam is set with transmission loss of a longest optical fiber as a reference in a system thereof (a system constituted by connecting optical communication apparatus to each other). 
     When a power value of laser beam is set to an intensity capable of sufficiently dealing with transmission loss in an optical fiber having a longest length in a system, the system can ensure a sufficient intensity (power value). 
     It is said that the life of a laser diode (LD) is inversely proportional to the second through the third power of an intensity of emitted laser beam. Therefore, in the case in which an intensity of laser beam which can communicate through an optical fiber having a longest length which is predicted in using the optical fiber in a system when communication is carried out by an optical fiber having a short length, the intensity becomes excessively heavy and the life of LD is significantly shortened. 
     That is, in the case in which the intensity of laser beam which can communicate through the optical fiber having the long length which is predicted in using the optical fiber in a system, when lengths of optical fibers used differ from each other significantly, the intensity of laser beam inputted to a reception unit of an optical communication apparatus similarly differs significantly. For example, in the case of LAN (Local Area Network) or the like, the length of an optical fiber used is varied significantly substantially from 1 m through 2 km and accordingly, a difference in transmission losses becomes about 16 dB and the intensity of laser beam is varied significantly in accordance therewith. Such a difference is particularly significant in POF (Plastic Optical Fiber) having large transmission loss. 
     When the intensity of inputted laser beam differs significantly in this manner, in order to ensure an error rate at a constant value or lower in respect of input of laser beam in any intensity, the dynamic range of light in an optical communication apparatus needs to provide sufficiently widely, as a result, there poses a problem in which design of the apparatus becomes complicated and fabrication cost of the apparatus is increased. 
     Further, when the problem of Eye Safe is considered, it is preferable to set the intensity of laser beam as small as possible. When the intensity of laser beam is set low, in a system having significant loss (for example, a system connected by POF or the like), there poses also a problem in which the design becomes difficult owing to the problem of the dynamic range as mentioned above. 
     A conventional optical communication apparatus is not constituted such that control of light emitting power and reception sensitivity is dynamically carried out in accordance with a kind, a length, a situation of laying thereof, a condition of using thereof or the like of an optical fiber used. Therefore, the optical communication apparatus including the optical fiber needs to fabricate under a severe specification conscious of the worst condition, as a result, the apparatus becomes expensive. This is significant particularly in the case of using an optical transmission medium having comparatively large transmission loss such as an optical fiber made of plastic. 
     Therefore, the present invention relates to an optical communication apparatus resolving the above-described problem and capable of firmly executing optical communication using an optical transmission medium among optical communication apparatus under an optimum condition. 
     SUMMARY OF THE INVENTION 
     Hence, according to a first aspect of the present invention, there is provided an optical communication apparatus connected to an optical communication apparatus on other party side via an optical transmission medium for communicating a data signal with the optical communication apparatus on the other party side, the optical communication apparatus comprising drive signal outputting means for controlling a signal level of an input signal in accordance with a light emitting power control signal and outputting the input signal the signal level of which has been controlled as a drive signal, a light emitting element for emitting light at an intensity in accordance with the signal level of the drive signal and transmitting an optical signal via the optical transmission medium, test signal generating means for forming a test signal having a specific signal pattern, selecting means for selectively outputting either of the test signal and the data signal to the drive signal forming means as the input signal, a light receiving element for receiving the optical signal via the optical transmission medium and converting the received optical signal into an electric signal, detecting means for detecting whether the electric signal outputted from the light receiving element coincides with the specific signal pattern when the selecting means selects the test signal and controlling means for controlling a parameter of the light emitting power control signal based on a result of detection by the detecting means, wherein when the detecting means detects that the electric signal does not coincide with the specific signal pattern, the controlling means controls the parameter of the light emitting power control signal such that an intensity of the optical signal outputted by the light emitting element is increased and when the detecting means detects that the electric signal coincides with the specific signal pattern, the controlling means sets a current value of the parameter of the light emitting power control signal as the parameter when the selecting means selects the data signal. 
     According to the first aspect of the invention, when the detecting means detects that the electric signal does not coincide with the specific signal pattern, the controlling means controls the parameter of the light emitting power control signal such that the intensity of the optical signal outputted by the light emitting element is increased and when the detecting means detects that the detected signal coincides with the specific signal pattern, the controlling means sets the current value of the parameter of the light emitting power control signal as the parameter when the selecting means selects the data signal. Thereby, the intensity of the optical signal is sets to be small initially. When the intensity of the optical signal is increased by controlling the parameter of the light emitting power control signal and the coincidence of the result of detection is established, the controlling means sets the parameter of the light emitting power control signal as the parameter when the selecting means selects the data signal. Accordingly, optical communication among the optical communication apparatus is firmly carried out by reducing transmission loss in optical transmission under an optimum condition in accordance with the length of the optical transmission media. 
     According to a second aspect of the invention, there is provided the optical communication apparatus according to the first aspect wherein the specific signal pattern of the test signal formed by the test signal generating means is previously set to be different from a signal pattern of a test signal outputted from the optical communication apparatus on the other party side, the selecting means comprises a first selector for selectively outputting either of the test signal formed by the test signal generating means and the electric signal outputted from the light receiving element, and a second selector for selectively outputting either of an output from the first selector and the data signal, wherein the controlling means controls the selecting means such that when the test signal having the signal pattern different from the specific signal pattern is detected, the first selector outputs the electric signal and the second selector outputs the electric signal which is the output from the first selector. 
     According to the second aspect of the invention, in the operation of the controlling means, when the test signal having the signal pattern different from the specific signal pattern is detected, the first selector can output the electric signal and the second selector can output the electric signal which is the output from the first selector. 
     According to a third aspect of the invention, there is provided the optical communication apparatus according to the first aspect, further comprising an intensity detecting light receiving element for detecting the intensity of the optical signal transmitted from the light emitting element, wherein the controlling means stops controlling the parameter which is carried out when the detecting means detects that the electric signal does not coincide with the specific signal pattern in a case in which the intensity of the optical signal detected by the intensity detecting light receiving element becomes a limit value or more. 
     According to the third aspect of the invention, in the operation of the controlling means, when the intensity of the optical signal detected by the intensity detecting light receiving element becomes equal to or more than the limit value, the operation can be stopped by stopping to control the parameter which is carried out when the detecting means detects the incoincidence and the optical communication can be prevented from being carried out at the intensity of the optical signal which is equal to or more than the limit value. 
     According to a fourth aspect of the invention, there is provided the optical communication apparatus according to the third aspect, further comprising storing means for storing the limit value of the light emitting element for emitting light, wherein the controlling means stop controlling the parameter when the intensity of the optical signal detected by the intensity detecting light receiving element is equal to the limit value. 
     According to the fourth aspect of the invention, the controlling means can stop controlling the parameter when the intensity of the optical signal detected by the intensity detecting light receiving element becomes equal to the limit value. 
     According to a fifth aspect of the invention, there is provided the optical communication apparatus according to the first aspect wherein the controlling means controls the selecting means such that the data signal is outputted after the parameter of the light emitting power control signal has been set. 
     According to a sixth aspect of the invention, there is provided the optical communication apparatus according to the first aspect, further comprising time measuring means for measuring a time period from a timing when the light emitting element transmits the test signal. 
     According the sixth aspect of the invention, there can be known the time period from the timing at which the test signal has been transmitted in accordance with the time period measured by the time measuring means. 
     According to a seventh aspect of the invention, there is provided the optical communication apparatus according to the sixth aspect, further comprising informing means for informing an abnormality to a user based on a signal indicating the abnormality outputted by the controlling means, wherein the informing means informs a user of the abnormality by outputting the signal indicating the abnormality when the controlling means has not set the parameter of the light emitting power control signal until the time measuring means has counted the predetermined time period from the timing when the light emitting element transmitted the test signal. 
     According to the seventh aspect of the invention, the informing means can inform a user of the abnormality by the signal indicating the abnormality. 
     According to an eighth aspect of the invention, there is provided the optical communication apparatus according to the first aspect, further comprising amplifying means connected between the light receiving element and the detecting means for amplifying the electric signal converted by the light receiving element based on a predetermined gain and outputting the amplified electric signal to the detecting means. 
     According to the eighth aspect of the invention, the amplified electric signal can firmly be provided to the. detecting means. 
     According to a ninth aspect of the invention, there is provided the optical communication apparatus according to the eighth aspect wherein the amplifying means comprises an analog/digital converting unit for analog/digital-converting the electric signal. 
     According to a tenth aspect of the invention, there is provided the optical communication apparatus according to the eighth aspect wherein the controlling means controls the gain based on the result of detection of the detecting means. 
     According to the tenth aspect of the invention, the gain in amplifying the electric signal of the light receiving element can be controlled optimally in accordance with the result of detection. 
     According to an eleventh aspect of the invention, there is provided the optical communication apparatus according to the first aspect wherein the test signal is a signal having a specific rule which is not provided to the data signal. 
     According to the eleventh aspect of the invention, the test signal can clearly be discriminated from the data signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a preferred embodiment of a communication system according to the present invention; 
     FIG. 2 is a diagram showing an example of the structure of an optical communication apparatus of the communication system shown by FIG. 1; 
     FIG. 3 is a diagram showing the structure of a power control circuit unit of the optical communication apparatus shown by FIG. 2 and a peripheral portion thereof; 
     FIG. 4 is a diagram showing an example of operation; 
     FIGS. 5A,  5 B,  5 C,  5 D and  5 E are diagrams showing an example in which a control signal of a light emitting power value is set in multiple stages when an optical signal is emitted from a light emitting element; 
     FIG. 6 is a diagram showing other preferred embodiment of an optical communication apparatus of a communication system according to the present invention; 
     FIG. 7 is a diagram showing an example of the structure of a power control circuit unit of the optical communication apparatus shown by FIG. 6; and 
     FIG. 8 is a diagram showing an example of a conventional optical communication apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A detailed explanation will be given of preferred embodiments according to the present invention in reference to the attached drawings as follows. 
     Further, although embodiments described below are preferable specific examples of the present invention and therefore, various technically preferable limitations are provided thereto, the scope of the present invention is not limited to these embodiments so far as there is no particular description of limiting the present invention in the following explanation. 
     FIG. 1 shows a preferred embodiment of a communication system according to the present invention. The communication system  100  constitutes an optical communication system by being provided with, for example, a first optical communication apparatus  20  and a second optical communication apparatus  21 . Optical fibers (optical transmission media) F 1  and F 2  are arranged between the first optical communication apparatus  20  and the second optical communication apparatus  21 . 
     The first optical communication apparatus  20  and the second optical communication apparatus  21  are provided with the same constitution. The first optical communication apparatus  20  is provided with a transmitting unit  20 A, a receiving unit  20 B and a control unit  20 C. The second optical communication apparatus  21  is provided with a transmitting unit  21 A, a receiving unit  21 B and a control unit  21 C. The transmitting units  20 A and  21 A are the same as each other, the receiving units  20 B and  21 B are the same as each other and the control units  20 C and  21 C of a digital type are the same as each other. 
     The transmitting units  20 A and  21 A modulate optical signals in accordance with information intended to transmit and transmit the optical signals to the receiving units  21 B and  20 B on the other parties via the optical fibers F 2  and F 1 . 
     The control units  20 C and  21 C adjust intensities (power values) of the optical signals outputted from the transmitting units  20 A and  21 A in reference to whether the optical signals received by the receiving units  20 B and  21 B are normal. 
     FIG. 2 shows a structure of the second optical communication apparatus  21  as a representative of the first optical communication apparatus  20  and the second optical communication apparatus  21  shown by FIG.  1 . The first optical communication apparatus  20  is provided with the same structure and accordingly, an explanation will be given of the structure and the operation of the second optical communication apparatus  21  to thereby substitute for an explanation of the structure and the operation of the first optical communication apparatus  20 . 
     As described above, the optical communication apparatus  21  is provided with the transmitting unit  21 A, the receiving unit  21 B and the control unit  21 C. 
     For the optical fibers F 1  and F 2 , for example, optical fibers made of plastic or optical fibers made of glass can be used. The optical fibers F 1  and F 2  can respectively be connected attachably and detachably to and from a connector portion of the transmitting unit  21 A and a connector portion of the receiving unit  21 B. 
     The transmitting unit  21 A is provided with a light emitting element  4  and a monitor light receiving element  5 , a driving circuit  3 , a selector  1  and a transmission data forming unit  110 . As the light emitting element  4 , for example, a laser diode or a light emitting diode (LED) or the like can be adopted. The monitor light receiving element  5  is an intensity detecting light receiving element for detecting an intensity of an optical signal transmitted by the light emitting element  4  and for the monitor light receiving element  5 , for example, a photodiode can be adopted. 
     The driving circuit  3  controls a signal level of an input signal s 1  from the selector  1  in accordance with a light emitting power value control signal s 2   c  and outputs the input signal s 1  the signal level of which has been controlled, as a drive signal s 3  to the light emitting element  4 . 
     The light emitting element  4  is driven by the driving circuit  4  to emit an optical signal  200  to an end portion of the optical fiber F 1 . The optical signal  200  emitted by the light emitting element  4  is received by the monitor light receiving element  5  for monitoring. 
     The selector  1  is selecting means for selecting either of transmission data sTx from the transmission data forming unit  110  and a test signal input s 2   a  from a power control circuit unit  2  and transmitting the input signal s 1  to the driving circuit  3 . 
     The receiving unit  21 B is provided with a light receiving element  6  and an amplifying circuit  7 . For the light receiving element  6 , for example, a photodiode or the like can be adopted and the light receiving element  6  receives and photoelectrically converts an optical signal  210  emitted from an end portion of the optical fiber F 2  and transmits a current signal s 6  to the amplifying circuit  7 . 
     The optical signal  210  is outputted from the transmitting unit  20 A of the first optical communication apparatus  20  and transmitted via the optical fiber F 2  or the optical signal  210  is generated from the transmitting unit  21 A of the second optical communication apparatus  21  and transmitted via the optical fiber F 1 , the first optical communication apparatus  20  and the optical fiber F 2 . 
     The amplifying circuit  7  amplifies and analog/digital-converts the current signal s 6  and produces a reception signal s 7   a  and a detection signal s 7   b . The reception signal s 7   a  is transmitted to a control circuit  115 , a comparing circuit  8  and a test pattern detecting circuit  9 . The reception signal s 7   a  is a communication signal (data signal) received by the light receiving element  6 . The detection signal s 7   b  is transmitted to the power control circuit unit  2 . The detection signal s 7   b  is a signal for detecting whether the received optical signal  210  is outputted with a constant amplitude or more and is a signal for detecting, for example, whether the optical fiber F 2  is normally connected or whether the first optical communication apparatus  20  is operated normally. 
     Next, an explanation will be given of the control circuit unit  21 C. The control circuit unit  21 C is provided with the power control circuit unit  2 , the comparing circuit  8 , the test pattern detecting circuit  9  and the control circuit  115 . The detection signal s 7   b  is a signal limiting (restricting output of) the driving circuit  3  and notified to the control circuit  115 . The comparing circuit  8  transmits to the power control circuit unit  2 , a signal s 8  which is a result of comparing signal patterns of a test signal s 2   d  generated by the power control circuit unit  2  and the reception signal s 7   a  generated by the amplifying circuit  7 . 
     The test pattern detecting circuit  9  transmits a test pattern signal s 9   a  and transmits a test data output signal s 9   b  to the power control circuit unit  2 . The test pattern signal s 9   a  is a signal in correspondence with the reception signal s 7   a  outputted by the amplifying circuit  7  for notifying a test pattern signal transmitted by the first communication apparatus  20  on the other party side to the power control circuit unit  2 . The test data output signal s 9   b  is a signal for detecting whether a signal is the test pattern signal or a data signal. The test pattern detecting circuit  9  and the comparing circuit  8  detect whether the electric signal outputted from the light receiving element  6  is a test signal having a specific signal pattern when the selector  1  selects the test pattern signal (test signal). 
     As a method by which the test pattern detecting circuit  9  recognizes the test pattern, the test pattern can be discriminated by using a code which is not allocated to normal data other than the test pattern in, for example, nBmB conversion or the like which is a generally used encoding method. According to the nBmB conversion, for example, in the case of  8 B 10 B, a code conversion is carried out such that 8 bits are converted into 10 bits and the nBmB conversion can be used as a code for forming the test pattern. When normal data comprises 8 bits, that is, is represented by 256 ways, by carrying out, for example,  8 B 10 B, a remainder produced by subtracting 256 ways from 1024 ways can be used for the test pattern. Among them, the test pattern signal is provided with a pattern in which, for example, higher order 4 bits are constituted by numerals 1, that is, 1111xxxxxxxx and the data signal is not provided with the above-described pattern by which the test pattern detecting circuit  9  can recognize the test pattern. 
     The control circuit  115  is provided with a display unit  115 A and an alarm sound generating unit  115 B and the display unit  115 A and the alarm sound generating unit  115 B inform abnormality of the test signal to a user. The control circuit  115  transmits a start signal sSt and the power control circuit unit  2  transmits an alarm signal sA 1  to the control circuit  115  when the optical communication is failed or the like. The control circuit unit  21 C is provided with the power control circuit unit  2 , mentioned above, and the power control circuit unit  2  transmits the test signal input s 2   a  and a selector signal s 2   b  to the selector  1 . The power control circuit unit  2  transmits a light emitting power value control signal s 2   c  to the driving circuit  3 . The monitor light receiving element  5  transmits a detection output s 5  to the power control circuit unit  2 . The power control circuit unit  2  transmits the test signal s 2   d  to the comparing circuit  8 . 
     FIG. 3 shows a detailed constitution of the power control circuit unit  2  shown by FIG.  2  and its peripheral portions. 
     The power control circuit unit  2  is provided with a timer circuit  18 , a selector  17 , a control circuit  10 , a test pattern generating circuit  16 , a count circuit  12 , a DAC circuit  12 A, a register  13 , an ADC circuit  16 A and a comparing circuit  15 . 
     When the start signal sSt from the control circuit  115  is received by the control circuit  10 , the control circuit  10  transmits a count start signal s 18 C to the timer circuit  18  by which the timer circuit  18  starts counting. 
     The timer circuit  18  transmits a time out signal s 18  to the control circuit  10  at a time point where a predetermined time period has been counted. The selector  17  receives a selecting signals s 10   a  from the control circuit  10 , the test pattern signal (detection output) s 9   a  and a test pattern signal s 16   a . The selector  17  selects either of the test pattern signal s 9   a  and the test pattern signal s 16   a  in accordance with the selecting signal s 10   a  and transmits the test signal input s 2   a  shown by FIG. 2 to the selector  1 . 
     The selector  17  of FIG. 3 constitutes a first selector for selectively outputting either of the test pattern signal (test signal) and the electric signal outputted from the light receiving element. 
     The test pattern signal s 9   a  is a signal for transmitting back to the first optical communication apparatus  20 , the test signal transmitted by the opposed first communication apparatus  20  for determining light emitting power and is detected by the test pattern detecting circuit  9 . When the test pattern transmitted by the opposed optical communication apparatus is detected, or by the signal s 8  from the comparing circuit  8  and the test data output signal s 9   b , that is, when the signal s 8  of the comparing circuit  8  is not the test pattern signal transmitted by the second optical communication apparatus  21  and the test pattern detecting circuit  9  detects the test pattern signal, the test pattern signal s 9   a  is transmitted to the driving circuit  3  via the selector  1 . 
     The test pattern signal s 16   a  is outputted from the test pattern generating circuit  16  and is transmitted to the opposed first optical communication apparatus  20  via the selector  17  and via the selector  1 . The test pattern signal s 16   a  is a test signal having a specific signal pattern. 
     The control circuit  10  supplies a power up signal s 10   b  to the count circuit  12 . The count circuit  12  counts the power up signal s 10   b  and transmits it to the DAC circuit (digital/analog conversion circuit)  12 A as a count output s 12 . The DAC circuit  12 A converts the count output s 12  into an analog signal and transmits the power control signal s 2   c  of the driving circuit to the driving circuit  3 . Thereby, the driving circuit  3  can control the power value of the optical signal  200  of the light emitting element  4 . 
     The control circuit  10  of FIG. 3 controls a total of the power control circuit unit  2 . The timer circuit  18  outputs the time out signal s 18  to the control circuit  10  when a predetermined time period has elapsed after transmitting the test signal. When the control circuit  10  is not inputted with the detection signal s 8  for detecting the test signal before the timer circuit  18  has counted the predetermined time period, the control circuit  10  outputs the power up signal s 10   b  to the count circuit  12  to thereby output the count output s 12  to the DAC circuit  11 . The DAC circuit  11  digital/analog-converts the count output s 12  and outputs the analog signal as the power control signal s 2   c  for the driving circuit. 
     The register  13  of FIG. 3 is a memory (storing means) for storing at least one, preferably, a plurality of stages of previously determined power values of the optical signal  200 . The ADC circuit (analog/digital-conversion circuit)  16 A receives and analog/digital-converts the detection output s 5  from the monitor light receiving element  5  and transmits an output s 14  to the comparing circuit  15 . 
     The comparing circuit  15  compares the plurality of stages of power values of the optical signal  200  stored in the register  13  with the output s 14  in correspondence with the detection output from the monitor light receiving element  5  to thereby detect what degree of the power value is the detection output s 5  received by the monitor light receiving element  5  and the comparing circuit  15  can transmit a comparison result signal s 15  to the control circuit  10 . 
     The test pattern generating circuit  16  receives a timing signal st from the control circuit  10  and can transmit the test pattern signal s 16   a  to the selector  17  in accordance with the timing signal st. 
     Next, an explanation will be given of an example of controlling operation in optical transmission when using the first optical communication apparatus  20  and the second optical communication apparatus  21  as well as the optical fibers F 1  and F 2  of the communication system  100 , mentioned above. 
     In normal optical communication operation, the power control circuit unit  2  of FIG. 2 transmits the selector signal s 2   b  to the selector  1  by which the selector  1  is switched to the side of the transmission data sTx intended to transmit. 
     Thereby, the transmission data sTx formed by the transmission data forming unit  110  is selected by the selector  1  as the input signal s 1  and the input signal s 1  is supplied to the driving circuit  3 . The driving circuit  3  operates the light emitting element  4  based on the input signal s 1  and the light emitting element  4  transmits the optical signal  200  to an end portion of the optical fiber F 1  in accordance with the transmission data sTx. 
     The optical signal  210  transmitted from the first communication apparatus  20  shown by FIG. 1 on the other party side via the optical fiber F 2  is received by the light receiving element  6  to thereby input the current signal s 6  to the amplifying circuit  7 . The amplifying circuit  7  amplifies the current signal s 6  and outputs the reception signal s 7   a  and the detection signal s 7   b.    
     Next, an explanation will be given of an example of setting an optimum power value of an optical signal in accordance with, for example, transmission path lengths of the optical fibers F 1  and F 2  and characteristics of the first optical communication apparatus  20  and the second optical communication apparatus  21  by actually controlling the power value of the optical signal  200  of the light emitting element  4 . 
     The power control circuit unit  2  of FIG. 2 starts operation by receiving the start signal sSt from the control circuit  115 . In the normal case, the operation of the power control circuit unit  2  is started when a main power supply is made ON and connectors of the optical fiber F 1  and the optical fiber F 2  are connected to respectively corresponding positions. 
     In this case, there is a method of confirming connection of the connector of the optical fiber as follows. 
     When the second optical communication apparatus  21  supplies the optical signal  200  to the first optical communication apparatus  20  on the other party side via the optical fiber F 1  and the optical signal  210  is received by the light receiving element  6  from the first optical communication apparatus  20  via the optical fiber F 2 , the detection signal s 7   b  of FIG. 2 is transmitted to the power control circuit unit  2  in the case where the received optical signal  210  is provided with an output of a predetermined amplitude or more. 
     In this case, when the second optical communication apparatus  2  transmits, for example, a signal shown by FIG. 5C as the light emitting power value control signal s 2   c  of the optical signal  200  from the power control circuit unit  2  to the driving circuit  3 , the power control circuit unit  2  determines that the optical fibers F 1  and F 2  are firmly connected to the connector portions in the case where the detection signal s 7   b  is outputted. In this way, when the power value of the optical signal  210  becomes larger than a certain level, the connection of the optical fibers is confirmed and the operation of power control is started. 
     Firstly, the power control circuit unit  2  outputs the test signal input s 2   a  to the selector  1 . Further, the power control circuit unit  2  controls to output the select signal s 2   b  and to have the selector  1  select the test signal input s 2   a . Further, the power control circuit unit  2  outputs the power control signal s 2   c  to the driving circuit  3  such that the light emitting element  4  emits light with a minimum light emitting power and the driving circuit  3  drives the signal s 1  outputted from the selector  1  by a power indicated by the power control signal s 2   c . In this case, the test signal s 2   a  is supplied as the output signal s 1  of the selector  1 . Further, the light emitting element  4  emits light based on the drive signal s 3  outputted from the driving circuit  3  and outputs the optical signal  200  to the first optical communication apparatus  20  via the optical fiber F 1 . 
     When the optical signal  200  is received by the opposed first optical communication apparatus  20  shown by FIG. 1, the received optical signal  200  returns to the light receiving element  6  as it is via the optical fiber F 2  as the optical signal  210  in FIG.  2 . When the light receiving element  6  receives the optical signal  210 , the reception signal s 7   a  is compared with the test signal s 2   d  (a signal the same as the test signal s 2   a ) by the comparing circuit  8  and when both are provided with the same signal pattern, the reception is regarded as normal and the current power value for the light emitting element is maintained. That is, while maintaining the value of the light emitting power value control signal s 2   c  transmitted from the power control circuit unit  2  to the driving circuit  3 , the selector  1  selects the transmission data sTx outputted by the transmission data forming unit  110  and there is brought about normal optical communication operation using the actual optical communication apparatus  20  and  21  and the optical fibers F 1  and F 2 . 
     This behavior is shown by step ST 1 , step ST 2  and step ST 4  of FIG.  4 . 
     At step ST 1  of FIG. 4, the main power supply is turned on and test data is transmitted from the first optical communication apparatus  20  to the second optical communication apparatus  21 . At step ST 2 , when the second optical communication apparatus  21  receives test data from the first optical communication apparatus  20 , at step ST 3 , the test data is transmitted as it is from the second optical communication apparatus  21  to the first optical communication apparatus  20  via the optical fiber F 1 . 
     Thereby, the light emitting element  4  of the second optical communication apparatus  21  can inform reception of the optical signal  210  of the test data emitted by the first optical communication apparatus  20  to the first optical communication apparatus  20  on the other party side via the optical fiber F 1 . 
     Meanwhile, when the second optical communication apparatus  21  transmits the optical signal  200  in correspondence with the test signal input s 2   a  to the first optical communication apparatus  20  on the other party side as indicated by step ST 1 , step ST 2  and step ST 4  of FIG. 4, as mentioned above, the test data is to be returned as it is from the first optical communication apparatus  20 . However, when the optical signal  210  is not returned within a certain time period, there is a case in which the optical signal  210  cannot normally be received by the light receiving element  6 . The reason of such an example is, for example, that optical path lengths of the optical fibers F 1  and F 2  are longer than predicted optical path lengths, that the optical characteristic of the first optical communication apparatus  20  differs from a predicted characteristic, that the first optical communication apparatus  20  is failed or the like. 
     Hence, the power control circuit unit  2  can transmit the light emitting power value control signal s 2   c  of FIG. 2 to the driving circuit  3  by increasing the power value little by little as shown by power values P 1 , P 2 , P 3 , P 4  and P 5  of the optical signal  200  in FIGS. 5A,  5 B,  5 C,  5 D and  5 E. That is, the power control circuit unit  2  can specify an optimum power value of the optical signal  200  for optical communication in the communication system  100  comprising the first optical communication apparatus  20  as well as the second optical communication apparatus  21  and the optical fibers F 1  and F 2  shown by FIG. 1 by transmitting the light emitting power value control signal s 2   c  having the light emitting power values as shown by FIGS. 5A,  5 B,  5 C,  5 D and  5 E. The optimum power value of the optical signal is a value capable of performing optical transmission by making transmission loss in optical transmission as small as possible without supplying excessive light to the system. 
     At step ST 4  of FIG. 4, in the case where, for example, the test signal input s 2   a  of the transmitting unit  21 A is given, the optical signal  200  is emitted to the optical fiber F 1  and the optical signal  210  cannot be received on the side of the receiving unit  21 B, the power control circuit unit  2  regards it as a deficiency in the power value of the optical signal  200  and supplies the light emitting power value control signal s 2   c  for increasing the power value as shown by FIGS. 5A,  5 B,  5 C,  5 D and  5 E. In FIGS. 5A,  5 B,  5 C,  5 D and  5 E, the power value of the optical signal is set respectively to P 1 , P 2 , P 3 , P 4  and P 5  which are gradually increased. In this way, in the case in which despite that the second optical communication apparatus  21  has transmitted the optical signal  200  to the first optical communication apparatus  20  on the other party side via the optical fiber F 1 , when it is prior to supplying the time out signal s 18  to the control circuit  10  by the timer circuit  18  shown by FIG. 3 as instep ST 5  of FIG. 4 (within a predetermined time period), in respect of the optical signal  210  received by the light receiving element  6 , the power control circuit  2  carries out processing of setting a successive power value of the optical signal (step ST 7 ) by which the light emitting power value control signal s 2   c  is controlled in a direction of increasing the light emitting power as shown by FIGS. 5A,  5 B,  5 C,  5 D and  5 E. 
     Further, data in correspondence with the light emitting power value control signal s 2   c  for the optical signal as shown by FIGS. 5A,  5 B,  5 C,  5 D and  5 E, is formed such that, for example, the control circuit  10  of the power control circuit unit  2  issues a count up instruction to the count circuit  12 , the DAC circuit  12 A digital/analog-converts the output s 12  of the count circuit  12  and supplies it to the driving circuit  3 . 
     Further, as shown by step ST 8  of FIG. 4, a limit is provided to the power value of the optical signal  200  on the transmitting side. The monitor light receiving element  5  of FIG. 2 monitors the optical signal  200  and the power control circuit unit  2  prevents the light emitting element  4  from emitting light more than necessary. The power control circuit unit  2  prevents the light emitting element  4  from emitting light more than necessary in manner since when the light emitting element  4  emits light at a high power value, the life of the light emitting element  4  is shortened and the light emitting element  4  outputs an optical signal having a power value which is excessive in optical communication. When the power value of the optical signal  200  exceeds a certain limit value, the power control circuit unit  2  of FIG. 2 transmits the alarm signal sA 1  to the control circuit  115 . Thereby, the control circuit  115  can inform the user of the alarm by displaying the alarm in the display unit  115 A or emitting alarm sound by using the alarm sound emitting unit  115 B such as a speaker. This operation is shown by step ST 6  of FIG.  4 . Further, when the timer circuit  18  of FIG. 3 outputs the time out signal s 18  to the control circuit  10  (time out), the control circuit  15  similarly issues alarm as in step ST 6 . 
     The selector  17  selects by the selecting signal s 10   a , which one of the test pattern signal s 16   a  formed by the test pattern generating circuit  16  of the second optical communication apparatus  21  and the test pattern signal from the opposed first optical communication apparatus  20 , is to be transmitted as the test pattern. For example, when the test pattern from the other party side is received, the control circuit  10  outputs the select signal s 10   a  for selecting the test pattern from the other party side. 
     According to the above-described embodiment, there is shown an example of controlling the light emitting power value of the optical signal  100  on the transmitting side. The present invention is not limited thereto but the light reception sensitivity of the light receiving element  6  may be controlled in addition to the control of the light emitting power value of the optical signal  200  from the light emitting element  4  as shown by FIG.  6  and FIG.  7 . 
     In this case, the power control circuit unit  2  supplies a reception sensitivity control signal r 2   c  to the amplifying circuit  7  of the light receiving element  6  and can change a rate of amplifying the optical signal  210  based on the reception sensitivity control signal r 2   c . By increasing the amplification rate of the amplifying circuit  7  to a degree at which the amplifying circuit  7  is not saturated, a higher optical reception sensitivity can be provided without increasing the power value of the light emitting element  4  by which transmission can be carried out by a smaller light emitting power value. 
     Or in FIG. 6, the power control circuit unit  2  may control only the reception sensitivity control signal r 2   c  without controlling the light emitting power value control signal s 2   c.    
     FIG. 7 shows a detailed constitution of the power control circuit unit  2  shown by FIG.  6  and its peripheral portions. Blocks having constitutions and operations the same as those in the blocks of FIG. 3 are attached with the same notations. 
     In FIG. 7, a count circuit  19  and a DAC circuit (digital/analog conversion circuit)  19 A are respectively provided with two routes of inputs and outputs for controlling the driving circuit  3  and the amplifying circuit  7 . 
     The control circuit  10  supplies a driving circuit power up signal s 10   c  to the count circuit  19 . The count circuit  19  counts the driving circuit power up signal s 10   c  and transmits a count value to the DAC circuit (digital/analog conversion circuit)  19 A as a driving circuit count output s 19   a . The DAC circuit  19 A converts the driving circuit counter output s 19   a  into an analog signal and transmits the power control signal s 2   c  of the driving circuit to the driving circuit  3 . The driving circuit  3  can control the power value of the optical signal  200  of the light emitting element  4  based on the power control signal s 2   c.    
     Further, the control circuit  10  supplies an amplifying circuit gain up signal s 10   d  to the count circuit  19 . The count circuit  19  counts the amplifying circuit gain up signal s 10   d  and transmits a count value to the DAC circuit (digital/analog conversion circuit)  19 A as an amplifying circuit count output s 19   b . The DAC circuit  19 A converts the amplifying circuit count output s 19   b  into an analog signal and transmits the reception sensitivity control signal r 2   c  of the amplifying circuit to the amplifying circuit  7 . The amplifying circuit  7  can control the reception sensitivity of the optical signal  210  of the light receiving element  6  based on the reception sensitivity control signal r 2   c.    
     Further, a current set value of the optical communication apparatus may be transmitted along with the test signal input s 2   a  for using in control. That is, a current light emitting power value may be included in the test pattern and may be transmitted along therewith and set the light emitting power of the opposed optical communication apparatus. In this case, for example, conditions of setting both of the optical communication apparatus  20  and  21  can be matched. 
     According to the embodiment of the present invention, the light emitting element  4  can be operated by a light emitting power value which is optimum in the communication system in accordance with kinds, lengths, a situation of laying them and a situation of using them of the connected optical fibers and accordingly, long life of the light emitting element can be expected. 
     The light emitting power of the light emitting element  4  and the light reception sensitivity of the light receiving element  6  can be controlled dynamically in accordance with conditions and accordingly, by using only one kind of the light emitting elements or the light receiving elements, transmission distances of the optical fibers F 1  and F 2  or the kind of the optical fibers can be dealt with. 
     Almost all of the functions can be realized by digital circuits as shown by FIG. 2 or FIG.  3  and cost reduction can be achieved by incorporating them in an LSI (large scale integrated circuit). 
     A system of digital control is adopted in the power control circuit unit  2  of the optical communication apparatus shown by FIG.  2  and FIG. 3, the register  13  shown by FIG. 3 can maintain a plurality of stages of power values of an optical signal for monitoring which are set data and accordingly, burst transmission is easily dealt with. That is, immediate transmission is feasible with a maintained power value when the transmission is intended. When burst transmission is going to carry out in analog, an optical communication apparatus needs to take a sufficient stabilizing time period such that a predicted test pattern can be transmitted. In contrast thereto, according to a digital system, a predicted pattern can be outputted immediately. 
     The present invention has been explained by one preferable embodiment of the optical communication apparatus using two optical fibers. However, the present invention can also be applied to the optical communication apparatus using one optical fiber. 
     As has been explained, according to the present invention, there can firmly be carried out optical communication using optical transmission media among optical communication apparatus under an optimum condition.