Abstract:
An optical switching system is disclosed which can achieve high speed optical switching with a simple configuration. Light from a light irradiation section is irradiated into an optical transmission line made of a material having a nonlinear optical effect and disposed on the upstream side with respect to an optical switch provided for performing switching of a transmission line to cause the nonlinear optical effect to occur. Thereupon, light is emitted externally from the optical transmission line by the nonlinear optical effect between the light irradiated by the light irradiation section and light propagating in the optical transmission line. The light emitted is received by a light reception section to acquire intensity information of the light propagating in the optical transmission line. The intensity information is used as driving signal for driving the optical switch.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to an optical communication apparatus, an optical communication information decoding method, an optical switching system and a driving method for an optical switching system, and more particularly to an optical communication apparatus, an optical communication information decoding method, an optical switching system and a driving method for an optical switching system suitable for use for a switching process of multiplexed optical signals. 
   The field of optical communication has been developing rapidly together with the progress of the information-based society in recent years. In the field of optical communication, the progress is significant in the field of the enhancement in function beginning with the enhancement in transfer rate and the multiplexing of data. 
   As a multiplexing technique, wavelength multiplexing techniques such as the WDM (Wavelength Division Multiplexing) and the DWDM (Dense Wavelength Division Multiplexing) have been developed. 
   In such a situation as described above, also with regard to a switching technique required for a repeating point of an optical fiber transmission line (hereinafter referred to merely as optical fiber), specifications for higher performances such as higher speed operation of an optical switch are demanded. 
   More particularly, it is demanded to raise the speed of an optical switch which quickly decodes header information included in information propagating in an optical fiber, that is, information in which a destination of information is recorded, and operates rapidly in response to the header information. 
   However, in an environment of the WDM or the DWDM, information propagating in an optical fiber and including header information cannot be read before optical wavelengths are demultiplexed from one another. Therefore, an optical switching system at a repeating point of an optical fiber cannot be avoided to have such a configuration as shown in  FIG. 1 . 
     FIG. 1  shows an optical switching system which distributes and outputs wavelength-multiplexed optical signals inputted from an optical fiber  51  to optical fibers  52  and  53  in accordance with header information of the wavelength-multiplexed optical signals. 
   Referring to  FIG. 1 , wavelength-multiplexed light transmitted along the optical fiber  51  in accordance with the WDM or DWDM system is demultiplexed for individual wavelengths by a demultiplexer  54  and individually received by light reception units  55   a  to  55   f . Information reading apparatus  56   a  to  56   f  read header information of information signals in the form of optical signals of the different wavelengths received by the light reception units  55   a  to  55   f , respectively. 
   The information reading apparatus  56   a  to  56   f  discriminate destinations of the individual information signals based on the header information to select output destinations of the information signals and signal the information signals to light emitting elements  57   a  to  57   f  or light emitting elements  58   a  to  58   f.    
   For example, if the information reading apparatus  56   a  discriminates that the output destination of the pertaining information signal is the optical fiber  52  side, then it outputs the information signal to the light emitting element  57   a . On the other hand, if the information reading apparatus  56   a  discriminates that the information signal is the optical fiber  53  side, then it outputs the information signal to the light emitting element  58   a.    
   When each of the light emitting elements  57   a  to  57   f  and the light emitting elements  58   a  to  58   f  receives an information signal, it emits light of an optical signal of a predetermined wavelength corresponding to the information signal. 
   Optical signals of different wavelengths outputted from all or some of the light emitting elements  57   a  to  57   f  are multiplexed in accordance with the WDM or DWDM system by a multiplexer  59  and signaled to the optical fiber  52 . On the other hand, optical signals of different wavelengths outputted from all or some of the light emitting elements  58   a  to  58   f  are multiplexed in accordance with the WDM or DWDM system by a multiplexer  60  and signaled to the optical fiber  53 . 
   In this manner, at a repeating point of an optical fiber, a demultiplexer for demultiplexing wavelength-multiplexed light into different wavelengths used in the WDM or DWDM, light receiving elements for the individual wavelengths and a number of light emitting sources for the individual wavelengths equal to the number of fiber transmission lines used for transmission are required. Therefore, the optical switching system has a configuration of a great scale. 
   Further, since the optical switching system is configured such that it uses a procedure including demultiplexing of multiplexed wavelengths, light reception and information reading in order to select transmission destinations, it has a limitation to satisfaction of the demand for high speed optical switching. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a method and an apparatus which can decode information included in optical signals transmitted, for example, in accordance with the WDM or DWDM system without demultiplexing the optical signals. 
   It is another object of the present invention to provide an optical switching system and a driving method for an optical switching system which can achieve high speed optical switching with a simple configuration. 
   In order to attain the objects described above, according to the first aspect of the present invention, there is provided an optical communication apparatus which includes an optical transmission line made of a material having a nonlinear optical effect, a light irradiation section for irradiating light into the optical transmission line to cause the nonlinear optical effect to occur, and a light reception section for receiving light emitted externally from the optical transmission line by the nonlinear optical effect between the light irradiated into the optical transmission line by the light irradiation section and light propagating in the optical transmission line to acquire intensity information of the light propagating in the optical transmission line. 
   According to the second aspect of the present invention, there is provided an optical communication information decoding method for an optical communication apparatus which includes an optical transmission line made of a material having a nonlinear optical effect, a light irradiation section for irradiating light into the optical transmission line to cause the nonlinear optical effect to occur, and a light reception section for receiving light emitted externally from the optical transmission line by the nonlinear optical effect of the optical transmission line, including the step of receiving the light emitted externally from the optical transmission line by the nonlinear optical effect between the light irradiated into the optical transmission line by the light irradiation section and light propagating in the optical transmission line by means of the light reception section to decode header information of the information propagating in the optical transmission line. 
   According to the third aspect of the present invention, there is provided an optical switching system for switching a transmission line in response to information propagating in an optical transmission line which includes an optical switch for performing switching of a transmission line, an optical transmission line made of a material having a nonlinear optical effect and disposed on the upstream side with respect to the optical switch, a light irradiation section for irradiating light into the optical transmission line to cause the nonlinear optical effect to occur, a light reception section for receiving light emitted externally from the optical transmission line by the nonlinear optical effect between the light irradiated into the optical transmission line by the light irradiation section and light propagating in the optical transmission line to acquire intensity information of the light propagating in the optical transmission line, and driving means for producing a driving signal for the optical switch from the intensity information acquired by the light reception section. 
   According to the fourth aspect of the present invention, there is provided a driving method for an optical switching system for switching a transmission line in response to information propagating in an optical transmission line, including the steps of irradiating light from a light irradiation section into an optical transmission line made of a material having a nonlinear optical effect and disposed on the upstream side with respect to an optical switch which performs switching of a transmission line, receiving light emitted externally from the optical transmission line by the nonlinear optical effect between the light irradiated by the light irradiation section and light propagating in the optical transmission line by means of a light reception section to acquire intensity information of the light propagating in the optical transmission line, and producing a driving signal for the optical switch based on the intensity information. 
   In the optical communication apparatus, optical communication information decoding method, optical switching system and driving method for an optical switching system, the light emitted externally from the optical transmission line by the nonlinear optical effect may have a wavelength different from that of the light propagating in the optical transmission line. 
   Where the light propagating in the optical transmission line has a plurality of wavelengths, the light emitted externally from the optical transmission line by the nonlinear optical effect may have a plurality of wavelengths corresponding to the plurality of wavelengths propagating in the optical transmission line. 
   Where the light propagating in the optical transmission line has a plurality of wavelengths, the light emitted externally from the optical transmission line by the nonlinear optical effect may be emitted in a plurality of directions corresponding to the plurality of wavelengths propagating in the optical transmission line. 
   Preferably, the light irradiated into the optical transmission line by the light irradiation section to cause the nonlinear optical effect to occur is a laser beam. 
   The light irradiation section may include a resonator, in which an optical transmission line made of a material having a nonlinear optical effect is disposed. 
   With the optical communication apparatus, optical communication information decoding method, optical switching system and driving method for an optical switching system, for example, where optical signals multiplexed with different wavelengths in accordance with the WDM system or the DWDM system are transmitted, information included in the optical signals can be decoded at a stage before they are demultiplexed from each other through the utilization of a nonlinear optical effect in the optical transmission line, and a switching operation for optical switching can be performed in response to the decoded information. Consequently, there is an advantage that a temporal intensity variation of the light propagating in the optical transmission line can be decoded for each of the wavelengths of the light signals before the light is demultiplexed. 
   Further, even in an environment of a system wherein different wavelengths are involved such as the WDM system or the DWDM system, information of each wavelength, specifically header information, can be decoded without using a demultiplexer. Therefore, the processing time when an optical switch is driven can be reduced. 
   Furthermore, the optical switching system can be formed in a simplified configuration because there is no necessity to prepare light emitting elements (light sources) for individually different wavelengths. 
   The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing a configuration of a conventional optical switching system; 
       FIG. 2  is a schematic view showing a configuration of an optical communication apparatus to which the present invention is applied; 
       FIGS. 3 and 4  are wave number vector diagrams where a frequency difference of a parametric oscillation phenomenon is used in the optical communication apparatus of  FIG. 2 ; 
       FIG. 5  is a schematic view showing a configuration of another optical communication apparatus to which the present invention is applied; 
       FIG. 6  is a schematic view showing a configuration of an optical switching system to which the present invention is applied; 
       FIG. 7  is a schematic view showing a configuration of a further optical communication apparatus to which the present invention is applied; and 
       FIGS. 8 and 9  are wave number vector diagrams where a frequency difference of a parametric oscillation phenomenon is used in the optical communication apparatus of  FIG. 7 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 2 , there is shown an optical communication apparatus to which the present invention is applied. The optical communication apparatus shown is formed as a repeating apparatus for supplying propagation light having communication information and transmitted thereto from an optical fiber  1  to another optical fiber  2 . 
   The propagation light here is light wavelength multiplexed, for example, in accordance with the WDM or DWDM system. 
   The optical communication apparatus of the first embodiment includes a lens  3 , a nonlinear optical crystal member  4  in which an optical waveguide  5  is formed, another lens  6 , a YAG laser lot  7 , mirrors  8  and  9 , and a PD (photo-detector) array  10 . 
   Propagation light having communication information propagates along the optical waveguide  5  (for example, an optical waveguide element made of a lithium niobate material) formed by the nonlinear optical material  4  in a transmission line, more particularly, between the optical fibers  1  and  2 . 
   The optical parts (YAG laser lot  7  and the mirrors  8  and  9 ) for irradiating a high-intensity laser beam from the outside of the optical waveguide  5  are arranged for the optical waveguide  5 . 
   The optical parts and the optical waveguide  5  are arranged such that an interaction between the propagation light having the communication information which propagates in the optical waveguide  5 . The laser beam irradiated from the outside of the optical waveguide  5  by the YAG laser lot  7  and the mirrors  8  and  9  occurs such that light having wavelengths different from those of the propagation light having the communication information which propagates in the optical waveguide  5  is emitted to the outside of the optical waveguide  5 . 
   The PD array  10  is arranged outside the optical waveguide  5  and includes light receiving elements (photo-detectors) PD for converting the light emitted to the outside of the optical waveguide  5  into electric signals. 
   Here, the interaction between the propagation light having communication information which propagates in the optical waveguide  5  and the laser beam irradiated from the outside particularly is a phenomenon such as parametric oscillation based on a nonlinear optical constant of the nonlinear optical material  4 . As seen in  FIG. 3 , the interaction is an action wherein light is emitted with a wavelength and in a direction which satisfy a wave number vector Ko 1  which depends upon a wave number vector Kf 1  of the light which propagates in the transmission line and a wave number vector Kr of the light irradiated from the outside. 
   It is to be noted that the parametric oscillation phenomenon includes two phenomena of a frequency difference and a frequency sum.  FIG. 3  illustrates a relationship of vectors where the phenomenon of the frequency difference is used. 
   The parametric oscillation phenomenon is a phenomenon wherein light of a wave number vector determined by a wave number vector of light which propagates in the transmission line and a wave number vector of light irradiated from the outside is emitted externally. Therefore, even if the light irradiated from the outside has a single frequency, if another light having a different wavelength propagates in the transmission line, then the light is emitted externally with a wavelength and in a direction which satisfy a wave number vector Ko 2  which depends upon a wave number vector Kf 2  of the light which propagates in the transmission line and a wave number vector Kr of the light irradiated from the outside as seen from a wave number vector diagram of  FIG. 4 . Consequently, lights having wavelengths different from each other are emitted externally in directions corresponding to the wavelengths of the lights which propagate in the transmission line. 
   Further, if the light irradiated from the outside is light fixed in time, then the externally emitted light includes a temporal intensity distribution corresponding to a temporal intensity variation of the light propagating in the transmission line. 
   In particular, temporal intensity variations for the individual wavelengths of the propagation lights which propagate in the transmission line, that is, signals corresponding to communication information, are inputted to two light receiving elements PD 1  and PD 2  seen in  FIG. 4 . 
   Then, even if the lights which propagate in the transmission line are week, if the light irradiated from the outside has a high intensity and there is a situation that the light which transmits in the transmission line is confined in the transmission line, then the light receiving elements PD 1  and PD 2  can read the optical information. 
   If the action described above is adapted to the configuration of  FIG. 2 , then the transmission line shown in  FIGS. 3 and 4  corresponds to the optical waveguide  5 , and propagation light having communication information is confined in the optical waveguide  5 . Then, a laser beam having a high intensity is irradiated from the YAG laser lot  7  upon the optical waveguide  5 . In this instance, the irradiated laser beam does not propagate in the optical waveguide  5 , and therefore, is not condensed by the lens  6  and does not propagate to the optical fiber  2 . 
   Accordingly, temporal intensity variations of the individual wavelengths included in the propagation light which propagates in the optical waveguide  5 , that is, signals corresponding to the individual multiplexed communication information, are inputted to a plurality of light receiving elements PD in the PD array  10 . 
   The optical communication apparatus of  FIG. 1  can read several kinds of information multiplexed with different wavelengths without demultiplexing the multiplexed information. 
   A configuration of another optical communication apparatus to which the present invention is supplied is shown in  FIG. 5 . Referring to  FIG. 5 , the optical communication apparatus has a resonator configuration provided at a location at which a light irradiation section which irradiates light upon the optical waveguide  5  is provided, and an optical transmission line formed from a material having a nonlinear optical effect is arranged in the resonator. 
   It is to be noted that the optical communication apparatus of  FIG. 5  further includes lenses  3  and  6 , an optical waveguide  5  and a PD array  10  similar to those of the optical communication apparatus described hereinabove with reference to  FIG. 2 . 
   In the optical communication apparatus of  FIG. 5 , a YAG laser lot  7 , a nonlinear optical crystal member  11 , and mirrors  8  and  12  are provided as components of the light irradiation section which irradiates a laser beam from the outside upon the optical waveguide  5 . The nonlinear optical crystal  11  arranged for the YAG laser lot  7  functions as a second harmonic production element. 
   In particular, in the optical communication apparatus of  FIG. 5 , the nonlinear optical crystal element  11  which is a second harmonic production element is used to reduce the wavelength of the laser beam. If the wavelength of the laser beam is reduced by the reduction of the wavelength just described to convert the laser beam into a laser beam of a wavelength shorter than, for example, 1.064 microns, that is, of a higher frequency, a higher conversion efficiency can be achieved. 
     FIG. 6  shows an optical communication system to which the present invention is applied. The optical communication system shown uses the optical information reading method of the optical communication apparatus shown in  FIG. 2 . 
   Referring to  FIG. 6 , the optical communication system uses the optical communication apparatus of  FIG. 2  and includes an optical switch  22  connected to the optical fiber  2  shown in  FIG. 2  for distributing light from the optical fiber  2  to an optical fiber  23  and another optical fiber  24 , and an information reading apparatus  21  for supplying a switching driving signal CSW to the optical switch  22  to drive the optical switch  22 . 
   It is to be noted that, although a particular configuration of the optical switch  22  is not shown in  FIG. 6 , a known optical switch such as an optical switch composed of a demultiplexer, a micro-mirror array and a multiplexer may be used as the optical switch  22 . 
   In the optical communication system shown in  FIG. 6 , a decoding operation of optical information is performed at a stage before signal light is introduced into the optical switch  22 , that is, at a stage wherein signal light is propagating in the optical waveguide  5  of the nonlinear optical crystal  4  before it is introduced into the optical fiber  2 . 
   In particular, since, as described hereinabove in connection with the optical communication apparatus of  FIG. 2 , intensity information of optical signals of different wavelengths which propagate in the optical waveguide  5  is inputted individually to the light receiving elements of the PD array  10 , the information reading apparatus  21  can decode the signals obtained by the light receiving elements of the PD array  10  to read information of the multiplexed optical signals such as, for example, header information. 
   Accordingly, the information reading apparatus  21  can discriminate output destinations of the optical signals of the different wavelengths and produce a driving signal CSW for the optical switch  22  in accordance with the output destinations. 
   Since, in the optical switching system having such a configuration as described above, decoding of optical information of optical signals of signal light is performed at a stage before the optical signals are inputted to the optical switch  22 , the decoding operation of the information is performed at an earlier stage when compared with an alternative case wherein the optical signals are demultiplexed to read the optical information after they have propagated in the optical fiber  2 . Accordingly, driving of the optical switch  22  can be performed at an earlier stage. In other words, higher speed optical switching can be achieved. 
   Further, in the optical switching system shown in  FIG. 6 , the necessity for preparation of a light source for each wavelength is eliminated when compared with the conventional optical switching system shown in  FIG. 1 . Therefore, the optical communication system can be formed with a reduced size and at a reduced cost. 
   It is to be noted that, while it is described that a frequency difference of a parametric oscillation phenomenon is used in the optical communication apparatus and the optical switching system according to the present invention described above, the present invention is not limited to such optical communication apparatus or optical switching system in which a frequency difference is used as described above. 
     FIG. 7  shows a further optical communication apparatus to which the present invention is applied. Referring to  FIG. 7 , the optical communication apparatus shown uses a frequency sum of a parametric oscillation phenomenon. The optical communication apparatus includes similar components to those of the optical communication apparatus described hereinabove with reference to  FIGS. 2 and 5 .  FIGS. 8 and 9  illustrate wave number vectors of the optical communication apparatus of  FIG. 7 . 
   Also the optical communication apparatus of  FIG. 7  externally emits light with a wavelength and in a direction which satisfy a wave number vector Ko 1  which depends upon a wave number vector Kf 1  of light propagating in the transmission line and a wave number vector Kr of light irradiated from the outside as seen in  FIG. 8 . 
   Further, even if the light irradiated from the outside has a single frequency, if another light having a different wavelength propagates in the transmission line, then the light is emitted externally with a wavelength and in a direction which satisfy a wave number vector Ko 2  which depends upon a wave number vector Kf 2  of the light which propagates in the transmission line and a wave number vector Kr of the light irradiated from the outside as seen from a wave number vector diagram of  FIG. 8 . Consequently, lights having wavelengths different from each other are emitted externally in directions corresponding to the wavelengths of the lights which propagate in the transmission line. 
   From  FIGS. 8 and 9 , it can be recognized that, even where a frequency sum of a parametric oscillation phenomenon is used, by irradiating a laser beam having a single frequency and fixed in time from the outside, a temporal intensity variation for each wavelength propagating in a transmission line can be detected by means of light receiving elements which are provided externally to monitor lights emitted externally with wavelengths and in directions different among different wavelengths from an optical waveguide element made of a nonlinear optical material. 
   Accordingly, also the optical communication apparatus having the configuration described above with reference to  FIG. 7  can read information of individual wavelengths from multiplexed optical signals propagating in the optical waveguide  5  by means of the light receiving elements PD of the PD array  10 . Naturally, the optical communication apparatus of  FIG. 7  can be used to construct such an optical switching system as described hereinabove with reference to  FIG. 6 . 
   In the following, examples of the wavelength and the direction of externally emitted light with respect to the wavelength and the incident angle of incident light are described with regard to two cases including a case wherein a frequency difference of a parametric oscillation phenomenon is used and another case wherein a frequency sum of a parameter oscillation phenomenon is used. 
   &lt;Where a Frequency Difference is Used&gt; 
   (1)-1 
   Wavelength propagating in optical transmission line: 1.550 microns 
   Wavelength of irradiated light: 1.064 microns 
   Incident angle: 10 degrees 
   Wavelength of externally emitted light: 3.08218 microns 
   Emitting angle: 3.43666 degrees 
   (1)-2 
   Wavelength propagating in optical transmission line: 1.552 microns 
   Wavelength of irradiated light: 1.064 microns 
   Incident angle: 10 degrees 
   Wavelength of externally emitted light: 3.07537 microns 
   Emitting angle: 3.444429 degrees 
   Position difference corresponding to wavelength difference 2 nm of propagating light where light receiving element is disposed at position spaced rearwardly by 10 mm from optical waveguide element: 369 microns 
   (2)-1 
   Wavelength propagating in optical transmission line: 1.550 microns 
   Wavelength of irradiated light: 0.532 microns 
   Incident angle: 10 degrees 
   Wavelength of emitting light: 0.800402 microns 
   Emitting angle: 6.62774 degrees 
   (2)-2 
   Wavelength propagating in optical transmission line: 1.552 microns 
   Wavelength of irradiated light: 0.532 microns 
   Incident angle: 10 degrees 
   Wavelength of emitting light: 0.799888 microns 
   Emitting angle: 6.63201 degrees 
   Position difference corresponding to wavelength difference 2 nm of propagating light where light receiving element is disposed at position spaced rearwardly by 10 mm from optical waveguide element: 56 microns 
   &lt;Where a Frequency Sum is Used&gt; 
   (3)-1 
   Wavelength propagating in optical transmission line: 1.550 microns 
   Wavelength of irradiated light: 1.064 microns 
   Incident angle: 10 degrees 
   Wavelength of emitting light: 0.633237 microns 
   Emitting angle: 16.96416 degrees 
   (3)-2 
   Wavelength propagating in optical transmission line: 1.552 microns 
   Wavelength of irradiated light: 1.064 microns 
   Incident angle: 10 degrees 
   Wavelength of externally emitted light: 0.633568 microns 
   Emitting angle: 16.95501 degrees 
   Position difference corresponding to wavelength difference 2 nm of propagating light where light receiving element is disposed at position spaced rearwardly by 10 mm from optical waveguide element: 188 microns 
   (4)-1 
   Wavelength propagating in optical transmission line: 1.550 microns 
   Wavelength of irradiated light: 0.532 microns 
   Incident angle: 10 degrees 
   Wavelength of externally emitted light: 0.397211 microns 
   Emitting angle: 13.4486 degrees 
   (4)-2 
   Wavelength propagating in optical transmission line: 1.552 microns 
   Wavelength of irradiated light: 0.532 microns 
   Incident angle: 10 degrees 
   Wavelength of externally emitted light: 0.397341 microns 
   Emitting angle: 13.4441 degrees 
   Position difference corresponding to wavelength difference 2 nm of propagating light where light receiving element is disposed at position spaced rearwardly by 10 mm from optical waveguide element: 144 microns 
   According to the accuracy in production of light receiving elements at present, it is easy to produce light receiving elements of the size of approximately 10 microns. Therefore, from the results of the calculation above, it can be seen that a sufficient resolution in position for wavelengths propagating in the optical waveguide  5  is obtained. In other words, information propagating in the optical waveguide  5  can be read for each of wavelengths of the light as described hereinabove in connection with the embodiments of the present invention. 
   While preferred embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.