Abstract:
There is disclosed an optical switch for switching between a plurality of main light emitters respectively emitting light components having wavelengths different from each other and a backup light emitter adapted to replace any of the main light emitters, a light emitter switching method for switching from one failed main light emitter to a backup light emitter by using the optical switch the above switch and a light receiver switching method for switching from one failed main light receiver to a backup light receiver by using the above.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims priority to Provisional Application Serial No. 60/411,098 filed on Sep. 17, 2002, which is/are hereby incorporated by reference in its/their entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an optical switch, a light emitter switching method, a light receiver switching method, a multiplexer, a demultiplexer, and an optical communication system which are used in optical communications and the like.  
           [0004]    2. Related Background Art  
           [0005]    [0005]FIG. 1 shows a typical configuration of a protection system  90  on the demultiplexer side in an optical communication technique. As depicted, the protection system  90  has a configuration in which 2×1 type switches  92  are respectively provided for eight waves of a WDM signal demultiplexed by a demultiplexer  91 , whereas 4×1 type switches  93  are disposed at their corresponding output ports. These switches  92 ,  93  switch from main lines  94  to backup system lines  95 . A similar technique is also disclosed in Japanese Patent Application Laid-Open No. 2002-135817  
           [0006]    From the viewpoint of optical signals transmitted to the backup system lines  95  in the conventional configuration shown in FIG. 1, two switches  92 ,  93  are inserted in series, whereby the above-mentioned switching cannot be carried out normally if any of the switches fails. Therefore, the failure probability becomes higher than that in the case where only one switch is inserted.  
           [0007]    Also, since the two switches  92 ,  93  are arranged in series, the number of junctions on transmission lines increases, which enhances transmission loss.  
           [0008]    Further, it is difficult for the apparatus to reduce its overall size since the switches  92 ,  93 , which are separate components, are combined together.  
         SUMMARY OF THE INVENTION  
         [0009]    In order to overcome the problem mentioned above, it is an object of the present invention to provide an optical switch, a light emitter switching method, a light receiver switching method, a multiplexer, a demultiplexer, and an optical communication system which can lower the failure probability, reduce the transmission loss, and decreases the size.  
           [0010]    It is one aspect of the present invention to provide an optical switch in accordance with the present invention is, as defined in claim 1, an optical switch for switching between a plurality of main light emitters respectively emitting light components having wavelengths different from each other and a backup light emitter adapted to replace any of the main light emitters, a base member formed with a plurality of main waveguides for respectively inputting main light components from the main light emitters and guiding the main light components to a multiplexer; and a backup waveguide, disposed so as to intersect the main waveguides obliquely, for introducing a backup light component from the backup light emitter from the downstream side to upstream side in the advancing direction of the main light components; a plurality of mirrors, disposed so as to be insertable into and retractable from respective intersections between the backup waveguide and the main waveguides, for blocking the main light components from the main light emitters and reflecting the backup light component from the backup light emitter toward the multiplexer when inserted; and a plurality of driving sections for the respective mirrors for inserting the mirrors into and retracting the mirrors from the intersections.  
           [0011]    In above optical switch, a base member is provided with not only a plurality of main waveguides for respectively inputting main light components from main light emitters and guiding the main light components to a multiplexer, but also a backup waveguide disposed so as to intersect the main waveguides obliquely. On this backup waveguide, a backup light component from a backup light emitter is made incident from the downstream side to upstream side in the advancing direction of main light components.  
           [0012]    Mirrors are provided at the respective intersections between the backup waveguide and the main waveguides so as to be insertable into and retractable from the intersections, and block the main light components from the main light emitters and reflect the backup light component from the backup light emitter toward the multiplexer when inserted. The optical switch is also provided with respective driving sections for the mirrors for inserting the mirrors into and retracting the mirrors from the intersections.  
           [0013]    When one main light emitter fails in the configuration mentioned above, a driving section inserts a mirror into the intersection on a main waveguide corresponding to the one main light emitter, while a backup light emitter whose optical output characteristic is adjusted so as to replace the one main light emitter is caused to emit a backup light component, whereby the backup light component is reflected by the mirror, so as to be guided to the main waveguide corresponding to the one main light emitter. As a consequence, the failed main light emitter can be replaced by the backup light emitter. Thus, instead of the conventional combination of a plurality of switches, a single switch can switch from main light emitters to a backup light emitter, whereby the failure probability can be made lower than the conventional one, so as to reduce the transmission loss, and the size can be decreased.  
           [0014]    It is another feature of the present invention that the optical switch is configured such that the base member is further formed with a verification waveguide for guiding the backup light component from the backup light emitter to a verification light receiver for verifying the backup light emitter when all the mirrors are retracted from the intersections.  
           [0015]    In this case, in a state where all the mirrors are retracted from the intersections, a backup light component from the backup light emitter can be guided to the verification light receiver by way of the verification waveguide, whereby the verification light receiver can receive the backup light component, so as to verify the backup light emitter, thus making it possible to improve the reliability of backup functions.  
           [0016]    It is another aspect of the present invention to provide an optical switch for switching between a plurality of main light receivers respectively receiving light components having wavelengths different from each other and a backup light receiver adapted to replace any of the main light receivers; and comprises a base member formed with a plurality of main waveguides for respectively inputting demultiplexed light components demultiplexed by a demultiplexer directed to the main light receivers and guiding the demultiplexed light components to the main light receivers; and a backup waveguide, disposed so as to intersect the main waveguides obliquely, extending from the downstream side to upstream side in the advancing direction of the demultiplexed light components so as to terminate at the backup light receiver; a plurality of mirrors, disposed so as to be insertable into and retractable from respective intersections between the backup waveguide and the main waveguides, for reflecting the demultiplexed lights component from the demultiplexer toward the backup light receiver when inserted; and a plurality of driving sections for the respective mirrors for inserting the mirrors into and retracting the mirrors from the intersections.  
           [0017]    In the above optical switch, a base member is provided with not only a plurality of main waveguides for respectively inputting demultiplexed light components to the main light receivers and guiding the demultiplexed light components to the main light receivers, but also a backup waveguide disposed so as to intersect the main waveguides obliquely. This backup waveguide is formed so as to extend from the downstream side to upstream side in the advancing direction of the demultiplexed light components and terminate at the backup light receiver.  
           [0018]    Mirrors are provided at the respective intersections between the backup waveguide and the main waveguides so as to be insertable into and retractable from the intersections, and reflect demultiplexed light components from the demultiplexer toward the backup light receiver. The optical switch is also provided with respective driving sections for the mirrors for inserting the mirrors into and retracting the mirrors from the intersections.  
           [0019]    When one main light receiver fails in the above-mentioned configuration, a driving section inserts a mirror into the intersection on a main waveguide corresponding to the one main light receiver, whereby a demultiplexed light component corresponding to the one main light receiver is reflected by the mirror, so as to be guided to the backup waveguide and received by the backup light receiver. As a consequence, the failed main light receiver can be replaced by the backup light receiver. Thus, instead of the conventional combination of a plurality of switches, a single switch can switch from main light receivers to a backup light receiver, whereby the failure probability can be made lower than the conventional one, so as to reduce the transmission loss, and the size can be decreased.  
           [0020]    It is another feature of the present invention that the optical switch is configured such that the base member is further formed with a verification waveguide for guiding a light component from a verification light emitter for verifying the backup light receiver into the backup light receiver when all the mirrors are retracted from the intersections.  
           [0021]    In this case, in a state where all the mirrors are retracted from the intersections, the light component from the verification light emitter can be guided to the backup light receiver byway of the verification waveguide, whereby the backup light receiver can be verified according to data of light received by the backup light receiver, thus making it possible to improve the reliability of backup functions.  
           [0022]    Preferably, it is another feature of the present invention that the driving section in each of the optical switch used on the multiplexer side and the optical switch used on the demultiplexer side includes a cantilever disposed on an upper face of the base member, and a first comb electrode formed on a predetermined surface of the cantilever at a predetermined position, the mirror being placed at a predetermined position of the cantilever near a free end thereof such that the mirror is inserted into or retracted from the intersection; a second comb electrode, placed on the upper face of the base member so as to oppose the first comb electrode, having teeth alternately inserted between teeth of the first comb electrode; and electrostatic force generating means for generating an electrostatic force between the first and second comb electrodes by applying a predetermined voltage between the first and second comb electrodes; the electrostatic force generating means generating the electrostatic force so as to drive the first comb electrode toward or away from the second comb electrode, thereby inserting the mirror into or retracting the mirror from the intersection.  
           [0023]    In this case, when an electrostatic force (attractive force or repulsive force) is applied between the first and second comb electrodes by applying a predetermined voltage between the first and second comb electrodes with the electrostatic force generating means, the cantilever flexes, so that the mirror is switchable between a state where the mirror placed near the free end of the cantilever is inserted in the intersection and the state where the mirror is retracted from the intersection. When the driving section is configured as such, the space can be saved in the mirror moving direction (i.e., a direction orthogonal to the cantilever extending direction), whereby a small-sized, highly-integrated optical switch can be realized.  
           [0024]    It is another aspect of the present invention to provide a light emitter switching method for switching from one failed main light emitter to a backup light emitter by using the optical switch of the present invention; and comprises an adjusting step of adjusting an optical output characteristic of the backup light emitter such that the backup light emitter replaces the one main light emitter; a backup light emitting step of emitting a backup light component from the backup light emitter adjusted in the adjusting step; a verifying step of receiving the backup light component with the verification light receiver and verifying whether the backup light emitter is adjusted normally or not according to data of thus received light; and a mirror inserting step of causing the driving section to insert a mirror into the intersection between the main waveguide corresponding to the one main light emitter and the backup waveguide when a result verifying that the backup light emitter is adjusted normally is obtained.  
           [0025]    Namely, the optical output characteristic of the backup light emitter is adjusted such that the backup light emitter replaces the failed main light emitter in the adjusting step, and the backup light component is emitted from thus adjusted backup light emitter in the backup light emitting step. In the verifying step, the backup light receiver receives the backup light component, and verifies whether the backup light emitter is adjusted normally or not according to data of thus received light. If a result verifying that the backup light emitter is adjusted normally is obtained here, a driving section inserts a mirror into the intersection between the main waveguide corresponding to the one main light emitter and the backup waveguide in the mirror inserting step. As a consequence, the backup light component is reflected by the mirror, so as to be guided to the main waveguide corresponding to the one main light emitter. Thus, the backup light emitter having yielded a result verifying that it is normally adjusted can replace the failed main light emitter, whereby the reliability of backup functions can be improved.  
           [0026]    It is another aspect of the present invention to provide a light receiver switching method for switching from one failed main light receiver to a backup light receiver by using the optical switch according to the present invention; and comprises a verification light receiving step of emitting a verification light component from the verification light emitter toward the backup light receiver and receiving the verification light component with the backup light receiver; a verifying step of verifying whether the backup light receiver operates normally or not according to data of verification light received by the backup light receiver; and a mirror inserting step of causing the driving section to insert a mirror into the intersection between the main waveguide corresponding to the one main light receiver and the backup waveguide when a result verifying that the backup light receiver operates normally is obtained.  
           [0027]    Namely, a verification light component is emitted from the verification light emitter toward the backup light receiver in the verification light receiving step, and it is verified whether the backup light receiver operates normally or not according to data of light received by the backup light receiver in the verifying step. If a result verifying that the backup light receiver operates normally is obtained here, a driving section inserts a mirror into the intersection between the main waveguide corresponding to the one main light receiver and the backup waveguide in the mirror inserting step. As a consequence, a demultiplexed light component corresponding to the one main light receiver is reflected by the mirror, so as to be guided to the backup waveguide and received by the backup light receiver. Thus, the backup light receiver having yielded a result verifying that it operates normally can replace the failed main light receiver, whereby the reliability of backup functions can be improved.  
           [0028]    The optical switch according to the present invention may be incorporated in a multiplexer. Namely, a multiplexer of the present invention comprising the optical switch according to the present invention can be constructed.  
           [0029]    The optical switch according to the present invention may be incorporated in a demultiplexer. Namely, a demultiplexer of the present invention comprising the optical switch according to the present invention can be constructed.  
           [0030]    It is further aspect of the present invention to provide an optical communication system including the multiplexer and demultiplexer sides comprising the optical switch according to one of claims 1 to 5 can be constructed.  
           [0031]    The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given byway of illustration only and are not to be considered as limiting the present invention.  
           [0032]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]    [0033]FIG. 1 shows a diagram of a protection system on the demultiplexer side in a conventional optical communication technique.  
         [0034]    [0034]FIG. 2 shows a diagram of the optical communication system in accordance with an embodiment of the present invention.  
         [0035]    [0035]FIG. 3 shows a diagram of an optical switch on the multiplexer side.  
         [0036]    [0036]FIG. 4 shows a diagram of an optical switch on the demultiplexer side.  
         [0037]    [0037]FIGS. 5A and 5B show views showing the arrangement of a mirror, wherein FIGS. 5A and 5B show respective states where the mirror is retracted from and inserted in an intersection.  
         [0038]    [0038]FIG. 6 show a plan view showing the driving section of the mirror.  
         [0039]    [0039]FIG. 7 show a side view showing the driving section of the mirror.  
         [0040]    [0040]FIGS. 8A, 8B and  8 C show Diagrams for explaining an operation of the optical switch on the multiplexer side, wherein FIGS. 8A, 8B and  8 C illustrate a state immediately after one light emitter fails, a verifying step for a backup light emitter, and a mirror inserting step, respectively.  
         [0041]    [0041]FIG. 9 show a flowchart showing processes concerning the optical switch on the multiplexer side.  
         [0042]    [0042]FIGS. 10A, 10B and  10 C show diagrams for explaining an operation of the optical switch on the demultiplexer side, wherein FIGS. 10A, 10B and  0 C illustrate a state immediately after one light receiver fails, a verifying step for a backup light receiver, and a mirror inserting step, respectively.  
         [0043]    [0043]FIG. 11 shows a flowchart showing processes concerning the optical switch on the demultiplexer side. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]    In the following, preferred embodiments of the optical switch, light emitter switching method, light receiver switching method, and optical communication system in accordance with the present invention will be explained with reference to the drawings.  
         [0045]    [Configuration of Optical Communication System] 
         [0046]    [0046]FIG. 2 shows an overall diagram of an optical communication system  1 . As shown in this drawing, the optical communication system  1  is provided with a multiplexer  14  and a demultiplexer  24  which are connected to each other by way of a main line  30 . Disposed on the multiplexer  14  side of the optical communication system  1  are four light emitters  11 A,  11 B,  11 C,  11 D (collectively referred to as light emitters  11 ), a backup light emitter  12  for backing up the light emitters  11 , an optical switch  10 , and a verification light receiver  13 . The four signal light components from the light emitters  11  are multiplexed by the multiplexer  14  by way of the optical switch  10 , and thus multiplexed light is transmitted toward the demultiplexer  24  by way of the main line  30 . Similarly disposed on the demultiplexer  24  side are four light receivers  21 A,  21 B,  21 C,  21 D (collectively referred to as light receivers  21 ), a backup light receiver  22  for backing up the light receivers  21 , an optical switch  20 , and a verification light emitter  23 . The four signal light components demultiplexed by the demultiplexer  24  are transmitted to their corresponding light receivers  21  by way of the optical switch  20 .  
         [0047]    [Configuration of Optical Switch  10  on Multiplexer  14  Side] 
         [0048]    [0048]FIG. 3 shows a diagram of the optical switch  10  on the multiplexer  14  side. As shown in this drawing, the optical switch  10  is provided with a planar waveguide  10 A, whereas the planar waveguide  10 A is provided with four parallel main waveguides  15 A,  15 B,  15 C,  15 D for inputting the respective signal light components from the light emitters  11  and guiding the signal light components to the multiplexer  14 ; and a backup waveguide  16 , disposed so as to intersect the main waveguides  15  obliquely, for guiding a backup light component from the backup light emitter  12  to the verification light receiver  13 . In FIG. 3, light emitters and light receivers are referred to as Tx and Rx (as in FIGS. 4, 8, and  10  which will be explained later), respectively. Also, the light emitters  11 A,  11 B,  11 C, and  11 D outputting signal light components having wavelengths λ 1 , λ 2 , λ 3 , and λ 4  are referred to as Tx(λ 1 ), Tx(λ 2 ), Tx(λ 3 ), and Tx(λ 4 ), respectively (as in FIGS. 8A, 8B and  8 C which will be explained later).  
         [0049]    In this planar waveguide  10 A, mirrors  17 A,  17 B,  17 C,  17 D are disposed at intersections between the backup waveguide  16  and individual main waveguides  15 , respectively, so as to be insertable therein and retractable therefrom.  
         [0050]    The arrangement of the mirror  17 A will be explained with reference to FIGS. 5A, 5B and  5 C. As shown in FIG. 5A, the mirror  17 A is disposed so as to be tilted by a predetermined angle α with respect to a plane orthogonal to the optical axis of signal light along the main waveguide  15 A. The mirror  17 A is inserted into the intersection along the direction of arrow P, so as to attain the inserted state of FIG. 5B. On the other hand, the mirror  17 A is retracted from the intersection along the direction of arrow Q, so as to attain the retracted state of FIG. 5A. The above-mentioned predetermined angle α is set to a half of the angle β formed between the main waveguide  15 A and backup waveguide  16 . Therefore, in the state inserted in the intersection as shown in FIG. 5B, the mirror  17 A blocks the signal light component from the light emitter  11 A and reflects the backup light component from the backup light emitter  12  (arriving from the direction of arrow S) toward the multiplexer  14  in the direction of arrow R. The mirrors  17 B,  17 C,  17 D are disposed at their corresponding intersections as with the mirror  17 A.  
         [0051]    The optical switch  10  is also provided with a driving section  60  (see FIGS. 6 and 7) for inserting each mirror into its corresponding intersection and retracting it therefrom. Here, the driving section  60  will be explained. FIG. 6 is a plan view showing the driving section  60  of mirror, whereas FIG. 7 is a side view thereof.  
         [0052]    As shown in FIG. 7, the driving section  60  formed by use of a microelectromechanical system (MEMS) technology is disposed on a planar waveguide  50 , and has the following configuration of actuator structure. Namely, a cantilever  40  is secured to the planar waveguide  50 , and has a free end  40 A positioned above a groove  50 A. The mirror  17 A is secured to the lower face of the free end  40 A and is inserted in the groove  50 A, so as to be switchable between the above-mentioned states inserted in the intersection and retracted therefrom in the planar waveguide  10 A.  
         [0053]    As shown in FIG. 6, one side face of the cantilever  40  is formed with a comb electrode  41 , whereas a comb electrode  42  equipped with teeth alternately inserted between the teeth of the comb electrode  41  is placed on the upper face of the planar waveguide  50  at the position opposing the comb electrode  41 . The cantilever  40  and the comb electrode  42  are electrically connected to each other by way of a voltage source  43 . When the voltage source  43  applies a predetermined voltage between the comb electrode  41  of the cantilever  40  and the comb electrode  42 , an electrostatic force is generated therebetween. Due to this electrostatic force, the cantilever  40  is attracted to the comb electrode  42 .  
         [0054]    When static electricity is used as such, the cantilever  40  can be driven with a small power consumption. Further, since each of the comb electrode  41  of the cantilever  40  and the comb electrode  42  is provided with a plurality of teeth, a large electrostatic force can be generated even by a low application voltage. Namely, an electrostatic force is generated, so as to drive the comb electrode  41  toward or away from the comb electrode  42 , whereby the mirror  17 A fixed at an end part of the cantilever  40  can be driven so as to be inserted into or retracted from the intersection.  
         [0055]    Constructing the driving section  60  as mentioned above is effective in that the space can be saved in the mirror moving direction (i.e., a direction orthogonal to the cantilever extending direction), whereby a small-sized, highly-integrated optical switch can be realized.  
         [0056]    [Configuration of Optical Switch  20  on Demultiplexer  24  Side] 
         [0057]    The configuration of the optical switch  20  on the demultiplexer  24  side will now be explained.  
         [0058]    [0058]FIG. 4 shows a diagram of the optical switch  20  on the demultiplexer  24  side. As shown in this drawing, the optical switch  20  is provided with a planar waveguide  20 A, whereas the planar waveguide  20 A is formed with four parallel main waveguides  25 A,  25 B,  25 C,  25 D for inputting signal light components from the demultiplexer  24  and guiding them to their corresponding light receivers  21 ; and a backup waveguide  26 , disposed so as to intersect the main waveguides  25  obliquely, for guiding a verification optical component from the verification light emitter  23  to the backup light receiver  22 . In FIG. 4, the light receivers  21 A,  21 B,  21 C, and  21 D receiving signal light components having wavelengths λ 1 , λ 2 , λ 3 , and λ 4  are referred to as Rx(λ 1 ), Rx(λ 2 ), Rx(λ 3 ), and Rx(λ 4 ), respectively (as in FIGS. 10A, 10B and  10 C which will be explained later).  
         [0059]    In this planar waveguide  20 A, mirrors  27 A,  27 B,  27 C,  27 D are disposed at intersections between the backup waveguide  26  and individual main waveguides  25 , respectively, so as to be insertable therein and retractable therefrom. The arrangement of each mirror is similar to that of the mirror  17 A in the above-mentioned optical switch  10 . Therefore, the mirror  27 A, for example, reflects the signal light from the demultiplexer  24  toward the backup light receiver  22  while in the state inserted in the intersection as in FIG. 5B. The same holds for the mirrors  27 B,  27 C,  27 D.  
         [0060]    The optical switch  20  is also provided with a driving section  60  for each mirror for inserting each mirror into its corresponding intersection and retracting it therefrom (see FIGS. 6 and 7). The configuration of the driving section  60  will not be explained since it is similar to that of the driving section  60  in the above-mentioned optical switch  10 .  
         [0061]    [Operation of Optical Switch  10  on Multiplexer  14  Side] 
         [0062]    With reference to FIGS. 8 and 9, an operation of the optical switch  10  on the multiplexer  14  side in accordance with the light emitter switching method of the present invention will now be explained. Here, assuming that the light emitter  11 A (referred to as Tx(λ 1 ) in the drawing) in the light emitters  11  failed as shown in FIG. 8A, the operation for switching from thus failed light emitter  11 A to the backup light emitter  12  will be explained. Though the flowchart of FIG. 9 illustrates a flow of processes related to the operation of the optical switch  10 , it does not indicate that all these processes are automatically executed by a controller or the like.  
         [0063]    First, at S 01  in FIG. 9, the optical output characteristic of the backup light emitter  12  is adjusted such that the backup light emitter  12  replaces the failed light emitter  11 A (i.e., outputs a signal light component having the wavelength λ 1 ).  
         [0064]    Then, at S 02 , a backup light component is emitted from thus adjusted backup light emitter  12  toward the verification light receiver  13  in the direction of arrow S in FIG. 8B.  
         [0065]    At S 03  subsequent thereto, the backup light component is received by the verification light receiver  13 , and it is verified whether the backup light emitter  12  is adjusted normally or not according to data of thus received light. If the result verifying that the backup light emitter is adjusted normally is not obtained here, a process for readjusting the backup light emitter  12  or the like is carried out at S 05 .  
         [0066]    If the result verifying that the backup light emitter is adjusted normally is obtained at S 03 , the driving section  60  inserts the mirror  17 A into the intersection between the main waveguide  15 A corresponding to the failed light emitter  11 A and the backup waveguide  16  at S 04 . As a consequence, the backup light component is reflected by the mirror  17 A as indicated by the arrow T in FIG. 8C, so as to be guided to the main waveguide  15 A. Thus, the backup light emitter  12  can replace the failed light emitter  11 A.  
         [0067]    Namely, instead of the conventional combination of a plurality of switches, the single optical switch  10  can switch from the failed light emitter  11 A to the backup light emitter  12 , whereby the failure probability can be made lower than the conventional one, so as to reduce the transmission loss, and the size can further be decreased. Also, the backup light emitter  12  having yielded the result verifying that it is normally adjusted replaces the failed light emitter  11 A, whereby the reliability of backup functions can be improved.  
         [0068]    [Operation of Optical Switch  20  on Demultiplexer  24  Side] 
         [0069]    With reference to FIGS. 10 and 11, an operation of the optical switch  20  on the demultiplexer  24  side in accordance with the light receiver switching method of the present invention will now be explained. Here, assuming that the light receiver  21 A (referred to as Rx(λ 1 ) in the drawing) in the light receivers  21  failed as shown in FIG. 10A, the operation for switching from thus failed light receiver  21 A to the backup light receiver  22  will be explained. Though the flowchart of FIG. 11 illustrates a flow of processes related to the operation of the optical switch  20 , it does not indicate that all these processes are automatically executed by a controller or the like.  
         [0070]    First, at S 11  in FIG. 11, a verification light component is emitted from the verification light emitter  23  toward the backup light receiver  22  in the direction of arrow S in FIG. 10B, so that the backup light receiver  22  receives the verification light component.  
         [0071]    Next, according to data of verification light received by the backup light receiver  22 , it is determined at S 12  whether the backup light receiver  22  operates normally or not. If the result verifying that the backup light receiver  22  operates normally is not obtained here, a process for readjusting the backup light receiver  22  or the like is carried out at S 14 .  
         [0072]    If the result verifying that the backup light receiver  22  operates normally is obtained at S 12 , the driving section  60  inserts the mirror  27 A into the intersection between the main waveguide  25 A corresponding to the failed light receiver  21 A and the backup waveguide  26  at S 13 . As a consequence, a demultiplexed light component having a wavelength λ 1  (i.e., demultiplexed light component corresponding to the light receiver  21 A) is reflected by the mirror  27 A as in the arrow U of FIG. 10C, so as to be guided to the backup waveguide  26  and received by the backup light receiver  22 . Thus, the backup light receiver  22  can replace the failed light receiver  21 A.  
         [0073]    Namely, instead of the conventional combination of a plurality of switches, the single optical switch  10  can switch from the failed light receiver  21 A to the backup light receiver  22 , whereby the failure probability can be made lower than the conventional one, so as to reduce the transmission loss, and the size can further be decreased. Also, the backup light receiver  22  having yielded the result verifying that it operates normally replaces the failed light receiver  21 A, whereby the reliability of backup functions can be improved.  
         [0074]    The optical switch  10  on the multiplexer side may be incorporated in the multiplexer  14 . Namely, the multiplexer  14  can be constructed as a multiplexer equipped with the optical switch  10  of the above-mentioned embodiment as well.  
         [0075]    Similarly, the optical switch  20  on the demultiplexer side may be incorporated in the demultiplexer  24 . Namely, the demultiplexer  24  can be constructed as a multiplexer equipped with the optical switch  20  of the above-mentioned embodiment as well.  
         [0076]    When one main light emitter fails in the present invention, as explained in the foregoing, a driving section inserts a mirror into an intersection on the main waveguide corresponding to the one main light emitter, while a backup light emitter whose optical output characteristic is adjusted so as to replace the one main light emitter emits a backup light component, so that the backup light component is reflected by the mirror and guided to the main waveguide corresponding to the one main light emitter, whereby the failed one main light emitter can be replaced by the backup light emitter. Thus, instead of the conventional combination of a plurality of switches, a single switch can switch from main light emitters to the backup light emitter, whereby the failure probability can be made lower than the conventional one, so as to reduce the transmission loss, and the size can further be decreased.  
         [0077]    When one main light receiver fails, on the other hand, a driving section inserts a mirror into the intersection on the main waveguide corresponding to the one main light receiver, so that the demultiplexed light component corresponding to the one main light receiver is reflected by the mirror and guided to the backup waveguide, so as to be received by the backup light receiver, whereby the failed one main light receiver can be replaced by the backup light receiver. Thus, instead of the conventional combination of a plurality of switches, a single switch can switch from main light receivers to the backup light receiver, whereby the failure probability can be made lower than the conventional one, so as to reduce the transmission loss, and the size can further be decreased.  
         [0078]    The basic Japanese Application No. 2002-264529 filed on Sep. 10, 2002 is hereby incorporated by reference.  
         [0079]    From the invention thus described, it will be obvious that the embodiments of the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.