Abstract:
A wavelength selection switch can decrease the amount of increase in size and cost of a node device by integrating and sharing the constituent components of a plurality of wavelength selection switches or optical components mounted in a node. The wavelength selection switch has: at least one input port that inputs light; at least one output port that receives light from the input port; at least one light-collecting element that alters the beam shape of the light entering from the input port; at least one scattering element that scatters the light entering from the input port into each wavelength; at least one wavefront control element that causes light of each wavelength scattered by the scattering element to be reflected to the output port for each wavelength.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an optical signal processing device. 
       BACKGROUND ART 
       [0002]    In recent years, in the field of optical communications, large capacity optical transmission via a single optical fiber has been implemented by WDM (Wavelength Division Multiplexing) technology that performs transmission by multiplexing signals while allocating one signal to one wavelength. As this optical communication technology has been developed, attention has been drawn to optical switches for changing a signal path without converting an optical signal into an electric signal, etc. Among these switches, a wavelength selective switch that can select an arbitrary wavelength from several tens of wavelengths and output the wavelength to one of a plurality of output fibers (see, for example, patent literature 1) has been proposed. An example Wavelength Selective Switch (WSS) is illustrated in  FIG. 1 . 
         [0003]    The wavelength selective switch in  FIG. 1  includes a fiber array  001 , a microlens array  002 , a condenser lens  003 , a cylindrical lens  004 , a first main lens  005 , a diffraction grating  006 , a second main lens  007  and an MEMS mirror array  008 , and has a configuration where these components are arranged in the order in the z direction. 
         [0004]    The fiber array  001  is provided by arranging a plurality of optical fibers in the y direction, and is demultiplexed into an input port for emitting input light and an output port for receiving output light. In the example in  FIG. 1 , one input port  0011  and four output ports  0012  are provided. The microlens array  002  is arranged in the y direction in the same way as the fiber array  001 , so that the individual microlenses are located opposite the corresponding optical fibers of the fiber array  001  on the output side of the input port and the input side of the output ports of the fiber array  001 . The individual microlenses of the microlens array  002  shape beams that are emitted from the corresponding input and output ports of the optical fibers of the fiber array  001 , and convert the beams into collimated rays. 
         [0005]    The condenser lens  0003  concentrates light from the optical fibers to cross the principal rays at a specific point  009  (hereinafter referred to as a point A). A distance between the condenser lens  003  and the point A  009  is equal to the focal length of the condenser lens  003 . The cylindrical lens  004  shapes the beam at the point A  009  into an elliptical form. 
         [0006]    The first main lens  005 , the second main lens  007  and the diffraction grating  006  constitute a 4 f optical system. The distance between the point A and the first main lens is equal to a focal length f 1  of the first main lens, and the distance between the second main lens and the MEMS mirror is equal to a focal length f 2  of the second main lens. Since the 4 f optical system is provided, the beam shaped at the point A  009  is projected to the MEMS mirror  008 . The diameter of the beam projected to the MEMS mirror  008  is enlarged or reduced at a focal length ratio of f 2 /f 1  relative to the beam diameter at the point A. The diffraction grating  006  serves to demultiplex, for each wavelength, signal light obtained by division multiplexing. The rays of the signal light demultiplexed for the individual wavelengths are emitted to the corresponding elements of the MEMS mirror through the second main lens  007 . 
         [0007]    The MEMS mirror  008  includes a plurality of mirror elements, which are aligned in the manner that the linear line that passes the centers of the individual mirror elements of the MEMS mirror  008  is extended in the x axial direction. The MEMS mirror  008  is arranged at the focal point of the second main lens in the state wherein the main faces of the individual mirror elements are located opposite the second main lens. The MEMS mirror  008  reflects, with an angle being changed to θx, the principal rays of the individual signal light that has been emitted, and selects output ports to which the rays enter. Since the individual mirror elements of the MEMS mirror  008  are rotated at the x axis that is perpendicular to the z axis for wavelength dispersion, the angle of incidence at the point A  009  is changed by changing the angle of emittance by the rotation. As a result, the wavelength selective switch can select the output port  0012  where the principal ray enters. 
         [0008]    The wavelength selective switch can select the output port for each wavelength by changing the emittance angle for the MEMS mirror that is allocated for each signal light beam. 
         [0009]    A plurality of these wavelength selective switches are mounted in a node  200  that is employed for an optical network.  FIG. 2  is a structural diagram showing a wavelength selective switching unit where two wavelength selective switches (WSSes) are mounted on a single node. A wavelength selective switch  201  demultiplexes an optical signal received at the node  200  into a signal that is directed to the following wavelength selective switch  202  and a signal that is directed to receivers  203 - 1  and  203 - 2 . The wavelength selective switch  202  at the succeeding stage multiplexes the signal received from the preceding wavelength selective switch  201  and the signal light received from transmitters  204 - 1  and  204 - 2 , and outputs signal light from the node  200 . 
         [0010]    In the above described manner, for each node, the signals that are received and are to be transmitted, or passed through, can be demultiplexed and multiplexed by the wavelength selective switches. The node generally includes not only the wavelength selective switches, but also the other optical parts, such as an optical monitor, an optical amplifier and an optical coupler, and has functions, such as detection of a failure, compensation for the optical quality and detection of deterioration of the optical quality. 
         [0011]    A configuration for a node employed when the number of routes is four is shown in  FIG. 3 . This node configuration can switch the individual signal wavelengths to arbitrary routes. At this time, eight wavelength selective switches are mounted. A case wherein the number of routes is four is employed for the description; however, an arbitrary number of routes can be employed, and as the number of routes is increased, the number of wavelength selective switches employed is also increased. 
         [0012]    When multiple wavelength selective switches and optical parts are mounted to the node, the size of the node is increased, and the cost for the node is increased by the cost required for the number of components, such as the wavelength selective switches. Therefore, if common parts for a plurality of wavelength selective switches can be commonized and parts for which functional integration is available can be provided by using a single part, the sizes of the individual devices in the node can be reduced, and the cost can also be decreased. 
         [0013]    In the present invention, the arrangement of input and output ports and the arrangement of an optical system, which are required for common use of parts, such as some optical parts included in a plurality of wavelength selective switches, are provided. Further, input/output port fabrication means for accurately mounting input and output ports, which will be increased by mounting a plurality of wavelength selective switches, is also provided. Furthermore, means for performing integration of the node function for the input and output ports of a wavelength selective switch is provided in order to reduce the sizes of the devices in the node. 
       CITATION LIST 
     Patent Literature 
       [0014]    PTL 1: Japanese Patent Laid-Open No. 2009-122492 
       SUMMARY OF INVENTION 
       [0015]    A wavelength selective switch array for the present invention is a wavelength selective switch array formed by mounting, on a single substrate, n wavelength selective switches, each of which includes at least one input port adapted to accept light, at least one output port adapted to receive light from the input port, at least one condenser element adapted to change a shape of a beam of light received from the input port, at least one dispersive element adapted to demultiplex, for each wavelength, the light received from the input port, and at least one wavefront control element adapted to permit the light demultiplexed by the dispersive element for each wavelength to be reflected to the output port according to each wavelength, and at least one of the condenser element, the dispersive element and the wavefront control element can be employed in common by the n wavelength selective switches. 
         [0016]    Further, at least the condenser element can be employed in common by the n wavelength selective switch of the present invention. 
         [0017]    Furthermore, according to the wavelength selective switch array of the present invention, for the wavelength selective switches that belong to the same group, principal rays for individual wavelengths of light entering and exiting the input port and the output port intersect at one point on the wavefront control element, and for the wavelength selective switches that belong to different groups, do not intersect on the wavefront control element. 
         [0018]    Moreover, according to the wavelength selective switch array of the present invention, for the wavelength selective switches that belong to the same group, the input port and the output port are arranged on an arc by employing, as the center, one point on the wavefront control element, and for the wavelength selective switches that belong to different groups, the input port and the output port are arranged on different arcs by employing, as the center, different points on the wavefront control element. 
         [0019]    Further, for the wavelength selective switch array of the present invention, angles of the principal rays entering and exiting the input port and the output port are varied among the wavelength selective switches that belong to different groups. 
         [0020]    Furthermore, according to the wavelength selective switch array of the present invention, for the wavelength selective switches that belong to the same group, the input port and the output port are arranged so that angles of incidence and angles of emittance of the principal rays are parallel to each other, and for the wavelength selective switches that belong to different groups, the input port and the output port are arranged so that the angles of incidence and the angles of emittance of the principal rays are not parallel. 
         [0021]    Moreover, according to the wavelength selective switch array of the present invention, for the wavelength selective switches that belong to the same group, the principal rays for the individual wavelengths of light entering and exiting the input port and the output port intersect at one point located outside the wavefront control element, and the point located outside the wavefront control element is different for the wavelength selective switches that belong to different groups. 
         [0022]    Further, for the wavelength selective switch array of the present invention, the input port and the output port are arranged so that, in the wavelength selective switches that belong to the same group, the angles of incidence and the angles of emittance of the principal rays are different. 
         [0023]    Furthermore, according to the wavelength selective switch array of the present invention, for the wavelength selective switches that belong to the same group, the input port and the output port are arranged, so that the angles of incidence and the angles of emittance of the principal rays are parallel, and the principal rays intersect at one point by at least one lens, and for the wavelength selective switches that belong to different groups, the input port and the output port are arranged, so that the angles of incidence and the angles of emittance for the principal rays are not parallel. 
         [0024]    Moreover, for the wavelength selective switch array of the present invention, either set of the input port and the output port, or of the input port, the output port, and at least one of the condenser element, the dispersive element and the wavefront control element can be produced by using a planar lightwave circuit. 
         [0025]    Since common use and integration of the components, such as a plurality of wavelength selective switches and optical parts, mounted to a node is promoted, the size of the node device and the additional increase of the cost can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0026]      FIG. 1  A diagram illustrating an example conventional wavelength selective switch described in patent literature 1; 
           [0027]      FIG. 2  A diagram illustrating a node where two of the wavelength selective switches described in patent literature 1 are mounted; 
           [0028]      FIG. 3  A diagram illustrating a node for which the number of routes of the wavelength selective switch described in patent literature 1 is four; 
           [0029]      FIG. 4A  A diagram illustrating a first embodiment for a wavelength selective switch according to the present invention; 
           [0030]      FIG. 4B  A diagram illustrating the first embodiment for the wavelength selective switch according to the present invention; 
           [0031]      FIG. 5  A diagram showing an example wherein an input port array and a microlens array for the first embodiment of the wavelength selective switch according to the present invention are integrated on a PLC; 
           [0032]      FIG. 6A  A diagram illustrating a second embodiment for the wavelength selective switch according to the present invention; 
           [0033]      FIG. 6B  A diagram illustrating the second embodiment for the wavelength selective switch according to the present invention; 
           [0034]      FIG. 7A  A diagram illustrating a third embodiment for the wavelength selective switch according to the present invention; 
           [0035]      FIG. 7B  A diagram illustrating the third embodiment for the wavelength selective switch according to the present invention; 
           [0036]      FIG. 8A  A diagram illustrating a fourth embodiment for the wavelength selective switch according to the present invention; 
           [0037]      FIG. 8B  A diagram illustrating the fourth embodiment for the wavelength selective switch according to the present invention; 
           [0038]      FIG. 9A  A diagram illustrating a fifth embodiment for the wavelength selective switch according to the present invention; 
           [0039]      FIG. 9B  A diagram illustrating the fifth embodiment for the wavelength selective switch according to the present invention; 
           [0040]      FIG. 10A  A diagram illustrating a sixth embodiment for the wavelength selective switch according to the present invention; 
           [0041]      FIG. 10B  A diagram illustrating the sixth embodiment for the wavelength selective switch according to the present invention; 
           [0042]      FIG. 11  A diagram illustrating a seventh embodiment for the wavelength selective switch according to the present invention; 
           [0043]      FIG. 12  A diagram illustrating an eighth embodiment for the wavelength selective switch according to the present invention; 
           [0044]      FIG. 13  A diagram illustrating a ninth embodiment for the wavelength selective switch according to the present invention; 
           [0045]      FIG. 14  A diagram illustrating a tenth embodiment for the wavelength selective switch according to the present invention; 
           [0046]      FIG. 15  A diagram illustrating an eleventh embodiment for the wavelength selective switch according to the present invention; 
           [0047]      FIG. 16A  A diagram illustrating a twelfth embodiment for the wavelength selective switch according to the present invention; 
           [0048]      FIG. 16B  A diagram illustrating the twelfth embodiment for the wavelength selective switch according to the present invention; and 
           [0049]      FIG. 17  A detailed diagram for the planar lightwave circuit of the wavelength selective switch shown in  FIGS. 16A and 16B . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0050]    The embodiments of the present invention will now be described; however, the present invention is not limited to these embodiments. It should be noted that the symbols and numbers employed for all the drawings denote the identical or corresponding portions. 
       First Embodiment 
       [0051]    A wavelength selective switch array  4100  for a first embodiment is shown in  FIGS. 4A and 4B . The wavelength selective switch array  4100  in  FIGS. 4A and 4B  includes input/output port arrays  4101 , microlens arrays  4102 , a dispersive element  4103 , a condenser lens  4104  and a reflective wavefront control element  4105 . The wavelength selective switch array of the present invention includes a plurality of input/output port arrays, and a plurality of input and output ports are provided in the individual input/output port arrays. 
         [0052]    A direction in which the ports are aligned is defined as a port direction.  FIG. 4A  is a cross-sectional view of the wavelength selective switch array taken in a wavelength dispersion direction that is perpendicular to the port direction, and  FIG. 4B  is a cross-sectional view of the wavelength selective switch array taken in the port direction. 
         [0053]    (Components of Optical System) 
         [0054]    The input/output port arrays  4101  are formed by aligning a plurality of optical fibers in a row, and are separated into input ports for emitting input light, and output ports for receiving the output light. In the examples in  FIGS. 4A and 4B , two input/output port arrays, i.e., a first input/output port array  4101   a  and a second input/output port array  4101   b , are prepared. The first input/output port array  4101   a  includes an input port  4101   a - 1  and two output ports  4101   a - 2  and - 3 . In contrast, the second input/output port array  4101   b  includes an input port  4101   b - 1  and two output ports  4101   b - 2  and - 3 . The microlens arrays  4102  are arranged in the same direction as the input/output port arrays  4101 , so that the individual microlenses are located, on the output side of the input ports and on the input side of the output ports of the input/output port arrays  4101 , opposite the corresponding optical fibers of the input/output port arrays  4101 . The individual microlenses of the microlens arrays  4102  adjust the shapes of the beams that are emitted from the input and output ports  4101   a - 1  to  4101   a - 3  and  4101   b - 1  to  4101   b - 3 , which correspond to the optical fibers of the fiber arrays, and convert the beams into collimated light. 
         [0055]    The dispersive element  4103  demultiplexes, by wavelengths, the light emitted from the individual input ports  4101   a - 1  and  4101   b - 1  of the input/output port arrays  4101 , and projects the demultiplexed light to the wavefront control element  4105  through the condenser lens  4104 . An example for the dispersive element  4103  is a diffraction grating, but the dispersive element is not limited to this component. 
         [0056]    The condenser lens  4104  is a cylindrical lens, and provides the effect for changing the shape of a beam to be projected to the wavefront control element  4105 . When the diameter of a beam projected to the wavefront control element  4105  in the wavelength demultiplexing direction is reduced, the passband for signal light can be wider. 
         [0057]    The reflective wavefront control element  4105  reflects the individual irradiated principal rays, while changing the angle of emittance by performing the wavefront control, and selects the output ports on which the principal rays are made incident. The wavefront control elements  4105  for the individual wavelength selective switches are aligned, in the wavelength dispersion direction, relative to the input/output port arrays, and are mounted on at least one substrate. Since the locations of irradiation of the principal rays to the dispersive control element  4105  differ for the wavelengths of the light demultiplexed by the dispersive element  4103 , a plurality of the wavefront control elements  4105  provided for the substrate can independently change the angle of emittance, and when the angle of emittance is changed, the output port  4101   a - 2  or  4101   a - 3 , or  4101   b - 2  or  4101   b - 3 , can be selected for each wavelength. 
         [0058]    The wavefront control element  4105  has a reflective face, and is arranged in the state wherein the reflective face is opposite the condenser lens. The reflective face of the reflective wavefront control element  4105  is supported in the state wherein rotation is enabled in a direction perpendicular to the axis in the wavelength dispersion direction, i.e., around the axis in the wavelength dispersion direction. Since the angle of emittance is changed by rotation, the output port on which the principal ray is made incident ( 4101   a - 2  or - 3  or  4101   b - 2  or - 3 ) can be selected. In this case, the light beams entering the wavefront control element  4105  is not limited to parallel beams, and may be focused beams or divergent beams. 
         [0059]    As the reflective wavefront control element  4015 , LCOS (Liquid Crystal on Silicon), an MEMS (Micro-Electro-Mechanical Systems) mirror, a liquid crystal panel or a DMD (Digital Micromirror Device), for example, can be employed. 
         [0060]    (Port Switching) 
         [0061]    When the light is emitted from the port  4101   a - 1  of the first input/output port array  4101   a , the light is transmitted through the corresponding microlens  4102   a - 1  of the first microlens array  4102   a , the dispersive element  4103  and the condenser lens  4104 , and is projected to the reflective wavefront control element  4105 . The light projected to the wavefront control element  4105  is reflected to change the emittance angle through the wavefront control, and the reflected light is transmitted again through the condenser lens  4104  and the dispersive element  4103 , and through the microlens  4102   a - 2  of the first microlens array  4102   a , and is coupled at the port  4101   a - 2  of the first input/output port array  4101   a . When the wavefront control element  4105  is appropriately controlled, the direction of the reflected light can be changed, and the reflected light can also be coupled at another port  4101   a - 3 . The output port for coupling may be the same port, i.e., the input port  4101   a - 1 , and in this case, the output light is demultiplexed by additionally providing a circulator. Since the optical system is designed so that the principal rays of a beam that enter or exit, according to the wavelengths, the same input/output port array, i.e., the first input/output port array  4101   a , intersect at the identical point  4106   a  on the wavefront control element  4105 , high coupling efficiency can be obtained. 
         [0062]    The similar port switching operation is performed for the second input/output port array  4101   b . Specifically, light emitted from the port  4101   b - 1  of the second input/output port array  4101   b  is transmitted through the corresponding microlens  4102   b - 1  of the second microlens array  4102   b , the dispersive element  4103  and the condenser lens  4104 , and is projected to the wavefront control element  4105 . The light projected to the wavefront control element  4105  is reflected to change the angle of emittance through wavefront control, and the reflected light is transmitted again through the condenser lens  4104  and the dispersive element  4103  and through the microlens  4102   b - 2  of the second microlens array  4102   b , and is coupled at the port  4101   b - 2  of the second input/output port array  4101   b . When the wavefront control element  4105  is appropriately controlled, the direction of the reflected light can be changed, and can also be coupled at another port  4101   b - 3 . As well as the case of the first input/output port array, the optical system is designed so that the principal rays of a beam that enter or exit the same input/output port array, i.e., the second input/output port array  4101   b , according to the wavelengths intersect at the identical point  4106   b  on the wavefront control element  4105 . 
         [0063]    Here, the focal point  4106   b  associated with the second input/output port array  4101   b  is provided at a different location from that for the focal point  4106   a  associated with the first input/output port array  4101   a . In order to provide different locations, in this embodiment, the fibers connected to the first input/output port array  4101   a  are arranged on the arc with the point  4106   a  being the center, while the fibers connected to the second input/output port array  4101   a  are arranged on the arc with the point  4106   b  being the center. 
         [0064]    When the electric field profile on the wavefront control element  4105  for a beam of light emitted from the input port is represented by E 0 , the electric field profile for a beam of light emitted from an arbitrary output port is represented by E 1 , and a phase to be corrected by the wavefront control element is represented by H, coupling efficiency η can be represented by 
         [0000]    
       
         
           
             
               
                 
                   η 
                   = 
                   
                     
                       ∫ 
                       
                         
                           E 
                           0 
                         
                          
                         
                           E 
                           1 
                           * 
                         
                          
                         H 
                          
                         
                            
                           s 
                         
                          
                         
                           ∫ 
                           
                             
                               
                                 E 
                                 0 
                                 * 
                               
                               · 
                               
                                 E 
                                 1 
                               
                             
                              
                             H 
                              
                             
                                
                               s 
                             
                           
                         
                       
                     
                     
                       ∫ 
                       
                         
                           E 
                           0 
                         
                          
                         
                           E 
                           0 
                           * 
                         
                          
                         
                            
                           s 
                         
                          
                         
                           ∫ 
                           
                             
                               E 
                               1 
                             
                              
                             
                               E 
                               1 
                               * 
                             
                              
                             
                                
                               s 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Expression 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0065]    Here, s denotes the dimension of the face of the wavefront control element  4105 . The electric field profiles for the beams of light emitted from the input and output ports of the input/output port arrays  4101  are in the same Gaussian shape. When the intensity distributions for the beam profiles emitted from the input and output ports can be obtained near each other, and the phases of the beam profiles of light emitted from the input and output ports can be matched according to the phase H of the wavefront control element, the coupling efficiency is increased. Therefore, as for coupling of the light at the ports that belong to the identical wavelength selective switch to be connected, when the configuration is so designed that the intensity distributions of the beam profiles can be provided near each other, and the phases of the beam profiles for arbitrary output and input ports can be matched by the wavefront control element, the coupling efficiency can be selectively increased by the wavefront control element. In contrast, as for coupling at the ports that belong to a different wavelength selective switch, the configuration is designed not to provide the intensity distributions of the beam profiles adjacent to each other, and the occurrence of crosstalk can be suppressed. 
         [0066]    (Input/Output Ports of PLC) 
         [0067]    Since the node where the wavelength selective switch array according to the present invention is arranged includes a plurality of (two in this embodiment) wavelength selective switches, a plurality of input/output port arrays and microlens arrays are at least provided. Therefore, a high-density arrangement is necessary for compact packaging, and high implementation accuracy is required. Thus, as shown in  FIG. 5 , the input/output port arrays and the microlens arrays are fabricated by being integrated on a Planar Lightwave Circuit (PLC) employing the photolithography technology, and thus, the accurate arrangement that is consonant with high mask overlay accuracy can be obtained. Referring to  FIG. 5 , input/output port arrays  4201  and microlens arrays  4202  are employed. The input/output port arrays  4201  correspond to the input/output port arrays  4101  in  FIG. 5 , and the microlens arrays  4202  correspond to the microlens arrays  4102 . Light emitted from one port  4201   a - 1  of a first input/output port array  4201   a  is transmitted through a corresponding microlens  4202   a - 1  of a first microlens array  4202   a , and is emitted to the following optical system beginning with the dispersive element  4103  shown in  FIGS. 4A and 4B . Light returned from the dispersive element  4103  is transmitted through a microlens  4202   a - 2  of the first microlens array  4202   a , and is coupled at a port  4201   a - 2  of the first input/output port array  4201   a . When the wavefront control element  4105  is appropriately controlled in the same manner as in  FIGS. 4A and 4B , the direction of reflected light can be changed, and can also be coupled at another port  4201   a - 3 . The same port switching operation is performed for a second input/output port array  4201   b . The arrangement where the input/output port arrays  4201  and the microlens arrays  4202  are produced by employing a PLC has been described by referring to  FIG. 5 , in the same manner by referring to  FIGS. 4A and 4B . However, only the input/output port arrays ( 4101   a  and  4101   b ) may be produced by employing a PLC, or some optical parts except for the wavefront control element  4105  may be integrated on the PLC. 
         [0068]    Further, the input and output ports and the microlens array may be integrated on a PLC for each of the input/output port arrays, and a number of PLCs equivalent to the number of wavelength selective switches may also be prepared. The PLC substrates for the individual wavelength selective switches may be arranged in parallel to each other, or may be arranged at appropriate angles to each other. When this three-dimensional arrangement is employed, it is easy that the number of ports is increased while the port density is increased for compact packaging. 
         [0069]    The other functional elements, such as an optical splitter, an optical combiner, a switch, a light receiving element and a grating, can also be integrated on the PLC. With this arrangement, addition of the functions to the wavelength selective switch is enabled, and when an optical tap (splitter) and optical monitors (a grating and a light receiving element), for example, are integrated, the function for detecting a failure of the wavelength selective switch can be additionally provided. 
         [0070]    According to this optical system, when the focal points of the principal rays are changed depending on the individual wavelength selective switches of the input/output port arrays  4101 , and the ports are arranged along the arc with the focal point being the center, a plurality of groups of switches can be provided with a simple structure. Further, a plurality of wavelength selective switches can be obtained by additionally providing the dispersive element  4103 . Furthermore, since the ports can be fabricated by using a planar lightwave circuit, a mounting error can be reduced, and the additional function can easily be mounted. 
         [0071]    In this embodiment, the fibers are employed as the ports; however, both the fibers and the microlens array may also be employed together as ports. 
       Second Embodiment 
       [0072]    A wavelength selective switch array  6100  for a second embodiment is shown in  FIGS. 6A and 6B . Referring to  FIGS. 6A and 6B , the arrangement includes input/output port arrays  6101 , microlens arrays  6102 , a condenser lens  6103 , a dispersive element  6104 , a cylindrical lens  6105  and a reflective wavefront control element  4106 . The wavelength selective switch array of the present invention includes a plurality of input/output port arrays, and a plurality of input and output ports are provided in the individual input/output port arrays. For the wavelength selective switch array  6100  in this embodiment, two wavelength selective switches are mounted on the same substrate. 
         [0073]    A direction in which the ports are aligned is defined as a port direction.  FIG. 6A  is a cross-sectional view of the wavelength selective switch array taken in a wavelength dispersion direction that is perpendicular to the port direction, and  FIG. 6B  is a cross-sectional view of the wavelength selective switch array taken in the port direction. 
         [0074]    (Components of Optical System) 
         [0075]    The input/output port arrays  6101  are identical to the input/output port arrays  4101  shown in  FIGS. 4A and 4B  for the first embodiment, and the microlens arrays  6102  are identical to the microlens arrays  4102 , except for the arrangement method employed. Further, the reflective wavefront control element  6106  is identical to the reflective wavefront control element  4105 . 
         [0076]    The dispersive element  6104  demultiplexes, by wavelengths, the light emitted from the individual input ports  6101   a - 1  and  6101   b - 1  of the input/output port arrays  6101 , and projects the demultiplexed light to the wavefront control element  6106  through the cylindrical lens  6105 . 
         [0077]    The condenser lens  6103  and the cylindrical lens  6105  provide the effect for changing the shape of a beam to be projected to the wavefront control element. When the diameter of a beam projected to the wavefront control element in the wavelength demultiplexing direction is reduced, the passband for signal light can be extended. Further, when the size of the beam is enlarged in the port switching direction, the angle of emittance required for switching can be reduced. 
         [0078]    (Port Switching) 
         [0079]    When the light is emitted from the port  6101   a - 1  of the first input/output port array  6101   a , the light is transmitted through the corresponding microlens  6102   a - 1  of the first microlens array  6102   a , the condenser lens  6103 , the dispersive element  6104  and the cylindrical lens  6105 , and is projected to the reflective wavefront control element  6106 . The light projected to the wavefront control element  6106  is reflected to change the emittance angle through the wavefront control, and the reflected light is transmitted again through the cylindrical lens  6105 , the dispersive element  6104  and the condenser lens  6103  and through the microlens  6102   a - 2  of the first microlens array  6102   a , and is coupled at the port  6101   a - 2  of the first input/output port array  6101   a . When the wavefront control element  6106  is appropriately controlled, the direction of the reflected light can be changed, and the reflected light can also be coupled at another port  6101   a - 3 . The condenser lens  6103  has a function whereby light rays having arbitrary angles, which intersect at an identical point  6107   a  on the wavefront control element, become parallel to each other on the face of the input/output port, and the ports that belong to the same switch group are arranged in parallel to each other. The input port  6101   a - 1  may also be employed as an output port for coupling, and in this case, the output light is demultiplexed by additionally providing a circulator. Since the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelengths, a single input/output port array, i.e., the first input/output port array  6101   a , intersect at the identical point  6107   a  on the wavefront control element  6106 , high coupling efficiency can be obtained. 
         [0080]    The similar port switching operation is performed for the second input/output port array  6101   b . Specifically, light emitted from the port  6101   b - 1  of the second input/output port array  6101   b  is transmitted through the corresponding microlens  6102   b - 1  of the second microlens array  6102   b , the condenser lens  6103 , the dispersive element  6104  and the cylindrical lens  6105 , and is projected to the wavefront control element  6106 . The light projected to the wavefront control element  6106  is reflected to change the angle of emittance through wavefront control, and the reflected light is transmitted again through the cylindrical lens  6105 , the dispersive element  6104  and the condenser lens  6103  and through the microlens  6102   b - 2  of the second microlens array  6102   b , and is coupled at the port  6101   b - 2  of the second input/output port array  6101   b . When the wavefront control element  6106  is appropriately controlled, the direction of the reflected light can be changed, and can also be coupled at another port  6101   b - 3 . As well as the case of the first input/output port array, the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelength, the same input/output port array, i.e., the first input/output port array  6101   b , intersect at the identical point  6107   b  on the wavefront control element  6106 . 
         [0081]    In this embodiment, the coupling efficiency is also improved when overlap between the input and output beams is increased, and the phases of the beams are aligned with each other. That is, as for coupling of the beams at the ports that belong to the same switch group to be connected, the coupling efficiency can be selectively improved by designing the arrangement to obtain overlap between the beams and to align the phases of the beams. As for coupling of the beams at the ports that belong to different switch groups, the occurrence of crosstalk can be reduced by designing the arrangement not to obtain overlap between the beams. 
         [0082]    Further, in this embodiment, when the input/output port arrays and the microlens arrays are provided by being integrated on a planer lightwave circuit by using the photolithography technology, the accurate arrangement consonant with high mask overlay accuracy can be implemented. 
         [0083]    According to this optical system, since the angles of incidence and the angles of emittance of the principal rays are changed depending on the individual wavelength selective switches of the input/output port arrays  6101 , and the fibers connected to the input/output ports of the individual wavelength selective switches are arranged in parallel to each other, a plurality of wavelength selective switches can be provided with a simple structure. Further, a plurality of wavelength selective switches can be obtained by additionally providing the dispersive element  6104 . Furthermore, since the ports can be fabricated by using a planar lightwave circuit, a mounting error can be reduced, and the additional function can easily be mounted. 
       Third Embodiment 
       [0084]    A wavelength selective switch array  7100  for a third embodiment is shown in  FIGS. 7A and 7B . Referring to  FIGS. 7A and 7B , the arrangement includes input/output port arrays  7101 , microlens arrays  7102 , a condenser lens  7103 , a dispersive element  7104 , a cylindrical lens  7105  and a reflective wavefront control element  7106 . The wavelength selective switch array of the present invention includes a plurality of input/output arrays, and a plurality of input and output ports are provided in the individual input/output port arrays. 
         [0085]    A direction in which the ports are aligned is defined as a port direction.  FIG. 7A  is a cross-sectional view taken in a wavelength dispersion direction that is perpendicular to the port direction, and  FIG. 7B  is a cross-sectional view taken in the port direction. 
         [0086]    (Components of Optical System) 
         [0087]    The input/output port arrays  7101  are identical to the input/output port arrays  4101  shown in  FIGS. 4A and 4B  for the first embodiment, and the microlens arrays  7102  are identical to the microlens arrays  4102 , except for the arrangement method employed. Further, the reflective wavefront control element  7106  is identical to the reflective wavefront control element  4105 . 
         [0088]    The dispersive element  7104  demultiplexes, by wavelengths, the light emitted through the condenser lens  7103  from the individual input ports  7101   a - 1  and  7101   b - 1  of the input/output port arrays  7101 , and projects the demultiplexed light to the wavefront control element  7106  through the cylindrical lens  7105 . 
         [0089]    The condenser lens  7103  and the cylindrical lens  7105  provide the effect for changing the shape of a beam to be projected to the wavefront control element  7106 . When the diameter of a beam projected to the wavefront control element  7106  in the wavelength demultiplexing direction is reduced, the passband for signal light can be extended. Further, when the size of the beam is enlarged in the port switching direction, the angle of emittance required for switching can be reduced. 
         [0090]    (Port Switching) 
         [0091]    When the light is emitted from the port  7101   a - 1  of the first input/output port array  7101   a , the light is transmitted through the corresponding microlens  7102   a - 1  of the first microlens array  7102   a , the condenser lens  7103 , the dispersive element  7104  and the cylindrical lens  7105 , and is projected to the reflective wavefront control element  7106 . The light projected to the wavefront control element  7106  is reflected to change the emittance angle through the wavefront control, and the reflected light is transmitted again through the cylindrical lens  7105 , the dispersive element  7104  and the condenser lens  7103  and through the microlens  7102   a - 2  of the first microlens array  7102   a , and is coupled at the port  7101   a - 2  of the first input/output port array  7101   a . When the wavefront control element  7106  is appropriately controlled, the direction of the reflected light can be changed, and the reflected light can also be coupled at another port  7101   a - 3 . The condenser lens  7103  has a function that crosses, at a point  7107   a  on a face other than that of the wavefront control element, light rays having arbitrary angles that intersect at an identical point  7108   a  on the wavefront control element, and the input/output port  7101   a  of the same input/output port array, i.e., the first input/output port array  7101   a , is located on the arc with the point  7107   a  being the center. The point  7101   a  may also be provided as a virtual point located on the line of extension of the principal ray. Since the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelengths, the same input/output port array, i.e., the first input/output port array  7101   a , intersect at the identical point  7106   a  on the wavefront control element  7106 , high coupling efficiency can be obtained. 
         [0092]    The similar port switching operation is performed for the second input/output port array  7101   b . Specifically, light emitted from the port  7101   b - 1  of the second input/output port array  7101   b  is transmitted through the corresponding microlens  7102   b - 1  of the second microlens array  7102   b , the condenser lens  7103 , the dispersive element  7104  and the cylindrical lens  7105 , and is projected to the wavefront control element  7106 . The light projected to the wavefront control element  7106  is reflected to change the angle of emittance through wavefront control, and the reflected light is transmitted again through the cylindrical lens  7105 , the dispersive element  7104  and the condenser lens  7103  and through the microlens  7102   b - 2  of the second microlens array  7102   b , and is coupled at the port  7101   b - 2  of the second input/output port array  7101   b . When the wavefront control element  7106  is appropriately controlled, the direction of the reflected light can be changed, and can also be coupled at another port  7101   b - 3 . As well as the case of the first input/output port array, the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelength, the same input/output port array, i.e., the second input/output port array  7101   b , intersect at the identical point  7108   b  on the wavefront control element  7106 , and also intersect at the identical point  7107   b  on a face outside the wavefront control element. 
         [0093]    In this embodiment, the fibers connected to the first input/output port array  7101   a  are arranged on the arc with the point  7107   a  being the center, while the fibers connected to the second input/output port array  7101   b  are arranged on the arc with the point  7107   b  being the center, and the focal point  7107   a  and the focal point  7107   b  are arranged at different locations. With this arrangement, as for coupling of the beams at the ports that belong to the same wavelength selective switch to be connected, the coupling efficiency can be selectively improved by designing the arrangement to obtain overlap between the beams and to align the phases of the beams. As for coupling of the beams at the ports that belong to different wavelength selective switches, the occurrence of crosstalk can be reduced by designing the arrangement not to obtain overlap between the beams. 
         [0094]    Further, in this embodiment, when the input/output port arrays and the microlens arrays are provided by being integrated on a planer lightwave circuit by using the photolithography technology, the accurate arrangement consonant with high mask overlay accuracy can be implemented. 
         [0095]    According to this optical system, since the focal points of the principal rays are changed depending on the individual wavelength selective switches of the input/output port arrays  7101 , and since the ports are arranged along the arc with the focal point  7107  being the center, and the point  7107  is projected to the wavefront control element  7106  by the condenser lens, a plurality of groups of switches can be provided with a simple structure. Further, a plurality of wavelength selective switches can be obtained by additionally providing the dispersive element  7104 . Furthermore, since the ports can be fabricated by using a planar lightwave circuit, a mounting error can be reduced, and the additional function can easily be mounted. 
       Fourth Embodiment 
       [0096]    A wavelength selective switch array  8100  for a fourth embodiment is shown in  FIGS. 8A and 8B . Referring to  FIGS. 8A and 8B , the arrangement includes input/output port arrays  8101 , microlens arrays  8102 , a cylindrical lens  8103 , a dispersive element  8104 , a condenser lens  8105  and a reflective wavefront control element  8106 . A plurality of input/output ports are arranged for the individual arrays, and in this embodiment, three input and output ports are provided in each array. 
         [0097]    A direction in which the ports are aligned is defined as a port direction.  FIG. 8A  is a cross-sectional view taken in a wavelength dispersion direction that is perpendicular to the port direction, and  FIG. 8B  is a cross-sectional view taken in the port direction. 
         [0098]    (Components of Optical System) 
         [0099]    The input/output port arrays  8101  are identical to the input/output port arrays  4101  shown in  FIGS. 4A and 4B  for the first embodiment, and the microlens arrays  8102  are identical to the microlens arrays  4102 , except for the arrangement method employed. Further, the reflective wavefront control element  8106  is identical to the reflective wavefront control element  4105 . 
         [0100]    The dispersive element  8104  demultiplexes, by wavelengths, the light emitted through the cylindrical lens  8103  from the individual input ports  8101   a - 1  and  8101   b - 1  of the input/output port arrays  8101 , and projects the demultiplexed light to the wavefront control element  8106  through the condenser lens  8105 . 
         [0101]    The cylindrical lens  8103  and the condenser lens  8105  provide the effect for changing the shape of a beam to be projected to the wavefront control element  8106 . When the diameter of a beam projected to the wavefront control element in the wavelength demultiplexing direction is reduced, the passband for signal light can be extended. Further, when the size of the beam is enlarged in the port switching direction, the angle of emittance required for switching can be reduced. 
         [0102]    (Port Switching) 
         [0103]    When the light is emitted from the port  8101   a - 1  of the first input/output port array  8101   a , the light is transmitted through the corresponding microlens  8102   a - 1  of the first microlens array  8102   a , the cylindrical lens  8103 , the dispersive element  8104  and the condenser lens  8105 , and is projected to the reflective wavefront control element  8106 . The light projected to the wavefront control element  8106  is reflected to change the emittance angle through the wavefront control, and the reflected light is transmitted again through the condenser lens  8105 , the dispersive element  8104  and the cylindrical lens  8103  and through the microlens  8102   a - 2  of the first microlens array  8102   a , and is coupled at the port  8101   a - 2  of the first input/output port array  8101   a . When the wavefront control element  8106  is appropriately controlled, the direction of the reflected light can be changed, and the reflected light can also be coupled at another port  8101   a - 3 . The cylindrical lens  8103  and the condenser lens  8105  have a function that crosses, at a point  8107   a  on a face other than that of the wavefront control element, light rays having arbitrary angles that intersect at an identical point  8108   a  on the wavefront control element, and the input/output port array  8101   a  of the same wavelength selective switch is located on the arc with the point  8107   a  being the center. The point  8101   a  may also be provided as a virtual point located on the line of extension of the principal ray. Since the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelengths, the same input/output port array, i.e., the first input/output port array  8101   a , intersect at the identical point  8106   a  on the wavefront control element  8106 , high coupling efficiency can be obtained. 
         [0104]    The similar port switching operation is performed for the second input/output port array  8101   b . Specifically, light emitted from the port  8101   b - 1  of the second input/output port array  8101   b  is transmitted through the corresponding microlens  8102   b - 1  of the second microlens array  8102   b , the cylindrical lens  8103 , the dispersive element  8104  and the condenser lens  8105 , and is projected to the wavefront control element  8106 . The light projected to the wavefront control element  8106  is reflected to change the angle of emittance through wavefront control, and the reflected light is transmitted again through the condenser lens  8105 , the dispersive element  8104  and the cylindrical lens  8103  and through the microlens  8102   b - 2  of the second microlens array  8102   b , and is coupled at the port  8101   b - 2  of the second input/output port array  8101   b . When the wavefront control element  8106  is appropriately controlled, the direction of the reflected light can be changed, and can also be coupled at another port  8101   b - 3 . As well as the case of the first input/output port array  8101   a , the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelength, the same input/output port array, i.e., the second input/output port array  8101   b , intersect at the identical point  8108   b  on the wavefront control element  8106 , and also intersect at the identical point  8107   b  on a face outside the wavefront control element. 
         [0105]    In this embodiment, the fibers connected to the first input/output port array  8101   a  are arranged on the arc with the point  8107   a  being the center, while the fibers connected to the second input/output port array  8101   b  are arranged on the arc with the point  8107   b  being the center, and the focal point  8107   a  and the focal point  8107   b  are arranged at different locations. With this arrangement, as for coupling of the beams at the ports that belong to the same switch group to be connected, the coupling efficiency can be selectively improved by designing the arrangement to obtain overlap between the beams and to align the phases of the beams. As for coupling of the beams at the ports that belong to different switch groups, the occurrence of crosstalk can be reduced by designing the arrangement not to obtain overlap between the beams. 
         [0106]    Further, in this embodiment, when the input/output port arrays and the microlens arrays are provided by being integrated on a planer lightwave circuit by using the photolithography technology, the accurate arrangement consonant with high mask overlay accuracy can be implemented. 
         [0107]    According to this optical system, since the focal points of the principal rays are changed depending on the individual wavelength selective switches of the input/output port arrays  8101 , and since the ports are arranged along the arc with the focal point  8107  being the center, and the point  8107  is projected to the wavefront control element  8106  by the condenser lens, a plurality of groups of switches can be provided with a simple structure. Further, a plurality of wavelength selective switches can be obtained by additionally providing the dispersive element  8104 . Furthermore, since the ports can be fabricated by using a planar lightwave circuit, a mounting error can be reduced, and the additional function can easily be mounted. 
       Fifth Embodiment 
       [0108]    A wavelength selective switch array  9100  for a fifth embodiment is shown in  FIGS. 9A and 9B . Referring to  FIGS. 9A and 9B , the arrangement includes input/output port arrays  9101 , microlens arrays  9102 , a cylindrical lens  9103 , a cylindrical lens  9104 , a condenser lens  9105 , a dispersive element  9106 , a condenser lens  9107  and a reflective wavefront control element  9108 . A plurality of input/output ports are arranged for the individual wavelength selective switches, and in this embodiment, three input and output ports are provided in each switch. 
         [0109]    A direction in which the ports are aligned is defined as a port direction.  FIG. 9A  is a cross-sectional view taken in a wavelength dispersion direction that is perpendicular to the port direction, and  FIG. 9B  is a cross-sectional view taken in the port direction. 
         [0110]    (Components of Optical System) 
         [0111]    The input/output port arrays  9101  are identical to the input/output port arrays  4101  shown in  FIGS. 4A and 4B  for the first embodiment, and the microlens arrays  9102  are identical to the microlens arrays  4102 , except for the arrangement method employed. Further, the reflective wavefront control element  9108  is identical to the reflective wavefront control element  4105 . 
         [0112]    The dispersive element  9106  demultiplexes, by wavelengths, the light emitted through the cylindrical lenses  9103  and  9104  and the condenser lens  9105  from the individual input ports  9101   a - 1  and  9101   b - 1  of the input/output port arrays  9101 , and projects the demultiplexed light to the wavefront control element  9108  through the condenser lens  9107 . 
         [0113]    The cylindrical lens  9103  and the cylindrical lens  9104  provide the effect for changing the shape of a beam to be projected at an intersection point  9109 . The size or shape of the beam on the plane at the intersection point  9109  is projected to the wavefront control element  9108  by the condenser lens  9106  and the condenser lens  9107 . When the diameter of a beam projected to the wavefront control element in the wavelength demultiplexing direction is reduced, the passband for signal light can be extended. Further, when the size of the beam is enlarged in the port switching direction, the angle of emittance required for switching can be reduced. 
         [0114]    (Port Switching) 
         [0115]    When the light is emitted from the port  9101   a - 1  of the first input/output port array  9101   a , the light is transmitted through the corresponding microlens  9102   a - 1  of the first microlens array  9102   a , the cylindrical lens  9103 , the cylindrical lens  9104 , the condenser lens  9105 , the dispersive element  9106  and the condenser lens  9107 , and is projected to the reflective wavefront control element  9108 . The light projected to the wavefront control element  9108  is reflected to change the emittance angle through the wavefront control, and the reflected light is transmitted again through the condenser lens  9107 , the dispersive element  9106 , the condenser lens  9105 , the cylindrical lens  9104  and the cylindrical lens  9103  and through the microlens  9102   a - 2  of the first microlens array  9102   a , and is coupled at the port  9101   a - 2  of the first input/output port array  9101   a . When the wavefront control element  9108  is appropriately controlled, the direction of the reflected light can be changed, and the reflected light can also be coupled at another port  9101   a - 3 . The condenser lens  9105  and the condenser lens  9107  have a function that crosses, at a point  9109   a  on a face other than that of the wavefront control element, light rays having arbitrary angles that intersect at an identical point  9110   a  on the wavefront control element. The cylindrical lens  9103  has a function that changes, to parallel light rays, the light rays of arbitrary angles that intersect at the point  9109   a  on the face outside the wavefront control element, and the input/output ports  9102   a  are located in parallel to each other. Since the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelengths, the same input/output port array, i.e., the second input/output port array  9101   a , intersect at the identical point  9110   a  on the wavefront control element  9108 , high coupling efficiency can be obtained. 
         [0116]    The similar port switching operation is performed for the second input/output port array  9101   b . Specifically, light emitted from the port  9101   b - 1  of the second input/output port array  9101   b  is transmitted through the corresponding microlens  9102   b - 1  of the second microlens array  9102   b , the cylindrical lens  9103 , the cylindrical lens  9104 , the condenser lens  9105 , the dispersive element  9106  and the condenser lens  9107 , and is projected to the wavefront control element  9108 . The light projected to the wavefront control element  9108  is reflected to change the angle of emittance through wavefront control, and the reflected light is transmitted again through the condenser lens  9107 , the dispersive element  9106 , the condenser lens  9105 , the cylindrical lens  9104  and the cylindrical lens  9103  and through the microlens  9102   b - 2  of the second microlens array  9102   b , and is coupled at the port  9101   b - 2  of the second input/output port array  9101   b . When the wavefront control element  9106  is appropriately controlled, the direction of the reflected light can be changed, and can also be coupled at another port  9101   b - 3 . As well as the case of the first input/output port array  9101   a , the optical system is designed so that the principal rays of a beam that enter or exit, according to wavelength, the same input/output port array, i.e., the second input/output port array  9101   b , intersect at the identical point  9110   b  on the wavefront control element  9108 , and also intersect at the identical point  9109   b  on a face outside the wavefront control element. 
         [0117]    In this embodiment, the fibers connected to the first input/output port array  9101   a  are arranged in parallel to each other, and the fibers connected to the second input/output port array  9101   b  are arranged also in parallel to each other; however, the angle for arranging the fibers differs between the first input/output port array  9101   a  and the second input/output port array  9101   b . Since the principal rays having different angles are focused on different positions by the cylindrical lens  9103 , the focal point  9109   a  and the focal point  9109   b  are provided at different locations, and the focal point  9107   a  and the focal point  9107   b  are provided also at different locations. With this arrangement, as for coupling of the beams at the ports that belong to the same wavelength selective switch to be connected, the coupling efficiency can be selectively improved by designing the arrangement to obtain overlap between the beams and to align the phases of the beams. As for coupling of the beams at the ports that belong to different wavelength selective switches, the occurrence of crosstalk can be reduced by designing the arrangement not to obtain overlap between the beams. 
         [0118]    Further, in this embodiment, when the input/output port arrays and the microlens arrays are provided by being integrated on a planer lightwave circuit by using the photolithography technology, the accurate arrangement consonant with high mask overlay accuracy can be obtained. 
         [0119]    According to this optical system, since the location of the focal point  9109  provided by the cylindrical lens  9103  is changed to change the angles of emittance for the principal rays depending on the individual wavelength selective switches of the input/output port arrays  9101 , and the point  9109  is projected to the wavefront control element  9108  by the condenser lenses  9105  and  9107 , a plurality of groups of switches can be provided with a simple structure. Further, a plurality of wavelength selective switches can be obtained by additionally providing the dispersive element  9106 . Furthermore, since the ports can be fabricated by using a planar lightwave circuit, a mounting error can be reduced, and the additional function can easily be mounted. 
       Sixth Embodiment 
       [0120]    A wavelength selective switch array  10100  for a sixth embodiment is shown in  FIGS. 10A and 10B . Referring to  FIGS. 10A and 10B , the arrangement includes input/output port arrays  10101 , microlens arrays  10102 , a cylindrical lens  10103 , and a cylindrical lens  10104 , a condenser lens  10105 , a dispersive element  10106 , a condenser lens  10107  and a reflective wavefront control element  10108 . 
         [0121]    A direction in which the ports are aligned is defined as a port direction.  FIG. 10A  is a cross-sectional view taken in a wavelength dispersion direction that is perpendicular to the port direction, and  FIG. 10B  is a cross-sectional view taken in the port direction. 
         [0122]    In the arrangement for  10100 , three input/output port arrays are employed. In the description for the above described embodiments, the number of wavelength selective switches is two; however, the number of wavelength selective switches may be two or greater. 
       Seventh Embodiment 
       [0123]    An input and output port unit  11100  of a wavelength selective switch array for a seventh embodiment is shown in  FIG. 11 . The arrangement in  FIG. 11  includes input/output port arrays  11101  and an optical function circuit  11102  that are produced by using a PLC. A first input/output port array  11101   a  corresponds to the input/output port array  4201   a  in  FIGS. 4A and 4B , and a second input/output port array  11101   b  corresponds to the second input/output port array  4201   b . The optical function circuit  11102  that is optically connected to the individual input and output ports of the input/output port arrays  11101  is provided by integrating functional elements, such as an optical splitter, an optical combiner, a switch, a light receiving element and a grating. Since the functional parts additionally provided for a ROADM can be incorporated for a WSS by integrating the functional elements to the input/output port arrays, reduction in the size of a node part can be expected. A specific function circuit for the optical function circuit  11102  will be described hereinafter in an eighth embodiment and the other embodiments. 
       Eighth Embodiment 
       [0124]    An optical function circuit portion  12100  for the input/output ports of a wavelength selective switch array for an eighth embodiment is shown in  FIG. 12 . The arrangement in  FIG. 12  includes optical waveguide arrays  12101   a  and  12101   b , optical couplers  12102   a - 1  to  12102   a - 3  and  12102   b - 1  to  12102   b - 3  and photodiodes  12103   a - 1  to  12103   a - 3  and  12103   b - 1  to  12103   b - 3 . This is an arrangement where an optical intensity monitor is mounted to the input and output ports. The input ports are ports  12101   a - 1  to  12101   b - 1 , and light is separated respectively by the optical couplers  12102   a - 1  and  12102   b - 1  into light directed to the WSS and light directed to the photodiodes  12103   a - 1  and  12103   b - 1 . Light emitted from the input port  12101   a - 1  toward the WSS is transmitted through the optical system and is returned to an output port  12101   a - 2  or  12101   a - 3 . Optical couplers  12102   a - 2  and  12102   a - 3  are provided for the output ports, as well as the input ports, and the output light is separated into light directed to the photodiodes  12103   a - 2  and  12103   a - 3  and light to be output. As well as the light emitted at the port  12101   a - 1 , the light emitted at the input port  12101   b - 1  is transmitted through the optical system, and is output from the output port  12101   b - 2  or  12101   b - 3 . Since light that is separated by the optical couplers and directed to the photodiodes is received, measurement of the optical intensity can be performed. Through the measurement of the optical intensity, it can be determined whether light having the optical intensity as designated is emitted to the output port, and therefore, detection of a failure can be performed. When the function of the WSS failure detection monitor is integrated to the input/output portion of the WSS in this manner, a small optical part for a node that enables failure detection can be obtained. 
         [0125]    In this embodiment, a Drop type WSS having a single input port has been described; however, the same effects can also be obtained for an Add type WSS having a plurality of input ports. 
       Ninth Embodiment 
       [0126]    An optical function circuit portion  13100  for the input/output ports of a wavelength selective switch array for a ninth embodiment is shown in  FIG. 13 . The arrangement in  FIG. 13  includes optical waveguide arrays  13101   a  and  13101   b , optical couplers  13102   a  and  13102   b , AWGs (Arrayed Waveguide Gratings)  13103   a  and  13103   b  and photodiodes  13104   a  and  13104   b . This is an arrangement where a wavelength monitor is mounted to the input ports. The input ports are ports  13101   a - 1  to  13101   b - 1 , and light is separated by the optical couplers  13102   a  and  13102   b , respectively into light directed to the WSS and light directed to the AWGs  13103   a  and  13103   b . Light emitted from the input port  13101   a - 1  toward the WSS is transmitted through the optical system, and is returned to an output port  13101   a - 2  or  13101   a - 3 . As well as the light emitted at the port  13101   a - 1 , the light emitted at the input port  13101   b - 1  is transmitted through the optical system, and is output from the output port  13101   b - 2  or  13101   b - 3 . Light separated by the optical couplers and directed to the AWGs is demultiplexed by wavelengths, and the wavelengths are received respectively by the photodiodes. Therefore, measurement of the optical intensity for the individual wavelengths can be performed. Through the measurement of the optical intensity for the individual wavelengths, the output values of the wavelengths can be controlled by the WSS. Furthermore, when a wavelength monitor having the same structure is additionally provided for the output port side, a failure of the WSS can be detected for each wavelength. When the wavelength monitor is functionally integrated to the input/output portion of the WSS in this manner, a small optical part for a node that enables output control or failure detection can be obtained. 
         [0127]    Also in this embodiment, a Drop type WSS having a single input port has been described; however, the same effects can also be obtained for an Add type WSS having a plurality of input ports. 
       Tenth Embodiment 
       [0128]    An optical function circuit portion  14100  for the input/output ports of a wavelength selective switch array for a tenth embodiment is shown in  FIG. 14 . The arrangement in  FIG. 14  includes optical waveguide arrays  14101   a  and  14101   b  and Mach-Zehnder interferometer arrays  14102   a  and  14102   b , and phase shifter units  14103   a  and  14103   b  are attached to the Mach-Zehnder interferometer arrays  14102   a  and  14102   b . This is the arrangement where a VOA (Variable Optical Attenuator) is mounted to input and output ports. The input ports are ports  14101   a - 1  and  14101   b - 1 , and light is transmitted through the Mach-Zehnder interferometers toward the optical system. The light emitted at the input port  14101   a - 1  is transmitted through the optical system, and is thereafter returned to an output port  14101   a - 2  or  14101   a - 3 . As well as the light emitted at the port  14101   a - 1 , the light emitted at the input port  14101   b - 1  is transmitted through the optical system, and is output from an output port  14101   b - 2  or  14101   b - 3 . The Mach-Zehnder interferometer  14102   a - 1  can change the intensity of light transmitted to the optical system by adjusting phase shifters  14103   a - 1 - 1  and  14103   a - 1 - 2 . Likewise, the Mach-Zehnder interferometers  14102   a - 2 ,  14102   a - 3 ,  14102   b - 2  and  14102   b - 3  can change the intensity of passing light by adjusting the respective phase shifters  14103   a - 2 - 1  to  14103   a - 3 - 2  and  14103   b - 2 - 1  to  14103   b - 3 - 2 . The optical intensities at the input and output ports can be collectively controlled by using the VOA function. Since the function of the VOA is integrated at the input/output portion of the WSS in this manner, a small optical part for a node that enables collective control for optical intensities can be obtained. 
         [0129]    Also in this embodiment, a Drop type WSS having a single input port has been described; however, the same effects can also be obtained for an Add type WSS having a plurality of input ports. 
       Eleventh Embodiment 
       [0130]    An optical function circuit portion  15100  for the input/output ports of a wavelength selective switch array for an eleventh embodiment is shown in  FIG. 15 . The arrangement in  FIG. 15  includes optical waveguide arrays  15101   a  and  15101   b  and Mach-Zehnder interferometer arrays  15102   a  and  15102   b  and photodiodes  15104   a ,  15104   b ,  15105   a  and  15105   b , and phase shifter units  15103   a  and  15103   b  are attached to the Mach-Zehnder interferometer arrays  15102   a  and  15102   b . This is the arrangement where an optical switch and a power monitor are mounted to input and output ports. The input ports are ports  15101   a - 1  and  15101   b - 1 , and light is transmitted through the Mach-Zehnder interferometers toward the optical system. The light emitted at the input port  15101   a - 1  is transmitted through the optical system, and is returned to an output port  15101   a - 2  or  15101   a - 3 . As well as the light emitted at the port  15101   a - 1 , the light emitted at the input port  15101   b - 1  is transmitted through the optical system, and is output from an output port  15101   b - 2  or  15101   b - 3 . 
         [0131]    The Mach-Zehnder interferometer  15102   a - 1  has an optical switching function that can adjust the phase shifters  15103   a - 1 - 1  and  15103   a - 1 - 2  to select a direction from the optical waveguide  15101   a - 1  to the photodiode  15104   a - 1  as a light traveling direction. Likewise, the Mach-Zehnder interferometers  15102   a  and  15102   a  can adjust the respective phase shifter units  15103   a  and  15103   b  to switch between light to be input or output to the ports and light directed to the monitor. 
         [0132]    With this function, the optical intensity can be periodically monitored by the optical switch. Since the functions of the optical switch and the monitor are integrated at the input/output portion of the WSS in this manner, a small optical part for a node that can periodically monitor the optical intensity can be obtained. 
         [0133]    Also in this embodiment, a Drop type WSS having a single input port has been described; however, the same effects can also be obtained for an Add type WSS having a plurality of input ports. 
       Twelfth Embodiment 
       [0134]    A wavelength selective switch array  16100  for a twelfth embodiment is shown in  FIGS. 16A and 16B . Referring to  FIGS. 16A and 16B , the arrangement includes a planar lightwave circuit  16101 , a collimating cylindrical lens  16102 , a cylindrical lens  16103 , a dispersive element  16104 , a condenser lens  16105  and a reflective wavefront control element  16106 . The planar lightwave circuit  16101  is shown in detail in  FIG. 17 . Referring to  FIG. 17 , the arrangement includes optical waveguide arrays  17101   a  and  17101   b , slab waveguides  17102   a  and  17102   b  and arrayed waveguides  17103   a  and  17103   b . The arrayed waveguides  17103   a  and  17103   b  are designed, so that the lengths of all the arrayed waveguides are equal, and a phase difference will not occur between the individual waveguides consisting of each arrayed waveguide. The input ports are ports  17101   a - 1  and  17101   b - 1 , and light is transmitted through the slab waveguides and the arrayed waveguides, and is directed to the optical system. In the individual switch groups, a plurality of light input and output ports are prepared, and in this embodiment, three light input and output ports are illustrated. 
         [0135]    A direction in which the ports are aligned is defined as a port direction.  FIG. 16A  is a cross-sectional view taken in a wavelength dispersion direction that is perpendicular to the port direction, and  FIG. 16B  is a cross-sectional view taken in the port direction. 
         [0136]    (Components of Optical System) 
         [0137]    The same arrangement is employed, except in that the input/output port arrays  8101  for the fourth embodiment in  FIGS. 8A and 8B  and the microlens arrays  8102  are integrated to the planar lightwave circuit  16101 . The reflective wavefront control element  16106  is identical to the reflective wavefront control element  8106 . 
         [0138]    The dispersive element  16104  demultiplexes, by wavelengths, the light emitted through the cylindrical lens  16103  from the individual input ports  17101   a - 1  and  17101   b - 1  of the input/output port arrays  16101 , and projects the demultiplexed light to the wavefront control element  16106  through the condenser lens  16105 . 
         [0139]    The cylindrical lens  16103  and the condenser lens  16105  provide the effect for changing the shape of a beam to be projected to the wavefront control element  16106 . When the diameter of a beam projected to the wavefront control element in the wavelength demultiplexing direction is reduced, the passband for signal light can be extended. Further, when the size of the beam is enlarged in the port switching direction, the angle of emittance required for switching can be reduced. 
         [0140]    (Port Switching) 
         [0141]    Light that is propagated through one port  17101   a - 1  of the first input/output port array  17101   a  is confined in the first slab waveguide  17102   a  in the direction of the thickness of a substrate, and the light in this state propagates while spreading in the port direction. The light is coupled at the arrayed waveguide  17103   a . Since the arrayed waveguides are arranged with the same length, the light is transmitted to the terminal end of the arrayed waveguide  17103   a  while the phase information for the slab waveguide  17102   a  is maintained. Since the terminal end of the arrayed waveguide  17103   a  is connected to the end face of the planar lightwave circuit  16101 , the phases of light rays emitted at the individual arrayed waveguides are aligned at the end face, and as a result, the light is emitted as a planar wave associated with the port direction. The emitted light is adjusted by the collimating cylindrical lens  16102  to collimated light associated with the wavelength demultiplexing axial direction, and this collimated light is transmitted through the cylindrical lens  16103 , the dispersive element  16104  and the condenser lens  16105 , and is projected to the wavefront control element  16106 . The light projected to the wavefront control element  16106  is reflected to change the angle of emittance through wavefront control, and the reflected light is transmitted again through the condenser lens  16105 , the dispersive element  16104 , the cylindrical lens  16103  and the collimating cylindrical lens  16102 , and thereafter through the first arrayed waveguide  17103   a  and the first slab waveguide  17102   a . The light for which the angle of emittance has been changed by the wavefront control element is propagated through the first slab waveguide  17102   a  with being inclined in accordance with the inclination, and is coupled at the port  17101   a - 2  of the first input/output port array  17101   a . When the wavefront control element  16106  is appropriately controlled, the direction of the reflected light can be changed, and the reflected light can be coupled also at another port  17101   a - 3 . The cylindrical lens  16103  and the condenser lens  16105  have a function that crosses, at a point  16107   a  on a face other than that of the wavefront control element, light rays having arbitrary angles that intersect at an identical point  16108   a  on the wavefront control element, and the input and output ports of the input/output port array  17101   a  of the same group are located on the arc with the point  17104   a  being the center. The point  17104   a  may also be provided as a virtual point located on the line of extension of the principal ray. Since the optical system is designed, so that the principal rays of a beam that enter or exit the same input/output port array  17101   a  according to wavelengths intersect at the identical point  16108   a  on the wavefront control element  16106 , high coupling efficiency can be obtained. 
         [0142]    The similar port switching operation is performed for the second input/output port array  17101   b . Since the same optical system as used for the fourth embodiment is employed for this embodiment, as for coupling of the beams at the ports that belong to the same wavelength selective switch to be connected, the coupling efficiency can be selectively improved by designing the arrangement to obtain overlap between the beams and to align the phases of the beams. As for coupling of the beams at the ports that belong to different wavelength selective switches, the occurrence of crosstalk can be reduced by designing the arrangement not to obtain overlap between the beams. 
         [0143]    Further, in this embodiment, when the input/output port arrays and the microlens arrays are provided by being integrated on a planer lightwave circuit by using the photolithography technology, the accurate arrangement consonant with high mask overlay accuracy, the reduction of mounting error and easy provision of an additional function can also be implemented. 
         [0144]    Furthermore, in this embodiment, the aspect ratio of beams can be freely changed. As previously described, it is necessary that for the wavelength selective switch, the diameter of the beam focused on the wavefront control element  16106  be increased in the port direction in order to increase the number of output ports. According to the arrangement of this embodiment, the beam diameter in the wavelength dispersion axial direction is determined in accordance with the relative refractive index and the thickness of a waveguide layer that is embedded, the adjustment of the aspect ratio can be performed by controlling the beam diameter in the port direction. At this time, a diameter w port  of abeam emitted at the planar lightwave circuit  16101  in the port direction can be represented by the following expression. 
         [0000]    
       
         
           
             
               
                 
                   
                     w 
                     y 
                   
                   = 
                   
                     
                       
                         λ 
                          
                         
                             
                         
                          
                         
                           f 
                           slab 
                         
                       
                       
                         π 
                          
                         
                             
                         
                          
                         
                           n 
                           s 
                         
                          
                         
                           w 
                           
                             I 
                             / 
                             O 
                           
                         
                       
                     
                      
                     
                       
                          
                         1 
                       
                       
                          
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Expression 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
         [0145]    In expression 2, λ represents the wavelength of signal light, f slab  represents the length of a slab waveguide, and w I/O  represents the diameter in the port direction of a beam entering the slab waveguide. According to expression 2, the beam diameter in the port direction can be increased in proportion to the length f slab  of the slab waveguide. 
         [0146]    The arrangement that includes a beam expander, an anamorphic prism pair, etc., is generally employed to adjust the aspect ratio of beams in a general special optical system. However, with this arrangement, the cost for newly added members and a workload for adjusting the alignment are increased. On this point, the arrangement of this embodiment where the anamorphic prism pair and the optical system for polarization diversity are integrated in the single planar lightwave circuit  16101  provides very great effects to reduce the cost required for members and the workload for adjusting the alignment.