Abstract:
A waveguide type optical switch that can reduce the number of intersections in a matrix optical switch having the configuration of connecting unit optical switches and optical combining devices or optical branching devices to have a connecting function from “multiple inputs to one output” to “one input to multiple outputs”. To reduce the number of intersections in an entire matrix optical switch, an optical combining device of M inputs and one output is divided into (M−1) pieces of unit optical combining elements each having two inputs and one output, which are arranged immediately after (N−1) pieces of respective output ports excluding one piece of the output port closer to the input in the matrix optical switch out of N pieces of the output ports in the optical switch of one input and N outputs.

Description:
TECHNICAL FIELD 
     The present invention relates to a waveguide type optical switch used in optical communications or the like, and in particular, to a matrix optical switch that is configured to connect optical switches and optical combining devices or optical branching devices, and has a connecting function from “multiple inputs to one output” to “one input to multiple outputs”. In addition, the present invention relates to a technique for realizing a circuit configuration in which the number of waveguide intersections is reduced. 
     BACKGROUND ART 
     An optical communication technique using an optical fiber as a transmission medium has brought in an increase on a transmission distance of a signal, thus building a large scale of an optical communication network. Recently along with wide spread of the Internet communications, communication traffic abruptly increases, thus increasing demands for large capacity, high bitrate and high functionality of the communication network. Until now, introduction of a multiple-wavelength communication technique for simultaneously transmitting a plurality of optical signals having different wavelengths by a single transmission route enables the transmission capacity between two points to be increased. 
     In the communication network, however, it is necessary to route or switch routes of signals in a node where a plurality of transmission paths combine, and along with an increase in transmission capacity, signal processing thereof has become a bottleneck. Until now, there is adopted a method in which the transmitted optical signal is once converted into an electrical signal, thereafter the route routing or route switching is performed, and the electrical signal is again converted into an optical signal, which is sent to a transmission path. From now on, it is expected that a method for executing the routing or switching processing of the signal route without converting the optical signal into the electrical signal can be adopted to significantly increase throughput of the node. An optical switch is a component absolutely necessary for introducing such a method to the optical communication network. 
     The optical switch is configured to connect a plurality of unit optical switch elements each having one input and two outputs or two inputs and one output, thereby making it possible to produce optical switches of various kinds of circuit configurations in regard to input/output port numbers or connecting patterns between ports, such as multiple connections of one input and multiple outputs (or multiple inputs and one output), multiple inputs and multiple outputs or two inputs and two output. Among them, a matrix optical switch of multiple inputs and multiple outputs is widely used as an optical switch for arbitrarily routing direction routes between a plurality of input and output ports. 
     Further, there is a demand for a matrix optical switch in which not only a regular connection of one input to one output but also a connection from “multiple inputs to one output” to “one input to multiple outputs” is made possible. That is, the matrix optical switch, which has a connecting function of multiple inputs to one output in which different optical signals that are input to a plurality of input ports combine, which is output to one output port among a plurality of output ports or a connecting function of one input to multiple outputs in which an optical signal that is input to one input port among a plurality of input ports is branched, which are output to a plurality of output ports, is required for building a flexible network. 
     There is known a configuration as shown in  FIG. 1  as the configuration of a waveguide type optical switch in which the matrix optical switch having this connecting function from “multiple inputs to one output” to “one input to multiple outputs” is realized by a waveguide type device (refer to Non-Patent Literature 1). 
     The matrix optical switch shown in  FIG. 1  comprises four optical switches  111  to  114  each having one input and four outputs (combination of four unit optical switch elements each having one input and two outputs), and four optical combining devices  131  to  134  each having four inputs and one output. The respective inputs in the optical switches  111  to  114  are connected to four external input ports  101  to  104 . The respective outputs in the optical combining devices  131  to  134  are connected to external output ports  141  to  144 . 
     The four output ports of the optical switch  111  are respectively connected to the input ports of the optical combining devices  131  to  134  via an intersection part  121 . Similarly the four output ports of each of the optical switches  112  to  114  are respectively connected to the input ports of the optical combining devices  131  to  134  via the intersection part  121 . 
     According to this configuration, the different optical signals that are input to the plurality of external input ports can combine to be output to one external output port. 
     In a case where the external input port and the external output port in the optical switch shown in  FIG. 1  are reversed and the optical combining device is thus used as the optical branching device as it is, an optical signal that is input to one external input port can be branched to be output to a plurality of external output ports. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         NPL 1: M. Kobayashi et al., Electronics Letters, vol. 36, no. 17, pp. 1451 to 1452, August 2000. 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The conventional matrix optical switch shown in  FIG. 1  has a problem that many intersections are generated between the optical switch and the optical combining device. That is, in the intersection part  121  in  FIG. 1 , 14 waveguides by removing two waveguides out of 16 waveguides are intersected to connect the optical switches and the optical combining devices. The route formed of the maximum intersection number is a route from the external input port  101  to the external output port  144  (or a route from the external input port  104  to the external output port  141 ), and the intersections are generated at nine locations in this route. Further, the number of the intersections increases with an increase of the external input/output port number in the matrix optical switch. That is, in a case where the matrix optical switch is configured of N inputs and N outputs, N 2  waveguides are generated in that intersection part, and a waveguide having the maximum intersections among them has (N−1) 2  intersections. 
     Generally in the waveguide type optical device, insertion losses and cross talk are generated in the intersection of the waveguide to degrade optical characteristics thereof. The insertion loss and the cross talk can be reduced to some degree by increasing the intersection angle, but the waveguide is required to be developed on a substrate for increasing the intersection angle, therefore requiring a large space. 
     Therefore, it is difficult to produce the matrix optical switch having the connecting function from “multiple inputs to one output” to “one input and multiple outputs” as the waveguide type optical switch on a single substrate, and the configuration, in which the optical switch and the optical combining device are respectively produced on different substrates and the intersection part therebetween is formed by using optical fiber wiring, is required. 
     The present invention is made in view of solving this problem, and an object of the present invention is to provide a waveguide type optical switch that can reduce the number of intersections and can be produced on a single substrate in a matrix optical switch having the configuration of connecting unit optical switch elements and optical combining devices or optical branching devices to have a connecting function from “multiple inputs to one output” to “one input to multiple outputs”. 
     Solution to Problem 
     The present invention provides a waveguide type optical switch having a form of a matrix optical switch of M inputs and N outputs formed on a single substrate, where M and N are integers different from each other, M and N each having a value greater than or equal to three, the matrix optical switch comprising M optical switches each having one input and N outputs, and N optical combining devices each having M inputs and one output, wherein the a-th input of the matrix optical switch is the input of the a-th optical switch, where a is an integer from 1 to M, the b-th output of the matrix optical switch is the output of the b-th optical combining device, where b is an integer from 1 to N, each of the optical switches consists of N−1 unit optical switch elements each having one input and two outputs, and each of the optical combining devices consists of M−1 unit optical combining elements each having two inputs and one output, wherein for each optical switch, the input of the first unit optical switch element forms the input of the optical switch, one of the outputs of the i-th unit optical switch element is connected to the input of the (i+1)-th unit optical switch element, where i is an integer from 1 to N−2, the other of the outputs of the i-th unit optical switch element forms the i-th output of the optical switch, and the two outputs of the (N−1)-th unit optical switch element form the (N−1)-th output and the N-th output of the optical switch, wherein for each optical combining device, two inputs of the first unit optical combining element form the first and second inputs of the optical combining device, one of the inputs of the j-th unit optical combining element is connected to the output of the (j−1)-th unit optical combining element, where j is an integer from 2 to M−1, the other of the inputs of the j-th unit optical combining element forms the (j+1)-th input of the optical combining device, and the output of the (M−1)-th unit optical combining element forms the output of the optical combining device, wherein in the matrix optical switch, the p-th optical switch and the q-th optical combining device are connected between any output in the p-th optical switch and any input in the q-th optical combining device, where p is an integer from 1 to M and q is an integer from 1 to N, wherein in a case where any output in the p-th optical switch is the k-th output in the connection, any input in the q-th optical combining device is the k′-th input, k being an integer from 1 to N and k′ being an integer from 1 to M, and in a case where k is from two to N−1 in the connection, a waveguide intersection is not included in the connection between the output of the unit optical switch element forming the k-th output in the p-th optical switch and the input of the unit optical combining element forming the k′-th input in the q-th optical combining device. 
     According to an embodiment of the present invention, for each optical combining device, each unit optical combining element includes two input terminals, and a combining optical power ratio between the two input terminals of the first unit optical combining element is 1:1, and a combining optical power ratio between an input terminal connected to the output of the optical switch of the j-th unit optical combining element and an input terminal connected to the other unit optical combining element is 1:j, where j is an integer from 2 to M−1. 
     The present invention provides a waveguide type optical switch having a form of a matrix optical switch of N inputs and M outputs formed on a single substrate, where M and N are integers different from each other, M and N each having a value greater than or equal to three, the matrix optical switch comprising N optical branching devices each having one input and M outputs, and M optical switches each having N inputs and one output, wherein the a-th input in the matrix optical switch consists of the input of the a-th optical branching device, where a is an integer from 1 to N, the b-th output of the matrix optical switch consists of the output of the b-th the optical switch, where b is an integer from 1 to M each of the branching devices consists of M-1 unit optical branching elements each having one input and two outputs, and each of the optical switches consists of N-1 unit optical switch elements each having two inputs and one output, wherein for each optical branching device, the input of the first unit optical branching element forms the input of the optical branching device, one of the outputs of the i-th unit optical branching element is connected to the input of the (i+1)-th unit optical branching element, where i is an integer from 1 to M-2, the other of the outputs of the i-th unit optical branching element forms the i-th output of the optical branching device, and two outputs of the (M−1)-th unit optical branching element form the (M−1)-th output and the M-th output of the optical branching device, wherein for each optical switch, two inputs of the first unit optical switch element form the first and second inputs for each optical switch, one of the inputs of the j-th unit optical switch element is connected to the output of the (j−1)-th unit optical switch element, where j is an integer from 2 to N-1, the other of the inputs of the j-th unit optical switch element forms the (j+1)-th input of the optical switch, and the output of the (N−1)-th unit optical switch element forms the output of the optical switch, wherein in the matrix optical switch, the p-th optical branching device and the q-th optical switch are connected between any output in the p-th optical branching device and any input in the q-th optical switch, where p is an integer from 1 to N and q is an integer from 1 to M, wherein in a case where any output in the p-th optical branching device is the k-th output in the connection, where k is an integer from 1 to M, any input in the q-th optical switch is the k′-th input, where k′ is an integer from 1 to M, and in a case where k is from 2 to M−1 in the connection, a waveguide intersection is not included in the connection between the output of the unit optical branching element forming the k-th output in the p-th optical branching device and the input of the unit optical switch element forming the k′-th input in the q-th optical switch. 
     According to an embodiment of the present invention, for each optical branching device, each unit optical combining element includes two input terminals, and a branching optical power ratio between the two output terminals of the (M−1)-th unit optical branching element is 1:1, and a branching optical power ratio between an output terminal connected to the input of the optical switch in the i-th unit optical branching element and an output terminal connected to the other unit optical branching element is 1:(M−i), where i is an integer from 1 to M=2. 
     Advantageous Effects of the Invention 
     According to the embodiment in the present invention, the optical combining device of M inputs and one output is divided into (M−1) pieces of the unit optical combining elements each having two inputs and one output, which are arranged immediately after (N−1) pieces of the respective output ports excluding one piece of the output port near the input in the matrix optical switch from N pieces of the output ports in the optical switch of one input and N outputs. Therefore the output port of each optical switch does not combine in the optical combining device after the intersection, but intersects after combining in the unit optical combining element. Therefore the number of the intersections in an entire matrix optical switch can be reduced. 
     According to the different embodiment in the present invention, the optical branching device of one input and M outputs is divided into (M−1) pieces of the unit optical branching elements each having one input and two outputs, which are arranged immediately before (N−1) pieces of the respective input ports excluding one piece of the input port near the output of the matrix optical switch from N pieces of the input ports in the optical switch of N inputs and one output. Therefore the output is not configured to be branched in the optical branching device, and thereafter intersect to be input to the optical switch, but intersects, which is thereafter branched in the unit optical branching element to be input to the optical switch. Therefore the number of the intersections in an entire matrix optical switch can be reduced. 
     Therefore it is possible to form the matrix optical switch having the connecting function from “multiple inputs to one output” to “one input to multiple outputs” on a single substrate. As a result, it is possible to miniaturize the optical switch, and the component number can be reduced since a component such as an optical fiber wiring plate is not necessary. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an explanatory diagram showing a circuit configuration of a conventional matrix optical switch of four inputs and four outputs; 
         FIG. 2  is an explanatory diagram showing a circuit configuration of a matrix optical switch of four inputs and four outputs according to a first embodiment in the present invention; 
         FIG. 3  is an explanatory diagram showing a circuit configuration of a matrix optical switch of eight inputs and eight outputs according to a second embodiment in the present invention; 
         FIG. 4A  is an explanatory diagram and a top view of a configuration example of an optical switch element used in the present invention; 
         FIG. 4B  is an explanatory diagram of the configuration example of the optical switch element used in the present invention, and a cross section taken along a cross section line IVB-IVB in  FIG. 4A ; 
         FIG. 5  is an explanatory diagram showing a circuit configuration of a matrix optical switch of six inputs and eight outputs according to a fifth embodiment in the present invention; and 
         FIG. 6  is an explanatory diagram showing a circuit configuration of a matrix optical switch of twelve inputs and eight outputs according to a sixth embodiment in the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Examples of a method of a waveguide type optical switch for carrying out the present invention include a method using a thermo-optic effect, a method using an electro-optical effect, a method using a refractive index change by current injection, and the like. 
     In addition, examples of a material that is used in the method using the thermo-optic effect include silica-based glass, organic polymer, silicon, and the like. Among them, a unit optical switch element using the thermo-optic effect of a silica-based optical waveguide has excellent consistency with an optical fiber, a low insertion loss, and in addition thereto, small principled polarization dependence, and the configuration material is physically and chemically stable and is excellent in reliability. Therefore it has the maximum practicability. However, for carrying out the present invention, a unit optical switch element other than the unit optical switch element using the thermo-optic effect of the silica-based optical waveguide may be used. 
     Hereinafter, embodiments in the present invention will be explained by specific examples with reference to the drawings. 
     First Embodiment 
       FIG. 2  is an explanatory diagram showing a first embodiment in the present invention, and shows an example configured of a matrix optical switch of four inputs and four outputs. 
     The matrix optical switch shown in  FIG. 2  comprises 16 pieces of unit optical switch elements ( 2511  to  2514 ,  2521  to  2524 ,  2531  to  2534 , and  2541  to  2544 ) each having one input and two outputs, and 12 pieces of unit optical combining elements ( 2611  to  2613 ,  2621  to  2623 ,  2631  to  2633 , and  2641  to  2643 ) each having two inputs and one output. The four unit optical switch elements  2511 ,  2512 ,  2513  and  2514  are connected in a vertical line, which forms an optical switch  211  of one input and four outputs (the code is not illustrated in the figure). Similarly the unit optical switch elements  2521  to  2524 , the unit optical switch elements  2531  to  2534 , and the unit optical switch elements  2541  to  2544  are respectively connected in a vertical line, and respectively form an optical switch  212 , an optical switch  213 , and an optical switch  214  (the code is not illustrated in the figure) each having one input and four outputs. 
     The three unit optical combining elements  2611 ,  2612 , and  2613  are connected in a vertical line, which form an optical combining device  231  of four inputs and one output (the code is not illustrated in the figure). Similarly the unit optical combining elements  2621  to  2623 , the unit optical combining elements  2631  to  2633 , and the unit optical combining elements  2641  to  2643  are respectively connected in a vertical line, and respectively form an optical combining device  232 , an optical combining device  233 , and an optical combining device  234  (the code is not illustrated in the figure) each having four inputs and one output. 
     Herein for making each ratio of optical powers combining from four respective input ports to one output port in the optical combining device  231  equal, each combining optical power ratio of the unit optical combining elements  2611 ,  2612  and  2613  is set as 1:1, 2:1, and 3:1. It is apparent that the combining optical power ratio is set in the order of 1:1, 2:1, . . . , and (N−1):1 from the unit optical combining element closer to the input of the matrix optical switch. For obtaining this combining optical power ratio, a directional coupler or an asymmetrical Y branch can be used as the unit optical combining element. One of the two input ports in the unit optical combining element  2612 , which has a larger combining optical power ratio, is connected to the output port in the unit optical combining element  2611 . One of the two input ports in the unit optical combining element  2613 , which has a larger combining optical power ratio, is connected to the output port in the unit optical combining element  2612 . The same configuration is applied to the unit optical combining elements  2621  to  2623 ,  2631  to  2633 , and  2641  to  2643  forming the optical combining devices  232  to  234 . 
     The respective inputs of the optical switches  211  to  214  are connected to the four external input ports  201  to  204 , and the respective outputs of the optical combining devices  231  to  234  are connected to the four external output ports  241  to  244 . 
     In the matrix optical switch shown in  FIG. 2 , the output port in the unit optical switch element  2511  included in the optical switch  211  is connected to the input port in the unit optical combining element  2612 . In addition, the unit optical combining element  2641  is arranged immediately after the unit optical switch element  2512 , and the output port in the unit optical switch element  2512  and the input port in the unit optical combining element  2641  are connected without the intersection with the other route. Similarly the output port in the unit optical switch element  2513  and the input port in the unit optical combining element  2632 , and the output port in the unit optical switch element  2514  and the input port in the unit optical combining element  2613  are respectively connected without the intersection with the other route. 
     The output port in the unit optical switch element  2521  included in the optical switch  212  is connected to the input port in the unit optical combining element  2611 . In addition, the unit optical combining element  2621  is arranged immediately after the unit optical switch element  2522 , and the output port in the unit optical switch element  2522  and the input port in the unit optical combining element  2621  are connected without the intersection with the other route. Similarly the output port in the unit optical switch element  2523  and the input port in the unit optical combining element  2642 , and the output port in the unit optical switch element  2524  and the input port in the unit optical combining element  2633  are respectively connected without the intersection with the other route. 
     The output port in the unit optical switch element  2531  included in the optical switch  213  is connected to the input port in the unit optical combining element  2641 . In addition, the unit optical combining element  2631  is arranged immediately after the unit optical switch element  2532 , and the output port in the unit optical switch element  2532  and the input port in the unit optical combining element  2631  are connected without the intersection with the other route. Similarly the output port in the unit optical switch element  2533  and the input port in the unit optical combining element  2612 , and the output port in the unit optical switch element  2534  and the input port in the unit optical combining element  2623  are respectively connected without the intersection with the other route. 
     The output port in the unit optical switch element  2541  included in the optical switch  214  is connected to the input port in the unit optical combining element  2631 . In addition, the unit optical combining element  2611  is arranged immediately after the unit optical switch element  2542 , and the output port in the unit optical switch element  2542  and the input port in the unit optical combining element  2611  are connected without the intersection with the other route. Similarly the output port in the unit optical switch element  2543  and the input port in the unit optical combining element  2622 , and the output port in the unit optical switch element  2544  and the input port in the unit optical combining element  2643  are respectively connected without the intersection with the other route. 
     According to this configuration, the output port of each optical switch does not combine in the optical combining device after the intersection, but intersects after combining in the unit optical combining element. Therefore the number of the intersections in an entire matrix optical switch can be reduced. Actually in the optical switch in  FIG. 2 , even in a case where the number of the intersections in one route (the route from the external input port  201  to the external output port  241  or the route from the external input port  204  to the external output port  244 ) is maximized, it is five locations at most. 
     It should be noted that in  FIG. 2 , the unit optical switch elements  2514 ,  2524 ,  2534  and  2544  each having one input and two outputs, each of which is illustrated as one input and one output by omitting one output, are arranged for enhancing an extinction ratio, and the present invention can perform a basic operation without them. This unit optical switch element has the effect for enhancing the extinction ratio of the matrix optical switch even if the extinction ratio of the unit optical switch element of one input and two outputs is insufficient. 
     In addition, in the first embodiment, even if the external input port is reversed to the external output port, the external output port is reversed to the external input port in the matrix optical switch, the optical combining device is reversed to the optical branching device, and the unit optical combining element is reversed to the unit optical branching element, it is apparent that the number of the intersections in the entire matrix optical switch can similarly be reduced. 
     In the above-mentioned example, for simplification, the matrix optical switch of four inputs and four outputs is explained, but it is obvious for those skilled in the art that the technical characteristics in the present embodiment can be applied also to a matrix optical switch of N inputs and N outputs. 
     Second Embodiment 
       FIG. 3  is an explanatory diagram showing a second embodiment in the present invention, and shows an example configured of a matrix optical switch of eight inputs and eight outputs. 
     The matrix optical switch shown in  FIG. 3  comprises 64 pieces of unit optical switch elements ( 3511  to  3518 ,  3521  to  3528 ,  3531  to  3538 ,  3541  to  3548 ,  3551  to  3558 ,  3561  to  3568 ,  3571  to  3578 , and  3581  to  3588 ) each having one input and two outputs, 64 pieces of gate optical switch elements ( 3711  to  3718 ,  3721  to  3728 ,  3731  to  3738 ,  3741  to  3748 ,  3751  to  3758 ,  3761  to  3768 ,  3771  to  3778 , and  3781  to  3788 ) each having one input and one output, and 56 pieces of unit optical combining elements ( 3611  to  3617 ,  3621  to  3627 ,  3631  to  3637 ,  3641  to  3647 ,  3651  to  3657 ,  3661  to  3667 ,  3671  to  3677 , and  3681  to  3687 ) each having two inputs and one output. The eight unit optical switch elements  3511 ,  3512 ,  3513 ,  3514 ,  3515 ,  3516 ,  3517 , and  3518  are connected in a vertical line, and further, the gate optical switch elements  3711  to  3718  for improving an extinction ratio are connected to the output ports of the respective unit optical switch elements, which forms an optical switch  311  of one input and eight outputs (the code is not illustrated in the figure). Similarly the unit optical switch elements  3521  to  3528 ,  3531  to  3538 ,  3541  to  3548 ,  3551  to  3558 ,  3561  to  3568 ,  3571  to  3578 , and  3581  to  3588  are respectively connected in a vertical line, and the gate optical switch elements  3721  to  3728 ,  3731  to  3738 ,  3741  to  3748 ,  3751  to  3758 ,  3761  to  3768 ,  3771  to  3778 , and  3781  to  3788  are connected to the output ports of the respective unit optical switch elements, which form optical switches  312 ,  313 ,  314 ,  315 ,  316 ,  317 , and  318  (the code is not illustrated in the figure) each having one input and eight outputs. 
     The seven unit optical combining elements  3611 ,  3612 ,  3613 ,  3614 ,  3615 ,  3616 , and  3617  are connected in a vertical line, which forms an optical combining device  331  of eight inputs and one output (the code is not illustrated in the figure). Similarly the unit optical combining elements  3621  to  3627 ,  3631  to  2637 ,  3641  to  3647 ,  3651  to  3657 ,  3661  to  2667 ,  3671  to  3677 , and  3681  to  3687  are respectively connected in a vertical line, which form optical combining devices  332 ,  333 ,  334 ,  335 ,  336 ,  337 , and  338  each having eight inputs and one output. 
     Herein for making each ratio of optical powers combining from eight respective input ports to one output port in the optical combining device  331  equal, each combining optical power ratio of the unit optical combining elements  3611 ,  3612 ,  3613 ,  3614 ,  3615 ,  3616 , and  3617  is set as 1:1, 2:1, 3:1, 4:1, 5:1, 6:1 and 7:1. It is apparent that the combining optical power ratio is set in the order of 1:1, 2:1, . . . , and (N−1):1 from the unit optical combining element closer to the input of the matrix optical switch. For obtaining this combining optical power ratio, a directional coupler or an asymmetrical Y branch can be used as the unit optical combining element. One of the two input ports in the unit optical combining element  3612 , which has a larger combining optical power ratio, is connected to the output port in the unit optical combining element  3611 . One of the two input ports in the unit optical combining element  3613 , which has a larger combining optical power ratio, is connected to the output port in the unit optical combining element  3612 . Hereinafter, similarly one of the two input ports in each of the unit optical combining elements  3614 ,  3615 ,  3616 , and  3617 , which has a larger combining optical power ratio, is connected to the output port in each of the unit optical combining elements  3613 ,  3614 ,  3615 , and  3616 . 
     The same configuration is applied to the unit optical combining elements  3621  to  3627 ,  3631  to  3637 ,  3641  to  3647 ,  3651  to  3657 ,  3661  to  3667 ,  3671  to  3677 , and  3681  to  3687  forming the optical combining devices  332  to  338 . 
     The respective inputs in the optical switches  311  to  318  are connected to eight external input ports  301  to  308 , and the respective outputs of the optical combining devices  331  to  338  are connected to external output ports  341  to  348 . 
     In the matrix optical switch shown in  FIG. 3 , the output port in the gate optical switch element  3711  included in the optical switch  311  is connected to the input port in the unit optical combining element  3621 . In addition, the unit optical combining element  3641  is arranged immediately after the gate optical switch element  3712 , and the output port in the gate optical switch element  3712  and the input port in the unit optical combining element  3641  are connected without the intersection with the other route. Similarly the output port in the gate optical switch element  3713  and the input port in the unit optical combining element  3662 , the output port in the gate optical switch element  3714  and the input port in the unit optical combining element  3683 , the output port in the gate optical switch element  3715  and the input port in the unit optical combining element  3674 , the output port in the gate optical switch element  3716  and the input port in the unit optical combining element  3655 , the output port in the gate optical switch element  3717  and the input port in the unit optical combining element  3636 , the output port in the gate optical switch element  3718  and the input port in the unit optical combining element  3617  are respectively connected without the intersection with the other route. 
     The output port in the gate optical switch element  3721  included in the optical switch  312  is connected to the input port in the unit optical combining element  3611 . In addition, the unit optical combining element  3621  is arranged immediately after the gate optical switch element  3722 , and the output port in the gate optical switch element  3722  and the input port in the unit optical combining element  3621  are connected without the intersection with the other route. Similarly the output port in the gate optical switch element  3723  and the input port in the unit optical combining element  3642 , the output port in the gate optical switch element  3724  and the input port in the unit optical combining element  3663 , the output port in the gate optical switch element  3725  and the input port in the unit optical combining element  3684 , the output port in the gate optical switch element  3726  and the input port in the unit optical combining element  3675 , the output port in the gate optical switch element  3727  and the input port in the unit optical combining element  3656 , the output port in the gate optical switch element  3728  and the input port in the unit optical combining element  3637  are respectively connected without the intersection with the other route. 
     Hereinafter, similarly eight output ports in each of the optical switches  313  to  318  are respectively connected to the unit optical combining elements. 
     According to this configuration, the output port of each optical switch does not combine in the optical combining device after the intersection, but intersects after combining in the unit optical combining element. Therefore the number of the intersections in an entire matrix optical switch can be reduced. Actually in the optical switch in  FIG. 3 , the intersections in one route are 13 locations at most. 
     It should be noted that in  FIG. 3 , the unit optical switch elements  3518 ,  3528 ,  3538 ,  3548 ,  3558 ,  3568 ,  3578 , and  3588  each having one input and two outputs, each of which is illustrated as one input and one output by omitting one output, and the gate optical switch elements are arranged for enhancing an extinction ratio, and the present invention can perform a basic operation without them. The unit optical switch element and the gate optical switch element have the effect for enhancing the extinction ratio of the matrix optical switch even if the extinction ratio of the unit optical switch element of one input and two outputs is insufficient. 
     In addition, in the second embodiment, even if the external input port is reversed to the external output port and the external output port is reversed to the external input port in the matrix optical switch, the optical combining device is reversed to the optical branching device, and the unit optical combining element is reversed to the unit optical branching element, it is apparent that the number of the intersections in the entire matrix optical switch can similarly be reduced. 
     The matrix optical switch of eight inputs and eight outputs based upon the circuit configuration shown in  FIG. 3  was produced by the optical circuit as follows. 
     A single mode optical waveguide having a clad layer formed by silica-based glass and an embedded type core portion on a silicon substrate having a thickness of 1 mm and a diameter of 6 inches was produced by a combination of a deposit technology of silica-based glass films using a flame hydrolysis reaction of raw material gas of SiCl 4  or GeCl 4 , and a reactive ion etching technology, and a thin-film heater and electrodes for power supply were produced on a surface of the clad layer by vacuum vaporization and patterning. The produced optical waveguide has a core dimension of 6 μm×6 μm, and a relative refractive index difference thereof from the clad layer was set as 1.5%. The waveguide type optical switch in the present embodiment was formed by using this optical waveguide and combining a straight waveguide and a curved waveguide. The optical switch element is a Mach-Zehnder interferometer circuit in which an effective optical path length of an arm waveguide is one-half of a signal optical wavelength as shown in  FIG. 4A  and  FIG. 4B . In the present embodiment, since the signal optical wavelength is 1.55 μm and a refractive index of the silica-based glass is 1.45, a difference in an actual arm optical waveguide length was set as 0.534 μm. Thin-film heaters ( 441  and  442 ) each having a thickness of 0.3 μm, a width of 20 μm and a length of 2 mm were formed on a surface of a clad layer ( 42 ) as a phase shifter by a thermo-optic effect. Further, heat-insulating grooves ( 451 ,  452  and  453 ) were formed along the thin-film heaters ( 441  and  442 ), each having a depth to the extent that the silicon substrate ( 41 ) is exposed. A length of the optical switch element configured by the Mach-Zehnder interferometer circuit as shown in  FIG. 4A  and  FIG. 4B  was 5.5 mm. The optical switch element and the Y branch type optical combining circuit were connected by a curved waveguide having the minimum bending radius R=2 mm, and the matrix optical switch of eight inputs and eight outputs based upon the circuit configuration shown in  FIG. 3  was arranged on one chip. The chip size was 110 mm×15 mm. 
     An optical fiber was connected to the external input port and the external output port in the matrix optical switch chip of eight inputs and eight outputs produced by the above-mentioned method to measure optical characteristics. As a result, the insertion loss was 12 dB or less including a principle loss 9 dB by the combining, and the extinction ratio was 45 dB or more. The input and output ports were reversed, wherein light was input from a side of the external output port and optical characteristics of the light that was output to the external input port were measured. As a result, the insertion loss and the extinction ratio had the same characteristics. 
     Third Embodiment 
     In the above-mentioned first and second embodiments, in a case where M=N=4, and M=N=8 (that is, in a case of M=N), the waveguide type optical switch in the form of the matrix optical switch of M inputs and N outputs is explained. However, if M and N differ with each other and are an integral number of three or more, the configuration of the present invention can be carried out. That is, if it has at least the following characteristics, the waveguide type optical switch in the present invention can be carried out. 
     [1] The waveguide type optical switch is a matrix optical switch comprising M pieces of optical switches each having one input and N outputs, and N pieces of optical combining devices each having M inputs and one output. The a-th input (a is an integral number of 1 to M) in the matrix optical switch comprises the input in the a-th optical switch of one input and N outputs. The b-th output (b is an integral number of 1 to N) in the matrix optical switch comprises the output in the b-th optical combining device of M inputs and one output. 
     [2] Each of the optical switches comprises (N−1) pieces of unit optical switch elements each having one input and two outputs, and each of the optical combining devices comprises (M−1) pieces of unit optical combining elements each having two inputs and one output. 
     [3] In the optical switch, the input of the first unit optical switch element forms the input of the optical switch. In addition, one of the outputs in the i-th (i is an integral number of 1 to (N−2)) unit optical switch element is connected to the input of the (i+1)-th unit optical switch element, and the other of the outputs in the i-th unit optical switch element forms the i-th output in the optical switch. Two outputs in the (N−1)-th unit optical switch element form the (N−1)-th output and the N-th output in the optical switch. 
     [4] In the optical combining device, two inputs of the first unit optical combining element forms the first and second inputs in the optical combining device, one of the inputs in the j-th (j is an integral number of 2 to (M−1)) unit optical combining element is connected to the output of the (j−1)-th unit optical combining element, and the other of the inputs in the j-th unit optical combining element forms the (j+1)-th input in the optical combining device. The output in the (M−1)-th unit optical combining element forms the output in the optical combining device. 
     [5] In the matrix optical switch, the p-th optical switch (p is an integral number of 1 to M) in the optical switches and the q-th optical combining device (q is an integral number of 1 to N) in the optical combining devices are configured to be connected between any output in the p-th optical switch and any input in the q-th optical combining device. In a case where any output in the p-th optical switch is the k-th (k is an integral number of 1 to N) output in the above-mentioned connection, any input in the q-th optical combining device is the k-th input. In a case where k is from 2 to (N−1) in the above-mentioned connection, the waveguide intersection is not included in the connection between the output of the unit optical switch element forming the k-th output in the p-th optical switch, and the input of the unit optical combining element forming the k-th input in the q-th optical combining device. 
     With the above-mentioned characteristics, the matrix optical switch in which the loss is reduced by reducing the number of the intersections can be realized by the waveguide type optical switch that is inexpensive in the producing process and is suitable for mass production. 
     The further characteristic of the present invention is that a combining optical power ratio between two input terminals of the first unit optical combining element in the above-mentioned optical combining device is 1:1, and a combining optical power ratio between an input terminal connected to the input of the optical switch in the j-th unit optical combining element (j is an integral number of 2 to (M−1)) and an input terminal connected to the other unit optical combining element is 1:j. Therefore even if the optical signal transmits through any number of the unit optical combining elements (any number of 1 to (M−1) pieces), variations in optical intensity by the number of the combining times can be suppressed in the output in the waveguide type optical switch. 
     It should be noted that also in the third embodiment, as similar to the first and second embodiments, the unit optical switch element of one input and one output and the gate optical switch element may be arranged for enhancing an extinction ratio. However, the present invention can perform a basic operation without them. The unit optical switch element of one input and one output and the gate optical switch element have the effect for enhancing the extinction ratio of the matrix optical switch even if the extinction ratio of the unit optical switch element of one input and two outputs is insufficient. 
     Fourth Embodiment 
     In the third embodiment, even if the external input port is reversed to the external output port and the external output port is reversed to the external input port in the matrix optical switch, the optical combining device is reversed to the optical branching device, and the unit optical combining element is reversed to the unit optical branching element, it is apparent that the number of the intersections in the entire matrix optical switch can similarly be reduced. 
     In a case where the input and the output are reversed, attention should be paid to that the closer to the output, the combining optical power ratio in the unit optical combining element is the larger, and similarly the closer to the input, the branching optical power ratio in the unit optical branching element is the larger. That is, a branching optical power ratio between two output terminals of the (M−1)-th unit optical branching element in the optical branching device is 1:1, and a branching optical power ratio between an output terminal connected to the output of the optical switch in the i-th unit optical branching element (i is an integral number of 1 to (M−2)) and an output terminal connected to the other unit optical branching element is 1:(M−i). Therefore even if the optical signal transmits through any number of the unit optical branching elements (any number of 1 to (M−1) pieces), variations in optical intensity by the number of the branching times can be suppressed in the output in the waveguide type optical switch. 
     Fifth Embodiment 
       FIG. 5  is an explanatory diagram showing a fifth embodiment in the present invention, and shows an example configured of a matrix optical switch of six inputs and eight outputs. 
     The matrix optical switch shown in  FIG. 5  comprises 48 pieces of unit optical switch elements ( 5511  to  5518 ,  5521  to  5528 ,  5531  to  5538 ,  5541  to  5548 ,  5551  to  5558 , and  5561  to  5568 ) each having one input and two outputs, 48 pieces of gate optical switch elements ( 5711  to  5718 ,  5721  to  5728 ,  5731  to  5738 ,  5741  to  5748 ,  5751  to  5758 , and  5761  to  5768 ) each having one input and one output, and 40 pieces of unit optical combining elements ( 5611  to  5615 ,  5621  to  5625 ,  5631  to  5635 ,  5641  to  5645 ,  5651  to  5655 ,  5661  to  5665 ,  5671  to  5675 , and  5681  to  5685 ) each having two inputs and one output. The eight unit optical switch elements  5511 ,  5512 ,  5513 ,  5514 ,  5515 ,  5516 ,  5517 , and  5518  are connected in a vertical line, and further, the gate optical switch elements  5711  to  5718  for improving an extinction ratio are connected to the output ports of the respective unit optical switch elements, which forms an optical switch  511  of one input and eight outputs (the code is not illustrated in the figure). Similarly the unit optical switch elements  5521  to  5528 ,  5531  to  5538 ,  5541  to  5548 ,  5551  to  5558 , and  3561  to  3568  are respectively connected in a vertical line, and the gate optical switch elements  5721  to  5728 ,  5731  to  5738 ,  5741  to  5748 ,  5751  to  5758 , and  5761  to  5768  are connected to the output ports of the respective unit optical switch elements, which form optical switches  512 ,  513 ,  514 ,  515 , and  516  (the code is not illustrated in the figure) each having one input and eight outputs. 
     The five unit optical combining elements  5611 ,  5612 ,  5613 ,  5614 , and  5615  are connected in a vertical line, which forms an optical combining device  531  of six inputs and one output (the code is not illustrated in the figure). Similarly the unit optical combining elements  5621  to  5625 ,  5631  to  5635 ,  5641  to  5645 ,  5651  to  5655 ,  5661  to  5665 ,  5671  to  5675 , and  5681  to  5685  are respectively connected in a vertical line, which form optical combining devices  532 ,  533 ,  534 ,  535 ,  536 ,  537 , and  538  each having six inputs and one output. 
     Herein for making each ratio of optical powers combining from each of six input ports to one output port in the optical combining device  531  equal, each combining optical power ratio of the unit optical combining elements  5611 ,  5612 ,  5613 ,  5614 , and  5615  is set as 1:1, 2:1, 3:1, 4:1, and 5:1. It is apparent that the combining optical power ratio is set in the order of 1:1, 2:1, and (M−1):1 from the unit optical combining element closer to the input of the matrix optical switch. For obtaining this combining optical power ratio, a directional coupler, an asymmetrical Y branch and the like can be used as the unit optical combining element. One of the two input ports in the unit optical combining element  5612 , which has a larger combining optical power ratio, is connected to the output port in the unit optical combining element  5611 . One of the two input ports in the unit optical combining element  5613 , which has a larger combining optical power ratio, is connected to the output port in the unit optical combining element  5612 . Hereinafter, similarly one of the two input ports in each of the unit optical combining elements  5614  and  5615 , which has a larger combining optical power ratio, is connected to the output port in each of the unit optical combining elements  5613  and  5614 . 
     The same configuration is applied to the unit optical combining elements  5621  to  5625 ,  5631  to  5635 ,  5641  to  5645 ,  5651  to  5655 ,  5661  to  5665 ,  5671  to  5675 , and  5681  to  5685  forming the optical combining devices  532  to  538 . 
     The respective inputs in the optical switches  511  to  516  are connected to six external input ports  501  to  506 , and the respective outputs of the optical combining devices  531  to  538  are connected to external output ports  541  to  548 . 
     In the matrix optical switch shown in  FIG. 5 , the output port in the gate optical switch element  5711  included in the optical switch  511  is connected to the input port in the unit optical combining element  5621 . In addition, the unit optical combining element  5641  is arranged immediately after the gate optical switch element  5712 , and the output port in the gate optical switch element  5712  and the input port in the unit optical combining element  5641  are connected without the intersection with the other route. Similarly the output port in the gate optical switch element  5713  and the input port in the unit optical combining element  5662 , the output port in the gate optical switch element  5714  and the input port in the unit optical combining element  5682 , the output port in the gate optical switch element  5715  and the input port in the unit optical combining element  5672 , the output port in the gate optical switch element  5716  and the input port in the unit optical combining element  5653 , the output port in the gate optical switch element  5717  and the input port in the unit optical combining element  5634 , and the output port in the gate optical switch element  5718  and the input port in the unit optical combining element  5615  are respectively connected without the intersection with the other route. 
     The output port in the gate optical switch element  5721  included in the optical switch  512  is connected to the input port in the unit optical combining element  5611 . In addition, the unit optical combining element  5621  is arranged immediately after the gate optical switch element  5722 , and the output port in the gate optical switch element  5722  and the input port in the unit optical combining element  5621  are connected without the intersection with the other route. Similarly the output port in the gate optical switch element  5723  and the input port in the unit optical combining element  5642 , the output port in the gate optical switch element  5724  and the input port in the unit optical combining element  5663 , the output port in the gate optical switch element  5725  and the input port in the unit optical combining element  5683 , the output port in the gate optical switch element  5726  and the input port in the unit optical combining element  5673 , the output port in the gate optical switch element  5727  and the input port in the unit optical combining element  5654 , the output port in the gate optical switch element  5728  and the input port in the unit optical combining element  5635  are respectively connected without the intersection with the other route. 
     Hereinafter, similarly eight output ports in the optical switches  513  to  516  are respectively connected to the unit optical combining elements. 
     According to this configuration, the output port of each optical switch does not combine in the optical combining device after the intersection, but intersects after combining in the unit optical combining element. Therefore the number of the intersections in an entire matrix optical switch can be reduced. Actually in the optical switch in  FIG. 5 , the number of the intersections in one route is 11 locations at most. 
     It should be noted that in  FIG. 5 , the unit optical switch elements  5518 ,  5528 ,  5538 ,  5548 ,  5558 , and  5568  each having one input and two outputs, each of which is illustrated as one input and one output by omitting one output, and the gate optical switch elements are arranged for enhancing an extinction ratio, and the present invention can perform a basic operation without them. The unit optical switch element and the gate optical switch element have the effect for enhancing the extinction ratio of the matrix optical switch even if the extinction ratio of the unit optical switch element of one input and two outputs is insufficient. 
     In addition, in the fifth embodiment, even if the external input port is reversed to the external output port and the external output port is reversed to the external input port in the matrix optical switch, the optical combining device is reversed to the optical branching device, and the unit optical combining element is reversed to the unit optical branching element, it is apparent that the number of the intersections in the entire matrix optical switch can similarly be reduced. 
     Sixth Embodiment 
     The matrix optical switch according to the present invention can be used independently as explained above, but may be configured by a combination of a plurality of matrix optical switches. 
       FIG. 6  is an explanatory diagram showing a sixth embodiment in the present invention, and shows an example in which two matrix optical switches each having six inputs and eight outputs according to the fifth embodiment are combined to configure a matrix optical switch of 12 inputs and eight outputs. 
     The matrix optical switch shown in  FIG. 6  comprises two matrix optical switches ( 611  and  612 ) each having six inputs and eight outputs, and eight optical combining devices  621  to  628  each having two inputs and one output, and each combining optical power ratio of the optical combining devices  621  to  628  is 1:1. 
     One of the two input ports in the first unit optical combining device  621  is connected to the first output out of the eight output ports in the matrix optical switch  611 , and the other of the two input ports in the optical combining device  621  is connected to the first output out of the eight output ports in the matrix optical switch  612 . 
     In addition, one of the two input ports in the second unit optical combining device  622  is connected to the second output ports out of the eight output ports in the matrix optical switch  611 , and the other of the two input ports in the unit optical combining device  622  is connected to the second output ports out of the eight output ports in the matrix optical switch  612 . 
     Hereinafter, similarly one of the two input ports in each of the third to eighth optical combining devices  623  to  628  is connected to each of the third to eighth output ports out of the eight output ports in the matrix optical switch  611 , and the other of the two input ports in each of the unit optical combining devices  623  to  628  is connected to each of the third to eighth output ports out of the eight output ports in the matrix optical switch  612 . 
     As shown in  FIG. 6 , a case where the two matrix optical switches each having six inputs and eight outputs are combined to configure the matrix optical switch, as compared to a case where the matrix optical switch of 12 inputs and eight outputs is configured independently, has an advantage that although many intersections are generated between the matrix optical switches  611  and  612 , and the optical combining devices  621  to  628  each having two inputs and one output, but it is possible to suppress an increase on kinds of the optical combining device. In a case where the matrix optical switch of 12 inputs and eight outputs is configured independently, 11 kinds of optical combining devices in which the combining optical power ratio is 1:1, 1:2, . . . , 1:11 are necessary. However, as shown in  FIG. 6 , in a case where the two matrix optical switches each having six inputs and eight outputs are combined to configure the matrix optical switch, the required kinds of the optical combining device are only five kinds in each of which the combining optical power ratio is 1:1, 1:2, . . . , 1:5. 
     REFERENCE SIGNS LIST 
     
         
         
           
               101  to  104 : External input port 
               111  to  114 : Optical switch of one input and four outputs 
               121 : Intersection part 
               131  to  134 : Optical combining device of four inputs and one output 
               141  to  144 : External output port 
               201  to  204 : External input port 
               211  to  214 : Optical switch of one input and four outputs 
               231  to  234 : Optical combining device of four inputs and one output 
               241  to  244 : External output port 
               2511  to  2514 ,  2521  to  2524 ,  2531  to  2534 , and  2541  to  2544 : Unit optical switch element of one input and two outputs 
               2611  to  2613 ,  2621  to  2523 ,  2631  to  6533 , and  2641  to  2643 : Unit optical combining element of two inputs and one output 
               301  to  308 : External input port 
               311  to  318 : Optical switch of one input and eight outputs 
               331  to  338 : Optical combining device of eight inputs and one output 
               341  to  348 : External output port 
               3511  to  3518 ,  3521  to  3528 ,  3531  to  3538 ,  3541  to  3548 ,  3551  to  3558 ,  3561  to  3568 ,  3571  to  3578 , and  3581  to  3588 : Unit optical switch element of one input and two outputs 
               3611  to  3617 ,  3621  to  3627 ,  3631  to  3637 ,  3641  to  3647 ,  3651  to  3657 ,  3661  to  3667 ,  3671  to  3677 , and  3681  to  3687 : Unit optical combining element of two inputs and one output 
               3711  to  3718 ,  3721  to  3728 ,  3731  to  3738 ,  3741  to  3748 ,  3751  to  3758 ,  3671  to  3768 ,  3771  to  3778 , and  3781  to  3788 : Gate optical switch element of one input and one output 
               401 ,  402 : Input port 
               411 ,  412 : Output port 
               41 : Silicon substrate 
               42 : Clad layer 
               431 ,  432 : Embedded core portion 
               441 ,  442 : Thin-film heater 
               451 ,  452 ,  453 : Heat-Insulating groove 
               461 ,  462 : Directional coupler 
               501  to  506 : External input port 
               511  to  516 : Optical switch of one input and eight outputs 
               531  to  538 : Optical combining device of six inputs and one output 
               541  to  548 : External output port 
               5511  to  5518 ,  5521  to  5528 ,  5531  to  5538 ,  5541  to  5548 ,  5551  to  5558 , and  5561  to  5568 : Unit optical switch element of one input and two outputs 
               5611  to  5615 ,  5621  to  5625 ,  5631  to  5635 ,  5641  to  5645 ,  5651  to  5655 ,  5661  to  5665 ,  5671  to  5675 , and  5681  to  5685 : Unit optical combining element of two inputs and one output 
               5711  to  5718 ,  5721  to  5728 ,  5731  to  5738 ,  5741  to  5748 ,  5751  to  5758 , and  5661  to  5768 : Gate optical switch element of one input and one output 
               601  to  612 : External input port 
               611 ,  612 : Optical switch of six inputs and eight outputs 
               621  to  628 : Optical combining device of two inputs and one output 
               631  to  638 : External output port