JP2005202241A - Optical branching circuit, optical transmitting and receiving circuit and optical network - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a loss accompanying the branching in an optical branching circuit. <P>SOLUTION: An optical branching circuit comprises a waveguide circuit constituted by two-dimensionally arranging wave transfer media; in the wave transfer media, a spatial refractive index distribution which is determined based on the refractive index of each of virtual pixels demarcated by virtual meshes so that an optical signal made incident from one port among three or more ports is branched while being subjected to multiple branching and is emitted from the other port is formed. In the spatial refractive index distribution, the phase of optical signal in a port is set so that each optical signal emitted from other ports is vertical to each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical branching circuit, an optical transmission / reception circuit, and an optical network, and more specifically, light using a holographic wave transmission medium that transmits waves holographically by multiple scattering according to a two-dimensional refractive index distribution. The present invention relates to a branch circuit, an optical transmission / reception circuit, and an optical network.

  In the optical communication field, integrated optical components using an optical waveguide structure have been developed as an optical circuit that can easily realize branching and interference of light. Integrated optical components that utilize the properties of light waves make it easy to manufacture optical interferometers by adjusting the length of the optical waveguide, or to easily integrate optical components by applying circuit processing technology in the semiconductor field. Become.

  Known optical circuits include the Y branch circuit shown in FIG. 1A and the directional coupler shown in FIG. By combining the Y branch circuit and the directional coupler, the 1 × N branch circuit shown in FIG. 2A and the N × M directional coupler shown in FIG. 2B can be configured. FIG. 3 shows an MMI (Multi Mode Interference) directional coupler, and an N × M connection can be configured by one circuit.

  However, when a conventional optical circuit is combined to form an NxN mesh type optical branch circuit, that is, a circuit in which all N ports are connected to each other, there is a problem that a loss during connection is large. This problem will be specifically described.

FIG. 4 shows a 3 × 3 mesh type optical branch circuit in which three Y branch circuits are combined. The optical signal input to one Y branch circuit causes a loss at both the input side and the output side coupling portions due to the branch in the input Y branch circuit and the coupling in the output Y branch circuit. The branching ratio is 1 / (N−1) (1 / number of ports facing each other), and the optical signal output to the facing port becomes 1 / (N−1) ² .

FIG. 5 shows a 4 × 4 mesh type optical branching circuit in which four MMI directional couplers are combined. As with the Y branch circuit shown in FIG. 4, the optical signal input to one MMI directional coupler is lossy at both the input and output coupling portions, and 1 / (N−1) ² will be smaller. The branching ratios of the 3 × 3 and 4 × 4 mesh type optical branch circuits are (1/2) ² = 1/4 and (1/3) ² = 1/9, respectively, resulting in a large loss. Further, in the optical branch circuit of 4 × 4 or more, as shown in FIG. 5, there is a problem that the loss further increases because the intersection of the waveguides occurs.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an optical branch circuit in which loss due to branching is reduced and to facilitate terminal interconnection using the optical branch circuit. It is an object to provide an optical transmission / reception circuit and an optical network.

  In order to achieve such an object, the invention according to claim 1 is characterized in that, among the three or more ports, the refractive index of each of the virtual pixels defined by the virtual mesh is determined. A wave transmission medium in which a spatial refractive index distribution determined so that an optical signal incident from one port branches while being scattered multiple times and is emitted from another port is arranged two-dimensionally. An optical branch circuit composed of a waveguide circuit configured as described above, wherein the spatial refractive index distribution is such that each optical signal emitted from the other port is vectorally orthogonal to each other at the port. The phase of the optical signal is set.

  According to the second aspect of the present invention, the optical signal incident from one of the three or more ports is subjected to multiple scattering by the refractive index of each of the virtual pixels defined by the virtual mesh. This is an optical branch circuit composed of a waveguide circuit configured by two-dimensionally arranging a wave transmission medium that is branched and has a spatial refractive index distribution determined so as to be emitted from another port. The spatial refractive index distribution is obtained when the phase of the optical signal at the port cannot be set so that the optical signals emitted from the other ports are vector orthogonal to each other. The phase is set so that the overlap integral of each optical signal field at the port is minimized.

  According to a third aspect of the present invention, in the optical branching circuit according to the first or second aspect, the branching ratio from the one port to the other port is different.

  According to a fourth aspect of the present invention, an amplification element is connected to each of the ports according to the first or second aspect.

  According to a fifth aspect of the invention, the amplification factor of the amplification element according to the fourth aspect is set such that the light intensity at the one port and the light intensity at the other port are constant. It is characterized by that.

  According to a sixth aspect of the present invention, an optical branch circuit according to any one of the first to fifth aspects of the present invention is connected to the one port of the optical branch circuit, and an optical signal is mutually transmitted to each of the other ports. It is an optical transmission / reception circuit including an optical transmission / reception element that performs transmission / reception.

  According to a seventh aspect of the invention, there is provided the optical branch circuit according to any one of the first to fifth aspects, and a network component connected to each port of the optical branch circuit. And an optical network configured to transmit and receive optical signals.

  According to an eighth aspect of the present invention, a plurality of network components to which the optical branch circuit according to any one of the first to fifth aspects is connected are connected in cascade with each of one port of the optical branch circuit. It is characterized by being an optical network comprised by doing.

  As described above, according to the present invention, a spatial refractive index distribution is formed in which the phase of the optical signal at the port is set so that the optical signals emitted from the other ports are orthogonal to each other. Since the wave transmission medium is provided, it is possible to reduce the loss due to branching.

  Further, according to the present invention, even if the phase of the optical signal at the port cannot be set so that the optical signals emitted from the other ports are orthogonal to each other, Since the phase is set so that the overlap is minimized, it is possible to reduce the loss due to branching.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As described above, in the conventional optical circuit, the optical signal is simply multiplexed / demultiplexed. When an NxN mesh type optical circuit is configured, the output optical signal is reduced to 1 / (N−1) ² . There was a problem of attenuation. The cause of such a problem is that the circuit design considering the phase of light is not made. Therefore, in the present invention, a wave transmission medium is used to realize a multiplexing / demultiplexing function in consideration of the phase, and a low loss optical branch circuit is configured. First, the basic concept of the wave transmission medium used in the present invention will be described.

  In the present invention, since it is applied to an optical circuit, “wave” propagating in the wave transmission medium is “light”. The theory relating to the wave transmission medium specifies the characteristics of the medium based on a general wave equation, and can also hold in principle in general waves. In order to input a coherent light pattern and output a desired light pattern, the wave transmission medium has a phase difference between forward propagation light and back propagation light propagating in the wave transmission medium. The refractive index distribution is determined so as to be small even at the location. A desired light pattern is output by repeatedly repeating holographic control at a local level according to the refractive index distribution.

With reference to FIG. 6, the basic structure of the wave transmission medium according to the present invention will be described. As shown in FIG. 6A, an optical circuit design area 1-1 composed of a wave transmission medium exists in the optical circuit board 1. One end surface of the optical circuit is an incident surface 2-1 on which the input light 3-1 is incident. The input light 3-1 propagates through the optical circuit having a spatial refractive index distribution constituted by the wave transmission medium while being subjected to multiple scattering, and is output as the output light 3-2 from the exit surface 2-2 which is the other end face. Is output. Coordinate z in FIG. 6 (a), the coordinates (z = 0 is the incident surface, z = z _e is output surface) of the propagation direction of the light is, the coordinate x is at a transverse coordinates for the light propagation direction is there. In this embodiment, it is assumed that the wave transmission medium is made of a dielectric, and the spatial refractive index distribution is based on the theory described below for the local refractive index of the dielectric constituting the wave transmission medium. This is realized by setting based on this.

  The “field” (input field) formed by the input light 3-1 is modulated according to the spatial distribution of the refractive index of the wave transmission medium constituting the optical circuit, and the “field” formed by the output light 3-2. "(Output field). In other words, the wave transmission medium of the present invention is (electromagnetic) field conversion means for correlating the input field and the output field according to the spatial refractive index distribution. For these input field and output field, the light field in the cross section (cross section along the x axis in the figure) perpendicular to the propagation direction (z axis direction in the figure) in the optical circuit is represented by its location (x, This is called a (forward) propagation image (propagation field or propagation light) in z) (see FIG. 6B).

  Here, “field” generally means an electromagnetic field (electromagnetic field) or a vector potential field of an electromagnetic field. The control of the electromagnetic field in this embodiment corresponds to changing the spatial refractive index distribution provided in the optical circuit, that is, the dielectric constant distribution. Although the dielectric constant is given as a tensor, since the transition between the polarization states is usually not so large, it is an approximation that may be a scalar wave approximation for only one component of the electromagnetic field. Therefore, in this specification, the electromagnetic field is treated as a complex scalar wave. Since the “state” of light includes an energy state (wavelength) and a polarization state, when the “field” is used to express the state of light, the light wavelength and polarization state are also included. Will get.

  In general, in an optical circuit that does not cause amplification or attenuation of propagating light, when the spatial distribution of the refractive index is determined, an image (input field) of the input light 3-1 other than the focal point is an image of the output light 3-2. (Output field) is determined uniquely. Such a field of light traveling from the exit surface 2-2 side to the entrance surface 2-1 side is referred to as a back propagation image (a back propagation field or a back propagation light) (see FIG. 6C). Such a back propagation image can be defined for each place in the optical circuit. That is, when a light field at an arbitrary place in the optical circuit is considered, if the place is considered as an emission point of a virtual “input light”, the image of the output light 3-2 can be obtained in the same manner as described above. The back-propagation image at that location can be considered. In this way, a back propagation image can be defined for each location in the optical circuit.

  In particular, in a single optical circuit, when the outgoing field is a propagation field of the incident field, the propagation field and the reverse propagation field coincide with each other at any point of the optical circuit. The field is generally a function over the entire target space, but the term “incident field” or “exit field” means a cross section of the field on the entrance surface or exit surface. In addition, even in the case of “field distribution”, when a discussion is made regarding a specific cross section, it means a cross section of the field with respect to that cross section.

In order to explain the method of determining the refractive index distribution, it is better to use symbols, so the following symbols are used to represent each quantity. Note that the light (field) targeted in the present invention is not limited to light in a single state, so that light in which a plurality of states are superimposed can be indexed to light in each state. It is generally written with j.
Ψ ^j (x): j-th incident field (complex vector value function, defined by intensity distribution and phase distribution set on the incident surface, and wavelength and polarization)
Φ ^j (x): j-th outgoing field (complex vector value function, defined by intensity distribution and phase distribution, wavelength and polarization set on the outgoing face)
Note that ψ ^j (x) and φ ^j (x) have the same total light intensity (or a negligible loss) unless intensity amplification, wavelength conversion, and polarization conversion are performed in the circuit. Their wavelength and polarization are the same.

{Ψ ^j (x), φ ^j (x)}: Input / output pair (a set of input / output fields)
{Ψ ^j (x), φ ^j (x)} is defined by the intensity distribution and the phase distribution, the wavelength and the polarization at the entrance surface and the exit surface.

{N _q }: Refractive index distribution (a set of values for the entire optical circuit design area)
When one refractive index distribution is given for a given incident field and outgoing field, the field of light is determined, so it is necessary to consider the field for the entire refractive index distribution given by the qth iteration. Therefore, the entire refractive index distribution may be expressed as n _q (x, z) with (x, z) as an indefinite variable, but the refractive index value n _q (x, z) at the location (x, z) For distinction, {n _q } is used for the entire refractive index distribution.

N _core : A symbol indicating a high refractive index value with respect to the surrounding refractive index, such as a core portion in an optical waveguide.
N _clad : a symbol indicating a low refractive index value with respect to n _core , such as a clad portion in an optical waveguide.
Ψ ^j (z, x, {n _q }): field at location (x, z) when the ^jth incident field ψ ^j (x) is propagated through the refractive index profile {n _q } to z The value of the.
Φ ^j (z, x, {n _q }): at the location (x, z) when the j-th outgoing field φ ^j (x) is propagated back to z in the refractive index profile {n _q } The field value.

In the present embodiment, the refractive index distribution, all j for _{^{ψ j (z e, x,}} {n q}) is given = φ ^j (x), or the so close state {n _q}.

  “Input port” and “output port” are “areas” where the fields at the entrance end face and the exit end face are concentrated. For example, by connecting an optical fiber to the part, the optical intensity can be propagated to the fiber. It is an area. Here, since the field intensity distribution and phase distribution can be designed to be different for the j-th and k-th ones, a plurality of ports can be provided on the entrance end face and the exit end face. Furthermore, when considering a pair of an incident field and an outgoing field, the phase generated by the propagation between them differs depending on the frequency of light. Therefore, for light having different frequencies (that is, light having different wavelengths), the field shape including the phase is included. Regardless of whether they are the same or orthogonal, they can be configured as different ports.

Here, the electromagnetic field is a field of a real vector value, and has a wavelength and a polarization state as parameters, but the value of the component is displayed as a complex number that can be easily handled in a general mathematical manner, and represents the solution of the electromagnetic wave. In the following calculation, it is assumed that the strength of the entire field is normalized to 1. As shown in FIGS. 6 (b) and 6 (c), the propagation field and the back-propagation field for the ^jth incident field ψ ^j (x) and output field φ ^j (x) As complex vector value functions, they are expressed as ψ ^j (z, x, {n}) and φ ^j (z, x, {n}). Since the values of these functions vary depending on the refractive index distribution {n}, the refractive index distribution {n} is a parameter. According to the definition of the symbols, ψ ^j (x) = ψ ^j (0, x, {n}) and φ ^j (x) = φ ^j (z _e , x, {n}). The values of these functions can be easily calculated by a known method such as a beam propagation method, given an incident field ψ ^j (x), an outgoing field φ ^j (x), and a refractive index distribution {n}. it can.

In the following, a general algorithm for determining the spatial refractive index distribution will be described. FIG. 7 shows a calculation procedure for determining the spatial refractive index distribution of the wave transmission medium. Since this calculation is repeatedly executed, the number of repetitions is represented by q, and the state of the qth calculation when the calculation is executed up to the (q−1) th is shown. Based on the refractive index distribution {n _q-1 } obtained by the (q-1) th calculation, the propagation field and the ^jth incident field ψ ^j (x) and the outgoing field φ ^j (x) The back propagation field is obtained by numerical calculation, and the results are expressed as ψ ^j (z, x, {n _q-1 }) and φ ^j (z, x, {n _q-1 }), respectively (step S220). ).

Based on these results, the refractive index n _q (z, x) at each location (z, x) is obtained by the following equation (step S240).
n _q (z, x) = n _q-1 (z, x) −αΣ _j Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })] ... (1)
Here, the symbol “·” in the second term on the right side means an inner product operation, and Im [] means an imaginary number component of the field inner product operation result in []. The symbol “*” is a complex conjugate. The coefficient α is a value obtained by dividing a value equal to or less than a fraction of n _q (z, x) by the number of field pairs, and is a small positive value. Σ _j means that the sum is taken for the index j.

Step S220 and S240 and repeats the value in the exit plane of the propagation field _{^{ψ j (z e, x,}} {n}) the absolute value of the difference between the exit field φ ^j (x) is than desired error d _j When it becomes smaller (step S230: YES), the calculation ends.

In the above calculation, the initial value {n ₀ } of the refractive index distribution may be set appropriately. However, if this initial value {n ₀ } is close to the expected refractive index distribution, the calculation converges faster accordingly ( Step S200). When calculating φ ^j (z, x, {n _q-1 }) and ψ ^j (z, x, {n _q-1 }) for each j, , J (that is, φ ^j (z, x, {n _q-1 }) and ψ ^j (z, x, {n _q-1 })). Thus, calculation efficiency can be improved (step S220). If the computer is configured with a relatively small memory, an appropriate j is selected for each q in the sum of the index j in equation (1), and φ ^j (z, x, { It is also possible to calculate only n _q-1 }) and ψ ^j (z, x, {n _q-1 }) and repeat the subsequent calculations (step S220).

In the above ^{operation, φ j (z, x,} {n q-1}) in the case of values and ^{ψ j (z, x, {} n q-1}) and the value of the near, the formula (1) Im [φ ^j (z, x, {n _q-1 }) ^* · ψ ^j (z, x, {n _q-1 })] is a value corresponding to the phase difference, and by reducing this value, It is possible to obtain a desired output.

The determination of the refractive index distribution can be rephrased as defining a virtual mesh in the wave transmission medium and determining the refractive index of a minute region (pixel) defined by the mesh for each pixel. In principle, such a local refractive index can be an arbitrary (desired) value for each location. The simplest system is a system consisting only of pixels having a low refractive index (n _L ) and pixels having a high refractive index (n _H ), and the overall refractive index distribution due to the spatial distribution of these two types of pixels. Is determined. In this case, the place where the low refractive index pixel exists in the medium is considered as a gap of the high refractive index pixel, and conversely, the place where the high refractive index pixel exists is considered as the gap of the low refractive index pixel. Can do. That is, the wave transmission medium of the present invention can be expressed as a desired place (pixel) in a medium having a uniform refractive index replaced with a pixel having a different refractive index.

  The calculation contents for determining the refractive index distribution described above are summarized as follows. An input port and an output port are provided in a medium capable of transmitting a wave in a holographic manner (dielectric in the case of light). Field distribution 1 (forward propagation light) of propagating light incident from the input port and from the input port A field distribution 2 (reverse propagation light) of phase conjugate light in which an output field expected when an incident optical signal is output from the output port is propagated backward from the output port side is obtained by numerical calculation. In the field distribution 1 and the field distribution 2, a spatial refractive index distribution in the medium is obtained so as to eliminate the phase difference at each point (x, z) of the propagating light and the counter propagating light. If the steepest descent method is adopted as a method for obtaining such a refractive index distribution, the refractive index is calculated by changing the refractive index in the direction obtained by the steepest descent method using the refractive index of each point as a variable. By changing as in (1), the difference between the two fields can be reduced. If such a wave transmission medium is applied to an optical component that emits light incident from an input port to a desired output port, an effective optical path length is reduced due to interference phenomenon caused by multiple scattering of propagation waves generated in the medium. An optical circuit having a sufficiently high optical signal controllability can be configured even with a long and gentle refractive index change (distribution).

  FIG. 8 shows the refractive index distribution of the wave transmission medium applied to the optical multiplexer / demultiplexer. According to the algorithm described above, an optical circuit having the refractive index distribution shown in FIG. 8 is obtained by repeating about 200 times. Here, the black part in the optical circuit design region 1-1 in the figure is a high refractive index part (dielectric multiple scattering part) 1-11 corresponding to the core, and the part other than the black part corresponds to the clad. Low refractive index portion 1-12. The refractive index of the clad assumes the refractive index of quartz glass, and the refractive index of the core has a value that is higher by 1.5% than the quartz glass. The size of the optical circuit is 300 μm in length and 140 μm in width.

  The mesh used for the calculation when obtaining the refractive index distribution is 140 × 300 (= 42000). Therefore, since the number of parameters of the refractive index distribution is 42,000, it is necessary to optimize these parameters. When the steepest descent method is simply applied and the parameters are optimized by obtaining a numerical derivative for each of these parameters, 42000 light propagation is required to perform one step of calculation. It is necessary to calculate. On the other hand, in this embodiment, it is sufficient to calculate the propagation of light twice, so that the optical circuit can be designed with a short time calculation that does not impede practical use.

  FIG. 9 shows a 4 × 4 mesh type optical branching circuit according to an embodiment of the present invention. The four ports of the optical branch circuit are connected by the above-described wave transmission medium, and can perform simultaneous simultaneous distribution and simultaneous reception. The optical port is used as input / output. FIG. 10 is a diagram schematically showing a signal flow between the ports of the optical branching circuit shown in FIG. 9 as a logical network. When the output of the reflected light is also divided for each direction in which the optical signal propagates, one port is divided into two according to the traveling direction of the optical signal. FIG. 11 shows a logical network in which the traveling direction is represented by superscripts + and −. The optical circuit has four ports, and each port has a circuit configuration that emits light toward the other three ports while receiving signals output independently from the other three ports.

  If each port of the optical branch circuit is configured such that an optical signal received from one port can be received independently of an optical signal received from the other two ports, the loss due to the branch described above can be reduced. it can. As shown below, distribution to each port is performed in consideration of the phase of each optical signal.

  Initially, the phase of each port is represented as a set of four numbers (ie, vectors). Here, the amplitude is 1. However, when there is no light distribution to a specific port, the component is set to zero. For example, if phase 1 is 0, port 2 is π, port 3 is π, and port 4 has no light,

Think of the vector Considering such a representation method, the field overlap integral can be calculated just as an inner product of vectors, and this can be used to find a desired set of vectors.

  Assuming that a signal is evenly distributed from one port to the other two ports, the component corresponding to the distributing port, that is, the overlap integral of each other's field is 0, and the absolute value of the other port is ,

Think of the field that becomes. By adjusting the phase of each optical signal in this way, all the vectors are orthogonal to each other, and each port can receive light independently of optical signals from other fields. At this time,

This combination is applicable. As a result, only the loss due to the branch on the input side is obtained, and the output optical signal becomes 1/3, and the optical signal is received with three times the intensity as compared with the conventional 4 × 4 mesh type optical branch circuit. be able to.

  FIG. 12 shows a 3 × 3 mesh type optical branching circuit according to an embodiment of the present invention. The three ports of the optical branch circuit are connected by the above-described wave transmission medium, and can perform simultaneous simultaneous delivery and simultaneous reception. The three-port optical circuit minimizes the overlap integral of the field of the optical signal because there is no orthogonal state. As shown below, a configuration with less loss can be realized by selecting a state as close to an orthogonal state as possible. here,

And Here, there is an output in its own port, but this can be handled as reflected return light. As a result, the output optical signal becomes 4/9 = 3.5 dB, which is a loss of 2.5 dB compared to the case where two conventional 3 dB couplers are combined.

  FIG. 13 shows a 3-port tap circuit according to an embodiment of the present invention. The tap circuit is used when a weak branch (tap) is required in order to monitor a light intensity by extracting a part of the optical signal or monitor destination information given to the optical signal. Since the optical signal has directionality, a bidirectional optical signal is transmitted to one optical fiber in order to effectively use the optical fiber. At this time, there are cases where it is desired to simultaneously tap bidirectional optical signals. However, if the conventional asymmetric branch circuit is used, it is necessary to multiplex the tapped bidirectional optical signals in order to process them at the same port. When an optical coupler is inserted for multiplexing, a loss of 3 dB occurs. Therefore, an optical circuit using the wave transmission medium according to the present invention is applied so that a loss of 3 dB is not generated.

  Similarly to FIG. 11 in the first embodiment, FIG. 14 shows a logical network diagram in which the traveling direction of the optical signal is indicated by a subscript. Paying attention to the phase state of the optical signal, the set value s of the reflected output intensity is set for both port 1 and port 2

And it is sufficient. Here, the intensity of the incident signal is set to 1, and the ratio of the light intensity to be tapped (port 1 to port 3 and port 2 to port 3) is defined as the tap rate t. FIG. 15 shows the relationship between s and t. When the tap rate is 10% or less, reflection of 20 dB or less may be set, which is very weak reflection. That is, even when applied to an optical transmission system, it is possible to tap with almost no influence on the main signal, and the 3 dB loss associated with the insertion of the optical coupler can be eliminated.

  FIG. 16 shows a 4-port tap circuit according to an embodiment of the present invention. The 4-port tap circuit uses a main port (port 1 to port 2) between opposing ports, and outputs to the orthogonal ports as tap ports (port 3 and port 4). The tap rate of the tap circuit is set as shown in FIGS. It represents the output amplitude of the optical signal input from each port to the other three ports, and if all outputs are selected to be orthogonal,

It becomes. Thereby, it is possible to tap to two ports without loss. Also, the tap port can be replaced with the main port. In particular, when t ₂ = 0, tap circuits with different ports to be tapped according to the traveling direction of the optical signal can be configured as shown in FIG.

  Next, a circuit combining a wave transmission medium and an amplifying element will be described. FIG. 19A shows a 3 × 3 mesh type optical branch circuit. The optical branch circuit includes a wave transmission medium 51 similar to the optical branch circuit shown in FIG. 12 and amplification elements 52a to 52c connected to the respective ports. As the amplifying element 52, for example, a semiconductor optical amplifying element can be applied. The amplification factor of the amplifying element 52 is the square root of the reciprocal of the branching ratio in order to compensate the loss of the branching ratio 4/9 (3.52 dB) with the two amplifying elements.

(1.76 dB) and the value obtained by adding the loss of the waveguide. The optical signal has a constant input / output power by passing through the amplifying element 52 twice.

  FIG. 19B shows a 4 × 4 mesh type optical branch circuit. It is composed of a wave transmission medium 53 similar to the optical branch circuit shown in FIG. 9 and amplification elements 54a to 54c connected to each port. The amplification factor of the amplifying element 54 is the square root of the reciprocal of the branching ratio in order to compensate for the loss of the branching ratio 1/3 (4.8 dB) with the two amplifying elements.

(2.4 dB) and the value obtained by adding the loss of the waveguide. The optical signal has a constant input / output power by passing through the amplifying element 54 twice.

  When the asymmetric branching ratio with the tap rate t is set, the main signal is kept constant, so the amplification factor may be set to the square root of 1-t. Further, the amplifying elements may be installed only at necessary ports. According to the present embodiment, since the amplification factor of the amplifying element is relatively low, an inexpensive optical branch circuit having a constant input / output power can be realized.

  Example 6 is a circuit in which a wave transmission medium and an optical transceiver are combined. FIG. 20A shows a configuration in which an optical transmission / reception element 62 is connected to one port of a 3 × 3 mesh optical branching circuit 61. Optical signals can be transmitted and received with low loss for two optical fibers. FIG. 20B further shows a configuration in which amplifying elements 63 a and 63 b are connected to the other two ports of the optical branching circuit 61. The intensity of the optical signal in the two optical fibers can be kept constant.

  FIG. 21A shows a configuration in which 3 × 3 mesh type optical branch circuits 71a and 72b are connected in cascade, and an optical transmission element 72 and an optical reception element 73 are connected to each of them. The function is the same as that of the optical circuit shown in FIG. 20A, and the optical transmission element and the optical reception element are separately provided. FIG. 21B shows a configuration in which amplifying elements 74a and 74b are connected to the remaining ports of the optical branch circuits 71a and 72b.

  FIG. 22A shows a configuration in which an optical transmission element 82 and an optical reception element 83 are connected to opposing ports of the 4 × 4 mesh optical branch circuit 81. Optical signals can be transmitted and received with low loss for two optical fibers. FIG. 22B shows a configuration in which amplifying elements 84 a and 84 b are further connected to the other two ports of the optical branch circuit 81. The intensity of the optical signal in the two optical fibers can be kept constant. FIG. 22C shows a configuration in which the optical transmission / reception element 85 is connected to one port of the 3 × 3 mesh type optical branch circuit 81 and the amplification elements 84 a to 84 c are connected to the remaining ports. Communication can be performed while keeping the intensity of the optical signal between the three optical fibers constant.

  A star network is configured using the optical branch circuit described above. FIG. 23 shows a star network composed of each port of the NxN mesh type optical branch circuit 101 and terminals 102a to 102e connected via one-core optical fiber. The terminal 102 incorporates a conventional single-core type optical transceiver element. According to this configuration, all terminals can communicate with each other with a simple configuration.

  FIG. 24 shows an unequal distribution star network. Like the tap circuit shown in FIG. 13, a star network is configured around the unequal distribution type optical branch circuit 104. An upper network 105 is connected to the main port, and the terminal 102 is connected to the slave port. In this way, it is possible to flexibly configure a communication network that can communicate with each other by connecting not only terminals but also other network components such as connection devices for connecting other networks and heterogeneous networks. can do.

  Next, the chain network will be described. An optical circuit in which the wave transmission medium and the optical transmission / reception element shown in FIG. In the chain network shown in FIG. 25, optical circuits 111a to 111f using 3 × 3 mesh type optical branch circuits or unequal distribution type optical branch circuits are connected in cascade, and terminals 112a to 112f are connected to ports of the respective optical circuits. . Terminators 113a and 113b are connected to the optical fibers at both ends to suppress reflection of the optical signal. By connecting terminals using the optical circuit shown in FIG. 20A, a network can be configured with a simple configuration, and all terminals can communicate with each other.

  FIG. 26 shows a loss compensation chain type network. The optical circuit combining the wave transmission medium, the optical transmitting / receiving element, and the amplifying element shown in FIG. 20B is applied. In the chain network shown in FIG. 26, optical circuits 114a to 114l are connected in cascade, and terminals 112a to 112l are connected to ports of the respective optical circuits. Terminators 113a and 113b are connected to the optical fibers at both ends to suppress reflection of the optical signal. Since the intensity of the optical signal can be kept constant irrespective of the position of the terminal, a larger-scale network can be configured as compared with the network shown in FIG.

  Finally, a hierarchical network will be described with reference to FIG. The chain type network shown in FIG. 25 or FIG. 26 is connected by the 3 × 3 mesh type optical branch circuits 121a and 121b or the 4 × 4 mesh type optical branch circuit 122 to form a hierarchical network. The optical branch circuit shown in FIG. 27 is a loss compensation optical circuit to which an amplifying element is connected. All terminals can communicate with each other, and a network that can be easily structured hierarchically can be constructed. Further, by providing the amplifying element, the intensity of the optical signal can be kept constant, and a highly scalable network can be obtained.

  An integrated network as shown in FIG. 28 can be constructed by combining the above-described N × N mesh optical branch circuit, star network, chain network, and the like. As described in the seventh embodiment, by connecting various network components via the optical branch circuit according to the present invention, a communication network capable of mutual communication can be flexibly configured.

It is a figure which shows the structure of the conventional Y branch circuit and a directional coupler. It is a figure which shows the structure of the conventional 1xN branch circuit and a NxM directional coupler. It is a figure which shows the structure of the conventional MMI directional coupler. It is a figure which shows the structure of the 3x3 mesh type | mold optical branch circuit which combined three Y branch circuits. It is a figure which shows the structure of the 4x4 mesh type | mold optical branch circuit which combined four MMI directional couplers. It is a figure for demonstrating the basic structure of a wave transmission medium. It is a flowchart which shows the calculation procedure for determining the spatial refractive index distribution of a wave transmission medium. It is a figure which shows the refractive index distribution of the wave transmission medium applied to an optical multiplexer / demultiplexer. It is a schematic diagram showing a 4x4 mesh type optical branch circuit according to an embodiment of the present invention. It is a figure which shows the logic network of a 4x4 mesh type | mold optical branch circuit. It is a logical network diagram in which the traveling direction of the optical signal is indicated by a subscript. It is a schematic diagram showing a 3 × 3 mesh type optical branch circuit according to an embodiment of the present invention. It is a mimetic diagram showing a 3 port tap circuit concerning one embodiment of the present invention. It is a figure which shows the logic network of a 3 port tap circuit. It is a figure which shows the relationship between the setting value of reflected output intensity, and a tap rate. It is a mimetic diagram showing a 4 port tap circuit concerning one embodiment of the present invention. It is a figure which shows the setting value of the tap rate of a 4-port tap circuit. It is a schematic diagram which shows the tap circuit from which the port to tap differs according to the advancing direction of an optical signal. It is a schematic diagram which shows the optical branch circuit which combined the wave transmission medium and the amplification element. It is a figure which shows the 1st example of the optical circuit which combined the optical transmission / reception element. It is a figure which shows the 2nd example of the optical circuit which combined the optical transmission / reception element. It is a figure which shows the 3rd example of the optical circuit which combined the optical transmission / reception element. It is a figure which shows the star type network comprised using the optical branch circuit. It is a figure which shows an unequal distribution star type | mold network. It is a figure which shows the chain type network comprised using the optical branch circuit. It is a figure which shows a loss compensation chain type | mold network. It is a figure which shows the hierarchical network comprised using the optical branch circuit. It is a figure which shows the integrated network comprised using the optical branch circuit.

Explanation of symbols

51, 53 Wave transmission medium 52, 54, 63, 74, 84 Amplifying element 61, 71, 121 3x3 mesh type optical branching circuit 62, 85 Optical transmitting / receiving element 72, 82 Optical transmitting element 73, 83 Optical receiving element 81, 122 4x4 Mesh-type optical branch circuit 101 NxN mesh-type optical branch circuit 102, 112 Terminal 104 Unequally distributed optical branch circuit 105 Upper network 111 Optical circuit 113 Terminator

Claims (8)

Due to the refractive index of each of the virtual pixels defined by the virtual mesh, the optical signal incident from one of the three or more ports is branched while being scattered multiple times and emitted from the other ports. An optical branching circuit comprising a waveguide circuit configured by two-dimensionally arranging a wave transmission medium in which a spatial refractive index distribution determined as described above is formed,
The spatial refractive index distribution is characterized in that the phase of the optical signal at the port is set so that the optical signals emitted from the other ports are vector-orthogonal to each other. Branch circuit. Due to the refractive index of each of the virtual pixels defined by the virtual mesh, the optical signal incident from one of the three or more ports is branched while being scattered multiple times and emitted from the other ports. An optical branching circuit comprising a waveguide circuit configured by two-dimensionally arranging a wave transmission medium in which a spatial refractive index distribution determined as described above is formed,
The spatial refractive index distribution is such that when the phase of the optical signal at the port cannot be set so that the optical signals emitted from the other ports are vector orthogonal to each other, An optical branching circuit characterized in that a phase is set so as to minimize the overlap integral of each optical signal field.   3. The optical branch circuit according to claim 1, wherein branching ratios from the one port to the other port are different from each other.   The optical branch circuit according to claim 1, wherein an amplification element is connected to each of the ports.   5. The optical branch circuit according to claim 4, wherein the amplification factor of the amplification element is set such that the light intensity at the one port and the light intensity at the other port are constant. An optical branch circuit according to any one of claims 1 to 5,
An optical transmission / reception circuit comprising: an optical transmission / reception element connected to the one port of the optical branching circuit and transmitting / receiving optical signals to / from each of the other ports. An optical branch circuit according to any one of claims 1 to 5,
A network component connected to each port of the optical branch circuit,
An optical network, wherein the network components are configured to transmit and receive optical signals to and from each other.   A plurality of network components connected to the optical branch circuit according to any one of claims 1 to 5 are configured by connecting each of one port of the optical branch circuit and connecting them in cascade. And optical network.

Images