JP2005250270A - Star coupler and optical integrated circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a star coupler in which variations in branching ratios of outputs is improved and losses are suppressed. <P>SOLUTION: In the star coupler, a plurality of input-side branch waveguides 5 are formed at one end of a main waveguide 4 and a plurality of output-side waveguides 6 are formed at another side of the main waveguide 4. Shape of waveguides are set so that the minimum radius of curvature in curved parts constituting the input-side branch waveguides 5 becomes smaller than the minimum radius of curvature in curved parts constituting the output-side branch waveguides 6 and each input-side branch waveguide 5 excites light of a higher-order mode from light of a lower-order mode. Moreover, respective output-side branch waveguides 6 propagate light of the higher-order mode excited in each input-side branch waveguide 5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a star coupler and an optical integrated circuit that include a plurality of input-side branch waveguides at one end of a main waveguide and a plurality of output-side branch waveguides at the other end to branch an optical signal into a plurality of branches. Specifically, by exciting the higher-order mode light in the input-side branch waveguide and allowing the output-side branch waveguide to propagate without emitting the higher-order mode light, This suppresses variation in the branching ratio and suppresses loss in each output-side branching waveguide.

  As the branching waveguide of the conventional optical waveguide type multi-mode optical star coupler, one having a constant width from the start point to the end point is used. In general, the star coupler has a problem that the branching ratio of the output becomes worse as the light enters from the outer input port.

  In order to improve the variation in the branching ratio, a waveguide is proposed in which the branching waveguide is tapered from the start point to the end point (see, for example, Patent Document 1).

Japanese Patent No. 3269505

  In the star coupler, a curved portion exists in the branching waveguide, and the curvature of the curved portion is related to the loss. The conventional star coupler is designed so that the input and output branch waveguides are symmetrical, and the minimum radius of curvature is as large as possible so that the loss at the curved portion is reduced.

  When the waveguide is tapered, the loss in the waveguide depends on the taper amount and the curvature. Therefore, when one parameter is changed, the optimum value of the other is changed accordingly. This makes it difficult to design.

  In addition, because the input and output branch waveguides are symmetrical, when the waveguide modes are different between the two branch waveguides, the curvature and taper amount are designed according to the part where higher order modes are propagated. The waveguide length becomes longer.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a star coupler and an optical integrated circuit that solve such problems, improve the variation of the output branching ratio, and suppress the loss.

  In order to solve the above-described problems, a star coupler according to the present invention is a star coupler having an optical circuit in which both ends of a main waveguide are divided into a plurality of branch waveguides, and the branch waveguide is formed at one end of the main waveguide. A plurality of input-side branch waveguides each having a curved portion and a plurality of output-side branch waveguides each formed at the other end of the main waveguide, each having a curved portion. A high-order mode excitation means is provided for exciting light of a higher-order mode from light of a lower-order mode, and the output-side branch waveguide is a high-order light that propagates light of a higher-order mode pumped by the input-side branch waveguide. Next mode propagation means is provided.

  An optical integrated circuit according to the present invention includes a star coupler in which a plurality of input-side branch waveguides are formed at one end of a main waveguide and a plurality of output-side branch waveguides at the other end, and a plurality of input-side branch waveguides A plurality of light emitting elements disposed opposite to the input ports formed on the plurality of light receiving elements, and a plurality of light receiving elements disposed opposite to the output ports formed respectively on the plurality of output side branch waveguides. The side branch waveguide includes high-order mode excitation means for exciting light of a higher order mode from light of a lower order mode, and the output-side branch waveguide is a high-order mode excited by the input-side branch waveguide. Higher order mode propagation means for propagating light is provided.

  According to the star coupler and the optical integrated circuit of the present invention, the light input to the input-side branching waveguide is excited from the low-order mode to the high-order mode as the propagation mode and is input to the main waveguide.

  For example, by setting the waveguide shape so that the minimum curvature radius in the curved portion constituting the input side branching waveguide is smaller than the minimum curvature radius in the curved portion constituting the output side branching waveguide, High-order mode light is excited from low-order mode light input to the input-side branching waveguide.

  The light input to the main waveguide is branched into each output-side branch waveguide and propagated through each output-side branch waveguide. For example, since the minimum curvature radius of the curved portion of the output-side branching waveguide is larger than that on the input side, the higher-order mode light excited by the input-side branching waveguide is propagated without being emitted.

  Further, even when the relative refractive index difference of the output side branching waveguide is made larger than that of the input side branching waveguide, the high-order mode light excited in the input side branching waveguide is propagated without being emitted.

  In the star coupler of the present invention, each output-side branch is formed by exciting higher-order mode light in the input-side branch waveguide and allowing the output-side branch waveguide to propagate without emitting higher-order mode light. Variation in the branching ratio to the waveguide is suppressed. Moreover, the loss in each output side branching waveguide can be suppressed.

  This makes it possible to optimize the waveguide length, the branching ratio, and the loss in accordance with the mode excited on the input side. Accordingly, it is possible to manufacture a multi-branch multi-mode optical star coupler having characteristics according to the application location with good yield.

  In the optical integrated circuit of the present invention, by using the above-described star coupler, the reliability of the multimode optical communication system can be improved and an inexpensive system can be constructed.

  Hereinafter, embodiments of a star coupler and an optical integrated circuit according to the present invention will be described with reference to the drawings. In addition, embodiment illustrated below demonstrates concretely and does not limit the embodiment and invention range of this invention.

<First Embodiment of Star Coupler>
FIG. 1 is a plan view showing a configuration example of the star coupler according to the first embodiment. The star coupler 1a according to the first embodiment is a planar optical waveguide having a core 2 and a clad 3 having a refractive index lower than that of the core 2, and a main waveguide 4, an input side branching waveguide 5 and an output constituting the core 2. An optical circuit capable of coupling and branching optical signals is formed by the side branching waveguide 6. In FIG. 1, the relationship between the dimensions of each part, such as the aspect ratio of the star coupler 1a, is not accurate.

  The main waveguide 4 has a uniform width, a plurality of input-side branch waveguides 5 (1) to 5 (6) are formed at one end, and a plurality of output-side branch waveguides 6 (1) at the other end. ~ 6 (6) are formed. The number of the input side branching waveguides 5 and the number of the output side branching waveguides 6 is arbitrary, but in the star coupler 1a of the first embodiment, description will be made assuming that each is six.

  Each of the input-side branching waveguides 5 (1) to 5 (6) has a uniform width, and an input port 5a is formed at each end, and each of the output-side branching waveguides 6 (1) to 6 (6). ) Also have a uniform width, and an output port 6a is formed at each end.

  Each of the input side branching waveguides 5 (1) to 5 (6) is configured as a curved waveguide having a curved portion, and gathers in the main waveguide 4. Each output-side branching waveguide 6 (1) to 6 (6) is also configured as a curved waveguide having a curved portion and branches from the main waveguide 4.

  In the star coupler 1a of the first embodiment, each of the input side branch waveguides 5 (1) to 5 (6) and each of the output side branch waveguides 6 (1) to 6 (6) has a uniform curvature. A curved waveguide is formed by combining circular arcs having radii.

  Further, the input-side branching waveguides 5 (1) to 5 (6) include high-order mode excitation means for exciting a higher-order mode as a light propagation mode, and output-side branching waveguides 6 (1) to 6 ( 6) includes high-order mode propagation means for propagating high-order mode light.

  Specifically, in the star coupler 1a of the first embodiment, the high-order mode excitation means and the high-order mode propagation means have different curvature radii between the input-side branch waveguide 5 and the output-side branch waveguide 6, The input-side branch waveguide 5 and the output-side branch waveguide 6 are asymmetrical.

  That is, the radius of curvature of the arc that forms the input side branching waveguides 5 (1) to 5 (6) is configured to be smaller than the radius of curvature of the arc that forms the output side branching waveguides 6 (1) to 6 (6). .

  As a result, the input-side branching waveguides 5 (1) to 5 (6) are bent waveguides having a small radius of curvature, and the discontinuity at the portion where the arcs are combined is increased. In the waveguides 5 (1) to 5 (6), a high-order mode is excited from a low-order mode as a propagation mode of light input from the input port 5a.

  Whichever light propagates through the input-side branching waveguides 5 (1) to 5 (6), it is branched from the main waveguide 4 to each of the output-side branching waveguides 6 (1) to 6 (6). However, when a higher-order mode is excited as a light propagation mode in the input-side branching waveguides 5 (1) to 5 (6), the output-side branching waveguides 6 (1) to 6 (6) are connected to each other. Variation in branching ratio is suppressed.

  Further, by making the radius of curvature of the output-side branch waveguide 6 larger than the radius of curvature of the input-side branch waveguide 5, the higher-order mode light excited by the input-side branch waveguide 5 is output from the output-side branch waveguide 6. Propagated to the output port 6a without being emitted.

  Next, specific examples of the shapes of the input side branching waveguide 5 and the output side branching waveguide 6 in the star coupler 1a of the first embodiment will be described.

  When the extending direction of the main waveguide 4 is the X axis, orthogonal to the X axis, and the direction in which the branched waveguides are arranged is the Y axis, the input ports 5a of the input side branched waveguides 5 (1) to 5 (6) are Are arranged in a line at equal intervals in the Y-axis direction. Similarly, the output ports 6a of the output-side branching waveguides 6 (1) to 6 (6) are arranged in a line at equal intervals in the Y-axis direction at the same pitch as the input ports 5a.

  The input side branch waveguides 5 (1) to 5 (3) and the input side branch waveguides 5 (4) to 5 (6) are symmetrical with respect to the X axis, and the output side branch waveguide 6 (1). ) To 6 (3) and the output side branching waveguides 6 (4) to 6 (6) have symmetrical shapes with respect to the X axis.

  That is, the outermost input side branch waveguide 5 (1) and the input side branch waveguide 5 (6) have the same shape, and the inner side input side branch waveguide 5 (2) and the input side branch waveguide 5 (5) has the same shape, and the innermost input side branching waveguide 5 (3) and the input side branching waveguide 5 (4) have the same shape.

  Similarly, the outermost output side branch waveguide 6 (1) and the output side branch waveguide 6 (6) have the same shape, and the output side branch waveguide 6 (2) and the output side branch waveguide inside thereof. 6 (5) has the same shape, and the innermost output side branch waveguide 6 (3) and the output side branch waveguide 6 (4) have the same shape.

  In the input-side branching waveguide 5 and the output-side branching waveguide 6, the outermost branching waveguides are each composed of a combination of arcs having the smallest radius of curvature, and the inner branching waveguide has a larger radius of curvature. Consists of

  As described above, the input-side branching waveguides 5 (1) to 5 (3) and the input-side branching waveguides 5 (4) to 5 (6) have a symmetrical shape. The relationship of the curvature radius of the branch waveguide located inside will be described using the input-side branch waveguides 5 (1) to 5 (3).

  In the input side branching waveguide 5, the radius of the outermost input side branching waveguide 5 (1) is R1 (1), the radius of the input side branching waveguide 5 (2) inside thereof is R1 (2), and the innermost side. R1 (1) <R1 (2) <R1 (3) where R1 (3) is the radius of the input side branching waveguide 5 (3). The output side branching waveguide 6 has the same configuration.

  Next, in the star coupler 1a of the first embodiment, a specific example of a configuration in which the curvature radius of the input-side branch waveguide 5 is reduced and the curvature radius of the output-side branch waveguide 6 is increased will be described.

  In order to make the radius of curvature different between the input-side branch waveguide and the output-side branch waveguide constituted by the curved waveguide, for example, the length of the input-side branch waveguide 5 from the length L1 in the X-axis direction can be changed. The length L2 in the X-axis direction is increased.

  As described above, in the star coupler 1a of the first embodiment, the number of the input side branching waveguides 5 and the number of the output side branching waveguides 6 are the same, and the pitches of the input ports 5a and the output ports 6a are also the same. Therefore, the input side branching waveguide 5 and the output side branching waveguide 6 are in a one-to-one correspondence.

  Accordingly, when L1 <L2, when the corresponding channels in the input side and output side branch waveguides, for example, the outermost branch waveguides, are compared, the arc constituting the input side branch waveguide 5 (1) The radius R2 (1) of the arc that forms the output-side branching waveguide 6 (1) is larger than the radius R1 (1).

  Similarly, when the input side branch waveguide 5 (2) and the output side branch waveguide 6 (2) corresponding to the input side branch waveguide 5 (2) are compared, the input side branch waveguide 5 (2). The radius of the arc constituting the output-side branching waveguide 6 (2) is larger than the radius of the arc constituting the arc.

  Furthermore, when comparing the innermost input side branching waveguide 5 (3) with the output side branching waveguide 6 (3) corresponding to the input side branching waveguide 5 (3), the input side branching waveguide 5 ( The radius of the arc constituting the output-side branching waveguide 6 (3) is larger than the radius of the arc constituting 3).

  The input side branch waveguides 5 (4) to 5 (6) and the output side branch waveguides 6 (4) to 6 (6) have the same configuration.

  Next, a simulation example that demonstrates the effect of the star coupler 1a of the first embodiment will be described.

  FIG. 2 is a simulation showing the relationship between the radius of curvature and the output optical power in the input-side branching waveguide. 2A shows a case where the radius of curvature is large, and FIG. 2B shows a case where the radius of curvature is small. Each of the simulated waveguide shapes and optical power graphs are shown side by side.

  Here, in the graph, the total power of light output from the input-side branching waveguide configured as a curved waveguide as described in FIG. 1 is indicated by a solid line, and the power of the basic mode (0th-order mode) is indicated by a broken line. ing. Note that the optical power of the higher-order mode output from the input-side branching waveguide is represented by the difference between the total power and the fundamental mode power.

  Assuming that the total power of light output from the input-side branching waveguide is “1”, the power of the fundamental mode is about 0.6 in FIG. It becomes the power of.

  On the other hand, in FIG. 2B where the radius of curvature is smaller than the example of FIG. 2A, the power of the fundamental mode is about 0.4, so the remaining about 0.6 is the power of the higher-order mode. Become. Therefore, it can be seen that the higher-order mode light is excited in the bent waveguide having a smaller radius of curvature.

  From the result of the simulation described with reference to FIG. 2, in the star coupler 1a of the first embodiment described with reference to FIG. Will be excited.

  When high-order mode light is excited in the input-side branching waveguide 5, the variation in the branching ratio from the main waveguide 4 to each of the output-side branching waveguides 6 (1) to 6 (6) can be suppressed. Variations in optical power output from the output port 6a can be suppressed.

  FIG. 3 is a simulation showing the relationship between the radius of curvature of the input side branch waveguide and the output side branch waveguide and the output optical power. FIG. 3A shows a symmetric star coupler in which the curvature radius is the same between the input side branch waveguide and the output side branch waveguide. FIG. 3B shows the input side branch waveguide as shown in FIG. The case of an asymmetric star coupler in which the curvature radius of the output-side branching waveguide is increased is shown, and the simulated waveguide shape and optical power graph are shown side by side. In FIG. 3, light leakage is shown by the degree of unevenness of the waveguide shape.

  Here, the number of star couplers to be simulated is four for both the input-side branch waveguide and the output-side branch waveguide, and light enters from the outermost input-side branch waveguide. The graph shows the power of light output from the output port of each output-side branching waveguide when the input light power is “1”.

  In FIG. 3A, there is light leakage (radiation) in the outer output side branch waveguide, and the optical power is reduced due to loss. In contrast, in FIG. 3B in which the radius of curvature of the output-side branch waveguide is larger than that of the input-side branch waveguide, light emission in the output-side branch waveguide is suppressed, and a decrease in optical power is suppressed. ing. Therefore, it can be seen that if the radius of curvature of the output side branch waveguide is made larger than that of the input side branch waveguide, loss due to radiation in the output side branch waveguide can be suppressed.

  From the result of the simulation described in FIG. 3, in the star coupler 1 a of the first embodiment described in FIG. 1, the output-side branch waveguide 6 is configured from the radius of curvature of the arc configuring the input-side branch waveguide 5. Since the radius of curvature of the arc to be increased is increased, loss due to radiation in the output-side branching waveguide 6 can be suppressed.

  Thereby, it is possible to suppress a decrease in optical power output from each output port 6a with respect to light incident from the input port 5a.

  In the star coupler 1a shown in FIG. 1, the radius of curvature increases toward the inner branch waveguide. For this reason, it is arranged on the outermost side in the output side branching waveguide 6 with respect to the radius R1 (3) of the input side branching waveguide 5 (3) arranged on the innermost side in the input side branching waveguide 5. The output side branch waveguide 6 (1) has a smaller radius R2 (1).

  In contrast, the radius R2 (1) of the output side branch waveguide 6 (1) is larger than the radius R1 (3) of the input side branch waveguide 5 (3). A relationship or the like may be set. By setting it as such a shape, the loss by radiation | emission in the output side branch waveguide 6 can be suppressed more.

  In addition, in the input-side branching waveguide 5, the shape of the inner input-side branching waveguide is such that the radius of curvature becomes small, so that the light incident from any of the input-side branching waveguides 5 has a branching ratio. Variation can be further suppressed.

<Second Embodiment of Star Coupler>
FIG. 4 is a plan view showing a configuration example of the star coupler according to the second embodiment. In the star coupler 1b of the second embodiment, the input side branch waveguide 5 and the output side branch waveguide 6 constituting the core 2 are configured as bent waveguides, and the input side branch waveguide 5 and the output side branch waveguide are formed. The waveguide 6 is provided with a refractive index adjusting means for making the refractive index (referred to as a relative refractive index difference) different from that of the clad 3.

  Each of the input-side branching waveguides 5 (1) to 5 (6) and each of the output-side branching waveguides 6 (1) to 6 (6) is configured as a bending waveguide in which arcs having uniform radii of curvature are combined. Is done.

  In the input-side branching waveguide 5 and the output-side branching waveguide 6, the outermost branching waveguides are each composed of a combination of arcs having the smallest radius of curvature, and the inner branching waveguide has a larger radius of curvature. Consists of

  The length L1 in the X-axis direction of the input-side branch waveguide 5 is equal to the length L2 in the X-axis direction of the output-side branch waveguide 6, and the input-side branch waveguide 5 and the output-side branch waveguide 6 are symmetric. Any shape can be used.

  The refractive index adjusting means for making the relative refractive index difference different between the input side branched waveguide 5 and the output side branched waveguide 6 includes, for example, a configuration in which a voltage is applied to the core 2 at a portion where the relative refractive index difference is desired to be changed.

  For this reason, in the star coupler 1b of the second embodiment, for example, the electrode 7 is provided with the output-side branching waveguide 6 interposed therebetween. Then, the relative refractive index difference of the output side branching waveguide 6 is changed using the electro-optic effect to be larger than the relative refractive index difference of the input side branching waveguide 5.

  Here, as described above, in the output-side branch waveguide 6, the outermost output-side branch waveguides 6 (1) and 6 (6) have the smallest radius of curvature, and thus the outermost output-side branch waveguide 6 In (1) and 6 (6), loss due to radiation is likely to occur.

  Therefore, the maximum relative refractive index difference Δnout of the outermost output side branching waveguides 6 (1) and 6 (6) is the maximum relative refractive index of the outermost input side branching waveguides 5 (1) and 5 (6). It is configured to be larger than the rate difference Δnin. Here, the maximum relative refractive index difference is a case where the relative refractive index difference is not uniform.

  In FIG. 4, an electrode 7 is provided so that a voltage can be applied to all the output-side branching waveguides 6, but the outermost output-side branching waveguides 6 (1) and 6 (6) have a loss due to radiation. Since the configuration is likely to occur, an electrode 7 may be provided so that a voltage can be applied to the output-side branching waveguide 6 positioned outside.

  For example, if the number of output-side branching waveguides 6 is about six as shown in FIG. 4, the electrode 7 is provided so that a voltage can be applied to the outermost output-side branching waveguides 6 (1), 6 (6). You may prepare. Although not shown, when the number of output-side branching waveguides 6 is large, an electrode 7 may be provided so that a voltage can be applied to a plurality of outer output-side branching waveguides 6.

  In the star coupler 1b of the second embodiment configured as described above, the relative refractive index difference of the output side branching waveguide 6 is made larger than the relative refractive index difference of the input side branching waveguide 5, whereby the output side In the branching waveguide 6, light confinement becomes strong.

  When the curvature radius of the input-side branching waveguide 5 is reduced, higher-order mode light is excited. As described above, by strengthening the light confinement in the output-side branching waveguide 6, the input-side branching waveguide 5 is excited. The higher-order mode light pumped at 5 can be propagated without being radiated by the output side branch waveguides 6 (1) to 6 (6).

  As a result, the input-side branching waveguide 5 is configured as a curved waveguide with a small radius of curvature, so that the input-side branching waveguide 5 excites high-order mode light and the main waveguide 4 outputs each output-side branching waveguide. Variation in the branching ratio to 6 (1) to 6 (6) can be suppressed.

  In addition, it is possible to propagate high-order mode light excited by the input-side branching waveguide 5 without radiating it from the output-side branching waveguide 6, thereby suppressing loss.

  In addition, since the relative refractive index difference is changed using the thermo-optic effect as a configuration in which the relative refractive index difference is different between the input side branched waveguide 5 and the output side branched waveguide 6, the relative refractive index difference is changed. For example, a thin film heater that performs temperature control of the core 2 may be provided.

Alternatively, the waveguide material may be partially changed by adding germania (GeO ₂ ) or the like to a part of the core 2.

  Further, in FIG. 4, a symmetric star coupler in which the length L1 in the X-axis direction of the input-side branching waveguide 5 and the length L2 in the X-axis direction of the output-side branching waveguide 6 are equal is used. Similarly to the star coupler 1a of the form, an asymmetric star coupler in which L1 <L2 may be used in order to reduce the radius of curvature of the input-side branch waveguide 5 and increase the radius of curvature of the output-side branch waveguide 6.

<Third embodiment of star coupler>
FIG. 5 is a plan view showing a configuration example of the star coupler according to the third embodiment. In the star coupler 1c of the third embodiment, a plurality of input side branching waveguides 5 are formed at one end of the main waveguide 4 having a uniform width, and the same number of output side branching waveguides 6 are formed at the other end. It is a configuration. The input-side branching waveguides 5 (1) to 5 (6) and the output-side branching waveguides 6 (1) to 6 (6) are S-shaped waveguides whose radii of curvature are changed sinusoidally. It is.

  Even when the input-side branching waveguide 5 and the output-side branching waveguide 6 are S-shaped waveguides, by setting L1 <L2, the minimum curvature radius Rin of the curved portion constituting the input-side branching waveguide 5 is The minimum curvature radius Rout of the curved portion constituting the output-side branching waveguide 6 becomes smaller, and the maximum change rate of the curvature on the input side becomes larger than that on the output side. Thereby, the effect of the present invention can be obtained in the same way as the star coupler 2a of the first embodiment.

  Further, by applying the second embodiment, the configuration in which the maximum relative refractive index difference Δnout of the output side branch waveguide 6 is larger than the maximum relative refractive index difference Δnin of the input side branch waveguide 5 is equivalent. The effect of can be obtained. In this case, the input-side branch waveguide 5 and the output-side branch waveguide 6 may have a symmetrical shape, or the output-side branch waveguide 6 may have a large curvature radius.

  Furthermore, the curved portions constituting the input-side branching waveguide 5 and the output-side branching waveguide 6 are not limited to sinusoidal shapes, and can be replaced with higher-order curves or the like.

<Fourth embodiment of star coupler>
FIG. 6 is a plan view showing a configuration example of the star coupler according to the fourth embodiment. In the star coupler 1d of the fourth embodiment, a plurality of input-side branch waveguides 5 are formed at one end of a main waveguide 4 having a uniform width, and the same number of output-side branch waveguides 6 are formed at the other end. It is a configuration. And the shape when the input port 5a and the output port 6a are not arranged at equal intervals, or when not arranged in a line in the Y-axis direction is shown.

  In this case, the channels corresponding to each other at the input side and output side branching waveguides, for example, the minimum radius of curvature Rin of the curved portion constituting the input side branching waveguide 5 (1), the output side branching waveguide 6 (1). The length in the X-axis direction of the output-side branch waveguide 6 (1) is made longer than the length in the X-axis direction of the input-side branch waveguide 5 (1) so as to be smaller than the minimum curvature radius Rout of the curved portion constituting the structure. To do.

  Alternatively, the maximum relative refractive index difference Δnout of the output side branch waveguide 6 (1) is larger than the maximum relative refractive index difference Δnin of the input side branch waveguide 5 (1). Furthermore, it is set as the structure which combined both.

  Thereby, the effect of this invention can be acquired similarly to 1st Embodiment or 2nd Embodiment.

<Fifth embodiment of star coupler>
FIG. 7 is a plan view showing a configuration example of the star coupler according to the fifth embodiment. In the star coupler 1e of the fifth embodiment, the first branch waveguide is formed at both ends of the main waveguide 4 having a uniform width, and the first branch waveguide is further divided into a plurality of second branches. A waveguide is formed, and a branching waveguide is formed by dividing the waveguide until a certain number of channels is reached.

  That is, a first input-side branch waveguide 51 is formed at one end of the main waveguide 4, the first input-side branch waveguide 51 is further divided into a plurality of parts, and a second input-side branch waveguide 52 is formed. Further, the input side branching waveguide 5 is formed by being divided until reaching a certain number of channels.

  In addition, a first output-side branch waveguide 61 is formed at the other end of the main waveguide 4, and the first output-side branch waveguide 61 is further divided into a plurality of parts to form a second output-side branch waveguide 62. The output side branching waveguide 6 is formed by dividing until the same number of channels as the input side is reached.

  With the above configuration, the curved portions of the portions that are symmetric with respect to the main waveguide 4 are compared, and the conditions of the first embodiment to the fourth embodiment described above are compared in each portion or some portions. By adopting a configuration that satisfies at least one of them, an equivalent effect can be obtained.

  FIG. 7A shows a 4 × 4 star coupler, and the comparison radius A and the comparison radius B are compared when the curvature radii of the curved portions of the branched waveguides on the input side and the output side are compared. The minimum curvature radius of the side branch waveguide is configured to be smaller than the minimum curvature radius of the output side branch waveguide. With the above configuration, the effect of the present invention can be obtained.

  FIG. 7B is a model diagram of a 16 × 16 star coupler produced in the same way. In FIG. 7, the number of branches at the branching point of the branching waveguide is fixed to 2, but the branching may be performed with other numbers of branches.

<Sixth Embodiment of Star Coupler>
FIG. 8 is a plan view showing a configuration example of the star coupler according to the sixth embodiment. In the star coupler 1f of the sixth embodiment, a plurality of branch waveguides are formed at one end of the main waveguide 4 having a uniform width, and the first branch waveguide is formed at the other end. In this configuration, the first branching waveguide is further divided into a plurality of parts to form a second branching waveguide, and the branching waveguide is formed by dividing the first branching waveguide until reaching a certain number of channels.

  For example, a first input-side branch waveguide 51 is formed at one end of the main waveguide 4, and the first input-side branch waveguide 51 is further divided into a plurality of parts to form a second input-side branch waveguide 52. The input side branching waveguide 5 is formed. A plurality of output side branching waveguides 6 are formed at the other end of the main waveguide 4.

  With the above configuration, when comparing the outermost waveguide of the input-side branch waveguide and the output-side branch waveguide, the minimum curvature radius Rin of the curved portion constituting the input-side branch waveguide is the output-side branch waveguide. Is configured to be smaller than the minimum radius of curvature Rout of the curved portion constituting the.

  Alternatively, the maximum relative refractive index difference Δnout of the output side branch waveguide is larger than the maximum relative refractive index difference Δnin of the input side branch waveguide.

  Alternatively, the configuration is such that the number of curvature discontinuities in the input-side branch waveguide is greater than the number of curvature discontinuities in the output-side branch waveguide.

  Alternatively, the maximum curvature change rate of the input side branch waveguide is set to be larger than the maximum curvature change rate of the output side branch waveguide.

  By configuring so as to satisfy at least one of the above conditions, the effect of the present invention can be obtained.

  In the star coupler 1f of the sixth embodiment, the relationship between the input and output branch waveguides may be reversed, but with the configuration of FIG. 8, the number of curvature discontinuities in the input side branch waveguide 5 is This is preferable because it is larger than the output side.

<Seventh Embodiment of Star Coupler>
FIG. 9 is a perspective view showing a configuration example of the star coupler according to the seventh embodiment. The star coupler 1g of the seventh embodiment is made of a film-like flexible material. Although the waveguide shape is schematically illustrated, a plurality of input side branching waveguides 5 are formed at one end of the main waveguide 4 and the same number of output side branching waveguides 6 are formed at the other end.

  The input-side branch waveguide 5 and the output-side branch waveguide 6 are configured so that the loss at the input / output port is as small as possible by increasing the radius of curvature or by gently changing the curvature.

  When the star coupler 1g is used, a roller 8 as an example of a bending means is abutted against a portion where the input side branching waveguide 5 is formed, and a portion where the input side branching waveguide 5 of the star coupler 1g is formed is in the thickness direction. Bend to. FIG. 9A shows an example of bending with one roller 8, and FIG. 9B shows an example of bending with two rollers 8.

  Even by bending the portion of the star coupler 1g where the input-side branch waveguide 5 is formed in the thickness direction, the input-side branch waveguide 5 excites high-order mode light, and the main waveguide 4 outputs each output-side branch waveguide 6. Variation in the branching ratio can be suppressed.

  In addition, the output-side branching waveguide 6 can propagate without emitting higher-order mode light by a configuration such as increasing the radius of curvature, and loss can be suppressed.

  Furthermore, an optimum shape can be found by adjusting the pressing position and pressing force of the roller 8 while monitoring the output, or by changing the curvature of the roller 8.

  In addition, as a structure of each waveguide of the star coupler 1g of 7th Embodiment, it is also possible to acquire an effect in combination with 1st Embodiment-6th Embodiment.

  As described above, in the star coupler of the present invention, the main waveguide 4 is provided with a plurality of input-side branching waveguides 5 composed of curved waveguides at one end and a plurality of outputs composed of curved waveguides at the other end. A side branching waveguide 6 is provided.

  The minimum curvature radius Rin of the curved portion constituting the input side branching waveguide 5 is set to be smaller than the minimum curvature radius Rout of the curved portion constituting the output side branching waveguide 6.

  Alternatively, the maximum relative refractive index difference Δnout of the output side branch waveguide 6 is larger than the maximum relative refractive index difference Δnin of the input side branch waveguide 5.

  Alternatively, the configuration is such that the number of curvature discontinuities in the input side branching waveguide 5 is larger than the number of curvature discontinuities in the output side branching waveguide 6.

  Alternatively, the maximum curvature change rate of the input-side branch waveguide 5 is set to be larger than the maximum curvature change rate of the output-side branch waveguide 6.

  By configuring so as to satisfy at least one of the above conditions, the effect of the present invention can be obtained.

<Embodiment of optical integrated circuit>
FIG. 10 shows a configuration example of the optical integrated circuit of the present embodiment. FIG. 10A is a plan view and FIG. 10B is a side view.

  The optical integrated circuit 11 of this embodiment includes a mounting substrate 12 and a star coupler 13 having the waveguide structure described with reference to FIG. In this example, the star coupler 13 includes the main waveguide 4, the input side branch waveguide 5, and the output side branch waveguide 6 described in FIG.

  The star coupler 13 is made of a quartz-based material, a polymer organic compound-based material, or the like, and includes inclined end surfaces 14 at both ends. The inclined end surface 14 is inclined at an angle of 45 degrees, for example. The input port 5a of each input side branching waveguide 5 is exposed to one inclined end face 14 to form a reflection surface. Further, the output port 6a of each output-side branching waveguide 6 is exposed to the other inclined end face 14 to form a reflection surface.

  The mounting substrate 12 includes a plurality of surface emitting semiconductor lasers (VCSEL) 15 as light emitting elements and a plurality of photodiodes (PD) 16 as light receiving elements on one surface. In the present embodiment, six surface emitting semiconductor lasers 15 are provided according to the number of input side branching waveguides 5, and six photodiodes 16 are provided according to the number of output side branching waveguides 6.

  A star coupler 13 is attached to one surface of the mounting substrate 12. Here, the input port 5a of each input side branching waveguide 5 exposed on one inclined end face 14 of the star coupler 13 and each surface emitting semiconductor laser 15 face each other, and each output side branch guide exposed on the other inclined end face 14 is exposed. The output port 6a of the waveguide 6 and the photodiode 16 face each other.

  Next, the operation of the optical integrated circuit 11 will be described. Laser light emitted from one of the plurality of surface-emitting semiconductor lasers 15 is reflected by the input port 5 a facing the surface-emitting semiconductor laser 15 and is input to the input-side branching waveguide 5.

  Since the star coupler 13 has the waveguide structure described with reference to FIG. 1, the input-side branching waveguide 5 is configured as a curved waveguide having a small curvature radius. As a result, the propagation mode of light input to the input-side branching waveguide 5 is excited from a low-order mode to a high-order mode.

  Since the light emitted from the semiconductor laser is mainly in the low-order mode, in the configuration in which the input port 5a is disposed in the immediate vicinity of the surface emitting semiconductor laser 15, the light incident on the input-side branching waveguide 5 is in the low-order mode. Is the main.

  For this reason, even if the input-side branching waveguide 5 is configured as a curved waveguide having a small curvature radius, light is propagated without being emitted in the input-side branching waveguide 5 to excite higher-order modes.

  The light propagated through the input-side branching waveguide 5 is input to the main waveguide 4 and branched to each output-side branching waveguide 6. Since light including higher-order modes is input from the input-side branching waveguide 5, variation in the branching ratio from the main waveguide 4 to each output-side branching waveguide 6 can be suppressed.

  As described with reference to FIG. 1, the output-side branching waveguide 6 is configured as a bent waveguide having a large curvature radius. Thereby, in each output side branching waveguide 6, the light of the higher mode excited by the input side branching waveguide 5 is propagated without being emitted. Light propagated through each output-side branching waveguide 6 is reflected by the output port 6 a and input to the photodiode 16.

  As described above, in the optical integrated circuit 11 of the present embodiment, 1 to N optical transmission / reception can be performed between an arbitrary surface emitting semiconductor laser 15 and each photodiode 16. And even if it is the light input from which input side branch waveguide 5, the dispersion | variation in the branch ratio to each output side branch waveguide 6 is suppressed, and the loss by radiation | emission is suppressed in each output side branch waveguide 6. , Reliability can be improved.

  In the embodiment of FIG. 11, the star coupler having the waveguide structure described with reference to FIG. 1 is used as the star coupler 13. However, the same effects can be obtained with the star couplers of the other embodiments described with reference to FIGS. Can be obtained. Moreover, the structure using the general semiconductor laser which packaged the element which light-emits from a cleavage plane as a light emitting element may be sufficient.

  The present invention can be applied to an interconnection between elements using a star coupler as a transmission means, and can enable large capacity and high speed communication.

It is a top view which shows the structural example of the star coupler of 1st Embodiment. It is a simulation which shows the relationship between the curvature radius in an input side branching waveguide, and the optical power output. It is a simulation which shows the relationship between the curvature radius of an input side branch waveguide and an output side branch waveguide, and the output optical power. It is a top view which shows the structural example of the star coupler of 2nd Embodiment. It is a top view which shows the structural example of the star coupler of 3rd Embodiment. It is a top view which shows the structural example of the star coupler of 4th Embodiment. It is a top view which shows the structural example of the star coupler of 5th Embodiment. It is a top view which shows the structural example of the star coupler of 6th Embodiment. It is a perspective view which shows the structural example of the star coupler of 7th Embodiment. FIG. 10A is a plan view, and FIG. 10B is a side view, illustrating a configuration example of an optical integrated circuit according to the present embodiment.

Explanation of symbols

1a to 1g: Star coupler, 2 ... Core, 3 ... Cladding, 4 ... Main waveguide, 5 (1) to 5 (6) ... Input side branching waveguide, 5a ... Input port, 6 (1) to 6 (6) ... output side branch waveguide, 6a ... input port, 7 ... electrode, 8 ... roller, 11 ... optical integrated circuit, 12. ..Mounting substrate, 13 ... Star coupler, 14 ... Inclined end face, 15 ... Surface emitting semiconductor laser, 16 ... Photodiode

Claims (15)

In a star coupler having an optical circuit in which both ends of the main waveguide are each divided into a plurality of branch waveguides,
The branching waveguide is formed at one end of the main waveguide, each of which has a curved portion, and a plurality of input side branching waveguides formed at the other end of the main waveguide, and each of the plurality of output sides having a curved portion. A branching waveguide,
The input-side branch waveguide includes high-order mode pumping means for pumping high-order mode light from low-order mode light, and the output-side branch waveguide is a high-order pump excited by the input-side branch waveguide. A star coupler comprising high-order mode propagation means for propagating light of the next mode. In the high-order mode excitation means and the high-order mode propagation means, the minimum curvature radius in the curved portion constituting the input-side branch waveguide is the minimum curvature in the curved portion constituting the output-side branch waveguide. The star coupler according to claim 1, wherein the waveguide shape is set to be smaller than the radius. The star coupler according to claim 2, wherein a waveguide length in the extending direction of the input side branching waveguide is shorter than a waveguide length in the extending direction of the output side branching waveguide. The input-side branching waveguide and the output-side branching waveguide are shaped to spread symmetrically with respect to the extending direction of the main waveguide,
The outermost input side branching waveguide has the smallest radius of curvature among the input side branching waveguides;
The star coupler according to claim 2, wherein the outermost output side branch waveguide has a minimum radius of curvature in the output side branch waveguide. In the higher-order mode excitation means and the higher-order mode propagation means, the curvature discontinuity point of the curved portion constituting the input-side branch waveguide is more than the curvature discontinuity point of the curved portion constituting the output-side branch waveguide. The star coupler according to claim 1, wherein the waveguide shape is set so as to increase. In the higher-order mode excitation means and the higher-order mode propagation means, the maximum curvature change rate of the curved portion constituting the input-side branch waveguide is greater than the maximum curvature change rate of the curved portion constituting the output-side branch waveguide. The star coupler according to claim 1, wherein the waveguide shape is set so as to be large. The higher-order mode excitation means and the higher-order mode propagation means include a refractive index adjustment means that makes the maximum relative refractive index difference of the output side branch waveguide larger than the maximum relative refractive index difference of the input side branch waveguide. The star coupler according to claim 1, wherein: In at least one of the input side branch waveguide and the output side branch waveguide, the main waveguide is divided into a plurality of parts to form a first branch waveguide, and the first branch waveguide is further divided into a plurality of parts. 2. The star coupler according to claim 1, wherein the second branch waveguide is formed, and thereafter, the branch waveguide is formed by being divided until a predetermined number of channels is reached. Comparing the input side branch waveguide disposed on the outermost side in the input side branch waveguide and the output side branch waveguide disposed on the outermost side in the output side branch waveguide,
The minimum curvature radius in the curved portion constituting the input side branching waveguide is configured to be smaller than the minimum curvature radius in the curved portion constituting the output side branching waveguide, or
A configuration in which the curvature discontinuity of the curved portion constituting the input-side branching waveguide is greater than the curvature discontinuity of the curved portion constituting the output-side branching waveguide,
The maximum curvature change rate of the curved portion constituting the input side branching waveguide is configured to be larger than the maximum curvature change rate of the curved portion constituting the output side branching waveguide,
9. The apparatus according to claim 8, comprising at least one of a configuration in which a maximum relative refractive index difference of the output side branch waveguide is made larger than a maximum relative refractive index difference of the input side branch waveguide. Star coupler. At least the input-side branching waveguide is configured to be bendable,
2. The star coupler according to claim 1, wherein the higher-order mode excitation unit includes a bending unit configured to bend the input-side branching waveguide into a predetermined shape. A star coupler in which a plurality of input-side branch waveguides are formed at one end of the main waveguide and a plurality of output-side branch waveguides are formed at the other end;
A plurality of light emitting elements arranged to face input ports respectively formed in the plurality of input side branching waveguides;
A plurality of light receiving elements disposed facing the output ports respectively formed in the plurality of output side branching waveguides;
The input-side branch waveguide includes high-order mode pumping means for pumping high-order mode light from low-order mode light, and the output-side branch waveguide is a high-order pump excited by the input-side branch waveguide. An optical integrated circuit comprising high-order mode propagation means for propagating light of the next mode. In the high-order mode excitation means and the high-order mode propagation means, the minimum curvature radius in the curved portion constituting the input-side branch waveguide is the minimum curvature in the curved portion constituting the output-side branch waveguide. The optical integrated circuit according to claim 11, wherein the waveguide shape is set to be smaller than the radius. In the higher-order mode excitation means and the higher-order mode propagation means, the curvature discontinuity point of the curved portion constituting the input-side branch waveguide is more than the curvature discontinuity point of the curved portion constituting the output-side branch waveguide. The optical integrated circuit according to claim 11, wherein the waveguide shape is set so as to increase. In the higher-order mode excitation means and the higher-order mode propagation means, the maximum curvature change rate of the curved portion constituting the input-side branch waveguide is greater than the maximum curvature change rate of the curved portion constituting the output-side branch waveguide. The optical integrated circuit according to claim 11, wherein the waveguide shape is set to be large. The higher-order mode excitation means and the higher-order mode propagation means include a refractive index adjustment means that makes the maximum relative refractive index difference of the output side branch waveguide larger than the maximum relative refractive index difference of the input side branch waveguide. The optical integrated circuit according to claim 11.

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