Optical input / output structure

Abstract

This light input / output structure comprises: a plurality of polarization-maintaining optical fibers (101); a plurality of two-dimensional grating couplers (102); and a V-groove substrate (105) that fixes the plurality of polarization-maintaining optical fibers (101). Each of the plurality of polarization-maintaining optical fibers (101) comprises two stress-applying portions (113) so as to sandwich a core (112) within a cladding (111). The two stress-applying portions (113) are disposed so as to sandwich the core (112) in the first direction or in the second direction perpendicular to the first direction, and the waveguide direction of each of a plurality of first optical waveguides (103) or of each of a plurality of second optical waveguides (104), which are provided for each of the plurality of two-dimensional grating couplers (102), is set in the first direction.

Description

Technical Field

[0001] The present invention relates to an optical input / output structure.

Background Art

[0002] In order to increase the communication capacity per device of an optical communication device, research and development of smaller and more highly functional optical modules have been actively promoted. As a promising technology therefor, there is silicon photonics (SiP) technology. Silicon photonics is an optical circuit technology using an optical waveguide formed on a silicon-on-insulator (SOI) wafer, with a core material of silicon (Si) and a cladding material of quartz glass (SiO2).

[0003] As one method of inputting / outputting light to / from a silicon photonics chip, there is a grating coupler. Further, when separating and coupling different orthogonal polarizations, a two-dimensional grating coupler is used (Non-Patent Document 1).

[0004] States in which a polarization-maintaining fiber (PMF) 301 and a two-dimensional grating coupler 302 are optically coupled are shown in FIGS. 4A and 4B. The polarization-maintaining fiber 301 is an optical fiber that maintains the polarization state of the guided light, and includes two stress-applying portions 313 so as to sandwich a core 312 in a cladding 311. The two-dimensional grating coupler 302 has a periodic structure (grating) in both the x direction and the y direction that are orthogonal to each other. Among the polarizations coupled to the two-dimensional grating coupler 302, the polarization in which the electric field vibrates in the y direction is guided to a first optical waveguide 303, and the polarization in which the electric field vibrates in the x direction is guided to a second optical waveguide 304.

[0005] In order to make the coupling ratios to the first optical waveguide 303 and the second optical waveguide 304 equal, the polarization-maintaining fiber 301 is arranged in a direction symmetric with respect to the first optical waveguide 303 and the second optical waveguide 304, that is, on the plane x + y = 0.

[0006] Furthermore, the angle of the light output from the two-dimensional grating coupler 302 is usually set to an angle of about θ=10° rather than vertical in order to prevent coupling to modes that return as reflected waves to each optical waveguide, and the polarization-maintaining optical fiber 301 is also most efficiently input and output when tilted to a similar degree.

[0007] Now, consider the case where we want to couple the linear polarization of the polarization-maintaining optical fiber 301 along the speed axis direction 314 and the slow axis direction 315 to the second optical waveguide 304 and the first optical waveguide 303, respectively (or vice versa). In this case, the speed axis direction 314 and the slow axis direction 315 must be aligned with the x and y axes, as shown in Figure 4A. For example, this case applies when evaluating the performance of the two-dimensional grating coupler 302 itself, as it is necessary to input a predetermined polarization.

[0008] Furthermore, consider the case where multiple such two-dimensional grating couplers 302 are arranged in a row. Figure 5 shows a configuration in which four two-dimensional grating couplers 302 are arranged in a row. Note that the multiple two-dimensional grating couplers 302 are formed on an optical circuit board (not shown). In this case, multiple polarization-maintaining optical fibers 301 are used for optical input and output, and a fiber array is used in which these are aligned and fixed to a V-groove substrate 305. The V-groove substrate 305 is arranged by inserting each of the multiple polarization-maintaining optical fibers 301 into each of the multiple V-grooves. The multiple polarization-maintaining optical fibers 301 are held down on the V-groove substrate 305 by a plate-shaped cover 306. The cover 306 is also bonded and fixed to the V-groove substrate 305 by an adhesive layer 307. In this configuration, as mentioned above, the stress-applying portion 313 of the polarization-maintaining optical fiber 301 is positioned at an angle with respect to the optical fiber alignment direction. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] S. Pathak et al., "Compact SOI-based polarization diversity wavelength de-multiplexer circuit using two symmetric AWGs", Optics Express, vol. 20, no. 26, pp. B493-B500, 2012. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] In the conventional fiber array described above, the points where the V-groove substrate 305 and the cover 306 touch the polarization-maintaining optical fiber 301 (indicated in the figure and in the line of sight) are asymmetrical with respect to the stress-applying section 313. As a result, there is a problem that the stress applied to the polarization-maintaining optical fiber 301 at these points may disrupt the stress balance within the polarization-maintaining optical fiber 301, potentially degrading characteristics such as polarization crosstalk.

[0011] This invention was made to solve the above-mentioned problems, and aims to enable optical input and output between multiple polarization-maintaining optical fibers fixed to a V-groove substrate and multiple two-dimensional grating couplers without degradation of polarization crosstalk. [Means for solving the problem]

[0012] The optical input / output structure according to the present invention comprises: a plurality of polarization-maintaining optical fibers arranged in a first direction; a V-groove substrate having a plurality of V-grooves into which each of the plurality of polarization-maintaining optical fibers is inserted and aligned; a lid that presses the plurality of polarization-maintaining optical fibers against the V-groove substrate; a plurality of two-dimensional grating couplers corresponding to each of the plurality of polarization-maintaining optical fibers, arranged on the input / output ends of the plurality of polarization-maintaining optical fibers and formed on an optical circuit board in a first direction; and a component formed on an optical circuit board that is optically connected to each of the plurality of two-dimensional grating couplers. The device comprises a plurality of first optical waveguides and a plurality of second optical waveguides, each of the plurality of polarization-maintaining optical fibers having two stress-applying sections arranged to sandwich the core in a first direction or a second direction perpendicular to the first direction, each of the plurality of two-dimensional grating couplers being composed of gratings intersecting a first direction and a second direction perpendicular to the first direction, the guidance direction of each of the plurality of first optical waveguides and the guidance direction of each of the plurality of second optical waveguides being perpendicular to each other, and each of the plurality of first optical waveguides or each of the plurality of second optical waveguides having its guidance direction as the first direction. [Effects of the Invention]

[0013] As described above, according to the present invention, optical input and output can be performed between a plurality of polarization-maintaining optical fibers fixed to a V-groove substrate and a plurality of two-dimensional grating couplers without degradation of polarization crosstalk. [Brief explanation of the drawing]

[0014] [Figure 1] Figure 1 is a perspective view showing the configuration of an optical input / output structure according to an embodiment of the present invention. [Figure 2] Figure 2 is a perspective view showing the configuration of another optical input / output structure according to an embodiment of the present invention. [Figure 3] Figure 3 is a perspective view showing the configuration of another optical input / output structure according to an embodiment of the present invention. [Figure 4A] Figure 4A is a diagram showing the optical input / output structure consisting of a polarization-maintaining optical fiber 301 and a two-dimensional grating coupler 302. [Figure 4B]FIG. 4B is a configuration diagram showing an optical input / output structure formed by a polarization-maintaining optical fiber 301 and a two-dimensional grating coupler 302. [Figure 5] FIG. 5 is a perspective view showing the configuration of a conventional optical input / output structure. Embodiments for Carrying Out the Invention

[0015] Hereinafter, an optical input / output structure according to an embodiment of the present invention will be described with reference to FIG. 1. This optical input / output structure includes a plurality of polarization-maintaining optical fibers 101, a plurality of two-dimensional grating couplers 102, and a V-groove substrate 105 for fixing the plurality of polarization-maintaining optical fibers 101.

[0016] Each of the plurality of polarization-maintaining optical fibers 101 includes two stress-applying portions 113 so as to sandwich a core 112 in a cladding 111. Further, the two stress-applying portions 113 are arranged to sandwich the core 112 in a first direction or a second direction perpendicular to the first direction. Also, the plurality of polarization-maintaining optical fibers 101 are arranged in a first direction (the x-axis direction in FIG. 1). Therefore, the stress-applying portions 113 are arranged to be aligned with the alignment (arrangement) direction of the plurality of polarization-maintaining optical fibers 101.

[0017] The V-groove substrate 105 includes a plurality of V-grooves, and each of the plurality of polarization-maintaining optical fibers 101 is inserted into and aligned with each of the plurality of V-grooves. The plurality of polarization-maintaining optical fibers 101 are pressed against the V-groove substrate 105 by a lid 106. Also, the lid 106 is adhesively fixed to the V-groove substrate 105 by an adhesive layer 107.

[0018] A plurality of two-dimensional grating couplers 102 are provided corresponding to each of the plurality of polarization-maintaining optical fibers 101. Further, the plurality of two-dimensional grating couplers 102 are arranged on the side of the input / output ends of the plurality of polarization-maintaining optical fibers 101, arranged in the first direction, and formed on an optical circuit board (not shown). Each of the plurality of two-dimensional grating couplers 102 is composed of a grating that intersects in the first direction and the second direction (the y-axis direction in FIG. 1). The second direction is a direction perpendicular to the first direction. Note that the two-dimensional grating coupler 102 has a periodic structure (grating) with respect to both the x-axis direction and the y-axis direction that are perpendicular to each other.

[0019] Also, each of the plurality of two-dimensional grating couplers 102 has a plurality of first optical waveguides 103 and a plurality of second optical waveguides 104 optically connected thereto. The plurality of first optical waveguides 103 and the plurality of second optical waveguides 104 are formed on the same optical circuit board together with the plurality of two-dimensional grating couplers 102. In addition, the waveguide direction of each of the plurality of first optical waveguides 103 and the waveguide direction of each of the plurality of second optical waveguides 104 are in directions perpendicular to each other. Additionally, the waveguide direction of each of the plurality of first optical waveguides 103 or the waveguide direction of each of the plurality of second optical waveguides 104 is the first direction. In this example, the arrangement direction of the plurality of two-dimensional grating couplers 102 is parallel to the waveguide direction of the first optical waveguide 103.

[0020] Note that the surfaces of the input / output ends of each of the plurality of polarization-maintaining optical fibers 101 and the surface of the optical circuit board on which the plurality of two-dimensional grating couplers 102 are formed are arranged facing each other.

[0021] According to the embodiment described above, the multiple two-dimensional grating couplers 102 can perform optical input and output without being subjected to undesirable stress, and with respect to the multiple two-dimensional grating couplers 102, the speed axis can be aligned with the second optical waveguide 104 and the slow axis can be aligned with the first optical waveguide 103. In other words, according to the embodiment, optical input and output can be performed such that polarization with an electric field oscillating in the speed axis direction is coupled to the first optical waveguide 103, and polarization with an electric field oscillating in the slow axis direction is coupled to the second optical waveguide 104.

[0022] For example, as shown in Figure 2, the plane perpendicular to the waveguide direction of the multiple polarization-maintaining optical fibers 101 can be tilted from the plane of the optical circuit board on which the multiple two-dimensional grating couplers 102 are formed. In this way, the multiple polarization-maintaining optical fibers 101 are installed at an angle from the plane of the optical circuit board to match the direction in which the light is output. Note that Figure 2 shows an example of a combination of three polarization-maintaining optical fibers 101 and three two-dimensional grating couplers 102.

[0023] Multiple two-dimensional grating couplers 102 are arranged in a direction where the angle they make with the x-axis in Figure 2 is φ = -45°. Each of the multiple polarization-maintaining optical fibers 101 lies in the zy-plane in Figure 2, and the angle it makes with the z-axis is θ = 20°. The multiple two-dimensional grating couplers 102 are designed to achieve an equal and maximum coupling ratio with respect to the first optical waveguide 303 and the second optical waveguide 304 when the multiple polarization-maintaining optical fibers 101 are arranged at this angle.

[0024] d spacing between multiple two-dimensional grating couplers 102 F d is the spacing between the arrays of the multiple two-dimensional grating couplers 102 as viewed from a direction along the multiple two-dimensional grating couplers 102, and the spacing between the arrays of the multiple two-dimensional grating couplers 102 on the optical circuit board is d G Therefore, d F and d G The relationship can be expressed by the following equation.

[0025]

number

[0026] For example, if φ = -45° and θ = 20°, d F ≒0.9703d G This is the result.

[0027] In the example shown in Figure 1, the arrangement direction of the multiple two-dimensional grating couplers 102 is parallel to the waveguide direction of the first optical waveguide 103, but this is not the only option. The arrangement direction of the multiple two-dimensional grating couplers 102 can also be parallel to the waveguide direction of the second optical waveguide 104.

[0028] Furthermore, depending on the angle between the first optical waveguide 103 and the second optical waveguide 104 and the design of the direction of light emission, they do not need to be perfectly parallel to the first optical waveguide 103 or the first optical waveguide 303. Also, the stress that the polarization-maintaining optical fiber 101 receives from the V-groove substrate 105 or the cover 106 only needs to be symmetrical with respect to the stress-applying section 113, and the direction in which the two stress-applying sections 113 sandwich the core 112 can be 90° different from the state illustrated in Figure 1.

[0029] Incidentally, in the example shown in Figure 2, the plane on which the input / output ends of each of the multiple polarization-maintaining optical fibers 101, the input / output end side of the V-groove substrate 105, and the input / output end side of the lid 106 are arranged is inclined with respect to the surface of the optical circuit substrate on which the multiple two-dimensional grating couplers 102 are formed.

[0030] In contrast, as shown in Figure 3, the plane 108 on which the input / output ends of each of the multiple polarization-maintaining optical fibers 101, the input / output end side surface of the V-groove substrate 105, and the input / output end side surface of the lid 106 are arranged can be made parallel to the surface of the optical circuit board on which the multiple two-dimensional grating couplers 102 are formed. The plane 108 on which the input / output ends of each of the multiple polarization-maintaining optical fibers 101, the input / output end side surface of the V-groove substrate 105, and the input / output end side surface of the lid 106 are arranged can be tilted from a plane perpendicular to the waveguide direction to achieve the state shown in Figure 3.

[0031] This configuration makes it possible to shorten and equalize the distance between the plane 108 and the two-dimensional grating coupler 102, thereby increasing and equalizing coupling efficiency. 、 Since the input and output surfaces of each of the multiple polarization-maintaining optical fibers 101 are not perpendicular to the waveguide direction, it goes without saying that the arrangement angle of the polarization-maintaining optical fibers 101 must be appropriately corrected, taking into account the refraction of light at the input and output surfaces.

[0032] As described above, in the present invention, two stress-applying sections are arranged on either the first direction or a second direction perpendicular to the first direction, sandwiching the core, with respect to the first direction in which multiple polarization-maintaining optical fibers are arranged. Furthermore, the waveguide directions of the multiple first optical waveguides or multiple second optical waveguides connected to the two-dimensional grating coupler are made parallel. As a result, according to the present invention, optical input and output can be performed between the multiple polarization-maintaining optical fibers fixed to the V-groove substrate and the multiple two-dimensional grating couplers without degradation of polarization crosstalk.

[0033] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be implemented within the technical concept of the present invention by those with ordinary skill in the art. [Explanation of Symbols]

[0034] 101…Polarization-maintaining optical fiber, 102…Two-dimensional grating coupler, 103…First optical waveguide, 104…Second optical waveguide, 105…V-groove substrate, 106…Lid, 107…Adhesive layer, 111…Cladding, 112…Core, 113…Stress application section.

Claims

1. Multiple polarization-maintaining optical fibers arranged in a first direction, A V-groove substrate having multiple V-grooves, in which each of the multiple polarization-maintaining optical fibers is inserted and aligned, A cover for pressing the plurality of polarization-maintaining optical fibers against the V-groove substrate, A plurality of two-dimensional grating couplers are formed on an optical circuit board, corresponding to each of the plurality of polarization-maintaining optical fibers, and arranged on the input and output ends of the plurality of polarization-maintaining optical fibers, and arranged in the first direction; Optically connected to each of the plurality of two-dimensional grating couplers and formed on the optical circuit board, a plurality of first optical waveguides and a plurality of second optical waveguides Equipped with, Each of the plurality of polarization-maintaining optical fibers comprises two stress-applying portions arranged to sandwich the core in the first direction or in a second direction perpendicular to the first direction, Each of the plurality of two-dimensional grating couplers is composed of a grating that intersects the first direction and a second direction perpendicular to the first direction. The guidance direction of each of the plurality of first optical waveguides and the guidance direction of each of the plurality of second optical waveguides are set to be perpendicular to each other. Each of the plurality of first optical waveguides, or each of the plurality of second optical waveguides, has its waveguide direction set to the first direction. The plane on which each of the front-printing exit ends, the front-printing exit end side of the V-groove substrate, and the front-printing exit end side of the lid are arranged is inclined from a plane perpendicular to the waveguide direction, and is further parallel to the plane of the optical circuit substrate. An optical input / output structure characterized by the following features.

2. In the optical input / output structure according to claim 1, An optical input / output structure characterized in that the plane perpendicular to the waveguide direction of the plurality of polarization-maintaining optical fibers is inclined from the plane of the optical circuit board.

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