Polymer and Composite Optical Waveguides

Abstract

The present invention provides a polymer optical waveguide that can achieve, with low loss even at an offset of 2 μm or less, adiabatic coupling with a silicon optical waveguide and butt (confronting) coupling with an optical fiber. A polymer optical waveguide of the present invention comprises a core, an underclad that has a lower refractive index than the core and is disposed around the core, and an overclad that is disposed around the core on an opposite side to the underclad, wherein: a first part in which the overclad is not provided and the core and the underclad around the core are exposed is provided on one end side in a light propagation direction along the light propagation direction; a second part in which the core is covered with the underclad and the overclad is provided on the other end side in the light propagation direction; and the relative refractive index difference between the core and the underclad and the overclad, the core width and the core height of the first part in an end surface on one end side, and the core width and the core height of the second part in an end surface on the other end side satisfy a predetermined relationship.

Description

[Technical field]

[0001] The present invention relates to polymer optical waveguides and composite optical waveguides. [Background technology]

[0002] Silicon photonics, a technology for integrating silicon optical circuits on a silicon chip, has been attracting attention. In silicon photonics, a polymer optical waveguide that uses adiabatic coupling is known as a waveguide for propagating optical signals between a silicon optical waveguide formed in an optical integrated circuit and an optical fiber (see, for example, Patent Document 1). The use of this polymer optical waveguide can reduce the propagation loss between the silicon optical waveguide and the optical fiber.

[0003] However, the degree of reduction in propagation loss between a silicon optical waveguide and an optical fiber when the polymer optical waveguide of Patent Document 1 is used is not sufficient, and there is a demand for connecting a silicon optical waveguide and an optical fiber with even lower loss.

[0004] When connecting a polymer optical waveguide to a silicon optical waveguide, or when connecting a polymer optical waveguide to an optical fiber, the relative positions of the two are not necessarily ideal, and a positional deviation (offset) of about 2 μm may occur. In this specification, an offset of about 2 μm means an offset of 1 μm or more and 3 μm or less. The offset of about 2 μm may occur either at the connection portion between the polymer optical waveguide and the silicon optical waveguide or at the connection portion between the polymer optical waveguide and the optical fiber, or may occur at both. For this reason, low connection loss at the ideal position alone is insufficient for the required performance; in terms of implementation, reduction in connection loss at an offset of 2 μm or less is also required. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2014-81586 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the problems of the conventional technology described above, the present invention aims to provide a polymer optical waveguide that can achieve adiabatic coupling with a silicon optical waveguide and butt (direct) coupling with an optical fiber with low loss even when the offset is 2 μm or less. [Means for solving the problem]

[0007] In order to achieve the above object, the polymer optical waveguide of the present invention has the following configuration. A polymer optical waveguide comprising a core, an undercladding having a refractive index lower than that of the core and surrounding the core, and an overcladding surrounding the core on the opposite side to the undercladding, The polymer optical waveguide has, at one end side in the light propagation direction, a first portion along the light propagation direction, in which there is no overclad and a core and an underclad around the core are exposed, and at the other end side in the light propagation direction, a second portion in which the core is covered with the underclad and the overclad; The relative refractive index difference D (%) represented by the following formula (i) is 0.6 or more, When the core width at an end face s on one end side of the first portion is Ws (μm), the core height at the end face s is Hs (μm), the core width at an end face f on the other end side of the second portion is Wf (μm), and the core height at the end face f is Hf (μm), k represented by the following formula (ii) is 7.5 or more and 11.5 or less, Ws / Hs is 1.50 or more and 6.00 or less, Ws / Wf is 1.20 or more, A polymer optical waveguide in which Wf+Hf is 2.6 or more. Relative refractive index difference D (%) = 100 × (refractive index of core - ((refractive index of underclad + refractive index of overclad) / 2)) / ((refractive index of underclad + refractive index of overclad) / 2) Formula (i) k=5D+Wf+Hf Formula (ii)

[0008] In the polymer optical waveguide of the present invention, the relative refractive index difference D is preferably 0.6 or more and 1.7 or less.

[0009] In the polymer optical waveguide of the present invention, Ws / Wf is preferably 1.20 or more and 10.00 or less.

[0010] In the polymer optical waveguide of the present invention, Wf+Hf is preferably 2.6 or more and 8.5 or less.

[0011] In the polymer optical waveguide of the present invention, the core is preferably made of a fluorine-containing polymer.

[0012] The polymer optical waveguide of the present invention is preferably a single mode optical waveguide.

[0013] The present invention also provides a composite optical waveguide comprising the polymer optical waveguide of the present invention and a connector that receives a second section of the polymer optical waveguide. Effect of the Invention

[0014] The polymer optical waveguide of the present invention can achieve adiabatic coupling with a silicon optical waveguide and butt (direct) coupling with an optical fiber with low loss even at an offset of 2 μm or less. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a perspective view showing one configuration example of a polymer optical waveguide of the present invention. [Diagram 2] FIG. 2 is a diagram of an end face s on the side of the first portion 14 of the polymer optical waveguide 10 shown in FIG. [Diagram 3]FIG. 3 is a diagram of an end face f on the second portion 15 side of the polymer optical waveguide 10 shown in FIG. [Figure 4] FIG. 4 is a graph showing the relationship between the sum of the core width and the core height (Wf+Hf) at the end face f and the relative refractive index difference D. [Diagram 5] FIG. 5 is a perspective view showing an example of a configuration of a composite optical waveguide in which a polymer optical waveguide and a silicon optical waveguide are adiabatically coupled. [Figure 6] FIG. 6 is a side view of the composite optical waveguide 20 of FIG. [Figure 7] Fig. 7 is a perspective view of the polymer optical waveguide 40 of Fig. 5. However, the polymer optical waveguide 40 is turned upside down. [Figure 8] 8(a) to 8(e) are plan views of further examples of the polymer optical waveguide. [Figure 9] FIG. 9 is a cross-sectional view of the evaluation model used in the simulation analysis. [Figure 10] FIG. 10 is a vertical cross-sectional view including the end face s on the first portion 74 side of the polymer optical waveguide 70 of the evaluation model of FIG. [Figure 11] FIG. 11 is a partial plan view of the vicinity of a butt-coupled portion between the polymer optical waveguide 70 and the single-mode optical fiber 90 of the evaluation model of FIG. [Figure 12] FIG. 12 is a diagram of an end face f on the second portion 75 side of the polymer optical waveguide 70 of the evaluation model of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention will now be described with reference to the drawings. Fig. 1 is a perspective view showing one example of the configuration of a polymer optical waveguide of the present invention. A polymer optical waveguide 10 shown in Fig. 1 includes two cores 11a and 11b, an underclad 12 having a lower refractive index than the cores 11a and 11b and surrounding the cores 11a and 11b, and an overclad 13 surrounding the cores 11a and 11b on the opposite side to the underclad 12. The polymer optical waveguide 10 has a first portion 14 at one end in the light propagation direction (the right side in the figure) where the overclad 13 is not present and the cores 11a, 11b and the underclad 12 around the cores 11a, 11b are exposed. The first portion 14 is used as an adiabatic coupling portion with the silicon optical waveguide. On the other hand, the other end side in the light propagation direction (left side in the figure) has a second portion 15 in which the cores 11a, 11b are covered with an underclad 12 and an overclad 13. The second portion 15 is used as a butt (facing) coupling portion with a single mode optical fiber.

[0017] FIG. 2 is a diagram of an end surface s on one end side (the right side in the figure) of the first portion 14. As shown in FIG. 2, the core widths of the cores 11a and 11b at the end face s are indicated as Wsa (μm) and Wsb (μm), respectively. The core heights of the cores 11a and 11b at the end face s are indicated as Hsa (μm) and Hsb (μm), respectively.

[0018] FIG. 3 is a diagram of an end face f of the other end side (left side in the figure) of the second portion 15. As shown in FIG. 3, the core widths of cores 11a and 11b at facet f are indicated as Wfa (μm) and Wfb (μm), respectively. The core heights of cores 11a and 11b at facet f are indicated as Hfa (μm) and Hfb (μm), respectively.

[0019] In the polymer optical waveguide 10 shown in Figures 1 to 3, two cores 11a, 11b are arranged in parallel along the direction of light propagation of the cores in the polymer optical waveguide 10 (hereinafter referred to as the "direction of light propagation in the polymer optical waveguide" in this specification). However, the number of cores in the polymer optical waveguide of the present invention is not limited to this, and the number of cores may be one, or three or more. The number of cores is preferably an even number, and for example, 8, 12, 16, or 24 is more preferable.

[0020] When the polymer optical waveguide of the present invention satisfies the following conditions 1 to 5, it can achieve adiabatic coupling with a silicon optical waveguide and butt (direct) coupling with an optical fiber with low loss even at an offset of 2 μm or less.

[0021] (Condition 1) In the polymer optical waveguide 10 of the present invention, the ratio (Wsa / Hsa, Wsb / Hsb) of the core widths Wsa, Wsb of the cores 11a, 11b to the core heights Hsa, Hsb at the end face s is 1.50 or more and 6.00 or less. If the ratio (Ws / Hs) of the core width Ws to the core height Hs at the end face s is within the above range, adiabatic coupling with a silicon optical waveguide and butt (direct) coupling with an optical fiber can be achieved with low loss even at an offset of 2 μm or less. If Ws / Hs is outside the above range, that is, Ws / Hs is less than 1.50 or exceeds 6.00, the connection loss at an offset of about 2 μm increases. Ws / Hs is preferably 1.80 or more and 5.00 or less, more preferably 2.00 or more and 3.50 or less.

[0022] (Condition 2) In the polymer optical waveguide 10 of the present invention, the ratio (Wsa / Wfa, Wsb / Wfb) of the core widths Wsa, Wsb of the cores 11a, 11b at the end face s to the core widths Wfa, Wfb of the cores 11a, 11b at the end face f is 1.20 or more. If the ratio (Ws / Wf) of the core width Ws at the end face s to the core width Wf at the end face f is 1.20 or more, adiabatic coupling with a silicon optical waveguide and butt (face-to-face) coupling with an optical fiber can be achieved with low loss even at an offset of 2 μm or less. In addition, since the core width is narrow and the portion with a large aspect ratio in the cross-sectional shape of the core is reduced, the yield rate during the production of the polymer optical waveguide is improved. If Ws / Wf is outside the above range, that is, if Ws / Wf is less than 1.20, the connection loss at an offset of about 2 μm may increase significantly. Ws / Wf is preferably 1.50 or more, and more preferably 1.80 or more. Ws / Wf is preferably 10.00 or less because it can reduce connection loss when offset is 2 μm or less, more preferably 5.00 or less, and even more preferably 3.50 or less. In addition, Ws / Wf of 10.00 or less is also preferable in that the polymer optical waveguide can be made compact, crosstalk (signal crosstalk) is unlikely to occur, and the difference in core width between end face s and end face f is not too large, improving the yield during production of the polymer optical waveguide.

[0023] (Condition 3) In the polymer optical waveguide 10 of the present invention, the sum (Wfa+Hfa, Wfb+Hfb) of the core widths Wfa, Wfb and the core heights Hfa, Hsf of the cores 11a, 11b at the end face f is 2.6 or more. If the sum (Wf+Hf) of the core width Wf and the core height Hf at the end face f is 2.6 or more, adiabatic coupling with a silicon optical waveguide and butt (direct facing) coupling with an optical fiber can be achieved with low loss even at an offset of 2 μm or less. In addition, since the core width is narrow and the portion with a large aspect ratio in the cross-sectional shape of the core is reduced, the yield rate during the production of the polymer optical waveguide is improved. If Wf+Hf is outside the above range, that is, if Wf+Hf is less than 2.6, the connection loss at an offset of about 2 μm may increase significantly. Wf+Hf is preferably 3.0 or more, more preferably 4.0 or more. Wf+Hf is preferably 8.5 or less because it reduces connection loss when offset is 2 μm or less, more preferably 7.5 or less, and even more preferably 6.0 or less. In addition, Wf+Hf of 8.5 or less is also preferable because it allows the polymer optical waveguide to be made compact, crosstalk (signal crosstalk) is less likely to occur, the core shape is easily controlled, and a single-mode optical waveguide is easily obtained.

[0024] The relative refractive index difference D (%) in the present invention is represented by the following formula (i). Relative refractive index difference D (%)=100×(refractive index of core−((refractive index of underclad+refractive index of overclad 13) / 2)) / ((refractive index of underclad+refractive index of overclad) / 2) Formula (i) The relative refractive index difference Da (%) of the core 11a is represented by the following formula (ia). Relative refractive index difference Da (%)=100×(refractive index of core 11a−((refractive index of underclad 12+refractive index of overclad 13) / 2)) / ((refractive index of underclad 12+refractive index of overclad 13) / 2) Formula (ia) The relative refractive index difference Db (%) of the core 11b is represented by the following formula (ib). Relative refractive index difference Db (%)=100×(refractive index of core 11b−((refractive index of undercladding 12+refractive index of overcladding 13) / 2)) / ((refractive index of undercladding 12+refractive index of overcladding 13) / 2) Formula (ib) If the core has a refractive index distribution, the average refractive index is used as a representative value. If the undercladding and overcladding have a refractive index distribution, the average refractive index of the region from the outer periphery of the core to 5 μm is used as a representative value. The absolute value of the refractive index difference between the undercladding and the overcladding is preferably 0.001 or less, more preferably 0.0008 or less, and even more preferably 0.0006 or less.

[0025] (Condition 4) In the present invention, the relative refractive index difference D (%) is 0.6 or more. If the relative refractive index difference D is 0.6 or more, adiabatic coupling with a silicon optical waveguide and butt (direct facing) coupling with an optical fiber can be achieved with low loss even at an offset of 2 μm or less. This is also preferable in that the bending loss of the polymer optical waveguide can be reduced. If D is outside the above range, that is, if D is less than 0.6, there is a possibility that the connection loss at an offset of about 2 μm will increase significantly. D is preferably 0.7 or more, and more preferably 0.8 or more. D is preferably 1.7 or less because it reduces the connection loss when the offset is 2 μm or less, more preferably 1.4 or less, and even more preferably 1.2 or less. D is also preferably 1.7 or less because the composition of the core, the composition of the undercladding, and the composition of the overcladding become similar, improving the adhesion between them. It is also preferable because it is easy to obtain a single-mode optical waveguide.

[0026] (Condition 5) In the present invention, k represented by the following formula (ii) is 7.5 or more and 11.5 or less. k=5D+Wf+Hf Formula (ii) (In formula (ii), D is the relative refractive index difference obtained under condition 4 above, and Wf+Hf is the sum of the core width Wf and the core height Hf at the end face f of the second portion obtained under condition 3 above.) The ka of the core 11a is represented by the following formula (iia). ka=5Da+Wfa+Hfa formula (iia) The kb of the core 11b is expressed by the following formula (iib). kb=5Db+Wfb+Hfb formula (iib) If k is within the above range, adiabatic coupling with a silicon optical waveguide and butt (direct facing) coupling with an optical fiber can be achieved with low loss even at an offset of 2 μm or less. If k is outside the above range, i.e., if k is less than 7.5 or more than 11.5, the connection loss may increase at an offset of about 2 μm. Furthermore, if k is more than 11.5, the propagation mode may become multimode. A single mode is preferable as the propagation mode because it allows propagation with low loss. k is preferably 7.8 or more and 10.5 or less, and more preferably 8 or more and 9.5 or less.

[0027] 4 is a graph showing the relationship between the sum of the core width and core height (Wf+Hf) (μm) at the end face f and the relative refractive index difference D (%). When conditions 3, 4, and 5 are satisfied, the polymer optical waveguide of the present invention falls within the region surrounded by the solid line in FIG. 4.

[0028] Fig. 5 is a perspective view showing one example of a composite optical waveguide in which the polymer optical waveguide of the present invention and a silicon optical waveguide are adiabatically coupled, and Fig. 6 is a side view of the composite optical waveguide 20 of Fig. 5. The polymer optical waveguides shown in Figs. 5 and 6 are examples of a different configuration from the polymer optical waveguide of Fig. 1. In the composite optical waveguide 20 shown in Fig. 5, a silicon optical waveguide 30 and a polymer optical waveguide 40 are adiabatically coupled. The polymer optical waveguide 40 shown in Fig. 5 is similar to the polymer optical waveguide 10 shown in Fig. 1 in that it includes a core 41, an underclad 42, and an overclad 43. Also, it is similar to the polymer optical waveguide 10 shown in Fig. 1 in that it includes a first portion 44 at one end (right side in the figure) in the light propagation direction where the overclad 43 is not present and the core 41 and the underclad 42 around the core 41 are exposed, and that it includes a second portion 45 at the other end (left side in the figure) in the light propagation direction where the core 41 is covered with the underclad 42 and the overclad 43. 5 is adiabatically coupled to the silicon optical waveguide 30 at a first portion 44. A second portion 45 of the polymer optical waveguide 40 is accommodated in a connector 50 for butt coupling (direct coupling) with a single mode optical fiber or the like.

[0029] Fig. 7 is a perspective view of the polymer optical waveguide 40 shown in Fig. 5. However, the polymer optical waveguide 40 is turned upside down. The polymer optical waveguide 40 shown in Fig. 7 has multiple, specifically eight, cores 41 arranged in parallel along the light propagation direction. These eight cores 41 satisfy the above-mentioned conditions 1 to 5. Note that in the polymer optical waveguide 40 shown in Fig. 7, the pitch between the multiple cores 41 is different between the first portion 44 and the second portion 45. The pitch between the multiple cores 41 in the first portion 44 is narrower than that in the second portion 45.

[0030] 8(a) to 8(e) are plan views of still another example of the polymer optical waveguide of the present invention. The polymer optical waveguides 60a to 60e shown in FIG. 8(a) to 8(e) include cores 61a to 61e, underclads 62a to 62e, and overclads 63a to 63e. However, the cores 61a to 61e are only the two cores arranged on the outermost side among a plurality of cores arranged in parallel along the light propagation direction. The right side of the figure shows first regions 64a to 64e in which the overclads 63a to 63e are not present and the cores 61a to 61e and the underclads 62a to 62e around the cores 61a to 61e are exposed, and the left side of the figure shows second regions 65a to 65e in which the cores 61a to 61e are covered with the underclads 62a to 62e and the overclads 63a to 63e.

[0031] 7, when the polymer optical waveguide 40 has a rectangular planar shape, there is a wide region on the first region 44 side where the pitch between the multiple cores 41 is narrow, outside the outermost cores 41, where only the undercladding 42 exists. This region does not have to exist because it does not contribute to the light propagation in the polymer optical waveguide 40. 8(a) to 8(e), the undercladdings 62a to 62e on the first portions 64a to 64e are removed by punching out the portions outside the outermost cores 61a to 61e. By using polymer optical waveguides of these shapes, the size of the silicon chip can be reduced.

[0032] The polymer optical waveguides of the present invention will now be further described.

[0033] (core) In the polymer optical waveguide of the present invention, the shape of the core at the end face s or end face f is not limited to the rectangle or approximately square shown in the figure. The shape of the core at the end face s or end face f (inside the polymer optical waveguide, the cross-sectional shape of the core perpendicular to the propagation direction of light in the polymer optical waveguide) may be, for example, a trapezoid, a circle, or an ellipse. In addition, when the end face shape of the core is a polygon such as a rectangle, an approximately square, or a trapezoid, the corners may be rounded. When the end face shape of the core is other than a rectangle or an approximately square, the core width Ws and core height Hs at the end face s, and the core width Wf and core height Hf at the end face f are the average values ​​of the core width and core height in the end face shape, respectively.

[0034] The core may have a refractive index distribution therein. In this case, the refractive index distribution may be such that the refractive index decreases toward the distal side from the center of the core. The core may also have a refractive index distribution in which the refractive index is high on the overclad side and low on the underclad side, or in which the refractive index is low on the overclad side and high on the underclad side.

[0035] (underclad, overclad) The undercladding and the overcladding have a lower refractive index than the core. The undercladding and the overcladding may have a single refractive index, or may have a portion with a different refractive index on the proximal side and the distal side with respect to the core. In this case, the refractive index may be lower toward the distal side with respect to the core, or may be higher toward the distal side with respect to the core.

[0036] The thickness of the undercladding and overcladding is not particularly limited, but when the polymer optical waveguide of the present invention is a single mode optical waveguide, the light propagating through the cladding portion within a range of about 10 μm from the center of the core leaks out, so that the thickness is preferably 10 μm or more in order to reduce the propagation loss of the light. The total thickness of the undercladding and overcladding is preferably 20 μm or more and 100 μm or less, more preferably 30 μm or more and 80 μm or less.

[0037] (First part) The first portion of the polymer optical waveguide of the present invention is required to have a length (length in the light propagation direction) sufficient to be used as an adiabatic bonding portion with the silicon optical waveguide. Specifically, the length of the first portion in the light propagation direction of the polymer optical waveguide is preferably 100 μm or more, more preferably 300 μm or more, even more preferably 500 μm or more, and particularly preferably 1000 μm or more. However, if the length of the first portion of the polymer optical waveguide in the light propagation direction is too long, there is a risk of increased connection loss due to absorption of the adhesive when connecting to the silicon optical waveguide using an adhesive (e.g., epoxy resin). Therefore, the length of the first portion of the polymer optical waveguide in the light propagation direction is preferably 10,000 μm or less, more preferably 5,000 μm or less, and even more preferably 3,000 μm or less.

[0038] (Second part) The length of the second portion is the total length of the polymer optical waveguide of the present invention minus the length of the first portion. Therefore, the length of the second portion in the light propagation direction is not particularly limited, but is preferably 1000 μm or more, more preferably 3000 μm or more, and even more preferably 5000 μm or more, from the viewpoints of ensuring the strength of the polymer optical waveguide, achieving propagation with low loss, and realizing a polymer optical waveguide with a large number of cores. On the other hand, the length of the second portion in the light propagation direction is preferably 35000 μm or less, more preferably 20000 μm or less, and even more preferably 10000 μm or less, from the viewpoints of compactness, reduction of absorption by the material, etc.

[0039] The total length in the light propagation direction of the polymer optical waveguide of the present invention is, for example, 1000 μm or more and 50000 μm or less, preferably 5000 μm or more and 20000 μm or less, and more preferably 7000 μm or more and 15000 μm or less.

[0040] The polymer optical waveguide of the present invention is preferably a single-mode optical waveguide since it can achieve propagation with low loss.

[0041] (Constituent materials) In the polymer optical waveguide of the present invention, the constituent materials of the core, underclad, and overclad are not particularly limited as long as they satisfy the required characteristics of a polymer optical waveguide. However, it is preferable that the core be made of a fluorine-containing polymer in order to suppress the loss of light propagating through the core. The undercladding and the overcladding may be made of the same material or different materials.

[0042] (Manufacturing method) The method for producing the polymer optical waveguide of the present invention is not particularly limited, and various methods can be used, such as a replication (stamper) method, a direct exposure method, a method combining reactive ion etching (RIE) and a photolithography process, a method based on injection molding, a photobleaching method, a direct writing method, and a self-forming method.

[0043] An example of a method for producing a polymer optical waveguide according to the present invention will be described. First, a coating liquid containing the curable composition (A), which is a constituent material of the undercladding, is applied onto a substrate by spin coating, and then the curable composition (A) is cured to form the undercladding. Next, a coating liquid containing the curable composition (B), which is a core constituent material, is applied onto the underclad by spin coating. Then, the curable composition (B) is patterned by a photolithography process to form a core on the underclad. At this time, in order to form a shape in which the width of the core varies along the light propagation direction, the core may be formed by exposure using a photomask in which the width of the core varies along the light propagation direction, and then development. After the core is formed, post-baking may be performed as necessary. Next, a coating liquid containing a curable composition (C), which is a constituent material of the overclad, is applied onto the underclad and the core by spin coating. The curable composition (C) is then cured to form the overclad. When forming the overclad, a photolithography process can be used to form a first portion in which the overclad is not present and the core and the underclad around the core are exposed. EXAMPLES

[0044] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. Examples 1 to 21 are examples, and Examples 22 to 36 are comparative examples.

[0045] The connection loss was evaluated by simulation analysis using a composite optical waveguide in which one end of a polymer optical waveguide is adiabatically coupled to a silicon optical waveguide and the other end is butt-coupled to a single-mode optical fiber as an evaluation model. The optical fiber / waveguide design and analysis software BeamPROP (RSoft Design Group) based on the bidirectional BPM method, which is a simulation engine, was used to simulate the optical propagation of TE mode using the finite difference beam propagation method.

[0046] Fig. 9 is a cross-sectional view of an evaluation model used in the simulation analysis. A polymer optical waveguide 70 in Fig. 9 includes a core 71, an underclad 72, and an overclad 73. A silicon optical waveguide 80 shown in Fig. 9 is composed of a core 81 and a clad 82. A single-mode optical fiber 90 shown in Fig. 9 is composed of a core 91 and a clad 92.

[0047] 9 has a first portion 74 at one end in the light propagation direction (the left side in the figure) where there is no overclad 73 and the core 71 and the underclad 72 around the core 71 are exposed. The first portion 74 of the polymer optical waveguide 70 is adiabatically coupled to a silicon optical waveguide 80.

[0048] Fig. 10 is a longitudinal cross-sectional view including an end face s on the first portion 74 side of the polymer optical waveguide 70 of the evaluation model of Fig. 9. In Fig. 9, a core 71 of the polymer optical waveguide 70 and a core 81 of the silicon optical waveguide 80 are disposed in a facing state and are joined by an adhesive 100. A barrier layer 110 is formed on the surface of the silicon optical waveguide 80 on the adhesive 100 side. As shown by the dashed line, the centers of the core 71 of the polymer optical waveguide 70 and the core 81 of the silicon optical waveguide 80 do not coincide with each other, and a center x1 of the core 81 of the silicon optical waveguide 80 is offset by a distance X in the horizontal direction from a center x2 of the core 71 of the polymer optical waveguide 70.

[0049] 9 has a second portion 75 in which a core 71 is covered with an underclad 72 and an overclad 73 at the other end side in the light propagation direction (the right side in the figure). The second portion 75 of the polymer optical waveguide 70 is butt-coupled to a single-mode optical fiber 90. Fig. 11 is a partial plan view of the vicinity of a butt-coupled portion between the polymer optical waveguide 70 and the single mode optical fiber 90 of the evaluation model in Fig. 9. As shown in Fig. 11, the centers of the core 71 of the polymer optical waveguide 70 and the core 91 of the single mode optical fiber 90 do not coincide as indicated by the dashed line, and the center y1 of the core 91 of the single mode optical fiber 90 is offset by a distance Y in the horizontal direction from the center y2 of the core 71 of the polymer optical waveguide 70. FIG. 12 is a diagram of an end face f on the second portion 75 side of the polymer optical waveguide 70 of the evaluation model of FIG.

[0050] The individual structures in the evaluation model are shown below. <Polymer Optical Waveguide (POW) 70> (Core 71) end face s Core width Ws (as shown in the table below) Core height Hs (as shown in the table below) end face f Core width Wf (as shown in the table below) Core height Hf (as shown in the table below) Refractive index (as shown in the table below) Length of adiabatic joint 76: 1750μm (Underclad 72) Thickness: 15μm Length 3050μm Refractive index (as shown in the table below) (Overclad 73) Thickness: 15μm Length 1000μm Refractive index (as shown in the table below) <Silicon Optical Waveguide (Si Waveguide) 80> (Core 81) Width: Narrows quadratically from 0.35 μm to 0.07 μm from the opposite side of the polymer optical waveguide 70 to the second portion 75 of the polymer optical waveguide 70 Height 0.16μm Refractive index 3.45 Length of adiabatic joint 83 1750μm Horizontal offset distance X: 0μm (non-offset) and 2μm (offset) (Clad 82) Thickness: 15μm Refractive index: 1.45 Length of region 84 where only cladding 82 exists: 250 μm <Adhesive 100> Resin thickness (distance between the surfaces of the core 71 of the polymer optical waveguide 70 and the core 81 of the silicon optical waveguide 80 facing each other) 0.5 μm Refractive index: 1.51 Length of the region 101 between the silicon optical waveguide 80 and the second portion 75 of the polymer optical waveguide 70: 50 μm <Barrier layer 110> Thickness: 0.03μm Refractive index 1.989 <Single mode optical fiber (SMF) 90> Core 91 diameter 8.4μm Core 91 Refractive Index 1.47 Cladding 92 Refractive Index 1.4652 Horizontal offset distance Y: 0μm (non-offset) and 2μm (offset)

[0051] As a result of the simulation analysis, the connection loss between the POW and the Si waveguide (without offset and with offset), the connection loss between the POW and the SMF (without offset and with offset), and the propagation mode were obtained. The simulation conditions and analysis results are shown in the table below. The total connection loss is the sum of the connection loss between the POW and the Si waveguide and the connection loss between the POW and the SMF. In the table below, the connection loss between the POW and the Si waveguide without offset is described as "Connection loss (Si waveguide)", the connection loss between the POW and the Si waveguide with offset is described as "Offset connection loss (Si waveguide)", the connection loss between the POW and the SMF without offset is described as "Connection loss (SMF)", the connection loss between the POW and the SMF with offset is described as "Offset connection loss (SMF)", the total connection loss without offset is described as "Connection loss (Total)", and the total connection loss with offset is described as "Offset connection loss (Total)".

[0052] [Table 1]

[0053] [Table 2]

[0054] [Table 3]

[0055] [Table 4]

[0056] [Table 5]

[0057] In Examples 1 to 21, which satisfy k of 7.5 to 11.5, Ws / Hs of 1.50 to 6.00, Ws / Wf of 1.20 or more, Wf+Hf of 2.6 or more, and D of 0.6 or more, the total connection loss at 2 μm offset was 2.50 dB or less, and the propagation mode was single mode. On the other hand, in Examples 22 to 25, which have Ws / Hs less than 1.50, Example 26, which have k of more than 11.5, Ws / Hs of less than 1.50, and Ws / Wf of less than 1.20, Example 27, which have k of more than 11.5, Example 28, which have k of less than 7.5, Example 29, which have a relative refractive index difference D of less than 0.6%, Example 30, which have Ws / Hs of more than 6.00, and Example 31, which have Ws / Hs of less than 1.50 and Ws / Wf of less than 1.20, Example 32 where k is greater than 11.5 and Ws / Wf is less than 1.20, Example 33 where Ws / Hs is less than 1.50 and Ws / Wf is less than 1.20, Example 34 where Ws / Wf is less than 1.20, Example 35 where Wf+Hf is less than 2.6, and Example 36 where Ws / Hs is less than 1.50 and k is greater than 11.5 all had a total connection loss of more than 2.50 dB at 2 μm offset. Example 36 has a multimode propagation mode and has a large propagation loss.

[0058] Although the present invention has been described in detail using specific embodiments, it is apparent to those skilled in the art that various modifications and variations are possible without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2019-088978) filed on May 9, 2019, and is incorporated by reference in its entirety. [Explanation of symbols]

[0059] 10: Polymer optical waveguide 11a, 11b: Core 12: Underclad 13: Overclad 14: First part 15: Second part 20: Composite optical waveguide 30: Silicon optical waveguide 40: Polymer optical waveguide 41: Core 42: Underclad 43: Overclad 44: First part 45: Second part 50: Connector 60a,60b,60c,60d,60e: Polymer optical waveguide 61a, 61b, 61c, 61d, 61e: Core 62a, 62b, 62c, 62d, 62e: Undercladding 63a, 63b, 63c, 63d, 63e: Overclad 64a, 64b, 64c, 64d, 64e: First part 65a, 65b, 65c, 65d, 65e: Second part 70: Polymer optical waveguide 71: Core 72: Underclad 73: Overclad 74: First part 75: Second part 76: Adiabatic Junction 80: Silicon optical waveguide 81: Core 82: Clad 83: Adiabatic Junction 84: Area where only cladding exists 90: Single mode optical fiber 91: Core 92: Clad 100: Adhesive 101: Region between the silicon optical waveguide and the second portion of the polymer optical waveguide 110: Barrier layer x1,x2,y1,y2:center X,Y: Offset distance

Claims

1. A polymer optical waveguide comprising a core, an underclad having a refractive index lower than that of the core and surrounding the core, and an overclad surrounding the core on the opposite side to the underclad, the polymer optical waveguide has, at one end side in the light propagation direction, a first portion along the light propagation direction, in which the overclad is not present and the core and the underclad around the core are exposed, and, at the other end side in the light propagation direction, a second portion in which the core is covered with the underclad and the overclad; The relative refractive index difference D (%) represented by the following formula (i) is 0.6 or more, When the core width at the end face s on the one end side of the first portion is Ws (μm), the core height at the end face s is Hs (μm), the core width at the end face f on the other end side of the second portion is Wf (μm), and the core height at the end face f is Hf (μm), Hs and Hf are both 1.2 μm or more and 2.0 μm or less, k represented by the following formula (ii) is 7.5 or more and 11.5 or less, Ws / Hs is 1.50 or more and 6.00 or less, Ws / Wf is 1.20 or more, A polymer optical waveguide, wherein Wf+Hf is 2.6 or more. Relative refractive index difference D (%)=100×(refractive index of core−((refractive index of underclad+refractive index of overclad) / 2)) / ((refractive index of underclad+refractive index of overclad) / 2) Formula (i) k=5D+Wf+Hf Formula (ii)

2. 2. The polymer optical waveguide according to claim 1, wherein the relative refractive index difference D is 0.6 or more and 1.7 or less.

3. 3. The polymer optical waveguide according to claim 1, wherein the Ws / Wf is 1.20 or more and 10.00 or less.

4. 4. The polymer optical waveguide according to claim 1, wherein Wf+Hf is 2.6 or more and 8.5 or less.

5. 5. The polymer optical waveguide according to claim 1, wherein the core is made of a fluorine-containing polymer.

6. 6. The polymer optical waveguide according to claim 1, which is a single mode optical waveguide.

7. There are a plurality of said cores, 7. The polymer optical waveguide according to claim 1, wherein the core is parallel to the propagation direction of the light in the first portion and the second portion.

8. 8. The polymer optical waveguide according to claim 1, wherein a pitch between the plurality of cores in the first portion is narrower than a pitch between the plurality of cores in the second portion.

9. 9. A composite optical waveguide comprising: the polymer optical waveguide according to claim 1; and a connector that houses the second portion of the polymer optical waveguide.

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