JP2007047320A - Optical waveguide for bidirectional communication and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical waveguide for bidirectional communication, which can adopt constitution in which no stray light is input in both light emitting and light receiving elements by using a light source of one wavelength. <P>SOLUTION: The optical waveguide 100 for bidirectional communication includes, on the surface of a clad substrate 120, a main waveguide core 10 having a curved part P and a sub-waveguide core 50. The main waveguide core 10 is composed of a pre-curve main waveguide core 20 having an optical axis in the direction of the arrow A and a post-curve main waveguide core 30 having an optical axis in the direction the arrow B, with a curved part P as the boundary between the two cores. The post-curve main waveguide core 30 is curvilinearly shaped. The main waveguide core 10 includes a main coupling face 12 on the projected side face of the curved part P, while the sub-waveguide core 50 includes a sub-inclined face 52. The main waveguide core 10 and the sub-waveguide core 50 are arranged closely in a manner facing oppositely. The pre-curve main waveguide core 20 needs to be formed with a curvature smaller than that of the main coupling face so as not to leak out from the side face of the main waveguide core. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a bidirectional communication optical waveguide constituting a transmission / reception module for transmitting an optical signal bidirectionally using an optical fiber, and a method of manufacturing the same.

  Conventionally, as a module for transmitting and receiving optical signals bidirectionally using a single optical fiber, a wavelength-selective reflector is inserted into the module using light of different wavelengths on the upstream and downstream. A method of separating upstream and downstream signals is often used. However, in this configuration, a reflector having wavelength selectivity must be separately provided in addition to the condenser lens, so that an increase in cost as a module is inevitable. Furthermore, since a transmission / reception module having a combination of a dedicated light receiving element and a light emitting element is required in accordance with the wavelengths used in uplink and downlink, it is complicated and causes a cost increase.

  As a method for avoiding such a problem, it is conceivable that bidirectional signals have the same wavelength. As such a method, for example, a configuration has been proposed in which a light receiving element is placed on a concentric circle of a surface light emitting element and bidirectional communication is performed (see, for example, Patent Document 1). Since it is inevitable that the transmitted light is reflected by the end face of the optical fiber and returns to the adjacent light receiving element on the same module side, there are many problems in terms of reception sensitivity.

  A technique for realizing bidirectional communication using the same wavelength using a waveguide is also disclosed (see, for example, Patent Document 2). In this method, there is no problem that the transmitted light from the light emitting element returns to the light receiving element on the same module side. However, input light from the optical fiber is also input to the light emitting element side as stray light to some extent. In this technique, the sub waveguide is made narrower than the main waveguide to prevent the input of stray light, but a slight amount of stray light input is inevitable. In the case where such stray light is present, if a semiconductor laser is used as a light emitting element, the output becomes unstable and the level of the optical signal changes. This problem occurs not only with edge-emitting lasers but also with VCSELs (surface-emitting lasers).

Thus, in order to realize a transmission / reception module that realizes bidirectional communication using optical signals of the same wavelength with a simple configuration, a module that stably propagates input / output signals from an optical fiber without loss is indispensable. However, the technology for constructing such a module is not sufficient.
JP 58-191543 A Japanese Patent Laid-Open No. 11-271548

  The present invention has been made in view of the problems as described above, and it is possible to adopt a configuration in which stray light is not input to both the light emitting element and the light receiving element using a light source having the same wavelength. An optical waveguide for bidirectional communication that realizes a bidirectional communication module is provided.

The above-mentioned subject is achieved by the following present invention. That is, the present invention
<1> A curved portion whose optical axis direction changes continuously in the middle of the optical path, a main coupling surface that couples light incident on a part of the curved portion is provided, and is smaller than the curvature of the main coupling surface A main waveguide core having a structure for guiding incident light with a curvature;
A sub-waveguide core having a sub-inclined surface at one end, the sub-inclined surface being opposed to or connected to the main coupling surface facing the main coupling surface, and having a refractive index equal to or lower than that of the main waveguide core When,
Have
The main waveguide core has a first core end that inputs and outputs bidirectional optical signals from the optical fiber, and a third core end that connects to the light receiving element, and receives input light from the first core end. Having a structure leading to the end of the third core via the curved portion;
The sub-waveguide core has a second core end connected to the light emitting element at an end opposite to the sub inclined surface, and the output light from the light emitting element is totally transmitted through the sub inclined surface. An optical waveguide for bidirectional communication having a structure for propagating to the main waveguide core.

<2> The main waveguide core and the sub-waveguide core are close to each other at the curved portion, and the main coupling surface and the sub-inclined surface are opposed to each other with a cladding portion interposed therebetween.
The curvature radius R of the curved portion, the main waveguide core width D ₁ , the angle between the sub-inclined surface and the optical axis of the sub-waveguide core is θ, the refractive index of the main waveguide core is n ₁ , and the sub-waveguide core <2> The optical waveguide for bidirectional communication according to <1>, wherein when the refractive index is n ₂ and the refractive index of the clad portion is n ₀ , these satisfy the following expressions (1) to (3): .
Expression (1): sin θ / (√ (n ₂ ² −n ₀ ² ) / n ₂ )> 1
Formula (2): √ (2 × D ₁ / R) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Formula (3): cos (β + γ) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Where β = sin ⁻¹ ((n ₂ / n ₁ ) cos θ), γ = (D ₁ / R) tan β

<3> The main waveguide core and the sub-waveguide core are close to each other at the curved portion, and the main coupling surface and the sub-inclined surface are directly connected,
The curvature radius R of the curved portion, the main waveguide core width D ₁ , the angle between the sub-inclined surface and the optical axis of the sub-waveguide core is θ, the refractive index of the main waveguide core is n ₁ , and the sub-waveguide core <2> The bidirectional communication according to <1>, wherein when the refractive index is n ₂ and the refractive index of the clad portion is n ₀ , these satisfy the following formulas (1) ′ to (3) ′: Optical waveguide.
Formula (1) ′: n ₂ > n ₀
Formula (2) ′: √ (2 × D ₁ / R) / (√ (n ₁ ² −n ₂ ² ) / n ₁ ) <1
Formula (3) ′: cos (β + γ) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Where β = sin ⁻¹ ((n ₂ / n ₁ ) cos θ), γ = (D ₁ / R) tan β

<4> The main waveguide core and the sub-waveguide core are close to each other at the curved portion, and the main coupling surface and the sub-inclined surface are opposed to each other at a predetermined interval. _1. The bidirectional communication according to <1>, wherein the distance between the tangent at the center of the main coupling plane and the sub-inclined plane is D _c , which satisfies the relationship of the following formula (4): Optical waveguide.
Equation _{(4): 0.1D 1 <D} c <D 1

<5> Both according to <1>, wherein when the width of the main waveguide core is D ₁ and the width of the sub-waveguide core is D ₂ , these satisfy the relationship of the following formula (5): Optical waveguide for communication.
Equation _{(5): 0.1D 1 ≦ D} 2 ≦ D 1

<6> A method for producing an optical waveguide for bidirectional communication according to any one of <1> to <5>,
At least 1) formed of a cured resin layer of a mold-forming curable resin, and at least connected in the thickness direction to a recess corresponding to the main waveguide core and the sub-waveguide core, and a resin entry end and a resin discharge end of the recess, respectively. 2) a step of preparing a mold provided with a through-hole, 2) a step of closely attaching a base material for clad to the mold, and 3) a resin entrance end of a recess corresponding to the main waveguide core and the sub-waveguide core. Filling the through-hole with a core-forming curable resin, bringing the core-forming curable resin into contact with the resin entry end, and entering the recesses corresponding to the main waveguide core and the sub-waveguide core; and 4 2) A method for producing an optical waveguide for two-way communication, which comprises a step of curing the entered core-forming curable resin.

<7> In the mold, a resin discharge end of a recess corresponding to the sub-waveguide core is provided at a tip on a recess side corresponding to the main waveguide core, and a linear communication path from the resin discharge end to the through hole A recess corresponding to is formed,
When the angle between the sub-inclined surface and the optical axis of the sub-waveguide core is θ, and the angle between the concave portion corresponding to the linear communication path and the concave portion corresponding to the sub-waveguide core is α, The method for producing an optical waveguide for bidirectional communication according to <6>, wherein α is in a range of the following formula (6).
Formula (6): θ <α ≦ 90 °

  The bidirectional communication optical waveguide according to the present invention can be applied to all communication modules that connect light emitting elements and light receiving elements having the same wavelength, so that it has high expandability and can further reduce costs. In addition, no separate parts such as a wavelength selection filter and a half mirror are required, and it is possible to transmit and receive bidirectionally in a stable light emission state by minimizing the return light to the light emitting element. Further, according to the method for manufacturing an optical waveguide for two-way communication of the present invention, since the process for producing the optical waveguide does not require an extra effort, not only can the cost be reduced, but a high-quality optical waveguide can be easily produced. can do.

Hereinafter, the present invention will be described in detail.
<Optical waveguide for bidirectional communication>
The optical waveguide for bidirectional communication according to the present invention has a curved portion whose optical axis direction continuously changes in the middle of the optical path, and has a main coupling surface for coupling light incident on a part of the curved portion, The main waveguide core has a structure that guides light incident with a curvature smaller than the curvature of the main coupling surface, and has a sub-inclined surface at one end, and the sub-inclined surface faces the main coupling surface. A sub-waveguide core that is close to or connected to the main coupling surface and has a refractive index equal to or lower than that of the main waveguide core, and the main waveguide core inputs and outputs bidirectional optical signals from the optical fiber. Having a third core end connected to the first core end and the light receiving element, and having a structure for guiding input light from the first core end to the third core end via the curved portion The second waveguide core is connected to the light emitting element at the end opposite to the sub-inclined surface. It has a section, and having a structure for propagating the main waveguide core by total transmission in the sub-inclined plane output light from the light emitting element.

First, the structure of the optical waveguide for bidirectional communication according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an example of a configuration of an optical waveguide for bidirectional communication (hereinafter sometimes simply referred to as “optical waveguide”) according to the present invention, and a module for bidirectional communication in which an optical fiber, a light receiving element, and a light emitting element are connected. It is a schematic block diagram (plan view) which shows. FIG. 5 is a partially enlarged plan view showing the periphery of the main waveguide core curve portion in the configuration example of the optical waveguide for bidirectional communication of the present invention.

  Here, although the waveguide core is configured to be covered with grad, the waveguide core is indicated by a solid line in the drawing for easy understanding.

  As shown in FIGS. 1 and 5, the bidirectional communication optical waveguide 100 of the present invention has a curved portion in which the optical axis direction continuously changes in the direction of arrow B in the middle of the optical path on the surface of the clad substrate 120. A main waveguide core 10 having P and a sub-waveguide core 50 that is close to the main waveguide core 10 through a cladding portion 40 are provided. The main waveguide core 10 includes a pre-curved main waveguide core 20 having an optical axis in the direction of arrow A and a post-curved main waveguide core 30 having an optical axis in the direction of arrow B, with the curved portion P as a boundary. The pre-curve main waveguide core 20 has a curvature smaller than that of the main coupling surface so that light incident from the sub-waveguide does not leak from the side surface of the main waveguide core before exciting the higher-order mode and reaching the end of the main waveguide. Need to be formed. In this example, it is a straight line (curvature 0). That is, a structure that guides incident light with a curvature smaller than the curvature of the main coupling surface corresponds to the pre-curved main waveguide core 20. The post-curved main waveguide core 30 is formed in a curved shape so that the optical axis direction continuously changes, and is formed in an S shape in this example.

  The main waveguide core 10 is provided with a main coupling surface 12 having a predetermined radius of curvature on the convex side surface of the curved portion P (the outer peripheral surface side having a large radius of curvature) for coupling incident light. At one end of the sub-waveguide core 50, a sub-inclined surface 52 is provided that forms an inclination angle θ (°) with the optical axis of the sub-waveguide core 50 (axis in the direction of arrow C). The main waveguide core 10 and the sub-waveguide core 50 are arranged close to each other so that the main coupling surface 12 and the sub-inclined surface 52 face each other with the cladding portion 40 therebetween. In this case, the main coupling surface 12 guides light entering the company from the clad portion.

In this case the sub-inclined surface 52 becomes primary connecting surface 12 centered generally parallel relationship between the tangent Q ₂ of. As a result, both are disposed close to each other with the clad portion 40 therebetween. Primary connecting surface 12, opposite ends of the auxiliary inclined surface 52 that faces (surfaces opposite widthwise ends, hereinafter the same) when subtracting the surface perpendicular imaginary line Q ₁ from the curve in the main waveguide core 10 surrounded by the line It is a part P side area. And the center of the arc-shaped main coupling surface 12 that is the side surface region of the curved portion P indicates a location where the width and thickness of the surface are halved.

  In the present invention, the main waveguide core 10 and the sub-waveguide core 50 may be close to each other with a certain distance therebetween via the main coupling surface 12 and the sub-inclined surface 52 as shown in FIGS. Alternatively, as shown in FIG. 6, the main coupling surface 12 and the sub-inclined surface 52 may be brought into contact with each other and connected.

  The main waveguide core 10 is connected to a communication optical fiber 150 to input / output bidirectional optical signals, and is connected to the pre-curve main waveguide core end 22 (first core end) and the light receiving element 70. It has a main waveguide core end 32 (third core end). The optical fiber 150 and the pre-curve main waveguide core end portion 22 or the light receiving element 70 and the post-curve main waveguide core end portion 32 can be directly opposed or connected via a condensing lens, a short light guide path, or the like. The input light propagated from the optical fiber 150 in the direction of arrow E propagates in the pre-curve main waveguide core 20 in the direction of arrow A from the pre-curve main waveguide core end 22 and reaches the main coupling surface 12.

And the primary connecting surface 12 the optical axis of the input light (optical axis of the main waveguide core 10), the radius of curvature R of the curved portion P, the width D ₁ of the main waveguide core, wherein the auxiliary inclined surface and the sub-waveguide core When the angle formed with the optical axis is θ, the refractive index of the main waveguide core is n ₁ , the refractive index of the sub-waveguide core is n _2, and the refractive index of the cladding is n ₀ ,
Formula (2): √ (2 × D ₁ / R) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
If the following relationship is satisfied, the input light that has reached the main coupling surface 12 does not escape from the main coupling surface 12, and the post-curved main waveguide core end that connects the inside of the curved main waveguide core 30 to the light receiving element 70 in the direction of arrow B is obtained. The part 32 can be guided.

Here, the radius of curvature R of the curved portion P is the main waveguide surrounded by the main coupling surface 12, that is, when a virtual line Q ₁ perpendicular to the surface is drawn from both ends of the opposing sub-inclined surface 52. The average curvature radius of the curved portion P region in the core 10 is shown.

  On the other hand, the sub-waveguide core 50 provided independently of the main waveguide core 10 has a sub-waveguide core end 54 (second core end) connected to the light-emitting element 60, and an arrow emitted from the light-emitting element 60. The output light in the C direction is guided in a direction parallel to the optical axis of the pre-curved main waveguide core 20 and reaches the sub-inclined surface 52 with the clad 40 interposed therebetween.

The optical axis of the output light is also inclined at an angle θ with respect to the sub-inclined surface 52, but the refractive index is selected so that the following equation (1) is satisfied when the refractive index of the sub-waveguide core 50 is n _2. Then, the output light reaching the sub inclined surface 52 is totally transmitted through the sub inclined surface 52. Further, by satisfying the following formula (3), the output light stays in the main waveguide, and the end of the pre-curve main waveguide core that connects the optical waveguide 150 in the pre-curve main waveguide core 20 in the direction of arrow D 22 is finally output to the optical fiber 150 through the connection end face with the optical fiber 150 and propagated in the direction of arrow F.

Expression (1): sin θ / (√ (n ₂ ² −n ₀ ² ) / n ₂ )> 1
Formula (3): cos (β + γ) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Where β = sin ⁻¹ ((n ₂ / n ₁ ) cos θ), γ = (D ₁ / R) tan β

  In the present invention, “total reflection” and “total transmission” include, of course, a case where incident light is 100% reflected or transmitted 100%, but other incident light is reflected or transmitted by 51% or more. It is meant to include cases.

  In the optical waveguide of the present invention, as described above, the input light from the optical fiber 150 is totally reflected by the main coupling surface 12, and the output light from the light emitting element 60 is totally transmitted by the sub-inclined surface 52. The return light to the optical fiber 150 and the light emitting element 60 and the leakage of the input light from the main waveguide core 10 to the sub-waveguide core 50 are almost eliminated, and bidirectional transmission / reception can be efficiently performed.

Then, in the bidirectional communication optical waveguide as in the present invention, the refractive index n ₁ as the basic conditions, the refractive index n ₂ of the sub-waveguide core 50 in the present invention is the main waveguide core 10 in order to achieve the above It is necessary to be the same or lower (n ₂ ≦ n ₁ ). In the optical waveguide for bidirectional communication of the present invention finally obtained when the refractive index n ₂ of the sub-waveguide core 50 exceeds the refractive index n ₁ of the main waveguide core 10 (n ₂ > n ₁ ), Input light from the optical fiber 150 cannot be reflected to the light receiving element 70, and it becomes extremely difficult to propagate output light from the light emitting element 60 to the optical fiber 150.

  Here, the left side of the equation (2) represents the ratio of the propagation angle of light from the optical fiber 150 to the confinement limit angle of the main waveguide core 10. Further, the left side of the equation (3) represents the ratio of the propagation angle of light from the sub-waveguide core 50 to the confinement limit angle of the main waveguide core 10. Therefore, it is desirable that the left side of both be smaller than 1. 0.9 or less is desirable, and 0.83 or less is more desirable.

  The left side of the formula (1) represents the ratio of the propagation angle of light from the light emitting element 60 to the confinement limit angle of the sub-waveguide core 50. Therefore, it is desirable to be larger than 1 as much as possible. 1.1 or more is desirable, and 1.2 or more is more desirable.

  1 and 5 show a configuration in which the clad portion 40 is sandwiched between the main coupling surface 12 and the sub-inclined surface 52. In the present invention, as shown in FIG. Even in a state where the surface 12 and the sub-inclined surface 52 are in contact, that is, in a state where the main waveguide core 10 and the sub-waveguide core 50 are directly connected, the following relationship, that is, the following relationship is obtained instead of the formulas (1) to (3). If the relationship of (1) '-(3)' is satisfy | filled, the above outstanding characteristics can be acquired.

  Here, when the main waveguide core 10 and the sub-waveguide core 50 are directly connected as shown in FIG. 6, the sub-inclined surface 52 is a planar joint surface between the main waveguide core 10 and the sub-waveguide core 50. 52A is shown. Further, the main coupling surface 12 indicates a virtual surface 12 </ b> A having a side shape of the main waveguide core 10 at the joint portion with the sub waveguide core 50. The curvature radius R of the curved portion P indicates the average curvature radius of the curved portion side surface of the main waveguide core 10, that is, the imaginary surface 12A, in a region surrounded by both ends of the joining surface 52A. The angle θ formed between the sub-inclined surface 52 and the optical axis of the sub-waveguide core 50 represents the angle formed between the joint surface 52A and the optical axis of the sub-waveguide core 50.

Formula (1) ′: n ₂ > n ₀
Formula (2) ′: √ (2 × D ₁ / R) / (√ (n ₁ ² −n ₂ ² ) / n ₁ ) <1
Formula (3) ′: cos (β + γ) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Where β = sin ⁻¹ ((n ₂ / n ₁ ) cos θ), γ = (D ₁ / R) tan β

  Further, as will be described later, the clad 40 is preferably formed integrally with the upper clad layer with the same material when used for the upper clad layer when forming the upper clad layer. As long as the refractive index is lower than that of the core or the sub-waveguide core, it may be formed of a material different from that of the upper cladding layer.

  According to the basic configuration as described above, the input light propagated from the optical fiber for communication 150 through the pre-curve main waveguide core 20 reaches the light receiving element 70 without leaking to the light emitting element 60 side, The output light can reach the communication optical fiber 150 without leaking to the light receiving element 70 side. Since this can be realized regardless of the wavelength of the light to be used, the input light and the output light can be made the same wavelength. In particular, by configuring the main coupling surface 12 in a curved shape, light leakage to the sub-waveguide core 50 is reduced as compared with a case where the main coupling surface 12 is bent.

  Further, in addition to the above basic configuration, in the present invention, the end face of the optical fiber that transmits the optical signal is opposed to the end of the pre-curved main waveguide core, that is, directly without using a condensing lens or the like. In the case of optical connection, it is preferable that the numerical aperture NA1 of the main waveguide core and the numerical aperture NAf of the optical fiber are substantially equal. That is, if the numerical aperture NA1 of the main optical waveguide core 10 is set to be equal to or larger than the numerical aperture NAf of the communication optical fiber 150, for example, even if the optical fiber for communication 150 is directly coupled to the main optical waveguide core without a lens, The connection loss of the input light propagated from can be minimized.

  On the other hand, there is a possibility that the output light from the light emitting element 60 has its spread angle increased by the main waveguide core 10, but the increase amount of the spread angle is when the length of the pre-curve main waveguide core 20 is 10 mm or less. Since it can be almost ignored, it does not contribute to an increase in the loss of output light to the optical fiber 150.

Note that the numerical aperture NA1 of the main waveguide core 10 is n ₁ when the refractive index of the main waveguide core 10 is n ₁ and the refractive index of the cladding portion 40 is n ₀ .
Formula: sin ⁻¹ √ (n ₁ ² −n ₀ ² )
If the numerical aperture NAf of the optical fiber 150 is known, the refractive index of the main waveguide core 10 and the cladding part 40 can be adjusted to make NA1 and NAf within the above ranges.

Therefore, the angle of the curve is more preferably (2 ± 0.5) θ °, and particularly preferably 2θ.
Of course, the downstream portion of the post-curved main waveguide core 30 can be reduced in size (width) of the entire waveguide by introducing a bending element or the like along the way.

FIG. 2 is a plan view showing in more detail the configuration of the bidirectional communication optical waveguide of the present invention used in the bidirectional communication module shown in FIG.
In FIG. 2, the optical fiber, the light emitting element, and the light receiving element connected in FIG. 1 are removed, and are shown as port 1, port 2, and port 3, respectively.

In the present invention, the main waveguide core 10 and the sub-waveguide core 50 as shown in FIGS. 2 and 5 are close to each other at the curved portion P, and the main coupling surface 12 and the sub-inclined surface 52 are spaced from each other by a distance D _c. for placed as opposed to each other constitute a may be a scattering loss of the output light propagating from the sub-waveguide core 50 by sufficiently small this distance D _c in the main waveguide core 10 a minimum. Here, the distance D _c indicates the distance between the tangent line Q _{2 at} the center of the main coupling surface 12 and the sub-inclined surface 52.

However, it goes without saying that the larger the distance D _c is, the easier it is to make from the viewpoint of the waveguide fabrication process. Therefore, in the present invention, the distance between the center tangent Q ₂ of the main coupling surface 12 and the sub-inclined surface 52 is D _c (μm), and the width of the main waveguide core 10 (usually, the main waveguide core 20 before the curve and the main curve surface after the curve). It is found that when the main waveguide core 30 has the same value (D ₁ (μm)), the optical waveguide can be easily manufactured while minimizing loss by satisfying the relationship of the following formula (4). It was.
Equation _{(4): 0.1D 1 <D} c <D 1

The D _c is more preferably 0.2D ₁ ≦ D _c ≦ 0.5D ₁ . It may be difficult in actual manufacturing to make D _c equal to or less than 0.1D ₁ . If D _c is greater than or equal to D ₁ , the propagation loss of the output light from the sub-waveguide core 50 to the main waveguide core 10 may increase significantly.

In the present invention, when the width of the main waveguide core 10 is D ₁ (μm) and the width of the sub-waveguide core 50 is D ₂ (μm), these satisfy the relationship of the following formula (5): The sub-waveguide core 50 is preferably close to or connected to the main waveguide core 10 so that the optical axis of the sub-waveguide core 50 and the optical axis of the pre-curved main waveguide core 20 are aligned with each other.
Equation _{(5) 0.1D 1 ≦ D 2} ≦ D 1

The D ₂ is more preferably 0.2D ₁ ≦ D ₂ ≦ 0.8D ₁ . By adopting such a configuration, it is possible to reduce the amount of input light propagating from the optical fiber 150 that passes through the main coupling surface 12 without being reflected and enters the sub-waveguide core 50 as stray light. . However, if D ₂ is unnecessarily small, positional tolerance in coupling with the light emitting element becomes strict or coupling efficiency decreases. Therefore, it is necessary to determine the balance in consideration of these balances.

  In the above description, an example in which the sub-waveguide core 50 is configured by only a straight line has been described. It goes without saying that there is no problem even if a bending element is inserted.

The bidirectional communication optical waveguide of the present invention described above usually has a waveguide core having a desired shape formed on the surface of a clad base material (in some cases, a clad layer is provided on a substrate). It is produced by forming an upper cladding layer on the surface. As a material for the waveguide core, either an inorganic material such as quartz or a polymer material such as polyimide may be used.
The details of the clad substrate will be described later.

  The waveguide core can be formed by a manufacturing method using photolithography or RIE (reactive ion etching), which is generally used, but generally has a problem of high cost. In particular, in the present invention, since it is desirable to produce a core shape having two types of refractive indexes, there is a problem that the cost is further increased. For this reason, for producing the optical waveguide for bidirectional communication of the present invention, for example, the polymer optical waveguide manufacturing method described in Japanese Patent Laid-Open No. 2004-29507, which has already been proposed by the present inventors as described later, is used. It is preferable to use an applied manufacturing method from the viewpoint of cost reduction.

<Method of manufacturing optical waveguide for bidirectional communication>
The method for manufacturing an optical waveguide for bidirectional communication according to the present invention is a method for manufacturing the optical waveguide for bidirectional communication according to the present invention,
At least 1) formed of a cured resin layer of a mold-forming curable resin, and at least connected in the thickness direction to a recess corresponding to the main waveguide core and the sub-waveguide core, and a resin entry end and a resin discharge end of the recess, respectively. 2) a step of preparing a mold provided with a through-hole, 2) a step of closely attaching a base material for clad to the mold, and 3) a resin entrance end of a recess corresponding to the main waveguide core and the sub-waveguide core. Filling the through-hole with a core-forming curable resin, bringing the core-forming curable resin into contact with the resin entry end, and entering the recesses corresponding to the main waveguide core and the sub-waveguide core; and 4 ) Including a step of curing the entered core-forming curable resin.

  By producing an optical waveguide by such a manufacturing method, waveguide cores having different refractive indexes can be formed at the same time, and not only the efficiency of manufacturing and cost reduction can be achieved, but also in the case of an etching method or the like. Thus, it is not necessary to form different waveguide cores in several steps, so that a high-quality optical waveguide can be produced without damaging the already formed waveguide core in other waveguide core forming processes. .

  First, the basic process of the method for manufacturing an optical waveguide for two-way communication according to the present invention will be outlined by the case where one waveguide core is provided.

  3A to 3G are conceptual diagrams showing each process of manufacturing the optical waveguide. FIG. 3A shows the master 200, and 220 is a convex portion corresponding to the waveguide core (hereinafter sometimes referred to as “waveguide core convex portion”). A mold forming curable resin is applied or cast on the convex forming surface of the master 200 and then cured (see FIG. 3B). In FIG. 3B, reference numeral 300a denotes a cured resin layer. Thereafter, when the cured resin layer 300a is peeled off, a cured resin layer 300a in which a recess corresponding to the waveguide core (hereinafter, also referred to as “waveguide core recess”) is formed (not shown). Through-holes 360 and 380 communicating with the waveguide core recess 320 are formed in the cured resin layer 300a in which the waveguide core recess 320 is formed by punching or the like at both ends of the recess 300 (see FIG. 3C). Get. In the mold 300, the end of the waveguide core recess 320 on the through hole 360 side is a resin input end 370, and the end of the through hole 380 side is a resin output end 390.

  Next, as shown in FIG. 3D, the clad substrate 400 is brought into close contact with the mold 300. Thereafter, a core-forming curable resin is placed in the through-hole 360 formed in the mold, the resin is brought into contact with the resin input end 370, and suction is performed from the resin output end 390 through capillary action or the through-hole 380 to reduce the pressure. The waveguide core recess 320 is filled with a core-forming curable resin. Thereafter, when the resin is cured and the mold is peeled off, a waveguide core 420 is formed on the clad substrate 400 as shown in FIG.

  Thereafter, an upper cladding layer 500 is formed (see FIG. 3F), and finally the resin portion cured in the through holes 360 and 380 is cut off with a dicer or the like to form an optical waveguide 110 (see FIG. 3G). ).

  In the above example, after the waveguide core is formed using the mold 300, the mold 300 is peeled off to provide the upper clad layer 500. However, in the present invention, depending on the material of the mold, the mold is used as described later. The mold can be used as it is as the upper clad layer without peeling off 300.

  Hereinafter, an example of the manufacturing method of the optical waveguide for bidirectional communication according to the present invention will be described in the order of steps with reference to FIG. 4A to 4E are schematic views (plan views) sequentially illustrating steps for manufacturing the bidirectional communication optical waveguide shown in FIG. Hereinafter, in FIGS. 4A to 4E, for easy understanding, the waveguide core and the concave and convex portions for manufacturing the waveguide core are shown by solid lines, and other portions (members) are omitted. May show.

(Process to prepare mold)
The template is preferably manufactured using the master having the convex portions corresponding to the waveguide core as described above, but is not limited thereto. In the following, a method using the master will be described.

  First, as shown in FIG. 4A, in addition to the main waveguide core convex portion 222 and the sub waveguide core convex portion 224 on the silicon substrate 202, the resin output of the concave portion corresponding to the sub waveguide core is further provided. In order to provide the end, a master plate 210 is prepared by adding a straight air vent passage (communication passage) convex portion 226 to the tip of the sub waveguide core convex portion 224 on the main waveguide core convex portion side.

  A conventional method such as a photolithography method, an RIE method, a machining method, or the like can be used for the production of the master 210 on which the convex portions are formed without particular limitation. The size (core diameter) of the convex portion corresponding to the waveguide core formed on the master is generally about 5 to 500 μm, preferably about 40 to 200 μm, and is appropriately determined according to the use of the optical waveguide. . For example, in the case of a single-mode optical waveguide, a core of about 10 μm square is generally used, and in the case of a multi-mode optical waveguide, a core of about 40 to 150 μm square is generally used. An optical waveguide having a larger core part of about several hundred μm is also used.

  The size of the air vent passage convex portion 226 is preferably sufficiently larger than that of the sub-waveguide core convex portion 224 corresponding to the sub-waveguide core because there is a possibility that light may be scattered from this portion in the finally completed optical waveguide. It is desirable to be thin. Thereby, as will be described later, when the core forming resin is made to enter by sucking from this portion, there is an advantage that the resin is hardly filled in this portion.

  The cured resin layer used as the mold is obtained by applying or casting a mold-forming curable resin to the surface on which the convex portion corresponding to the waveguide core of the master produced as described above is formed. After the drying treatment as necessary, the resin is cured, and then the cured resin layer is peeled off.

  FIG. 4B shows a state in which the produced mold is viewed from the side opposite to the peeling surface. In addition to the main waveguide core recess 322 and the sub waveguide core recess 324 corresponding to each core, the mold 310 made of the cured resin layer is further provided with a resin output end of the corresponding recess of the sub waveguide core. Therefore, a straight air vent passage recess 326 (communication passage 326) is formed at the tip of the sub waveguide core recess 324 on the main waveguide core recess 322 side.

Here, it is conceivable that the air vent passage recess 326 is slightly filled with a resin for forming a core. Even in this case, it is preferable to minimize the scattering loss in this portion. For this reason, the angle between the sub-inclined surface and the optical axis of the sub-waveguide core is θ, and a recess corresponding to the linear communication path (air vent path recess 326) and a recess corresponding to the sub-waveguide core (sub-guide) When the angle formed by the waveguide core recess 324) is α, it is preferable that α be in the range of the following formula (6). In the figure, α and θ indicate angles formed by corresponding concave portions.
Formula (6): θ <α ≦ 90 °

  When α is 90 °, that is, orthogonal to the side surface of the sub-waveguide, the size of the defect on the side surface of the sub-waveguide due to the provision of the air vent passage can be minimized. In addition, when the angle approaches the angle θ of the sub-inclined surface, the blunting of the tip of the sub-inclined surface can be minimized. Therefore, it is desirable to select an angle between α. The diameter of the air vent passage recess 326 can be selected to have an appropriate size and shape in consideration of the above-described purpose and ease of manufacture.

  Further, the mold 310 made of a cured resin layer is formed with a resin entry end for filling the recesses with the core-forming curable resin and a resin discharge end for discharging the curable resin from the recesses. However, as a method of forming these, as shown in FIG. 4B, through holes 362, 364, 382, and 384 are formed at both ends of the concave portion (and the end portion of the concave portion for the communication path) in the cured resin layer. It is effective to provide

  By providing these through holes, the resin entrance end and the resin discharge end are formed at the same time. Further, the through hole on the resin entrance end side can be used as a liquid (resin) reservoir, and the through hole at the resin discharge end is a vacuum suction pipe. The inside of the recess can be connected to a vacuum suction device. It is also possible to connect the through hole on the resin entry end side to the core forming curable resin injection tube and inject the resin under pressure.

  As the mold forming curable resin, the cured product can be easily peeled from the master, the mold (repetitively used) has a certain level of mechanical strength and dimensional stability, and the hardness (hardness to maintain the concave shape) ) And good adhesion to the clad substrate. Various additives can be added to the mold-forming curable resin as necessary.

  When the mold-forming curable resin is in an uncured state, it can be applied or cast onto the surface of the master, and the projection corresponding to the core of each optical waveguide formed on the master can be accurately copied. Since it must be taken, it is preferable to have a certain appropriate viscosity, for example, in the range of about 500 to 7000 mPa · s. (Note that the “mold forming curable resin” used in the present invention also includes a resin that becomes a rubber-like body having elasticity after curing.) In addition, a solvent is used for other members to adjust the viscosity. It may be added to the extent that there is no adverse effect.

  The mold-forming curable resin is a silicone rubber (silicone elastomer) or a silicone resin in terms of peelability, mechanical strength / dimensional stability, hardness, and adhesion to a clad substrate. An organopolysiloxane is preferably used. The curable organopolysiloxane preferably contains a methylsiloxane group, an ethylsiloxane group, or a phenylsiloxane group in the molecule. The curable organopolysiloxane may be a one-component type or a two-component type used in combination with a curing agent, and may be a thermosetting type or a room temperature curable type (for example, cured with moisture in the air). The other) (further ultraviolet curing or the like) may be used.

  The curable organopolysiloxane is preferably in a rubbery state after curing, which is usually referred to as a liquid silicone rubber (“liquid” includes those having a high viscosity such as a paste). The two-part type used in combination with a curing agent is preferable. Among them, the addition type liquid silicone rubber cures uniformly in a short time on the surface and the inside, and at that time, a by-product is formed. It is preferably used because it has no or little, excellent releasability and low shrinkage.

  Among the liquid silicone rubbers, liquid dimethylsiloxane (PDMS) rubber is particularly preferable in terms of adhesion, peelability, controllability of strength and hardness. In addition, since the cured product of liquid dimethylsiloxane rubber generally has a low refractive index of about 1.43, the cured resin layer as a mold made from it is used as it is as the upper cladding layer without being peeled off from the cladding substrate. can do. In this case, it is necessary to devise such that the cured resin layer is not peeled off from the filled core forming resin and the clad base material.

  The liquid silicone rubber has a viscosity that accurately captures the convex portion corresponding to the core portion of the optical waveguide, reduces bubbles and facilitates defoaming, and forms a mold with a thickness of several millimeters. To about 500 to 7000 mPa · s, more preferably about 2000 to 5000 mPa · s.

The hardness of the mold 310 made of the cured resin layer is preferably in the range of 10-50 in Shore A hardness. By using such a cured resin layer having a soft rubbery characteristic, it is possible to improve the molding characteristics of the peeling after the core part is formed and to give a precise core forming ability. As the thickness of the cured resin layer, an appropriate value can be selected with high accuracy so that the molding accuracy can be maintained with respect to vibration and pressure change when the core-forming curable resin is injected.
The hardness (Shore A hardness) of the mold 310 can be measured according to JIS K 6253 using a durometer.

The surface energy of the mold 310 made of the cured resin layer is preferably in the range of 7 to 30 mN / m, and more preferably in the range of 12 to 21 mN / m. The surface energy is preferably in the above range from the viewpoint of adhesion to the clad substrate and penetration rate of the core-forming curable resin.
In the present invention, the surface energy is measured by a method for calculating a critical surface tension by the Zisman method.

Furthermore, the arithmetic average roughness Ra of the concave portion of the mold 310 made of the cured resin layer is preferably 0.1 μm or less, more preferably 0.05 μm or less. By setting the surface roughness of the recess to the above range, the optical loss can be significantly reduced in the optical waveguide characteristics of the formed core portion.
In the present invention, the arithmetic average roughness Ra can be measured under the conditions of JIS (B0601).

(Step of closely attaching the mold to the clad substrate)
The clad base material used in the present invention is a silicon substrate or an electronic circuit substrate, and as the base material, a silicon wafer, a glass base material, a ceramic base material, a plastic base material or the like is used without limitation.

  In addition, in the case of a base material having an appropriate refractive index, it is used as it is as a base material for a clad. However, a resin coat or an inorganic material as a clad layer is entirely or partially applied to the base material for a clad when the refractive index control is required. A film formed by PVD (Physical Vapor Deposition) is also used. In the present invention, the substrate provided with the cladding layer is also referred to as a cladding substrate.

The refractive index of the clad substrate in the present invention (when the clad layer is provided) is preferably less than 1.55, and more preferably less than 1.49. In particular, it is necessary to be 0.01 or more smaller than the refractive index of the waveguide core.
In addition, the refractive index of each said base material and layer is measured using a prism coupler, an ellipsometer, and an Abbe refractometer (The measurement of refractive indexes of other core parts etc. is also the same).

  In addition, as the characteristics of the base material for cladding, in terms of smoothness, the arithmetic average roughness Ra of the surface is 0.1 μm or less, and it has excellent adhesion to the mold (cured resin layer). What does not produce a space | gap other than a recessed part is preferable. Also, if the clad substrate is not very good in adhesion to the mold and / or the core, the treatment with an ozone atmosphere and ultraviolet irradiation with a wavelength of 300 nm or less should be performed to improve the adhesion with the mold or the like. Is preferred.

  An optical waveguide using a flexible film base material among the plastic base materials as a clad base material can be used as an optical wiring between a coupler and a board, an optical demultiplexer, or the like. The film base material has optical properties such as refractive index and light transmittance, mechanical strength, surface smoothness, heat resistance, adhesion to a mold, and flexibility according to the use of the polymer optical waveguide to be produced. It is selected in consideration of tee (flexibility) and the like.

  Examples of the material for the film base include acrylic resins (polymethyl methacrylate, etc.), alicyclic acrylic resins, styrene resins (polystyrene, acrylonitrile / styrene copolymers, etc.), olefin resins (polyethylene, polypropylene, ethylene Propylene copolymer, etc.), alicyclic olefin resin, vinyl chloride resin, vinylidene chloride resin, vinyl alcohol resin, vinyl butyral resin, arylate resin, fluorine-containing resin, polyester resin (polyethylene terephthalate, polyethylene naphthalate) Phthalate, etc.), polycarbonate resin, cellulose di- or triacetate, amide resin (aliphatic, aromatic polyamide, etc.), imide resin, sulfone resin, polyether sulfone resin, polyether ether ketone resin, polyphenyle Sulfide resins, polyoxymethylene-based resin, or a blend or the like of the resins.

  Examples of the alicyclic olefin resin include those having a norbornene structure in the main chain, and those having a norbornene structure in the main chain and an alkyloxycarbonyl group in the side chain (the alkyl group having 1 to 6 carbon atoms or a cycloalkyl group). ) And the like having polar groups. Among them, the alicyclic olefin resin having a norbornene structure in the main chain and a polar group such as an alkyloxycarbonyl group in the side chain as described above has a low refractive index (refractive index is around 1.50, core clad It has excellent optical characteristics such as high refractive index and high optical transparency, excellent adhesion to the mold, and excellent heat resistance. Is suitable.

The thickness of the film substrate is appropriately selected in consideration of flexibility, rigidity, ease of handling, and the like, and is generally preferably in the range of 0.03 mm to 0.5 mm.
Further, the smoothness of the film substrate surface to be used is preferably 10 μm or less, more preferably 1 μm or less, and still more preferably 0.1 μm or less in terms of arithmetic average roughness Ra.

(Step of allowing the core-forming curable resin to enter the recess of the mold)
In order to allow the core-forming curable resin to enter the recess of the mold, the base material for cladding, which is one size larger than the mold, is brought into close contact with the mold, and a small amount of the core-forming curable resin is dripped at the resin entrance end of the recess. , Filling the resin entrance end of the recess with pressure-filling curable resin for core formation, suctioning the resin discharge end of the recess under reduced pressure, or both the pressure filling and vacuum suction It can be filled by performing.

  FIG. 4C shows a state in which the core-forming curable resin is made to enter the waveguide core recess using the mold made of the PDMS rubber. In FIG. 4C, core-forming curable resins having different refractive indexes are filled in the through-holes 362 and 364 of the mold 310 that are in close contact with the film base material 410 serving as the clad base material, By suctioning from 384 under reduced pressure, the resin enters the main waveguide core recess 322 and the sub-waveguide core recess 324 at the same time from the two resin entrance ends on the left side in the drawing.

  In this case, in particular, the sub-waveguide core recess 324 needs to be sucked from the side of the communication path 326 (air vent path recess 326). The tip portion on the main waveguide side of the sub-waveguide core that is finally formed is required to have a shape accuracy that prevents the output light of the light emitting element from leaking. Therefore, a thin suction port such as a communication passage 326 (air vent passage recess 326) is provided at the tip portion (resin discharge end) as shown in the figure, and even if the resin reaches this portion, the communication passage 326 is opened. It is desirable that the resin is filled only in a part.

In this way, by forming the sub-waveguide core by providing the narrow communication path 326 at the resin discharge end on the front end side of the sub-waveguide core recess 324, the sub-waveguide core intersects with the communication path at the front end of the sub-waveguide core. Although some shape defects occur in the portion (see FIG. 4D), the size can be reduced to 10 μm or less, so that it does not cause a large loss factor.
The width of the communication path 326 is preferably 0.5 D ₂ or less with respect to the width D ₂ of the sub-waveguide core.

As the core-forming curable resin, resins such as radiation curable, electron beam curable, and thermosetting can be used, and among them, an ultraviolet curable resin and a thermosetting resin are preferably used. As the ultraviolet curable resin or thermosetting resin for forming the core, an ultraviolet curable or thermosetting monomer, an oligomer, or a mixture of a monomer and an oligomer is preferably used. In particular, the mixing of the oligomer helps the curing speed and improves the accuracy of the shape.
As the ultraviolet curable resin, an epoxy, polyimide or acrylic ultraviolet curable resin is preferably used.

  The core-forming curable resin needs to have a sufficiently low viscosity so as to be able to be filled in a gap (a concave portion of the mold) formed between the mold and the clad substrate. The uncured viscosity of the core-forming curable resin is preferably in the range of 50 mPa · s to 2000 mPa · s, more preferably in the range of 100 mPa · s to 1000 mPa · s, and still more preferably in the range of 300 mPa · s to 700 mPa · s. The range is desirable in terms of filling speed, good core shape, and low light loss.

  In addition, in order to accurately reproduce the original shape of the convex portion corresponding to the waveguide core formed on the master, it is necessary that the volume change before and after curing of the curable resin is small. For example, a decrease in volume causes a large waveguide loss. Therefore, it is desirable that the curable resin has a volume change as small as possible, preferably 10% or less, and more preferably 0.01 to 4%. Lowering the viscosity using a solvent is preferably avoided if possible because the volume change before and after curing is large.

In order to reduce the volume change (shrinkage) after curing of the core-forming curable resin, a polymer can be added to the resin. The polymer is preferably compatible with the core-forming curable resin and does not adversely affect the refractive index, elastic modulus, and transmission characteristics of the curable resin. In addition to reducing the volume change by adding a polymer, the viscosity and the glass transition point of the cured resin can be highly controlled.
Examples of the polymer include acrylic, methacrylic acid, and epoxy polymers, but are not limited thereto.

  The refractive index of the cured product of the core-forming curable resin is preferably in the range of 1.20 to 1.60, more preferably in the range of 1.4 to 1.6. In the present invention, the refractive index of the sub-waveguide core needs to be equal to or lower than the refractive index of the main waveguide core.

  The refractive index of the cured product of the core-forming curable resin needs to be larger than the clad base material (or the clad layer and the clad portion). The difference in refractive index between the core and the clad base material varies depending on whether it is a multimode waveguide or a single mode waveguide, but is 0.01 or more, preferably 0.02 or more in the case of a multimode waveguide. In the case of a main waveguide core for connecting an optical fiber, it is desirable to determine the refractive index difference between the core and the clad so that the numerical aperture of the optical fiber can be matched.

In this step, it is desirable to reduce the pressure of the entire system (about −0.1 to −100 kPa with respect to normal pressure) in order to promote filling of the core-forming curable resin into the mold recess by capillary action. .
In order to promote the filling, it is also an effective means to lower the viscosity by heating the core-forming curable resin filled from the entrance of the mold in addition to the pressure reduction of the system.

(Step of curing the core-forming curable resin that has entered)
In this step, the entered core-forming curable resin is cured by various means. In order to cure the ultraviolet curable resin, an ultraviolet lamp, an ultraviolet LED, a UV irradiation device or the like is used. In order to cure the thermosetting resin, means for accelerating curing such as heating in an oven is also effective.

In the present invention, the following steps can be provided if necessary.
(Process of peeling the mold from the clad substrate)
This step is a step of peeling the mold from the clad substrate after the step of curing the core-forming curable resin. As described above, the cured resin layer as a mold used in each step can be used as an upper clad layer as long as the refractive index and other conditions are satisfied. In this case, it is not necessary to peel off the mold as it is. Used as the upper cladding layer. In this case, it is preferable to treat the mold with ozone in order to improve the adhesion between the mold and the waveguide core.

In the present invention, it is preferable to use the mold repeatedly from the viewpoint of cost reduction, etc., and this step and the following upper clad layer forming step are usually performed.
FIG. 4D shows a plan view of the clad base material on which the waveguide core is formed with the mold peeled off. As shown in the figure, the main waveguide core 16 and the sub-waveguide core 56 with the resin portions 17 and 57 cured in the through holes remaining on the end portions on the film base 410 are interposed via the cladding portion 42. Are formed in close proximity. As described above, some shape defects (convex portions) are seen at the leading end of the sub-waveguide core on the main waveguide side as shown in the enlarged view.

(Process of forming the upper cladding layer on the cladding substrate on which the core is formed)
In this process, an upper clad layer is formed on a clad base material on which a waveguide core is formed. As the upper clad layer, a film (for example, the base material of the clad base material is also used), a clad Examples thereof include a layer obtained by applying a curable resin for curing and a polymer film obtained by applying and drying a solution of a polymer material. As the clad curable resin, an ultraviolet curable resin or a thermosetting resin is preferably used. For example, an ultraviolet curable or thermosetting monomer, an oligomer, or a mixture of a monomer and an oligomer is used.

  In order to reduce the volume change (shrinkage) of the clad-forming curable resin after curing, it is compatible with the curable resin and does not adversely affect the refractive index, elastic modulus, and transmission characteristics of the resin. A polymer (for example, methacrylic acid type, epoxy type) can be added to the resin.

  When a film is used as the upper clad layer, it is bonded using an adhesive. At this time, it is desirable that the refractive index of the adhesive is close to the refractive index of the film. As the adhesive to be used, an ultraviolet curable resin or a thermosetting resin is preferably used. For example, an ultraviolet curable or thermosetting monomer, an oligomer, or a mixture of a monomer and an oligomer is used. Further, in order to reduce the volume change (shrinkage) after curing of the ultraviolet curable resin or thermosetting resin, a polymer similar to the polymer added to the upper cladding layer can be added.

  In the present invention, as shown in FIG. 4D, the main waveguide core 16 and the sub-waveguide core 56 are close to each other, and the clad portion 42 is provided between the main coupling surface and the sub-inclined surface. In this case, the clad portion 42 can be filled with a curable resin or the like simultaneously with the formation of the upper clad layer. In this case, the resin filled in the clad portion 42 may be the same resin as the upper clad layer or a different resin. The upper clad layer may be a film and the clad portion 42 may be an air layer.

  The difference in refractive index between the clad substrate and the upper clad layer is preferably small, and the difference is preferably within 0.1, more preferably within 0.05, still more preferably within 0.001, It is most preferable from the viewpoint of light confinement.

  In the production of the optical waveguide described above, in particular, a liquid silicone resin that is cured as a curable resin for mold formation and becomes a rubbery state, in particular a liquid dimethylsiloxane liquid, has a norbornene structure in the main chain as a cladding substrate. In addition, the combination using an alicyclic olefin resin having a polar group such as an alkyloxycarbonyl group in the side chain has particularly high adhesion between the two, there is no deformation of the mold concave structure, and the sectional area of the concave structure is extremely high. Even if it is small (for example, a 10 × 10 μm rectangle), the concave portion can be quickly filled with the curable resin.

  Thereafter, as shown in FIG. 4 (E), the resin portions 17 and 57 finally cured in the through holes are cut off by a dicer or the like to form the post-curved main waveguide core end portion 34 and the sub-waveguide core end portion 58. Further, the pre-curve main waveguide core end 24 is formed to form the optical waveguide 111. In addition, the core end surface of each edge part formed by cutting off has mirror smoothness.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.
<Example 1>
(Production of optical waveguide for bidirectional communication)
An optical waveguide for bidirectional communication having an overall length of 3 mm and a width of 1 mm as shown in FIG. 2 was produced.

-Production of mold-
As shown in FIG. 4 (A), a thick film resist (manufactured by Micro Chemical Co., Ltd., SU-8) is applied on a silicon substrate 202 by a spin coating method, then pre-baked at 80 ° C., exposed through a photomask, After development, the main waveguide core convex portion 222 (width D ₁ : 50 μm, height: 50 μm) and sub-waveguide core convex portion 224 (width D ₂ : 50 μm, height: 50 μm) of the bidirectional communication waveguide. ), And an air vent (communication path) convex portion 226 (width: 20 μm, height: 50 μm) connected to the tip of the main waveguide core side of the sub-waveguide core convex portion 224 at a right angle. This was post-baked at 120 ° C. to produce a master 210 for producing an optical waveguide core.

In the above, the angle θ between the linear direction (optical axis) of the convex portion for the sub-waveguide core and the surface corresponding to the sub-inclined surface is 9 °, and the convex portion for the main waveguide core is such that this angle θ is tangent. It arrange | positioned so that it might adjoin to the main joint surface of the curved part side surface. At that time, the distance D _c between the tangent at the center of the surface corresponding to the main coupling surface and the surface corresponding to the sub-inclined surface was 12 μm. The curvature radius R of the main coupling surface was 4.

  Next, a mold release agent was applied to the master 210, and then a thermosetting dimethylsiloxane resin (manufactured by Dow Corning Asia Co., Ltd .: SYLGARD 184) and the curing agent were poured into the master 210 and heated at 120 ° C. for 30 minutes to be cured. After curing, the cured resin layer was peeled off to produce a mold (thickness: 5 mm) having recesses corresponding to the main waveguide core, sub-waveguide core, and air vent hole.

  Further, as shown in FIG. 4B, through holes 362 and 382 having a diameter of 3 mm are opened in the mold so that both ends of the main waveguide core recess 322 are exposed, and the sub-waveguide core recess 324 is formed. Similarly, through holes 364 and 384 are formed in the end portion on the side having no sub-inclined surface and the end portion of the air vent passage recess 326 (communication passage 326), and the resin input end and the resin discharge end of the core forming curable resin described below. The mold 310 was made.

-Formation of waveguide core and upper cladding layer-
As shown in FIG. 4C, this mold 310 and a film substrate 410 having a film thickness of 188 μm (Arton Film, manufactured by JSR Corporation, refractive index 1.510) were brought into close contact with each other. Next, one through hole 362 of the main waveguide core recess 322 formed in the mold 310 is sufficiently filled with an ultraviolet curable resin (refractive index after curing: 1.535) having a viscosity of 800 mPa · s. When suction is performed with a suction force of −20 kPa using a diaphragm suction pump (maximum suction pressure: −33.25 kPa) from the through hole 382 on the opposite side, the UV curable resin is filled in the main waveguide core recess 322. It was done.

  At the same time, one through hole 364 of the sub-waveguide core recess 324 formed in the mold is sufficiently filled with an ultraviolet curable resin having a viscosity of 1700 mPa · s (refractive index after curing: 1.52). Using a diaphragm suction pump (maximum suction pressure: −33.25 kPa) from a through hole 384 connected to the recess 326 for the air vent passage (communication passage), when the suction force is −20 kPa, the air vent hole is removed. The sub-waveguide core recess 324 was filled with an ultraviolet curable resin. The filling time at this time was about 20 seconds.

  Next, UV light having a light intensity of 50 mW / cm 2 is irradiated from the arton film side for 5 minutes to cure the ultraviolet curable resin, and then the mold is peeled off to prepare an arton film as another upper clad layer. Then, the waveguide core was bonded with an ultraviolet curable resin having a refractive index of 1.510 as an adhesive. At this time, the adhesive was also filled in the gap between the main waveguide core and the sub-waveguide core.

Thereafter, UV light having a light intensity of 50 mW / cm ² is irradiated for 5 minutes to cure, and finally the waveguide film end is cut with a dicer, and the optical waveguide for bidirectional communication as shown in FIG. Got.

Table 1 shows the configuration and characteristics of this optical waveguide. In Table 1, R is the radius of curvature of the curved portion (main coupling surface) in the main waveguide core, θ is the angle formed by the sub-inclined surface and the optical axis of the sub-waveguide core, D ₁ is the width of the main waveguide core, D ₂ is the width of the sub-waveguide core, D _c is the distance between the tangent at the center of the main coupling surface of the main waveguide core and the sub-inclined surface, n ₁ is the refractive index of the main waveguide core, and n ₂ is the refraction of the sub-waveguide core. The index, n ₀ , indicates the refractive index of the cladding part.

  The bidirectional communication waveguide thus manufactured has an unnecessary curved surface of 10 μm added to the straight portion facing the sub-inclined surface, but there is no significant loss, and good performance as shown in the previous embodiment. Was able to demonstrate.

(Evaluation of optical waveguide for bidirectional communication)
As shown in FIG. 1, a GI-type multimode having a core diameter of 62.5 μm and a numerical aperture NAf of 0.275 as a communication optical fiber 150 is provided at the pre-curved main waveguide core end 22 of the produced optical waveguide for bidirectional communication. Bidirectional optical input / output was performed with the fibers in close proximity.

  As a bidirectional communication device, a VCSEL (manufactured by Fuji Xerox, AM-0001, emission wavelength: 850 nm) is used as the light emitting element 60 (LD) at the sub-waveguide core end 54, and the main waveguide core end 32 after the curve is provided. A photo detector (PD) was attached as a light receiving element 70 with an optical adhesive. Here, the optical fibers for measurement were brought close to each other for loss evaluation, and input / output light from each optical fiber was measured. In the measurement, matching oil was used between the optical fiber 150 and the waveguide, and the wavelength of input light from the optical fiber 150 was 850 nm.

  Table 2 shows optical loss when bidirectional optical input / output is performed under the above conditions. For the loss P in Table 2, the waveguide core end on the communication optical fiber side (curved main waveguide core end) is subscript 1, and the waveguide core end on the light emitting element side (sub-waveguide core end). Is the subscript 2, and the waveguide core end (curved main waveguide core end) on the light receiving element side is subscript 3, and the input position of light in “Pxy” is x and the output position is y. The output was expressed and the optical loss was expressed in dB (the larger the number, the greater the attenuation).

<Example 2 to Example 8, Comparative Example 1 to Comparative Example 3>
The width of the sub-waveguide core (D ₂ ), the width of the cladding (D _c ), and the refractive index (n ₁ , n ₂ ) of the main waveguide core and the refractive index of the sub-waveguide core are changed as shown in Table 1, respectively. Except that, an optical waveguide for bidirectional communication was produced in the same manner as in Example 1, and the same evaluation was performed.
The evaluation results are summarized in Table 2.

  As is clear from the results shown in Table 2, in Examples 1 to 8 using the bidirectional communication waveguide of the present invention, stray light components reaching from the light emitting element (LD) side to the adjacent light receiving element (PD) side. A certain P23, the return light component P22 to the light emitting element (LD) itself, the stray light component P12 reaching the light emitting element (LD) side of the input light, and the return light component P11 to the communication optical fiber are values that are more than a certain value. Since stray light and return light are at a low level, there is no risk of malfunction in both the light emitting element and the light receiving element. Moreover, the values of P21 indicating the loss from the light emitting element to the communication optical fiber and P13 indicating the loss from the communication optical fiber to the light receiving element are very small, and it can be seen that transmission / reception with low loss is possible.

  On the other hand, in Comparative Example 1 in which the main waveguide core and the sub-waveguide core are directly coupled and the core refractive indexes of both are the same, even if the core diameter of the sub-waveguide core is reduced, the light emitting element It is unavoidable that stray light at a level that makes the output of the light enters the light emitting element side. This is almost the same in Japanese Patent Application Laid-Open No. 11-271548, which is a prior art.

  Even if the main waveguide core and the sub-waveguide core are separated from each other, if the core refractive indexes are the same, the light from the light-emitting element may be totally reflected on the sub-inclined surface and reach the optical fiber for communication. (Comparative Example 2) Or, since the input light component from the communication optical fiber hardly reflects on the main coupling surface, the light does not reach the light receiving element and enters the light emitting element side as stray light, making the light emitting element output unstable. (Comparative Example 3)

It is a schematic block diagram which shows an example of the module for two-way communication containing the optical waveguide for two-way communication of this invention. It is a top view which shows the structural example of the optical waveguide for two-way communication of this invention. (A)-(G) are the conceptual diagrams which show the preparation processes of a waveguide. (A)-(E) are schematic which shows an example of the manufacturing process of the optical waveguide for two-way communication of this invention. It is the elements on larger scale showing the main waveguide core curve part periphery in the example of composition of the optical waveguide for bidirectional communications of the present invention. It is the elements on larger scale which show the main waveguide core curve part periphery in the other structural example of the optical waveguide for two-way communication of this invention.

Explanation of symbols

10, 16 Main waveguide core 12 Main coupling surface 20 Before curve main waveguide core 22, 24 Before curve main waveguide core end 30 After curve main waveguide core 32, 34 After curve main waveguide core end 40, 42 Clad portion 50, 56 Sub-waveguide core 52A Joint surface 52 Sub-inclined surfaces 54, 58 Sub-waveguide core end portion 60 Light-emitting element 70 Light-receiving element 100 Bidirectional communication optical waveguide 111 Optical waveguide 120 Clad base material 150 Optical fiber 200, 210 Master 202 Silicon substrate 222 Convex portion for main waveguide core 224 Convex portion for sub waveguide core 226 Convex portion for air vent (communication path) 300a Cured resin layer 300, 310 Mold 320 Recess for waveguide core 322 Concavity for main waveguide core 324 For sub waveguide core Recess 326 Air vent recess (communication path)
360, 362, 364 Through hole 370 Resin input end 380, 382, 384 Through hole 390 Resin output end 400 Clad substrate 410 Film substrate 420 Waveguide core 500 Upper clad layer

Claims (7)

It has a curved portion whose optical axis direction changes continuously in the middle of the optical path, and a main coupling surface that couples light incident on a part of the curved portion is provided, and is incident with a curvature smaller than the curvature of the main coupling surface. A main waveguide core having a structure for guiding the transmitted light;
A sub-waveguide core having a sub-inclined surface facing or connected to the main coupling surface opposite to the main coupling surface at one end, and a refractive index equal to or lower than the main waveguide core;
Have
The main waveguide core has a first core end that inputs and outputs bidirectional optical signals from the optical fiber, and a third core end that connects to the light receiving element, and receives input light from the first core end. Having a structure leading to the end of the third core via the curved portion;
The sub-waveguide core has a second core end connected to the light emitting element at an end opposite to the sub inclined surface, and the output light from the light emitting element is totally transmitted through the sub inclined surface. An optical waveguide for bidirectional communication having a structure for propagating to the main waveguide core. The main waveguide core and the sub-waveguide core are close to each other at the curved portion, and the main coupling surface and the sub-inclined surface are opposed to each other with a cladding portion interposed therebetween,
The curvature radius R of the curved portion, the main waveguide core width D ₁ , the angle between the sub-inclined surface and the optical axis of the sub-waveguide core is θ, the refractive index of the main waveguide core is n ₁ , and the sub-waveguide core when the refractive index was the index of refraction of n ₂ and the cladding portion and n _0, these following formulas (1) to (3) two-way communication optical waveguide according to claim 1, characterized by satisfying the relation of .
Expression (1): sin θ / (√ (n ₂ ² −n ₀ ² ) / n ₂ )> 1
Formula (2): √ (2 × D ₁ / R) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Formula (3): cos (β + γ) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Where β = sin ⁻¹ ((n ₂ / n ₁ ) cos θ), γ = (D ₁ / R) tan β The main waveguide core and the sub waveguide core are close to each other at the curved portion, and the main coupling surface and the sub inclined surface are directly connected,
The curvature radius R of the curved portion, the main waveguide core width D ₁ , the angle between the sub-inclined surface and the optical axis of the sub-waveguide core is θ, the refractive index of the main waveguide core is n ₁ , and the sub-waveguide core _2. The bidirectional communication according to claim 1, wherein when the refractive index is n ₂ and the refractive index of the clad portion is n ₀ , these satisfy the following formulas (1) ′ to (3) ′: Optical waveguide.
Formula (1) ′: n ₂ > n ₀
Formula (2) ′: √ (2 × D ₁ / R) / (√ (n ₁ ² −n ₂ ² ) / n ₁ ) <1
Formula (3) ′: cos (β + γ) / (√ (n ₁ ² −n ₀ ² ) / n ₁ ) <1
Where β = sin ⁻¹ ((n ₂ / n ₁ ) cos θ), γ = (D ₁ / R) tan β The main waveguide core and the sub-waveguide core are close to each other at the curved portion, and the main coupling surface and the sub-inclined surface are opposed to each other at a constant interval, and the width of the main waveguide core is set to D ₁ , 2. The bidirectional optical waveguide according to claim 1, wherein when a distance between a tangent at the center of the main coupling surface and the sub-inclined surface is D _c , these satisfy a relationship of the following formula (4).
Equation _{(4): 0.1D 1 <D} c <D 1 _2. The bidirectional communication according to claim ₁ , wherein when the width of the main waveguide core is D ₁ and the width of the sub-waveguide core is D ₂ , these satisfy the relationship of the following formula (5): Optical waveguide.
Equation _{(5): 0.1D 1 ≦ D} 2 ≦ D 1 It is a manufacturing method of the optical waveguide for bidirectional communications according to any one of claims 1 to 5,
At least 1) formed of a cured resin layer of a mold-forming curable resin, and at least connected in the thickness direction to a recess corresponding to the main waveguide core and the sub-waveguide core, and a resin entry end and a resin discharge end of the recess, respectively. 2) a step of preparing a mold provided with a through-hole, 2) a step of closely attaching a base material for clad to the mold, and 3) a resin entrance end of a recess corresponding to the main waveguide core and the sub-waveguide core. Filling the through-hole with a core-forming curable resin, bringing the core-forming curable resin into contact with the resin entry end, and entering the recesses corresponding to the main waveguide core and the sub-waveguide core; and 4 2) A method for producing an optical waveguide for two-way communication, which comprises a step of curing the entered core-forming curable resin. In the mold, a resin discharge end of a recess corresponding to the sub-waveguide core is provided at a tip of the recess corresponding to the main waveguide core, and corresponds to a linear communication path from the resin discharge end to the through hole. A recess is formed,
When the angle between the sub-inclined surface and the optical axis of the sub-waveguide core is θ, and the angle between the concave portion corresponding to the linear communication path and the concave portion corresponding to the sub-waveguide core is α, The method of manufacturing an optical waveguide for bidirectional communication according to claim 6, wherein α is in the range of the following formula (6).
Formula (6): θ <α ≦ 90 °

Images