JP3900921B2 - Manufacturing method of optical waveguide coupling plate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for reducing coupling loss when coupling an optical fiber and an optical waveguide or between optical waveguides, and more particularly to a method of manufacturing an optical waveguide coupling plate .
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a method for coupling an optical waveguide and an optical fiber or another optical waveguide, a method in which both end surfaces are bonded and fixed with a translucent adhesive is known.
[0003]
For example, when the optical fiber and the optical waveguide are coupled, the end face of the optical fiber 1 and the end face of the optical waveguide 2 are bonded and fixed by the adhesive layer 3 as shown in FIG. The optical fiber 1 has a configuration in which a core 1a is disposed along the center line inside a clad 1R, and the optical waveguide 2 has a core 2A formed on a layered lower clad 2L covered with a layered upper clad 2U. It is a configuration. As the adhesive layer 3, one having a refractive index that matches or approximates the cores 1a and 2A is used. In addition, another optical waveguide may be coupled to the optical waveguide 2 by the adhesive layer 3 instead of the optical fiber 1.
[0004]
[Problems to be solved by the invention]
According to the above-described conventional technology, the size or shape of the core end faces facing each other between the optical waveguide 2 and the optical fiber 1 (or other optical waveguide) do not match, so that light is transmitted at the coupling portion (location where the adhesive layer 3 is disposed). There is a problem in that it leaks outside and the coupling loss is large (coupling efficiency is low).
[0005]
For example, the end face of the core 1a of the optical fiber 1 is a circle having a diameter of 8 to 10 μm, whereas the end face of the core 2A of the optical waveguide 2 is a square (square) having a side length of 4 to 6 μm. is there. Also, since the light propagation mode varies depending on the structure and constituent materials of the optical waveguide, the diameter of the core light spot is different from the diameter of the core of the coupling partner, or the end face shape of the core is not circular but elliptical. . Therefore, light leakage cannot be avoided by simply bonding the end faces of the cores with the adhesive layer 3.
[0006]
19 to 24 show the results of the computer simulation performed on the coupled system of FIG. FIG. 19 shows an example of the distribution of effective refractive index. In this example, the diameter of the core 1a is 9 μm, the core 2A is 6 μm square, and the adhesive has a thickness of 50 μm between the cores 1a and 2A. The case where the layer 3 is disposed and disposed is shown. The effective refractive indexes of the core 1a, the adhesive layer 3, and the core 2A are 1.45, 1.44, and 1.45, respectively. The effective refractive index 1.44 of the adhesive layer 3 is the cladding 1R, 2U, 2L. Is equal to the effective refractive index of. 20 shows the distribution state of the optical amplitude when the effective refractive index distribution is in the state shown in FIG. 19, and FIG. 21 shows the effective refractive index N for the cross section in FIGS. ₁ and shows the distribution of optical amplitude _{a 1.} According to FIG. 21, it can be seen that the peak level of the light amplitude is low, the peak portion is split, and the propagating light is converted into a multimode.
[0007]
FIG. 22 shows another example of the effective refractive index distribution, and the sizes of the cores 1a and 2A and the thickness of the adhesive layer 3 are the same as those described above with reference to FIG. The effective refractive indexes of the core 1a, the adhesive layer 3, and the core 2A are 1.45, 1.45, and 1.45, respectively, and the effective refractive indexes of the claddings 1R, 2U, and 2L are 1.44. FIG. 23 shows the distribution state of the optical amplitude when the effective refractive index distribution is in the state shown in FIG. 22, and FIG. 24 shows the effective refractive index N for the cross section in FIGS. shows the ₂ and distribution of optical amplitude _{a 2.} According to FIG. 24, it can be seen that the peak level of the light amplitude is low, the peak portion is split, and the propagating light is converted to multimode.
[0008]
The purpose of the invention is to provide a method of optical waveguide coupling plate with a reduced coupling loss.
[0009]
[Means for Solving the Problems]
The manufacturing method of the optical waveguide coupling plate according to the present invention is as follows:
Forming a sacrificial layer on one principal surface of the substrate;
A step of forming a tapered resist layer whose top is narrower than the bottom on the sacrificial layer, with the focus position set at a position close to the surface of the substrate in the resist formed on the sacrificial layer. After the resist is exposed to light, the exposed resist is subjected to development, and the resist after development is further baked to obtain the tapered resist layer;
Covering the resist layer and depositing a plate component layer on the sacrificial layer;
Removing the plate constituent layer flatly until at least the resist layer is exposed, and leaving the resist layer and the plate constituent layer in a predetermined thickness; and
Forming a tapered through hole in the plate constituting layer remaining at the predetermined thickness by removing the resist layer remaining at the predetermined thickness;
Separating the plate-constituting layer having the through hole from the substrate by removing the sacrificial layer;
After the step of separating, a step of loading a core member into the through hole so as to constitute a tapered light guide that connects one end and the other end of the through hole;
Is included.
[0015]
According to the method for manufacturing an optical waveguide coupling plate of the present invention, an optical waveguide coupling plate can be easily manufactured using a normal thin film process. In addition, since the optical axis direction in which light propagates matches the thickness direction of the resist layer and the thickness direction of the plate component layer, the degree of freedom in design is high and it can be used for various optical fibers and optical waveguides. is there. That is, the thickness of the coupling plate (the length of the through hole) can be set to an arbitrary thickness of, for example, 100 μm or less simply by appropriately setting the thickness of the resist layer, the deposition thickness of the plate constituent layer, and the removal thickness. Moreover, the opening size or opening shape in the one end and other end of a through-hole can be arbitrarily set only by setting a size or a shape suitably about the bottom part and top part of a resist layer. In particular, when forming the resist layer, if the shape of the top portion is different from the shape of the bottom portion, in the tapered through hole, the opening shape on one end side becomes different from the opening shape on the other end side, and the core shape or light spot Shape conversion is possible.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an optical waveguide coupling system according to an embodiment of the present invention, and a cross section taken along line XX ′ of FIG. 1 is shown in FIG.
[0017]
1 and 2, the optical fiber 10A includes a clad 10R having an annular cross section perpendicular to the longitudinal direction and a core 10a having a circular cross section perpendicular to the longitudinal direction. The core 10a is arranged along the center line. As an example, the refractive indexes of the cladding 10R and the core 10a are 1.44 and 1.45, respectively. The optical fibers 10B to 10D are configured in the same manner as the optical fiber 10A, and have cores 10b to 10d, respectively. Optical fiber 10A-10D is arrange | positioned so that it may extend in parallel.
[0018]
The optical waveguide 12 has a configuration in which four cores 12A to 12D are arranged in parallel on a layered clad 12L, and a layered clad 12U is disposed on the clad 12L so as to cover the cores 12A to 12D. The core 12A has a square cross section perpendicular to the longitudinal direction, and the light spot 12a in a predetermined light propagation mode has a circular cross section perpendicular to the light propagation direction. As an example, the refractive indexes of the claddings 12L and 12U and the core 12A are 1.44 and 1.45, respectively. The cores 12B to 12D are configured in the same manner as the core 12A, and the cross section of the light spot is circular like the core 12A. The clad 12L is provided on a substrate (not shown).
[0019]
The four optical fibers 10 </ b> A to 10 </ b> D and the optical waveguide 12 arranged in parallel are arranged so that the end faces thereof are opposed to each other, and the optical waveguide coupling is provided between the opposing end faces of the optical fibers 10 </ b> A to 10 </ b> D and the optical waveguide 12. A plate 14 is interposed.
[0020]
The optical waveguide coupling plate 14 is a rectangular thin plate made of silicon oxide or the like having a thickness of 100 μm or less (for example, 50 μm), and connects the end surface of the core 10a of the optical fiber 10A and the end surface of the core 12A of the optical waveguide 12 to each other. Thus, a tapered through-hole 14a is provided so as to penetrate between the main surface on the optical fiber side and the main surface on the optical waveguide side. Similarly, tapered through holes 14b to 14d are provided in the coupling plate 14 so that the end faces of the cores 10b to 10d of the optical fibers 10B to 10D communicate with the end faces of the cores 12B to 12D of the optical waveguide 12, respectively. . In the coupling plate 14, the opening size and the opening shape of each through-hole such as 14 a on the main surface on the optical fiber side match (match or approximate) the end surface size and end surface shape of the core such as 10 a, respectively. The opening size and the opening shape of each through-hole such as 14a on the main surface match (match or approximate) the size and shape of the light spot such as 12a, respectively.
[0021]
A core member 14A is formed in the through hole 14a by filling with a translucent adhesive. Similarly, core members 14B to 14D are also formed in the through holes 14b to 14d. Each core member such as 14A constitutes a tapered light guide path connecting the end face of each core such as 10a and the end face of each core such as 12A. As an example, the refractive index of the coupling plate 14 can be 1.44, and the refractive index of each core member such as 14A can be 1.45. When the core members 14A to 14D are made of an adhesive, the optical fibers 10A to 10D and the optical waveguide 12 are optically coupled, and at the same time, the optical fibers 10A to 10D, the coupling plate 14 and the optical waveguide 12 are bonded and fixed. can do.
[0022]
As the core member, a plug-like core member 14A ′ formed in advance so as to be fitted to the through hole as shown in FIG. 1 may be used. In this case, the plug-shaped core member 14A ′ is fitted into a through hole such as 14a. As the core member 14A ′, one having adhesiveness by heat treatment or the like may be used, and in this way, optical coupling and adhesive fixation can be achieved simultaneously. When the core member 14A ′ having no adhesiveness is used, the optical fiber 10A to 10D, the coupling plate 14, and the optical waveguide 12 may be separately bonded and fixed.
[0023]
According to the above-described embodiment, since the coupling plate 14 is disposed between each optical fiber such as 10A and the optical waveguide 12, the core such as 10a and the core such as 12A are provided as the core member 14A (or 14A ′). ) Is optically and smoothly coupled by a tapered light guide. For this reason, light leakage at the coupling portion is prevented, and coupling loss can be reduced (coupling efficiency can be improved). The light propagation direction may be either from the optical fiber side to the optical waveguide side or from the optical waveguide side to the optical fiber side.
[0024]
3 and 4 show the results of computer simulation performed on the coupled system of FIG. FIG. 3 shows an example of the distribution of the effective refractive index. In this example, the diameter of the core 10a is 9 μm, the diameter of the light spot 12a of the core 12A is 6 μm, and 50 μm between the cores 10a and 12A. The case where the core member 14A held by the coupling plate 14 having a thickness is interposed is shown. The effective refractive indexes of the core 10a, the core member 14A, and the core 12A are all 1.45, and the effective refractive indexes of the claddings 10R, 12U, and 12L are all 1.44. 4 shows the distribution state of the light amplitude when the effective refractive index distribution is in the state shown in FIG. 3, and FIG. 5 shows the effective refractive index N for the cross section having a distance of 0.30 in FIGS. ₁₁ and shows the distribution of light amplitude _{a 11.} According to FIG. 5, it can be seen that the peak level of the light amplitude is high and light propagates in a single mode.
[0025]
In the above-described embodiment, in each through hole such as 14a, the opening size and the opening shape at one end are matched with the end surface size and the end surface shape of the corresponding optical fiber core, and the opening size and the opening shape at the other end are matched with the optical waveguide. In the above, the size and shape of the light spot of the corresponding core are adapted to each other, but the opening size and the opening shape of one end of each through hole may be adapted to the size and shape of the light spot of the corresponding optical fiber core, The opening size and opening shape at the other end of each through hole may be adapted to the end face size and end face shape of the corresponding core in the optical waveguide.
[0026]
In the above-described embodiment, instead of the optical fibers 10A to 10D, another optical waveguide having four cores corresponding to the cores 10a to 10d (not shown but denoted by reference numeral 12 'for convenience) is coupled. The optical waveguide 12 may be coupled via the plate 14. In this case, in the coupling plate 14, the opening size and opening shape of each through-hole such as 14 a on the main surface on the optical waveguide 12 side are set to the end surface size and end surface shape of the corresponding core in the optical waveguide path 12 (or the light spot of the core). And the opening size and the opening shape of each through hole such as 14a on the main surface on the optical waveguide 12 ′ side are matched with the end surface size and the end surface shape of the corresponding core in the optical waveguide 12 ′ (or the shape of the core). The size and shape of the light spot.
[0027]
In the above-described embodiment, the opening shape of one end and the other end of the through hole such as 14a in the coupling plate 14 is exemplified as a circular shape, but is not limited thereto. That is, the opening shape of one end and the other end of the through hole is appropriately determined according to the end face shape of the core of the coupling partner (or the shape of the light spot of the core), for example, FIG. There can also be a shape as shown in (B).
[0028]
6 (A) is in the through-hole 14a, the opening shape S ₁ of the one end while a circular, in which the opening shape S ₂ of the other end has an elliptical shape. As another example, S ₁ may be elliptical and S ₂ may be circular. FIG. 6 (B) in the through hole 14a, the opening shape S ₁ of the one end while a circular, in which the opening shape S ₂ of the other end was a square such as square. As another example, S ₁ may be a square, and S ₂ may be a circle or an ellipse.
[0029]
FIGS. 7 to 11 show a first manufacturing method of the optical waveguide coupling plate according to the present invention, and this manufacturing method is similar in opening shape at one end and the other end (for example, circular as shown in FIG. 1). It is suitable for manufacturing a coupling plate having a through hole.
[0030]
In the process of FIG. 7, a Cr layer 22 and a Cu layer 24 are sequentially formed on the surface of a substrate 20 such as glass or ceramic by sputtering. The Cr layer 22 is an adhesion layer used to help the Cu layer 24 as a sacrificial layer adhere to the substrate 20.
[0031]
Next, resist layers 26a to 26d corresponding to desired tapered through holes are formed on the upper surface of the substrate by a known photolithography process. Each resist layer has a tapered shape whose top is narrower than the bottom. Exposure is performed by setting the focus position of the stepper (exposure device) to a position close to the substrate surface in the resist, and baking (or applying ultraviolet rays after development) It can be obtained by baking.
[0032]
In the process of FIG. 8, a plate constituent layer 28 made of silicon oxide is formed by sputtering on the upper surface of the substrate so as to cover the resist layers 26a to 26d. The thickness of the plate constituting layer 28 can be appropriately set to 100 μm or less, and can be set to 50 μm, for example.
[0033]
In the process of FIG. 9, the plate constituting layer 28 is removed in a planar manner until it reaches at least the tops of the resist layers 26a to 26d, and the plate constituting layer 28 and the resist layers 26a to 26d are left with a predetermined thickness. As the planar removal method, a chemical mechanical polishing process or an etch back process can be used.
[0034]
In the process of FIG. 10, tapered through-holes 28a to 28d are formed in the remaining plate constituting layer 28 by removing the remaining resist layers 26a to 26d by chemical treatment or the like.
[0035]
In the step of FIG. 11, the plate layer 28 having the through holes 28 a to 28 d is separated from the substrate 20 by removing the Cu layer 24 by etching. The plate constituting layer 28 can be used as the optical waveguide coupling plate 14 shown in FIGS. The substrate 20 having the Cr layer 22 can be used repeatedly by returning to the process of FIG.
[0036]
12 to 17 show a second manufacturing method of the optical waveguide coupling plate according to the present invention, and this manufacturing method is not similar in opening shape at one end and the other end (for example, different shapes as shown in FIG. 6). ) Suitable for manufacturing a coupling plate having a through hole.
[0037]
In the process of FIG. 12, after the Cu layer 24 is formed on the substrate 20 via the Cr layer 22 as described above with reference to FIG. 7, the resist layer 30 is formed on the Cu layer 24 by spin coating or the like. . Then, obtain the exposure unit 30A~30D by irradiating ultraviolet light UV through a mask _{M 1} with respect to the resist layer 30. Each of the exposure units 30A to 30D exposes in a cylindrical shape as representatively shown for the exposure unit 30A. At the time of resist exposure, the focus position is set to a position close to the substrate surface in the resist, and the exposure amount is set so as not to break the bottom circular shape.
[0038]
In the process of FIG. 13, the resist layer 30 is irradiated with ultraviolet light UV through the mask M < _b > 2 to transfer the oval pattern 30 </ b> A ′ to the exposure units 30 </ b> A to 30 </ b> D. The focus position at this time is a position close to the surface of the resist layer 30.
[0039]
In the process of FIG. 14, the resist layer 30 that has been double-exposed is subjected to development processing to obtain resist layers 30 a to 30 d that correspond to desired tapered through holes.
[0040]
In the step of FIG. 15, as described above with reference to FIG. 8, the plate constituent layer 32 made of silicon oxide is formed on the upper surface of the substrate so as to cover the resist layers 30a to 30d by sputtering.
[0041]
In the step of FIG. 16, the plate constituting layer 32 and the resist layers 30 a to 30 d are removed in a planar manner until the plate constituting layer 32 reaches at least the top of the resist layers 30 a to 30 d in the same manner as described above with reference to FIG. 9. Let it remain.
[0042]
In the step of FIG. 17, tapered through holes 32 a to 32 d are formed in the remaining plate constituent layer 32 by removing the remaining resist layers 30 a to 30 d by chemical treatment or the like. Each through hole such as 32a has a circular opening shape on the lower surface side and an elliptical opening shape on the upper surface side. Thereafter, the Cu layer 24 is removed by etching to separate the plate constituent layer 32 having the through holes 32 a to 32 d from the substrate 20. The plate constituting layer 32 can be used as an optical waveguide coupling plate having the through hole 14a described above with reference to FIG.
[0043]
According to the manufacturing method of the optical waveguide coupling plate described above, the optical waveguide coupling plate can be easily manufactured with high accuracy using a thin film process, and the length of the tapered through hole, the opening size of the hole end, or the opening Various shapes can be obtained simply by changing the resist thickness, resist pattern, and the like.
[0044]
The material of the plate constituent layers 28 and 32 is not limited to an insulating material such as silicon oxide, and a conductive material such as a Ni-Fe alloy may be used, and a plating method or the like can be used as a deposition method. .
[0045]
【The invention's effect】
As described above, according to the present invention, the optical waveguide coupling plate is interposed between the opposing end faces of the optical waveguide and the optical fiber (or other optical waveguide), and both cores are tapered in the through hole of the coupling plate. Since the optical coupling is performed via the optical waveguide, it is possible to prevent light leakage at the coupling portion and to reduce coupling loss (improve coupling efficiency).
[0046]
In addition, according to the method for manufacturing an optical waveguide coupling plate of the present invention, an effect of easily manufacturing optical waveguide coupling plates having different lengths of tapered through holes, hole end sizes or shapes, etc. by a thin film process is obtained. It is done.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an optical waveguide coupling system according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along line XX ′ of FIG.
FIG. 3 is a graph showing an example of an effective refractive index distribution in the coupled system of FIG. 2;
4 is a graph showing the distribution state of light amplitude when the effective refractive index distribution is in the state of FIG. 3 in the coupled system of FIG. 2;
5 is a graph showing the distribution of effective refractive index and light amplitude for a cross section with a distance of 0.30 in FIGS. 3 and 4. FIG.
FIG. 6 is a perspective view showing a modification of the through hole in the optical waveguide coupling plate.
FIG. 7 is a cross-sectional view showing a resist layer forming step in the first manufacturing method of the optical waveguide coupling plate according to the present invention.
8 is a cross-sectional view showing a plate constituent layer forming step that follows the step of FIG. 7. FIG.
FIG. 9 is a cross-sectional view showing a polishing step following the step of FIG. 8;
10 is a cross-sectional view showing a resist removal step subsequent to the step of FIG.
11 is a cross-sectional view showing a coupling plate separating step subsequent to the step of FIG.
FIG. 12 is a cross-sectional view showing a first resist exposure step in the second manufacturing method of the optical waveguide coupling plate according to the present invention.
13 is a cross-sectional view showing a second resist exposure process following the process of FIG. 12. FIG.
14 is a cross-sectional view showing a resist development step subsequent to the step of FIG.
15 is a cross-sectional view showing a plate constituent layer forming step that follows the step of FIG. 14;
16 is a cross-sectional view showing a polishing process subsequent to the process in FIG. 15. FIG.
17 is a cross-sectional view showing a resist removal step and a bonding plate separation step that follow the step of FIG. 16. FIG.
FIG. 18 is a cross-sectional view showing a conventional optical waveguide coupling system.
19 is a graph showing an example of an effective refractive index distribution in the coupled system of FIG.
20 is a graph showing the distribution state of light amplitude when the effective refractive index distribution is in the state of FIG. 19 in the coupled system of FIG.
FIG. 21 is a graph showing the distribution of effective refractive index and light amplitude for a cross section having a distance of 0.30 in FIGS.
22 is a graph showing another example of effective refractive index distribution in the coupled system of FIG.
23 is a graph showing the distribution state of light amplitude when the effective refractive index distribution is in the state of FIG. 22 in the coupled system of FIG.
24 is a graph showing the distribution of effective refractive index and light amplitude for a cross section having a distance of 0.30 in FIGS. 22 and 23. FIG.
[Explanation of symbols]
10A to 10D: optical fiber, 12: optical waveguide, 14: optical waveguide coupling plate, 14a to 14d, 28a to 28d, 32a to 32d: through hole, 14A to 14D: core member, 14A ': plug-shaped core member, 20 : Substrate, 22: Cr layer, 24: Cu layer, 26a-26d, 30, 30a-30d: resist layer, 28, 32: plate constituent layer.

Claims (1)

Forming a sacrificial layer on one principal surface of the substrate;
A step of forming a tapered resist layer whose top is narrower than the bottom on the sacrificial layer, the focus position being set at a position close to the surface of the substrate in the resist formed on the sacrificial layer; Steps for obtaining the tapered resist layer by subjecting the resist to an exposure treatment, subjecting the resist after the exposure to a development treatment, and further subjecting the resist after the development to a baking treatment;
Covering the resist layer and depositing a plate component layer on the sacrificial layer;
Removing the plate constituent layer flatly until at least the resist layer is exposed, and leaving the resist layer and the plate constituent layer in a predetermined thickness; and
Forming a taper-shaped through hole in the plate constituting layer remaining at the predetermined thickness by removing the resist layer remaining at the predetermined thickness;
Separating the plate constituent layer having the through-hole from the substrate by removing the sacrificial layer;
After the step of separating, a step of loading a core member into the through hole so as to constitute a tapered light guide that connects one end and the other end of the through hole;
Of an optical waveguide coupling plate comprising:

Images