JP3552592B2 - Manufacturing method of optical waveguide - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a manufacturing method of the optical waveguide path.
[0002]
[Prior art]
In order to reduce the size, integration, and cost of optical devices, research and development of optical devices having a waveguide structure have been actively conducted.
[0003]
FIG. 6A is a cross-sectional view of a conventional optical waveguide, FIG. 6B shows a refractive index distribution in a cross section taken along line AA of FIG. 6A, and FIG. It is a figure which shows the refractive index distribution in the BB line cross section of a).
[0004]
In FIG. 6B, the horizontal axis indicates the position in the width direction, and the vertical axis indicates the refractive index. In FIG. 6C, the horizontal axis indicates the refractive index, and the vertical axis indicates the position in the thickness direction.
[0005]
The waveguide has a structure in which a high refractive index core layer 2 having a substantially rectangular cross section is embedded in a low refractive index cladding layer 3 formed on a substrate 1. The refractive index distribution in the width and thickness directions of the core layer 2 has a flat distribution having substantially uniform values.
[0006]
FIG. 7A shows the curvature radius R and the waveguide radiation loss (radiation loss at the curved portion) of the waveguide bent at 90 ° among the waveguides shown in FIG. 6, and the relative refraction between the core layer and the cladding layer. FIG. 7B shows the result of calculation using the index difference Δ as a parameter. FIG. 7B shows the curvature radius R and the radiation loss of the S-shaped curved waveguide among the waveguides shown in FIG. FIG. 9 is a diagram showing a result of calculation using a relative refractive index difference Δ with a layer as a parameter. In both figures, the horizontal axis shows the radius of curvature, and the vertical axis shows the coupling loss.
[0007]
Both figures show that the radiation loss increases as the relative refractive index difference Δ decreases or as the radius of curvature R decreases. In order to reduce the radiation loss to 0.02 dB or less, the radius of curvature R must be 0.8 cm or more, which makes it difficult to miniaturize the waveguide type optical device. Conversely, if the radius of curvature R is reduced to reduce the size, an optical device with a large loss will be obtained.
[0008]
[Problems to be solved by the invention]
As described above, the conventional waveguide type optical device has the following problems.
[0009]
(1) It is difficult to realize a small and low-loss waveguide type optical device.
[0010]
(2) The interface between the core layer and the cladding layer tends to be non-uniform due to the manufacturing process, and the scattering loss shows a very large value. In particular, the scattering loss due to the unevenness of the interface between the core layer and the cladding layer from the curved waveguide portion as shown in FIG. 7 is very large.
[0011]
(3) Since the core layer having a substantially rectangular cross-sectional shape is formed by dry etching, scattering loss and radiation loss due to roughness of both side surfaces of the core layer and edge surfaces of the core layer are large.
[0012]
Therefore, an object of the present invention is to solve the above-mentioned problems and to provide a small-sized low-loss optical waveguide having small scattering loss and radiation loss, and a method for manufacturing the same.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, in the method of manufacturing an optical waveguide according to the present invention, a step of forming a first clad layer on a substrate and a step of reducing a refractive index on the first clad layer in accordance with an irradiation amount of UV light are performed. Forming a photobleaching layer, disposing a first photomask having a pattern of a core layer on the photobleaching layer, and irradiating UV light from above the first photomask to form a substantially rectangular cross-sectional shape Forming a high-refractive-index core layer having at least one curved portion and forming a low-refractive-index side cladding layer on both sides of the core layer; and a central core layer on the side cladding layer and the core layer. A second photomask having the following pattern is arranged, and UV light is irradiated from above the second photomask to form a central portion of the core layer on the central core layer having a high refractive index. Refractive index better than the central core layer Forming a low profile core layer, said central core layer, and a step of laminating a second cladding layer on the side core layer and the side cladding layer.
[0014]
In addition to the above configuration, a step of laminating a UV cut layer or a UV absorption layer on the second clad layer is provided.
[0015]
According to the present invention, since the core layer has a refractive index distribution of at least two steps in the width direction, most of the light propagating in the core layer is confined in the high refractive index portion and propagates. Since the core layer and the cladding layer are made of a photobleaching material, the interface is uniform. As a result, it is possible to provide a small-sized low-loss optical waveguide having small scattering loss and radiation loss and a method of manufacturing the same.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0017]
FIG. 1A is a cross-sectional view showing one embodiment of the low-loss optical waveguide of the present invention, and FIG. 1B shows a refractive index distribution in a cross section taken along line CC of FIG. 1A. FIG. 1C is a diagram showing a refractive index distribution in a section taken along line DD of FIG. 1A. In FIG. 1B, the horizontal axis indicates the position in the width direction from the center, and the vertical axis indicates the refractive index. In FIG. 1C, the horizontal axis indicates the refractive index, and the vertical axis indicates the position in the thickness direction.
[0018]
The substrate 1 is a Si substrate (however, a substrate made of glass, a semiconductor such as GaAs or InP, a magnetic material, a polymer material, a ferroelectric material, or a combination of these materials may be used).
[0019]
On the substrate 1, a first cladding layer (refractive index n _C1 ) 4 is formed. The first cladding layer 4 is made of SiO ₂ having a thickness of 5 μm or more (provided that at least one kind of refractive index controlling dopant such as F, B, P, Ti, Ge, etc. is added to SiO ₂ , PMMA Or a polymer material such as polyvinylidene fluoride, polystyrene, polyimide, silicone, or polysilane.).
[0020]
On the first cladding layer 4, a second core layer 5a, a side core layer 5b, and side cladding layers 6a and 6b made of a photobleaching material are formed. The photobleaching layer made of this photobleaching material can reduce the refractive index substantially continuously by increasing the irradiation amount of UV light. As the photobleaching material, for example, polysilane is used.
[0021]
Side cladding layer 6a, 6b are those adjusted to have a refractive index n _CP comparable with the refractive index n _C1 of the first cladding layer 4 is irradiated UV light a long time. As shown in FIG. 1B, the side cladding layers 6a and 6b function as ordinary cladding layers.
[0022]
The side core layer 5b is adjusted to have a refractive index n _WS higher than the refractive index n _CP so as to function as a core layer by making the amount of UV irradiation smaller than that of the side cladding layers 6a and 6b.
[0023]
The second core layer 5a is a layer that is not irradiated with UV light or has a small amount of UV light irradiation, and its refractive index _nWC is adjusted to the highest value, and acts as a core layer through which light predominantly propagates.
[0024]
Next, a second cladding layer (refractive index n _C2 , n _C2 ≒ n _C1 ) 7 is formed on the second core layer 5a, the side core layer 5b, and the side cladding layers 6a and 6b. A UV cut layer (or UV absorption layer) 8 is formed on the upper surface.
[0025]
For the second cladding layer 7, a material equivalent to the material of the first cladding layer 4 described above can be used. As the UV cut layer 8, a multi-layer in which several tens of layers of ZrO ₂ (or TaO ₅ ) and SiO ₂ are alternately deposited at a temperature of 120 ° C. in a multilayer shape is used. This multi-layer is a multilayer deposited layer having a characteristic of a reflectance of 80% or more in a wavelength range of 300 nm to 500 nm. Note that a UV light absorbing layer may be used instead of the UV light cut layer 8. The UV light absorbing layer is, for example, a material obtained by adding a benzophenone-based, salicylate-based, benzotriazole-based additive to a polymer material, or a material obtained by adding a metal oxide pigment such as titanium dioxide, iron oxide, or zinc oxide to a polymer material. Can be used.
[0026]
As shown in FIG. 1B, a core layer composed of the second core layer 5a and the side core layer 5b is provided with a two-stage refractive index distribution in the width direction of the second core layer 5a and the side core layer 5b. The radiation loss of the optical signal propagating in the curved portion as shown in FIGS. 7A and 7B can be greatly reduced by using the central portion of Can be. That is, most of the optical signal propagates while being confined in the central portion of the core layer, so that radiation and scattering loss due to structural nonuniformity due to the manufacturing process in the curved portion can be reduced.
[0027]
In particular, since the second core layer 5a, the side core layer 5b, and the side cladding layers 6a and 6b are formed of a photobleaching material, the interface is uniform, and the scattering loss at the interface is small. Radiation and scattering losses can be reduced. As a result, the radius of curvature R of the 90 ° curve pattern and the S-curve pattern as shown in FIGS. 7A and 7B can be reduced, and a small waveguide device can be realized.
[0028]
Further, since the core layer pattern is not formed in a curved pattern in the thickness direction of the second core layer 5a and the side core layer 5b, refraction in the thickness direction in the second core layer 5a and the side core layer 5b is performed. The rate distribution is formed uniformly and flat. Further, since there is almost no step in the refractive index distribution in the thickness direction, it is possible to further reduce the loss.
[0029]
2A to 2D are process diagrams showing one embodiment of a method for manufacturing the low-loss waveguide shown in FIG. FIGS. 3A and 3B are plan views of a photomask used during the steps shown in FIGS. 2A to 2D.
[0030]
A first cladding layer 4 made of SiO ₂ is formed on a Si substrate 1 to a thickness of about 10 μm. A photobleaching layer 5 is formed on the first cladding layer 4.
[0031]
Here, the photobleaching layer 5 is formed as follows. Hexamethyldisilazane (CH ₃ SiNHSiCH ₃ ) is applied on the first cladding layer 4. Hexamethyldisilazane is baked at 120 ° C. for about 1 hour to make it hydrophobic, then polysilane dissolved in toluene at a concentration of 10% by weight is spin-coated, and baked at 120 ° C. for about 1 hour (FIG. 2 (a) )).
[0032]
A first photomask 9 is arranged on the photobleaching layer 5, and UV light 10 having a wavelength of 370 nm is irradiated from above the first photomask 9. As the first photomask 9, a mask having a pattern of a first core layer as shown in FIG. The first photomask 9 is a mask for forming, for example, a linear core pattern (UV light reflection region) 12, and has a UV light reflection region 12 and a UV light transmission region 13. When the first photomask 9 is used and the first photomask 9 is irradiated with UV light from above, the photobleaching layer 5 below the UV light transmission region 13 has a lower refractive index due to the UV light irradiation (refractive). Rate: 1.460).
[0033]
On the other hand, since the photobleaching layer 5 below the UV light reflection region 12 is not irradiated with UV light, the refractive index does not decrease (refractive index value: 1.475).
[0034]
As described above, as shown in FIG. 2B, the first core layer 5 ′ having a high refractive index and the side cladding layers 6 a ′ and 6 b ′ having a low refractive index are formed on both side surfaces of the first core layer 5 ′. You.
[0035]
Next, as shown in FIG. 2C, a second photomask 11 is arranged on the first core layer 5 'and the side cladding layers 6a' and 6b ', and the UV light 10 is irradiated.
[0036]
As the second photomask 11, a mask as shown in FIG. 3B is used. As the second photomask 11, a mask having a UV light reflection region 12 'and a UV light transmission region 13 is used. When the second photomask 11 is irradiated with UV light 10 from above, the refractive index of the side cladding layers 6a 'and 6b' below the UV light transmitting region 13 further decreases (refractive index value: 1.450). Since the central portion of the first core layer 5 'below the UV light reflection region 12' is not irradiated with UV light, the refractive index does not decrease (refractive index value: 1.475).
[0037]
However, since the UV light is applied to the portion (both sides of the first core layer 5 ') other than the portion corresponding to the UV light reflection region 12' in the UV light reflection region 12, the first core layer 5 ' Decreases from 1.475 to 1.460.
[0038]
That is, as shown in FIG. 2D, the refractive index of the second core layer 5a is 1.475, the refractive index of the side core layer 5b is 1.460, and the refractive indexes of the side cladding layers 6a and 6b are 1. 450.
[0039]
A second clad layer 7 (silicone resin, refractive index: 1.450) is formed on the second core layer 5a, the side core layer 5b, and the side clad layers 6a and 6b, and a UV light is absorbed on the second clad layer 7. By forming the layer 8, the low-loss optical waveguide shown in FIG. 1 is obtained.
[0040]
FIG. 4A is a cross-sectional view showing another embodiment of the low-loss optical waveguide of the present invention, and FIG. 4B shows a refractive index distribution in a cross section taken along line EE of FIG. 4A. FIG. 4C is a diagram showing a refractive index distribution in a cross section taken along line FF of FIG. 4A. In FIG. 4B, the horizontal axis indicates the position in the width direction from the center, and the vertical axis indicates the refractive index. In FIG. 4C, the horizontal axis represents the refractive index, and the vertical axis represents the position in the thickness direction.
[0041]
This optical waveguide is provided on the first cladding layer 4 by two core layers (one (left side in the figure) second core layer 5aa, one side core layer 5ba, and the other (right side in the figure) second core layer 5ab). , And the other side core layer 5bb) is arranged in parallel.
[0042]
One high refractive index second core layer 5aa is provided between the one side core layer 5ba having a lower refractive index than the second core layer 5aa, and the other second core layer 5ab having a higher refractive index is provided in the second core layer 5ab. The side cladding layer 6c is provided between the other side core layers 5bb having a lower refractive index than the core layer 5ab, and a photo-bleaching layer having a low refractive index is provided between the two core layers.
[0043]
Outside the one side core layer 5ba (left side in the figure), a side cladding layer 6a made of a low refractive index photobleaching layer is formed. Outside the other side core layer 5bb (the right side in the figure), a side cladding layer 6b made of a low refractive index photobleaching layer is formed.
[0044]
Since this optical waveguide has a juxtaposed core layer, 90 ° curve pattern, S-curve pattern, etc., devices such as directional couplers, multiplexers / demultiplexers, filters, switches, and modulators can be realized with low loss. It is effective in doing. In addition, since these devices frequently use a 90 ° curve pattern or an S-shaped curve pattern as shown in FIG. 7 in the width direction, low loss can be achieved by using the waveguide of the present invention, and miniaturization can be realized. Can be.
[0045]
FIG. 5A is a cross-sectional view showing another embodiment of the low-loss optical waveguide according to the present invention, and FIG. 5B shows a refractive index distribution in a cross section taken along line GG of FIG. FIG. 5C is a diagram showing a refractive index distribution in a cross section taken along line HH of FIG. 5A. In FIG. 5B, the horizontal axis indicates the position in the width direction from the center, and the vertical axis indicates the refractive index. In FIG. 5C, the horizontal axis represents the refractive index, and the vertical axis represents the position in the thickness direction.
[0046]
This optical waveguide has a multi-functional, highly integrated type of laminated structure in which a first waveguide 14-1 is formed on a substrate 1 and a second waveguide 14-2 is formed on the first waveguide 14-1. Is an optical waveguide.
[0047]
The first waveguide 14-1 includes a first cladding layer 4-1, a second core layer 5a-1, a side core layer 5b-1, and a side cladding layer 6a formed on the first cladding layer 4-1. -1, 6b-1, the second core layer 5a-1, the side core layer 5b-1, and the second cladding layer 7-1 formed on the side cladding layers 6a-1, 6b-1; And a UV cut (or UV absorbing) layer 8-1 formed on the clad layer 7-1.
[0048]
The second waveguide 14-2 includes a first cladding layer 4-2, a second core layer 5a-2, a side core layer 5b-2, and a side cladding layer 6a formed on the first cladding layer 4-2. -2, 6b-2, a second cladding layer 7-2 formed on the second core layer 5a-2, the side core layer 5b-2, and the side cladding layers 6a-2, 6b-2; And a UV cut (or UV absorption) layer 8-2 formed on the clad layer 7-2.
[0049]
In this laminated optical waveguide, the same or different optical signal processing circuits may be formed in the first waveguide 14-1 and the second waveguide 14-2.
[0050]
The present invention is not limited to the above embodiment.
[0051]
First, the refractive indices of the first cladding layers 4-1 and 4-2 and the second cladding layers 7-1 and 7-2 may be equal or different. The refractive indices of the side cladding layers 6a-1, 6b-1, 6a-2 and 6b-2 are also equal to the refractive indices of the first cladding layers 4-1 and 4-2 and the second cladding layers 7-1 and 7-2. Or may be different. The optical waveguide may be for multi-mode transmission other than for single-mode transmission. Silicone-based or epoxy-based materials can be used as the photobleaching material. Further, as specific examples other than the above-described embodiment, dye polymer, 4-dialkylamino-4′-nitro-stillene, DMAPN, 2-nitrostillene, and the like can be used. One, two, or three or more core layers may be arranged in the width direction of the substrate. On the substrate 1, waveguides can be formed in a multilayer structure such as one layer, two layers, three layers, four layers,... To achieve high integration and multifunctionality.
[0052]
Electronic circuits, electronic components, and electric wiring may be mounted on the front surface, the back surface, or inside the substrate 1. An optical component other than the optical circuit, an electronic circuit, an electronic component, an electric wiring, or the like may be mounted on the upper surface, the lower surface, both end surfaces, or inside the waveguide. Further, an optical fiber may be connected to the input / output end face side of the waveguide. Further, as the photobleaching material, an inorganic material (for example, a material obtained by adding GeO ₂ to a SiO ₂ material, etc.) may be used in addition to the polymer material.
[0053]
The refractive index distribution in the core layer may be a three-stage type, a four-stage type, or the like, other than the two-stage type. These multi-step refractive index distribution manufacturing methods can be easily realized by using a plurality of photomasks.
[0054]
As described above, according to the present invention,
(1) A low-loss waveguide can be formed because a refractive index distribution similar to the optical power distribution in the width direction of the core layer of the waveguide can be formed and the interface between the core layers can be formed uniformly. Is obtained.
[0055]
(2) A low-loss waveguide with reduced radiation loss and scattering loss can be realized by a simple process.
[0056]
(3) An optical signal processing circuit that makes extensive use of a 90 ° curve pattern or an S-shaped curve pattern in the width direction of the substrate can be formed with a small radius of curvature, realizing a compact, highly integrated optical device. it can.
[0057]
(4) By forming the core layer with a photobleaching layer, it is possible to uniformly form the boundary of each step of the refractive index distribution, and the refractive index controls the irradiation power and irradiation time of UV light. Therefore, it is possible to easily design an optical signal processing circuit in addition to reducing the loss and the cost.
[0058]
(5) Since there is almost no step in the thickness direction of each layer, the loss can be further reduced. Further, it becomes easy to mount an optical component, an electric component, an electric circuit, an electric wiring, or the like on the front surface (or the back surface) of the substrate, in the substrate or on the upper surface (or the back surface) of the waveguide, or in the waveguide.
[0059]
【The invention's effect】
In short, according to the present invention, the following excellent effects are exhibited.
[0060]
It is possible to provide a small-sized low-loss optical waveguide having small scattering loss and radiation loss and a method for manufacturing the same.
[Brief description of the drawings]
FIG. 1A is a cross-sectional view showing one embodiment of a low-loss optical waveguide of the present invention, and FIG. 1B shows a refractive index distribution in a cross section taken along line CC of FIG. (c) is a diagram showing a refractive index distribution in a section taken along line DD of (a).
FIGS. 2A to 2D are process diagrams showing one embodiment of a method for manufacturing the low-loss waveguide shown in FIG.
FIGS. 3A and 3B are plan views of a photomask used during the steps shown in FIGS. 2A to 2D.
4A is a cross-sectional view showing another embodiment of the low-loss optical waveguide of the present invention, FIG. 4B shows a refractive index distribution in a cross section taken along line EE of FIG. (C) is a diagram showing a refractive index distribution in a cross section taken along line FF of (a).
FIG. 5A is a cross-sectional view showing another embodiment of the low-loss optical waveguide of the present invention, and FIG. 5B shows a refractive index distribution in a cross section taken along line GG of FIG. (C) is a diagram showing a refractive index distribution in a cross section taken along line HH in (a).
6A is a cross-sectional view of a conventional optical waveguide, FIG. 6B shows a refractive index distribution in a cross section taken along the line AA in FIG. 6A, and FIG. 6C shows a BB in FIG. It is a figure which shows the refractive index distribution in a line cross section.
FIG. 7A is a graph showing the radius of curvature R of the waveguide bent at 90 ° and the radiation loss of the waveguide in the waveguide shown in FIG. 6 using the relative refractive index difference Δ between the core layer and the cladding layer as parameters. FIG. 6B shows the result of calculation, and FIG. 6B shows the relative radius difference Δ between the core layer and the cladding layer, where the curvature radius R and the waveguide radiation loss of the S-shaped curved waveguide among the waveguides shown in FIG. FIG. 9 is a diagram showing a result of calculation using as a parameter.
[Explanation of symbols]
Reference Signs List 1 substrate 5a, 5b core layer 4, 6a, 6b, 7 cladding layer 8 UV cut layer (UV absorption layer)

Claims (2)

A step of forming a first cladding layer on the substrate, a step of forming a photobleaching layer whose refractive index is reduced in accordance with the irradiation amount of UV light on the first cladding layer, and a step of forming a photobleaching layer on the photobleaching layer A first photomask having a pattern of a core layer is disposed on the first photomask, and UV light is irradiated from above the first photomask to form a high refractive index core layer having a substantially rectangular cross-sectional shape and having at least one curved portion. Forming a low refractive index side cladding layer on both sides of the core layer, and disposing a second photomask having a pattern of a central core layer on the side cladding layer and the core layer; Irradiating UV light from above to form a central portion of the core layer in the central core layer having a high refractive index, and to form side core layers on both sides of the central core layer having a lower refractive index than the central core layer; , The central core layer, the above Method of manufacturing an optical waveguide, characterized by a step of laminating a second cladding layer on the surface the core layer and the side cladding layer. The method for manufacturing an optical waveguide according to claim 1, further comprising a step of laminating a UV cut layer or a UV absorption layer on the second clad layer .

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