JP2002062446A - Laminated interlayer optical directional coupler and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical directional coupler between laminated waveguides and its manufacturing method with respect to a laminated optical waveguide realizing high density integration. SOLUTION: In the laminated directional coupler wherein clad layers 313, 314 and 315, and cores 302 and 303 are formed by being repeated a plurality of times on one surface of a substrate 312 to form optical waveguides consisting of n layers in a laminated shape and also optical coupling is performed between respective optical waveguides, the cores 302 and 303 are arranged closely to each other in the direction orthogonal to the substrate only in optical coupling areas 316 and 317 via the optical waveguide which is smoothly curved in the direction orthogonal to the substrate. The cores 302 and 303 are satisfactorily separated in an area other than the coupling area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a laminated optical waveguide which enables high-density integration, and more particularly to an optical directional coupler between laminated waveguides and a method of manufacturing the same.

[0002]

2. Description of the Related Art With the rapid development of optical communication technology, various optical components have been researched and developed. Among them, a waveguide type optical component based on an optical waveguide on a flat substrate occupies the most important position. . This is because the waveguide type optical component has a feature that it can be mass-produced with a precision equal to or less than the light wavelength and with good reproducibility by a photolithography technique and a fine processing technique.

[0003] However, the scale of these waveguide type optical components is smaller than the scale of the communication system, and it is necessary to realize a system by combining a large number of components. For example, in a cross-connect system that is realizing 256 input lines and 256 output lines in any combination, even if an 8 × 8 matrix switch is used, 1000 or more modules are required. That is, there is a strong demand for a large-scale individual optical component.

In order to increase the scale of an optical circuit, there are a method of increasing the size of a circuit board for integration, and a method of increasing the degree of integration by reducing the size of element elements constituting the circuit. In order to increase the chip size, it is necessary to increase the size of the waveguide manufacturing apparatus, and development of the apparatus requires much time, and it is difficult to respond in a short time. Further, an increase in the chip size causes an increase in the size of a module on which the chip is mounted, but the substrate mountable on the module has a prescribed size, and the chip size cannot be increased indefinitely.

On the other hand, in order to reduce the size of the element element, the relative refractive index difference between the core and the surrounding clad in the optical waveguide is increased to enhance the effect of confining light in the core and to bend the waveguide. It is effective to reduce the radius.
However, as the relative refractive index difference increases, the error in the optical path length for the same amount of fabrication error also increases. Even if the relative refractive index difference changes, the geometric manufacturing accuracy is the same, so in a waveguide type optical component that controls it by light interference, the larger the relative refractive index difference, the more the optical interference state is greatly disturbed. As a result, the performance of the component is reduced.
For this reason, there is a limit to the method of increasing the relative refractive index difference and increasing the degree of integration.

As another method for increasing the integration degree,
There is a multilayer circuit structure in which a plurality of optical waveguide structures are formed in multiple layers in a direction perpendicular to a substrate, and circuits are stacked vertically on the substrate. When a laminated circuit structure is used, it is indispensable to realize an optical coupler that transmits and receives light using waveguides having different upper and lower layers.

FIGS. 13, 14 (A) and 14 (B) are diagrams related to a conventional two-layer laminated type inter-layer optical directional coupler which has been studied. Here, FIG. 13 is a schematic diagram showing a state in which two optical waveguides extending in parallel are bent in the middle and overlap each other vertically, and FIGS. 14 (A) and (B) are A in FIG.
It is sectional drawing of the lamination type interlayer optical directional coupler along each line of A ', BB'.

As shown in FIG. 14, the laminated interlayer optical directional coupler uses, for example, a silicon substrate as a substrate 312, a lower cladding layer 313 on the surface of the substrate 312, and a lower cladding layer 313 on the surface of the lower cladding layer 313. Intermediate cladding layer 31
4. An upper cladding layer 315 is sequentially formed on the surface of the intermediate cladding layer 314. After forming the lower core 302 for forming one optical waveguide on the lower cladding layer 313, forming the intermediate cladding layer 314, forming the upper core 303 on the intermediate cladding layer 314, and forming the upper core 303 on the lower cladding layer 314. The structure is such that a clad layer 315 is formed. Therefore, the intermediate cladding 314 extends thinly between the lower core 302 and the upper core 303.

In FIG. 13, the two waveguides extend parallel to each other from left to right in the figure, but bend so as to approach each other at an intermediate portion, overlap vertically, and then separate again. Bend again and extend in parallel. 13, reference numerals 304 and 308 denote a lower layer input waveguide and an upper layer input waveguide, respectively, and reference numerals 307 and 311 denote a lower layer output waveguide and an upper layer output waveguide, respectively.
Is a coupling region between upper and lower layers composed of two upper and lower linear waveguides, 305 and 309 are bent waveguide portions from the input waveguides 304 and 308 to the coupling region 110, 306 and
Reference numeral 310 denotes the output waveguide 30 from the coupling region 110.
The bent waveguide portions 7 and 311 are illustrated.

This structure comprises a lower core 302 and an upper core 3
03, an intermediate cladding layer 314 is interposed therebetween, and a desired coupling ratio can be obtained by adjusting the thickness of the intermediate cladding layer 314 and the length of the coupling region 110. ing.

[0011]

In the above-mentioned conventional laminated type interlayer optical directional coupler, the upper and lower waveguide cores 302, 30 are provided.
By bringing the geometrical positional relationship of 3 closer in the plane of the substrate to realize a stacked directional coupler, there is a problem that the circuit design lacks flexibility. Specifically, FIG.
As shown in FIG. 4, when the upper and lower waveguide cores 302 and 303 are inadvertently arranged close to each other because the intermediate cladding layer 314 is thin, unnecessary coupling occurs there. For example, in FIG. 13, the input / output waveguide portion of the coupler is bent to prevent the coupling of the upper and lower waveguides from being carelessly performed.
5,306,309,310,
It is necessary to separate the waveguides so that the upper and lower waveguides are not coupled. As described above, since the two cores are largely separated from each other, a redundant area is required regardless of the circuit function.

Further, the waveguides cannot be brought close to each other in order to avoid unnecessary coupling in areas other than the coupler region, so that not only a free waveguide layout cannot be realized, but also the degree of integration is limited. Thus, the thin intermediate cladding layer 314 required for forming the stacked type interlayer optical directional coupler is provided.
However, there is a problem in that the degree of freedom and the degree of integration of the waveguide layout are impaired.

In view of the above problems, an object of the present invention is to provide a laminated interlayer optical directional coupler capable of increasing the degree of freedom in waveguide layout and a method of manufacturing the same.

[0014]

According to a first aspect of the present invention, which solves the above-mentioned problems, a multilayer inter-layer optical directional coupler is formed by repeatedly forming a cladding layer and a core on one surface of a substrate. A laminated directional coupler in which n layers of optical waveguides are formed in a laminated manner and optical coupling is performed between the respective optical waveguide cores, wherein each of the cores is an optical waveguide that smoothly curves in a direction perpendicular to the substrate. It is characterized in that it is close to the optical coupling region in the vertical direction of the substrate only through the wave path, and is sufficiently separated outside the coupling region.

According to a second aspect of the present invention, in the first aspect, the coupling region has a smooth bulge in the cladding layer sandwiched between the n-th layer core and the (n-1) -th layer core located thereabove. The n-th layer core and the n-th layer
The +1 layer core is close to the optical coupling region only.

According to a third aspect of the present invention, in the first aspect, the coupling region has a smooth depression in the clad layer sandwiched between the n-th layer core and the n-1-th layer core located thereunder. , The n-th layer core and an n-th layer
-1 layer core is close only in the optical coupling region.

According to a fourth aspect of the present invention, in the second or third aspect, at least one input waveguide portion and at least one output waveguide portion are provided.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the waveguide is formed of a silica glass waveguide.

According to a sixth aspect of the invention, there is provided a method for manufacturing a laminated type inter-layer optical directional coupler, wherein a clad layer and a core are repeatedly formed on one surface of a substrate a plurality of times to form a plurality of optical waveguides. A method for manufacturing a laminated directional coupler in which each core has a coupling region where optical coupling is performed, wherein a step of forming an n-th cladding layer and a mask disposed so as to float on the substrate A step of processing the n-th cladding layer so as to gradually protrude toward the optical coupling region, and a step of forming an n-th core film on the n-th cladding.

According to a seventh aspect of the present invention, there is provided a coupling region in which a plurality of optical waveguides are formed by repeatedly forming a clad layer and a core on one surface of a substrate a plurality of times, and the respective cores are optically coupled. A method of manufacturing a laminated directional coupler formed to have a step of forming an n-th cladding layer, and optically coupling the n-th cladding layer by using a mask provided so as to float on the substrate. The method is characterized by including a step of processing so as to be gradually depressed toward the region, and a step of forming an n-th core film on the n-th cladding layer.

The invention of claim 8 provides a method of forming a cladding by using one of the method of raising the coupling region of claim 6 and the method of forming a depression of claim 7, or a method combining these. Forming a layer.

According to a ninth aspect of the present invention, in any one of the sixth, seventh and eighth aspects, a mask provided so as to float on the substrate after forming a predetermined n-th core layer is used to form the (n + 1) th clad. The method is characterized by including a step of processing to flatten the layer or a step of processing to flatten the clad layer by polishing.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION An outline of a typical invention disclosed in the present invention will be briefly described as follows. A laminated interlayer optical directional coupler having a lower cladding layer, a lower waveguide core, an intermediate cladding layer, an upper waveguide core and an upper cladding layer on one surface of a substrate, wherein only the coupling portion has an upper waveguide core and a lower waveguide. The waveguide cores are close to each other, and in other portions, the lower waveguide core extends below the coupling portion, and the upper waveguide core extends above the coupling portion. That is, the upper and lower waveguide cores are adjacent to each other with a thin intermediate layer only at the coupling portion, and have a bend in the vertical direction of the substrate so that an intermediate layer having a sufficient thickness exists between the upper and lower waveguide cores except at the coupling portion. It has become. Therefore, according to such a configuration, regardless of the layout of the optical circuit, the upper and lower waveguides are coupled only at the directional coupler portion, and the other portions are sufficiently separated by the thick intermediate cladding layer. Since there is no coupling, a waveguide layout having a high degree of freedom can be ensured similarly to the single-layer waveguide regardless of the position of the directional coupler.

Such a laminated interlayer optical directional coupler is manufactured by the following method.

A cladding layer and a core are repeatedly formed on one surface of a substrate to form a plurality of laminated optical waveguides, and each core is formed so as to have a coupling region where optical coupling is performed. A method of manufacturing a mold interlayer optical directional coupler, wherein the coupling region brings a predetermined core close to a core via a cladding adjacent to the upper side of the core by raising a cladding layer adjacent to the lower side of the core. Alternatively, the predetermined core is formed by forming a depression in a cladding layer adjacent to the lower side of the core so as to approach the core located below the core via the cladding layer. Alternatively, the connection region may be formed by using both a method of forming a protrusion and a method of forming a depression.

Further, when the waveguide is formed of a glass waveguide, the fabrication is easy and the fabrication cost is low, and the cost of the laminated interlayer optical directional coupler can be reduced.

[0027]

Embodiments of the present invention will be described below in detail with reference to the drawings, but the present invention is not limited thereto. In all the drawings for describing the embodiments of the present invention, components having the same functions are denoted by the same reference numerals, and their repeated description will be omitted.

In the following embodiments, a part of the lower cladding layer,
The upper and lower core layers are formed by flame hydrolysis deposition of a quartz glass film (FH
Although the case of manufacturing by the method D) will be described, the present invention is not limited to the method of manufacturing a glass film, and a part or all of them can be replaced with a sputtering method, a CVD method, or the like. The case where the raised portion and the recessed portion are formed by sputtering a quartz glass film by a sputtering method will be described. However, the present invention is not limited to the method of manufacturing a glass film. It is also possible to produce by the vapor phase glass film forming method.

[First Embodiment] In the first embodiment, the present invention is applied to a two-input, two-output, two-layer, laminated inter-layer optical directional coupler using a quartz-based optical waveguide formed on a silicon substrate as the optical waveguide. An example will be described.

FIGS. 1 to 5 show an embodiment 2 of the present invention.
A stacked directional coupler having two inputs and two outputs and a method of manufacturing the same.

FIG. 1A is a schematic plan view showing a state in which two optical waveguides extending in parallel are vertically stacked, and FIG. 1B is a plan view of FIG. 1A. 2 along CC '
FIG. 1 is a cross-sectional view of a layered laminated optical directional coupler having a layer configuration.
(C) and (d) are DD 'and E in FIG. 1 (b), respectively.
FIG. 4 is a cross-sectional view of a two-layer laminated interlayer optical directional coupler along E ′.

As shown in FIG. 1, the two-layer laminated type interlayer optical directional coupler uses a substrate made of silicon, for example.
A lower cladding layer (cladding layer) 313, an intermediate cladding layer (cladding layer) 314, and an upper cladding layer 315 are sequentially formed on one surface (surface) of the substrate (silicon substrate) 312, and the lower cladding layer 313 is formed. After forming a lower optical waveguide core (abbreviated as lower core) 302 thereon, the intermediate cladding layer 314 is formed, and an upper optical waveguide core (abbreviated as upper core) 303 is formed in the intermediate cladding layer 314. The upper core 303 is covered with an upper clad 315. As shown in FIG. 1B, the lower optical waveguide core 302 includes an input waveguide 304, bent waveguides 305 and 306, an output waveguide 307, and an optical coupler 316. On the other hand, the upper optical waveguide core 303 includes an input waveguide section 308,
It is composed of bent waveguide sections 309 and 310, an output waveguide section 311 and an optical coupling section 317.

This is one of the features of the present invention. As shown in FIG.
Is connected to the upper optical coupling region 317 via a curved waveguide 309 that curves downward, and the lower input waveguide core 304 is connected to the lower optical coupling region 31 via a curved waveguide 305 that curves upward.
It leads to 6. Further, the upper optical coupling region 317 is connected to 311 via a curved waveguide 310 which curves upward, and the lower waveguide core 316 is connected to 307 via a curved waveguide 306 which curves downward. That is, the upper coupling region 317 exists below the plane where the upper core 303 extends, and the lower coupling region 316 exists above the plane where the lower core 302 extends. At this time, the upper and lower coupling regions 317 and 316 extend in parallel via the thin intermediate cladding layer 318, and in other regions, the upper and lower waveguide cores 30
4,307,308,311 are thick intermediate cladding layers 31
4 are provided. In FIG. 3A, the two optical waveguides 302 and 303 extend from left to right.

Next, a method of manufacturing the laminated directional coupler of the first embodiment will be described. Figure 2 shows a stacked directional coupler.
Steps 1 to 3, steps 4 to 6 in FIG. 3, steps 7 to 9 in FIG.
5 and steps 10 to 11 in FIG. 5 or steps 5 to 6 in FIG. 6 as an intermediate step. In the drawings, (a) is a sectional view in the direction of the core axis, and (b) is a sectional view in the direction perpendicular to the core axis.

That is, as shown in FIG. 1, for example, as a step 1, a silicon substrate 3 having a diameter of 4 inches and a thickness of 1 mm
First, a silica-based glass fine particle layer serving as the lower cladding layer 313a is deposited on one surface of the substrate 12 by a flame hydrolysis deposition method (FHD method). This quartz glass fine particle layer is melted and solidified in a high-temperature furnace to form a transparent lower clad layer flat portion 313a (about 20 μm in thickness).

In step 2, as shown in FIG. 1, a mask 321 is set at a distance of 1 mm from the surface of the substrate, and a quartz glass layer serving as a lower cladding raised portion 313b is deposited by sputtering. That is, a mask 321 having a rectangular hole having a size corresponding to the raised portion is fixed at a distance of 1 mm from the substrate, and the silica-based glass layer serving as the lower clad layer raised portion 313b is at least 4 μm in height and 4 mm in length. .4 mm,
Deposit over a width of 10 μm. At this time, the bending radius of the curved portion of the protrusion can be set to 10 mm or more, and the loss in the bent waveguide can be sufficiently reduced.

Although the distance of the mask 321 from the substrate surface is set to 1 mm in this embodiment, a protrusion having a desired bending radius can be produced by adjusting the distance. Also, the following description does not limit arbitrary setting of the distance of the mask from the substrate surface.

In step 3, as shown in FIG. 1, quartz glass fine particles to be the lower core layer 302a are deposited by the FHD method. The transparent lower core layer 302a (about 7 μm in thickness) is formed by placing the quartz glass fine particles in a high-temperature furnace as in Step 1.

In step 4, as shown in FIG. 3, unnecessary portions of the lower core layer are removed by reactive ion etching (RIE) to form a lower core 302.

In step 5, as shown in FIG. 3, a mask 322a covering the raised portion 313b is set at a position 1 mm away from the raised surface, and a quartz glass serving as a part 314a of the intermediate cladding layer is formed by sputtering. Deposit the layer. Further, a mask 322b covering the lower core 302 formed in the step 4 is placed on the surface of the core 302 by one step.
mm, and a quartz glass is deposited by a sputtering method.

In step 6, as shown in FIG. 3, a silica glass fine particle layer which becomes a part 314b (thickness: 3 μm) of the intermediate cladding layer is deposited by the FHD method, and the silica glass fine particles are placed in a high-temperature furnace. A transparent intermediate cladding layer (thickness: 3 μm) is formed by placing.

Here, instead of the steps 5 and 6 shown in FIG. 3, steps 5 and 6 shown in FIG. 6 can be performed. That is, in step 5 shown in FIG. 6, a silica-based glass fine particle layer serving as an intermediate clad layer is deposited by the FHD method, and the quartz-based glass fine particles are placed in a high-temperature furnace to thereby form a part 314e ( Thickness 3
μm). Thereafter, in step 6 shown in FIG. 6, the masks 332a and 332b are arranged at a distance of 1 mm from the raised surface, and quartz glass serving as a part 314f of the intermediate cladding layer is deposited by sputtering. After step 6, the substrate surface is sufficiently flat, but if the flatness is insufficient, polishing may be performed to reduce surface irregularities. In addition to the method used in step 5, the intermediate cladding layer 314a is made sufficiently thick (10 μm) by a method such as a method of reducing unevenness of a quartz glass by a bias sputtering method or a FHD method, a sputtering method, or a CVD method without using a mask at all.
After deposition, it is also possible to obtain flatness by polishing.

In step 7, as shown in FIG. 4, the mask 322a is arranged at a position 1 mm from the surface of the substrate, and a silica glass fine particle layer to be a part 314c of the intermediate cladding layer is deposited by sputtering.

In step 8, as shown in FIG. 4, quartz glass fine particles to be the upper core layer 303a are deposited by the FHD method. By placing these quartz glass fine particles in a high-temperature furnace, a transparent upper core layer 303a (about 6 μm in thickness) is obtained.
Is formed.

In step 9, as shown in FIG.
Unnecessary portions of the upper core layer are removed by a method to form the upper core 303.

In step 10, as shown in FIG. 5, a mask 323 is arranged at a position 1 mm from the substrate surface, and fine quartz glass particles to be a part 315a of the upper clad layer are deposited by a sputtering method to form a depression on the substrate surface. Flatten.

In step 11, as shown in FIG. 5, fine silica glass particles to be a part 315b of the upper cladding layer
Deposited by HD method. The transparent upper clad layer 315b is formed by placing the quartz glass fine particles in a high-temperature furnace. Here, the substrate surface is sufficiently flat, but if the flatness is insufficient, it is possible to reduce the unevenness of the surface by polishing.

In the above steps, Ge is added to the quartz glass so that the relative refractive index difference becomes Δ = 0.75% in the upper and lower core layers.

Regarding step 10 shown in FIG. 5, in addition to the method applied in the first embodiment, a method of reducing unevenness of a quartz glass by a bias sputtering method or an FHD method, a sputtering method, After the upper cladding layer 315a is deposited sufficiently thick (10 μm or more) by a CVD method or the like, it is also possible to obtain flatness by polishing.

FIG. 7 shows a relative refractive index difference Δ = 0.75%, a core size of 7 μm × 7 μm, and an intermediate cladding layer 31 in an optical coupling region.
4 shows the dependence of the coupling ratio on the length of the optical coupling region when 3 is 3 μm. By changing the coupling ratio as a periodic function of the optical coupling region length and adjusting the length of the coupling region, an arbitrary coupling ratio can be obtained.

In the first embodiment, the example of two layers has been described. However, since the substrate surface is flattened in the above steps,
Furthermore, it is also possible to form a laminated structure and to produce a laminated directional coupler having a two-input two-output laminated structure between the second layer and the third layer or more layers. In addition, here, an example of the convex process in which the waveguide pattern is extended by depositing a thin film serving as a core and then processing the core thin film has been described. Obviously, a concave process for deposition is also feasible.

[Embodiment 2] FIG. 8 is a view showing a laminated directional coupler according to another embodiment (Embodiment 2) of the present invention, and shows a cross-sectional view of a core along a traveling direction of light. I have. In the above-described first embodiment, an example is shown in which the lower waveguide core is bent upward and the upper waveguide core is bent downward to cause coupling between the two waveguides, but only the deformation of the lower core and the upper core is performed. If this is sufficient, only one of them may be used.

Embodiment 2 is an example of a power converter between laminated waveguides to which the present invention is applied. In FIG. 8, 312 is a substrate, 313 is a lower cladding layer, 314 is an intermediate cladding layer, 315 is an upper cladding layer, 304 is a lower input waveguide core, 316 is a lower optical coupling part, 317 is an upper optical coupling part,
311 is an output waveguide core, 310 is the upper optical coupling unit 3
17 is a bent waveguide leading from 17 to the output waveguide core 311. The intermediate cladding layer 314 sandwiched between the upper and lower linear waveguides 316 and 317 serving as an optical coupling portion has a thickness of 3 mm.
μm, and the length of the optical coupling portions 316 and 317 is 4.4 m.
m. At this time, the coupling between the upper and lower waveguides becomes 100%, and the optical power incident on the lower optical coupling section 316 from the lower input waveguide 304 is coupled to the upper optical coupling section 317 by 100%. As is apparent from FIG. 8, the lower waveguide layers 304 and 316 have a configuration in which the output waveguide section is omitted.
The upper waveguide layers 317, 310 and 311 are characterized in that the input waveguide section is omitted. That is, the second embodiment has an advantage that the substrate area required for the circuit configuration of the stacked interlayer optical directional coupler can be reduced when the purpose is to convert the power between the upper and lower waveguide layers. It is a feature. In the second embodiment, the lower waveguide core 304 and the lower optical coupling unit 316 are linear waveguides, while the upper waveguide cores 317, 310, 31
Although the shape including the bent waveguide is shown in FIG. 1, it is needless to say that the upper waveguide core may be straight and the lower waveguide core may include the bent waveguide.

[Embodiment 3] FIG. 9 is a diagram related to a 3.times.3 stacked interlayer optical directional coupler in a three-layer optical waveguide.

In FIG. 9, reference numeral 334 denotes an intermediate optical waveguide core (also referred to as an intermediate core). The intermediate core 334 comprises an intermediate input waveguide section 331, an intermediate optical coupling section 333, and an intermediate output waveguide section 332. The 3 × 3 stacked directional coupler includes a lower cladding layer (cladding layer) 313, a first intermediate cladding layer (cladding layer) 314-1, and a second cladding layer (cladding layer) on one surface (surface) of a substrate 312. 314
-2, the upper clad layer 315 is sequentially formed, and the lower core 30 is formed on the lower clad layer 313.
2, the first intermediate cladding layer 314-1 is formed, the intermediate core 334 is formed on the first intermediate cladding layer 314-1, and the second intermediate cladding layer 314-2 is formed on the intermediate core 334. And forming the second intermediate cladding layer 3
An upper core 303 is formed on 14-2, and the upper core 303 is covered with an upper clad 315. The lower optical waveguide core 302 is connected to the input waveguide section 30.
4. Bent waveguide sections 305, 306, output waveguide section 30
7 and an optical coupling section 316, and the upper optical waveguide core 303 has an input waveguide section 308, a bent waveguide section 3
09, 310, output waveguide section 311 and optical coupling section 31
7 is comprised.

The third embodiment is characterized in that the waveguide is a three-layered waveguide and the lower core 302
Are curved upward, close to the intermediate core 334, and the upper core 3
Reference numeral 05 denotes a laminated interlayer optical directional coupler which curves downward and approaches the intermediate core 334.

The first intermediate cladding layer 314-1 has a thickness of 3 μm at the optical coupling section and has a lower optical coupling section 316 and an intermediate optical coupling section 3.
Similarly, the second intermediate cladding layer 314-2 has a thickness of 3 μm at the optical coupling portion and is sandwiched between the intermediate optical coupling portion 333 and the upper optical coupling portion 317. The three-layer laminated type interlayer optical directional coupler of the second embodiment is a quartz-based optical waveguide that becomes the intermediate waveguide core 332 between the steps 6 and 7 in the manufacturing process shown in FIGS. Glass fine particles are deposited by the FHD method. By placing the quartz glass fine particles in a high-temperature furnace, a transparent intermediate core layer is formed. Next, unnecessary portions of the intermediate core layer are removed by RIE or the like, and a lower core 332 is formed. Also,
The relative refractive index of each waveguide is Δ = 0.75%.

FIG. 10 shows an upper output waveguide 311, an intermediate output waveguide 332, and a lower output waveguide 307 with respect to the coupling region length of the three-input three-output laminated interlayer optical directional coupler of the third embodiment. It is the result of having calculated the coupling ratio of. FIG.
Thus, the stacked three-input three-output directional coupler of the third embodiment has one
It can be seen that it has a 20 ° hybrid characteristic and is a periodic function of the coupling length. The third embodiment means that a single directional coupler can branch optical power to a multilayer circuit.

[Embodiment 4] FIG. 11 is a cross-sectional view of FIG.
Shows another realization method of step 1 and step 2 in
FIG. 12 shows another method of realizing the steps 6 and 7 in FIGS. FIG. 12 is a cross-sectional view of a step of forming a raised portion of the lower cladding layer in FIG. 11.

First, steps 1 and 2 which are the method of forming the raised portion of the lower cladding layer shown in FIG. 10 will be described.

In step 1 of FIG. 11, FH is
Silica-based glass particles to be the lower cladding layer 313 are deposited by the D method by the FHD method. By placing these glass particles in a high-temperature furnace, the transparent lower cladding layer 313 is formed.
(Thickness: 20 μm).

In step 2 of FIG. 11, the mask 322a is arranged at a position 1 mm from the surface of the substrate, and unnecessary portions of the lower clad layer 313 are removed by RIE so that a raised portion (height 4 mm) of the lower clad layer is formed. Form.
That is, in the first embodiment, the raised portion 313b of the lower clad layer is formed by depositing the silica-based glass fine particles, whereas in the fourth embodiment, the raised portion of the lower clad layer 313 is formed by the RIE method. Has formed.

FIG. 12 shows a step 6 and a step 7 which are the method of forming the recess of the intermediate cladding layer.

In step 6 of FIG. 12, fine silica glass particles, which also become part 314b of the intermediate cladding layer, are deposited on the flattened part 314a of the intermediate cladding layer by the FHD method. By placing these glass particles in a high-temperature furnace, a transparent intermediate cladding layer 314b (4 μm in thickness) is formed.

In step 7 of FIG. 12, the mask 321 is set at a position 1 mm from the surface of the substrate, and an unnecessary portion of the intermediate cladding layer 314b is removed by RIE to form a depression (4 μm depth) in the intermediate cladding layer. I do. That is, in the first embodiment, the hollow portion of the intermediate cladding layer is formed by depositing the silica-based glass particles, whereas in the fourth embodiment, the hollow portion of the intermediate cladding layer 314b formed in advance is formed by the RIE method. are doing.

In step 2 of FIG. 11, the height of the raised portion of the lower cladding layer is 4 μm, in step 7 of FIG. 12, the depth of the recess of the intermediate cladding layer is 4 μm, and the thickness of the intermediate cladding layer in the coupling region is 3 μm. Therefore, the distance between the upper and lower waveguide cores other than the optical coupling region is 11 μm, and optical coupling does not occur.

[0067]

As described above, according to the present invention, in the optical directional coupler formed by laminating a plurality of optical waveguide cores, the directional coupling is achieved by bringing the cores closer to the substrate in the vertical direction. Since a container is formed, the cores can be brought closer to each other or only one of them can be brought closer. Thereby, in a plane parallel to the substrate except for the coupling portion, the cores are separated from each other by the cladding having a sufficient thickness, and thus the effect of increasing the degree of freedom of the waveguide layout is achieved. That is, in a laminated waveguide having no coupling between the upper and lower optical waveguides, a waveguide layout with a high degree of freedom can be ensured by applying the laminated interlayer optical directional coupler of the present invention, and an optical circuit with a high degree of integration can be realized. Can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a laminated interlayer optical directional coupler according to an embodiment (Example 1) of the present invention.

FIG. 2 is a cross-sectional view of each step in a manufacturing process of a two-input, two-output stacked interlayer optical directional coupler of the first embodiment.

FIG. 3 is a cross-sectional view of each step in a manufacturing process of a two-input, two-output laminated interlayer optical directional coupler of the first embodiment.

FIG. 4 is a cross-sectional view of each step in a manufacturing process of the two-input, two-output stacked interlayer optical directional coupler of the first embodiment.

FIG. 5 is a cross-sectional view of each step in the manufacturing process of the two-input, two-output stacked interlayer optical directional coupler of the first embodiment.

FIG. 6 is a view showing Steps 5 and 6 for forming an intermediate cladding layer of the two-input two-output stacked type interlayer optical directional coupler of the first embodiment;
It is sectional drawing of each process.

FIG. 7 is a graph showing the coupling ratio with respect to the coupling region length of the two-input, two-output stacked interlayer optical directional coupler of the first embodiment.

FIG. 8 is a cross-sectional view along a waveguide of a mode converter between laminated waveguides according to another embodiment 2 of the present invention.

FIG. 9 is a cross-sectional view taken along a waveguide of a laminated three-input three-output directional coupler between three-layer laminated waveguides according to another embodiment 3 of the present invention.

FIG. 10 is a graph showing the coupling ratio to the upper, middle, and lower output waveguides with respect to the coupling region length of the three-input, three-output stacked interlayer optical directional coupler of the third embodiment.

FIG. 11 is a sectional view showing a step 1 of depositing a lower cladding layer and a step 1 and a step 2 of forming a raised portion of a stacked type interlayer optical directional coupler according to a fourth embodiment of the present invention.

FIG. 12 is a cross-sectional view of Step 6 of depositing an intermediate cladding layer and Steps 6 to 7 of forming a recessed portion of the laminated interlayer optical directional coupler of Example 4;

FIG. 13 is a schematic plan view showing a configuration of a conventional laminated interlayer optical directional coupler.

FIG. 14 is a cross-sectional view showing a cross section of each part of a conventional laminated interlayer optical directional coupler.

[Explanation of symbols]

 302 Lower core 303 Upper core 304 Lower input waveguide core 305 Bend waveguide 306 Bend waveguide 307 Output waveguide 308 Upper input waveguide core 309 Bend waveguide 310 Bend waveguide 311 Output waveguide 312 Substrate 313 Lower cladding layer 314 Intermediate cladding layer 315 Upper cladding layer 316 Optical coupling part 317 Optical coupling part

Claims (9)

[Claims] 1. A lamination direction in which an n-layer optical waveguide is formed in a laminated shape by repeatedly forming a clad layer and a core on one surface of a substrate a plurality of times, and optical coupling is performed between the respective optical waveguide cores. Wherein each core is close to the substrate vertical direction only in the optical coupling region via an optical waveguide that smoothly curves in the substrate vertical direction, and is sufficiently separated in regions other than the coupling region. Stacked type interlayer optical directional coupler. 2. The method according to claim 1, wherein the coupling region includes an n-th layer core and an n-th layer core located above the n-th layer core.
The clad layer sandwiched between the single-layer cores has a smooth protrusion, and the n-th core and the (n + 1) -th
A stacked interlayer optical directional coupler, wherein the layer cores are close to each other only in the optical coupling region. 3. The method according to claim 1, wherein the coupling region includes an n-th layer core and an n-th layer core located below the n-th layer core.
The clad layer sandwiched between the single-layer cores has a smooth depression, and the n-th core and the n-1
A stacked interlayer optical directional coupler, wherein the layer cores are close to each other only in the optical coupling region. 4. The laminated interlayer optical directional coupler according to claim 2, comprising at least one input waveguide section and at least one output waveguide section. 5. The laminated interlayer optical directional coupler according to claim 1, wherein the waveguide is formed of a silica glass waveguide. 6. A lamination in which a plurality of optical waveguides are formed by repeatedly forming a clad layer and a core on one surface of a substrate to form a plurality of optical waveguides, and the respective cores are formed so as to have a coupling region where optical coupling is performed. A method of manufacturing a mold directional coupler, comprising: a step of forming an n-th cladding layer; and a step of gradually raising the n-th cladding layer toward an optical coupling region by using a mask provided so as to float on the substrate. And forming a n-th core film on the n-th cladding. 7. A laminate in which a plurality of optical waveguides are formed by repeatedly forming a clad layer and a core on one surface of a substrate to form a plurality of optical waveguides, and each core is formed so as to have a coupling region where optical coupling is performed. A method of manufacturing a mold directional coupler, comprising: forming an n-th cladding layer; and using a mask provided so as to float on the substrate, thereby gradually recessing the n-th cladding layer toward the optical coupling region. And forming a n-th core film on the n-th cladding layer. 8. A laminate in which a plurality of optical waveguides are formed by repeatedly forming a cladding layer and a core on one surface of a substrate to form a plurality of optical waveguides, and each core is formed so as to have a coupling region where optical coupling is performed. A method for manufacturing a mold directional coupler, wherein the cladding layer is formed by using any one of a method of raising a coupling region according to claim 6 and a method of forming a depression according to claim 7, or a combination thereof. A method for manufacturing a laminated interlayer optical directional coupler, comprising: 9. The method according to claim 6, wherein the n + 1-th cladding layer is flattened by using a mask placed on the substrate after forming a predetermined n-th core layer. A method for manufacturing a laminated type inter-layer optical directional coupler, comprising a step of processing or a step of flattening the clad layer by polishing.