JP3602514B2 - Fabrication method of quartz optical waveguide circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a silica optical waveguide circuits, and more particularly, relates to a method for manufacturing a silica optical waveguide circuits which can reduce the coupling loss to other optical waveguide or optical fiber.
[0002]
[Prior art]
With the rapid progress of optical communication, demands for large-scale, high-integration, low-cost, and mass-productivity improvement of a silica-based optical waveguide, like the semiconductor optical waveguide, are increasing. For large scale and high integration, light confinement to the core must be strengthened. As a result, the distance between adjacent optical waveguides can be reduced, the bending radius of the optical waveguide can be reduced, and more optical waveguides can be arranged in a limited area.
[0003]
In a silica-based waveguide, when light confinement is enhanced, coupling loss with an optical fiber or other optical components increases. Several methods for reducing this coupling loss are known. For example, a method of enlarging the core size in the input / output unit so as to match the spot size of the fiber is practical because the manufacturing tolerance and the tolerance when connecting the fiber can be increased. As an example, JP-A-2001-56415 describes a spot size conversion structure using a vertical and horizontal tapered waveguide.
[0004]
FIG. 7 shows a conventional spot size conversion structure. In the spot size conversion structure, a lower cladding layer 52 is formed on a substrate 51, and a core 53a is formed on the lower cladding layer 52. The core 53a is further covered with the upper cladding layer 54. Such a spot size conversion structure has a simple structure and a large effect of reducing coupling loss. For example, in a core specification in which a coupling loss of about 2 dB occurs due to a difference between a fiber and a spot size, the coupling loss can be reduced to 0.2 dB or less by performing spot expansion using vertical and horizontal tapers.
[0005]
[Problems to be solved by the invention]
However, since the optical waveguide having such a spot size conversion structure has a thicker core at the input / output portion as compared with a normal optical waveguide, the time required for processing the core by reactive ion etching is reduced. There was a problem that would be long. That is, mass productivity is lower than that of a normal process.
[0006]
The present invention has been made in view of such problems, and an object, while fully functional the spot size conversion function, fabrication of silica-based waveguide circuits which can shorten the manufacturing time It is to provide a method.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method according to claim 1, wherein the lower clad layer is formed on a substrate and the core layer is formed on the lower clad layer. A core for guiding the reflected light, an upper cladding layer covering the lower cladding layer and the core, and a core of the input / output unit formed thicker than the thickness of the inner core. In a method of manufacturing a silica-based optical waveguide circuit having a core of an output part and a tapered part connecting the internal core, the core layer having the same thickness as the core of the input / output part on the lower clad layer. And a layer forming a change in the thickness of the core layer such that a part of the core layer is etched to have different thicknesses between the core of the input / output unit and the inner core. Forming a thickness change step, etching the core layer, Forming a core of the force portion and the inner core, and forming a core layer of the input / output portion having the same composition as the core of the input / output portion on a side surface of the core of the input / output portion. In the core forming step, the core layer of the input / output unit whose layer thickness T in contact with the side surface of the core of the input / output unit is smaller than the thickness H of the core of the input / output unit is formed. Characterized by being formed on the side surface .
[0017]
The invention according to claim 2 , wherein a core for guiding light formed from a lower cladding layer mounted on a substrate, a core layer mounted on the lower cladding layer, and the lower cladding layer. A core of the input / output unit formed to be thicker than a thickness of the internal core, and a taper connecting the core of the input / output unit and the internal core. In the method for manufacturing a silica-based optical waveguide circuit having a portion, a deposition step of depositing the core layer having the same thickness as the thickness of the internal core on the lower clad layer, further depositing the core layer, A layer thickness change forming step of forming the input / output unit core and the internal core to have different thicknesses; and etching the core layer to form the input / output unit core and the internal core. And has the same composition as the core of the input / output unit Forming a core layer of the output unit on the side surface of the core of the input / output unit, wherein the core forming step includes: A core layer having a thickness of less than H is formed on the side surface of the core of the input / output unit.
[0018]
According to a third aspect of the present invention, in the layer thickness change forming step according to the first or second aspect , a change in the layer thickness of the core layer is formed using a mask disposed above the core layer. It is characterized by.
[0019]
The invention described in claim 4 is characterized in that the mask according to claim 3 is separated from the core layer by 100 μm or more.
[0020]
The invention according to claim 5 is characterized in that the mask according to claim 3 or 4 has a marker forming portion for alignment in the core forming step.
[0021]
The invention according to claim 6 is characterized in that the marker forming section according to claim 5 is formed so as to be in contact with the core layer.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, a case will be described in which a quartz-based glass film serving as a core layer, a lower clad layer, and an upper clad layer is formed using a flame deposition method. However, the present invention is limited to a method for forming a glass film. Instead, some or all of the glass layers can be formed by a glass film formation method such as a sputtering method or a CVD (Chemical Vapor Deposition) method. In the present embodiment, description will be made on the assumption that an optical communication wavelength of a 1.55 μm band and a single mode optical fiber are used.
[0023]
FIG. 1 is a structural diagram showing a spot size conversion structure according to an embodiment of the present invention. In the spot size conversion structure, a lower cladding layer 12 is formed on a substrate 11, and a waveguide core 13 a (internal core) for guiding light formed from a core layer 13 deposited on the lower cladding layer 12. The input / output unit core 13b and the core layer 13 left with a certain layer thickness in portions other than the input / output unit core 13b are further covered with the upper cladding layer 14.
[0024]
Here, the input / output unit core 13b has a tapered structure on the upper surface and both side surfaces, performs spot enlargement, and connects the waveguide core 13a and the input / output unit core 13b. In FIG. 1, the cross-sectional shape of the input / output unit core 13b is shown as a rectangle, but may be a trapezoid or a shape in which the upper edge is chamfered with a straight line or an arc. Although the core layer 13 left with a certain layer thickness is also shown as a rectangle, the core layer 13 does not need to have a certain layer thickness and may have a trapezoidal shape. The length of the tapered portion in the tapered structure is preferably 100 μm or more in the direction in which light is guided in order to enlarge the spot while suppressing loss. In addition, in order to stabilize the enlarged spot size, it is desirable that the thickness and width of the input / output unit core 13b be constant over a length of 100 μm or more in the direction in which light is guided from the input / output end face.
[0025]
FIG. 2 is a diagram illustrating a method of manufacturing the spot size conversion structure according to the first embodiment of the present invention. First, on a substrate 11 made of silicon or quartz, by flame hydrolysis _deposition, depositing a lower cladding layer 12 composed mainly of S i _{O 2} (see FIG. 2 (a).), _{Then, G} e O after ₂ was deposited core layer 13 consisting primarily of S _i O ₂ was added with dopant (see FIG. 2 (b).), vitrification is performed in an electric furnace. The layer thickness of the lower cladding layer 12 is 20 μm, and the layer thickness of the core layer 13 is 11 μm.
[0026]
A shadow mask 15 is set in a state of being floated at a distance of 1 mm from the substrate 11 on which the lower clad layer 12 and the core layer 13 are formed (see FIG. 2C). In this state, a predetermined amount of the core layer other than the input / output portion is removed by using the reactive ion etching method (see FIG. 2D). In the first embodiment, 6 μm is removed and the layer thickness of the waveguide core 13a is set to 5 μm. At this time, at the boundary of the shadow mask 15, the plasma goes under the shadow mask 15, and the etching slightly progresses also in this portion to form a gently tapered structure in the vertical direction. In this way, an optical waveguide circuit in which the input / output unit core and the waveguide core have different thicknesses and the input / output unit core and the waveguide core are connected in a smooth taper shape is formed.
[0027]
Then, a core for guiding light is patterned using photolithography and reactive ion etching (see FIG. 2E). At this time, the etching is terminated without removing the entire layer thickness of 11 μm of the core layer 13 of the input / output section, leaving a constant layer thickness. Therefore, the cross-sectional shape of the core of the input / output unit, that is, the cross-section of X shown in FIG. 2E has a convex cross-sectional shape. The two constant thicknesses T of 2.5 μm and 5 μm in the first embodiment were able to reduce the etching time by 23% and 45%, respectively.
[0028]
Lastly, the upper cladding layer 14 was deposited and vitrified to produce the spot size conversion structure shown in FIG. 1 (see FIG. 2 (f)). The specifications of the optical waveguide used in the first embodiment are that the relative refractive index difference between the core and the clad is 1.5%, the width of the waveguide core 13a is 5 μm, and the thickness D of the waveguide core 13a is D. Is 5 μm, the width of the input / output unit core 13b is 11 μm, and the thickness H of the input / output unit core 13b is 11 μm.
[0029]
FIG. 3 is a diagram illustrating coupling loss of the spot size conversion structure according to one embodiment of the present invention. FIG. 3 is a diagram illustrating a coupling loss between a silica-based optical waveguide circuit and a single-mode optical fiber manufactured by the method illustrated in FIG. 2. When the constant layer thickness T of the core layer in the input / output unit is 0 μm, the coupling loss is 0.21 dB / point. When the constant layer thickness T is 2.5 μm, the coupling loss is 0.22 dB / point, and when the constant layer thickness T is 5 μm, the coupling loss is 0.25 dB / point. That is, in the input / output unit, even if the core layer other than the input / output unit core is left at 5 μm, the coupling loss increases only by 0.04 dB.
[0030]
This result is in good agreement with the result of numerical calculation performed using the finite difference method. FIG. 3 also shows a waveguide in which the relative refractive index difference is 3% or 5%, the width of the input / output unit core is 11 μm, and the thickness H of the input / output unit core is 11 μm. As in the case where the relative refractive index difference is 1.5%, it can be seen that the coupling loss increases when the constant layer thickness T exceeds 5 μm. That is, regardless of the relative refractive index difference, if the constant layer thickness T in the core layer other than the input / output unit core is equal to or less than half the thickness H of the input / output unit core, the coupling loss does not increase excessively. .
[0031]
In the present embodiment, the layer thickness of the portion other than the input / output unit core is constant, but the cross-sectional shape does not need to be rectangular as described above. The layer thickness of portions other than the input / output unit core may be such that the layer thickness T in contact with the side surface of the input / output unit core is smaller than the thickness H of the core of the input / output unit. In order to prevent light propagating through the input / output unit core from seeping out to portions other than the input / output unit core and increasing the coupling loss, the layer thickness T in contact with the side surface of the input / output unit core must be It is sufficient that the thickness be equal to or less than half of the thickness H.
[0032]
FIG. 4 is a diagram illustrating a method for manufacturing a spot size conversion structure according to the second embodiment of the present invention. First, on a substrate 11 made of silicon or quartz, by flame hydrolysis _deposition, depositing a lower cladding layer 12 composed mainly of S i _{O 2} (see FIG. 4 (a).), _{Then, G} e O after ₂ was deposited core layer 13 consisting primarily of S _i O ₂ was added with dopant (see FIG. 4 (b).), vitrification is performed in an electric furnace. Here, the layer thickness of the core layer 13 is the same as the thickness D of the waveguide core.
[0033]
The shadow mask 17 is set at a position other than the input / output unit on the substrate 11 while being floated at a distance of 1 mm (see FIG. 4C). In this state, a core layer 13 having a layer thickness of HD is additionally deposited (see FIG. 4D). Hereinafter, the formation of the core is the same as the method shown in FIG. (See FIGS. 4E and 4F).
[0034]
The method of depositing the core layer 13 having the HD layer thickness by installing the shadow mask 17 is difficult to form a gradual layer thickness change portion in the vertical direction by the flame deposition method. A vapor phase film forming method such as a sputtering method or a plasma CVD method is suitable.
[0035]
The above-described shadow mask will be described in detail. In the manufacturing methods according to the first and second embodiments, the taper manufactured by using the shadow mask and the pattern of the waveguide core manufactured by photolithography and reactive ion etching must be accurately aligned. .
[0036]
FIGS. 5A and 5B show a shadow mask used in the manufacturing method according to the first embodiment of the present invention. The shadow mask 15 is for providing a taper to the input / output portion 16b of the circuit pattern 16a formed by the photomask 16 shown in FIG. The shadow mask 15 has an opening 15a provided in the center where the circuit pattern 16a is formed, a mask 15b corresponding to the input / output unit 16b, and a marker forming unit 15c for alignment. The thickness of the shadow mask 15 where the marker forming portion 15c is formed is thicker than the thickness of the central portion.
[0037]
Such a shadow mask 15 is arranged such that the marker forming portion 15c is in contact with the core layer 13, as shown in FIG. By performing shadow etching in this state, a gentle taper structure is formed in the input / output section, and a steep concave structure 13c is formed in the marker forming section 15c (see FIG. 5E). The steep concave structure 13c formed by the marker forming section 15c can facilitate alignment with the marker section 16c of the photomask 16 used for photolithography.
[0038]
FIGS. 6A and 6B show a shadow mask used in the manufacturing method according to the second embodiment of the present invention. The shadow mask 17 is for providing a taper in the input / output section 16b of the circuit pattern 16a formed by the photomask 16 shown in FIG. The shadow mask 17 has a central mask 17a where a circuit pattern 16a is formed, an opening 17b provided in a portion corresponding to the input / output unit 16b, and a marker forming unit 17c for alignment. I have. The thickness of the shadow mask 17 at the portion where the marker forming portion 17c is formed is larger than the thickness at the central portion.
[0039]
Such a shadow mask 17 is arranged so that the marker forming portion 17c is in contact with the core layer 13 as shown in FIG. In this state, by further depositing a core layer, a gentle taper structure is formed in the input / output portion, and a steep convex structure 13d is formed in the marker forming portion 17c (see FIG. 6E). The steep convex structure 13d by the marker forming portion 17c can facilitate alignment with the marker portion 16c of the photomask 16 used for photolithography.
[0040]
In addition, although the markers for positioning the shadow mask and the photomask have the same shape, they may have different shapes as long as they do not hinder the positioning. Further, in the present embodiment, the distance between the central portions of the shadow masks 15 and 17 and the core layer 13 is set to 1 mm. Just fine. Further, the shadow masks 15 and 17 are arranged so that the marker forming portions 15c and 17c are in contact with the core layer 13, but may be arranged apart if sufficient irregularities can be formed for alignment.
[0041]
When the above-described first and second embodiments are used for an optical communication wavelength in a 1.3 μm band or used for connection with a dispersion-shifted fiber, it is possible to apply them by changing the specifications of the optical waveguide. Needless to say.
[0042]
In the present embodiment, the thickness H of the core of the input / output unit and the thickness D of the inner core are defined by a layer thickness T in contact with the side surface of the core of the input / output unit.
0 <T <HD (when D> H / 2)
0 <T ≦ H / 2 (when D ≦ H / 2)
May be arbitrarily set in consideration of the load on the process and the specifications of the optical waveguide to be used.
[0043]
It is apparent that the same effect can be obtained even if the substrate is quartz or a structure in which a core is formed directly on the quartz substrate. The present invention can be applied to all silica-based optical waveguide circuits requiring a spot size conversion structure.
[0044]
Further, the spot size conversion structure according to the present invention can be applied to a glass of a silica-based optical waveguide circuit if the thickness of the core of the input / output unit is formed thicker than the thickness of the inner core and connected by a gentle taper structure. It can be applied irrespective of the composition and the production method.
[0045]
【The invention's effect】
As described above, according to the present invention, a core layer having the same composition as the core of the input / output unit and having a thickness less than the thickness of the core of the input / output unit is formed on the side surface of the core of the input / output unit. Accordingly, it is possible to shorten the manufacturing time of the quartz-based waveguide circuit while sufficiently functioning the spot size conversion function.
[Brief description of the drawings]
FIG. 1 is a structural diagram showing a spot size conversion structure according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a method for manufacturing a spot size conversion structure according to the first embodiment of the present invention.
FIG. 3 is a diagram showing coupling loss of a spot size conversion structure according to an embodiment of the present invention.
FIG. 4 is a diagram illustrating a method for manufacturing a spot size conversion structure according to a second embodiment of the present invention.
FIG. 5 is a view showing a shadow mask used in the manufacturing method according to the first embodiment of the present invention.
FIG. 6 is a view showing a shadow mask used in a manufacturing method according to a second embodiment of the present invention.
FIG. 7 is a structural diagram showing a conventional spot size conversion structure.
[Explanation of symbols]
11, 51 Substrate 12, 52 Lower cladding layer 13 Core layer 13a Waveguide core 13b Input / output section core 14, 54 Upper cladding layer 15, 17 Shadow mask 16 Photo mask 53a Core

Claims (6)

A lower clad layer mounted on a substrate, a core for guiding light formed from a core layer mounted on the lower clad layer, and the lower clad layer and the core are covered. A quartz optical waveguide circuit including an upper cladding layer, a core of an input / output unit formed thicker than a thickness of an internal core, and a tapered portion connecting the core of the input / output unit and the internal core; In the method for producing
A deposition step of depositing the core layer having the same thickness as the core of the input / output unit on the lower clad layer;
A layer thickness change forming step of forming a change in the layer thickness of the core layer, such that a part of the core layer is etched so that the core of the input / output unit and the inner core have different thicknesses;
The core layer is etched to form the input / output unit core and the internal core, and the input / output unit core layer having the same composition as the input / output unit core is formed as the input / output unit core. Core forming step for forming on the side surface,
In the core forming step, the core layer of the input / output unit whose layer thickness T in contact with the side surface of the core of the input / output unit is less than the thickness H of the core of the input / output unit is formed by removing A method for manufacturing a quartz-based optical waveguide circuit, comprising: A lower clad layer mounted on a substrate, a core for guiding light formed from a core layer mounted on the lower clad layer, and the lower clad layer and the core are covered. A quartz optical waveguide circuit including an upper cladding layer, a core of an input / output unit formed thicker than a thickness of an internal core, and a tapered portion connecting the core of the input / output unit and the internal core; In the method for producing
A deposition step of depositing the core layer having the same thickness as the inner core on the lower cladding layer;
A layer thickness change forming step of further depositing the core layer and forming the core of the input / output unit and the inner core to have different thicknesses;
The core layer is etched to form the input / output unit core and the internal core, and the input / output unit core layer having the same composition as the input / output unit core is formed as the input / output unit core. Core forming step for forming on the side surface,
In the core forming step, a core layer having a layer thickness T in contact with a side surface of the core of the input / output unit is smaller than a thickness H of the core of the input / output unit, is formed on a side surface of the core of the input / output unit. A method for producing a silica-based optical waveguide circuit, comprising: The layer thickness change formation step, using a mask arranged above the core layer, the silica-based optical waveguide circuit according to claim 1 or 2, characterized in that to form a change in the thickness of the core layer Method of manufacturing. 4. The method according to claim 3 , wherein the mask is at least 100 μm away from the core layer. 5. The mask, a method for manufacturing a silica optical waveguide circuit according to claim 3 or 4, wherein a marker formation portion for alignment in the core formation step. 6. The method according to claim 5 , wherein the marker forming portion is formed so as to be in contact with the core layer.

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