JPH0843653A - Method for manufacturing optical waveguide circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] Silica-based optical fiber with high reproducibility regardless of the shape of the optical waveguide, which solves the deformation of the core and the limitation of the waveguide size when the core is made of low melting point glass material. A method for manufacturing a waveguide is provided. A method of manufacturing an optical waveguide circuit in which a core portion having a rectangular cross section is surrounded by a clad portion having a refractive index lower than that of the core portion. This method includes 1) a step of forming a core layer on the lower clad layer, a step of processing the core layer into a rectangular core part, and a step of forming a convex waveguide including a step of embedding the core part with an intermediate clad layer, 2) Fabrication of a concave waveguide including a step of forming a groove having a rectangular cross section in the intermediate cladding layer, a step of forming a core layer in the groove, and a step of removing the core layer and the intermediate cladding layer to a desired thickness. And 3) a step of forming a convex waveguide and a step of forming a concave waveguide, and covering the entire region with an upper cladding layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to optical communication, optical signal processing,
The present invention relates to a method of manufacturing a waveguide type optical component in the field of optical measurement.

[0002]

2. Description of the Related Art Since a silica-based waveguide type optical component has good compatibility with a silica-based optical fiber, it has been attracting attention as a means for realizing a practical waveguide type optical component. In order to manufacture this type of silica-based waveguide, a technique of forming a silica-based glass film with a thickness of several μm to several tens of μm and a pattern with a width of several μm using photolithography are applied to the formed silica-based glass film. It is used in combination with the technology of processing into shapes.
How the glass film forming technology and the processing technology are combined determines the structure and characteristics of the optical waveguide and the final optical circuit.

FIG. 4 and FIG. 5 show steps of manufacturing two kinds of basic silica-based optical waveguide circuits. FIG. 4 shows a manufacturing procedure called a convex process, and FIG. 5 shows a manufacturing process called a concave process. 4 and 5 show waveguide cross sections. In the convex process of FIG. 4, the lower clad layer 2 is first formed on the substrate 1 (see FIG. 4A), and the core film 3 is formed thereon (see FIG. 4B). 2 is processed into a convex shape so as to become a waveguide pattern (core portion) 4 (see FIG. 4).
(C)). Finally, the glass film 5 to be the upper clad glass is formed, and the embedded optical waveguide is manufactured. On the other hand, in the concave process of FIG. 5, the lower clad layer 7 is first formed on the substrate 6 (see FIG. 5A), and after the lower clad 7 is processed into a concave form (see FIG. 5B), the core film is formed. 8 is formed (see FIG. 5C). Next, after the core film 8 up to the upper surface of the lower clad layer 7 is removed to form the core portion 9 (see FIG.
(See (d)), the embedded optical waveguide is manufactured by forming the glass film 10 to be the upper clad layer.

[0004]

However, since the core portion of the optical waveguide manufactured by the convex process is convex when the upper clad is formed, the core portion is essentially deformed as compared with the concave process. There was a problem that it was easy. For this reason, the reproducibility of the coupling rate is particularly poor in a directional coupler having a waveguide spacing of 2 to 3 μm. Further, when an optical waveguide is manufactured using a core glass having a low softening temperature, the core portion is easily deformed in a narrow waveguide having a waveguide width of 2 to 3 μm, which causes deterioration of reproducibility. Furthermore, when the glass of several μm required for the optical waveguide is removed by a method using photolithography and reactive ion etching, which are general processing techniques, the actual waveguide width of the core is smaller than the core width on the mask. There is essentially a thinning pattern, a phenomenon of thinning.

On the other hand, in the optical waveguide manufactured by the concave process, the core film needs to be flattened in the step of removing the unnecessary core film by etching (see FIG. 5D). However, when a wide waveguide is manufactured, the core film flows into the recesses to form dents in the core film, which limits the size of the pattern. In particular, when the concave process is applied to an optical waveguide having a waveguide width of 50 μm or more or a slab waveguide, it was impossible to make the cores uniform in height.

Conventionally, an optical waveguide manufacturing process for realizing an optical circuit including a slab waveguide with low loss by using an optical waveguide manufactured by a convex process and a concave process by fusing a convex process and a concave process has been performed. It was not revealed.

The present invention has been made in view of these problems, and an object thereof is to solve the deformation of the core and the limitation of the waveguide size when the core portion is made of a low melting point glass material, and An object of the present invention is to provide a method for manufacturing a silica-based optical waveguide with high reproducibility regardless of the shape of the waveguide.

[0008]

In order to achieve the above object, in the method of manufacturing an optical waveguide circuit according to the present invention, a core portion having a rectangular cross section is provided with a clad portion having a lower refractive index than the core portion. In the method for manufacturing an enclosed optical waveguide circuit, 1) a step of forming a core layer on a lower clad layer, a step of processing the core layer into a core part having a rectangular cross section, and a step of forming the core part with an intermediate clad layer. A step of forming a convex waveguide including a step of burying; 2) a step of forming a groove having a rectangular cross section in the intermediate clad layer; a step of forming a core layer in the groove; and a step of forming the core layer and the intermediate clad layer as desired. And a step of covering the entire region where the convex waveguide forming step and the concave waveguide forming step are performed with an upper clad layer. And

Here, the groove may be formed at a place other than the upper part of the core portion formed by the convex waveguide forming step, and the core portion formed by the convex waveguide forming step and the core portion formed by the convex waveguide forming step. The groove may be formed continuously in a horizontal plane.

The depth of the groove in the concave waveguide manufacturing process is
It may be equal to the thickness of the intermediate cladding layer.

The step of processing the core portion into a rectangular cross section in the step of forming the convex waveguide comprises a photolithography step and etching, and the intermediate clad layer including the core portion in the step of forming the concave waveguide has a desired thickness. The step of removing until further may be etching.

Furthermore, the present invention is a method of manufacturing an optical waveguide circuit comprising a slab waveguide and a waveguide other than the slab waveguide, using the above-mentioned convex waveguide manufacturing step and concave waveguide manufacturing step, and It is characterized in that the above-mentioned convex waveguide manufacturing process is used for manufacturing the waveguide.

Furthermore, the present invention is a method for manufacturing an optical waveguide circuit comprising a channel waveguide and a waveguide other than the channel waveguide, using the above-mentioned convex waveguide manufacturing step and concave waveguide manufacturing step, and It is characterized in that the above-mentioned concave waveguide manufacturing process is used for manufacturing a channel waveguide.

Here, the optical waveguide circuit to be produced may be an array waveguide diffraction grating.

According to the present invention, in the method of manufacturing an optical waveguide circuit including an active waveguide, the above-mentioned convex waveguide manufacturing step and concave waveguide manufacturing step are used, and the concave waveguide manufacturing step is used for active waveguide manufacturing. Is used.

Here, the active waveguide may contain a rare earth element, and a low melting point glass may be used for the core portion.

[0017]

According to the present invention, an optical circuit portion utilizing interference such as a directional coupler is formed by a concave process without pattern thinning or core deformation, and a slab waveguide having a large core shape is formed with a constant height of the core portion. It will be manufactured by a convex process capable of Therefore, an optical circuit including the slab waveguide can be manufactured with high accuracy. Further, by applying a glass material having a low softening temperature and a glass material having a high softening temperature to the core formation, a highly accurate and low loss optical waveguide circuit can be realized on the same substrate. As a result, it is possible to realize a functional optical waveguide circuit using a different material for the core, and at the same time, increase the degree of freedom in circuit design.

The present invention is particularly effective in that an array type diffraction grating is used as an optical waveguide circuit including a slab waveguide, and a rare earth-doped optical waveguide and a passive optical waveguide are used as an optical waveguide circuit including glass materials having different softening temperatures. It is the integration into the substrate.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 FIG. 1 shows a process of manufacturing a convex-concave fusion type optical waveguide by the flame deposition method of this example. FIG. 1A is a schematic view of the waveguide viewed from above, and FIGS. 1B to 1I and 1D ′ to 1I ′.
Is a schematic cross-sectional view. 1 (d) to 1 (i) show a convex process portion, and FIGS. 1 (d ') to 1 (i') show a concave process portion. A lower clad glass film 12 having a low refractive index and a film thickness of 30 μm is formed on a silicon substrate 11 by a flame deposition method.
Are formed (see FIG. 1B). Next, a core glass film 13 having a film thickness of 6 μm is formed on the lower clad layer 12 by a flame deposition method, and processed into a convex core portion 14 having a rectangular cross section by a photolithography process and etching (FIG. 1 ( c), (d), (d ')). Next, film thickness 15μ
The first optical waveguide is manufactured by embedding the core with the intermediate cladding layer 15 having a low refractive index of m (FIG. 1).
(See (e) and (e ')). Next, a groove 15A having a rectangular cross section is formed in the intermediate cladding layer 15 by a photolithography process and etching so that the depth of the groove becomes 15 μm (see FIGS. 1F and 1F ′). Next, the second core glass film 16 having a film thickness of 15 μm is formed by using the flame deposition method (see FIGS. 1G and 1G ′). Next, the cores 14 and 1 of the first optical waveguide and the second optical waveguide are etched by etching.
The second core glass 16 and the intermediate cladding glass 15 are removed by etching so that the height of 7 becomes 6 μm (see FIGS. 1 (h) and 1 (h ′)). Finally, the upper clad glass 18 having a low refractive index is formed to fabricate an embedded optical waveguide (see FIGS. 1 (i) and 1 (i ')).

Using the optical waveguide circuit manufacturing method of this embodiment,
An arrayed-waveguide grating optical multiplexer / demultiplexer with selectable optical frequency was fabricated. FIG. 2 shows a schematic circuit configuration. Reference numeral 19 is a silicon substrate, 20 is an input waveguide, 21 is an input side slab waveguide, 22 is an array waveguide diffraction grating consisting of channel waveguides, 23 is an output side slab waveguide, and 24 is an output waveguide. Based on this example, the input waveguide 20, the array waveguide diffraction grating 22, and the output waveguide 24 were manufactured by the concave process, and the input side slab waveguide 21 and the output side slab waveguide 23 were manufactured by the convex process. That is, the core portion formed by the convex process and the groove formed by the concave process are continuous in the horizontal plane. In designing the optical multiplexer / demultiplexer, the optical path length difference ΔL between the channel waveguides forming the array waveguide is set to 122 so that a wavelength multiplexing interval of 1 nm can be obtained in the wavelength 1.55 μm band used in optical communication.
μm.

In order to operate this optical multiplexer / demultiplexer, first, a single-mode optical fiber on the transmission side is connected to the input waveguide 20 and frequency-multiplexed signal light is made incident. Input side slab waveguide 21
The signal light spread by the diffraction effect propagates to the plurality of channel waveguides forming the arrayed waveguide diffraction grating 22, reaches the output side waveguide, and is further focused on the output waveguide 24. In this case, the lengths of the individual channel waveguides forming the arrayed waveguide diffraction grating 22 are changed to change the optical path length difference Δ.
By providing L, the phase of the signal light after propagating in the channel waveguide is deviated, and the wavefront of the focused light in the output side slab waveguide 23 is inclined according to the amount of the phase deviation. The position where light is collected is determined by this tilt angle. The amount of phase shift depends on the frequency of the signal light, and the condensing position of the frequency-multiplexed signal light is determined for each optical frequency. By arranging the output waveguide 24 at the condensing position, the signal light is extracted for each optical frequency. I can do it.

By using the method for manufacturing an optical waveguide circuit of this embodiment, an arrayed waveguide diffraction grating for setting the optical path length difference ΔL is manufactured by a concave process without core deformation, and an input side slab conductor having a large core area is manufactured. The waveguide and the slab waveguide on the output side can be manufactured by a convex process that allows the height of the core to be uniform. Therefore, as a result of improving the accuracy of the optical path length difference ΔL, crosstalk between adjacent optical waveguides, which is an important characteristic of the present multiplexer / demultiplexer, can be improved. Moreover, since the pattern thinning can be avoided at the connection portion between the output side slab waveguide and the output waveguide, the signal light can be coupled to the output waveguide with low loss. Further, in the present embodiment, the concave process is applied to the fabrication of the channel waveguide, and the convex process is applied to the fabrication of the slab waveguide. However, the concave process and the convex process are used separately, and a Y branch circuit, a directional coupler, etc. It is also possible to apply to a wide variety of circuit elements.

The transmission spectrum of this optical multiplexer / demultiplexer at a wavelength of 1.55 μm was measured.
Good light transmission characteristics with a multiplexing number of 13 were obtained. Further, it was found that the crosstalk in the adjacent channels was 35 dB, and the crosstalk value 25 dB of the multiplexer / demultiplexer manufactured only by the conventional convex process was improved by 10 dB.
Furthermore, when the insertion loss of this optical multiplexer / demultiplexer was measured,
It was 1 dB. The insertion loss of the optical multiplexer / demultiplexer having the same structure manufactured by the conventional convex process is 3 dB, and it has been clarified that the loss can be reduced by eliminating the pattern thinning.

As described above, in the optical multiplexer / demultiplexer manufactured according to the present invention, by applying the concave process to the fabrication of the channel waveguide which constitutes the arrayed waveguide diffraction grating, the deformation of the waveguide core is suppressed and the optical path length difference ΔL. It has been clarified that a multiplexer / demultiplexer can be manufactured with high precision, high crosstalk can be realized, and pattern insertion can be suppressed by suppressing pattern thinning.

Embodiment 2 Next, in the present invention, an example in which the convex process is applied to the passive optical waveguide and the concave process is applied to the rare earth-doped waveguide is shown. An optical amplifier having a multiplexer / demultiplexer for pumping light and signal light was manufactured by using Er as a rare earth element and adding Er ions only to the optical amplification section. FIG. 3 shows a schematic diagram of the circuit configuration. A 20 cm long Er-doped silica optical waveguide 26, a pumping light introducing optical waveguide 27, a pumping light deriving optical waveguide 28, a signal light introducing optical waveguide 29, a signal light deriving optical waveguide 30, on a silicon substrate 25. Directional couplers I, II, III and IV were constructed. In order to fabricate this optical amplifier, Er is placed at the position of the Er-doped silica-based optical waveguide section 26 which is the optical amplification section.
Using a mask on which the doped optical waveguide film is formed, FIG.
Accordingly, the Er-doped optical waveguide is formed by the concave process. The pumping light introducing optical waveguide 27, the pumping light deriving optical waveguide 28, the signal light introducing optical waveguide 29, the signal light deriving optical waveguide 30, and the directional couplers I, II, III, and IV have a height of 6 μm.
A passive optical waveguide having a width of 6 μm and containing no rare earth element was formed by a convex process.

In order to operate this optical amplifier, first, the pumping light having a wavelength of 0.98 μm and the signal light having a wavelength of 1.55 μm are introduced using a single mode optical fiber into the optical waveguide 27 for introducing the pumping light and the signal light. It is incident on the optical waveguide 29. The excitation light has a Mach-Zehnder interferometer composed of directional couplers I and II, and has a light intensity of 99% with respect to the intensity of light propagating through the excitation light introducing optical waveguide 27.
And excites Er ions, and the signal light propagates to the Er-doped silica optical waveguide 26 with a light intensity of 98% with respect to the signal light introducing optical waveguide 27. The excited Er ions amplify the signal light propagating through the Er-doped silica optical waveguide 26. Further, the pumping light is generated by the Mach-Zehnder interferometer composed of the directional couplers III and IV by the same operation principle as that of the Mach-Zehnder interferometer used for the pumping light signal light demultiplexing unit.
In the optical waveguide 28 for deriving the excitation light, which is demultiplexed at the coupling rate of 9%,
The signal light amplified by the Er-doped waveguide 26 propagates to the signal light guide optical waveguide 30 at a coupling rate of 98%, and only the signal light is extracted by the single mode optical fiber.

By using the method for manufacturing an optical circuit of the present embodiment, in an optical amplifier in which a multiplexer / demultiplexer for pumping light and signal light is integrated, a pumping light introducing portion and a signal light introducing portion where Er ions act as an absorber. It is possible to form the pumping light signal light demultiplexer and the signal light derivation part by the Er-free optical waveguide having a low propagation loss, and only the optical amplification part can be manufactured by the Er-doped optical waveguide. Further, in the present embodiment, a Mach-Zehnder interferometer using two directional couplers capable of accurately adjusting two lights having large wavelength intervals is used as a multiplexer / demultiplexer for pumping light and signal light. However, it is also suitable to use a multiplexer / demultiplexer composed of one directional coupler. Further, although the rare earth-doped glass is used as the optical waveguide manufactured by the concave process in this embodiment, it goes without saying that it can be applied to a glass material having a low softening temperature. For example, it is also effective to use it for glass to which rare earth ions such as Nd and Pr are added or for semiconductor-added glass.

When the optical loss of this optical amplifier at a wavelength of 1.3 μm was estimated, the connection loss between the Er-doped optical waveguide and the Er-free optical waveguide was 0.3 dB, and good connection was obtained. Furthermore, an optical amplification experiment in the 1.5 μm band was performed using this optical amplifier. As a result, the signal light intensity was 30 mW when the single-mode optical fiber emission pumping light intensity was 30 mW.
It was found that the signal was amplified by dB.

From the above, it is clear that in the optical amplifier manufactured according to the present invention, Er ions can be added only to the optical amplification section, and an optical amplifier in which a multiplexer / demultiplexer for pumping light and signal light is integrated can be manufactured. It was

In Examples 1 and 2 above, the flame deposition method was used for producing the glass film, because this method is suitable for depositing a relatively thick and high quality glass film. In some cases, another method for synthesizing glass membranes, such as C
The VD method or the sputtering method can be used partially or entirely.

[0032]

As described above, according to the method for manufacturing an optical circuit of the present invention, an optical waveguide can be manufactured by combining a convex process and a concave process, and the core deformation is achieved regardless of the waveguide shape. It is possible to manufacture an optical waveguide with less fluctuation. Therefore, the present invention is extremely effective in manufacturing a directional coupler, an arrayed waveguide, or a Y-branched waveguide in a stable and reproducible manner. In addition, since it is possible to divide the optical waveguide with rare earth ions added and the optical waveguide with no rare earth ions into arbitrary positions on the same substrate, it is possible to freely set the rare earth addition region in the waveguide circuit and It is possible to increase the degree of freedom.
As a result of the above, a rare earth-doped core is used in the waveguide section that simultaneously guides the excitation light and the signal light to perform optical amplification, and it is desirable to add the rare earth-free core to the portion where it is desirable to guide the excitation light or the signal light alone. Since an optical waveguide can be used, loss of signal light and excitation light due to absorption of rare earth ions can be minimized, and device characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of an optical waveguide circuit of the present invention.

FIG. 2 is a plan view showing a circuit configuration of an arrayed waveguide diffraction grating type optical multiplexer / demultiplexer according to the first embodiment of the present invention.

FIG. 3 is a plan view showing a circuit configuration of an optical amplifier in which an Er ion of Example 2 of the present invention is added only to an optical amplification section and a multiplexer / demultiplexer for pumping light is integrated.

FIG. 4 is a cross-sectional view showing a process of manufacturing an optical waveguide circuit by a conventional convex process.

FIG. 5 is a cross-sectional view showing a process of manufacturing an optical waveguide circuit by a conventional recess process.

[Explanation of symbols]

 1, 6, 11, 19, 25 Silicon substrate 2, 7, 12 Lower cladding layer 3, 8, 13, 16 Core layer 4, 9, 14, 17 Optical waveguide core portion 5, 10, 18 Upper cladding layer 15 Intermediate cladding Layer 20 Input Waveguide 21 Input Slab Waveguide 22 Array Waveguide Diffraction Grating 23 Output Side Slab Waveguide 24 Output Waveguide 26 Er-doped Silica Optical Waveguide 27 Pumping Light Introducing Optical Waveguide 28 Pumping Light Deriving Optical Waveguide 29 Signal Light guiding optical waveguide 30 Signal light guiding optical waveguide I, II, III, IV, V, VI Directional coupler

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Manabu Oguma 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (11)

[Claims] 1. A method of manufacturing an optical waveguide circuit in which a core section having a rectangular cross section is surrounded by a clad section having a refractive index lower than that of the core section, and 1) a core layer is formed on a lower clad layer. And a step of processing the core layer into a core portion having a rectangular cross section, a step of forming a convex waveguide including a step of embedding the core portion with an intermediate cladding layer, and 2) a rectangular cross section of the intermediate cladding layer. The step of forming a groove, the step of forming a core layer in the groove, and the step of removing the core layer and the intermediate clad layer to a desired thickness, A method of manufacturing an optical waveguide circuit, which comprises a step of covering the entire region subjected to the step of forming the waveguide and the step of forming the concave waveguide with an upper cladding layer. 2. The method for manufacturing an optical waveguide circuit according to claim 1, wherein the groove is formed at a position other than an upper portion of the core portion formed by the convex waveguide forming step. Wave circuit manufacturing method. 3. The method for manufacturing an optical waveguide circuit according to claim 2, wherein the groove is formed continuously with the core portion formed by the convex waveguide forming step in a horizontal plane. Wave circuit manufacturing method. 4. The method for manufacturing an optical waveguide circuit according to claim 1, wherein the depth of the groove in the step of forming the concave waveguide is equal to the thickness of the intermediate cladding layer. Wave circuit manufacturing method. 5. The method of manufacturing an optical waveguide circuit according to claim 1, wherein the step of processing the core portion into a rectangular cross section in the convex waveguide manufacturing step comprises a photolithography step and etching. Further, the method of manufacturing an optical waveguide circuit, wherein the step of removing the intermediate cladding layer including the core portion in the step of forming the concave waveguide to a desired thickness is etching. 6. A method for manufacturing an optical waveguide circuit comprising a slab waveguide and a waveguide other than the slab waveguide, wherein the manufacturing method according to claim 1 is used, and the slab waveguide is manufactured by the method described above. A method of manufacturing an optical waveguide circuit, characterized by using a convex waveguide manufacturing process. 7. A method for manufacturing an optical waveguide circuit comprising a channel waveguide and a waveguide other than the channel waveguide, wherein the method for manufacturing an optical waveguide circuit according to any one of claims 1 to 5 is used. A method for manufacturing an optical waveguide circuit, characterized in that the step of forming a concave waveguide is used for forming a waveguide. 8. The method of manufacturing an optical waveguide circuit according to claim 6, wherein the optical waveguide circuit to be manufactured is an array waveguide diffraction grating. 9. A manufacturing method of an optical waveguide circuit including an active waveguide, wherein the manufacturing method according to claim 1 is used, and the concave waveguide manufacturing step is used for manufacturing the active waveguide. A method for manufacturing an optical waveguide circuit, comprising: 10. The method of manufacturing an optical waveguide according to claim 9, wherein the active waveguide contains a rare earth element. 11. The method of manufacturing an optical waveguide circuit according to claim 1, wherein a low melting point glass is used for the core portion.