JP3137165B2 - Manufacturing method of optical waveguide circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to optical communication, optical signal processing,
The present invention relates to a method for manufacturing a waveguide-type optical component in the field of optical measurement.

[0002]

2. Description of the Related Art Silica-based waveguide optical components have attracted attention as means for realizing practical waveguide-type optical components because of their good matching with silica-based optical fibers. In order to fabricate 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 of a width of several μm using the formed silica-based glass film using photolithography. A combination with a technology for processing into a shape is used.
How to combine the glass film forming technique and the processing technique will determine the structure and characteristics of the optical waveguide and the final optical circuit.

FIGS. 4 and 5 show the steps of manufacturing two basic types of silica-based optical waveguide circuits. FIG. 4 shows a manufacturing process called a convex process, and FIG. 5 shows a manufacturing process called a concave process. 4 and 5 show cross sections of the waveguide. In the convex process shown in FIG. 4, first, a lower clad layer 2 is formed on a substrate 1 (see FIG. 4A), and a 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 (FIG. 4).
(C)). Finally, a glass film 5 serving as an upper clad glass is formed, and a buried 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 shape (see FIG. 5B), the core film is formed. 8 (see FIG. 5C). Next, after the core film 8 up to the upper surface of the lower clad layer 7 is removed to form a core portion 9 (FIG. 5).
(See (d)), a buried optical waveguide is formed by forming a glass film 10 to be an 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 ratio is poor especially in a directional coupler having a waveguide interval of 2 to 3 μm. Further, when an optical waveguide is manufactured using a core glass having a low softening temperature, a core portion is easily deformed in a narrow waveguide having a waveguide width of 2 to 3 μm, which causes deterioration in reproducibility. Furthermore, when a few μm of glass required for an optical waveguide is removed by a method using photolithography and reactive ion etching, which are general processing techniques, the actual core waveguide width becomes larger than the core width on a mask. There is an inherent pattern thinning phenomenon of becoming smaller.

On the other hand, in the optical waveguide manufactured by the concave process, the core film needs to be flattened in a step of removing an unnecessary core film by etching (see FIG. 5D). However, when fabricating a wide waveguide, the size of the pattern is limited because the core film flows into the concave portion to cause a depression in the core film. In particular, when applying a concave process to an optical waveguide or a slab waveguide having a waveguide width of 50 μm or more, it was impossible to make the core height uniform.

Conventionally, an optical waveguide manufacturing process for realizing an optical circuit including a slab waveguide having 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 is known. It was not disclosed.

The present invention has been made in view of these problems, and an object of the present invention is to solve the deformation of the core and the limitation of the waveguide size when the core is made of a low-melting glass material, and to solve the problem. It is an object of the present invention 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, a method of manufacturing an optical waveguide circuit according to the present invention is characterized in that a core portion having a rectangular cross section is formed around 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 using the intermediate part with an intermediate clad layer A step of forming a convex waveguide including a step of embedding; 2) 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 desirably forming the core layer and the intermediate cladding layer. And 3) a step of covering the entire area where the convex waveguide forming step and the concave waveguide forming step have been performed with an upper cladding layer. And

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

[0010] The depth of the groove in the concave waveguide manufacturing step is
It may be equal to the thickness of the intermediate cladding layer.

The step of processing the core into a rectangular cross section in the step of forming the convex waveguide comprises a photolithography step and etching, and the intermediate cladding layer including the core in the step of forming the concave waveguide is formed to a desired thickness. The step of removing to the extent possible may be etching.

Further, the present invention provides a method for manufacturing an optical waveguide circuit comprising a slab waveguide and a waveguide other than the slab waveguide, wherein the above-mentioned convex waveguide manufacturing step and concave waveguide manufacturing step are used, and The present invention is characterized in that the above-mentioned convex waveguide manufacturing step is used for manufacturing a waveguide.

Further, the present invention provides a method for manufacturing an optical waveguide circuit comprising a channel waveguide and a waveguide other than the channel waveguide, wherein the above-mentioned convex waveguide manufacturing step and concave waveguide manufacturing step are used, and The method is characterized in that the concave waveguide manufacturing step is used for manufacturing a channel waveguide.

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

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

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

[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 fixed at a constant height. It will be manufactured by the convex process which can be performed. Therefore, an optical circuit including a slab waveguide can be manufactured with high accuracy. In addition, by applying a glass material having a low softening temperature and a glass material having a high softening temperature to the core, a highly accurate and low-loss optical waveguide circuit can be realized on the same substrate. As a result, a functional optical waveguide circuit using a different material for the core can be realized, and the degree of freedom in circuit design is increased.

The present invention is particularly effective when 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 type optical waveguide are used as an optical waveguide circuit including glass materials having different softening temperatures. This is integration within the substrate.

[0019]

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

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

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

In order to operate the 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 incident. Input side slab waveguide 21
In (2), the signal light spread by the diffraction effect propagates to a plurality of channel waveguides constituting the arrayed waveguide diffraction grating 22, reaches the output side waveguide, and is further condensed on the output waveguide 24. In this case, the length of each channel waveguide constituting the arrayed waveguide diffraction grating 22 is changed to change the optical path length difference Δ
By providing L, the phase of the signal light after propagation through the channel waveguide is shifted, and the wavefront of the focused light in the output side slab waveguide 23 is inclined according to the amount of the phase shift. The light condensing position is determined by the inclination angle. The amount of phase shift depends on the signal light frequency, and the focus position of the frequency-multiplexed signal light is determined by the optical frequency. The signal light is extracted by the optical frequency by disposing the output waveguide 24 at the focus position. I can do this.

By using the method of 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 formed. The waveguide and the output-side slab waveguide can be manufactured by a convex process capable of uniformly manufacturing the height of the core portion. 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. In addition, since the thinned pattern can be avoided at the connection 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 this embodiment, the concave process is applied to fabricate the channel waveguide, and the convex process is applied to fabricate the slab waveguide. However, the concave process and the convex process are selectively used to form a Y-branch circuit, a directional coupler, and the like. Can be applied to various kinds 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 multiplex number of 13 were obtained. The crosstalk between adjacent channels was 35 dB, which proved that 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. In an optical multiplexer / demultiplexer having the same structure manufactured by the conventional convex process, the insertion loss is 3 dB, and it has been clarified that the loss can be reduced by eliminating the pattern thinness.

As described above, the optical multiplexer / demultiplexer manufactured according to the present invention suppresses the deformation of the waveguide core by applying the concave process to the manufacturing of the channel waveguide forming the arrayed waveguide diffraction grating, and suppresses the optical path length difference ΔL. It was clarified that it was possible to manufacture a multiplexer / demultiplexer with high insertion loss, high crosstalk, and low insertion loss by suppressing pattern thinning.

Embodiment 2 Next, in the present invention, an example in which a convex process is applied to a passive optical waveguide and a concave process is applied to a rare earth-doped waveguide will be described. An optical amplifier having a multiplexer / demultiplexer for pump light and signal light was manufactured by using Er as a rare earth element and adding Er ions only to the optical amplifier. FIG. 3 shows a schematic diagram of the circuit configuration. On a silicon substrate 25, an Er-doped silica-based optical waveguide 26 having a length of 20 cm, an optical waveguide 27 for introducing excitation light, an optical waveguide 28 for deriving excitation light, an optical waveguide 29 for introducing signal light, an optical waveguide 30 for deriving signal light, Directional couplers I, II, III and IV were constructed. To manufacture this optical amplifier, Er is added to the position of the Er-doped silica-based optical waveguide 26, which is an optical amplifier.
Using a mask on which an additional optical waveguide film is formed, FIG.
, An Er-doped optical waveguide is formed by a 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, 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, a pump light having a wavelength of 0.98 μm and a signal light having a wavelength of 1.55 μm are converted into a pump light introducing optical waveguide 27 and a signal light introducing light using a single mode optical fiber. The light enters the optical waveguide 29. The Mach-Zehnder interferometer composed of the directional couplers I and II makes the excitation light have a 99% light intensity with respect to the light intensity propagating through the excitation light introduction optical waveguide 27 in the Er-doped optical waveguide 26.
To excite Er ions, and the signal light propagates to the Er-doped silica-based optical waveguide 26 with a 98% light intensity with respect to the signal light introducing optical waveguide 27. The excited Er ions amplify the signal light propagating through the Er-doped quartz optical waveguide 26. Further, the pump light is transmitted by a Mach-Zehnder interferometer composed of directional couplers III and IV according to the same operating principle as that of the Mach-Zehnder interferometer used for the pump light signal demultiplexing unit.
The light is demultiplexed at a coupling rate of 9%, and the light is guided to the pumping light guiding optical waveguide 28,
The signal light amplified by the Er-doped waveguide 26 propagates to the signal light deriving 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 optical circuit manufacturing method of the present embodiment, in an optical amplifier in which a multiplexer / demultiplexer of pumping light and signal light is integrated, a pumping light introducing section and a signal light introducing section in which Er ions act as an absorber. The pumping light signal demultiplexer and the signal light deriving section can be formed by an Er-free optical waveguide having a low propagation loss, and only the optical amplifying section can be manufactured by the Er-doped optical waveguide. In this embodiment, a Mach-Zehnder interferometer using two directional couplers capable of accurately adjusting two lights having a large wavelength interval is used as a multiplexer / demultiplexer of the pump light and the signal light. However, it is also preferable to use a multiplexer / demultiplexer composed of one directional coupler. In this embodiment, the rare-earth-doped glass is used as the optical waveguide manufactured by the concave process. However, it goes without saying that the present invention can be applied to a glass material having a low softening temperature. For example, it is also effective to use glass or semiconductor-added glass to which rare earth ions such as Nd and Pr are added.

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-doped optical waveguide was 0.3 dB, and a good connection was obtained. Further, when an optical amplification experiment in the 1.5 μm band was performed using this optical amplifier, the intensity of the signal light was 30 mW while the intensity of the pump light emitted from the single mode optical fiber 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 integrated with a multiplexer / demultiplexer of pumping light and signal light can be manufactured. Was.

In the above Examples 1 and 2, 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 of synthesizing the glass film, for example, C
The VD method or the sputtering method can be used for part or all.

[0032]

As described above, according to the method of 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 can be deformed regardless of the waveguide shape. For example, it is possible to manufacture an optical waveguide with small fluctuation. Therefore, the present invention is extremely effective in producing a directional coupler, an array waveguide, or a Y-branch waveguide stably and with good reproducibility. In addition, since an optical waveguide doped with rare earth ions at an arbitrary position on the same substrate and an optical waveguide not doped with rare earth ions can be manufactured separately, a rare earth added region in a waveguide circuit can be freely set, and circuit design can be improved. It is possible to increase the degree of freedom.
As a result, a rare-earth-doped core is used for the waveguide portion that simultaneously guides the pump light and the signal light and performs optical amplification, and a portion where it is desirable to guide the pump light or the signal light alone is rare-earth-free. An optical waveguide can be used, and the loss of signal light and pump light due to absorption of rare earth ions can be minimized, which has the advantage of improving device characteristics.

[Brief description of the drawings]

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

FIG. 2 is a plan view showing a circuit configuration of an arrayed waveguide grating 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 Er ions of Example 2 of the present invention are added only to an optical amplification section and a multiplexer / demultiplexer of pump light is integrated.

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

FIG. 5 is a cross-sectional view showing a manufacturing process of an optical waveguide circuit by a conventional concave 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 part 5, 10, 18 Upper cladding layer 15 Intermediate cladding Layer 20 Input waveguide 21 Input side slab waveguide 22 Array waveguide diffraction grating 23 Output side slab waveguide 24 Output waveguide 26 Er-doped silica-based optical waveguide 27 Excitation light introduction optical waveguide 28 Excitation light derivation optical waveguide 29 Signal Optical waveguide for introducing light 30 Optical waveguide for deriving signal light I, II, III, IV, V, VI Directional coupler

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Manabu Oguma Nippon Telegraph and Telephone Corporation, 1-6-1, Uchisaiwai-cho, Chiyoda-ku, Tokyo (56) References JP-A-57-604 (JP, A) JP-A Sho 54-34847 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02B 6/12-6/14

Claims (11)

(57) [Claims] 1. A method of manufacturing an optical waveguide circuit in which a core section having a rectangular cross section is surrounded by a cladding section having a lower refractive index than the core section. 1) Forming a core layer on a lower cladding layer Forming a core section having a rectangular cross section; embedding the core section with an intermediate cladding layer; and 2) forming a rectangular section in the intermediate cladding layer. Forming a groove, forming a core layer in the groove, removing the core layer and the intermediate cladding layer to a desired thickness, and forming a concave waveguide; 1. A method of manufacturing an optical waveguide circuit, comprising: a step of covering an entire region in which a step of forming a concave waveguide and a step of forming a concave waveguide are covered with an upper cladding layer. 2. The method of manufacturing an optical waveguide circuit according to claim 1, wherein the groove is formed at a position other than an upper portion of a core portion formed in the step of forming the convex waveguide. Wave circuit manufacturing method. 3. The method of manufacturing an optical waveguide circuit according to claim 2, wherein the groove is formed continuously in a horizontal plane with a core portion formed in the step of forming the convex waveguide. Wave circuit manufacturing method. 4. The method of manufacturing an optical waveguide circuit according to claim 1, wherein a depth of the groove in the concave waveguide manufacturing step is equal to a thickness of the intermediate cladding layer. Wave circuit manufacturing method. 5. The method for manufacturing an optical waveguide circuit according to claim 1, wherein 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; The method of manufacturing an optical waveguide circuit, wherein the step of removing the intermediate cladding layer including the core portion to a desired thickness in the concave waveguide manufacturing step comprises etching. 6. A method of manufacturing an optical waveguide circuit comprising a slab waveguide and a waveguide other than the slab waveguide, wherein the method according to claim 1 is used, and said method is used for manufacturing a slab waveguide. A method for manufacturing an optical waveguide circuit, comprising using a convex waveguide manufacturing step. 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 claim 1 is used, and A method for manufacturing an optical waveguide circuit, wherein the concave waveguide manufacturing step is used for manufacturing a waveguide. 8. The method for 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 method for manufacturing 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 an active waveguide. The manufacturing method of the optical waveguide circuit characterized by the above-mentioned. 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.