JPS6325644B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical circuit with a fiber guide that facilitates direct connection between an optical fiber and an optical waveguide necessary for optical communication, and a method for manufacturing the same. .

[Prior art]

When introducing waveguide optical components such as optical branching circuits and optical multiplexers/demultiplexers into optical communication systems, there is a method for connecting these optical components and optical fibers that is efficient, reliable, and quick. A method is required. Conventionally, an end face connection method has been mainly used in which the end face of the optical fiber and the end face of the optical waveguide are simply brought into direct contact and connected. However, this method requires (i) cutting and polishing of the end face of the waveguide prior to connection, (ii) precise alignment between the optical fiber and the optical waveguide, and (iii) the connection part. There are disadvantages such as lack of mechanical reliability.

As a method to solve these conventional problems, there is a connection method in which a guide for optical fiber alignment is formed on the silica glass optical waveguide at the same time as the optical circuit pattern is formed, and the connection is made using this guide. No. 125699]. This method solves the above-mentioned conventional problems and enables highly efficient connection between an optical fiber and an optical waveguide without the need for cutting or polishing the end face of the optical waveguide or aligning the optical fiber and the waveguide. be.

[Problem that the invention seeks to solve]

In the above method of forming the guide, the outer diameter
When connecting an optical fiber with a core diameter of 125μm and a core diameter of 50μm to an optical waveguide, the depth of the silica glass optical waveguide is
It is necessary to etch about 90μm. For this processing, amorphous Si (a-Si) is used as a mask, C ₂ F ₆ ,
Reactive ion etching is used using a mixed gas of C ₂ and H ₄ as an etchant, but when this method is used to perform deep etching up to a depth of 90 μm, the width of the formed waveguide is different from the patterning at the photomask stage. When comparing the widths, there was a problem that they decreased significantly. Therefore, in order to suppress the amount of pattern width reduction, conventionally the etching depth of the optical circuit has been reduced to approximately
The connection was made using an optical fiber with an outer diameter of about 70 μm and an etched outer diameter of about 70 μm at the fiber end.

[Means for solving problems]

The fiber-guided optical circuit of the present invention has a configuration in which a silica glass optical waveguide is formed on a Si substrate, and has a structure in which an optical circuit pattern is formed near the end of the optical waveguide. It has a guide for positioning the end of the optical fiber formed at the same time, and at least the Si substrate near the guide is suitable so that when the optical fiber is inserted into the guide, the optical fiber core and the optical waveguide core are aligned. It is characterized by being etched to a deep depth.

In addition, the present invention, which is a method of manufacturing the above fiber-guided optical circuit, involves forming a silica glass optical waveguide on a Si substrate, and using photolithography technology to reach the silica glass optical waveguide onto the Si substrate. A desired optical waveguide pattern and a guide for positioning the optical fiber are simultaneously formed by etching to a depth of 100 nm, and then etching is performed at least so that when the optical fiber is inserted into the guide, the optical fiber core portion and the optical waveguide core portion coincide with each other. This method is characterized in that the Si substrate near the guide is etched to an appropriate depth using the guide as a mask.

〔Example〕

FIG. 1 is a perspective view of a fiber-guided optical circuit according to an embodiment of the present invention. 1 is a Si substrate, 1a
is a Si (100) plane, 1b is a Si (111) plane formed by etching, 2 is a fiber guide, 3 is an optical waveguide, 3a is a clad layer, 3b is a core layer, and 3c is a buffer layer. be. Both the optical waveguide 3 and the fiber guide 2 are made of silica glass.

FIG. 2 shows the positional relationship among the guide 2 in FIG. 1, the core portion 3b of the optical waveguide 3, and the core portion 7b of the optical fiber 7 to be connected. The distance between the guides 2, 2 corresponds to the outer diameter of the optical fiber, and the depth of the guide 2 is adjusted by etching the Si substrate.
and the core portion 3b of the optical waveguide 3 are made to coincide with each other. Therefore, by simply inserting the optical fiber 7 into the guides 2, 2, the optical fiber 7
The optical fiber 7 is positioned in the horizontal and lateral directions by the guides 2, 2, and the height direction is determined by the grooves etched into the Si substrate 1. High-precision alignment with the circuit is completed.

FIG. 3 shows a method of manufacturing the fiber-guided optical circuit as described above. Figure 3a
is a step of forming a quartz-based optical waveguide film 31 on the Si substrate 1. In this example, a (100) plane substrate is used as the Si substrate 1, and SiCl ₄ , TiCl ₄ , GeCl ₄ ,
A quartz-based optical waveguide film 31 is formed on this Si substrate 1 using a flame hydrolysis reaction using BCl ₃ , PCl _{3 ,} etc. as a raw material gas. The thickness of the quartz-based optical waveguide film 31 is
It has a three-layer structure with a thickness of 53 μm, and 31a is a clad layer (3 μm thick), 31b is a core layer (45 μm thick),
31c is a buffer layer (5 μm thick). FIG. 3b shows a step of etching the quartz-based optical waveguide film 31 to pattern a desired optical waveguide and fiber guide. For this purpose, first, an amorphous Si film 4 is formed on the quartz-based optical waveguide film 31, and an AZ-based photoresist 5 is applied thereon. Next, using the photomask 6, the AZ-based photoresist 5 is patterned by photolithography. In the photomask 6, 26 is a fiber guide pattern, and the guide interval ₁₁ is set to 120 μm. 36 is an optical waveguide pattern, and the optical waveguide width l ₂ is set to 45 μm. In this way, the fiber guide pattern 26 and the optical waveguide pattern 3
By using the photomask 6 having This can be done with a pattern drawing accuracy of approximately 0.1 to 0.2 μm.

In addition, when patterning the AZ resist,
The fiber guide pattern 26 is made to be approximately parallel to the [110] direction of the Si substrate 1. AZ
Following the patterning of the resist, the amorphous Si film 4 is patterned by reactive ion etching using the patterned AZ resist as a mask and CBrF ₃ as an etchant. Finally, by reactive ion etching using this amorphous Si as a mask and a mixed gas of C ₂ , F ₆ , C ₂ , and H ₄ as an etchant, a silica-based optical waveguide is formed on the Si substrate 1 as shown in Figure 3c. A fiber guide 2 and an optical waveguide 3 consisting of a film are patterned. The etching depth of the quartz-based optical waveguide film is required to be 53 μm. As a result of these etching steps, the pattern width of the formed pattern is slightly reduced, so that the guide interval l ₃ becomes approximately 125 μm and the optical waveguide width l ₄ becomes approximately 40 μm. Next, a step is performed to adjust the guide depth by etching the Si substrate. In this process, when the Si substrate 1 is immersed in an alkaline etchant such as ethylenediamine pyrocatechol, the guide 2 made of a silica-based optical waveguide film and the optical waveguide 3 serve as a mask, and the Si substrate 1 is anisotropically etched. . That is, when the above etchant is used, Si
The relationship between crystal plane and etching rate is (100):
(110):(111)=50:30:3μm/h, so
Once a (111) surface appears, that surface will no longer be etched. As a result, an optical circuit having the shape shown in FIG. 1 is obtained. In this example, the Si substrate is etched to a depth of 35 μm using the method described above. As a result, as shown in FIG. 2, alignment with the silica optical waveguide can be achieved simply by inserting an optical fiber with an outer diameter of 125 μm and a core diameter of 50 μm into the guide.

In this way, by introducing the step of etching the Si substrate, the etching depth of the silica-based optical waveguide film is sufficient to be 53 μm. On the other hand, when forming a guide for an optical fiber with an outer diameter of 125 μm only by etching the silica-based optical waveguide film without performing an etching process on the Si substrate, the etching depth of the silica-based optical waveguide film is approximately 90μm is required. By the way, Figure 3c
As mentioned in the description of the process, the etching process causes a slight reduction in the pattern width, and the pattern width finally formed is narrower than the originally designed photomask pattern width. This occurs through the mechanism shown in FIG. FIG. 4a shows a case where the etching depth of the silica-based optical waveguide film 31 is relatively shallow. In reactive ion etching,
The etching speed of sharp portions, such as the edge portion 4a of the amorphous Si mask 4, tends to be faster than other portions. For this reason, as shown in 4a in the figure, this portion is shaved off and the verticality of the side surface of the mask is degraded. However, if the etching is shallow, this effect will not appear on the silica-based optical waveguide film 31 under the mask, so the pattern width d formed by etching will not change from the width at the photomask stage. . However, as shown in FIG. 4B, when the etching becomes deep to a certain extent, the verticality of the side surface 4a of the amorphous Si mask 4 deteriorates, and the width of the pattern formed by etching decreases by 2Δd. FIG. 4c shows the case where the etching becomes even deeper. Since the deterioration of the verticality of the side surface 4a of the amorphous Si mask 4 is more remarkable than that shown in FIGS. 4a and 4b, the amount of decrease 2Δd in the pattern width as the etching progresses becomes even larger, and the rate of decrease also becomes faster. . FIG. 5 shows an investigation of the relationship between the pattern width reduction amount and the etching depth. From this graph, when the etching depth is about 50μm,
The pattern width reduction amount is about 5 μm, but when the etching depth becomes 90 μm, the pattern width reduction amount is about 5 μm.
It can be seen that it reaches about 20 μm.

In this way, according to the example, the outer diameter can be accurately determined.
A guide for 125μm optical fiber can be formed. length
When measuring splice loss in an optical circuit with guides installed at both ends of a 15 mm straight waveguide, a 0.85 μm
When LEDs were used, the combined connection loss at the input and output sections was 1.9 dB. This value is comparable to the connection loss in the case of normal end-face connection, which was performed for comparison, and it is clear that high-efficiency connection can be achieved with this method as well. In this example, the dimensions of the core portion of the optical waveguide formed as described above are 40 μm wide x 45 μm high, but this is because a graded index fiber (50GI fiber) with a core diameter of 50 μm is used. Therefore, 50GI fiber = optical circuit (step index) = dimension that minimizes connection loss when connected to 50GI fiber.

〔Effect of the invention〕

As explained above, according to the present invention, the optical fiber is inserted into the guide for aligning the axis of the optical fiber and the optical circuit, which is formed at the same time as the formation of the optical circuit, and the optical fiber and the optical circuit are coupled. Therefore, high-efficiency connections between optical fibers and optical circuits can be made without any adjustment. In addition, in the present invention, the Si substrate near the guide is etched to an appropriate depth, making it easy to connect with a normal optical fiber and positioning the optical fiber and optical circuit. Alignment can be performed with high precision. Further, according to the method of the present invention, in the optical circuit and guide forming step,
The etching depth of the silica-based optical waveguide film is kept to the necessary minimum, and the insufficient depth is adjusted by etching the Si substrate. Therefore, the amount of decrease in pattern width, which is a problem when performing deep etching using reactive ions and etching, can be greatly reduced, so that processing accuracy can be improved. In addition, according to the method of the present invention, the optical waveguide pattern and the guide are formed at the same time, and the Si substrate near the guide is etched using the guide as a mask, so the position of the guide is aligned with the position of the optical waveguide. This has the effect that it can be matched with extremely high precision.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a guided optical circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the dimensions of the guide, optical waveguide, and optical fiber in the optical circuit of FIG. 1, and FIG. Figures a to c are explanatory diagrams showing a method for manufacturing a guided optical circuit, Figures 4 a to c are schematic diagrams showing how the optical circuit width is reduced, and Figure 5 is a
7 is a graph showing the relationship between etching depth and pattern width reduction amount. 1...Si substrate, 1a...Si (100) plane, 1b...
Si (111) surface, 2... optical fiber, guide, 3...
... Optical waveguide, 3a ... Cladding layer, 3b ... Core layer, 3c ... Buffer layer, 7 ... Optical fiber, 7
b... Core portion of optical fiber, 31... Silica-based optical waveguide film, 31a... Clad layer, 31b... Core layer, 31c... Buffer layer, 4... Amorphous
Si mask, 4a...Amorphous Si mask side,
5...AZ resist, 6...Photomask, 2
6... Guide pattern, 36... Optical circuit pattern.

Claims (1)

[Claims] 1. In an optical circuit in which a silica glass optical waveguide is formed on a Si substrate, a guide for positioning the end of the optical fiber formed at the same time as the patterning of the optical circuit is provided near the end of the optical waveguide. and at least the Si substrate near the guide is etched to an appropriate depth so that the optical fiber core and the optical waveguide core coincide when the optical fiber is inserted into the guide.・Optical circuit with guide. 2 Step of forming a silica glass optical waveguide on a Si substrate, and etching the silica glass optical waveguide to a depth that reaches the Si substrate using photolithography technology to form a desired optical waveguide pattern and position the optical fiber. a step of forming a guide at the same time;
Subsequently, the step of etching at least the Si substrate near the guide to an appropriate depth using the guide as a mask so that when the optical fiber is inserted into the guide, the optical fiber core portion and the optical waveguide core portion coincide with each other. A method for manufacturing a guided optical circuit.