JPH0664217B2 - Fiber-guided optical waveguide - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical waveguide with a fiber guide, which facilitates direct connection between an optical fiber and an optical waveguide necessary for optical communication.

[Summary of Disclosure] In the optical waveguide with a fiber guide according to the present invention, the distance between the fiber guides is wide on the side close to the end of the optical waveguide and narrow on the side distant from the fiber guide. A technique for easily achieving alignment is disclosed.

It should be noted that this outline is provided only for quick access to the technical contents of the present invention, and has no influence on the technical scope and the interpretation of rights of the present invention.

[Prior Art] Optical waveguide circuits are expected to be applied to optical communication circuits such as optical multiplexers / demultiplexers and optical switches, and optical signal processing circuits. For this purpose, these optical circuits and optical fibers can be easily combined. A reliable and reliable connection method is required. Conventionally, as shown in FIG. 2, a method has been used in which the end face of the optical fiber and the end face of the optical waveguide are directly butted and connected. In the figure, 1 is a fiber, 2 is a substrate, and 3 is an optical waveguide. However, this method requires (i) cutting and polishing of the waveguide end face prior to connection, (ii) precise alignment between the optical fiber and the optical waveguide, and (iii) connection There were drawbacks such as lack of mechanical reliability. Especially, when connecting the single mode optical waveguide and the single mode optical fiber, the alignment accuracy is 1
It is necessary to perform extremely high-precision alignment within μm and angle alignment precision within 1 °. Therefore, it takes a very long time to align the optical fiber and the optical waveguide in the conventional direct butting method. Further, even if fine alignment can be achieved, there is a great possibility that an axis shift will occur when fixing the fiber and the optical waveguide in the next stage. That is, an adhesive is generally used to fix the fiber and the optical waveguide, but in the conventional method, an axis shift is likely to occur when the adhesive hardens. As described above, it is difficult to manufacture a practical optical waveguide circuit by the conventional end face connection method.

As a method of solving these problems of the conventional direct butting method, there is a connecting method in which two parallel guides for aligning the optical fibers are formed on the optical waveguide substrate and the guides are used to make the connection. [Japanese Patent Application No. 58-125699 and Y. Yamada e
t al, Electron. Letl. 20 (1984) 313].

FIG. 3 is an explanatory view of this method, in which 1 is a fiber and 2 is a fiber.
Is a substrate, 3 is an optical waveguide, and 4 is a fiber guide.
FIG. 4 shows the optical fiber 1, the optical waveguide 3 when the fiber is inserted,
FIG. 6 is a cross-sectional view showing a positional relationship of the fiber guide 4. 3a
Is an optical waveguide core layer, 3b is a buffer layer, 1a is an optical fiber
The core portion 1b is a clad layer, and is manufactured so that the core portion 1a of the optical fiber and the core layer 3a of the optical waveguide are aligned when the optical fiber is inserted. Therefore, according to this method, the problems of the conventional direct butting method can be solved, and the high efficiency of the optical fiber and the optical waveguide can be achieved without the steps of cutting and polishing the end face of the optical waveguide and aligning the optical fiber and the optical waveguide. In addition, reliable connection is possible. Now, assuming that the buffer layer thickness d ₁ and the core layer thickness d _{2 of} the optical waveguide are present, the interval w of this guide needs to be set to the following dimension.

_{w = 2 (d 1 + d} 2/2) (1) Thus, if the film thickness of the fabricated optical waveguide _{(d 1} or _{d 2)} are different, it is necessary to change the guide interval accordingly. Normally, the guide distance w cannot be adjusted because it depends on the size of the photomask pattern, and in this case, the film thickness of the optical waveguide must be kept constant. Therefore, when manufacturing an optical waveguide with a fiber guide, the dimensional accuracy of the optical waveguide and the guide must be increased. Particularly, in the case of a single-mode optical waveguide, since the allowable amount of dimensional error is as small as 1 μm or less, it is necessary to perform processing with extremely high precision, and there is a problem that the yield of optical circuit production is low.

[Problems to be Solved by the Invention] An object of the present invention is to solve the problem that the allowable dimensional error of an optical waveguide with a fiber guide is extremely small, and tolerate a dimensional error even when a single-mode optical circuit is manufactured. An object of the present invention is to provide an optical waveguide with a fiber guide which is large and has a high yield.

[Means for Solving the Problems] Therefore, according to the present invention, in the optical waveguide with a fiber guide, the spacing between the guides for positioning the fiber is tapered so that the guide spacing on the side closer to the end of the optical waveguide is on the far side. It is wider than the guide interval.

[Operation] In the present invention, the side where the center line of the fiber guide coincides with the center of the optical waveguide, and the optical fiber guide spacing is not smaller than the optical fiber diameter on the side close to the optical waveguide end, Since the diameter of the optical fiber is smaller than that of the optical fiber, the center of the optical fiber can be easily aligned with the center of the optical waveguide by guiding the optical fiber with this guide.

[Examples] Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view for explaining an optical waveguide with a fiber guide, which is an embodiment of the present invention.
Is a substrate, 3 is an optical waveguide, and 4 is a fiber guide.
The spacing between the fiber guides 4 is wide on the side close to the optical waveguide 3 and narrow on the opposite side. FIG. 5 shows an example of a photomask pattern used for manufacturing this taper structure. The alternate long and short dash line 00 'in the figure indicates the center line between the fiber and the guide. Fiber guides spacing the wider portion W ₁ [mu] m, a narrow portion and W ₂ [mu] m. Further, the length of the portion having the interval W ₁ μm is l ₁ μm, the length of the portion having the interval W ₂ μm is ₁₂ μm, and the length of the tapered portion is lt μm. Further, the width of the optical waveguide 3 is Wo μm. Next, the function of this tapered fiber guide will be described with reference to FIG. In FIG. 6, 1a is a fiber core portion, 1b is a fiber clad layer, 3a is a waveguide core layer, and 3b is a waveguide buffer layer. The symbol D ₁ in the figure is the outer diameter of the optical fiber 1, and D ₂ is the core diameter of the optical fiber. d ₁ is the buffer layer thickness of the optical waveguide 3, and d ₂ is the core layer thickness of the optical waveguide 3. Fiber outer diameter _{D 1} is in accordance with the thickness of the core layer 3a and the buffer layer 3b of the waveguide 3, it is set in advance _{D 1 = 2 (d 1 +} d 2/2) (2). The value of D _{1 is in} the range of W ₂ <D ₁ ≦ W ₁ . When this fiber is inserted into the guide, the positioning between the fiber and the waveguide can be performed as follows.
FIG. 6 (a) shows the case where the fiber is in the narrow region with the guide interval W ₂ μm. Since the outer diameter D ₁ of the fiber is larger than the guide interval W ₂ , the fiber is on the guide as shown in FIG. However, the position of the center of the fiber core is on the centerline 00 'in FIG. In FIG. 6B, the guide interval is D ₁ in the tapered region of the guide.
Shows the state when it matches. At this time, the fiber fits into the guide. The center of the core is also on the center line 00 'in FIG. FIG. 6 (c) shows the guide distance W ₁
Indicates the area. In this region, the fiber 3 contacts the substrate. Since D ₁ is set as in equation (2), the fiber core and the waveguide core are aligned in the height direction. On the other hand, when the guide width W ₁ is wider than the fiber outer diameter D ₁ , there is no lateral positioning action in this region. However, as shown in FIGS. 6 (a) and 6 (b), the center of the fiber core is located on the center line 00 'in these regions. Even in the state, the fiber center lies on the center line 00 '. Therefore, the fiber core 1a and the waveguide core 3 can be aligned as shown in FIG. Since the fiber is positioned by the functions as described above, the mask pattern of FIG. 5 can be applied within the range where the fiber outer diameter D ₁ satisfies W ₂ <D ₁ ≦ W ₁ by using the guide of this embodiment. . Therefore, from the equation (2), the setting tolerance of the waveguide film thicknesses d ₁ and d ₂ is widened in this range.

To form such an optical waveguide with a fiber guide using a silica optical waveguide, for example, the following may be performed.
First, a quartz optical waveguide film having a three-layer structure of a buffer layer, a core layer, and a clad layer is formed on a Si substrate. For this purpose, for example, SiO 2 is formed by flame hydrolysis reaction of SiCl ₄ , GeCl ₄ , and TiCl _4.
Direct flame deposition method by depositing glass particles such as ₂ , ₂ , GeO ₂ , and TiO ₂ on a substrate and then making it transparent to form an optical waveguide film [M.Kawa
chi et al, Jpn. J. Appl. Phys. 22 (1983), 1932]. Next, the unnecessary portion of the silica-based optical waveguide film is removed by reactive ion etching using a photomask pattern as shown in FIG. 5 to form an optical circuit pattern as shown in FIG. If the Si substrate is exposed, etching will not proceed any further. Next, the outer diameter of the fiber to be connected is determined according to the equation (2) according to the film thickness of the formed silica optical waveguide, and the fiber outer diameter is set to this value. For this purpose, the end of a normal fiber may be immersed in hydrofluoric acid for etching. At this time, the outer diameter of the fiber can be set to a desired value with an accuracy within 1 μm by using a wire diameter monitor or the like. Next, the result of a connection experiment using the silica-based optical waveguide with a fiber guide manufactured by such a method will be described. The size of the photomask used is w ₀ = 6μ in FIG.
m, l ₁ = 1000 μm, lt = 3500 μm, l ₂ = 500 μm, w ₁ = 7
The setting was 0 μm, w ₂ = 50 μm. Three types of optical waveguides were manufactured. The film thickness was i) buffer layer d ₁ = 25 μm ii) d ₁ = 27 μm iii) d ₁ = 30 μm, and the core layer thickness d ₂ was d ₂ = 6 μm for all three types. The optical fiber used corresponding to this has a core diameter r ₂ = 6 μm, and its outer diameter is i) D ₁ = 56 μm, ii) D ₁ = 60 μm, iii) D ₁ = 6 according to the equation (2).
It was 6 μm. As a result of using these, connection between the fiber waveguides was possible with a connection loss of about 0.5 dB for all three types.

As described above, according to the present invention, there is an advantage that the tolerance of the set value of the film thickness of the waveguide can be widened for one photomask. In the case of the above embodiment, it is understood that the allowable setting range of the film thickness of the waveguide can be at least 10 μm when connecting the single mode optical fiber and the optical waveguide. Further, according to the present invention, there is an effect that the tolerance is increased even for a pattern thin (a finished pattern width is narrower than a design value) that may occur in a process of manufacturing an optical waveguide by reactive ion etching. is there. This is because even if the fiber guide spacing becomes wider than the photomask pattern as a result of the pattern thinning, the situation shown in FIG. 6 does not change, and the fiber core portion is always on the center line.

On the other hand, in the case of the conventional fiber guide, especially when it is applied to a single mode system, the allowable range of the waveguide thickness and the pattern thin becomes extremely narrow. For example, when the fiber guide spacing is set to 60 μm with a photomask pattern and a single mode optical waveguide is manufactured, if the optical waveguide core layer is 6 μm, the buffer layer must be set within the range of 27 ± 1 μm. . In addition, it is necessary to suppress the pattern thinness to 1 μm or less, and extremely high processing accuracy is required.

FIG. 7 shows another embodiment of the present invention, which is applied to a buried waveguide. 4a is the tapered fiber of the present invention
A guide, in which a part of the cladding layer of the optical waveguide is used as a fiber guide. This type of fiber
To form a buried waveguide with a guide, for example,
It can be done as shown in the figure. This figure is an example of a quartz optical waveguide formed on a Si substrate. First, the pattern of FIG. 8A is formed by the flame direct deposition method and the subsequent reactive ion etching. At this time, the buffer layer thickness d
₁ and the core layer thickness d ₂ . Next, as shown in FIG. 8 (b), the flame direct deposition method is performed again to embed the core layer 3a with the cladding layer 3c. Then, reactive ion etching is performed using a photomask as shown in FIG. 8C to form the optical waveguide with a fiber guide shown in FIG. By inserting the optical fiber was set outside diameter _{2 (d 1 + d 2/} 2) in this guide, automatically between the optical fiber waveguide by exactly the same principle as FIG. 6 of Example Alignment can be achieved. Further, similar to the above-described embodiment, there is a merit that the allowable range of the set value of the waveguide film thickness required for the processing of the optical waveguide can be made large and the pattern thinning allowance accompanying the reactive ion etching becomes large. Is. This type of fiber-guided optical waveguide is also applicable to waveguides made of materials other than quartz optical waveguides, such as ion diffusion type multi-component glass optical waveguides and LiNbO ₃ optical waveguides. is there.

[Advantages of the Invention] As described above, by using the tapered fiber guide of the present invention, precise alignment between the fiber and the waveguide can be achieved only by inserting the optical fiber into the fiber guide. Moreover, in this case, there is an advantage that the allowable error range in setting the optical waveguide film pressure can be widened, and the allowable amount can be large with respect to the pattern thinning at the time of processing. Therefore, if the optical waveguide with a fiber guide of the present invention is applied to a single mode system, a single mode optical waveguide with good yield and easy fiber connection can be manufactured.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of an optical waveguide with a fiber guide of the present invention, FIG. 2 is a perspective view showing a connection method by the conventional end face butting, and FIG. 3 is a conventional optical waveguide with a fiber guide. FIG. 4 is a perspective view, FIG. 4 is a cross-sectional view of the connection portion of FIG. 3, FIG. 5 is a view of a photomask pattern used to form the pattern of FIG. 1, and FIG. 6 is an operation of the fiber guide of the present invention. FIG. 7 is a perspective view of another embodiment of the present invention, and FIG. 8 is a diagram showing the manufacturing dimensions of the optical waveguide of the embodiment of FIG. 1 ... Optical fiber, 1a ... Optical fiber core part, 1b ... Optical fiber clad layer, 2 ... Substrate, 3 ... Optical waveguide, 3a ... Optical waveguide core layer, 3b ... Optical waveguide buffer layer , 3c …… optical waveguide cladding layer, 4,4a …… fiber guide.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Himeno 162 Shirahane, Shirahoji, Tokai-mura, Naka-gun, Ibaraki Prefecture, Nippon Steel and Telegraph Laboratories, Ibaraki Telecommunications Research Institute (72) Morio Kobayashi, Naka-gun, Ibaraki Prefecture Tokai-mura, Oita, Shirahoji, 162, Shirane, Nippon Telegraph and Telephone Corporation, Ibaraki Telecommunications Research Laboratory

Claims (1)

[Claims] 1. An optical waveguide formed on a substrate, and a fiber guide formed at an end of the optical waveguide for fitting and fixing an optical fiber to optically connect the optical fiber and the optical waveguide. In the optical waveguide with a fiber guide, the characteristic is that the distance between the fiber guides is tapered and is not smaller than the fiber diameter on the side closer to the end of the optical waveguide, and smaller than the optical fiber diameter on the side farther from the end of the optical waveguide. Optical guide with fiber guide.