JP3450068B2 - Optical waveguide coupling structure - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coupling structure between an optical waveguide and an optical element, and more particularly to an optical waveguide for obtaining a highly efficient and easy coupling between an optical fiber and an optical waveguide. The present invention relates to a structure and a manufacturing method of a waveguide. 2. Description of the Related Art An optical waveguide which is considered to be used as an optical communication device may have a pigtail type mounting structure which is generally combined with a single-mode optical fiber to be integrated due to practical demands. Is desired. The most commonly used conventional mounting structure is, for example, an optical fiber array in which a plurality of optical fibers are previously fixed in parallel on an optical fiber holding substrate in which a V-groove is formed, and A so-called butt-joint method, in which the position of an optical coupling portion of an optical waveguide fixed to a substrate is adjusted and then the coupling surface between the optical fiber array and the optical waveguide substrate is bonded with an adhesive, is often used. [0004] Among the characteristics required for the coupling portion between an optical fiber and a waveguide, an important one is a connection loss characteristic. To reduce the connection loss, the optical axis between the waveguide and the optical fiber core is reduced. There is a need for accurate alignment of
The core diameter of a normal single mode fiber is about 10 μm, and the cross-sectional size of the optical waveguide of various waveguides is less than several μm for devices used in a single mode transmission system. A slight displacement of the optical axis causes a large connection loss. Therefore, the V-groove formed on the holding substrate of the optical fiber must be manufactured with high precision so that the positional shift of the coupling portion between the optical fiber and the optical waveguide does not occur. Further, when the diameter of the optical waveguide and the diameter of the optical fiber core are different, the distribution diameter of the propagating mode is different (mode mismatch), resulting in a coupling loss. butt-
In the joint method, the end face of the optical fiber is simply coupled directly to the end face of the waveguide. Therefore, the coupling loss cannot be avoided in the connection between the optical waveguide and the optical fiber having different modes, and a connection method with lower loss is desired. It is rare. Various studies have been made to reduce the connection loss at the coupling portion. One of the means is to match the propagation mode shapes of the waveguide and the optical fiber. As a specific means, a coupling structure by distributed coupling using an auxiliary waveguide has been proposed. An auxiliary waveguide having the same mode distribution diameter as that of the optical fiber core is formed parallel to the optical waveguide near the optical input / output waveguide on the end face of the waveguide substrate. The optical fiber is not directly connected to the optical waveguide, but is coupled to the end face of the auxiliary waveguide to input or output light. The light incident on the auxiliary waveguide gradually moves to the adjacent optical waveguide while propagating in the auxiliary waveguide, and eventually all the propagating light moves into the waveguide and propagates in the waveguide. Go. At this time, since the structure of the auxiliary waveguide is such that the mode shape of the propagating light is equal to the mode shape of the light propagating in the optical fiber, the mode mismatch at the connection surface between the optical fiber and the auxiliary waveguide is obtained. Can be eliminated. In this way, the coupling between the waveguides having different waveguide diameters and the optical fiber can be performed with high coupling efficiency. [0006] However, a method of fabricating a waveguide having a distributed coupling type connection structure using the above-mentioned auxiliary waveguide has not been sufficiently established. First, when an auxiliary waveguide is manufactured using the same microfabrication technology as the method for manufacturing a waveguide on a substrate, since the waveguide diameter and the auxiliary waveguide diameter are different, both are actually mounted on the same substrate. There is a problem in that it requires many steps and is difficult to manufacture. In addition, when an auxiliary waveguide is mounted on a waveguide substrate to form a distributed coupling structure, since the substrate has a rib-shaped cross-section at the coupling portion, sufficient characteristics cannot be secured for the coupling portion strength. . An object of the present invention is to solve the above-mentioned problems in the conventional manufacturing method, and to provide a method for manufacturing a waveguide coupling portion having an auxiliary waveguide by an easy and practical means and an easy method. It is intended to provide a joint structure. [0008] In view of the above, the present invention provides
An optical waveguide core made of quartz glass is formed on a waveguide substrate, and an auxiliary waveguide is provided separately from the optical waveguide core on an end surface of the waveguide substrate facing the optical fiber, and the auxiliary waveguide is provided with the optical waveguide. The waveguide length, the distance from the optical waveguide, the refractive index, and the cross-sectional diameter are determined so that the incident light from the fiber is coupled with low loss, and the light is transferred to the optical waveguide core with high efficiency. A coupling structure of an optical waveguide for performing signal input / output via an auxiliary waveguide by performing distributed coupling with the optical waveguide core, wherein the waveguide substrate is provided separately from the waveguide substrate on which the optical waveguide core is formed. A cover mounted on the waveguide substrate is provided, and a rectangular groove is formed by grinding at a position near the waveguide core when the cover is mounted on the waveguide substrate, and is optically transparent at a used wavelength. Filling and hardening the groove with a polymer resin Characterized in that to constitute a waveguide. According to the above means, the auxiliary waveguide 12 for performing distributed coupling can be easily formed without using the fine processing means for manufacturing the waveguide 11 in the process of manufacturing the waveguide device. It is possible to do. FIG. 1 is a reference example of an optical fiber end structure.
The optical waveguide device 13 has an optical waveguide 11 formed on a waveguide substrate 16. The refractive index of the optical waveguide 11 is higher than the refractive index of the waveguide substrate 16, so that light propagates without leaking. On the side surface of the optical waveguide 11, a rectangular auxiliary waveguide 12 is formed in parallel with the optical waveguide. Regarding the cross-sectional diameter and the waveguide length of the auxiliary waveguide 12, the distance from the optical waveguide 11, and the refractive index, the incident light from the optical fiber is coupled with low loss, and the light is transferred to the optical waveguide 11 with high efficiency. Need to be decided. The auxiliary waveguide 12 is formed directly from the surface of the waveguide, and is formed by curing an optically transparent resin at the wavelength used for the optical waveguide device. FIG. 2 shows a process for manufacturing such an auxiliary waveguide in the optical waveguide device 16. First, the waveguide substrate 16
An optical waveguide 11 is formed thereon (FIG. 2A). Next, a groove 14 having an opening in the device surface 15 is formed from the end face of the optical waveguide on the substrate along the optical waveguide 11 by means such as mechanical grinding (FIG. 2B). This auxiliary waveguide groove 14
Is filled with a polymer resin and cured. After the curing, polishing is performed so that the surfaces are aligned with the waveguide surface 15 and the end surface of the waveguide, thereby completing the auxiliary waveguide (FIG. 2C). In this embodiment, there is no clad layer on the upper part of the auxiliary waveguide,
After forming the auxiliary waveguide in the above-described process, a low refractive index resin may be coated or a cladding layer or a protective layer may be provided on the upper surface of the auxiliary waveguide. The method of manufacturing the auxiliary waveguide in this manner requires a smaller number of steps and can provide a low-cost device as compared with the case of manufacturing using a fine processing technique such as photolithography. It becomes possible. The reason why the polymer resin is used as the material of the auxiliary waveguide is that there is an advantage that filling and curing can be easily performed. The polymer resin is inferior in propagation loss to waveguide materials such as silica glass, but if used only for the auxiliary waveguide, the waveguide length is small and the propagation loss due to the material can be ignored. . FIG. 3 shows a reference example of the present invention, in which an auxiliary waveguide 12 is formed above a waveguide 11 of a waveguide device 13. FIG. 3A shows a sectional view of the reference example, and FIG. 3B shows a perspective view thereof. FIG. 4 shows an example of the manufacturing process of the reference example. V-groove 24 extends from waveguide device surface 15 to upper portion of waveguide 11
Is manufactured to a desired length (FIG. 4A). Further, the cover 25 having the similar V-shaped grooves 26 is positioned so that the V-shaped grooves are opposed to each other, and is fixed by overlapping (FIG. 4B). A rectangular gap formed by overlapping the waveguide device 13 and the cover 25 has a square cross-section when the angle of the V-groove is set to 90 degrees. A polymer resin is filled therein and cured to form an auxiliary waveguide. After curing, the end face of the device is polished to remove excess resin, and the end faces are aligned (FIG. 4C). In this embodiment, the resin is filled after the waveguide device 13 and the cover 25 are overlapped. However, the resin is previously filled in the V-grooves 24 and 26 formed in the waveguide device 13 and the cover 26, respectively. It may be superposed after hardening and polishing the bonding surface. FIG. 5 shows an embodiment of the present invention. FIG.
FIG. 5A is a sectional view of an embodiment of the present invention, and FIG.
Shows a perspective view thereof. In the optical waveguide device 13, a groove for forming an auxiliary waveguide is not formed, and the waveguide device surface 15 is not formed.
After forming a rectangular groove 36 in the cover 25 to be superimposed on the optical waveguide device and filling and curing a polymer resin to form the auxiliary waveguide 12, the optical waveguide 1 formed in the optical waveguide device 13 is formed.
The desired structure is obtained by superimposing the auxiliary waveguide 12 of the cover 25 on the upper part of 1 so as to match. If the thickness of the cladding layer 37 from the waveguide device surface 15 to the waveguide 11 is large enough to perform distributed coupling, the device surface 15 where the cover 25 including the auxiliary waveguide overlaps is polished in advance to form the cladding layer. It is also possible to reduce the thickness of 37. As described above, according to the present invention, an optical waveguide device having a distributed coupling type optical coupling portion can be provided by means of fine processing for producing a waveguide. , And can be easily manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a reference example of an optical waveguide coupling unit. FIG. 2 is a diagram illustrating a manufacturing process of a reference example of an optical waveguide coupling portion. FIG. 3 is a diagram showing a reference example. FIG. 4 is a view showing a manufacturing process of a reference example. FIG. 5 is a diagram showing an embodiment of the present invention. [Description of Signs] 11: Optical waveguide 12: Polymer resin 13: Optical waveguide device 14: 24, 26, 36, groove 15: Optical waveguide device surface 16: Optical waveguide substrate 25: Cover 37: Cladding layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/12-6/14 G02B 6/30

Claims (1)

(57) [Claim 1] An optical waveguide core made of quartz glass is formed on a waveguide substrate, and is opposed to an optical fiber of the waveguide substrate.
An auxiliary waveguide is provided on the end face side in addition to the optical waveguide core, and the auxiliary waveguide has low incident light from the optical fiber.
Loss coupled and highly efficient light transfer to the optical waveguide core
The length of the waveguide determined to perform the row,
A coupling structure of an optical waveguide having a distance, a refractive index, and a cross-sectional diameter, performing distributed coupling with the optical waveguide core, and performing signal input / output through an auxiliary waveguide, wherein the waveguide in which the optical waveguide core is formed is provided. Separately from the waveguide substrate, a cover mounted on the waveguide substrate is provided, and a rectangular groove is formed by grinding at a position near the waveguide core when the cover is mounted on the waveguide substrate. A coupling structure for an optical waveguide, wherein the auxiliary waveguide is formed by forming and filling the groove with a polymer resin which is optically transparent at a used wavelength.