JPH03103805A - Connecting method for optical waveguide and optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] A method for connecting an optical waveguide and a fiber, which eliminates reflected return light from an 8I waveguide end face, and... In order to easily adjust the optical axis and position of the fiber and waveguide, we made the fiber and the chip side and surface parallel, and introduced a curved waveguide. The angular relationship between the waveguide and the end face was configured to satisfy Snell's law.

[Industrial application field]

The present invention relates to optical waveguide devices such as external modulators, switches, and demultiplexers in optical communication equipment, and in particular to optical waveguides that facilitate the reduction of reflected return light from optical waveguide devices and the adjustment of optical axes between fibers and waveguides. and how to connect fibers.

? [Prior Art] In optical waveguide devices generally used in optical switches, optical modulators, etc., an electric field is applied to an optical waveguide formed on the surface of an electro-optic crystal substrate such as lithium niobate (LiNbOs) to change the refractive index. , performs switching and phase modulation of the optical signal traveling through the waveguide. Since the refractive index of such a substrate material (LiNbOs: 2.1) is generally different from that of a fiber material (SiO2: 1.45), light is reflected at the interface. Such reflected return light causes problems such as the semiconductor laser used as a light source not operating stably.

Conventional countermeasures have been to reduce the absolute value of the reflected light by forming an anti-reflection film on such interfaces, and to change the wavefront of the reflected light into guided light by slanting the optical axis to the interface. The antenna is tilted significantly from the center to prevent reflected light from coupling into the guided light.

FIG. 5 is a structural diagram showing a conventional connection between an optical waveguide and a fiber, and particularly shows an example where the end face of the waveguide is shaped obliquely with respect to the waveguide and the fiber. Figure 5(a)
5(b) is a perspective view of the connection part, FIG. 5(b) shows a cross section of the end face of the waveguide, and 1 shows a lithium niobate substrate, on the surface of which a titanium (T i ) vapor-deposited film is patterned into a belt shape. Thereafter, the titanium is thermally diffused into the waveguide substrate 1 to form an optical waveguide 2 having a diameter of about 7 μm and having a larger refractive index than the waveguide substrate 1.

Also. The light propagating through the waveguide leaks out of the waveguide to some extent. For this reason, if an absorptive substance or a high refractive index substance adheres to the waveguide, the propagating light will be affected, so the table of the waveguide substrate 1 is set separately, and after aligning the fiber with this line, the fiber is held It is necessary to rotate the fiber by a certain angle using a rotation mechanism installed in the jig, and then perform X, Y, and Z alignment.
This is time-consuming and requires high-precision equipment with little play in the rotating mechanism.

[Problem that the invention seeks to solve]

In the conventional connection between an optical waveguide and a fiber, there is a problem in that when the end face of the waveguide is formed at an angle, it is difficult to adjust the angle of the fiber.

[Means for solving problems]

The above problem is that by introducing a curved waveguide into the optical waveguide, the end face of the waveguide is formed obliquely to the optical axis, and the side surface and surface of the waveguide chip are formed so that they are parallel to the fiber. solved by.

[For production]

Silicon dioxide (Si○2) with a refractive index of about 1.45 is deposited on the entire surface to a thickness of 0.4 μm using ordinary chemical vapor deposition (CVD) technology to form an eight-sophage layer 3. ing.

Furthermore, lithium niobate chloride 4, which is the same as the substrate material, is adhesively fixed to the upper part of the end face of the waveguide using epoxy resin 5. This block has the role of a polishing aid when forming the end face and the role of reinforcing when holding the fifer 6.

Also. The end face of the waveguide is made of Fiha 5 with a rounded tip.
is fixed using a UV (ultraviolet) curing adhesive 7.

At this time, the waveguide, the waveguide end face, and the fiber are arranged in such an angular and positional relationship that the waveguide end face becomes a boundary surface that satisfies Snell's law when the waveguide and the waveguide end face are regarded as the path of a light ray. . In this connection, angular and positional alignment is important, and a slight deviation in this adjustment will result in large losses. In particular, the process of tilting the fiber at a certain angle from the waveguide end face is performed so that the fiber is parallel to the side surface and surface of the line waveguide chip that serves as a reference, and the five waveguide end faces are deviated from perpendicular to the fiber. This end face is formed at an angle. By shaping the connection so that the fiber and waveguide have an angular relationship that satisfies Snell's law, it is possible to reduce the amount of reflected light at the connection. Adjusting the angle of the fiber becomes extremely easy. This is when adjusting the angle. This is because a satisfactory angular relationship of the fiber with respect to the waveguide and the end face of the waveguide can be achieved simply by aligning the fiber parallel to the Chisop surface and side surface.

In this adjustment, the length of the waveguide chip is usually several cm.
Because of the above length, it is easy to adjust the angle gIJ to less than 0.5° even if the angle gIJ is determined visually without using a special device such as a microscope.

In addition, the waveguide is bent near the end face of the waveguide. The end faces are formed to have an angular relationship that satisfies Snell's law. Since this curved waveguide has the property of easily emitting higher-order mode light, it has the function of a mode filter. Normally, waveguides are symmetrical to single-mode light, so it is desirable to remove higher-order mode light. Therefore, for the light that has entered the waveguide, it has the function of removing higher-order mode light that has been guided through the fiber and higher-order mode light that is generated at the connection between the fiber and the waveguide. It has a function to radiate higher-order mode light that is inadvertently generated within the waveguide device through a curved line at the rear.

moreover. Since the fiber and waveguide can be formed in a straight line,
The device has a simple structure and has the advantage of being easy to handle and incorporate into equipment.

〔Example〕

FIG. 1 is an example showing a connection between an optical waveguide and a fiber according to the present invention.

In FIG. 1, l is a waveguide chip made of a lithium niobate (LiNbOs) substrate as in FIG. 5. Further, the surface 1d of the waveguide chip 1 can be similarly constructed by patterning titanium (Ti) and then heating it to form the above-mentioned hollow or polygonal lines.

FIG. 3 shows an embodiment in which a connection using this curved optical waveguide 2 is used at the entrance and exit. In this case, the waveguide end faces 1c at the entrance and exit are shaped symmetrically with respect to a plane perpendicular to the fiber 6 at the center of the chip. By adopting such a structure, the inlet and outlet fibers 6 can be arranged in a straight line. For this reason, conversely, the prewarmed fiber 6
After adjusting it in a straight line. It is also possible to insert the tip 1 between fibers, and the structure is simple and easy to adjust.

FIG. 4 is another embodiment according to the present invention, and shows an example of a configuration in which a curved waveguide is not used.

In this case, the waveguide end face 1c is formed point symmetrically with respect to the chip center, and the chip side faces 1a, 1b and the surface 1
d is parallel to the input/output fiber 6. Further, the optical waveguide 2 includes a fiber 6, an end face IC. A strip-shaped optical waveguide 2 with a diameter of about 7 μm is formed by thermally diffusing titanium into the waveguide chimp 1 by forming the optical waveguide 2 at an angle with respect to the chip side surfaces 1a and lb so that the optical waveguide 2 satisfies Snell's law. ing.

6 is a single mode fiber with a spherical tip. Further, 8 is a perpendicular to the waveguide end face 1c, and the angle between this perpendicular and the optical waveguide 2 is θ, and the angle between the optical waveguide 2 and the fiber 6 is θ2, and the refractive index of the optical waveguide 2 is nl+. When the refractive index of is n2, Snell's law expressed by equation (1) is satisfied between them.

n, sin θ1 = n2 sin θ2 −−−−−−−−
(L) Also, at this time, the side surface 1a or 1b and the surface 1d of the waveguide chip 1 are designed and manufactured so as to be parallel to the fiber 6. At this time. The fiber 6 is fixed to the waveguide end face 1c using a UV curing adhesive 7.

FIG. 2 is an embodiment showing the waveguide structure near the end face of the embodiment according to the present invention. In the figure, the optical waveguide 2 is bent at a desired angle with a radius R (30 to 40 mm).

Note that this curved optical waveguide 2 also has a total reflection core.In this case, a curved waveguide is not used. There is no excessive loss due to curved waveguides. Furthermore, since both end surfaces are parallel, it has the advantage that chips can be easily cut out from the wafer.

In the above-described example, the presence of the block 4 and the bathophore layer 3 provided at the end face of the waveguide as shown in FIG. 5 is omitted.

Also, in the above example, waveguide functional parts such as switches, modulators, and filters within the chip are omitted.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to realize a connection method that allows fiber alignment to be easier than those of the conventional structure and also has the function of removing higher-order mode light.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a connection between an optical waveguide and a fiber according to the present invention. FIG. 2 is a diagram showing a waveguide structure of an embodiment according to the present invention. FIG. 3 shows an embodiment according to the present invention. FIG. 4 shows another embodiment according to the present invention. FIGS. 5(a) and 5(b) are diagrams showing the connection between a conventional optical waveguide and a fiber. [Explanation of symbols] 1 is the waveguide chip, la, lb are the side surfaces of the waveguide chip, l
c is the waveguide end face, ld is the waveguide chip surface 1d, and 2 is the optical waveguide. 3 is the buffer layer 4 fast block. 5 is an epoxy resin, 6 is a fiber, and 7 is a UV curing adhesive.

Claims (1)

[Claims] (1) The waveguide chip side surface and surface are formed parallel to the fiber, and the waveguide end face is formed at an angle deviated from perpendicular to the fiber, and this end face, the fiber, and the waveguide are formed in a Snell shape. An optical waveguide and a fiber connection method characterized in that the optical waveguide is formed to have an angular relationship that satisfies the law.