JPS6120910A - Optical coupler and its production - Google Patents

Abstract

PURPOSE:To obtain an efficient optical coupler by allowing the light to be incident on and be discharged from a smoothly worked plane of cleavage of a lithium niobate Z plate (a substrate having a surface cut vertically to the Z axis) where an optical waveguide is formed. CONSTITUTION:An optical waveguide 2 is formed by Ti thermal diffusion on a lithium niobate Z plate (a substrate having a surface cut vertically to the Z axis) 1 so that an angle theta to the Y axis is 57 deg., and this Z plate 1 is treated with a mixed liquid of a fluoric acid and a nitric acid (=2:1) at about 110 deg.C for about 5min to form an end part 6 of a (01.2) face 5 into a shape curved with a certain curvature. A semiconductor laser 7 is approximated to this end part 6 to make the light incident on it, and about 60% high coupling efficiency is the reflection loss is not taken into consideration. In another method, the optical waveguide 2 is produced on the lithium niobate Z plate 1 by ion exchange in a benzoic acid, and a single mode optical fiber 8 has the optical axis aligned to the end part 6, which is obtained by cleaving the plate 1 along the (01.2) face and etching it, and is coupled to the end part 6 to obtain 60% coupling efficiency; and thus, direct coupling is performed easily without lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical coupler and an optical coupler that enable the coupling of an optical waveguide, a laser, and a fiber, which are conveniently used in the information processing field, optical communication, and optical applied measurement and control field. The present invention relates to a method for manufacturing an optical coupler.゛Structure of conventional example and its problems Conventionally, an optical waveguide is provided on lithium niobate, and an optical switch, an optical modulator, a second harmonic generation element, etc. are configured. In this case, if the optical waveguide is formed on a lithium niobate X plate (a substrate with a surface cut perpendicular to the When forming an optical waveguide, there is a drawback that the shape of the waveguide expands in the lateral direction. In order to avoid this, lithium niobate2, which is easy to form a waveguide in the depth direction,
Many plates (substrates with a surface cut perpendicular to the Z axis) have been used.

Methods used for making light enter and exit the optical waveguide include a method using a prism coupler, a method using a grating cup 2-, and a method using end face polishing. Among these methods, the method using a prism coupler has many practical difficulties, such as the difficulty of making the light incident on a three-dimensional waveguide, and the fact that the prism must be brought into close contact with the substrate, which increases the size of the entire device. In addition, the method using a grating kaglar is difficult to manufacture, so that only a method with a low coupling efficiency can be obtained. At present, the most widely used method is edge polishing.

The end surface Me will be explained below using the drawings.

FIG. 1 is a sectional view for explaining end face polishing of lithium niobate. 1 is a lithium niobate substrate, 2
is an optical waveguide, and 3 is an optically polished end face. As shown in FIG. 1(a), optical polishing is performed by bringing a Yato 1' made of the same material into close contact with the surface of the lithium niobate substrate 1 on which the optical waveguide 2 is formed, and as shown in FIG. 1(b). As shown in FIG. 2, if the adhesion of the Yato 1' is poor, surface sag 4 will occur and the coupling efficiency will decrease. Further, as shown in FIG. 1C, if the end face 3 is not perpendicular to the optical waveguide 2, the coupling efficiency will decrease. As described above, the method of polishing the end face is difficult and has many problems, such as being laborious and time-consuming because it involves optical polishing.

On the other hand, it has been reported that light is incident from the cleavage plane (01, 2) on the X plate in element elements made of Ink, GaAs, etc., where folds are used, and in the case of lithium niobate ( 1. P, Kaminow and etc, J, A
pplPhys 51(8) August 1980
F4379-4384).

FIG. 2 is a perspective view and a sectional view showing the relationship between the interfold plane, that is, the (01,2) plane, and each axis of lithium niobate according to the above report. Lithium niobate is a crystal belonging to the trigonal system and has axes a1ja2$a3 and a C axis called the optical axis. Of these, the a1 axis is the X axis.

The C axis is the Z axis, and the axis rotated 90 degrees from the al axis around the C axis is the Y axis. In the lithium niobate Z plate 1 in the cleavage plane (o 1.2) plane 6 as shown in FIG. 2(a), the angle θ with the Y axis is 57 degrees, so the optical waveguide 2 It is impossible for light to enter.

OBJECTS OF THE INVENTION An object of the present invention is to provide an optical coupler and a method for manufacturing the same, which eliminates the above-mentioned drawbacks and realizes optical coupling to a lithium niobate optical waveguide simply and with high efficiency.

DESCRIPTION OF THE INVENTION The optical coupler of the present invention has a structure in which light enters and exits from smoothly processed interfold surfaces of a niobate Z plate on which an optical waveguide is formed.

Further, in the method of manufacturing an optical coupler of the present invention, the interfold surface of the lithium niobate Z plate on which the optical waveguide is formed is interfolded, and then etched.

Further, the optical coupler and the method for manufacturing the same according to the present invention have a configuration in which the (01,2) plane is used as the open and open planes.

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

FIG. 3 is a perspective view showing an embodiment of the method for manufacturing an optical coupler according to the present invention. In FIG. 3(a), 1 is a lithium niobate Z plate, and 2 is an optical waveguide fabricated on the -Z plane by thermally diffusing Ti. Further, this optical waveguide 2 is fabricated in the Y-axis direction and has a width of 8 μm and a depth of 2 μm. 5 is (01,2
) surface is formed between the folds, and the angle θ with the Y axis is 67
degree. Next, a hydrofluoric acid mixture (hydrofluoric acid: nitric acid = 2:1)
The above-mentioned lithium niobate 2 plate 1 was immersed for 6 minutes in a solution heated to about 110° C. for etching. The result of manufacturing as described above is shown in Figure 3.
, 2) A shape in which the end portion 6 of the surface 5 was curved with a constant curvature was obtained.

FIG. 4 is a configuration diagram when the optical coupler manufactured above and a semiconductor laser are coupled. A semiconductor laser 7 was brought close to the spherical end 6 of the (01,2) plane 5 of the optical waveguide 2 formed on the lithium niobate Z plate 1, and light was incident thereon.

The coupling efficiency was 60% excluding reflection loss. In this way, the semiconductor laser and the optical waveguide can be coupled with high efficiency without using a lens.

FIG. 6 is a block diagram showing the coupling between another embodiment of the optical coupler according to the present invention and the original fiber. An optical waveguide 2 was fabricated on lithium niobate 1 by performing ion conversion in benzoic acid. The optical waveguide 2 has a width of 6 μm and a depth of 3 μm, and the propagation direction is the y-axis direction. The optical waveguide was folded and etched on the (01,2) plane to obtain a spherical end 6. A single mode optical fiber 8 having a core diameter of 6 μm was coupled to this with its optical axis aligned. Further, the end portion 6 is coated with an anti-reflection coating.

As a result of the experiment, a binding efficiency of 80% was obtained.

In this embodiment, the (01,2) plane is used as the interfold plane, but any plane that is cleaved at an angle of 20 degrees to 70 degrees with respect to the Y axis may be used. Furthermore, the etching solution, etching temperature, and etching time are not limited to those shown in this detailed description.

As described above, according to the present invention, a highly efficient optical coupler can be manufactured easily. Also, direct fiber without using a lens.

Can be combined with semiconductor laser.

[Brief explanation of drawings]

Figures 1 (a) to (C) are schematic cross-sectional views of main parts to explain conventional edge polishing of lithium niobate, and Figures 2 (a) and (b) are cleavage planes of lithium niobate. (01.2) A perspective view and a sectional view showing the relationship between the plane and each axis, FIGS. 3(a) and 3(b) are perspective views showing an embodiment of the method for manufacturing an optical coupler according to the present invention, The figure is a perspective view of a structure in which an optical coupler according to an embodiment of the present invention is coupled with a semiconductor laser, and FIG. 5 is a perspective view of a structure in which another embodiment of an optical coupler according to the present invention is coupled with an optical fiber. It is. 1... Lithium niobate, 2... Optical waveguide, 5... (01,2) plane, 6...
End portion, 7... Semiconductor laser, 8... Optical 7 fiber. Name of agent: Patent attorney Toshio Nakao and 1 other person 1
Figure 2 Figure 3 (Phantom Figure 4 Figure 5

Claims (2)

[Claims] (1) An optical coupler characterized in that light enters and exits from a smoothly processed cleavage surface of a lithium niobate Z plate on which an optical waveguide is formed. (2) A method for manufacturing an optical coupler, characterized in that the cleavage plane of a lithium niobate Z plate on which an optical waveguide is formed is cleaved, and the edges of the cleavage plane are smoothed by etching.