JPS58129402A - Optical waveguide - Google Patents

Abstract

PURPOSE:To easily conduct the optical coupling of an optical waveguide to optical fibers with high coupling efficiency by placing heating elements on the coupling ends of the waveguide formed on a substrate whose refractive index changes in accordance with temp. CONSTITUTION:Ti is thermally diffused in an LiNbO3 substrate 1 to form a plane or linear optical waveguide 2, and Ni-Cr heating electrodes 11 are placed on the coupling ends of the waveguide 2. An optical deflector or other optical functional element is generally placed on the substrate 1. By supplying electric currents to the electrodes 11 from power sources 12, the electrodes 11 generate heat to heat the substrate 1, and the refractive index of the heated parts is increased. Accordingly, by making the refractive index of the parts under the electrodes 11 almost equal to that of the waveguide 2 by temp. control, the apertures of the waveguide 2 at the coupling ends are equivalenty extended.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveguide device using a material whose refractive index changes depending on temperature.

2. Description of the Related Art In optical fiber communication and other optical application technologies, it is necessary to optically couple an optical fiber and an optical waveguide formed on a substrate with high coupling efficiency. However, the diffusion length of an optical waveguide formed on a substrate by a method such as thermal diffusion is about several μm, and the diameter and size of the optical fiber core are different, making coupling difficult and causing problems such as low coupling efficiency. There is. This situation is shown in Figure 1. The depth of the optical waveguide (2) formed on the substrate (1) is approximately several μm, but the diameter of the core (4) of the optical fiber (3) covered with the cladding layer (5) is smaller than this. is also much larger. Therefore, in the optical coupling between the optical fiber (3) and the optical waveguide (2), it is difficult to set up the optical coupling, and the coupling efficiency determined from the field distribution is not high.

Moreover, when both are shifted from the optimum position, the coupling efficiency decreases rapidly.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide that allows easy optical coupling between an optical waveguide formed on a substrate and an optical fiber and provides high coupling efficiency.

The optical waveguide according to the present invention is characterized in that a heating element is provided on the coupling end of a guiding waveguide formed on a substrate whose refractive index changes depending on humidity. By passing a current through the heating element to generate heat, the refractive index of the substrate under the heating element changes, and the opening at the coupling end of the leading waveguide becomes equivalently larger. Therefore, coupling between the guide waveguide and the optical fiber becomes easier, and since the aperture of the optical waveguide becomes wider, more light enters the guide waveguide, increasing the coupling efficiency. Further, even if the positional relationship between the optical fiber and the guide waveguide deviates from the optimal coupling state, the coupling efficiency does not suddenly decrease. As the leading waveguide, both a planar layered waveguide and a linear waveguide can be applied.

Embodiments of the present invention will be described in detail below with reference to FIGS. 2 and 3.

In Figure 2, lithium niobate crystal (LlNbos
) ill as a substrate, a planar or linear optical waveguide (2) is formed by thermally diffusing titanium (T1) onto the surface of this crystal (1).

The refractive index of LiNbO3 changes linearly with temperature, and the rate of change is on the order of 10 2 for a temperature change of 1°C. On the coupling end of this optical waveguide (21), lift
A Ni-0° C. heating electrode (11) is produced by an off-method. When the optical waveguide (2) is linear, the heating electrode (11) is placed so as to cover the entire inside of the optical waveguide (2), and when the optical waveguide (2) is planar, the heating electrode (11) is placed in an appropriate area at the point where light should enter and exit, for example, an optical fiber (2). It is provided over a size comparable to the diameter of the core (4) in 3). Generally, on the substrate (1),
Optical deflectors and other optical functional elements are assembled.

When a current is passed through the heating electrode Cl1l when the power is turned off, the electrode fill generates heat and the temperature of the substrate (1) under the electrode 011 increases, and the refractive index of this part increases as shown by the broken line in Figure 3. . Therefore, by controlling the temperature, the electrode (11
) by making the refractive index 1 of the optical waveguide (2) approximately equal to the refractive index of the optical waveguide (2), the aperture at the coupling end of the leading waveguide (2) becomes an equivalent curve.

The refractive index of the portion below the electrode (111) of the leading waveguide (2) also increases somewhat, but although the refractive index changes continuously, it hardly affects the waveguide of light.

By widening the aperture at the coupling end of the optical waveguide (2), even if the depth of the optical waveguide (2) is on the order of microns, the size of this aperture is larger than that of the core of the optical fiber (3). As the aperture approaches the diameter of the aperture, it becomes easier to set up optical coupling with the optical fiber, and more light enters the aperture, increasing the coupling efficiency. The light incident from the aperture passes through the leading wavepath (
2). In addition, the optical fiber (3) and the leading waveguide (
Even if the positional relationship with the aperture (2) deviates somewhat from the optimal coupling state, the coupling efficiency will not drop suddenly. The heating electrode ti11 may be provided only on the side where light is incident.

Although LlNbos is used as the substrate in the above embodiment, it goes without saying that other materials can be used as long as the refractive index changes depending on temperature. Further, the leading waveguide may be formed by a method other than the diffusion of T1, and the heating element may be formed from a material other than Ni-Or. −

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional example, and FIGS. 2 and 3 are block diagrams showing an embodiment of the present invention. indicates a energized state. fil ee@L i N b 03 board, f21e
*e optical waveguide, optical fiber for 13i, core for +41, heat generating N pole for tu). Patent applicant: Tateishi Electric Co., Ltd.

Claims (1)

[Claims] A waveguide device in which a heating element is provided on the coupling end of an optical waveguide formed on a substrate whose refractive index changes depending on temperature.