DE4418751A1 - Refractive index changer for planar waveguide in optical switch for telecommunication - Google Patents

Abstract

A refractive index changer for a planar light waveguide has a variable mechanical stress generator on the waveguide. The stress generator is pref. a ferroelectric element (3) producing electrostriction or magnetostriction or a dielectric element producing a piezo-effect. A cavity is pref. situated on the opposite side of the waveguide to the stress generator. The dielectric layer producing the piezo-effect may consist of ZnO, PbTiO3, PbZrO3, Pb(Ti,Zr)O3, BaTiO3 or AlN. When a voltage is applied the layer is exposed to an electrical field and undergoes distortion which is transmitted to the waveguide.

Description

The invention relates to a device for changing the Refractive index of a planar optical fiber. The material of one Optical fiber, for example one in the optical Communication technology used optical fiber, is optical isotropic d. H. is the speed of light in the optical fiber regardless of the direction.

In optical communications technology, however, the local and directional properties of optical fibers for Components of optical communications technology can be used. At such a component can be, for example act optical switch. The Mach-Zehnder interferometer can can be used for example as such an optical switch if there is a change in the branch of the same Light propagation speed is made. It is a Mach-Zehnder interferometer known (see brochure: "Single-Mode Thermo-Optic Switch "from Photonic Integration Research, Inc., Columbus, Ohio), where a thin film heater over one Branch is arranged, causing the speed of light in this Branch can be influenced, which via interference to a Switching effect can lead. This known optical switch has the disadvantage that its switching speed for some Application is too small; it is in the millisecond range.

The technical problem underlying the invention exists therefore in it a device for changing the refractive index of a planar optical fiber with a higher switching speed to accomplish.

This technical problem is solved according to the invention in that a variable mechanical tension on the waveguide generating device is arranged.

With this solution, refractive index changes can be carried out at high switching speeds. Advantageous embodiments of the invention are contained in claims 2 to 5. It is explained below with reference to FIGS. 1 to 4. Show it:

Fig. 1 shows schematically the structure of a Mach-Zehnder interferometer in which a voltage generating device is arranged on a branch,

Fig. 2 is a longitudinal section through part of the apparatus of FIG. 1

Fig. 3 explains the operation of the invention and

Fig. 4 shows another embodiment of the device according to the invention.

In Fig. 1, the basic structure can be seen of a Mach-Zehnder interferometer having the optical waveguide branches 1 and 2. Arranged above the branch 1 is a voltage-generating device which consists of a layer 3 made of a piezoelectric material. A plurality of electrodes 4 and 5 are arranged above and below the layer 3 .

FIG. 2 shows a longitudinal section through part of the device according to FIG. 2. It can be seen that the optical waveguide core 6 is arranged between the upper cladding layer 7 and the lower cladding layer 8 . Zinc oxide (ZnO), lead titanate (PbTiO₃), lead zirconate (PbZrO₃), lead titanate zirconate (Pb (Ti, Zr) O₃), barium titanate (BaTiO₃) or AlN (aluminum nitride) are suitable as materials for the dielectric layer 3 .

The operation of the device according to the invention is illustrated in FIG. 3. When a voltage is applied to the electrodes 4 and 5 , the dielectric layer 3 is exposed to an electric field, as a result of which the dielectric layer undergoes mechanical deformation (contraction, expansion, shear), which - as indicated by the arrows - on the optical waveguide is transmitted, whereby the light propagating in the optical waveguide experiences a change in the propagation speed. The direction of the forces acting on the optical waveguide can be influenced by the arrangement of the electrodes, the polarity of the field and the polarity of the dielectric layer.

The switching speed is determined by the ohmic resistance and determines the capacitance of the electrode arrangement; therefore it can Switching times in the microsecond range can be realized.

Fig. 4 illustrates a solution with which the force acting on the optical waveguide ( 6 , 7 , 8 ) can be increased, namely in that a cavity 10 is provided in the substrate 9 below the voltage-generating device, whereby this from the relatively rigid substrate is mechanically decoupled.

If instead of the piezoelectric layer a ferromagnetic Body is used, then it must pass through a magnetic field be influenced to achieve the same effect.

Claims (5)

1. A device for changing the refractive index of a planar optical waveguide, characterized in that a, a variable mechanical tension generating device is arranged on the waveguide. 2. Device according to claim 1, characterized in that the voltage-generating device is a, an electrostriction-causing ferroelectric body ( 3 ). 3. Device according to claim 1, characterized in that the voltage generating device is a dielectric body causing a piezo effect.   4. The device according to claim 1, characterized in that the voltage generating device a ferromagnetic body causing magnetostriction is. 5. The device according to claim 1 and one of claims 2 to 4, characterized in that a cavity ( 10 ) is provided on the side of the optical waveguide facing away from the voltage-generating device.