DE19911964A1 - Optical waveguide coupler with mode-converting grid forming non-reflecting add or drop multiplexers, has slanting Bragg grating grid in optical waveguide enabling mode conversion - Google Patents

Abstract

A slanting Bragg grid (25) is written into the second waveguide (20) within the coupling region (15) of the optical waveguide coupler by ultraviolet (UV) exposure, which increases the effective refractive index of this waveguide, thus preventing complete over coupling of optical effect from first waveguide (10) in the second. The mode converter disposed in the first optical waveguide has characteristic wavelengths which differ from those of the mode converter in the second optical waveguide. The mode converter consists of slanting Bragg grating which produce gitter by UV recording/writing process. Adaptation of the effective refraction indices of the two waveguides is accomplished by exposure using UV light.

Description

The present invention relates to a device in which a light waveguide coupler and a mode converter form an add / drop multiplexer. On Add / drop multiplexer is an optical component with which it is possible to make one Extract or add certain wavelengths to the wavelength spectrum.

For an add / drop multiplexer, in addition to a low crosstalk between the channels to be separated important that the back reflections in the input arm very be strongly suppressed. An add / drop multiplexer with one is therefore desirable very high back reflection loss.

This can be ensured by the fact that reflected light is in a mode which cannot be propagated outside the add / drop multiplexer. This can be achieved by a mode converter which converts the incident basic mode ( 4 ) of the single-mode waveguide ( 1 ) in a counter-directional manner into a higher mode ( 5 ).

Specifically, an oblique Bragg grating in an optical waveguide, which allows the waveguide in the region of the grating to become two-mode or even higher-mode due to the refractive index voltage induced in the grating writing process ( 2 ), meets the conditions for the converter described above. Such a Bragg grating effects a coupling of the leading basic mode ( 4 ) to the returning basic mode ( 6 ) and to one or more returning higher modes ( 5 ). In transmission, both couplings cause a drop in the transmitted power ( 7 ). In the measurement of the reflection ( 8 ), however, a peak only occurs when the basic mode ( 6 ) is reflected; the reflected power of the higher mode ( 5 ) is emitted in the single-mode waveguide ( 1 ). In particular, by choosing the grating angle α ( 3 ) it can be achieved that there is no coupling to the returning basic mode ( 6 ), but only to a returning higher mode ( 5 ).

In order for an optical fiber coupler (see Fig. 2) the optical power at one wavelength to be able to couple completely from one waveguide to the other waveguide, the propagation constants in both waveguides must be the same. This condition should be fulfilled for all wavelengths not equal to the characteristic wavelength of the mode converter. Due to the influence of the mode converter, the difference in the propagation constants of the two waveguides ( 10 and 20 ) is so great at the wavelength characteristic of the mode converter that no optical power is coupled from one to the other waveguide at this wavelength.

In order to implement this add / drop multiplexer, an oblique Bragg grating ( 25 ) is written into the second waveguide ( 20 ) within the coupling region ( 15 ) of the optical waveguide coupler by UV exposure.

This UV exposure increases the effective refractive index of this one waveguide. A complete coupling of optical power from the first waveguide into the second waveguide can no longer take place. The effective refractive indices of the two waveguides are adjusted again by a subsequent UV exposure of the first waveguide. At all wavelengths not equal to the characteristic wavelength of the mode converter there is again a complete coupling of the optical power, ie optical power of these wavelengths coupled into input 1 ( 11 ) emerges at output 2 ( 13 ). Optical input at input 1 ( 11 ) at the characteristic wavelength of the mode converter, however, is output at output 1 ( 12 ).

Claims (11)

1. Optical waveguide coupler with at least one optical waveguide ( 10 ) which is coupled in a coupling area ( 15 ) to a second optical waveguide ( 20 ) in such a way that at least part of the power carried in the first optical waveguide is coupled into the second optical waveguide, characterized in that the second optical waveguide has a mode converter ( 25 ) located in the core, at least two-mode in the area of this mode converter and by means of which the coupling of optical power from the first optical waveguide into the second optical waveguide is prevented at the wavelengths characteristic of the mode converter. 2. Optical fiber coupler according to claim 1, characterized in that we All optical power with wavelengths not equal to the characteristic ones Wavelengths of the mode converter from the first waveguide to the second Waveguides are coupled over. 3. Optical fiber coupler according to one of claims 1 to 2, characterized net that there is a mode converter in the first optical fiber, where whose characteristic wavelengths from the characteristic wavelengths of the Distinguish the mode converter in the second optical fiber. 4. Optical fiber coupler according to one of claims 1 to 3, characterized in that the mode converter ( 25 ) extends beyond the coupling region of the two optical fibers ( 15 ). 5. Optical fiber coupler according to one of claims 1 to 4, characterized in that as optical fibers optical glass fibers or integrated optical waveguides be used. 6. Optical fiber coupler according to one of claims 1 to 5, characterized in that the mode converter consists of an oblique Bragg grating. 7. Optical fiber coupler according to claim 6, characterized in that the Bragg Lattice is made by a UV writing process. 8. Optical fiber coupler according to one of the preceding claims, characterized records that the higher fashion by inserting a higher fashion light waveguide is reached in the second optical fiber. 9. Optical fiber coupler according to one of the preceding claims, characterized records that the optical fibers are initially single-mode and the more modernity by exposure to UV light or another suitable light is achieved.   10. Optical fiber coupler according to one of the preceding claims, characterized records that the adjustment of the effective refractive indices of the two waves reached by exposure to UV light or another suitable light becomes. 11. Optical fiber coupler according to one of the preceding claims, characterized net that the two optical fibers initially different refractive indices to have.