Optics: measuring and testing – For optical fiber or waveguide inspection
Patent
1991-06-06
1992-03-17
Fisher, Richard V.
Optics: measuring and testing
For optical fiber or waveguide inspection
385123, 385 76, 385139, 65 311, 65 312, 65 605, 356399, 356400, 356445, G01N 2100
Patent
active
050963015
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an optical device having an optical waveguide.
It is often necessary to align a passive or active optical device with an optical waveguide, in order to obtain maximum efficiency in coupling optical signals between the waveguide and the device. When the waveguide is an optical fibre the light guiding region of the fibre, that is, the inner core region, must be aligned with the light emitting or light receiving region of the device.
In a known method of aligning an optical fibre with a laser, an optical signal from the laser is arranged to be incident on the fibre. The intensity of the signal emerging from the fibre is measured, and the position of the fibre relative to the laser is altered in order to obtain maximum intensity of the signal emerging from the fibre. The alignment is thus set initially by measurement. A disadvantage of this known method is that the alignment is set only initially and assumed to remain satisfactory thereafter. However, subsequent movement, vibration or temperature stresses may result in movement of the laser relative to the fibre. Any such movement therefore remains undetected, and maximum efficiency in coupling may no longer be achieved.
In a known method of detecting pits which form tracks in a compact disc, the pits are detected by a servo mechanism which detects the pits and adjusts a laser relative to the pits in order that the laser is locked onto the tracks. The servo mechanism acts to dynamically adjust the relative positions of the laser and the pits in order to maintain maximum efficiency. The mechanism detects the pits in the compact disc, by detecting a difference in reflectivity between the pits and the remaining surface of the disc. Such servo laser devices are mass produced and therefore relatively cheap optical sources. However, they cannot be used to align the laser with known optical waveguides. It is an object of the present invention to solve this problem.
According to a first aspect of the present invention there is provided an optical apparatus comprising an optical waveguide having an endface; a light guiding region exposed at the endface and bounded at the endface by at least two opposing boundary regions, the reflectivity of the light guiding region being different to that of the boundary regions, characterised in that the apparatus further includes and optical source; alignment means responsive to the difference in reflectivity between the light guiding region and the boundary regions for aligning the optical source with the light guiding region.
An optical device can be arranged to scan the endface of the waveguide and thus detect and locate the position of the light guiding region. This thus enables the mass produced servoed laser devices to be used as optical sources for waveguide systems although, it is to be understood that some modification of the devices used in relation to compact discs may be necessary. For instance, the coupling arrangement between the laser and the waveguide may require modification.
According to a second aspect of the present invention there is provided a method of fabricating an optical waveguide having an endface; a light guiding region exposed at the endface and bounded at the endface by at least two opposing boundary regions exposed at the end-face, the reflectivity of the light guiding region at the end-face being different to that of the boundary regions, the method comprising coating at least a portion of the endface of the waveguide with a material which is of the type which breaks down when heated; passing an optical signal through the light guiding region thereby producing heat sufficient to cause the material to break down in the light guiding region of the endface but not in the boundary regions.
Conveniently, the waveguide is an optical fibre and the light guiding region is an inner core region, and the boundary region is an outer cladding region.
Alternatively, a planar waveguide such as lithium niobate with a titanium in-diffused channel may be used.
Preferably, the optical fibre com
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Electronic Letters, Jul. 10, '75, vol. 11, No. 14, Direct Coupling from a laser into a fibre, R. B. Dyott, pp. 308-309.
British Telecommunications public limited company
Bruckner John J.
Fisher Richard V.
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