Fiber optic switch arrangement

A fiber optic switch utilizes an unclad light guide arranged adjacent to a diaphragm of absorbing material. Operation of a push-button presses the diaphragm into contact with the light guide for attenuating the light. Several light guides may be employed to provide an n-of-m code switch matrix.

FIELD OF THE INVENTION 
This invention relates to optical key switches and in particular to a 
push-button switch arrangement for selectively controlling light 
travelling along an unclad region of an optical fibre. 
SUMMARY OF THE INVENTION 
According to the invention there is provided an optical fibre switch 
arrangement, including an unclad fibre through which light is transmitted, 
means for supporting said fibre without substantially attenuating the 
light propagated therein, and means for selectively contacting a portion 
of the surface of the fibre with a resilient light absorbing material so 
as to attenuate the propagated light. 
According to the invention there is further provided an optical fibre 
matrix switch arrangement, including a rigid substrate having a flat 
surface, a coating of relatively low refractive index on said surface and 
a substantially parallel array of light guides of a selectively high 
refractive index arranged on the coating. An elastic diaphragm is mounted 
adjacent the light guides and an array of bar members is arranged 
substantially perpendicular to the light guides. Each of the fibres is 
selectively coated along its length with a protective layer of low 
refractive material, and the bar members and protective coatings are so 
arranged that depression of any one bar member distorts the diaphragm into 
contact with the light guides thus attenuating light only in the guides 
that have no coating in that region so as to provide an n out of m switch 
code.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1 and 2, the switch assembly includes an elongated 
channel member 11 having a V-shaped longitudinal groove 12 the surface of 
which groove is coated with a layer 13 of a transparent cladding material. 
The channel member 11 supports an unclad optical fibre 14, which fibre is 
located in the V groove 12. The transparent coating 13, which may be made 
from a plastics material, has a refractive index significantly lower than 
that of the fibre 14 so as to minimise light losses from the fibre. In 
some applications the faces of the V groove 12 may be highly polished and 
the coating 13 may then be dispensed with. 
The V groove 12 is bridged by a light absorbing elastic, e.g. polyurethane 
diaphragm member 15 adjacent which a push-button or key 16 is mounted. 
Depression of the push-button 16 deforms the elastic diaphragm member 15 
as shown in FIG. 2 and forces it into abutment with the surface of the 
fibre 14 so that light travelling along the fibre is severely attenuated. 
FIG. 3 is a schematic cross sectional view of an optical fibre switch 
matrix employing the principle of the switch arrangement of FIGS. 1 and 2. 
A flat baseplate 31 is coated with a layer 32 of a transparent material of 
relatively low refractive index. An array of light guides 33 of relatively 
high refractive index material is arranged on the layer 32. 
At various points along the length of the switch matrix selected ones of 
the light guides 33 are coated with a layer 34 of the low refractive index 
material as shown in FIG. 3. An elastic light absorbing diaphragm 35 is 
mounted above the array of light guides 33 and is movable into abutment 
with the light guides via an array of switch bars 36, the switch bars 
being arranged substantially perpendicular to the light guides. Operation 
of any one switch bar 36 forces the corresponding portion of the diaphragm 
35 into contact only with the individual light guides 33 that are 
unprotected by the low refractive index material 34 in that region thus 
providing an n out of m switch code arrangement. 
Both the layer 32 and the light guides 33 may advantageously be formed from 
plastics materials, the latter e.g. by deposition through a lithographic 
mask. 
The switch matrix shown in FIG. 4 is similar to that of FIG. 3 except that 
the parallel light guides 41 are unprotected throughout their length. A 
flexible diaphragm 42 arranged adjacent the light guides 41 is pressed 
into contact with selected light guides by means of an array of switch 
bars 43 each bar having cut-outs 44 arranged according to the switch code 
to be generated. 
It is to be understood that the foregoing description of specific examples 
of this invention is made by way of example only and is not to be 
considered as a limitation on its scope.