Structure for reducing optical beam spacing

Parallel optical beams emitted by an array of optical devices e.g. collimators are spaced by a distance that is not smaller than the diameter of the collimators etc. devices. To reduce the spacing of the beams at the point of incidence on the receiving element or device, a structure is provided having a first and a second array of reflective surfaces e.g. mirrors or prisms, the arrays defining pairs of corresponding reflective surfaces. The surfaces are arranged such that the beams reflected from the second array have a reduced spacing compared to the initial distance.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 illustrates an exemplary receptor, a multiple input device such as a 5×5 switch 10 with five input ports 12 and five output ports 14 . The corresponding light beams 16 coupled to the input ports and outputted from the output ports are passed in free space or through optical fibers 15 from an array of collimators 18 shown in FIG. 2 . As shown schematically in FIG. 2 and FIG. 3 , an array of collimators 18 may be arranged with the collimators side-by-side for space saving. It is of course possible to arrange the collimators in a different array, still with a view to outputting optical beams with a minimal spacing therebetween. Each collimator 18 has a holder 26 . The diameter of the collimator and the size of the holder determine the minimum spacing between the centers of the collimators which corresponds to the spacing L1 between adjacent collimated optical beams 19 emitted from the collimators. Typically, the beams are parallel to each other. To reduce the spacing of the beams at their incidence on the receptor (e.g. isolator) 10 , an array of mirrors 28 , 30 is provided. The array of mirrors includes a first sub-array of mirrors 28 and a second sub-array of mirrors 30 . As seen in FIG. 3 , the mirrors of the sub-array 28 are disposed at an angle 450 to the optical beams emitted from the collimators 18 so as to reflect the beams towards respective mirrors of the sub-array 30 . The mirrors 28 are spaced such as to correspond to the spacing L1 between the collimators. As shown in FIG. 4 , the mirrors of the sub-array 30 are spaced “horizontally” to receive respective optical beams reflected from the mirrors 28 , but their spacing L2 as seen in the direction towards the receptor (horizontal in FIG. 4 ) is smaller than L1. This beneficial result is of course dependent on the size of the mirrors 30 so that they do not obscure the adjacent light beams. It is not necessary for the reflective surfaces of the mirrors 28 and 30 to be disposed at 45° to the incident light beams, but such arrangement may be advantageous for various reasons. The mirrors 28 and 30 may be provided by prisms 32 ( FIG. 4 ) with reflective surfaces that cause total internal reflection of the light beams within the prisms. Alternatively, as illustrated in FIG. 3 , prisms 34 may extend the entire distance (vertical in FIG. 3 ) between the optical axes of the respective collimators and the optical axes of the beams reflected from the respective mirrors 30 . Thus, the prisms function as waveguides, each waveguide having a first reflective surface and a second reflective surface opposite the first reflective surface and parallel thereto. As a result, for most of their optical path, the optical beams are guided e.g. in a glass waveguide that has two reflective surfaces at the respective ends. The advantage of such arrangement over free space travel of the optical beams is that the respective optical paths of the light beams can be adjusted e.g. by varying the refractive indexes of the respective prisms/waveguides 34 . In one embodiment of the invention, illustrated in FIG. 3 , the structure has n prisms, the number corresponding to the number of output elements (collimators) and the input ports on the device 10 . The prisms are arranged in parallel and are of different length selected to reduce (left-hand part of FIG. 3 ) or expand (right-hand part of FIG. 3 ) the spacing between a plurality of optical beams outputted from the output devices (collimators) 18 . As further shown in the right-hand side of FIG. 3 , the arrangement of the invention can be reversed such that the relatively small spacing L2 of the optical beams emitted from the device 10 is converted, through an arrangement of first and second reflective surfaces, into a larger spacing L3, suitable to accommodate the spacing of receiving devices 40 . The above examples are for illustrative purposes and not intended to limit the scope of the invention which is to be interpreted solely by the appended claims. For example, the prisms 32 and 34 may be replaced by other optical elements having the respective reflective surfaces.