Fiber optic directional coupler

Claim 1

In a method of making a fiber optic directional coupler, the steps of: providing two unitary blocks of rigid material with first and second parallel planar faces; forming a slot across the first face of each of the blocks, each said slot having a greater depth towards the edges of the blocks than towards the center of the slot; mounting a strand of single mode fiber optic material in each of the slots so that the strand extends along a path corresponding to the bottom wall of the slot, said fiber optic material having a core and a cladding; removing material from each of the strands and the first faces of the blocks in a planar fashion to form a cutaway portion on each strand, said removing continuing until the cladding of each strand is within a few microns of the core in the center of the slot and no material is removed from the strand at the edges of the block; determining the location of the core beneath the cladding at the cutaway portion during said removing step, said determining step comprising: measuring the size of the cutaway portion of each strand; and measuring the thickness of the blocks, between the first face and the second face to locate the core during the removal of the material from the blocks and strands, the step of measuring the size being performed prior to the step of measuring the thickness; and placing the blocks together with the first faces in facing relationship and the cores of the strands in close proximity to each other where the cladding has been removed to form a region in which guided modes of the strands interact through their evanescent fields to cause light to be transferred between the cores of the two strands.