a multiple - port optical device uses improved fiber ferrules comprising various capillary designs and shapes to precisely position optical fibers and , in particular , the optical fiber cores . the fibers are screened for geometric characteristics which further aide in precisely positioning the fiber cores . the ferrules , capillaries , fibers , and adhesives are combined to reduce adverse thermal effects and maintain the position of the fibers over a broad range of environmental conditions in which dwdm packages and modules are required to operate .