OPTICAL MODE TRANSFORMER, IN PARTICULAR FOR COUPLING AN OPTICAL FIBER AND A HIGH-INDEX CONTRAST WAVEGUIDE

摘要

A semiconductor-based optical mode transformer (100, 100, 100 ') is described for coupling an optical mode of an optical fiber (3) with an optical mode of a waveguide (2a). The optical mode transformer comprises a first waveguide (1a) extending along a first main longitudinal direction (Z) and including an end facet (9) being apt to be coupled to the optical fiber (3), said first waveguide (1a) including a first core (1) and a first cladding (6,4)and having a first refractive index contrast (?n1); and a second waveguide (2a) arranged with respect to said first waveguide so as to realize an evanescent optical coupling with said first waveguide (1a), the second waveguide (2a) comprising a second core (2) and a second cladding (4,7) and having a second refractive index contrast (?n2). In addition, the second core (2) comprises a tapered region (13,13 ), in at least a portion of which said evanescent coupling takes place. The first core (1) of the first waveguide (1a) and the second core (2) of the second waveguide (2a) are separated by a gap (g). The thickness (T2) of said second waveguide (2a) is comprised between 120 nm and 180 nm and the second refractive index contrast ?n 2is greater than 40%, or the thickness (T2) of said second waveguide (2a) is comprised 100 nm and 400 nm and the second refractive index contrast ?n2 is comprised between 18% and 30%. The first refractive index contrast is smaller than the second refractive index contrast.