Selective mode excitation and discrimination of four-core homogeneous coupled multi-core fiber.

Coupled modes of homogeneous coupled multi-core fiber are selectively excited and discriminated utilizing the difference of equivalent propagation angle. To quantatively evaluate the extinction ratio (selectivity) of adjacent modes, a new mode discrimination technique is developed by measuring the visibility of far-field patterns under small change of wavelength of the launching beam. The peak angles of discriminated far-field patterns show a strong correlation with the incident angle of the launching beam, which means that the coupled modes were selectively excited and discriminated.