Linear and triangle order of NX3 optical directional couplers: variation coupling coefficient

Abstract

Fabrication of single-mode fiber coupler has widely expands. However, directional fiber coupler geometry always affects the power propagation either two or three ports. This paper describes power launching by NX3 single mode fiber, examined using a matrix transfer for linear and triangle order, calculated from the eigenvalue and the eigenvector. This eigenvalue is referred to the coupling coefficient, where it can be expressed as an effective power transmitted to another fiber. The ratio of coupling coefficient between adjacent axial fibers varies, which can be achieved by adjusting separation of fiber and refractive index of core and cladding. A calculation has been shown in 3D that both power transmission and phase are affected by not only the geometry order, but also the variation of coupling coefficient, assuming the propagation constants, cross section, and separation of coupling length fiber axis are held constant. This calculation can be applied for any sources of wavelength and junction.