Optical return loss of angled-facet waveguides by rotation and power overlap of the guided modes

Optical reflection is an important concern in all commercial optical systems because of their potential performance degradation effects. Various approaches are employed to minimize the reflections in the optical couplings/connections, such as anti-reflective (AR) coating, index-matching fluids, and angled surfaces/facets. This manuscript investigates the Optical Return Loss (ORL) of different kinds of angled-facet waveguides using the power overlap between the incoming mode and the reflected one. We present a novel and straightforward analytic method to analyze the reflectance of tilted-facet waveguide modes with the advantage of no analytical approximation of the guided modes profiles that can be used to design integrated photonic waveguides. The dependence of the reflectance on the Mode Field Diameter (MFD) of optical fibers is examined. It is shown that an angle of \(6^{\circ }\) $6^{\circ }$ is sufficient to get an ORL of \(-50\) $-50$ dB for an SMF-28 optical fiber. For High Numerical Aperture (HNA) fibers, an angle greater than \(15^{\circ }\) ${15}^{\circ }$ is necessary to achieve \(-25\) $-25$ dB. In silicon photonics edge couplers, the reflectance is \(-25\) $-25$ dB when the coupler is \(15^{\circ }\) ${15}^{\circ }$ tilted for the Transversal Electric (TE) polarization. Finally, the mode reflectance of a typical edge-emitting diode laser is also calculated for a tilted interface in two directions, and a dramatic difference between the reflectances is noticed, which is caused by the mode asymmetry.