Nonparaxial Fresnel diffraction from oblique end facets of optical fibers

摘要

When optical fibers are connected with other optical or opto-mechanical components, free space propagation phenomena of the light emitted from cleaved end facets of fiber need to be precisely known to maximize coupling efficiency. Besides, optical fibers are widely used in interferometers design as point-diffraction sources to replace conventional pinholes, in which case the far-field wave front of the light emitted from fibers is of major concern. End facets may be cleaved normal to the optical axis of fibers or with oblique angles to suit specific purposes such as anti-reflection or propagation direction alteration. In this investigation, diffraction from oblique end facets of single-mode fibers is studied with emphasis on Fresnel propagation in nonparaxial zones based on the Rayleigh-Sommerfeld scalar diffraction theory. The result is a closed-form explicit solution expressed in terms of spherical coordinates, which enables to determine the propagation field generated over an entire hemispherical observation surface. In comparison to exiting solutions of numerical or infinite series forms, the explicit solution obtained in this investigation saves a considerable amount of computation time and provides better estimation accuracy. Finally, as an example, the wave front sphericity emitted from an oblique single-mode fiber used in a new design of the Fizeau interferometer is determined and discussed in detail.