Direct near-field phase measurements of lensed fiber employing a single-mode fiber interferometer

A method of direct measurement of near-field wavefront and intensity distribution of lensed fiber employing a single-mode fiber interferometer is proposed and demonstrated. The wavefront of lensed fiber showed a curved wave with the radius of curvatures from 8 to 32 μm at various locations along the z axis. The wavefront radius of curvatures of laser diode and lensed fiber were in good agreement with each other that the similar curved wavefront distributions between laser and lensed fiber was mode matching, results in high coupling from laser to fiber. Detailed measurements of the near-field phase and intensity distributions of laser and fiber are essential for micro-optic design with better mode matching to achieve efficient coupling.