Optical fiber tip in front of a phase conjugator: focused light spot with inclusion of evanescent field contribution

 Within the framework of electric dipole approximation, the focused light spot produced by a tiny optical fiber tip in front of a phase conjugate mirror is investigated numerically. The fiber tip is the probe of a reflection scanning near field optical microscope and the incident light is guided through the fiber. Intensity distribution of local field is calculated in the half space where the fiber tip locates. Both homogeneous (q _‖≤ω/c ₀) and part of inhomogeneous (ω/c ₀<q _‖≤ωn/c ₀) fields are included in establishing a field propagator (Green’s function) which is employed to calculate the local field distribution. The local field forms at the tip position a diffraction light spot with a finite central value and a finite size, and when the tip-surface distance is sufficient small, the strength and the shape of the light spot become a function of the distance, which is due to the contribution of evanescent field. Fairly good agreements are found with the existing experimental reports. Received: 30 April 1996/Accepted: 19 August 1996