Direct measurement of optical phase in the near field

To fully characterize photonic crystal guided wave optical devices, one needs to measure the spatial variation of both the phase and amplitude of the electromagnetic field. In this work, we simultaneously measure the intensity and phase in the near field of both propagating and evanescent fields by incorporating a scanning near-field optical microscope into one arm of a Mach-Zehnder interferometer. We demonstrate the technique by imaging the phase fronts of an evanescent wave formed by total internal reflection and by measuring the phase variation in the LP11 mode in an overmoded optical fiber. (C) 2000 American Institute of Physics. [S0003-6951(00)00405-8].