Measurement of the local optical phase and amplitude in photonic devices using scanning near-field microscopy

摘要

This thesis presents the optical characterisation of various photonic devices using scanning near-field microscopy (SNOM). The SNOM technique has a unique capability of achieving a resolution beyond the diffraction limit. Placing the SNOM into the arm of a heterodyne interferometer also enables the measurement of both the optical phase and amplitude in the near infrared. In this work three different photonic devices are investigated. The optical field distribution within a fibre Bragg grating is investigated as a function of wavelength. This work details the direct observation of the spatial shift of the standing wave across the stop band of a fibre grating. The shift is an explicit feature of fibre Bragg gratings and has previously only been theoretically predicted. The thesis also details three analytical techniques for measuring the microscopic loss of planar or channel waveguides. Two of the techniques are experimentally tested. The techniques exploit a standing wave generated within the waveguide, the visibility of the standing wave provides sufficient information to determine to loss between two points. The present limitations of the techniques are presented. The SNOM technique has also been applied to the measurement of a large mode holey fibre. The work details the accurate characterisation of the mode at the end face of the fibre and as it propagates into free space. The results are compared to theoretically predicted modes.