The scanning near-field optical microscope (SNOM) is well known as a tool for observing nano-structures. On that account, a SNOM to which a certain magneto-optical (MO) measurement technique is applied, or MO-SNOM, is likely to become a powerful tool for nanometric studies on magnetism. In our study, a transmission-illumination mode SNOM with a bent optical fiber probe, which operates as a cantilever in atomic force microscopy (AFM), was employed. Incorporation of the polarization modulation technique into this system has made it possible to resolve magnetic structures with a high sensitivity of up to 1 mrad and a resolution of approximately 1/5 times the wave-length of the light source (argon ion laser: 488 nm). The behavior of polarized light in the probes, however, prevents quantitative analysis of MO effects. This paper describes an investigation into the polarization properties of the bent optical fiber probes, based on their Stokes parameters. A method for acquiring pure signals dependent on ellipticity or rotation in MO imaging is presented.
