  We investigate intermodal forward Brillouin scattering in a solid-core PCF,
demonstrating efficient power conversion between the HE11 and HE21 modes, with
a maximum gain coefficient of 21.4/W/km. By exploring mechanical modes of
different symmetries, we observe both polarization-dependent and
polarization-independent intermodal Brillouin interaction. Finally, we discuss
the role of squeeze film air damping and leakage mechanisms, ultimately
critical to the engineering of PCF structures with enhanced interaction between
high order optical modes through flexural mechanical modes.
