We demonstrate the fabrication of the helical
long-period grating (HLPG) in a two-mode fiber (TMF) with
CO2 laser. The torsion characteristics of the helical gratings
are experimentally investigated. It was found that the resonance
wavelength of the TMF-HLPG linearly shifts with a twist sensitivity
of 0.47 nm/(rad/m), which is an order magnitude higher
than that of the conventional long-period fiber gratings (LPFGs).
The temperature sensitivity of the TMF-HPFG was measured to
be 23.9 pm/°C, which is one third of that of the conventional
LPFGs. The proposed TMF-HLPG-based twist sensor would
have a promising application for the twist monitor.