To provide a light transmitting material which has high transmission at wavelength ranges used for communication and excellent characteristic properties such as heat resistance, water resistance and chemical resistance, and makes it possible to produce a grating and incorporate it in a mounting module with ease. The second winding axis is orthogonal to the first winding axis. The temperature during growth is in the range of \u2212100\xb0 C. In an embodiment the derotating optical element comprises a Dove prism. After successful verification of all connections and catheter integrity, the algorithm allows the power control system to output power signals for ablation therapy.