Displacement actuator controlled by a femtosecond comb and Fabry-Perot cavity in the feedback

The work is scoped to application of the passive optical resonator as a length sensor which determines the distance changes driven by a piezoelectric actuator. The exact value of generated distance changes is derived from the optical absolute frequency of femtosecond comb modes. A single frequency tunable DFB laser with a narrow line-width is phase locked to a nearest “tooth” of the femtosecond comb spectrum. Then the length of the optical resonator cavity is locked to the optical frequency of this tunable DFB laser. Thanks to possibility of additional rf frequency mixing with the DFB laser and tooth frequency beat-note, the length of the cavity can be determined at any displacement step. The comparison record of the actuator and a tested homodyne interferometer scales is done for 650 nm displacement range.