Dual-Comb Laser Interferometer for Temperature Independent Strain Sensing

We demonstrate experimentally a novel passively mode-locked dual comb interferometer source made from a single fiber laser cavity and capable of strain sensing. We have built a 10.1 m long ring laser cavity [1], [2], mode-locked using a carbon nanotubes saturable absorber, and featuring an in-cavity Mach-Zehnder interferometer (MZI) made with 2 m long fiber couplers (Fig. 1(a)). Slightly changing the length of one of the MZI arms with respect to the other creates two different optical paths inside the cavity. This results in interference between two mode-locked pulse trains. The interference pattern can be observed from the optical spectrum and consists of equally spaced peaks separated by about 0.715 nm (Fig. 1(b)). A similar multi-peak pattern with about 45.6 KHz spacing can be observed in Radio-Frequency (RF) domain (Fig. 1(c)).