Figure 3. Schematic overview of the measurement setup for comparing distance measurement up to 50 m with a counting helium-neon laser and a frequency comb.

The comb light is delivered to the setup with a single mode (SM) fiber, providing a clean mode profile. Both the HeNe laser (orange line) and comb laser (red line) measure the displacement quasi-simultaneously. PBS: polarizing beam splitter, POL: polarizer, λ/2: half-waveplate, CCD: charge-coupled device camera, M: planar mirror, RR: hollow retro reflector, CL: cylindrical lens (100 mm focal length), SL: spherical lens (400 mm focal length).