Fig. 1. Schematic diagram of superresolution interferometry principle. (a) Birefringence MZI. (b) Nonlinear birefringence MZI including SHG process. (c) Birefringence MZI with KTP crystal rotation angle δ. (d) Nonlinear birefringence MZI with KTP crystal rotation angle δ. The interference curve on the right side of the interferometer represents a simplified simulation schematic based on the KTP crystal parameters from Ref. [13] at the wavelength of 1550 nm.

Fig. 2. Experimental setup for superresolution measurement. FC, fiber collimator; HWP, half-wave plate; DHWP, dichroic HWP; PBS, polarizing beam splitter; DPBS, dichroic PBS; KTP, potassium titanyl phosphate crystal; PPLN, periodically poled lithium niobate crystal; BBO, β-barium borate crystal; DM, dichroic mirror; BPF, 390-10 nm bandpass filter; OPM, optical power meter.

Fig. 3. Interference beating versus temperature for the FW, SH, and FH. The panels on the left (from top to bottom) represent the FW cases at rotation angles of δ = 0, π/6, π/3, π/2. The panels on the middle and right represent the corresponding interference results of the SH and FH, respectively. Different offsets in each of the interference fringes come from different initial phases between the two arms of the interferometer.

Fig. 4. Power conversion efficiency of the (a) first and (b) second polarization-independent SHG modules.