Fig. 1. Numerical simulations of poling period for different types and orders of QPM processes. The four named lines Λ_ZZZ, 3Λ_ZZZ, Λ_YYZ, 3Λ_ZYY represent type-0 first-order QPM (ZZZ), type-0 third-order QPM (ZZZ), type-II first-order QPM (YYZ), and type-I third-order QPM (ZYY), respectively. Λ = 8.95 µm represents the poling period of the PPKTP crystal used for experimental testing.

Fig. 2. Experimental setup for testing various QPM processes. QWP, quarter-wave plate; HWP, half-wave plate; SMF, single-mode fiber; FC, fiber collimator; DM, dichroic mirror; L1–L3, lenses; F, filters; PM, power meter; PPKTP, periodically poled potassium titanyl phosphate.

Fig. 3. Measurements of temperature phase matching and generated multi-color laser. (a)–(c) Temperature tuning curve of PPKTP crystal for different types and orders of QPM processes: (a) type-0 first-order QPM for SHG of 1063.8 to 531.9 nm; (b) type-0 third-order QPM for SHG of 783.9 to 391.95 nm; (c) type-II first-order QPM for SHG of 796.94 to 398.47 nm. (d) Photo of an RGB laser beam is obtained by splitting the multi-color laser beam with a visible grating.

Fig. 4. Measured spectrum of the multi-color lasers that are composed of different QPM processes.