Fig. 1. (a) Geometric of the prepared Z-cut PPMgLN waveguide with a poling period of 10.2 μm, where w= 11.2 μm, h₁ = 10.9 μm, h₂ = 0.5 μm, and θ = 75.1°. (b) Characteristic mode profiles of the SFG light at 25°C, described by the y-component of the electric field, where the arrows indicate directions of the electric field. (c) Effective indices for the TM modes of the SFG light, as the functions of the waveguide temperature. (d–f) Theoretical conversion efficiencies (CEs) by coupling among TM₀₀, TM₀₁, TM₁₀, and TM₁₁ modes of the high-intensity pump and signal lights for the SFG lights with (d) TM₀₀. (e) TM₀₁, and (f) TM₁₀ modes, respectively. (g) Predicted temperature conditions for producing the TM₀₀ (F⁰⁰, cyan area), TM₁₀ (F¹⁰, red area), and TM₀₁(F⁰¹, blue area) modes of the SFG light by comparing the maximum CE.

Fig. 2. (a) Schematic of the temperature/wavelength-dependent spatial mode steerable SFG device. (b) In the temperature steering scheme, the detected up-conversion lights with (i) TM_01, (ii) TM₁₀, and (iii) TM₀₀ modes at 30°C, 40°C, and 60°C, respectively, on a white broad. (c) In the wavelength steering scheme, the detected SFG lights with (i) TM₀₀, (ii) TM₀₁, and (iii) TM₁₀ modes at 597.46, 597.99, and 598.41 nm, respectively, on a white broad. (d) Microscope image of the fabricated PPMgLN waveguide array on an LT wafer (Inset: detail profile of the third waveguide). (e) Cross-section view of the fifth waveguide selected in the experiments. (f) The fabricated polling structure with a period of 10.2 μm. EDFLs, Erbium-ion doped fiber laser system; SM LD, single-mode fiber-coupled diode laser; WDM, wavelength division multiplexer; CLEN, collimating lens; ASL, aspherical lens; TEC, thermoelectric cooler.

Fig. 3. Characterizing the temperature-dependent spatial mode steering scheme in the SFG waveguide. (a) Power curves of the waveguide at typical temperatures of 35 °C, 45 °C, 55 °C, and 65 °C. (b) Evolution in SFG power under the maximum incident pump power of 27.8 dBm, in which the gray color denotes the regions without clear TM₀₁, TM₁₀, or TM₀₀ modes. (c) Experimental efficiency (η_exp = 100·P_F/P_P/P_S) and theoretical efficiency (η_cal = max(η_F^jk, η_F^jk, η_F^jk)) of the inter-mode up-conversion process. (d) Temperature windows for preparing mode TM₀₁, TM₁₀, and TM₀₀, where state1 and state2 denote the transition process from TM₁₀ to TM₀₁ and TM₀₁ to TM₀₀, respectively. (e) Mode profiles captured by the CCD camera to tell the exact modes during rising the waveguide temperature. (f) Evolutions in the SFG wavelength during the spatial mode steerable SFG process.

Fig. 4. Transition states from two-mode coupling (first state), three-mode coupling (second state), to quasi TM₀₀ mode (third state). (a–c) Evolutions of the (a) inter-mode QPM efficiency (sinc(ΔKL/2)), (b) integral, and (c) conversion efficiency for TM₀₀, TM₁₀, and TM₀₁, respectively. (d–f) Typical mixing mode pattern in the (d) first state, (e) second state, and (f) third state, respectively, where the upper picture is experimentally captured by a CCD camera, and the bottom picture is reproduced based on Eq. (3) with I= |E_F|².

Fig. 5. Characterizing the wavelength-dependent spatial mode steering scheme in the SFG waveguide. (a, b) The changed SFG wavelength by increasing the signal wavelength from 1546 to 1556 nm: (a) spectral profiles, (b) fitted slop rate Δλ_P/Δλ_S = 0.14; (c) at waveguide temperature of 25 °C, the evolution of the spatial mode from TM₀₀ to TM₁₀, TM₁₀ to TM₀₁, and TM₀₁ to TM₁₀.

Fig. 6. (a) Evolution in SFG power at varied waveguide temperature under an incident pump and signal powers of 25.1 and 27.8 dBm, respectively, where characterized regions for the TM₀₀, TM₀₁, and TM₁₀ modes are denoted with cyan, red, and blue colors, respectively. (b) Wavelength windows for preparing the spatial mode during red shifting the SFG wavelength.