Fig. 2. Design and characterization of key components.

a 3D view of the tunable delay line. b Microscope image of the testing structure. c Measured transmittances (|t|²) at varying wavelengths (λ) when different voltages were applied. d Measured first- and second-order tuning efficiencies (∂n_g/∂P, ∂²n_g/∂P²). e 3D view of the adiabatic directional coupler (ADC). f Calculated conversion efficiencies of symmetric (S) and anti-symmetric (AS) modes with varying coupling lengths (L_ADC). g Upper panel: microscope image of the fabricated testing structure. The arrows indicate the locations of ADCs. Lower panel: Measured |t|² at varying λ. h Calculated and measured coupling ratios (|κ_ADC|²) of the ADC. i 3D view of the Y-branch splitter (YBS). j Calculated conversion efficiencies with varying coupling lengths (L_YBS). k Upper panel: microscope image of the fabricated testing structure. The arrows indicate the locations of YBSs. Lower panel: Measured |t|² at varying λ. l Calculated and measured coupling ratios (|κ_YBS|²) of the YBS. In the calculation, the central core is shifted by Δy = 10 nm.