Fig. 1. (a) Dual-pump BS FWM working principle. When two pumps (P1 and P2) and a seeding signal (S) are input into a third-order nonlinear waveguide, BS FWM can occur under the assumption that the phase matching condition is fulfilled. In this scenario, photons are scattered from the signal S to two idlers (IBS,b and IBS,r), with a simultaneous energy exchange between the two pumps. The solid arrows indicate the loss (down) and gain (up) of the photon energy, while the dashed arrows indicate the direction of the energy exchange for the IBS,r (red) and IBS,b (blue) cases. (b) Graphical illustration of the phase matching mechanism for the BS-IM-FWM scheme. If P1 and P2 are placed in the TE00 mode and the signal and idlers in the TE10 mode of a multimode waveguide, the phase matching condition can be satisfied and retained if it is possible to draw a horizontal line that crosses the IGV curves of the two considered modes at the average frequencies (yellow dots in the figure) of the two pumps and of the signal and one idler (either IBS,b or IBS,r).

Fig. 2. Numerically simulated group index ng for the first two horizontal modes TE00 and TE10 as a function of wavelength λ and sketch of the cross-section of the Si-rich SiN multimode waveguide employed in this work (note that dimensions are not to scale).

Fig. 3. Simulated BS-IM-FWM normalized CE for different P2 and S detuning values for (a) IBS,b and (b) IBS,r. The P1 wavelength was set equal to λP1=1540  nm for all the considered cases. The phase matching wavelength for the signal S is λS=1600  nm (which corresponds to a signal-detuning equal to zero).

Fig. 4. Schematic layout and working principle of the fully integrated intermodal FWM-based wavelength converter. P1, pump 1; P2, pump 2; S, signal; MMI, multimode interference coupler; PS, phase shifter; Y-junct, Y-junction; mode-MUX, mode converter and multiplexer; wg, waveguide; mode-DEMUX, mode converter and demultiplexer.

Fig. 5. Schematic layout of the fabricated device along with top-view SEM images of (a) MMI, (b) PS and Y-junction sections of the mode-MUX and (c) an optical microscope image of the full mode-DEMUX and output section.

Fig. 6. Linear characterization of the full device: measured transmission curves as a function of wavelength for the different combinations of input–output ports.

Fig. 7. Sketch of the experimental setup used in the nonlinear experiments. P1, pump 1; P2, pump 2; S, signal; EDFA, erbium-doped fiber amplifier; FA, fiber array; OSA, optical spectrum analyzer. The inset shows a microscope image of the optical coupling between the input FA and the on-chip integrated device.

Fig. 8. (a) Experimentally measured CE for the IBS,r (red diamonds) and IBS,b (blue squares) idlers and corresponding numerically simulated CE (red and blue dashed lines, respectively) as a function of the P2 detuning with P1 and S wavelengths fixed at 1540 and 1600 nm, respectively. (b) Experimentally measured CE for the IBS,r idler as a function of the signal wavelength λS for a P2 detuning of 2 nm (red diamonds, pump-to-pump detuning ΔλPP=2  nm) and 30 nm (green squares, ΔλPP=30  nm) and corresponding numerically simulated CE (red and green dashed lines, respectively), with P1 wavelength fixed at 1540 nm.

Fig. 9. Optical spectra measured at port 4 for P2 detuning values ΔλPP of (a) 2 nm, (b) 26 nm and (c) 76 nm. The wavelengths of P1 and S are set at 1540 and 1600 nm, respectively.

Fig. 10. Schematic view of the left side of the integrated wavelength converter with the parameter names used to indicate the device dimensions. MMI coupler, multimode interference coupler; PS, phase shifter; MM waveguide, multimode waveguide.