Observation of temporal optical solitons in a topological waveguide

Abstract

Photonic topological systems may be exploited in topological quantum light generation, the development of topological lasers, the implementation of photonic routing systems and optical parametric amplification. Here, we leverage the strong light confinement of an ultra-silicon-rich nitride (USRN) topological waveguide adopting the 1D Su-Schrieffer-Heeger (SSH) system with a topological domain wall. We present the formation and propagation of temporal optical solitons in the topological waveguide, exhibiting two-fold temporal compression. We further observe a saturation in the output power at sufficiently high input powers. It is further observed that pulse propagation through a trivial, non-topological waveguide does not lead to similar temporal soliton dynamics. The demonstrated topological system allows for the temporal compression to be manipulated through power tuning via topological control of delocalization of the topological mode. This design degree of freedom allows temporal solitons to be generated in a topological waveguide while providing straightforward control of temporal pulses in practical applications.

Fig. 1

(a) Energy band, (b) the mode shape for the boundary state (red dot) in Fig. 1a, and (c) spatial amplitude evolution for the center waveguide input at low peak power. (d) Energy band, (e) the mode shape for the boundary state (red dot) in Fig. 1d and (f) spatial amplitude evolution at high peak power; The red circle in the energy band corresponds to the topological boundary mode. For the amplitude propagation, the blue line represents the central waveguide (domain wall), the red line is for nearest neighbour waveguide and the green line is for next neighbour waveguide.

Fig. 2

(a) The schematic of the topological waveguide with a domain wall (The light comes in and out at the center waveguide called a domain wall). W = 600 nm is the width of USRN waveguides. The gap between the waveguides, G_w = 0.15 μm for the narrower gap and G_v = 0.25 μm for the wider gap. The inset shows a scanning electron micrograph of the topological waveguide where the scale bar corresponds to a length of 100 nm. (b) Measured output power as a function of input coupled average power. The red line depicts theoretical calculation using the nonlinear Schrödinger equation. (c) Reduced power factor (η) as a function of input coupled peak power.

Fig. 3

(a) GVD, (b) TOD (red line) and FOD (blue line) at a wavelength of 1550.1 nm, used in the numerical modelling of the SSH device. (c) and (d) are the evolution of temporal traces for the peak power of the lowest (5.58 W) and the highest (45.3 W) along propagation, respectively. T₀ = T_{FHWM_}/1.76 (for sech² pulse), where T_{FHWM_} is the input FWHM of 0.93ps.

Fig. 4

(a) Experimental and (b) theoretical temporal traces at the output as a function of peak power. Experimental traces are obtained by applying the deconvolution factor on the autocorrelation traces to compare the pulse FWHM between the theoretical and experimental ones. The black dashed line in Fig. 3a depicts the input pulse. (c) Experimental pulse FWHM (empty circles) are compared with the theoretical ones (black line) on peak power. (d) The compression factor (F_c) of experimental (black triangles) and theoretical (red line) are compared as a function of peak power.

Fig. 5

Nonlinear optical properties of non-topological waveguide. (a) Measured output average power as a function of input peak power. (b) Experimental autocorrelation trace at the output (orange line), which is compared to the input autocorrelation trace (black line).