Fig. 2

Demonstration of \(p\)-orbital topological corner states in a photonic BKL. a1, a2 Experimental BKLs in the nontrivial (a1) and trivial (a2) regimes. b1, b2 Zoom-in interferograms of the probe beam with a reference plane wave, showing the out-of-phase relation between the corner site 1 and its NNN site 3 for both \({p}_{x}\)- (b1) and \({p}_{y}\)-type (b2) orbital excitations. The white ellipses identify the three-dipole probe beams, where the plus/minus signs represent \(0/\pi\) phases for each dipole, and dashed straight lines are added to see the phase structure from the shifted (b1) and the aligned (b2) interference fringes, confirming the staggered phase structures (see also numerical results in right insets). c1, c2 Observed output intensity patterns in nontrivial (c1) and trivial (c2) BKLs stemming from a \({p}_{x}\)-orbital corner excitation. d1, d2 Numerical simulations corresponding to (c1, c2). Results from a \({p}_{y}\)-orbital corner excitation are shown in (e1, e2) and (f1, f2). Grey circles in (c1–f2) mark the BKL sites. Lattice parameters are \({d}_{1}=\) 39 μm and \({d}_{2}=\) 31 μm for \(p\)-orbital excitation in the nontrivial BKL. Note the zero amplitude at the nearest-neighbor site 2 in (c1–f1)