**2.3 Spatial field distribution**

332 Photonic Crystals – Innovative Systems, Lasers and Waveguides

1580 nm to 1615 nm, where the interference transmission is rather constant (red curve in Figure 4b) with ~ 14dB transmission difference between the two domains. In the next

Fig. 3. **Band diagram of the PhC and the calculated effective index. a,** Band diagram of the PhC with the parameters given in Figure1. Insets: first Brillouin zones of the hexagonal PhC (top) and the 1D superlattice (bottom). The TM-like (TE-like) photonic bands are depicted in blue (darker) [red (lighter)]. The light cone is denoted by the green lines. **b,** A zoom-in of the

spectral domain corresponding to experimental region of interest. Experiments were performed in the spectral region marked by the two horizontal lines. **c,** Calculated effective index of refraction of the PhC, corresponding to the two TM-like bands shown in Figure2b. Insets: zoom-in of the two bands. **d,** Black (solid) line: MZI transmission with 100 unit cells of PhC on one arm and an homogeneous slab waveguide on the other arm. Red (dashed)

line: transmission spectrum for non-MZI PhC superlattice with

60 unit cells.

section, we show high spatial resolution images for this experiment.

In addition, we performed high spatial resolution imaging of the radiated input-output ports for the devices that have been used for the experiment presented in Figure 4. Results are illustrated in the Figure 5 as follows: In the case of the reference arm (**i-iii)**, we see light transmission for all three wavelengths, which corroborates the characteristics of the transmission spectrum in Figure 4b. For the device arm (**iv-vi**) there is transmission for 1600 nm and 1530 nm but not for 1570 nm. This agrees with the transmission spectra in Figure 4b. Note that although there is similar transmission for both arms at 1530 and 1600 nm, the interference output has 14dB difference.
