One of the key tasks in integrated photonics is the separation or demultiplexing of multiple different wavelength channels that are transported through the same waveguide.
One way to separate different wavelength is to use refraction in a prism and the photonic crystal community has taken this further, developing superprism. A superprism is a prism, but with stronger refraction than possible from the normal refractive index difference and so it can get a better wavelength separation in a smaller footprint.
In our work, we have now demonstrated a flat-band superprism that has a particularly constant refraction. So different wavelength channels, with a fixed wavelength spacing, will exit our superprism with almost identical spacing, making subsequent collection and processing easier.