Question

2πc/15
a) 24
b) 12
c) 18
d) 36
​

Answer 1

Step-by-step explanation:

An anomalous dispersion for modes of a material resonator is highly desired to form frequency combs. A resonator free-spectral-range (FSR) controlled by shape so as to increase with frequency ω/2π compensates the normal index dispersion ∂n/∂ω > 0, producing evenly spaced resonances. Only special shapes achieve this scope. We show here that broad periodic corrugated waveguides working at Littrow regime feature such an increasing trend ∂FSR/∂ω > 0. We outline experimentally this trend on silicon-on-insulator devices designed for 45° Littrow operation. We predict dispersion-free silicon-based designs across the 1.4–4.0 μm mid-infrared range.