Multi-mode optical microcavities have enabled the emergence of compact optical sources such as parametric oscillators and nonlinear combs for quantum information and metrology. Efficient nonlinear interactions take place, owing to a combination of large Q factor, small modal volume and large material index. The control of the frequency spacing of the resonances is also a critical aspect.
Here we demonstrate an effective harmonic potential for photons owning to the concept of bichromatic lattice in a photonic crystal structure. Wide gap semiconductor material, i.e. GaInP, is used here to prevent any detrimental non-linear absorption such as two photons.
The experimental evidence is given through the statistical analysis of the frequency spacing of high-Q resonances over 68 cavities.
For each structure, the complex reflection spectra is measured using Optical Coherent Tomography (OCT) with a resolution of 20 MHz.
The dispersion of the resonator is extracted through a polynomial fit. It appears to be small and more importantly crosses zero as the radius of the holes is changed.
Moreover, each of these resonators have many modes, typically four, with loaded Q factor in the 10^5 to 7x10^5 range and intrinsic Q factor well above one million.
Equi-spaced resonances in a very compact structure should lead to ultra-strong nonlinear interactions, particularly resonantly enhanced Four Wave Mixing and parametric oscillation.
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