Fig. 2: Design and fabrication of coupled nanolasers.

a A schematic of the photonic molecule laser under investigation. It consists of two coupled photonic crystal nanocavities. The coupling strength between the two cavities can be controlled by changing the radii of the nanoholes that lie exactly at the center between the two cavities. This changes the resonant frequencies as well but by the same amount in both cavities. In turn, the individual cavity frequencies of the cavities are independently tuned by changing the size of a neighboring hole (highlighted in yellow close to cavity 1). Finally, two pump beams with different intensities providing pump rates P_1,2 are used to provide unequal gain for the two nanocavities. b SEM image of the fabricated sample: the material is InP with embedded InGaAsP quantum wells. The lattice constant a = 430nm, r₀ = 0.266a, h = −0.25 and d = −0.1. The coupling is controlled by the barrier between two cavities, which is displayed in an orange dashed box (r_b = (1 + h)r₀). The yellow hole is the detuning hole (r_d = (1 + d)r₀). The brown boxes indicate engineered holes to improve the beaming quality of the radiated photons (r_beaming = r₀ + 0.05a). The overlaps between the beaming holes and the barrier, colored in red, have radii of \({r}^{{\prime} }={r}_{{{{{{{{\rm{beaming}}}}}}}}}(1+h)\). c Detuning as a function of radii d. Fabrication imperfections are dominant for d > 0; therefore, we restrict our studies to the range of −0.2 ≤ d ≤ 0, where the cavity detuning is well-controlled by design.