Nonclassical Optical Bistability and Resonance-Locked Regime of Photon-Pair Sources Using Silicon Microring Resonator

We generate correlated photon pairs in an all-pass silicon microring resonator using continuous-wave pumped spontaneous four-wave mixing and we characterize in detail the optical bistability in the nonclassical single-photon regime. Special attention is given to the resonance-locked method by balancing the pump-induced heating and the active off-chip cooling, leading to stable operation of the photon-pair source. The maximal coincidence rate of $20.53\pm 0.34\mathrm{Hz}$, maximal coincidence-to-accidental ratio of $654\pm 125$, and minimal zero-delayed heralded second-order correlation of $0.14\pm 0.09$ are achieved. The wavelengths of photon pairs remain unchanged at different pump power, indicating that our source is more compatible with the common communication systems than those using conventional on-resonance strategies, that tunes the pump wavelength. This work not only experimentally validates the nonclassical bistability behaviors, but also puts forward a simple method of pump-resonance matching for high-quality performance.

Figure 1

Schematic experimental setup: (a) pair source, (b) collection scheme, (c) detection for (1) pair rate, coincidence rate, coincidence-to-accidental ratio and (2) heralded second-order correlation. EDFA denotes the erbium-doped fiber amplifier; TBPF, tunable band-pass filter; ATT, tunable attenuator; PC, polarization controller; TCM, temperature-controlling module; FBG, fiber Bragg grating; and SPD, single-photon detector. (d) The transmittance of the investigated MRR: the pump, signal, and idler wavelengths are at $1549.78$, $1545.33$, and $1554.25\mathrm{nm}$, respectively. The FWHM of the resonance corresponding to the pump is $26\mathrm{pm}$.

Figure 2

The measured normalized transmittance versus the external temperature in the cooling process (a) and heating process (b), and the corresponding pair rate versus the external temperature in the cooling process (c) and heating process (d). The incident powers in the bus waveguide are $3.98\mathrm{mW}$ (red solid), $3.16\mathrm{mW}$ (blue solid), $2.51\mathrm{mW}$ (green solid), $1.99\mathrm{mW}$ (black solid), $1\mathrm{mW}$ (red dotted), $0.63\mathrm{mW}$ (blue dotted), $0.32\mathrm{mW}$ (green dotted), and $0.16\mathrm{mW}$ (black dotted), respectively.

Figure 3

(a) The output power and (b) the pair rate versus the input power, with an external temperature of $18.8{}^{\circ }\mathrm{C}$.

Figure 4

The measured raw coincidence counts $N_{\mathrm{cc}}$ (red circle) and accidental coincidence counts $N_{\mathrm{acc}}$ versus input power per minute. The fitted slope of $N_{\mathrm{cc}}$ at all powers, $N_{\mathrm{cc}}$ at low powers, and $N_{\mathrm{acc}}$ at all powers are 1.53, 1.91, and 2.74, respectively.

Figure 5

The CAR versus the input power. The inset is the temporal histogram at $P_p=1.99\mathrm{mW}$.

Figure 6

The heralded second-order correlation function $g_H^{(2)}(\tau )$ versus input power with zero delay (red diamond) and $25$-$\mathrm{ns}$ delay (blue circle), respectively. The inset is $g_H^{(2)}(\tau )$ versus the delay at $P_p=1.58\mathrm{mW}$.