Correlated-photon-pair emission from a cw-pumped Fabry-Perot microcavity

We study a dispersion-compensated high-finesse optical Fabry-Perot microcavity under high-intensity cw pumping. The Kerr nonlinearity in the optical coatings causes a spontaneous four-wave mixing process, which leads to the emission of time-correlated photon pairs. The photon frequencies are shifted by $\pm 1$ free spectral range relative to the pump frequency. This setup allows for constructing a photon-pair source with precisely adjustable frequency difference between the emitted photons, which may have applications in quantum communication.

Figure 1

(a) Setup of the Fabry-Perot cavity consisting of a machined and coated end facet of an optical fiber and a conventional mirror in an ultrahigh vacuum chamber. The outcoupled light is dispersed by a grating spectrometer and photons of the two longitudinal modes ${\omega }_{1,\pm }$ adjacent to the pump mode $\omega$ are guided to single photon counters. Further filtering is performed by narrow-linewidth interference filters (IF). (b) Simulation of the laser field in the optical coating. Light gray: ${\mathrm{SiO}}_2$; dark gray: ${\mathrm{Nb}}_2{\mathrm{O}}_5$. Since the Kerr coefficient for ${\mathrm{Nb}}_2{\mathrm{O}}_5$ is more than one order of magnitude larger than that of ${\mathrm{SiO}}_2$, the main effect results from the second layer of the coating. (c) Sample of pair correlations.

Figure 2

(a) Determination of the zero dispersion of the cavity. Shown is the frequency difference between the higher and lower free-spectral range of the cavity. The zero crossing denotes the pump frequency for which the cavity dispersion disappears. (b)–(g) Optical bistability by absorption in the mirrors. The top row shows the scan from blue to red detuning and the bottom row shows the scan from red to blue detuning for the following intracavity powers: (b)/(e) 700 mW, (c)/(f) 7 W , and (d)/(g) 14 W.

Figure 3

Sample trace of detected photon pair correlations (binning $\mathrm{\Delta }\tau =250\mathrm{ps}$). Data are taken for an intracavity power of 19 W.

Figure 4

(a) Pair correlations vs pump intensity. The solid line is a quadratic fit to the data to extract the pair generation efficiency. (b) Width of the pair correlation peak vs pump intensity. The dashed line indicates the lifetime of the photons in the cavity. The hollow points in both plots signal the data set shown in Fig. 3.