Frequency-Multiplexed Photon Pairs Over 1000 Modes from a Quadratic Nonlinear Optical Waveguide Resonator with a Singly Resonant Configuration

We demonstrate a frequency multiplexed photon pair generation based on a quadratic nonlinear optical waveguide inside a cavity which confines only signal photons without confining idler photons and the pump light. We monolithically constructed the photon pair generator by a periodically poled lithium niobate (PPLN) waveguide with a high reflective coating for the signal photons around 1600 nm and with antireflective coatings for the idler photons around 1520 nm and the pump light at 780 nm at the end faces of the PPLN waveguide. We observed a comblike photon pair generation with a mode spacing of the free spectral range of the cavity. Unlike the conventional multiple resonant photon pair generation experiments, the photon pair generation was incessant within a range of 80 nm without missing teeth due to a mismatch of the energy conservation and the cavity resonance condition of the photons, resulting in over 1000-mode frequency multiplexed photon pairs in this range.

Figure 1

Our experimental setup for photon pair generation. DM2 reflects the 780-nm light and transmits the telecom photons. FC is a fiber coupler.

Figure 2

(a) Reflectances of the coating at the surfaces of lithium niobate samples coated at the same batches for the PPLN waveguide. The inset shows the reflectances for around the pump wavelength. The orange and the blue curves are for the back and the front ends of the PPLN, respectively. (b) Observed power of the light passing through the PPLN-QNWR for 1600, 1580, and 1560 nm light from the top. The gray lines describe voltages applied to the ECDL for the wavelength sweep. Each peak is fitted by a function $A[(f-f_0{)}^2+({\gamma }_f/2{)}^2{]}^{-1}+d$ with fitting parameters $A$, $f_0$, ${\gamma }_f$, and $d$.

Figure 3

Observed coincidence counts with the filter bandwidths of 1 nm. The wavelengths of the signal and the idler photons are (a) 1600 nm and 1522 nm and (b) 1580 nm and 1540 nm. (c) The case of the degenerated photon pair around 1560 nm. The non zero values of the minimum of the fringes is caused by the timing jitter about 80 ps of the SSPDs.

Figure 4

The coincidence counts with exponential decay (rising) described by blue (orange) show the signal (idler) photon counts heralded by the idler (signal) photons of the photon pair. The measurement was performed with the bandwidths 0.03 nm of the BPFs.

Figure 5

$g^{(2)}$ vs pump power. The blue circles are about signal photons heralded by idle photons, and the orange triangles are about idler photons heralded by signal photons.

Figure 6

Pump dependencies of single counts of signal photons (blue circles) and idler photons (orange triangles), and coincidence counts when signal (idler) photons are used as start of TDC which are plotted by blue circles (orange triangles).

Figure 7

Observed single counts. The bandwidth of the BPF is set to 3 nm.