Compact linearly uncoupled resonators for efficient spontaneous parametric downconversion via angular phase matching

Abstract

We report an integrated platform for efficient second-order nonlinear interactions based on linearly uncoupled resonators and angular phase matching. The proposed architecture confines phase control to a limited section of the device, maximizing field enhancement and effective nonlinear interaction length while simultaneously reducing the overall footprint. As an example we show the results for an AlGaAs-on-insulator structure demonstrating a photon-pair generation rate of 3.16 GHz/mW in the continuous-wave regime and 5.89 MHz under pulsed pumping. The generated biphoton state exhibits a Schmidt number K=1.02, indicating nearly uncorrelated photon pairs. The compact and reconfigurable nature of this approach, together with its independence from material-specific poling techniques, makes it applicable to a broad class of integrated $χ_2$ nonlinear platforms.

Figures (4)

• Figure 1: Sketch of the proposed structure. In the inset we show the field distributions for the TM mode at 775 nm and the TE mode at 1550 nm.
• Figure 2: Coupling coefficients of the DC, for the fundamental harmonic (FH, red) and second harmonic (SH, green) as a function of the coupling length.
• Figure 3: Calculated field enhancement for (a) the SH and (b) the FH. Insets show the device sketch and the regions where the optical fields are evaluated. Dark green (a) and red (b) solid lines indicate the field enhancement in the outer right arm, while light green (a) and purple (b) lines correspond to the inner right arm for FH and to the outer right arm for SH. The vanishing field in these sections confirms the expected behavior of the DC and the effective confinement of the SH field in Resonator 1.
• Figure 4: Plot of $|\phi(\lambda_1,\lambda_2) |^2[pm^{-2}]$ for the SPDC process in the proposed resonant structure. The color encodes the cosine of the phase. The calculation assumes a Gaussian pump pulse with a temporal length of 49ps, a pulse energy of $1.22pJ$, and repetition rate of 10MHz. The resulting spectral decomposition yields a Schmidt number $K = 1.02$, indicating nearly uncorrelated photon pairs.