Single-photon optical nonlinearity using electronic avalanche multiplication process.

Light–light interactions play a critical role in a variety of photonic applications spanning fields such as telecommunications, microscopy, computing, and quantum optics. However, generating such effects at the single-photon level, where a single photon can significantly affect a larger light beam, remains a challenging task. Single-photon nonlinearity has been demonstrated using optical or photonic cavities tightly coupled to atoms, quantum dots, other single-photon emitters, and polaritons. However, achieving high-speed, single-photon, all-optical modulation at room temperature over a wide wavelength range remains a difficult task.

One of the approaches for high-intensity modulation involves the injection of free carrier charge in a semiconductor via optical pumping. Usually, this process requires many photons to induce meaningful changes in the optical properties of the materials, limiting progress toward single-photon applications. In our work, we utilize the process of avalanche multiplication, a well-known effect of avalanche photodetectors, to enhance changes in charge density in a semiconductor, allowing observation of all-optical modulation even with single-photon intensities. Recently, we experimentally demonstrated all-optical modulation with single-photon intensities on an avalanche diode structure. In this work, we present our recent findings about the dynamics and strength of avalanche-based all-optical modulation, which exceed classical optical Kerr-type nonlinearities by several orders of magnitude. We have demonstrated modulation of telecommunications light using an 810 nm light pulse with an average number of photons ranging from approximately 0.1 to 1 per pulse. Our method demonstrates exceptional performance over a wide range of wavelengths (400 to 1000 nm for silicon SPAD) at room temperature. We believe that our approach holds significant potential for achieving powerful optical nonlinearity at the single-photon level and potentially at THz frequencies, thereby stimulating the development of photonics for a number of applications operating at single-photon level intensities.