Efficient photoinduced second-harmonic generation in silicon nitride photonics

Silicon photonics lacks a second-order nonlinear optical (χ(2)) response in general, because the typical constituent materials are centrosymmetric and lack inversion symmetry, which prohibits χ(2) nonlinear processes such as second-harmonic generation (SHG). Here, we realize high SHG efficiency in silicon photonics by combining a photoinduced effective χ(2) nonlinearity with resonant enhancement and perfect phase matching. We show a conversion efficiency of (2,500 ± 100)% W−1 that is two to four orders of magnitude larger than previous field-induced SHG works. In particular, our devices realize milliwatt-level SHG output powers with up to (22 ± 1)% power conversion efficiency. This demonstration is a breakthrough in realizing efficient χ(2) processes in silicon photonics, and paves the way for further integration of self-referenced frequency combs and optical frequency references. By combining a photoinduced effective χ(2) nonlinearity with resonant enhancement and perfect phase matching in a silicon nitride microring resonator, second-harmonic generation with milliwatt-level output powers with up to 22 ± 1% power conversion efficiency is demonstrated.