Intracavity Laser Wavelength Tuning by a Programmable Forward-Only Silicon Photonics Interferometer Mesh

We exploit a recently proposed concept for a programmable, mechanically robust, and tunable nonresonant silicon photonic integrated circuit filter and experimentally demonstrate it for tuning an erbium-doped fiber laser ring cavity. This filter integrates forward-only interferometer meshes together with a waveguide delay line array for fully programmable and tunable filtering. Unlike more popular microresonator-based filters, this approach offers transmission function engineering, broad free spectral range and smooth tuning without matching individual resonances, and extension to multiwavelength operation. Moreover, this filter can be readily fabricated in a commercial foundry with standard dispersive components. For a first experimental verification, we designed a filter with a 100 GHz (∼0.8 nm) free spectral range and a 25 GHz (∼0.2 nm) bandpass width at center wavelengths around 1550 nm. We show numerically that dispersion effects are negligible across >40 nm bandwidth aside from grating coupler loss. Experimentally, we confirm single-wavelength laser operation with a continuous tuning range of ∼0.6 nm around 1555 nm and output power up to 25 mW.