In this paper we elaborate on our development of silicon photonic integrated circuits operating at wavelengths beyond the telecommunication wavelength window. Silicon-on-insulator waveguide circuits up to 3.8 μm wavelength are demonstrated as well as germanium-on-silicon waveguide circuits operating in the 5-5 μm wavelength range. The heterogeneous integration of III-V semiconductors and IV-VI semiconductors on this platform is described for the integration of lasers and photodetectors operating in the 2-3 μm wavelength range. GeSn is proposed as an appealing approach to monolithically integrated long-wavelength detectors. Finally, nonlinear optics in silicon waveguide circuits beyond the two-photon absorption threshold is explored.