Narrow-Linewidth lasers on a silicon chip

Abstract

Diode-pumped distributed-feedback (DFB) channel waveguide lasers were demonstrated in Er3+-doped and Yb3+-doped Al2O3 on standard thermally oxidized silicon substrates. Uniform surface-relief Bragg gratings were patterned by laser-interference lithography and etched into the SiO2to cladding. The maximum grating reflectivity exceeded 99 %. Monolithic DFB cavities with Q-factors of up to 1:35×106were realized. The Er3+-doped DFB laser delivered 3mWof output power with a slope efficiency of 41% versus absorbed pump power. Single-longitudinalmode operation at a wavelength of 1545.2 nm was achieved with an emission line width of 1.70 ±0:58 kHz, corresponding to a laser Q-factor of 1.14×1011. Yb3+- doped DFB lasers were demonstrated at wavelengths near 1,020 nm with output powers of 55mW and a slope efficiency of 67% versus launched pump power. An Yb3+-doped dual-wavelength laser was achieved based on the optical resonances induced by two local phase shifts in the DFB structure. A stable microwave signal at ~15 GHz with a –3–dB width of 9 kHz and a long-term frequency stability of ±2.5MHz was created via the heterodyne photo-detection of the two laser wavelengths. Interaction of the intra-cavity evanescent laser field with microparticles in contact with the grating surface induces changes in the microwave beat signal, whose detection enabled real-time detection and accurate size measurement of single micro-particles with diameters ranging between 1 and 20µm, which represents the typical size of many fungal and bacterial pathogens. A limit of detection of ~500 nm was deduced.