Visible light emitting waveguide on Si chip

Abstract

Photonic lab-on-a-chip portable platforms have proved to be very sensitive, rapid in analysis and easy-to-use. However, they still rely on a bulk light source to operate, thus hindering the actual portability and potential for commercial realization. In the present paper we have proposed a design for a light emitting structure that could be easily implemented on chip. The design consists of a Si3N4 strip waveguide on SiO2 substrate, with an active material that emits light as top and lateral cladding. The cross-section of the waveguide was optimised to support both excitation and emission as guided modes, with a high mutual overlap and high confinement to the cladding. This ensures an efficient light emission activation from the cladding and a stable propagation along the waveguide. The proposed structure shows to be operative along the visible range; demonstrated from 400nm to 633nm. The procedure we have followed along this report can be virtually used for designing the cross-section geometry of any strip waveguide system so that the performance is optimised for a given cladding refractive index and emission and excitation wavelengths. In addition we have proposed the use of polymeric quantum dots as the gain material to be used as active cladding. The ease of on-chip integration of this gain material via spin-coating, together with the simplicity of our light emitting waveguide, makes our light source design suitable for large-scale integration on Si chip. Specially, for lab-on-chip applications where multiplexed operation is essential.