Embodiments of the present disclosure generally relate to apparatus for and methods of detecting light utilizing the spin Seebeck effect (SSE). In an embodiment, a method for detecting broadband light is provided. The method includes generating a SSE in a device by illuminating the device with light, the device comprising a bilayer structure disposed over a substrate, the bilayer structure comprising a non-magnetic metal layer and a magnetic insulator layer. The method further includes measuring the SSE based on a field modulation method, determining, based on the measuring, an optically-created thermal gradient of the device, and detecting a wavelength range of the light. Apparatus for detecting broadband light are also described.