a transparent substrate layer;

a light source and a light detector spaced apart laterally relative to one another on a first side of the substrate layer;

at least a first spatial filter disposed on a second side of the substrate layer, a first side of the first spatial filter being optically coupled to the substrate layer, the first spatial filter including an anti-reflective layer having a near critical angle; and

a cladding detection layer disposed on a second side of the first spatial filter, the cladding detection layer having a refractive index that is modulated by infrared light incident on an exterior surface of the cladding detection layer;

wherein when the light source injects light into the substrate layer, the injected light passes through the substrate layer into the at least first spatial filter and is spectrally and spatially filtered by wave interference and strong refraction such that the injected light impinges the cladding detection layer at a predetermined angle near a critical angle of the injected light, and

when infrared light impinges the exterior surface of the cladding detection layer, the refractive index of the cladding detection layer is modulated and thereby changes an amount of injected light reflected through the at least first spatial filter from the cladding detection layer through the at least first spatial filter to the light detector; and

wherein a combined thickness of the first spatial filter and cladding detection layer is equal to or greater than about 3500 nm.