The present disclosure relates to a reflective optical sensor module, an optical sensing accessory, and an optical sensing device. A reflective optical sensor module comprises a light source (110) and a first encapsulant (111), a photodetector (120) and a second encapsulant (121), and a substrate (140). The light source (110) is configured to convert electric power into radiant energy and to emit light to an object surface. The photodetector (120) is configured to receive the light from an object surface and to convert radiant energy into electrical current or voltage. A partition (130) is located between the light source(110) and the photodetector (120). At least one of the encapsulants (111, 121) has multiple refractive index layers wherein the refractive index of adjacent layers gradually mediates a refractive index difference towards the environmental medium. The optical sensing accessory and the optical sensing device comprise the reflective optical sensor module and other electronic modules to have further applications.
