The invention relates to a light-emitting diode (LED) light source which produces light through a semiconductor band gap structure, in particular to an electromagnetic wave transmission structure, namely an active polarized light emission optical device with a composite micro-nano surface grating structure. The LED comprises a substrate (1), an n-type layer (2), a quantum well (3), a p-type layer (4) and a metal grating (6) and is characterized in that: a composite structure of a medium transition layer (5) and the metal grating (6) is plated or etched on the upper surface of the p-type layer (4); the refraction index of the medium transition layer meets the conditions that: n is greater than 1.0 and less than the refraction index of the p-type layer medium (4); and the transition layer is one of a thin film structure, a grating structure and an embedded structure. Due to the adoption of the structure, the transmission and extinction characteristics of the LED can be enhanced effectively; and in a period, the flatness of the side face of the grating, the duty ratio of the grating, and the range of working wavelengths are obviously improved compared with those of a conventional single-layer metal grating.