Reflective waveplate with subwavelength grating structure

A reflective waveplate with subwavelength grating structure of the photoresist was fabricated using two-beam interference technology. From the optical measurement, it is found that the phase retardation of the fabricated reflective element (period: 400 nm, fill factor: 0.5, depth: 280 nm) was almost the same as that of the transmission waveplate with the around twice deeper grating depth (period: 400 nm, fill factor: 0.5, depth: 450 nm). This is because the optical length of the reflective element was twice of the transmissive one by using reflection. By changing the period and depth to 285 nm and to 300 nm, respectively, it is also confirmed from the experimental result that the phase retardation of the reflective waveplate exceeded 150° for 450 nm wavelength at the incident angle of 45°.