Research On Tricolor-shifting Device With An Embedded Sub-wavelength Sinusoidal Grating Structure

The rectangular structure sub-wavelength grating has an important application in the field of optical security,but some disadvantages are still remained to be solved,such as the difficulty of manufacturing and the reduce of the diffractive efficiency.This paper combined the rigorous couple wave theory(RCWA)and genetic algorithm(GA),proposed a tricolor-shifting device with an embedded sub-wavelength one-dimension simple periodic sinusoidal grating structure.The result shows that,three certain wavelength bands of visible light can achieve a very high reflection efficiency while the reflection efficiency of the other wavelength bands of visible light are very low when the nature light pass through the device.Additionally the model structure of sinusoidal grating was manufactured by two-beam laser interference lithography experimentally in this paper.The main contents of this paper are summarized as follows:1.The Corresponding relations between sinusoidal structure tri-color shifting device and rectangular one is proposed.We applied the rigorous couple wave theory(RCWA),derived the solution array of the diffraction efficiency of the embedded rectangular structure grating and and built the mapping relationship between the sinusoidal structure and the rectangular structure.2.We design the program by genetic algorithm(GA),and set the reasonable parameters and a novel evaluation function.And unceasingly optimize the evaluation function and its weights.And based on the PET substrate and Zn S coating,we finally derived a tricolor-shifting device with an embedded sub-wavelength one-dimension simple periodic sinusoidal grating structure.When the incident angle is 45°,for TE and TM polarization,the highest reflectivity of 90%,89%,100% in blue,green and red can be get at 24°,63°,90°azimuths,respectively.3.Considering about the manufacturing of the device,we analyzed the redundancyof four key parameters of the device,including the grating period,the grating depth,the coating thickness and the incident angle,and proposed a reasonable redundancy rates.This could benefits the followed manufacturing of the grating.4.For proving the manufacturability of the structure,we fabricated the structure of sinusoidal grating sample by two-beam laser interference lithography.And the sample was precisely observed by the Laser-microscope.All the key parameters are acceptable according to the redundancy rates.This paper proposed an embedded sub-wavelength one-dimension simple periodic sinusoidal grating structure achieves a remarkable characteristic with a compact structure,can be applied in optical security field wildly.