High refractive index contrast grating and its preparation method and application
A high refractive index contrast, grating technology, applied in diffraction gratings, optics, optical components, etc., can solve the problems of high cost, difficult processing, and time-consuming processing, and achieve the effect of low aspect ratio and low loss.
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[0040] The preparation process of HCG grating described in the present invention is as follows:
[0041] S1, bonding the SOI sheet to the transparent substrate;
[0042] S2, thinning the silicon substrate on the SOI sheet by physical grinding, and then etching the grating on the silicon substrate of the SOI sheet by an inductively coupled plasma etching (ICP) method;
[0043] S3. Etching the insulating layer on the SOI sheet by a chemical method to obtain single crystal silicon on the transparent substrate.
[0044] Such as figure 1 , figure 2 As shown, the designed basic unit HCG grating has a width w=70nm, a thickness h=100nm and a period a=300nm. When circularly polarized light is incident, the HCG structure has a guided-mode resonance with high transmittance for s-polarization, but no resonance for p-polarization, where the incident light phase of s-polarization is Φ i and the transmitted light phase Φ t The phase difference follows Bragg modulation:
[0045] Φ t -Φ ...
Embodiment 1
[0052] In this embodiment, the above-mentioned high refractive index contrast grating (HCG) is designed and processed with a normal incidence deflector. Such as Figure 4 , Figure 5 As shown, the vertically incident light will exit at a certain deflection angle after passing through the structure. The deflection angle is calculated by the general Snell's law:
[0053]
[0054] Among them, n i and n t are the ambient refractive indices at the incident end and the transmitted end, respectively, θ i and θ t are the angle of incidence and transmission, respectively, k 0 is the wave vector in vacuum, is the phase gradient. Among them, dΦ t is the phase difference between two adjacent basic units, and dΔ is the lattice period of the basic unit.
[0055] Therefore, as long as an appropriate phase gradient is designed, a deflector with a specific exit angle can be obtained.
[0056] In this embodiment, eight basic units are selected, and the 2π total phase is divided i...
Embodiment 2
[0060] In this embodiment, an OAM generator is designed and fabricated using the above-mentioned high-index contrast grating (HCG).
[0061] The vortex light is a hollow circular beam with a helical phase distribution, and the phase along the propagation direction has where l is the number of topological charges, which can be any integer, is the azimuth angle.
[0062] The wavefront of vortex light consists of helical surfaces, and each photon carries orbital angular momentum (OAM), is Planck's constant. Especially when l=1, each photon of the circular polarization mode carries The orbital angular momentum of , the sign depends on the polarization chirality.
[0063] The function of the vortex light generator can be described as follows:
[0064] Incident unit left-handed polarized light E in =E o ×(1, i), after passing through the vortex light generator, the outgoing light is a right-handed polarization E with a geometric phase of 2α(x,y) out =E o exp(i2α(x,y))...
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Abstract
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