Metasurface design for the generation of an arbitrary assembly of different polarization states

Manipulation of polarization states with metasurfaces is a compelling approach for on-chip photonics and portable information processing. Yet it remains challenging to generate different types of polarization states with a single piece of a metasurface. This paper demonstrates a metasurface to resolve this issue, which is made of L-shaped resonators with different geometrical sizes. Each resonator diffracts a right- or left-handed circularly polarized state with an additional geometrical-scaling-induced phase. The type of polarization state of each diffracted beam is determined by the enantiomorphism, size, and spatial sequence of the resonators in the unit cell. The number of the beams is modulated by the geometry and separation of the resonators. We provide examples to illustrate how to achieve the specific number of diffracted beams with the desired polarization states in experiments. We suggest that this strategy can be applied for integrated photonics and portable quantum information processing.

Figure 1

The simulation results of 16 L-shaped resonators ($S_1, S_2$,..., $S_8$ and ${S_1}^{\prime }, {S_2}^{\prime }$,..., ${S_8}^{\prime }$) in PS1, where the $x$-polarized incident light propagates in $-z$ direction. (a) The detailed topography of the L-shaped resonator sitting on top of a ${\mathrm{SiO}}_2$-gold-silicon substrate. For the resonators in PS1, the thickness of the ${\mathrm{SiO}}_2$ layer $h_1$ and that of the solid gold layer $h_2$ are 200 and 100 nm, respectively. The thickness of the gold L-shaped structure $h_3$ is 50 nm. The center-to-center separation of each resonator is set as 700 nm. The length $l$ and width $w$ of the eight resonators generating $|R\rangle$ (RCP state), $\{S_1,S_2,\cdots ,S_8\}$, and their mirror-imaged counterparts generating $|L\rangle$ (LCP state), $\{{S_1}^{\prime },{S_2}^{\prime },\cdots ,{S_8}^{\prime }\}$, are listed in Table 1. (b) The plot showing the simulated reflectance ratio, and phase difference of the $y$ and $x$ components of the reflected beam when the incident beam interacts with $S_1$. (c) The simulated GSI phase $\varphi$ added to the diffracted state from the elements in $\left\{S_i\right\}$ ($i=1$, 2,..., 8). The incident wavelength is 1300 nm. (d) The simulated GSI phase $\varphi$ added to the diffracted state from the elements in $\left\{{S_i}^{\prime }\right\}$ ($i=1$, 2,..., 8). The incident wavelength is 1300 nm.

Figure 2

(a) The plot to show the GSI phase $\varphi$ and the handedness (represented by the red/blue dots) of each resonator in the unit cell. The resonators are selected from PS1. Four from $\left\{S_i\right\}$ and four from $\left\{{S_i}^{\prime }\right\}$. The metasurface generates two LP and two CP states. (b) SEM micrograph of the fabricated metasurface as designed in Fig. 2. The inset is the enlarged SEM micrograph. The dash line box marks the unit cell. Both the white and yellow bars represent $1\mu \mathrm{m}$. (c) Measured angle-resolved diffraction spectra. Four bright lines represent the diffracted beams measured at different wavelength at different diffraction angles. The color bar stands for the intensity. (d) The normalized beam intensity of four diffracted beams. $I_{pol,num}$ represents the intensity of $nu{m}^{\mathrm{th}}$ order with $pol$ polarization. (e) The measured light intensity ratio of each beam.

Figure 3

The simulation results of 16 L-shaped resonators ($S_1, S_2$,..., $S_8$ and ${S_1}^{\prime }, {S_2}^{\prime }$,..., ${S_8}^{\prime }$) in PS2, where the $x$-polarized incident light propagates in $-z$ direction. For the resonators in PS2, the thickness of the ${\mathrm{SiO}}_2$ layer $h_1$ and that of the solid gold layer $h_2$ are selected as 110 and 100 nm, respectively. The gold L-shaped structure $h_3$ is set as 50 nm. The separation of each resonator is 400 nm. The length $l$ and width $w$ of the eight resonators generating $|R\rangle$ and their mirror-imaged counterparts generating $|L\rangle$ are listed in Table 2. (a) The plot to show the simulated reflectance ratio, and phase difference of the $y$ and $x$ components of the reflected beam when the incident beam interacts with $S_1$. (b) The simulated GSI phase $\varphi$ added to the diffracted state from the elements in $\left\{S_i\right\}$ ($i=1$, 2,..., 8). The incident wavelength is 1200 nm. (c) The simulated GSI phase $\varphi$ added to the diffracted state from the elements in $\left\{{S_i}^{\prime }\right\}$ ($i=1$, 2,..., 8). The incident wavelength is 1200 nm.

Figure 4

(a) The plot to show the GSI phase $\varphi$ and the handedness (represented by the red/blue dots) of each resonator in the unit cell. The resonators are selected from PS2. Four from $\left\{S_i\right\}$ and four from $\left\{{S_i}^{\prime }\right\}$. The metasurface generates one LP and one CP state. (b) SEM micrograph of the fabricated metasurface as designed in Fig. 4. The inset is the enlarged SEM micrograph. The dash line box marks the unit cell. Both the white bar and yellow bar represent $1\mu \mathrm{m}$. (c) Measured angle-resolved diffraction spectra. Two bright lines represent the diffracted beams measured at different wavelength at different diffraction angles. The color bar stands for the intensity. (d) The normalized beam intensity of two diffracted beams. $I_{pol,num}$ represents the intensity of $nu{m}^{\text{th}}$ order with $pol$ polarization. (e) The measured light intensity ratio of each beam.

Figure 5

(a) The plot to show the GSI phase $\varphi$ and the handedness (represented by the red/blue dots) of each resonator in the unit cell. The resonators are selected from PS2. Two from $\left\{S_i\right\}$ and two from $\left\{{S_i}^{\prime }\right\}$. The metasurface generates one vertically and one horizontally LP state. (b) SEM micrograph of the fabricated metasurface as designed in Fig. 5. The inset is the enlarged SEM micrograph. The dash line box marks the unit cell. Both the white and yellow bars represent $1\mu \mathrm{m}$. (c) Measured angle-resolved diffraction spectra. Two bright lines represent the diffracted beams measured at different wavelength at different diffraction angles. The color bar stands for the intensity. (d) The normalized beam intensity of two diffracted beams. $I_{pol,num}$ represents the intensity of $nu{m}^{\text{th}}$ order with $pol$ polarization. (e) The measured light intensity ratio of each beam.

Figure 6

(a) The plot to show the GSI phase $\varphi$ and the handedness (represented by the red dots) of each resonator in the unit cell. The resonators are all selected from $\left\{S_i\right\}$ of PS2. The metasurface generates one RCP state. (b) SEM micrograph of the fabricated metasurface as designed in Fig. 6. The inset is the enlarged SEM micrograph. The dash line box marks the unit cell. Both the white bar and yellow bar represent $1\mu \mathrm{m}$. (c) Measured angle-resolved diffraction spectra. The bright line represents the diffracted beam measured at different wavelength at different diffraction angles. The color bar stands for the intensity. (d) The normalized beam intensity of the diffracted beams. $I_{pol,num}$ represents the intensity of $nu{m}^{\text{th}}$ order with $pol$ polarization. (e) The measured light intensity ratio of the beam.