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Triple-helical nanowires by tomographic rotatory growth for chiral photonics.

Esposito M, Tasco V, Todisco F, Cuscunà M, Benedetti A, Sanvitto D, Passaseo A - Nat Commun (2015)

Bottom Line: Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy.These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB).Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

View Article: PubMed Central - PubMed

Affiliation: National Nanotechnology Laboratory-NNL, CNR-IMIP, VIA Arnesano, 73100 Lecce Italy.

ABSTRACT
Three dimensional helical chiral metamaterials resulted in effective manipulation of circularly polarized light in the visible infrared for advanced nanophotonics. Their potentialities are severely limited by the lack of full rotational symmetry preventing broadband operation, high signal-to-noise ratio and inducing high optical activity sensitivity to structure orientation. Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy. Here we report three dimensional triple-helical nanowires, engineered by the innovative tomographic rotatory growth, on the basis of focused ion beam-induced deposition. These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB). Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

No MeSH data available.


Related in: MedlinePlus

Optical Rotatory Dispersion and Circular Birefringence(a) Optical setup scheme to measure ORD at different sample angles. Linearly polarized light transmitted by the sample is analyzed with an half-wave plate cascaded with a second polarizer. The half wave plate is rotated in steps of α=2° with respect to the transmission axis of the linear polarizer, by means of a mechanically rotating stage, to obtain polar diagrams for the transmitted light intensity at each wavelength, like the one reported in (b) at 980 nm for Φin=0°. (c-h) Measured ORD at different sample angles by linearly polarized incident light. For each sample angle, the ORD shows similar trends, as expected by isotropic structures. (i) FDTD simulation of the ORD as a function of the input angle. The higher rotation value with respect to measurements is mainly related to the theoretical hypothesis of infinite array.(l) Optical activity measured in the crossing point (980 nm) where the linear polarization state is preserved. We note a very weak modulation (related to the extremely residual anisotropy of the nanostructures) around the mean value of 7.5° representing the polarization rotation only due to the circular birefringence. (m-n)Transmission maps of THN 6x6 array, as obtained with the microscope in polarized light configuration with a 100x objective lens under normal incidence excitation. When the linear polarizer and the analyzer are aligned, a bright-field image is created away from the THN region, while it appears darker in correspondence of each THN due to the circular birefringence effect (m). The situation is inverted when the analyzer and the linear polarizer are crossed (n).
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Figure 4: Optical Rotatory Dispersion and Circular Birefringence(a) Optical setup scheme to measure ORD at different sample angles. Linearly polarized light transmitted by the sample is analyzed with an half-wave plate cascaded with a second polarizer. The half wave plate is rotated in steps of α=2° with respect to the transmission axis of the linear polarizer, by means of a mechanically rotating stage, to obtain polar diagrams for the transmitted light intensity at each wavelength, like the one reported in (b) at 980 nm for Φin=0°. (c-h) Measured ORD at different sample angles by linearly polarized incident light. For each sample angle, the ORD shows similar trends, as expected by isotropic structures. (i) FDTD simulation of the ORD as a function of the input angle. The higher rotation value with respect to measurements is mainly related to the theoretical hypothesis of infinite array.(l) Optical activity measured in the crossing point (980 nm) where the linear polarization state is preserved. We note a very weak modulation (related to the extremely residual anisotropy of the nanostructures) around the mean value of 7.5° representing the polarization rotation only due to the circular birefringence. (m-n)Transmission maps of THN 6x6 array, as obtained with the microscope in polarized light configuration with a 100x objective lens under normal incidence excitation. When the linear polarizer and the analyzer are aligned, a bright-field image is created away from the THN region, while it appears darker in correspondence of each THN due to the circular birefringence effect (m). The situation is inverted when the analyzer and the linear polarizer are crossed (n).

Mentions: An additional property related to the complex geometry of THN structures is the ability to rotate the linear polarization state of the incident light. We performed the analysis of the Optical Rotatory Dispersion (ORD) of the THN array through the experimental set-up schematically described in figure 4a. The longer axis of the transmitted polarization ellipse (induced by the sample dichroic properties) was used to measure the rotation of the polarization angle with respect to the linearly polarized incident light. The ORD was measured for different sample orientations, by rotating the sample (Φin) in steps of 30°, as shown in figure 4c-h.


Triple-helical nanowires by tomographic rotatory growth for chiral photonics.

Esposito M, Tasco V, Todisco F, Cuscunà M, Benedetti A, Sanvitto D, Passaseo A - Nat Commun (2015)

Optical Rotatory Dispersion and Circular Birefringence(a) Optical setup scheme to measure ORD at different sample angles. Linearly polarized light transmitted by the sample is analyzed with an half-wave plate cascaded with a second polarizer. The half wave plate is rotated in steps of α=2° with respect to the transmission axis of the linear polarizer, by means of a mechanically rotating stage, to obtain polar diagrams for the transmitted light intensity at each wavelength, like the one reported in (b) at 980 nm for Φin=0°. (c-h) Measured ORD at different sample angles by linearly polarized incident light. For each sample angle, the ORD shows similar trends, as expected by isotropic structures. (i) FDTD simulation of the ORD as a function of the input angle. The higher rotation value with respect to measurements is mainly related to the theoretical hypothesis of infinite array.(l) Optical activity measured in the crossing point (980 nm) where the linear polarization state is preserved. We note a very weak modulation (related to the extremely residual anisotropy of the nanostructures) around the mean value of 7.5° representing the polarization rotation only due to the circular birefringence. (m-n)Transmission maps of THN 6x6 array, as obtained with the microscope in polarized light configuration with a 100x objective lens under normal incidence excitation. When the linear polarizer and the analyzer are aligned, a bright-field image is created away from the THN region, while it appears darker in correspondence of each THN due to the circular birefringence effect (m). The situation is inverted when the analyzer and the linear polarizer are crossed (n).
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Figure 4: Optical Rotatory Dispersion and Circular Birefringence(a) Optical setup scheme to measure ORD at different sample angles. Linearly polarized light transmitted by the sample is analyzed with an half-wave plate cascaded with a second polarizer. The half wave plate is rotated in steps of α=2° with respect to the transmission axis of the linear polarizer, by means of a mechanically rotating stage, to obtain polar diagrams for the transmitted light intensity at each wavelength, like the one reported in (b) at 980 nm for Φin=0°. (c-h) Measured ORD at different sample angles by linearly polarized incident light. For each sample angle, the ORD shows similar trends, as expected by isotropic structures. (i) FDTD simulation of the ORD as a function of the input angle. The higher rotation value with respect to measurements is mainly related to the theoretical hypothesis of infinite array.(l) Optical activity measured in the crossing point (980 nm) where the linear polarization state is preserved. We note a very weak modulation (related to the extremely residual anisotropy of the nanostructures) around the mean value of 7.5° representing the polarization rotation only due to the circular birefringence. (m-n)Transmission maps of THN 6x6 array, as obtained with the microscope in polarized light configuration with a 100x objective lens under normal incidence excitation. When the linear polarizer and the analyzer are aligned, a bright-field image is created away from the THN region, while it appears darker in correspondence of each THN due to the circular birefringence effect (m). The situation is inverted when the analyzer and the linear polarizer are crossed (n).
Mentions: An additional property related to the complex geometry of THN structures is the ability to rotate the linear polarization state of the incident light. We performed the analysis of the Optical Rotatory Dispersion (ORD) of the THN array through the experimental set-up schematically described in figure 4a. The longer axis of the transmitted polarization ellipse (induced by the sample dichroic properties) was used to measure the rotation of the polarization angle with respect to the linearly polarized incident light. The ORD was measured for different sample orientations, by rotating the sample (Φin) in steps of 30°, as shown in figure 4c-h.

Bottom Line: Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy.These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB).Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

View Article: PubMed Central - PubMed

Affiliation: National Nanotechnology Laboratory-NNL, CNR-IMIP, VIA Arnesano, 73100 Lecce Italy.

ABSTRACT
Three dimensional helical chiral metamaterials resulted in effective manipulation of circularly polarized light in the visible infrared for advanced nanophotonics. Their potentialities are severely limited by the lack of full rotational symmetry preventing broadband operation, high signal-to-noise ratio and inducing high optical activity sensitivity to structure orientation. Complex intertwined three dimensional structures such as multiple-helical nanowires could overcome these limitations, allowing the achievement of several chiro-optical effects combining chirality and isotropy. Here we report three dimensional triple-helical nanowires, engineered by the innovative tomographic rotatory growth, on the basis of focused ion beam-induced deposition. These three dimensional nanostructures show up to 37% of circular dichroism in a broad range (500-1,000 nm), with a high signal-to-noise ratio (up to 24 dB). Optical activity of up to 8° only due to the circular birefringence is also shown, tracing the way towards chiral photonic devices that can be integrated in optical nanocircuits to modulate the visible light polarization.

No MeSH data available.


Related in: MedlinePlus