nanowire-grid polariser (rus. нанополяризатор) — a synthetic three-dimensional or film-type composite material characterised by anisotropy of transmission and/or reflection depending on the structure of its components.

Description

Near infra-red band three-dimensional polarisers are manufactured from glass containing oblong metallic nanoparticles aligned along a certain axis. Polar Cor polarisers produced by Corning, USA, are manufactured from borosilicate glass containing anisotropic nanoparticles of silver, while polarisers produced by Japanese HOYA Corp. contain copper particles instead of silver particles.

Two new types of film polarising materials have been developed recently that employ different reflection anisotropy [1-3] mechanisms. Film polariser developed by NanoOpto Corporation (USA) is based on the anisotropy of a reflection from a metallic mirror represented by a nanosized periodic lattice (see Fig. 1). Film polariser designed by Photonic Lattice Inc. (Japan) is based on the anisotropy of a reflection from a corrugated multilayer dielectric film whose structure is demonstrated in Fig. 2.

In polarisers based on multilayer structured films, periodic dielectric structures provide form birefringence. This means that effective refraction of its layers depends on the polarisation of light. The reflection spectrum of the multilayer dielectric mirror depends on the values of refraction in the layers. Thus, if we use anisotropic structures to build a multilayer coating, the reflection spectrum of the resultant mirror will be characterised by a strong anisotropy. Transmission spectra of a typical multilayer dielectric mirror based on a periodic nanostructure for two orthogonal polarisation patterns are shown in Fig. 3. Note that multilayer structured film is basically an anisotropic one-dimensional photon crystal.

Operation of polarisers built with metallic linear nanostructures (linear grids) is based on a sharp fall in the index of reflection from such structures of radiation whose electric field vector is perpendicular to the grid slits. Linear grids with metallic “slits” have been used as polarisers ever since Hertz’s first experiments in electromagnetic waves. However, these devices have been used only in the electromagnetic wave band until recently. If a linear grid consists of thin conducting slits with a spacing period smaller than the wavelength, this structure has a different effect on light waves polarised along the slits and perpendicular to them. In the first case, the grid will work as a solid metallic surface, and in the second case, as a dielectric.

Today, polarisers are widely used in passive and active components of fibre optic communication systems. They transmit linearly polarised radiation whose electric field vector matches the direction of the transmission axis, and block the orthogonal polarisation component (see Fig. 4). If the blocked component is reflected instead of being absorbed, the device may function as a polarisation splitter or multiplexer of light beams.

Illustrations

Fig. 1. Metal-dielectric nanopolarizer is a grid of intermittent (located with the spacing of around
Fig. 1. Metal-dielectric nanopolarizer is a grid of intermittent (located with the spacing of around a hundred nanometers) wire-like conductors on a dielectric surface. Radiation polarized in a manner that the electric field is parallel to the wire-like conductors is reflected from the nanostructure, and radiation polarized normally to the wires passes through the nanostructure almost with no loss.
Source: Lightwave Russian Edition, 2006, № 3, с. 50.
Fig. 2. Dielectric reflecting nanopolarizer is a corrugated multilayer dielectric film. Materials wi
Fig. 2. Dielectric reflecting nanopolarizer is a corrugated multilayer dielectric film. Materials with high and low refraction index are represented by silicon (Si) and silicon dioxide (SiO2), respectively.
Source: Lightwave Russian Edition, 2006, № 3, с. 50.
Fig. 3. Typical transmission spectrum of a multilayer periodic nanostructure. Δ - effective spect

Fig. 3. Typical transmission spectrum of a multilayer periodic nanostructure. Δ - effective spectral range of polarizer based on such structure: ТЕ - wave in which electric vector is perpendicular to the incident plane. ТМ - wave in which magnetic vector is perpendicular to the incident plane.

Source: Lightwave Russian Edition, 2006, № 3, с. 50.
Fig. 4. Light beam passing through a polarizer. On the right, non-polarized light falls on the polar
Fig. 4. Light beam passing through a polarizer. On the right, non-polarized light falls on the polarizer, but only the light polarized along the polarizer's transmission axis passes through. Normal polarization light may be directed otherwise. In this case, the polarizer becomes a light beam splitter. If the direction of all light rays is reversed, the device will function as a multiplexer of polarized light beams.
Source: Lightwave Russian Edition, 2006, № 3, с. 49.

Author

  • Pavlova Elena G.

Sources

  1. Pavlova E.G. Polarizers based on film nanostructures and their applications in fiber optic communication systems (in Russian)// Lightwave Russian Edition - № 3, 2006 - P. 49–52.
  2. Wang J.J. et al. Innovative high performance nanowire-grid polarizers and integrated isolators // IEEE j. of Selected Topics in QE.- vol. 11, 2005 - pp. 241–253.
  3. Tyan R., Sun P. et al. Polarizing beam splitter based on the anisotropic spectral reflectivity characteristic of form birefringent multilayer gratings // Opt. Lett. - vol. 21, 1996, - pp. 761–763.
  4. Taylor M., Bucher G. High contrast polarizers for the near infrared // Proc. SPIE, Polarization Considerations for Optical Systems II - vol. 1166, 1989 - pp. 446–453.

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