Optical axis gratings (OAGs) are gratings of

optical axis An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. The optical axis is an imaginary line that defines the path along which light propagat ...

of a

birefringent Birefringence is the optics, optical property of a material having a refractive index that depends on the Polarization (waves), polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or ...

material. In OAGs, the birefringence of the material is constant, while the direction of optical axis is periodically modulated in a fixed direction. In this way they are different from the regular phase gratings, in which the

refractive index In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

is modulated and the direction of the optical axis is constant. The optical axis in OAGs can be modulated in either transverse or the longitudinal direction, which causes it to act as a diffractive or a reflective component. Numerous modulation profiles allow variation in the optical properties of the OAGs.

Examples

The optical axis in a transverse or ''cycloidal'' OAG is monotonously modulated in transverse direction. This grating is capable of diffracting ''all'' incident light into either +1st or −1st order in a

micrometer Micrometer can mean: * Micrometer (device), used for accurate measurements by means of a calibrated screw * American spelling of micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...

-thick layer . Cycloidal OAGs have already been proven to be very efficient in

beam steering Beam steering is a technique for changing the direction of the main lobe of a radiation pattern. In radio and radar systems, beam steering may be accomplished by switching the antenna elements or by changing the relative phases of the RF signa ...

and

optical switching An optical transistor, also known as an optical switch or a light valve, is a device that switches or amplifies optical signals. Light occurring on an optical transistor's input changes the intensity of light emitted from the transistor's output wh ...

. In another type of OAG, the optical axis is modulated in the direction of light propagation with a modulation period equal to a fraction of the wavelength (200–3000 nm). This modulation prevents these frequencies from propagating within the grating, acting as a

band-stop filter In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. It is the opposite of a band-pass filter. A notch filter is a ba ...

. As a result, any light with frequency within the matching range will be reflected from the OAG. However, unlike cholesterics which reflect only one of two circular polarizations of incident light, this OAG reflects any polarization.

Applications

Optical axis gratings can be implemented in various materials, including

liquid crystals Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. Th ...

polymers A polymer (; Greek '' poly-'', "many" + ''-mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

, birefringent crystals,

magnetic Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particle ...

crystals and sub

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

gratings. This new type of grating has broad potential in imaging,

liquid crystal display A liquid-crystal display (LCD) is a flat panel display, flat-panel display or other Electro-optic modulator, electronically modulated optical device that uses the light-modulating properties of liquid crystals combined with polarizers. Liqui ...

, communication, and numerous military applications.

References

{{reflist

Examples

Applications

References

See also