Optical mechanical (OM) deflectors are devices, which control an optical ray in space using a mechanical method of moving of refractive or reflective elements. They are divided into refractive and reflective devices.

As refractive elements the optical wedges and prisms are used. Refractive optical mechanical deflectors are complicated for manufacturing and possess by relatively small amplitude of angle of scanning and low resolving power.

On fig.1,a the construction of OM refractive deflector on the basis of two optical wedges is shown. They are revolving in opposite directions from middle neutral position onto equal angles. An optical beam here moves along a certain line with variable speed.

In the basis of work of reflective optical mechanical (OM) deflectors the principle of mirror reflection of optical beam from moving mirror surfaces underlies. Such devices structurally can be executed as prism polygon mirror (fig.1,b), pyramid polygon mirror (fig.1,c) and single inclined mirror (fig.1,d) that are revolved or hesitated under action of electromechanic drive. Axis of rotation of prism polygon mirror is usually perpendicular to the axis of scanning optical beam. Correction of linear distortion of trajectory of scanning of optical beam is achieved by the use together with optical deflectors of additional reflective or refractive elements, anamorphic elements in the number (fig.2) that executes the functions of correction of motion trajectory of optical rays.

According to disposition relatively of focusing optics OM deflectors are divided onto preobjective scanner (deflector is located before lens) and postobjective scanners (deflector is located after lens); in accordance with correlation of linear aperture of scanning optical beam and sizes of working facet - onto deflectors with complete illumination, surplus illumination and partial illumination of facet. In deflectors with complete illumination of facet the diameter of the transversal crossing (linear aperture) of optical beam is equal to the light diameter of facet. In deflectors with surplus illumination of facet the linear aperture of optical beam is larger than light diameter of facet. In deflectors with partial illumination of facet the linear aperture of optical beam is smaller than light diameter of facet.

In the given time OM deflectors are worked better than other and found large application in scanning systems. But OM scanning devices own also substantial failings. Instability of work and curvature of scanning trajectory of optical beam are the major among them.

Optical mechanical holographic (OMH) deflectors. From the end of 60th of past century in connection with considerable distribution of apparatus and facilities of holography, in scientific and technical literature the numerous publications appeared that concerned of the new scanning devices - optical-mechanical holographic (OMH) deflectors, in which deflection of optical beam in space is achieved by diffraction of the beam on the diffraction structure of hologram that is inflicted onto substrate and mechanically moved in accordance with a certain law (fig. 3). In holographic deflectors a role of prism polygon mirrors and pyramid polygon mirrors is executed by holograms.

Holographic deflectors possess the row of advantages in comparison with traditional OM deflectors. OMH deflectors provide 1D-, 2D- and 3D- scanning of optical rays, focusing without additional lenses, have the high fast-acting and can simultaneously execute the function of optical spectral filter.

Depending on the type of interaction of optical beam with hologram the OMH deflectors are divided into transmittive and reflective devices. In accordance with the form of substrate that is used for disposing of holograms, OMH deflectors (fig.3) are divided onto disk holographic deflectors (a,b), cylinder-shaped deflectors (c), prismatic holographic deflectors (d) and conical holographic deflectors (e). OMH deflector usually includes m_h holograms-«facets» (diffraction gratings or Fresnel zone plates). For one rotation of substrate an optical beam forms n lines of scanning. Basic advantages of OMH deflectors in comparison with traditional OM deflectors are:

·     possibility of internal focusing with the use of the Fresnel focusing holograms;

·     possibility the 2D-scanning;

·     possibility the 3D-scanning;

·     removal of coordinate distortions, distortions  of speed (linear and angular) of scanning of optical beam;

·     simplicity of the serial making;

·     small sizes and mass.

The presence of chromatic aberrations in OMH deflectors needs in careful choice of radiation wave-length of optical beam that is used for recording and scanning, and practically lowers the possibility of their application for the multispectral scanning.

By Vasil Sidorov on September 06, 2010 in queltanews.com

Technopark QUELTA,

Nizhyn Laboratories of Scanning Devices

sidorovvasil@gmail.com

References

1.       Rebrin Y.K., Sidorov V.I. // Optical Deflectors. Kiev: Tékhnika, 1988. 136 pp.

2.       Rebrin Y.K., Sidorov V.I. Optical mechanical and holographic deflectors // Results in science and technology. Radio engineering. Vol. 45. - Moscow: VINITI, 1992. - 252 pp.

3.       Rebrin Y.K., Sidorov V.I. Holographic devices of control of optical ray. – Kiev: KHMAES, 1986. - 124 pp.

4.       Rebrin Y.K., Sidorov V.I. Piezoelectric multielement devices of control of optical ray. – Kiev:  KHMAES, 1987. - 104 pp.