2D Beamscanner

   

            High speed alignment and tracking remains a major challenge for free space optical communications.  By combining two dispersive elements orthogonally, we can tilt a monochromatic beam both vertically and horizontally.  Typically, the first dispersive element will have a short free spectral range (spectral difference between diffraction orders) while the free spectral range of the second element is greater than the total working wavelength range.  In this arrangement, the direction of the beam is adjusted by tuning its wavelength, whereby increasing the wavelength rasters the beam direction.  The scanning speed is now determined by the wavelength switching speed; current technology can scan the wavelengths over an adequate range with less than 50 ns scan times.

            In our work, we used a 1x8 channel arrayed waveguide grating (AWG) demultiplexer followed by a free space optical grating demultiplexer.  The output spot is collimated and directed by a microscope objective.  Because the AWG gives discrete outputs at specific wavelengths, we achieved an 8x6 grid of achievable directions over an 11.0° by 10.3° directional range.

Two gratings are used in series to accomplish two-dimensional beamsteering. A sweep through wavelengths creates a raster scan through the directions where the first grating accomplish vertical scanning and the second one carries out horizontal scanning.

Beamscanner output at increasing wavelengths.

Transient response using a CoreTek tunable filter to switch the optical wavelength.

Additional Information:

T. Chan, E. Myslivets, and J. Ford, "2-Dimensional beamsteering using dispersive deflectors and wavelength tuning," Opt. Express 16, 14617-14628 (2008).

T.K. Chan and J.E. Ford, “Fast, Two-Dimensional Optical Beamscanning by Wavelength Switching,” Lasers and Electro-Optics Society, 2007. LEOS 2007. The 20th Annual Meeting of the IEEE, pp.592-593, 21-25 Oct. 2007. For presentation, click here.