Abstract-Active terahertz beam steering by photo-generated graded index gratings in thin semiconductor films

T. P. Steinbusch, H. K. Tyagi, M.C. Schaafsma, G. Georgiou, and J. Gómez Rivas  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-22-26559

Optics Express, Vol. 22, Issue 22, pp. 26559-26571 (2014)
http://dx.doi.org/10.1364/OE.22.026559

We demonstrate active beam steering of terahertz radiation using a photo-excited thin layer of gallium arsenide. A constant gradient of phase discontinuity along the interface is introduced by an spatially inhomogeneous density of free charge carriers that are photo-generated in the GaAs with an optical pump. The optical pump has been spatially modulated to form the shape of a planar blazed grating. The phase gradient leads to an asymmetry between the +1 and −1 transmission diffracted orders of more than a factor two. Optimization of the grating structure can lead to an asymmetry of more than one order of magnitude. Similar to metasurfaces made of plasmonic antennas, the photo-generated grating is a planar structure that can achieve large beam steering efficiency. Moreover, the photo-generation of such structures provides a platform for active THz beam steering.

© 2014 Optical Society of America