Is ‘Superluminal’Light Propagation Possible in Dispersive Media?
CHEN Kai1, WU Ling-An1, SHIH Yan-Hua2
1Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080
2Department of Physics, University of Maryland, Baltimore County, Baltimore, Maryland 21250, USA
Is ‘Superluminal’Light Propagation Possible in Dispersive Media?
CHEN Kai1;WU Ling-An1;SHIH Yan-Hua2
1Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080
2Department of Physics, University of Maryland, Baltimore County, Baltimore, Maryland 21250, USA
Abstract： In a dispersive medium, different monochromatic modes of light have different phase velocities. Under special circumstances, a superposition of these modes results in an interesting effect wherein the group velocity (the velocity at which the peak of the wavepacket propagates) could be greater than c or even negative although the phase velocities of the modes are all less than c. Can this superluminal group velocity be used for information transfer? We show here that the‘superluminal’effect is due to a coherent optical wave superposition effect. Whatever the velocity of the‘peak’, the whole pulse cannot travel with a speed greater than the fastest phase velocity of its component modes. Thus the maximum speed for information transfer, which involves the sending of a finite pulse, cannot be greater than the maximum phase velocity in the medium.
2004, Vol. 21 
