Group velocity, energy velocity, and superluminal propagation in finite photonic band-gap structures.
We have analyzed the notions of group velocity V(g) and energy velocity V(E) for light pulses propagating inside one-dimensional photonic band gap structures of finite length. We find that the two velocities are related through the transmission coefficient t as V(E)=/t/(2)V(g). It follows that V(E)=V(g) only when the transmittance is unity (/t/(2)=1). This is due to the effective dispersive properties of finite layered structures, and it allows us to better understand a wide range of phenomena, such as superluminal pulse propagation. In fact, placing the requirement that the energy velocity should remain subluminal leads directly to the condition V(g)<or=c//t/(2). This condition places a large upper limit on the allowed group velocity of the tunneling pulse at frequencies of vanishingly small transmission.
D'Aguanno
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INFM at Dipartimento di Energetica, Università di Roma La Sapienza, Via Scarpa 16, I-00161 Rome, Italy.
Centini
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Scalora
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Sibilia
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Bloemer
M J
MJ
Bowden
C M
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Haus
J W
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Bertolotti
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