Features of exciton-polariton eigenmodes in a series of light-coupled In0.0
4Ga0.96As/GaAs semiconductor multiple quantum wells with varying number of
quantum wells N from 1 to 100, and with various periodicities (Bragg, near-
Bragg, and anti-Bragg), are studied in linear measurements of reflection, t
ransmission, and absorption. At Bragg periodicity (period d = lambda(x)/2),
a photonic band-gap mode grows in amplitude and increases linearly in line
width with increasing N. The N times increased radiative damping rate is se
en to arise from the light character of the eigenmode being swept out of a
photonic band-gap structure. The slope of linewidth versus N gives the radi
ative linewidth of the exciton. Away from Bragg periodicity two branches of
energy levels can he resolved in absorption, corresponding to the N excito
n-polariton normal modes in the multiple-quantum-well structure. Signatures
of individual modes becoming optically active are observed in the rich str
ucture of reflection spectra for changing quantum-well periodicity. Antiref
lection coating of the samples is shown to be an effective way of thus isol
ating the multiple-quantum-well response.