  Following up on previous studies on parity-time-symmetric gain-loss
bi-layers, and inspired by formal analogies with plasmonic waveguides, we study
non-Hermiticity-induced wave confinement and guiding phenomena that can occur
in loss-gain-loss three-layers. By revisiting previous well-established
"gain-guiding" concepts, we investigate analytically and numerically the
dispersion and confinement properties of guided modes that can be supported by
this type of structures, by assuming realistic dispersion models and parameters
for the material constituents. As key outcomes, we identify certain modes with
specific polarization and symmetry that exhibit particularly desirable
characteristics, in terms of quasi-real propagation constant and sub-wavelength
confinement. Moreover, we elucidate the effects of material dispersion and
parameters, and highlight the potential advantages by comparison with the
previously studied gain-loss bi-layer configurations. Our results provide
additional perspectives on light control in non-Hermitian optical systems, and
may find potentially intriguing applicability to reconfigurable nanophotonic
platforms.
