  We show the existence of a flat band consisting of photonic zero modes in a
gain and loss modulated lattice system, as a result of the underlying
non-Hermitian particle-hole symmetry. This general finding explains the
previous observation in parity-time symmetric systems where non-Hermitian
particle-hole symmetry is hidden. We further discuss the defect states in these
systems, whose emergence can be viewed as an unconventional alignment of a
pseudo-spin under the influence of a complex-valued pseudo-magnetic field.
These defect states also behave as a chain with two types of links, one rigid
in a unit cell and one soft between unit cells, as the defect states become
increasingly localized with the gain and loss strength. A realistic photonic
design is presented based on coupled InP/InGaAsP waveguides, and we also extend
the discussion to two- and three-dimensional lattices.
