  This paper investigates the capacity region of the optical intensity
broadcast channels (OI-BCs), where the input is subject to a peak-intensity
constraint, an average-intensity constraint, or both. By leveraging the
decomposition results of several random variables, i.e., uniform, exponential,
and truncated exponential random variables, and adopting a superposition coding
(SC) scheme, the inner bound on the capacity region is derived. Then, the outer
bound is derived by applying the conditional entropy power inequality (EPI). In
the high signal-to-noise ratio (SNR) regime, the inner bound asymptotically
matches the outer bound, thus characterizing the high-SNR asymptotic capacity
region. The bounds are also extended to the general K-user BCs without loss of
high-SNR asymptotic optimality.
