  This paper provides new inner and outer bounds on the capacity region of
optical intensity multiple access channel (OIMAC) with per-user average or peak
power constraint. For the average power constrained OIMAC, our bounds at high
power are asymptotically tight, thereby characterizing the asymptotic capacity
region. The bounds are extended to K-user OIMAC with average power constraint
without loss of asymptotic optimality. For the peak power constrained OIMAC, at
high power, we bound the asymptotic capacity region to within 0.09 bits, and
determine the asymptotic capacity region in the symmetric case. At moderate
power, for both types of constraints, the capacity regions are bounded to
within fairly small gaps.
