The spectral efficiency (channel capacity) of the optical direct-detection channel is studied. The modeling of the optical direct-detection channel as a discrete-time Poisson channel is reviewed. Closed-form integral representations for the entropy of random variables with Poisson and negative binomial distributions are derived. The spectral efficiency achievable with an arbitrary input gamma density is expressed in closed integral form. Simple, nonasymptotic upper and lower bounds to the channel capacity are computed. Numerical results are presented and compared with previous bounds and approximations.
© 2007 Optical Society of America
Fiber Optics and Optical Communications
Original Manuscript: July 14, 2006
Revised Manuscript: November 7, 2006
Manuscript Accepted: November 7, 2006
Published: March 15, 2007
Alfonso Martinez, "Spectral efficiency of optical direct detection," J. Opt. Soc. Am. B 24, 739-749 (2007)