The need for low-complexity and cost-effective systems has motivated the usage of affordable optical hardware (e.g., incoherent transmitters, optical intensity modulators, multimode fibers, direct-detection receivers) to design short-haul optical fiber links (e.g., fiber to the home and optical interconnects)[@4528765; @5875697] and diffuse indoor wireless optical links [@gfeller2005wireless; @kahn2002wireless; @hranilovic2005design]. These devices impose three important constraints on the signaling design. First, the transmitter only modulates information on the instantaneous intensity of an optical carrier, contrary to conventional coherent channels where the amplitude and phase of the carrier can be used to send information . In the receiver, only the optical intensity of the incoming signal will be detected [@kahn2002wireless]. Due to these limitations, the transmitted signal must be nonnegative. Such transmission is called intensity modulation with direct detection (IM/DD). Second, the peak and average optical power (i.e., the peak and average of the transmitted signal in the electrical domain) must be below a certain threshold for eye- and skin-safety concerns [@kahn2002wireless] and to avoid nonlinearities present in the devices [@westbergh200932; @inan2009impact]. In conventional channels, such constraints are usually imposed on the peak and average of the squared electrical signal. Third, the bandwidth is limited due to the impairments in the optoelectronic 