the paper is organized as follows. Section \[sec:SYSTEM-MODEL\] presents the system model. In Section \[sec:Pulse-shaping\], we define the Nyquist pulses that have been used extensively for conventional bandlimited channels, as well as the ones that have been suggested for nonnegative bandlimited channels. In Section \[sec:RootPulse-shaping\], the root-Nyquist pulses used in this study are introduced. Section \[sec:Required-DC-bias\] discusses a method of computing the required DC bias for a general pulse. Section \[sec:RESULTS\] introduces the performance measures and analyzes the performance of the system under different scenarios. Finally, conclusions are drawn in Section \[sec:CONCLUSIONS\] on the performance of the system.

System Model\[sec:SYSTEM-MODEL\]
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In applications such as diffuse indoor wireless optical links and short-haul optical fiber communications, where inexpensive hardware is used, IM/DD is often employed. In such systems, the data is modulated on the optical intensity of the transmitted light using an optical intensity modulator such as a laser diode or a light-emitting diode. This optical intensity is proportional to the transmitted electrical signal. As a result, the transmitted electrical signal must be nonnegative. This is in contrast to conventional electrical channels, where the data is modulated on the amplitude and phase of the carrier . In the receiver, the direct-detection 