In intensity-modulation and direct-detection (IM/DD) fiber-optic communications, it is hard to pre- or post-compensate for chromatic dispersion (CD) by digital signal processing due to one-dimensional modulation and detection. In this Letter, we propose joint optical and digital signal processing to effectively compensate for CD-caused distortions for IM/DD optical systems. As a reasonable optical signal processing, negative chirp based on self-phase modulation can suppress a part of CD to take pressure off digital signal processing. Digital signal processing is designed based on the model of a dispersive channel to accurately compensate for CD-caused distortions. To the best of our knowledge, we present a record C-band 72 Gbit/s optical on-off keying over 100 km dispersion-uncompensated link (i.e., ∼1700ps/nm dispersion), achieving a 7% hard-decision forward error correction limit. We conclude that joint optical and digital signal processing is effective in dealing with CD-caused distortions to achieve a higher capacity-distance product in IM/DD fiber-optic communications.