Underwater communication (UWC) has become an important data transmission technology for commercial and military marine applications in the past couple of decades. Besides regular communication inside the water, other applications include Remotely Operated Vehicles (ROV), Underwater Sensor Networks (UWSN), Autonomous Underwater Vehicles (AUV), underwater sports, coastal surveillance systems, environmental research, oil-rig maintenance, linking submarines to land, etc. The main limitations of Underwater Acoustic Communication are frequency-dependent attenuation, short range of communication, very low bandwidth, and very low data rates for monitoring applications because of velocity of sound in water. To beat the restrictions of acoustic communication is to use optical communication whose wavelength lies within the visible region. Consistent with our survey on the properties of acoustic and optical communication, results have shown significant trade-offs between bandwidth, propagation delay, power consumption, SNR, BER and effective communication range. We propose a hybrid solution that mixes the uses of both acoustic and optical communication with the assistance of opto-acoustic modems. Hence, this hybrid approach leads to high data rates, low latency, and an energy-efficient system. Thus, an underwater opto-acoustic modem plays an important role for long distance signal transmission in underwater. This paper provides a comprehensive study of the recent developments and challenges in various underwater modems and also addresses the gaps in development of modems for long distance under water communication. This paper not only provides exhaustive research in underwater acoustic/optical communication using opto-acoustic modems but also aims to provide the development of new ideas that would help in the growth of future underwater communication using fifth generation (5G) communication techniques.