Cross-Medium Photoacoustic Communications: Challenges, and State of the Art

Abstract

The current era is notably characterized by the major advances in communication technologies. The increased connectivity has been transformative in terrestrial, space, and undersea applications. Nonetheless, the water medium imposes unique constraints on the signals that can be pursued for establishing wireless links. While numerous studies have been dedicated to tackling the challenges for underwater communication, little attention has been paid to effectively interfacing the underwater networks to remote entities. Particularly it has been conventionally assumed that a surface node will be deployed to act as a relay using acoustic links for underwater nodes and radio links for air-based communication. Yet, such an assumption could be, in fact, a hindrance in practice. The paper discusses alternative means by allowing communication across the air–water interface. Specifically, the optoacoustic effect, also referred to as photoacoustic effect, is being exploited as a means for achieving connectivity between underwater and airborne nodes. The paper provides background, discusses technical challenges, and summarizes progress. Open research problems are also highlighted.

Optical Focusing-Based Adaptive Modulation for Air-to-Underwater Optoacoustic Communication

“…This plasma formation is associated with a breakdown shockwave and the subsequent cavitation bubble expansion-collapse shockwaves, which generate the acoustic signal. The breakdown threshold, plasma formation, and acoustic signal generation depend on the laser parameters, as discussed in detail in [22]. In order to generate acoustic signals in the water, the irradiance threshold values are in the order of 10 11 W/cm 2 for a few nanosecond pulse durations and rise up to 10 13 W/cm 2 for a 100 femtosecond pulse duration laser source [35].…”

“…While microwaveinduced thermoacoustic signals can be another alternative [21], the generated signal is not strong enough to support long-haul communication. The optoacoustic process is a more attractive option and enables reaching nodes in deep water from the air, where an acoustic signal is generated when high-intensity light (laser) impinges on a liquid medium like water [22].…”

A Review–Unguided Optical Communications: Developments, Technology Evolution, and Challenges

“…In the other two methods, a relay (light absorbers-refer to Figure 31) absorbs the light and generates the acoustic wave by thermal expansion, i.e., temperature rise [209,218]. These phenomena bring the photoacoustic effect, which is being increasingly used in medicinal [219] as well as industrial applications [220]. Furthermore, because of the high optical absorption coefficient of contrasting agents of relay, the strength of a photoacoustic pulse is directly related to its absorbing factor and it can enhance the acoustic energy transfer performance [209].…”

A Comprehensive Review on Photoacoustic-Based Devices for Biomedical Applications

“…Figure 3 exhibits a graphical explanation of the photoacoustic effect. At its core, the photoacoustic effect lies in the formation of a US wave from light absorption in a material with specific characteristics [ 73 ]. Thereupon, a source of modulated or pulsed light, a material/composite with both high optical absorption and high thermal expansion coefficient, and a US detector are indispensable to efficiently convert the light pulse into the US and subsequently detect it [ 34 , 50 , 54 , 63 , 68 , 74 , 75 ].…”