# A Review-Unguided Optical Communications: Developments, Technology Evolution, and Challenges
## 6 Contemporary Developments with UOC Technology
### FSO and VLC with Energy Harvesting
The access point comprised four coordinators that managed the functions of illumination and data communication. The devices were passive, i.e., not originally powered, and harvested energy from the access point. The power distribution for EH within a room to all the devices were analyzed considering the obstruction probability from moving people. Throughput in terms of transmit power over all the devices were analyzed, and fairness indices of 0.72 and 0.57 were achieved with and without the EH technique, respectively. Gaofeng Pan and Zhiguo Ding proposed a hybrid visible light-RF communication system with a legitimate receiver (R) and an eavesdropper (E). In the proposed hybrid system, R harvested energy from the optical signal that was emitted for data communication between R and the RF receiver stations. Characterization of the statistics of the received optical SNR at the RF and E stations was conducted considering the random locations of R and E. The stochastic geometry method was used to derive and validate analytical expressions for the exact and asymptotic secrecy outage probability [476]. In Ref. [477], three main folds of VLC: illumination, communication, and EH, were highlighted. The VLC-based EH technique for wireless networks and high-speed data transmission connectivity fulfilled the requirements of next-generation high-data-rate, energy-efficient, and sustainable wireless communication demands. Hongjiang Lei et al. analyzed a secure wireless downlink data and power transmission technique over a hybrid RF-FSO system. It was found from the experiment that the Gamma-Gamma fading model shows close correlation with FSO channels and the Nakagami-m fading model for RF channels. The impact of pointing errors, beam centroid, atmospheric turbulence, the data detection algorithm, optical path attenuation, and EH on the secrecy performance are also discussed and the associated closed-form models were derived. Monte Carlo simulations were used to verify the accuracy of the results. It was shown that the total number of antennas at the receiver and fading parameters of the relay-to-receiver channel contribute more and determine the optical secrecy diversity order [478]. Panagiotis et al. presented a technique for linking indoor wireless IoT devices by transferring data and power, called simultaneous light-wave information and power transfer (SLIPT). A new SLIPT stage consists of a visible light or IR communication system and a solar panel as an optical receiver. Three strategies: adjusting the transmission, reception, and both, for maximizing the transmission of both information and power were suggested. The quality of service, efficiency of EH, and their trade-off at the receiver for the proposed SLIPT were analyzed and optimally solved. Results obtained from this SLIPT scheme were compared to a static (fixed policy) EH system and the significant improvements attained were highlighted [479]. A wireless VLC/IR downlink data and power transmission model via SLIPT is shown in Figure 40a. Due to the fast increase in the demand for the deployment of wireless IoT sensor nodes, harvesting energy from the surrounding environment becomes a mandatory requirement to increase the existence of energy-constrained IoT wireless nodes that build wireless sensor networks. Gaofeng Pan et al. presented a technique for transferring data and power over a light wave. In the proposed technique, the authors designed a realizable receiver, signals/component integration system, and photoelectric conversion module. This work also addressed several possible research scopes in the field of network topologies, hybrid RF-VLC, wireless optical communications, secure communications, etc. [480]. Three receiver architectures, proposed in [480], for separating the signals for EH and information decoding are shown in Figure 40b-d. Signal separation is simply achieved in the first architecture by using two disconnected circuits. Each has a different functionality, i.e., EH via a diode (D) or data decoding via a capacitor (C).