# A Review-Unguided Optical Communications: Developments, Technology Evolution, and Challenges
## 7 UOC Near-Future Network Scenarios and Research Challenges
### UOC--Today's Research Challenges
#### 7.2.5 Li-Fi Technology Concept for All-Optical Networks for Both Fixed and Mobile Terminals  
Soon, Li-Fi technology will more than likely be used to create both residential and public hotspots for internet access for both fixed and mobile users. The IoT and 5G/6G will certainly benefit from Li-Fi technology. Thus, all UOC terminals will eventually be integrated with global Internet gateways and optical nodes that integrate optical devices and laser/optical transceivers. Some recent advances in infrared (IR) and VLC for high-data-rate communications are discussed below. Infrared technology has advanced to the point where it can be used for a wide range of applications and devices that adhere to Infrared Data Associations (IrDA) standards. Home-access networks (HANs) using bi-directional Gb/s IR optical wireless communications are reported in [497]. The research approach explains how to expand the indoor FOV of high-speed IR links by combining many narrow FOV links to generate a broader FOV, utilizing a cellular communication scheme. Their results show that when using an 825 nm laser diode Tx source and an APD receiver with integrated preamplifier, a BER of 10-9 at a 1.25 Gbit/s data rate was measured. At an optimal wavelength of 1550 nm, a broad FOV IR transparent wireless fiber link with a capacity of more than 100 Gbps has been achieved by combining a narrow beam (\(\pm 0.15^{\circ}\)) link with wide-angle holographic beam splitting at both Tx and receiver, utilizing a spatial light modulator (SLMs). Furthermore, digital coherent WDM transmission at 112 Gbps and 224 Gbps at full angles of \(60^{\circ}\) and \(360^{\circ}\) was presented. The employment of a high-speed photoreactor (>GHz) in conjunction with QAM-OFDM offers the potential to improve data rates.  
Light fidelity (Li-Fi) is a wireless optical networking technology that uses light-emitting diodes (LEDs) or laser diodes (LD) to transmit data. At the same time, Li-Fi functions as a source of illumination and communication. The photodetector is a light sensor that can be a laptop, tablet, smartphone, or other optically equipped device, while the Tx is an LED/LD source. A light bulb connected to a microchip for processing (which can turn OFF or ON at very high speeds) sends light to a microchip, which then flicks the bulb from OFF to ON. The data are encoded first and then modulated. The data from a wireless modem are retrieved via a card reader or dongle (for both uplink and downlink) that is plugged into a laptop or tablet through a USB. Multiple users can be connected to a single light source with a networking component without losing connectivity due to movement, which is a necessity for 5G/6G and IoT applications [498]. The photodetector can be changed for scanning and retrieving data with a simple modification, such as an ultra-small camera in a mobile phone, allowing Li-Fi to be used as a receiving platform. A microchip can be placed into LED/LD lamps to turn them into internet hotspots. Li-Fi technology can meet the massive future connectivity demands of mobile consumers connecting to IoT applications. Reference [491] has more thorough information on the architecture of connecting to the internet using Li-Fi technology and on various sorts of data applications for numerous users.