Photonics & VLC for 6G : Features, Benefits and Limitations

Introduction : The integration of photonics and Visible Light Communications (VLC) represents a significant expansion of 6G’s capabilities beyond the traditional radio frequency (RF) spectrum.

In 6G contect, these are two related but distinct concepts.

• Photonics is the broad, underlying science and technology of generating, controlling and detecting photons (light particles).

• Visible Light Communications (VLC) is a specific application of photonics for wireless data transmission.

1. Photonics : It is poised to be an integral part of the entire 6G network architecture. Its roles include Transforming the Core Network, enabling ultra-secure communications using Quantum Key Distribution (QKD) and use of Photonic Integrated Circuits (PICs) for complex routing & processing of light. It uses concept called “open all photonics network (APN)” which uses light to represent data signals traveling through fiber optics and photonic switches.

2. Visible Light Communications (VLC) : It is popularly known as Li-Fi (“Light Fidelity”). It is a wireless communication technology that uses the light from commercial LED bulbs to transmit data. Following steps describe end to end Li-Fi system.

• An LED light is a semiconductor that can be turned on and off extremely quickly.
• By modulating the intensity of the light at speeds imperceptible to the human eye, a stream of binary data (1s and 0s) can be encoded into the light itself.
• A receiver, such as a simple photodiode on a laptop or smartphone, detects these rapid changes in light intensity and decodes them back into data.

VLC is a “complementary technology” to RF systems like Wi-Fi and cellular. It is not intended to replace them entirely but to provide a powerful alternative in specific environments.

Advantages of Photonics and VLC

Following are some of the benefits of photonics and VLC.

1. The visible light spectrum offers approximately 300 THz of license free bandwidth. This is thousands of times more bandwidth than the entire RF spectrum combined, offering the potential for extremely high data rates.
2. Light does not penetrate opaque surfaces like walls. This physical limitation is a major security advantage. A VLC network is contained within a room, preventing eavesdropping from outside.
3. VLC operates in a different part of the electromagnetic spectrum and does not interfere with radio waves. This makes it perfect for use in RF sensitive environments like hospitals (around MRI machines), airplane cabins and industrial plants where RF interference can be a major problem.
4. The vast available bandwidth can support multi Gigabit per second data rates. When combined with an “all-photonics network” backbone, it can contribute to an end to end low latency communication link.
5. VLC can leverage existing infrastructure. Since buildings are already equipped with LED lighting, the same infrastructure used for illumination can be dual purposed for data communication with minimal additional hardware, leading to low deployment costs.

Disadvantages of Photonics and VLC

Following are some of the Limitations and Challenges of photonics and VLC.

1. The receiver must have a direct, unobstructed path to the light source. If a person walks under the light or an object blocks the path, the connection can be interrupted.
2. A single light source (like an LED bulb) provides coverage in a relatively small area, typically a cone of light beneath it. Providing seamless coverage throughout a large room or building would require a dense network of Li-Fi-enabled lights and a sophisticated system to hand over the connection as a user moves from one light’s coverage zone to another.
3. While receiving data from a ceiling light (downlink) is straightforward, transmitting data back from the user device (uplink) is more complex. The device would need its own light transmitter (likely infrared) which must be pointed towards a receiver in the ceiling, consuming battery and requiring careful orientation. Often, a hybrid approach is proposed where the uplink falls back to a traditional RF channel like Wi-Fi.
4. Strong external light sources, particularly direct sunlight, can “dazzle” the photodiode receiver and interfere with the data signal, degrading performance.

Summary: VLC and photonics technologies offer a compelling avenue to break through the limitations of RF wireless systems; providing large bandwidth, low interference and dual use illumination/communication. Nonetheless, the technology faces intrinsic constraints such as line of sight dependency, limited uplink support and sensitivity to ambient light conditions.