India has reached a landmark milestone in its journey toward digital sovereignty and secure communication infrastructure. STL (Sterlite Technologies Limited), a global leader in optical and digital networking, in partnership with C-DOT (Centre for Development of Telematics), has successfully demonstrated India’s first Quantum Key Distribution (QKD) transmission over a 100-km long, 4-core Multi-Core Fibre (MCF) network. This is a first-of-its-kind deployment in India, pushing the boundaries of secure and high-capacity telecom networks.

Strategic Collaboration: STL and C-DOT Join Forces

The collaboration between STL and C-DOT is an example of public-private partnership in next-generation telecom R&D. C-DOT, the telecom R&D centre under India’s Department of Telecommunications (DoT), joined hands with STL, which is known for its expertise in optical networking, connectivity, and digital infrastructure solutions. Their combined capabilities made this quantum-secured communication breakthrough possible.

Dr. Rajkumar Upadhyay, CEO of C-DOT, lauded the effort, calling it a "key milestone" in India’s fibreisation and secure communication journey. Rahul Puri, CEO of STL’s Optical Networking Business, emphasized that the project reflects India’s growing leadership in cutting-edge digital infrastructure.

Quantum Key Distribution (QKD): The Future of Secure Communication

Quantum Key Distribution (QKD) is a method of secure communication that uses quantum mechanics to enable two parties to generate a shared, random secret key known only to them. It is virtually impossible to hack, as any eavesdropping attempt changes the quantum state of the data, making it detectable.

However, one of the major challenges in implementing QKD is the requirement for dedicated dark fibre, which increases deployment costs and infrastructure complexity. STL and C-DOT’s innovation solves this issue using Multi-Core Fibre (MCF) technology.

What is Multi-Core Fibre and Why It Matters

Multi-Core Fibre (MCF) is an optical fibre that contains multiple independent cores within a single fibre cladding. In this demonstration, STL used a 4-core fibre, where:

• One core was used for transmitting quantum signals

• The remaining three cores carried high-speed user data

This innovative design allowed both quantum communication and classical data transmission to occur simultaneously over a single fibre, without interference or compromise in signal integrity. It addresses two major industry challenges:

1. Eliminates the need for dark fibre for quantum channels

2. Optimizes network infrastructure to handle growing data demands, including 5G and upcoming 6G networks

End-to-End Multi-Core Fibre Deployment by STL

STL’s role in this achievement goes beyond innovation—it extends to design, development, cabling, connectivity, and installation of the entire solution. STL became the first company globally to deploy MCF for both aerial and underground networks.

The deployment was carried out at the Advanced Optical Communications (AOC) Test Bed at IIT Madras, supported by the DoT. STL's MCF cable and deployment solutions were in full compliance with Essential Requirements (ER) led by Telecommunication Engineering Centre (TEC) standards.

Real-World Validation over 100+ Km

The demonstration was not a lab test—it was a real-world deployment that proved the stability and resilience of the network under field conditions. STL and C-DOT successfully transmitted:

• Quantum signals via one core using QKD

• High-speed classical user data via the remaining three cores

over more than 100 km of optical fibre.

The error-free QKD link, combined with simultaneous high-capacity data transmission, validated the solution’s feasibility for actual telecom networks and nationwide rollout.

Implications for 5G/6G and National Security

The successful integration of QKD with MCF directly contributes to:

• Secure and scalable 5G/6G networks

• Enhanced cybersecurity for government and enterprises

• Optimized telecom infrastructure with reduced cost

As India scales up its data-intensive services, from smart cities to IoT, defence communications to AI applications, the need for a resilient and secure optical backbone is paramount. This project offers a future-ready solution that meets those demands.

Global Significance and Standardization Leadership

Beyond India's borders, this breakthrough places STL at the forefront of global telecom standardization. The company is now leading efforts in developing test and measurement technologies for MCF globally. This ensures that India is not just a consumer of innovation, but a contributor to global telecom standards.

Public-Private Synergy: The Future of India’s Digital Infrastructure

This milestone is a shining example of how synergies between public institutions and private technology leaders can fast-track India’s journey toward a digitally sovereign and secure future.

The integration of quantum technologies with advanced optical infrastructure is set to be a game-changer in secure communications, paving the way for quantum internet, secure financial systems, military-grade data networks, and more.

Conclusion

The successful demonstration by STL and C-DOT marks a critical turning point in India’s telecom evolution. By achieving simultaneous quantum and classical data transmission over a single MCF, they have not only overcome long-standing technical challenges but also set the stage for a nationwide quantum communication network.

As STL continues to lead in innovation, and with government-backed institutions like C-DOT driving strategic R&D, India is well-positioned to shape the future of secure global communication infrastructure.

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