Characterising the insertion loss of quantum-grade components and connectors (i.e., quantum grade patch cords, novel fibre, or quantum photonic integrated circuits) is crucial for evaluating their performance and suitability for transmitting fragile quantum information. Insertion loss refers to the amount of signal power that is lost when passing through a component or connector compared to the input power. Excessive loss can significantly degrade the quality of the transmitted quantum signal, leading to errors and reduced success rates in communication protocols like quantum key distribution (QKD) and entanglement-based communication.
Flawless photon flow
The range of interconnects utilised within any Quantum Internet or entanglement distribution system must possess extremely high propagating signal efficiencies. The inevitable inclusion of connectorized links, within a network, will potentially add to the loss budgets drastically reducing operating ranges. Knowledge of key parameters such as the insertion loss and mode field diameter (MFD) of these links and components are vital to maintain performance.
The National Physical Laboratory has developed a precision insertion loss system to measure the intrinsic losses of ultra-low loss interconnects such as Quantum grade patchcords and quantum photonics integrated circuits (QPIC’s) for use within a quantum network. Insertion loss can also fluctuate depending on the operating wavelength of the quantum signal. Components like filters or gratings can exhibit varying loss characteristics across the signal spectrum.
In addition to insertion losses, the transmission of entangled photons over long distances is dependent on coupling efficiencies that relate directly to connector build and the subsequent effect it may have on the key parameter called Mode Field Diameter, i.e., the guided width of the fundamental mode. MFD mismatching between network links and non-circularities of the MFD can be a significant cause of decoherence by affecting the polarisation of the entangled photons. Measurements of MFD using NPL’s far-field scanning system can assess the build performance of commercial quantum grade connectors therefore providing direct support for industry.
Building resilient Quantum Networks
By meticulously analysing the insertion loss and MFD of quantum-grade components and connectors, network designers can meet the challenges through careful characterisation, optimisation of systems and developing standards for efficient and reliable transmission of quantum information, laying the groundwork for the development of robust and secure quantum communication infrastructure.
The NPL systems provide the capability to provide direct support and quality assurance in key quantum challenges. This is of interest to those working in quantum key distribution (QKD) or developing components such as quantum grade patchcords, novel fibre or QPICs as well as providing measurement capability for few photons metrology.
Beyond loss
Other well-established optical fibre services will help to support the successful deployment of a quantum network infrastructure capable of enabling maximum quantum efficiency and entanglement distribution. NPL is well-placed to characterise other key parameters that impact network efficiency, such as mode field diameter, effective area and fibre geometry.
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