High Rate CV-QKD Secured Mobile WDM Fronthaul for Dense 5G Radio Networks

Abstract

A coherent transmission methodology for a continuous-variable quantum key distribution (CV-QKD) system based on quantum-heterodyne measurement through a coherent intradyne receiver is experimentally demonstrated in the framework of 5G mobile fronthaul links. Continuous optical carrier synchronization is obtained through training information, which is multiplexing to the quantum signal as pilot tone in both, frequency and polarization. Spectral tailoring by means of optical carrier suppression and single-sideband modulation is adopted to simultaneously mitigate crosstalk into the quantum channel and self-interference for the pilot tone, thus allowing for a high signalto-noise ratio for this training signal. Frequency offset correction and optical phase estimation for the free-running local oscillator of the receiver is accurately performed and guarantees low-noise quantum signal reception at high symbol rates of 250 MHz and 500 MHz with additional Nyquist pulse shaping. A low excess noise in the order of 0.1% to 0.5% of shot-noise units is obtained for fiber-based transmission over a fronthaul link reach of 13.2 km. Moreover, co-existence with 11 carrier-grade classical signals is experimentally investigated. Joint signal transmission in the C-band of both, quantum signal and classical signals, is successfully demonstrated. Secure-key rates of 18 and 10 Mb/s are obtained under strict security assumptions, where Eve has control of the receiver noise, for a dark and a lit fiber link, respectively. Moreover, rates of 85 and 72 Mb/s are resulting for a trusted receiver scenario. These secure-key rates are well addressing the requirements for time-shared CV-QKD system in densified 5G radio access networks with cloud-based processing.

Chip-Level GHz Capable Balanced Quantum Homodyne Receivers

“…The linearity depends on the magnitude of the input signal. Even though boosted by the LO, the expected quantum signal levels are still relatively weak, but strong pilot tones can exist for synchronization and LO training [21], which means that TIAs of sufficiently high linearity need to be employed. To determine the linearity range, a single tone was produced by heterodyne beating of two lasers, including a probe laser with variable output power and a LO laser set for a fixed power of 100 µW 8(a)).…”

Experimental Demonstration of LLO Continuous-Variable Quantum Key Distribution With Polarization Loss Compensation

“…GMCS protocol is also the most widely used protocol because the preparation and reception of quantum states can be realized entirely by commercial optical devices such as lasers, optical modulators, and balanced homodyne detectors [11], [12]. In addition, there are also important theories and implementations in the application of networking [13], [14]. In the GMCS CV-QKD scheme, there are two types of systems named by transmitting local oscillator (TLO) and local local oscillator (LLO) for whether Alice sends the local oscillator (LO) signal to Bob.…”

Digital synchronization for continuous-variable quantum key distribution

“…The disadvantage of this method is of course requiring another transmitter (Tx) and receiver (Rx) at this wave-length. Many proof-of-principle experiments in the lab therefore resort to electrical synchronization of the waveform generator and the data acquisition device [9,[15][16][17][18].…”