Fast optical source for quantum key distribution based on semiconductor optical amplifiers

TL;DR

This paper presents a fast, integrated optical source for quantum key distribution using semiconductor optical amplifiers, achieving high secure key rates suitable for satellite communication.

Contribution

A novel, compact optical source with high indistinguishability and polarization control for quantum key distribution, demonstrated with record secure key rates.

Findings

Achieved a secure key rate of 3.64 Mbps in lab conditions.

Demonstrated low quantum bit error ratio of 1.14×10⁻².

System suitable for space applications due to size, power, and component robustness.

Abstract

A novel integrated optical source capable of emitting faint pulses with different polarization states and with different intensity levels at 100 MHz has been developed. The source relies on a single laser diode followed by four semiconductor optical amplifiers and thin film polarizers, connected through a fiber network. The use of a single laser ensures high level of indistinguishability in time and spectrum of the pulses for the four different polarizations and three different levels of intensity. The applicability of the source is demonstrated in the lab through a free space quantum key distribution experiment which makes use of the decoy state BB84 protocol. We achieved a lower bound secure key rate of the order of 3.64 Mbps and a quantum bit error ratio as low as $1.14\times 10^{-2}$ while the lower bound secure key rate became 187 bps for an equivalent attenuation of 35 dB. To our knowledge, this is the fastest polarization encoded QKD system which has been reported so far. The performance, reduced size, low power consumption and the fact that the components used can be space qualified make the source particularly suitable for secure satellite communication.