A directly phase-modulated light source

TL;DR

This paper introduces a novel directly phase-modulated light source that overcomes limitations of traditional direct modulation, enabling high-speed, stable, and pure phase states suitable for secure quantum communication and coherent optical systems.

Contribution

It presents an innovative phase modulation technique separating phase preparation from pulse generation, achieving sub-volt halfwave modulation at high rates, advancing quantum communication technology.

Findings

Achieved sub-volt halfwave phase modulation at high signal rates.

Produced very pure phase states suitable for quantum cryptography.

Demonstrated a compact, stable, and versatile light source.

Abstract

The art of imparting information onto a light wave by optical signal modulation is fundamental to all forms of optical communication. Among many schemes, direct modulation of laser diodes stands out as a simple, robust, and cost effective method. However, the simultaneous changes in intensity, frequency and phase are a drawback which has prevented its application in the field of secure quantum communication. Here, we propose and experimentally demonstrate a directly phase-modulated light source which overcomes the main disadvantages associated with direct modulation and is suitable for diverse applications such as coherent communications and quantum cryptography. The source separates the tasks of phase preparation and pulse generation between a pair of semiconductor lasers leading to very pure phase states. Moreover, the cavity enhanced electro-optic effect enables the first example of sub-volt halfwave phase modulation at high signal rates. The source is compact, stable and versatile, and we show its potential to become the standard transmitter for future quantum communication networks.