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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Classical and quantum coherence modulation

J.-P. Goedgebuer, Jean-Marc Mérolla

Published Nov 10, 1995• 0 citations
Publisher

Abstract

Coherence modulation of light consists in coding a signal as an optical delay greater than the coherence length of light. It makes use of interferometers powered by sources which exhibit a short coherence length. Such sources can be operated either as classical sources or quantum sources. We describe some applications dealing with optical communications and quantum cryptography.

DOI
10.1117/12.226676

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Coherence modulation of light consists in coding a signal as an optical delay greater than the coherence length of light. It makes use of interferometers powered by sources which exhibit a short coherence length. Such sources can be operated either as classical sources or quantum sources. We describe some applications dealing with optical communications and quantum cryptography.
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In this conference, we demonstrate a new communication system exhibiting a double security level. Information coding is based on differential phase shift keying of the light emitted from a highly coherent CW source. An imbalanced Mach-Zehnder interferometer whose time delay matches the bit duration is used to decode the data. Since the optical power is constant in the transmission link, security levels comparable with those obtained in coherence modulation may be achieved. To further enhance the security, a low coherent source is used to send false data down the transmission link. The discrimination between real and false signal is based on common mode rejection. A study of the signal to noise ratio achieved with this system is also discussed in this manuscript.
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 have 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 subvolt half-wave 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 based on attenuated laser pulses.
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 have 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 subvolt half-wave 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 based on attenuated laser pulses.