A simple method for detecting a signal encoded by coherence modulation without the use of any decoder interferometer is demonstrated. The technique is based on wavelength filtering of the channelled spectrum in the transmission link. To overcome this vulnerability in the scheme, more secure coherence modulation arrangements are proposed.
In this presentation, we discuss the security aspect of coherence modulation for telecommunications. Recently, we demonstrated a simple technique for decoding the signal without any decoder interferometer. We now demonstrate a secure alternative method based on the corruption of the interferometer's optical path difference. Experimental results at low bit rate using fiber interferometers as well as transmission at high bit rates using large-imbalanced integrated optic interferometers are presented. Considerations about the polarization state of the light are also discussed.
We show that key-specified interferometer path-length difference modulation (often referred to as coherence modulation), operating in the photon-counting regime with a broadband source, can provide a quantifiably high level of physics-guaranteed security for binary signal transmission. Each signal bit is associated with many photocounts, perhaps numbering in the thousands. Of great importance, the presence of an eavesdropper can be quickly detected. We first review the operation of key-specified coherence modulation at high light levels, illustrating by means of an example its lack of security against attack. We then show, using the same example, that, through the reduction of light intensities to photon-counting levels, a high level of security can be attained. A particular attack on the system is analyzed to demonstrate the quantifiability of the scheme's security, and various remaining research issues are discussed. A potential weakness of the scheme lies in a possible vulnerability to light amplification by an attacker.
We develop a spread-spectrum-based approach to security-enhanced transmission over an existing public wavelength-division-multiplexing (WDM) lightwave network. Secure transmission for a dedicated user is achieved by overlaying a covert channel onto a multichannel WDM network. The covert channel is spectrally encoded using the technique of frequency hopping and then temporally spread by a dispersive element, with the resulting average power below the noise floor in the fiber. The presence of the WDM channels provides an ad hoc security expansion and increases the difficulty for an eavesdropper to intercept and decode the secure signal
This paper proposes a novel communication protocol leveraging the principles of quantum coherence decay for enhanced security. The core idea is to utilize the inherent fragility of quantum coherence – the tendency of a quantum system to lose its superposition and entanglement – to both protect and encrypt quantum information during transmission. The protocol utilizes a specific measurement strategy designed to exploit the decay of coherence, introducing a level of uncertainty that significantly increases the difficulty for eavesdroppers to intercept and reconstruct the transmitted information. Mathematical formalism is presented to describe the key aspects of the protocol, including the encoding scheme based on coherent state manipulation and the measurement process designed to detect and mitigate decoherence. The proposed approach represents a significant advancement in quantum communication security by directly addressing the fundamental vulnerability of quantum states to environmental noise. The protocol's effectiveness is demonstrated through theoretical analysis, highlighting the potential for creating secure quantum communication channels.