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Journal of China Institute of Metrology

Performance of optical fiber as a quantum channel

Xiao Chen

Published Jan 1, 2001• 0 citations
OpenAlex

Abstract

In this paper we investigate the noise properties and classical capacity of an optical fiber which is considered as a quantum channel. The noise is due to nonlinear crosstalk between the modes of dense wavelength division multiplexing system. With displacement operator method the total quantum noise is obtained, and a quantum channel model with attenuation and noise is proposed. We conclude that the noise of the mode is of thermal radiation type if all other modes contribute an equally crosstalk to the one considered. Classical capacity is obtained for given parameters of channel.

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In this paper we investigate the noise properties and classical capacity of an optical fiber which is considered as a quantum channel. The noise is due to nonlinear crosstalk between the modes of dense wavelength division multiplexing system. With displacement operator method the total quantum noise is obtained, and a quantum channel model with attenuation and noise is proposed. We conclude that the noise of the mode is of thermal radiation type if all other modes contribute an equally crosstalk to the one considered. Classical capacity is obtained for given parameters of channel.
The primary goal in this paper is to verify the possibility of combining a quantum channel into a single optical fiber with other classical channels by using the so-called attenuation method. Since the quantum channel is very weak in terms of power, combining it into a single fiber with much more powerful classical channels is challenging. Thus, sufficiently high-quality filtering is important to avoid possible crosstalk. A second and more difficult problem to address is the interference caused by Raman noise, which increases with the fiber length and is also dependent on the input power of the classical channel. Thus, in this paper the focus is on the possibility of suppressing the Raman noise effect, both in advance by means of wavelength positioning and by means of installed optical components. Such phenomena must be considered in the route design, as the quantum channel must be placed at a suitable wavelength with respect to the classical channels. The influence of other nonlinear phenomena has been neglected. In this paper, a practical experiment aimed at building a fully functional multiplexed quantum key distribution link is also described.
Integrating a quantum communication channel with classical optical communication is a cost-effective, deployment-friendly solution to provide secure data transmission over optical fibres. However, the noise introduced by intense classical signals into the quantum channel severely impacts the performance of quantum communication. This paper evaluates the impact of optical attenuation and Spontaneous Raman Scattering in the quantum communication system. A hybrid Dense Wavelength Division Multiplexing (DWDM) and Coarse Wavelength Division Multiplexing (CWDM) solution is investigated by combining experimental and theoretical work. The optimal wavelength allocation strategy is defined.
The optical signal transmitted on a fiber with thermal noise, attenuation and amplification is studied. The channel is considered as a quantum channel while the signal to be transmitted is classical. The classical information is encoded in a quantum state then it is transmitted in optical fiber. At the receiving end, measurement is performed on the output quantum state to retrieve the classical information. The optimal distribution of the input quantum state achieving the channel capacity is Gaussian. The capacity is characterized by the attenuation/amplification coefficient and thermal noise in the transmission and at the measurement process together by the power of the input. The loss (or attenuation) of an optical fiber usually should be compensated by the amplification. We show that when they coexist, additional noise occurs
Integrating Quantum Key Distribution service with classical high-speed optical data transmission using a dense wavelength division multiplexing technique in a fiber is a cost-effective solution to improve the network's security. In this multichannel system, several noise sources degrade the quality of the quantum channel. The dominant degradation effect is determined by modeling in different cases. Optical filtering cannot decrease spontaneous Raman Scattering caused by the classical optical channels. So this nonlinear optical effect is investigated in detail with different system parameter setups. The optimal channel allocation and the required bandgap between the classical and quantum channels are determined.
Mode-division multiplexing using multimode optical fibers has been intensively studied in recent years, in order to alleviate the transmission capacity crunch. Moreover, the need for secure information transmission based on quantum encryption protocols leads to investigating the possibility of multiplexing both quantum and classical signals in the same fiber. In this work, we experimentally study the modal multiplexing of both quantum and classical signals at telecom wavelengths, by using a few-mode fiber of 8 km and modal multiplexers/demultiplexers. We observe the existence of random-mode coupling at the quantum level, leading to cross-talk among both degenerate and non-degenerate channels. Our results demonstrate the feasibility of using few-mode fibers for simultaneously transmitting classical and quantum information, leading to an efficient implementation of physical information encryption protocols in spatial-division multiplexed systems.