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Optics Letters

Quantum-limited transmission distance of optically repeating systems using a hybrid EDFA/Raman-amplifier

Kyo Inoue

Published Aug 28, 2024• 1 citation
Publisher

Abstract

The transmission distance of optically repeating systems is ultimately bounded by quantum noises arising from attenuation and amplification. It is known that fiber Raman amplifiers (FRAs) can achieve longer quantum-limited distances than other amplification schemes owing to their distributed amplification characteristics. However, all-FRA systems are difficult to implement in practice. Therefore, a hybrid erbium-doped fiber amplifier (EDFA)/FRA system may be a reasonable solution for long-haul transmission. In this study, the quantum-limited transmission distance of hybrid EDFA/FRA systems is investigated. A formula for the quantum fluctuation variance during transmission was derived based on quantum mechanical treatment. Calculation results obtained with the derived formula quantitatively indicate that the quantum-limited transmission distance increases as the EDFA/FRA hybrid ratio varies from EDFAs alone to FRAs alone.

DOI
10.1364/ol.537117

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Quantum noise intrinsically restricts the ultimate transmission distance in fiber communication systems that use optical repeating amplifiers. This study theoretically investigates the quantum-noise-limited distance of optical coherent transmission using fiber Raman amplifiers. An analytical formula for the upper bound of the transmission distance is derived based on full quantum mechanics, considering the amplification noise and intrinsic fluctuation of a coherent state (or vacuum noise), and calculations are performed using the derived formula. The results quantitatively indicate that the Raman amplified systems potentially achieve considerably longer transmission distances, more than ten times, than a system with erbium-doped fiber amplifiers under ideal conditions.
The performance of optical transmissions is intrinsically and ultimately determined by quantum noise. This study theoretically investigates the quantum-noise-limited performance of BPSK transmission using EDFAs, PSAs, or Raman amplifiers as optical repeaters. Amplifier noise, quantum noise in a coherent state, and vacuum noise accompanied with attenuation are considered. Calculations based on the theoretical analysis qualitatively show that bidirectionally pumped Raman amplification systems achieve considerably long transmission distances.
The performance of optical transmissions is intrinsically and ultimately determined by quantum noise. This study theoretically investigates the quantum-noise-limited performance of BPSK transmission using EDFAs, PSAs, or Raman amplifiers as optical repeaters. Amplifier noise, quantum noise in a coherent state, and vacuum noise accompanied with attenuation are considered. Calculations based on the theoretical analysis qualitatively show that bidirectionally pumped Raman amplification systems achieve considerably long transmission distances.
Bidirectional erbium-doped fiber amplifiers(Bi-EDFAs) are needed for optical amplification in long distance fiber frequency transmission. Erbium-doped fiber is used in optical amplifiers. With the increase of the asymmetric length of erbium-doped fiber, the transmission stability of the system will be deteriorated. We built a simulation platform for fiber frequency transmission, and set erbium fiber with different lengths based on it to observe its influence on frequency stability. The results show that the stability of the system decreases obviously with the increase of the asymmetric length of the Erbium fiber.
A version of an erbium doped fiber amplifier (EDFA) application scheme designed to increase the efficiency of the simultaneous quantum key distribution session and transmission of information by classical channels in a single optical fiber is explored.A theoretical study of the possibility to use EDFA in the explored way was conducted by numerical simulation methods.The mathematical model is based on the EDFA dynamics equations and the equations that determine the secure key generation rate in case of the subcarrier-wave quantum key distribution.A method for determining the optimal parameters of the scheme under study is described and the evaluation of the feasibility of using EDFA in the explored way is performed.A comparative analysis of the subcarrier-wave quantum key distribution system performance when integrated into an optical network is made in terms of the secure key generation rate for the cases when EDFA is either used or not.The results obtained demonstrate high efficiency of the scheme under study, i.e., the maximum achievable distance of the secure key distribution is increased while maintaining the efficiency of the information transmission.
We demonstrate an optical frequency transfer over a 377 km-long fiber link using three bi-directional Erbium-doped fiber amplifiers (EDFAs) to compensate the fiber attenuation. Through active phase noise cancellation, we obtain a transfer instability of 2.2×10-14 at 1 s and 6.2×10-17 at 2000 s. The lasing effects induced by EDFAs are observed in the transfer link which reduce the gain performance of the EDFAs and deteriorate the stability of the signal. In the paper, the factors that may induce the lasing effects is discussed, specially, improper phase locking parameters may stimulate the lasing effects. The phase noise of the 377 km link and the transfer instability versus fiber lengths is also researched. This work makes a good foundation for our future research on long-distance optical frequency transfer.