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Tenth International Conference on Information Optics and Photonics

Optical frequency transfer over 377 km urban fiber link using EDFAs

Xue Deng, Jie Liu, Qi Zang, Dongdong Jiao, Tao Liu, Ruifang Dong, Xiang Zhang, Dan Wang, Weicheng Kong

Published Nov 15, 2018• 0 citations
Publisher

Abstract

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.

DOI
10.1117/12.2506390

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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.
We demonstrate coherent optical frequency dissemination over a distance of 972 km by cascading two spans where the phase noise is passively compensated for. Instead of employing a phase discriminator and a phase locking loop in the conventional active phase control scheme, the passive phase noise cancellation is realized by feeding double-trip beat-note frequency to the driver of the acoustic optical modulator at the local site. This passive scheme exhibits fine robustness and reliability, making it suitable for long-distance and noisy fiber links. An optical regeneration station is used in the link for signal amplification and cascaded transmission. The phase noise cancellation and transfer instability of the 972-km link is investigated, and transfer instability of 1.1 × 10−19 at 104 s is achieved. This work provides a promising method for realizing optical frequency distribution over thousands of kilometers by using fiber links.
We transfer an optical frequency over 251 km of optical fiber with a residual instability of 6x10(-19) at 100 s. This instability and the associated timing jitter are limited fundamentally by the noise on the optical fiber and the link length. We give a simple expression for calculating the achievable instability and jitter over a fiber link. Transfer of optical stability over this long distance requires a highly coherent optical source, provided here by a cw fiber laser locked to a high finesse optical cavity. A sufficient optical carrier signal is delivered to the remote fiber end by incorporating two-way, in-line erbium-doped fiber amplifiers to balance the 62 dB link loss.
We demonstrated the optical frequency transfer over a 96 km urban business network in Shanghai. The key factors affecting the optical frequency transmission system, such as fiber link quality, feedback compensation strength, and out-of-loop fiber temperature variation, are studied for the urban fiber link characteristics. The effective suppression technique of complex urban fiber link noise with different feedback compensation parameters is studied. With active phase noise suppression, the optical frequency stability can reach 1.9 × 10 − 16 at 1 s and 2.2 × 10 − 18 at 10,000 s over a 96 km urban fiber link. This work potentially plays an important role in optical clock frequency comparison, and it makes a good foundation for future research on long-distance optical frequency transfer over an urban business network.
SummaryPrecise and stable coherent optical frequency transfer over long-haul fiber link is required by diverse scientific applications, such as large-scale optical clock networks, global positioning and timing, very-long baseline interferometry, and high-sensitivity tests of fundamental physics. To meet the needs of the above applications, active compensation schemes for cancelling fiber-induced phase noise has developed considerably over the past ten years. However, optical signal severely reduces across distant fiber-optic networks, which degrades optical beat signal and feedback control.Here, we adopt active phase compensation and bidirectional optical frequency locking to achieve ultra-stable optical carrier transfer. The phase noise of the fiber link is effectively suppressed, meanwhile, the ultra-stable optical frequency signal is regenerated accurately at the remote site.Preliminary experiment over 100 km fiber link indicates that the additional frequency stability exhibits 1.9×10-16and 2.5×10-17at an averaging time of 1 s and 100 s, respectively. This approach has a capacity of extending to the parallel transfer of microwave and optical frequency, and free-space optical frequency transfer.
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.
We demonstrate optical frequency transfer over an 1840 km underground optical fiber link using a single-span stabilization. To compensate for more than 420 dB of optical attenuation of the light we use twenty Erbium doped fiber amplifiers along the entire link and two additional fiber Brillouin amplifiers. The good passive stability of our fiber link allows us to reach short term instabilities expressed as the modified Allan deviation of 3 × 10-15for a gate time τ of 1 s reaching 4 × 10-19in just 100 s. By comparing the sent and transferred frequencies we find no systematic offset within the statistical uncertainty of about 3 × 10-19. The spectral noise distribution of our fiber link at low Fourier frequencies leads to a τ-2slope in the modified Allan deviation.