Hitoshi TAKESHITA
Keiichi MATSUMOTO
Hiroshi HASEGAWA
Ken-ichi SATO
Emmanuel Le Taillandier de GABORY
Spatial division multiplexing has attracted attention as a key technology in expanding the capacity of optical transmission systems in the future. As one of the optical transmission technologies utilizing spatial division multiplexing, research and development of a multi-core fiber transmission system have been active. In order to migrate a conventional single core fiber based transmission system into a multi-core optical fiber based one, a multi-core optical amplifier which is used as a repeater is indispensable, as in a conventional system using a single core fiber. Multi-core optical amplifiers have a different optical signal amplification mechanism from conventional single-core optical amplifiers, and their weak point is that they have low optical amplification efficiency compared with conventional single-core optical amplifiers. This is a serious problem to introducing multi-core fiber into actual transmission system.
In this paper, a novel pumping scheme was devised to improve the optical amplification efficiency of cladding pumped multi-core optical amplifiers. In cladding pumped multi-core optical amplifiers, the interaction between the pump light and the gain medium (MC-EDF, Multi-Core Erbium-Doped Fiber) is small due to the structure of the multi-core fiber. This is a fundamental problem. Therefore, in this paper, a pump recycling technology including a spatial pump splitting device was newly developed so that the remaining pump light can be re-injected into the MC-EDF. As a result, the remaining pump light can be used without waste and an improvement in the optical amplification efficiency of the cladding pumping can be realized. Although it depends on the operating conditions of the multi-core optical amplifier, such as the input optical signal intensity into the multi-core optical amplifier and the pump laser output intensity, our proposed pump recycling technology improves the optical gain by up to 2.4 dB and reduces 32% of the electric power consumption to the drive pump laser diode. The reduction of electric power consumption by using our proposed pump recycling technology has been confirmed. Furthermore, it has been experimentally confirmed that the pump light recycling scheme does not adversely affect the noise figure of the cladding pumped multi-core optical amplifier or the transmission signal quality. In practice, several optical amplifiers in an optical network will operate under different conditions. Therefore, we estimated the power consumption reduction effect of the entire optical network by the proposed method in a real major optical network topology and found that there was a maximum 33.5% electric power consumption reduction effect.
This paper is highly evaluated as a paper that deserves the Best Paper Award because it contributes to the improvement of performance of optical amplification technology, which is indispensable for the practical realization of next generation high-capacity multi-core optical transmission systems.
