Multicore erbium doped fiber amplifiers

Abstract

ABSTRACT We review recent progress of multi -core erbium -doped fiber amplifiers (MC -EDFA). We confirmed by demonstrating a core -pumped MC -EDFA that MC -EDFs have practical amplification characteristic s and core -to-core crosstalk . Three types of cladding -pumped MC -EDFAs are also reviewed , one uses free space optics, other uses a fiber b undled fan -in, and the other uses a side -coupled pump combiner for cladding pumping . Finally, we demonstrate a desktop -type prototype of a cladding -pumped MC -EDFA using the pump combiner that consumes power of 33 W and has size of 430 u 430 u 99 mm 3 (width u depth u height ). Keywords: M ulticore , Multicore EDFA , S pace division multiplexing , Fiber amplifier 1. INTRODUCTION Space division multiple xing (SDM) have recently been proposed and demonstrated to increase capacity limit in one optical fiber for overcoming exponential growth of internet traffic in a backbone network. Two SDM technologies such as multi -core fiber (MCF) and few -mode fiber (FMF ) are being intensively investigated and break a transmission record in one optical fiber [1 -3]. MCF s used in Ref. 4-6 are optical fiber s with several cores embedded in a common cladding. On the other hand, FMF s used in Ref. 7, and 8 are optical fiber s wit h several transverse modes in a common core. In order to increase further transmission capacity with SDM technologies, it is important to increase core and/or transverse mode number without any property degradation. In addition, one of the remaining key mi lestones to realiz e optical transmission systems based on SDM is introduction of SDM amplifiers. In this paper, we review recent progress of multi -core amplifiers and provide amplification characteristics of multi -core amplifiers based on core - and claddi ng -pumping scheme s. One of key optical components of optical amplifiers is signal/pump light combiner with low insertion losses. Core -pumping technology is to launch signal and pump light together into multi -core erbium -doped fiber (MC -EDF) cores embedded in a common cladding and to pump each of the cores by separat ing single mode pumping laser diode (LD) . Therefore, standard signal/pump light combiner can be employed into multi -core amplifiers with core -pumped scheme. It should be noticed that number of si ngle mode pumping LD for core -pumped multi -core amplifier depend s on number of core s embedded in a common cladding. In contrast, cladding -pumping technology is to launch signal light into multi -core erbium -doped fiber cores and pump light into the silica c ladding of double -cladding structured multi -core erbium -doped fiber. The cladding -pumping with double -cladding structured multi -core erbium -doped fiber has possibilities to show low power consumption, low cost, and downsizing by utilizing high power multi -mode pumping LD with tens of watts, which significantly decreases costs than single mode pumping LD s, because one multi -mode pumping LD excite all cores simultaneously and amplify all signals passed through the multi -core erbium -doped fiber cores. In secti on 2, we demonstrate core -pumped multi -core erbium -doped fiber in order to confirm that all cores have the ability to have amplification characteristics as a standard single -core core -pumped erbium -doped fiber amplifier ( EDFA ). These results with core -pump ed MC -EDFA indicate that multi -core erbium -doped fiber amplifier with core -pumped scheme has practical characteristics . In section 3, we review MC -EDFAs using a low loss signal/pump light combiner for the inner cladding excitation.