Abstract
The capacity and reach of long-haul fiber optical communication systems is limited by in-line amplifier noise and fiber nonlinearities. Phase-sensitive amplifiers add 6 dB less noise than conventional phase-insensitive amplifiers, such as erbium-doped fiber amplifiers, and they can provide nonlinearity mitigation after each span. Realizing a long-haul transmission link with in-line phase-sensitive amplifiers providing simultaneous low-noise amplification and nonlinearity mitigation is challenging and to date no such transmission link has been demonstrated. Here, we demonstrate a multi-channel-compatible and modulation-format-independent long-haul transmission link with in-line phase-sensitive amplifiers. Compared to a link amplified by conventional erbium-doped fiber amplifiers, we demonstrate a reach improvement of 5.6 times at optimal launch powers with the phase-sensitively amplified link operating at a total accumulated nonlinear phase shift of 6.2 rad. The phase-sensitively amplified link transmits two data-carrying waves, thus occupying twice the bandwidth and propagating twice the total power compared to the phase-insensitively amplified link.
Highlights
PSAs can be realized, for example using, parametric gain in χ(2) nonlinear materials through three-wave mixing (TWM)[11], or χ(3) nonlinear materials through four-wave mixing (FWM)[12]
We present experimental evidence that in-line PSAs, can provide an unprecedented nonlinear tolerance and transmission reach extension[9,10]. In this demonstration of a recirculating loop transmission experiment with in-line PSAs, we benefit from the inherent simultaneous low-noise amplification and nonlinearity mitigation. This scheme, which is both modulation format-independent and multi-channel compatible[5], is shown experimentally to have a 5.6 times reach improvement compared to a transmission link using conventional in-line erbium-doped fiber amplifiers (EDFAs) when transmitting a 10 GBd quadrature phase-shift keying (QPSK) signal
Where us,i are the signal and idler wave amplitudes, ns,i represents vacuum noise present at the input, and the amplifier is characterized via the scalar coefficients μ and ν, where jμj2Àjνj21⁄4 1 ensures photon-number conservation, i.e., two pump photons are converted into one signal and one idler photon
Summary
PSAs can be realized, for example using, parametric gain in χ(2) nonlinear materials through three-wave mixing (TWM)[11], or χ(3) nonlinear materials through four-wave mixing (FWM)[12]. Using other PSA-based schemes, regeneration of more advanced modulation formats such as quadrature phase-shift keying (QPSK)[18,19], and star 8-quadrature amplitude modulation (QAM)[20], have been demonstrated as well as simultaneous regeneration of more than one channel[21,22] Another way to benefit from PSAs is to utilize their capabilities of low-noise amplification and nonlinearity mitigation. In this demonstration of a recirculating loop (i.e., long-haul) transmission experiment with in-line PSAs, we benefit from the inherent simultaneous low-noise amplification and nonlinearity mitigation This scheme, which is both modulation format-independent and multi-channel compatible[5], is shown experimentally to have a 5.6 times reach improvement compared to a transmission link using conventional in-line erbium-doped fiber amplifiers (EDFAs) when transmitting a 10 GBd QPSK signal. The concept of amplification using cascaded PSAs might find applications in the field of quantum information science, where generation and processing of quantum states are of interest
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