Abstract
We experimentally optimize a single pump fiber optical parametric amplifier in terms of gain spectral bandwidth and gain variation (GV). We find that optimal performance is achieved with the pump tuned to the zero-dispersion wavelength of dispersion stable highly nonlinear fiber (HNLF). We demonstrate further improvement of parametric gain bandwidth and GV by decreasing the HNLF length. We discover that Raman and parametric gain spectra produced by the same pump may be merged together to enhance overall gain bandwidth, while keeping GV low. Consequently, we report an ultra-flat gain of 9.6 ± 0.5 dB over a range of 111 nm (12.8 THz) on one side of the pump. Additionally, we demonstrate amplification of a 60 Gbit/s QPSK signal tuned over a portion of the available bandwidth with OSNR penalty less than 1 dB for Q2 below 14 dB.
Highlights
The fiber optical parametric amplifier (FOPA) is an optical amplifier with the potential to increase the capacity of wavelength-division-multiplexing (WDM) transmission systems by providing wideband gain at arbitrary wavelengths [1,2]
We find that optimal performance is achieved with the pump tuned to the zero-dispersion wavelength of dispersion stable highly nonlinear fiber (HNLF)
We demonstrate further improvement of parametric gain bandwidth and gain variation (GV) by decreasing the HNLF length
Summary
The fiber optical parametric amplifier (FOPA) is an optical amplifier with the potential to increase the capacity of wavelength-division-multiplexing (WDM) transmission systems by providing wideband gain at arbitrary wavelengths [1,2]. The underlying process of the FOPA is based on four-wave mixing (FWM) which provides significant scope for obtaining low gain variation (GV) ‘flat’ unfiltered spectra compared with single pump Raman and Erbiumdoped amplifiers [3]. Low unfiltered GV is important in a FOPA because nonlinear crosstalk scales as the square of the output signal power [4]. Other particular FOPA-specific features are: symmetrical gain around a central frequency fc and the emergence of phase conjugate idlers possessing symmetry with any amplified signals about fc [1]. Idler generation typically constrains WDM signal gain within a FOPA (single or dualpumped) to one side of fc and this will be the assumption of this paper when defining gain bandwidth and comparing other reported results. Note that for a single-pump FOPA, fc coincides with the pump frequency [1]
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