Backreflection and loss in single-fiber loopback networks

Loss budget expansion technique using gain-saturated SOA in WDM single-fiber loopback access networks

“…To reduce the intensity noise caused by the interference, it has been proposed that the SNR degradation due to backreflection can be overcome by signal amplification at ONU [5,6]. Reflection-I is the backreflection of CW light at the CO; it causes intensity noise as it interferes with the upstream signal.…”

“…However, our recent research showed that the impact of Reflection-II increased strongly with ONU gain [7,8] and limited the loss budget of the transmission line. Previous works have described some techniques for reducing the impact of interference between the signal and backreflection such as broadening the linewidth of the laser-diode (LD) against signal bit rate [4] and using a sliced amplified spontaneous emission (ASE) light source instead of a LD [5]. However, these techniques induce serious original SNR degradation for high speed data signals due to the low coherency of such light sources.…”

“…For upstream transmission in these networks, a continuous wave (CW) light is distributed from the CO to each ONU, modulated, and sent back to the CO. This round-trip transmission is achieved by using two-fibers [1][2][3] or single-fiber [4][5][6]. Single-fiber loopback transmission is attractive because the number of optical fibers used can be reduced.…”

“…To introduce WDM access networks, a wavelength-independent optical network unit (ONU), the colorless ONU, is the key technical issue. Some recently proposed WDM loopback access networks locate a WDM light source at the central office (CO) and each ONU includes an optical modulator [1][2][3][4][5][6]. For upstream transmission in these networks, a continuous wave (CW) light is distributed from the CO to each ONU, modulated, and sent back to the CO.…”

Performance analysis of bidirectional hybrid WDM/SCM‐PON link based on reflective semiconductor optical amplifier

“…Examples of remodulators are wavelength channel data rewriters based on saturated semiconductor optical amplifier (SOA) modulators [1] and RSOAs [2,3]. However, for bidirectional transmissions based on this technique, noises are inevitably generated from the backreflection and the backscattering of the up and downstream that has exact same wavelength [4]. Popular methods to alleviate such problems take advantage of the fact that the noise is interferometric and its level has a strong relationship with the linewidth of the optical source.…”