In this paper we investigated the gain and noise figure characteristics of Bi-doped fiber in single and doublepass configurations. A maximum gain of 25dB and noise figure of 3.6dB is measured in single pass configuration whereas in double pass configuration the gain of the amplifier is improved significantly to 14dB and achieved the best results of 39dB gain with a noise figure of 5dB. To the best of our knowledge this is the maximum gain reported to date with Bi-doped fiber as a gain media. Further, we also studied the effect of pump power, signal power and pump wavelength on gain and noise figure characteristics in double pass configuration. It is reported that similar gain and NF performance can be achieved in double pass configuration with less pump power and shorter length of the Bi-doped fiber compared to single pass configuration.
In this paper, we experimentally demonstrate an allfiber optical amplifier using Bi-doped phosphosilicate fiber (BPSF) operating in both the O-band and the E-band, providing >20dB gain from 1345nm to 1460nm for an input signal power of -23dBm. A maximum gain of 31dB with a noise figure (NF) of 4.8dB was achieved at 1420nm for -23dBm input signal, whereas for an input signal power of -10dBm it was 26dB with a NF of 5.3dB. The in-band OSNR of the proposed Bi-doped fiber amplifier (BDFA) was >22dB from 1345nm to 1460nm for a -23dBm input signal. The gain coefficient was found to be 0.04dB/mW for a -23dBm input signal. Also, the temperature dependent gain and NF performance of the BDFA within -40 to +60℃ were characterized. The temperature-dependent-gain (TDG) coefficient for a -23dBm input signal was found to be -0.015dB/℃ at a signal wavelength of 1420nm where the BDFA gain is maximum, while for an input signal power of -10dBm it was -0.01dB/℃ at 1420nm. The TDG coefficient of the proposed BDFA from 1350-1460nm was in the range from -0.079dB/℃ to -0.008dB/℃. The BDFA gain and NF performance were also measured and compared using BPSFs with different unsaturable loss (UL) characteristics.
In this paper, we report high-speed multi-band direct-detection (DD) transmission over a hollow-core nested antiresonant nodeless fiber (NANF). Thanks to the ultrawide bandwidth of the NANF, we demonstrate dual-band transmission across the O-and C-bands over a ~1-km length of a hollow-core fiber for the first time. Eight wavelength-division multiplexed (WDM) channels were transmitted using 100-Gb/s/ Nyquist 4-ary pulse-amplitude modulation (PAM4) signals, which to the best of our knowledge, is the highest aggregate capacity ever transmitted in a DD hollow-core fiber-based transmission system. Optical pre-amplification was adopted for signal reception in both bands, achieved using an in-house built bismuth-doped optical fibre amplifier (BDFA) and a commercial erbium-doped fiber amplifier (EDFA) in the O-and C-band, respectively. We further demonstrate beyond 100-Gb/s/λ adaptively-loaded discrete multitone (DMT) transmission over the S+C+L-bands using the same NANF, without the use of optical amplification. Our experiments show that apart from fiber loss, the use of the NANF did not introduce any additional transmission penalties. The demonstrated results validate the ultrawide bandwidth and excellent modal purity of the fabricated NANF, which allow beyond 100-Gb/s/ penalty-free transmission over multiple bands, highlighting the potential of this fiber technology for high-speed short-to intermediate-reach applications.
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