29 dB Gain Single-Pass Bismuth-Doped Fiber Amplifier Operating in the Short Wavelength Range of the O-Band

Several options are currently being studied to increase the data transmission capacity of optical fiber networks. While solutions involving multicore or few-mode fibers impose the installation of new fibers, a better exploitation of the bandwidth of standard single-mode fibers (SSMF) already in place is a very attractive approach, especially for terrestrial networks where G.652.D type, low OH fibers are widespread. For this, new optical amplifiers are needed and it has been demonstrated that increasing the optical bandwidth beyond the C- and L- band currently covered by the Erbium-doped fiber amplifiers (EDFA) is possible thanks to Bismuth-doped fiber amplifiers (BDFA) operating in O- (1260–1360 nm), E- (1360–1460 nm), S- (1460–1530 nm) or U- (1625–1675 nm) band. In the case of the O-band, the majority of work on BDFA has focused on the range around 1350 nm. However, it seems relevant to also exploit the 1280–1320 nm window, closer to the zero-dispersion wavelength of SSMF. To date, the performances reported in this spectral range are limited to gain values of 20–25 dB when single-mode pumping laser diodes are used [2]. In this work, we report improved performances of a BDFA based on a phosphosilicate fiber operating in the short wavelength range of the O-band in a conventional single-pass amplifier configuration. The fiber is drawn from a preform prepared using the MCVD process in combination with solution doping technique. The used amplifier configuration is shown in Fig. 1(a). A 186 m-long fiber is bidirectionally pumped at 1195 nm in a single-pass configuration. The signal source is composed of nine signal wavelengths obtained from a white-light source filtered by fiber Bragg gratings. Input and output signals are presented in Fig. 1(b) from which the fiber gain is calculated (Fig. 1(c)). 29 dB gain is achieved at a wavelength of 1310 nm for a total input signal of −20 dBm and a total pump power of 835 mW. The good performances of this fiber are attributed to a limited non-saturable absorption (NSA), a well-known process in Bismuth-doped fibers that alter their performances. The spectral dependence of NSA has been evaluated (see Fig. 1(d)) and a value of 14% is deduced at the pump wavelength, which is quite low when compared to the state-of-the-art [3]. Additional results will be nresented at the conference.