Pumping scheme for Holmium-doped fiber amplifiers using traditional 1480?nm pumps exploiting cascaded lasers implemented using fiber Bragg gratings

Diversity in design is an important factor that enables developers to explore techniques aiming to reduce cost, complexity, and manufacturability. The optical window around 2000 nm is attracting rapid research considerations for the next generation optical networks as a continuation of C-, L-, and U-bands. Optical amplifier is considered to be one of the major research directions in this optical window. Holmium-doped fiber amplifier is an appropriate component to amplify signals in this optical window. But, the major issue is the pump laser for pumping the Holmium-doped fiber (HDF) is that it is costly and not readily procurable. In a pioneering design, the authors introduced a method to pump the HDF using traditional 1480 nm pump diode by taking the advantage of cascaded lasers which were made of Erbium-doped fiber (EDF) and Thulium-doped fiber (TDF). In this paper, we propose an alternate method for pumping the HDF using commercially available 1480 nm pump diode by exploiting cascaded lasers implemented using two pairs of reflective fiber Bragg gratings (FBGs) and pieces of EDF and TDF. The EDF in the first laser is excited with a standard 1480 nm pump diode to create 1610 nm continuous wave (CW) laser which is used to excite the TDF in the second laser to generate 1950 nm CW laser that is used to pump the HDF. Peak gain of 40.5, 36, and 23 dB can be attained corresponding to -30, -15, and 0 dBm signal powers, respectively at 2055.6 nm signal wavelength. Output powers of 10.5, 21, and 23 dBm are obtained for -30, -15, and 0 dBm signal powers, respectively at 2055.6 nm signal wavelength. Noise figures (NFs) of 5, 4.2, and 4 dB are observed at signal wavelength of 2066.7 nm for signal powers of -30, -15, and 0 dBm, respectively. Penalty of 4.5 dB has been observed both in peak gain and power at 2055.6 nm signal wavelength for signal power of -15 dBm considering the pair induced quenching. Finally, the proposed alternate pumping scheme is compared with the previous pumping scheme in terms of 3 dB gain bandwidth and NF. It has been observed that 88% increase in 3 dB gain bandwidth and 19% decrease in NF at a signal wavelength of 2044.4 nm for signal power of -30 dBm is noticed in the proposed pumping scheme.