GRAPHS DETERMINED BY THEIR -GAIN SPECTRA

An undirected graph $G$ is determined by its $T$ -gain spectrum (DTS) if every $T$ -gain graph cospectral to $G$ is switching equivalent to $G$ . We show that the complete graph $K_{n}$ and the graph $K_{n}-e$ obtained by deleting an edge from $K_{n}$ are DTS, the star $K_{1,n}$ is DTS if and only if $n\leq 2$ , and an odd path $P_{2m+1}$ is not DTS if $m\geq 2$ . We give an operation for constructing cospectral $T$ -gain graphs and apply it to show that a tree of arbitrary order (at least $5$ ) is not DTS.

Evaluation of Gain Spectrum of Silica-Based Single/Dual-Pumped Thulium-Doped Fiber Amplifier (TDFA) by Optimizing Its Physical and Pumping Parameters in the Scenario of Dense Wavelength Division Multiplexed Systems (DWDM)

Thulium-doped fiber amplifier is a very proficient broadband fiber amplifier in S-band. Silica-based TDFA is a popular choice due to some of its evident features such as non-toxic nature, easy splicing and simple assembling. In this work, we have simulated and optimized various TDFA’s physical and operational parameters in order to obtain required gain spectra at different channel spacings. Further, a comparative study has been carried out between single and dual-pumped TDFAs. By using dual pumping scheme (1040 nm and 1000 nm) as fundamental source of excitation, maximum gain of 23.31 dB has been achieved at 1468.8 nm in region spanning 1400 nm to 1470 nm wavelengths with noise figure of 3.72 dB.