We present a simple analytical model to approximately analyze the TDFA for silica glass as well as fluoride glass based
optical fibers. We have verified the validity of method using the in-house fabricated Tm-doped alumino-germano-silicate
glass fiber as well as reported results for the Tm-doped fluoride glass fiber. The spectral variation of gain
obtained with the silica glass fiber TDFA after pumping with pump power of 275 mW at 1064 nm showed good
agreement between the simulated and the measured values. The pump power dependence of gain in the fluoride glass
fibers calculated by our method also showed a good agreement with the experimental results reported. The maximum
error in determination of gain was limited to 12%.