We propose and demonstrate the use of multiple angle-tuned in-line Fabry-Perot etalon filters for tunable optical channel selection in wavelength-division multiplexed and optical frequency-division multiplexed direct-direction fiber transmission systems. Feasibility is experimentally demonstrated with two stacked identical etalons [free spectral range (FSR) of 74 nm with a finesse of 50 for each etalon] and with two stacked nonidentical etalons (FSR of 8 and 2 nm, respectively, with a finesse of 76 for both etalons). The stacked etalons are used to select the individual modes of a multilongitudinal-mode semiconductor laser output in the 1550-nm region. The method allows the selection of tens or possibly hundreds of closely spaced optical channels, because the reduction of channel spacing to much less than 1 mm is feasible, and the resultant FSR of stacked nonidentical etalons can be made much larger than their individual FSR’s.