A method includes transmitting optical signals through a heterogeneous sequence of spans of an all-optical transmission line. Each span has an optical transmission fiber connected to an optical amplifier. Each amplifier launches the signals into a sequential remainder of the line. The transmitting includes launching the optical signals into the highest loss fibers with substantially equal average optical launch powers or operating the spans with the highest loss fibers to have substantially equal quality products. The average optical launch powers are substantially equal to the inverse of a sum of (1−Tj)γj/[φNL·αj] over the highest loss fibers. The parameters Tj, γj, and αj are the respective are, respectively, transmissivity, nonlinear optical coefficient, and loss coefficient of the fiber of the j-th span. The parameter φNL is the line's cumulative nonlinear phase shift. Each quality product is the per-span optical signal-to-noise ratio of the associated span times the nonlinear phase shift of the associated span.