Optically excited (Fa, In, As, P) film lasers at 1. 3 and 1. 5 mu m have been investigated. The lasers showed single-mode emission and a tuning range of up to 160 nm. The laser threshold P//t and the differential quantum efficiency eta //D have been investigated in resonators with different reflectivities. Optimum results (P//t equals 100 mw/cm2, eta //D equals 2, 5%) have been achieved in an asymmetric resonator with R//1 equals 0. 92, R//2 equals 0. 75. An upper limit for the carrier density during excitation of n less than equivalent to 1. 1919 cm minus **3 is estimated from near-field measurements.