We examine nonlinear optical effects in the active medium of the thin-film quasiwaveguide amplifier-oscillator with injection of the external signal. The injection locking has been obtained in the case when both the frequency and the direction of propagation of the injected signal differ from those for a free-running thin-film laser which offers a possibility for the frequency and directional switching of the output of the thin-film laser. The effects of four wave mixing and phase conjugation have been discussed in the active medium of the thin-film laser when additional mirrors forming an external resonator have been used.