Tuneability of amplified spontaneous emission through control of the waveguide-mode structure in conjugated polymer films

We show that the position of the amplified spontaneous emission ~ASE! in poly@2-methoxy-5~28-ethylhexyloxy!-1,4-phenylene vinylene #~ MEH-PPV! can be controlled by the effect of the film thickness on waveguide modes. We demonstrate that the ASE can be tuned over 31 nm corresponding to a gain bandwidth of 25 THz. By modeling the waveguide modes we find that the ASE position for films thinner than 76 nm is determined by the cutoff wavelength for the waveguide and is shifted to shorter wavelengths with decreasing film thickness. We also demonstrate a simple method for measuring the cutoff wavelength and show that this correlates well with calculated values.