Consider two identical optic fibers with deeply subwavelength tips. Let their tips be placed next to each other, at a distance much smaller than the wavelength. Let light of equal intensity come out of them in phase. Then, by the principle of linear superposition, at some distance much bigger than the distance between the tips, the intensity of light is 4 times greater than it would be if we had light coming only from one tip. If each tip sends power P, then out there we have power 4P.