# Laser HW-1 3.7. Single mode fibre For a typical step-index fibre (NA = 0.11, cut-off = 620 nm) operated in the single-mode regime, estimate the portion of the total power of the LP01 mode which travels in the core and cladding, respectively, as a function of the wavelength. How do you focus a free-space Gaussian TEM00 mode onto the fibre end for optimal coupling efficiency?