A fiber lens assembly is configured to optically couple an optical fiber to a signal processing device having free-space optical elements. The fiber lens assembly includes a diverging lens having a focal length that may be around 2 to 6 times the diameter of the optical fiber core. Sensitivity of the fiber lens assembly to angular misalignment and positional displacement is reduced by coupling the optical fiber to the signal processing device using a diverging lens rather than a collimating lens, and by configuring the diverging lens with a suitable focal length.