Before revision: This allows a compact relatively unstable laser to be used as a local oscillator, with the system stability being obtained from a master 'comb source' (usually a pulsed laser, such as a mode-locked laser), possibly common to many receivers within an URL
After revision: This allows a compact relatively unstable laser to be used as a local oscillator, with the system stability being obtained from a master 'comb source' (usually a pulsed laser, such as a mode-locked laser), possibly common to many receivers within an exchange.