Broadband short pulse fiber lasers capable of generating output spectra broader than gain bandwidth

A method for operating a fiber laser to generate broadband laser pulses with a spectral bandwidth greater than a gain spectral bandwidth of a gain fiber segment in the fiber laser, comprising:

• providing a ring laser cavity to include a gain fiber segment having a gain spectral bandwidth, a spectral broadening fiber segment coupled to receive output light from the gain fiber segment, and an optical spectral filter coupled to receive light from the spectral broadening fiber segment to circulate laser pulses in a closed optical loop to, sequentially, pass through the gain fiber segment, the spectral broadening fiber segment and the optical spectral filter;
• operating the optical spectral filter to output filtered light to the gain fiber segment downstream in the closed optical loop to selectively transmit light in a narrow spectral band while rejecting light outside the narrow spectral band and to have a bandwidth for the narrowband that is sufficiently narrow to cause each laser pulse to be self similar after propagating through the gain fiber segment;
• and
• directing amplified laser pulses out of the gain fiber segment into the spectral broadening fiber segment to produce chirped self-similar laser pulses circulating in the fiber laser to have a pulse spectral bandwidth in each laser pulse output by the spectral broadening fiber segment to be greater than the gain spectral bandwidth of the gain fiber segment, wherein the spectral broadening fiber segment and the optical spectral filter collected to cause each laser pulse to have a varying spectral width in the closed optical loop that reaches a maximum spectral width value at the exit of the spectral broadening fiber segment and a minimum spectral width value at the output of the optical spectral filter.