A fiber laser for producing high energy ultrashort laser pulses, having a positive-dispersion fiber segment and a negative-dispersion fiber segment joined in series with the positive-dispersion fiber segment to form a laser cavity. With this configuration, soliton effects of laser pulse circulation in the cavity are suppressed and widths of laser pulses circulating in the cavity undergo large variations between a maximum laser pulse width and a minimum laser pulse width during one round trip through the cavity. The fiber laser also provides means for modelocking laser radiation in the laser cavity, means for providing laser radiation gain in the laser cavity, and means for extracting laser pulses from the laser cavity. Using selected positive- and negative-dispersion fiber segments, the laser cavity exhibits a net positive group velocity dispersion, and the ratio of the maximum laser pulse width to the minimum laser pulse width attained during one round trip through the cavity is greater than 5, and preferably greater than 10. The laser cavity may be configured as a linear cavity geometry, a ring cavity geometry, a figure eight geometry, or a Sagnac loop reflector geometry, among others. Preferably the ring cavity is configured to achieve unidirectional circulation of laser pulses in the ring cavity, and with this configuration, is shown to produce laser pulses having a pulse width of less than 100 fs and a pulse energy of at least 80 pJ.