An optical fiber is optically coupled to an optical multiplexer. First and second wavelength-selective reflectors are formed onto the optical fiber. The first wavelength selective reflector is configured to reflect radiation of a first wavelength and the second wavelength reflective selector is configured to reflect radiation of a second wavelength that is longer than the first wavelength. A resonant laser cavity is formed between transmission fiber acting as distributed Rayleigh mirror and first and second wavelength selective reflectors. The first and second wavelength-selective reflectors and the optical fiber are configured such that Raman scattering and gain in the transmission fiber converts pump radiation at a pump wavelength less than the first wavelength to radiation of the first wavelength and also convert radiation of the first wavelength to radiation of the second wavelength.

A laser utilizes a cavity design which allows the stable generation of high peak power pulses from mode-locked multi-mode fiber lasers, greatly extending the peak power limits of conventional mode-locked single-mode fiber lasers. Mode-locking may be induced by insertion of a saturable absorber into the cavity and by inserting one or more mode-filters to ensure the oscillation of the fundamental mode in the multi-mode fiber. The probability of damage of the absorber may be minimized by the insertion of an additional semiconductor optical power limiter into the cavity.

According to one aspect, the invention relates to a device comprising an optical fibre having a high Brillouin threshold, said device including an optical fibre (101) suitable for propagating a high-power optical signal beam, means (11) for coupling a signal beam to an entrance end of the optical fibre (101) and a tubular structure (10) comprising at least one first tube (103) and at least one first adhesive material (102). According to the present description, at least one portion of the optical fibre is immobilized in the tubular structure (10) by means of the first adhesive material (102), which adheres both to the internal surface of the first tube (103) and to the external surface of the optical fibre (101). Furthermore, at room temperature and with no other external stresses on the device, the immobilized portion of the optical fibre (101) is maintained in a compressive state by the tubular structure, the compressive state being such that the relative deformation of the optical fibre is negative or zero in its portion immobilized in the tubular structure, the maximum value of the relative deformation of the immobilized portion of the optical fibre being higher in absolute value than 0.3%.

In an example, the present invention provides a system for amplifying a laser pulse. The system comprises a coherent beam combining (CBC) system coupled to an optical enhancement cavity each of which is configured to operably work together to amplify a laser pulse from a laser source through the CBC and then through the cavity.