We demonstrate a high-power cladding-pumped Er-Yb codoped fiber laser with 74% efficiency. A pump-limited output power of 264 W is obtained using in-band pumping at 1535 nm. We compare the efficiency of 1480 and 1535 nm pumping through numerical simulations and experimental measurements.
The highest average power that has been achieved with a frequency-shifted feedback modelocked fiber laser is reported. Subpicosecond pulses with 40 kW peak power are obtained by this technique for the first time by using external pulse compression. The pulsing is self starting and environmentally stable. The measured pulse energy in modelocked operation is 120 nJ. The pulses could be compressed to 855 fs. The pulse energy was increased to 1muJ with controlled Q-switched modelocking.
We present a numerical study of stimulated Brillouin scattering in optical fibers based on a full modal analysis of the acoustic and optical properties. The computation of each acoustic mode supported by the fiber structure allows us a deep and detailed investigation of the characteristics of the Brillouin gain spectrum. We focus our attention on optical fibers acting as acoustic antiwaveguides where the biggest contribution to the Brillouin response often comes from very high-order modes but it is sometimes overlooked because of computational issues. Our analysis clearly highlights their role and their dependence on the physical and geometrical structure of the fiber.
INTRODUCTIONFiber lasers are nowadays emerging as the most powerful solid-state laser technology because of their compactness, their reliable and efficient operation, and the high power levels attainable. However several issues degrading the laser performance arise and need to be tackled when increasing the light intensity in the fiber. Stimulated Brillouin scattering (SBS) is often the most detrimental effect for narrow-line lasers [1]. Moreover SBS sets a limit to the power which can be transmitted in a fiber communication system. On the other hand SBS can be conveniently employed for sensing applications and for all-optical signal elaboration. A great deal of research has thus been devoted to the design of fiber geometries in terms of their Brillouin response. The Brillouin gain spectrum (BGS) summarizes all the main properties characterizing a fiber from this point of view and hence is usually the object of the numerical investigations of SBS.Several approaches have been exploited for the computation of the BGS starting from the modal properties of the fiber [2,3]. The usual assumption is that the fiber can support a single optical mode so that only a limited set of axially-symmetric acoustic modes are evaluated. In this paper we present a numerical study of SBS in optical fibers based on a full modal analysis of the acoustic behaviour. The computation of the characteristics of each acoustic mode supported by the fiber structure allows a deep and detailed investigation of the BGS. This is particularly important in the case of optical fibers acting as acoustic antiwaveguides as higher-order modes often provide the biggest contribution to the Brillouin response.
We demonstrate simultaneous mode locking of more than 24 wavelengths at 3 GHz in an actively mode-locked erbium-doped fiber laser operating at room temperature. The multiwavelength operation is achieved when a frequency shifter and an all-fiber 50-GHz periodic filter are inserted into a ring cavity. Active mode locking is performed with an amplitude modulator, and pulses with a FWHM of 30 ps are obtained.
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