Femtosecond lasers based on dispersion compensation with hybrid fiber

The key point in fabrication of all-fiber ultra-fast lasers operating near 1 μm is utilization of fibers with anomalous dispersion. A number of works were devoted to design of specialty fibers for this aim (Photonic Crystal fibers, Photonic Bandgap fibers, hollow core fibers, high order mode fiber and etc). However none of these fiber types have found wide commercial use due to its inherent disadvantages (high nonlinearity, high loss, few-modes operation regime and etc). Recently we have developed a novel promising fiber design, so called hybrid fiber [1]. Operating hybrid mode has anomalous dispersion of 10-100 ps/(nm-km), and could be excited by simple splicing with a standard step-index fiber. Asymptotically singlemode operation regime of hybrid fiber can be obtained by introduction in the structure of absorbing layer that suppresses all unwanted modes [2].In the current communication we utilize the developed asymptotically single-mode hybrid fiber for dispersion compensation in different laser schemes. Refractive index profile (RIP) of the fiber is shown in Fig.1a. The fiber has anomalous dispersion of about 60 ps/(nm km) at 1064 nm and a negative dispersion slope. Use of the hybrid fiber with length of 10.5 m allowed us to compress chirped pulse from duration of 7 ps to 440 fs with a perfect quality (without pedestal). In addition master oscillator scheme based on intra-cavity dispersion compensation with a help of the developed hybrid fiber was realized (Fig.2a). Typical high-order soliton spectrum was detected at the output of the laser (Fig.2b). The pulse duration was as short as 700 fs. Output power was 8.6 mW, the repetition rate was 15.75 MHz, the pulse energy was 0.55 nJ.