Design of all-solid W-type index fluorotellurite fibers with near-zero-flattened chromatic dispersion for optical frequency comb generation.

All-solid W-type index fluorotellurite fibers (AWFTFs) with near-zero-flattened dispersion profiles are designed for optical frequency comb (OFC) generation. The fiber core and cladding materials are TeO2-BaF2-Y2O3 (TBY) and fluoroaluminate glasses. Those two glasses have large refractive index contrast as well as similar thermal expansion coefficients and softening temperatures. The zero-dispersion wavelength of the TBY glass is about 2517 nm. By introducing fluoroaluminate glasses with relatively low refractive index as the cladding material and controlling the core diameter, the zero-dispersion wavelength of the fiber is shifted from 2517 nm to the wavelength region of 1500-1600 nm. Furthermore, two layers of thin annular glasses including a fluoroaluminate-glass-based inter-layer and a TBY-glass-based outer layer are added around the fiber core, which makes the fiber have a flat dispersion profile in the wavelength range of 1500-1600 nm. By optimizing the parameters (the core diameter, the thickness of the thin annular glass, etc.) of AWFTFs, the fiber with the chromatic dispersion value between -0.2 and 0.35 ps/nm/km in the wavelength range of 1500-1600 nm is achieved. To investigate the application of the AWFTFs for OFC generation via cascaded four-wave mixing, we perform numerical simulations. The simulated results show that flat-top OFC spectrum expanding from 1450 to 1700 nm with tunable mode spacing from 25 to 100 GHz can be generated in 2 m long fiber by using a 1550 nm laser with a pulse width of 0.825 ps and a peak power of 60 W as the pump source. (C) 2019 Optical Society of America