Design of zero dispersive double clad fiber for high efficiency operation of two color light

A double clad solid silica fiber is newly designed for applications which need the high efficiency operation of two colors of light. Ultrashort pulses with a central wavelength of 800 nm are delivered by the core of the double clad fiber which can realize the transmission of the optical pulses with a net chromatic dispersion of zero. This is achieved by integrating the double clad fiber with a pair of long period gratings, which allows optical pulses to propagate in a higher order mode (LP 02) in the middle of the fiber as well as in a fundamental mode (LP 01) at the beginning and end of the fiber. The index profile of the double clad fiber is engineered so that the higher order mode has high anomalous dispersion that can be used to compensate for normal dispersion of the fundamental mode. By controlling the lengths of the fiber where pulses are in a fundamental and in a higher order modes, the fiber with total zero dispersion can be realized. The double clad fiber can collect 100 % of visible light within the numerical aperture of 0.21 with a loss of the optical pulses less than 1%. The design of this fiber is essential for applications including fiber-optic nonlinear imaging for compactness, robustness, and low optical power loss in dispersion compensation.