In this proposal, we propose to demonstrate and build a 1.55 micron single frequency high energy and high peak power fiber amplifier by developing an innovative Er-doped gain fiber with large core diameter and high gain per unit length. 1.55 micron single frequency high energy and high peak power fiber amplifier is needed for coherent lidar and sensing. In Phase II, we will further optimize the Er-doped glasses and fibers based upon Phase I results, further increase the pulse energy and peak power, and build a prototype with peak power of 15kW. The output laser beam is diffraction limited. Successful demonstration of such a fiber amplifier will enable many new NASA and commercial applications.