All Fiber Approach to Locking Carrier-Envelope Phase of Ultrafast Fiber Lasers

Due to their advantages, fiber lasers have become major platforms for high average and peak power ultrafast laser sources. Coherent beam combining of many mode- locked fiber lasers is a very promising route to achieving ultrafast laser sources with kW-level or higher average power required for DOE accelerator applications. Scalable, robust, low-cost, and low-noise carrier envelope phase (CEP) locking technology is crucial for coherent beam combining of large numbers of ultrafast fiber lasers. Current CEP locking systems are mainly based on f-to-2f interferometer in which a broad-band supercontinuum is generated with a highly nonlinear silica fiber and second harmonic generation is realized with a nonlinear crystal. However, these systems usually contain free-space optics which severely constrain the stability and reliability. Moreover, the size and cost of CEP locking systems will become significant when large numbers of fiber lasers need to be locked. These problems can be solved with our proposed all-fiber f-2f interferometer in which the mode-locked laser amplification is achieved with a centimeter-long highly doped fiber amplifier and the supercontinuum generation and second harmonic generation are realized with centimeter-long tellurite fibers. In this Phase I program, we will focus on developing highly nonlinear tellurite fibers for octave-spanning supercontinuum generation and second harmonic generation and demonstrating the feasibility of CEP locking technology in all-fiber format. All-fiber CEP locking technology applicable to large numbers of ultrafast fiber lasers will be developed in Phase II. Our proposed all-fiber CEP locking technology can also be used for nonlinear signal processing, optical communications, frequency metrology, optical sensing, and high-precision spectroscopy.