200 fs-pulse coupled cavity stretched pulse fiber laser with enhanced repetition rate

Summary form only given. Stretched-pulse mode-locked all-fiber ring lasers have provided an efficient method of creating high-energy sub picosecond pulses. By assembling positive and negative dispersion fibers together in an erbium fiber laser and using the nonlinear polarization rotation (NPR) method to mode lock it, it is possible to achieve these high quality pulses. The main disadvantage of the laser, due to its long cavity, is the low repetition rate of about 20-30 MHz. One method which enables increasing the repetition rate in soliton fiber lasers, is the use of a dual cavity configuration. In this each cavity provides a different mode spacing, which must be a common factor of the dual cavity mode spacing. By adjusting the length of one of the cavities one can therefore force higher repetition rates on the laser. While attempting several configurations of this method on the stretched pulse laser, we found that the use of fibers in the coupled cavity modified the non linear polarization rotation of the main cavity and hence no mode locking could be achieved. Since NPR mode locking is based on polarization rotating through the fiber cavity, any change in fiber length demands a new evaluation of the locking system. Moreover, at the convergence point of the two cavities, the polarization of the cavity pulses may not match and hence the overall pulse is destroyed. In addition, the width of the supported pulses in each cavity may be different, due to the difference in the cavity length, which may cease the pulsing operation.