GHz fundamental mode-locking of a highly integrated Er-doped all-fiber ring laser

Abstract: High repetition rate ultrafast fiber lasers are important tools for both fundamental science and industry applications. However, achieving over GHz repetition rate in passively mode-locked fiber ring lasers is still challenging. Here, we demonstrate the first ring-cavity Er-doped fiber laser that achieves over GHz fundamental repetition rate by using an all-integration cavity design. In the proposed laser oscillator, all functions are integrated into one device, making it an ultra-compact laser cavity. The laser is mode-locked by carbon nanotubes (CNTs) film that is directly deposited on the pigtail active fiber connectors. The laser produces ultrafast optical pulses at 1562 nm, with a pulse width of 682 fs and a fundamental repetition rate of 1.028 GHz with improved performance. Stable and low-noise mode-locking is characterized by high signal-to-noise ratio (SNR) radiofrequency signal and low relative intensity noise (RIN). The proposed all-integration laser design may serve as a reference for compact fiber ring lasers using other mode-locking mechanisms or at diverse wavelengths.