Linearly Wavenumber-Swept Active Mode Locking Short-Cavity Fiber Laser for In-Vivo OCT Imaging

We demonstrate a highly linearly wavenumber-swept active mode locking (AML) fiber laser in the 1.3 μm region for in-vivo imaging in optical coherence tomography (OCT) without wavenumber space resampling. In this all-electric AML wavenumber-swept mechanism, the conventional wavelength selection filter is eliminated, and instead a suitable programmed electric modulation signal is applied directly to the gain medium. For a high sweep rate (up to 1 MHz) along the wavenumber, the fiber cavity structure is made as short as possible (0.88 m in air). A 15 ps/nm chirped fiber Bragg grating and a circulator are used for a shorter ring cavity configuration. A linewidth of 0.1 nm and tuning range of 42 nm are obtained under the mode-locking condition. Various types of wavenumber (or wavelength) tunings can be implemented because of the filterless cavity configuration. Therefore, we successfully demonstrate a linearly wavenumber-swept AML fiber laser with 26.5 mW of output power for obtaining in-vivo OCT images at a sweep rate of 100 kHz.