Ultra Compact Passive Mode-Locked All-Fiber 2 Micron Fiber Laser

This Small Business Innovation Research (SBIR) Phase I project focuses on the development of a compact all-fiber-based, short pulse (< ps) mode-locked laser operating in the 2-micron wavelength band. The laser will be constructed from Tm-doped germanate glass fiber, which provides high optical gain in a short length, and the fiber is embedded with carbon nanotubes (CNT), which act as a saturable absorber for mode-locking operation. Mode-locking will be realized through the interaction between the laser field?s evanescent wave with the saturable absorption from the carbon nanotubes localized within the fiber near the active core. Chirped fiber Bragg gratings will be used to provide cavity feedback and dispersion compensation. This approach promises to produce a few centimeter long all-fiber based ultrafast mode-locked laser suitable for cost-effective integration into optical systems and instruments. More generally, optical fibers embedded with CNTs may provide a flexible method for the integration of CNTs into photonics devices. The broader impact/commercial potential of this project will be to open the 2-micron wavelength window to ultrafast short pulse optical technology. This project will develop an all-fiber self-starting passive mode-locked fiber laser capable of delivering sub-picosecond pulses in the 2-micron wavelength band. Its compact size, environmental stability, wavelength tunability, scalability to high power, high repetition rate, portability, and high wall-plug efficiency will make it readily suitable for adoption into many commercial markets, such as medical applications, high efficiency THz generation, 3-5 micron supercontinuum generation, time-resolved molecular spectroscopy, optical frequency comb, Light Detection and Ranging (LIDAR), free space communication, high-order harmonic generation, MID-IR frequency conversion, air pollution monitor, and high efficiency soft X-ray generation. Among those applications, medical applications are particularly interesting due to the 2-micron?s strong water absorption, but weak absorption by human tissue. The strong point of using 2-micron ultrashort pulses on human tissue is the absence of an appreciable thermal effect. Therefore such lasers could find applications in surgery, dentistry, and dermatology where ancillary heating of tissue is undesirable.