What are fiber lasers?

Most existing laser systems are confined to the laboratory because they are large, heavy, fragile, and power consumptive.

At Sandia we are creating a new generation of compact, efficient, laser sources based on optical fibers that promise to overcome these limitations and are suitable for field application. This work builds on our breakthroughs in power scaling of fiber lasers.

Many modern solid-state lasers employ a rare-earth element (e.g, Yb, Nd, or Er) doped into a crystalline host as the gain medium. In a fiber laser, the rare-earth dopant is incorporated into the core of an optical fiber (similar to those that transmit telecommunication signals). This approach offers numerous advantages, especially for practical applications, including ultra-sensitive detection of chemical and biological compounds, remote sensing, and secure communications.

How do fiber lasers work?

The gain medium in a fiber laser is a rare-earth element (e.g, Yb, Nd, or Er) doped into the core of an optical fiber (similar to those used to transmit telecommunications signals). Both the pump and signal beams propagate along the length of the fiber. Many bulk solid-state lasers employ rare-earth-doped crystals, but use of a fiber offers a number of advantages, especially for practical applications.

Fiber lasers show advantages over other technologies:

• high efficiency (we have demonstrated 39% electrical-to-optical efficiency, an order of magnitude higher than conventional solid-state lasers);
• high-gain (~50 dB) and low-threshold operation;
• diffraction-limited beam quality that is insensitive to thermal or mechanical fluctuations, optical power level, or aging of the laser system;
• continuous tunability;
• broad wavelength coverage in the near-IR by selection of various rare-earth dopants;
• pumping with low-cost, reliable diode lasers;
• low heat dissipation and facile thermal management;
• scalability to high power;
• efficient nonlinear conversion to the visible and UV wavelength

What has Sandia accomplished?

Sandia researchers have developed a number of enabling technologies associated with fiber lasers, including:

• a power-scaling method (bend-loss-induced mode filtering) that allows the peak and average power of fibers sources to be scaled up by at least two orders of magnitude compared with standard single-mode fiber sources while maintaining diffraction-limited beam quality. This method has become the de facto standard for power scaling, and the patent has been licensed to industry.
• a versatile pumping method (embedded-mirror side pumping) for launching pump light into double-clad fibers. This method is the only one capable of directly coupling the output of an unformatted diode bar (the most cost-effective pump source) into double-clad fiber.
• polarization-maintaining, Yb-doped, double-clad fiber, which is required for applications requiring stable, linear output polarization.
• generation of the 2nd, 3rd, 4th, and 5th harmonics of a pulsed, Yb-doped fiber amplifier, which covers wavelengths from the near-IR through the deep-UV. This compact system is being used for sensitive, remote chemical detection.
• waveguide and laser/amplifier models for use in the design and analysis of new fibers and fiber sources.
• compact microchip lasers optimized for seeding fiber amplifiers.

In addition to developing enabling technologies, we are pursuing high-priority applications in national security and energy surety.