Photonic Crystal Fiber Amplifier Module for High Peak Power Lasers
Abstract
This effort will carry out the design, construction, and test of an advanced, two-stage photonic crystal fiber amplifier system operating at the wavelength of 1030 nm; the system will operate in both a continuous-wave mode and pulsed mode. It will be based on ytterbium-doped photonic crystal fibers. The first stage will be comprised of a flexible optical fiber whose core is solid and has a diameter of 25 or 40 μm; this is surrounded by a cladding that has a hexagonal array of air holes along the entire length of the fiber. Ytterbium atoms in the 25- or 40-μm core of the fiber provide the gain and hence the amplification property of the medium. The photonic crystal structure provides a 258-μm diameter waveguide for transporting light energy to the exit facet. Because of the unique properties of photonic crystals, this waveguide can be designed to be single-mode with a high beam quality (M2 ~1.2) at the exit facet of the fiber. The external cladding of the flexible fiber has a diameter of 410 μm. The mode-field diameter of these fibers is much larger than that of most standard high power amplifiers generally used in the construction of fiber lasers. For the 25-µm core fiber, for example, the mode-field is ~21 µm. It therefore offers the potential to carry significantly much high power than standard high power amplifiers of similar length. The second stage of the systems is comprised of a rigid photonic crystal rod whose core diameter is 85 μm; the mode-field diameter of the photonic crystal rod is ~65 µm. The dimensions of the inner and outer cladding for the rod are identical to those of the flexible fiber. The function of the rigid photonic crystal rod is to boost the amplification of the preamplifier to much higher levels than is possible in standard fibers of equivalent lengths. Both the preamplifier and the booster amplifier are pumped by diode laser sources at 976 nm. These are readily available commercially. The photonic crystal fiber and the rod, however, must be designed and manufactured to custom specifications. The outlined approach provides a path to constructing a high power laser system in a compact form factor. Furthermore, because coiled optical fibers have extremely large surface area to volume ratios, they provide natural thermal management through air convection along the total length of the fiber—thus simplifying overall thermal management.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 11, 2016
- Source ID
- HR00111510009
Entities
People
- E. Towe
Organizations
- Defense Advanced Research Projects Agency
- Massachusetts Institute of Technology