Craig D. Nie

Ho:YAG Single Crystal Fiber: Fabrication and Optical Characterization

0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) was fabricated using Laser Heated Pedestal Growth (LHPG) method and characterized for its optical absorption and emission properties involving transitions between the 5I8 and 5I7 energy levels. The results verified the absorption peaks suitable for in-band direct pumping at 1908 nm and 1932 nm with the emission occurring between 2050 and 2150 nm. Small signal gain measurements were also performed for demonstrating the fiber like characteristics of the SCF.

Growth of single-crystal YAG fiber optics.

Single-crystal YAG (Y3Al5O12) fibers have been grown by the laser heated pedestal growth technique with losses as low as 0.3 dB/m at 1.06 μm. These YAG fibers are as long as about 60 cm with diameters around 330 μm. The early fibers were grown from unoriented YAG seed fibers and these fibers exhibited facet steps or ridges on the surface of the fiber. However, recently we have grown fibers using an oriented seed to grow step-free fibers. Scattering losses made on the fibers indicate that the scattering losses are equal to about 30% of the total loss.

Lasing characteristics of Ho:YAG single crystal fiber

Lasing was demonstrated for the first time at 2.09 μm in 0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) fabricated using the Laser Heated Pedestal Growth (LHPG) method. Output power of 23.5 W with 67.5% optical-to-optical slope efficiency is, to the best of our knowledge, the highest output power achieved at 2 µm from a SCF fabricated using LHPG. With continued improvement in the quality of the SCF and better thermal management, output power of few 100s W and higher, especially in the 2 µm spectral region, is realizable in the very near future.

Investigation of the amplification properties of Ho:YAG single crystal fiber

0.5% Holmium (Ho) doped YAG single crystal fiber (SCF) was fabricated using the laser heated pedestal growth (LHPG) method and amplification properties of the fabricated Ho:YAG SCF were studied. The relatively large lengthto- diameter ratio provides guiding for both the pump and signal beams propagating in the SCF. The propagation and gain of signals with different modes were studied. A numerical method based on finite difference (FD) beam propagation method (BPM) combined with the rate equations was developed for theoretical simulation. The results are encouraging to demonstrate the advantages of SCF for its fiber-like beam guiding property and solid state material gain property. The simulation tool provides details about how the fiber shape and launched mode affect the gain and output beam shape as well as predicts the amplification behavior of such unique specialty fibers.

Growth of rare-earth doped single crystal yttrium aluminum garnet fibers using laser heated pedestal growth technique

Rare-earth doped single crystal (SC) yttrium aluminum garnet (YAG) fibers have great potential as high-power laser gain media. SC fibers combine the superior material properties of crystals with the advantages of a fiber geometry. Improving processing techniques, growth of low-loss YAG SC fibers have been reported. A low-cost technique that allows for the growth of optical quality Ho:YAG single crystal (SC) fibers with different dopant concentrations have been developed and discussed. This technique is a low-cost sol-gel based method which offers greater flexibility in terms of dopant concentration. Self-segregation of Nd ions in YAG SC fibers have been observed. Such a phenomenon can be utilized to fabricate monolithic SC fibers with graded index.

Cladding single crystal YAG fibers grown by laser heated pedestal growth

Rare-earth doped single-crystal (SC) Yttrium Aluminum Garnet (YAG) fibers are excellent candidates for high power lasers. These SC fiber optics combine the favorable low Stimulated Brillouin Scattering (SBS) gain coefficient and excellent thermal properties to make them an attractive alternative to glass fiber lasers and amplifiers. Various rare-earth doped SC fibers have been grown using the laser heated pedestal growth (LHPG) technique. Several cladding methods, including in-situ and post-growth cladding techniques, are discussed in this paper. A rod-in-tube approach has been used by to grow a fiber with an Erbium doped SC YAG fiber core inserted in a SC YAG tube. The result is a radial gradient in the distribution of rare-earth ions. Post cladding methods include sol-gel deposited polycrystalline.

Erbium distribution in single crystal YAG fibers grown by laser-heated pedestal growth technique

Single crystal (SC) yttrium aluminum garnet (YAG, Y3Al5O12) as a host material has the ability to be doped with high concentrations of Er3+ ions. We utilize this ability to grow a 50% Er3+ doped YAG SC fiber, which was inserted into a SC YAG tube. This rod-in-tube was used as a preform in our laser-heated pedestal growth (LHPG) apparatus to grow a fiber with a radial distribution of Er3+ ions. The work shows that there is a distribution of Er3+ ions from their fluorescence and two different techniques were used to measure the index of refraction.

Single-crystal, rare-earth doped YAG fiber lasers grown by the laser- heated pedestal growth technique

High concentrations of the rare-earth elements erbium, holmium and thulium have been successfully doped into single crystal (SC) yttrium aluminum garnet (YAG, Y3Al5O12) fibers by use of the laser heated pedestal growth (LHPG) method. The spontaneous emission spectra and fluorescence were measured in the near-infrared (NIR). The results show progress towards forming a solid state laser able to produce a wavelength in the NIR, for high power applications.