Abstract

Single-crystal optical fibers (SCF) are attractive for device applications because of their combination of fiber geometry and single-crystal material properties. For example, high temperature, laser, and second-order nonlinear devices are all feasible in SCF. We have grown SCF of a number of materials with a laser-heated miniature pedestal growth technique. Our efforts have focused on the technologically important refractory oxides, particularly sapphire, Nd:YAG, and lithium niobate. Oriented SCF with diameters ranging from 20 to 500 µm have been obtained in lengths up to 20 cm. To minimize scattering losses and allow phase matching of nonlinear interactions it is necessary to maintain a constant fiber diameter. With a real-time interferometric diameter sensor and closed-loop control, it has been possible to grow SCF with 0.1 % rms diameter variations, sufficient for many device applications. Cladding the SCF with low index of refraction material is important for mode control, reduction of scattering losses, and isolation from environmental contamination. Several types of cladding for SCF have been demonstrated, including liquid, fused glass, and diffused surface layers. Losses as low as 0.01 dB/cm at 6328 A have been measured, along with near single-mode propagation. Several devices have already been demonstrated, including millikelvin resolution, sapphire fiber thermometers, monolithic ruby fiber lasers, and monolithic Nd:YAG fiber lasers. These results, as well as progress in nonlinear devices in lithium niobate fibers and UV and IR losses of sapphire fibers, are reported.

© 1985 Optical Society of America