Although single-crystal Y2O3-ZrO2 (zirconia) fibers are more resistant to high temperatures than sapphire strands, they typically suffer large optical losses in the 900-nm range. That drawback appears to be absent when they are fabricated into rectangular waveguides from a bulky cubic. Research at Harvard University in Cambridge, Mass., and at Zhejiang University in Hangzhou, China, demonstrated that such waveguides reduced optical losses to 0.016 dB/cm, a level comparable to sapphire waveguides. Also, the rectangular guides withstood temperatures approaching 2400 °C.The work, published in the July 1 issue of Applied Optics, also described a trial application, which indicated that the waveguides have potential for accurate sensing above 1800 °C.