The fiber attenuation was measured by using the cut-back method. The Tungsten lamp was used as the whitelight source. A 300 mm focal length scanning spectrometer (Bentham Instruments TMc300) was used for all spectral measurements at mid-infrared wavelengths, which has a 300 lines/mm grating and a liquid-nitrogen-cooled InAs detector (Electro-Optical Systems S-010-LN4).