Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber

Saturated absorption spectroscopy is performed on the acetylene v(1) + v(3) band near 1532 nm inside photonic bandgap fibers of small (similar to 10 mu m) and large (similar to 20 mu m) core diameters. The observed linewidths are narrower in the 20 Am fiber and vary from 20 to 40 MHz depending on pressure and power. Variations in the background light transmission, attributed by others to surface modes, are significantly reduced in the 20 Am fiber. The optimum signal for use as a frequency reference in a 0.8 m long, 20 Am diameter fiber is found to occur at about 0.5 torr for 30 mW of pump power. The saturation power is found by modeling the propagation and attenuation of light inside the fiber. (c) 2006 Optical Society of America.