Computer Controlled Dispersion Measurements and Investigation of New Optical Fibers

Abstract

A dispersion measurement setup for short length fibers based on Mach Zehnder interferometer was automatized and tested using standard telecommunication fiber. This setup is based on low coherence sources which enable interference to occur only in a narrow wavelength range. Dispersion in new optical fibers such as Ge-doped fiber and Yb:Tm doped fiber were measured over the wavelength range 1700nm-2400nm. Two broadband sources: - a superluminiscent Tm-doped fiber source (ASE source) and a modelocked Cr:ZnS oscillator were used for 1700nm-2000nm and 2150nm-2400nm wavelength ranges respectively. Manual measurements were first conducted before automation for comparison. During automation TRA25PPD stepper motor was used for position control and a CONEX IOD device was used to convert the analog signal from the oscilloscope into digital signal which was used to control the motor. A computer control program for the devices was written in the LabView environment. The setup is able to measure short length fibers of typically 40 cm - 250 cm. Different fiber lengths were tested to assess the measurement precision (70cm, 75cm and 207cm). The shorter the length, the less is the precision, although the results still remain in agreement with the results obtained using the long length fiber. The values of the measured second order dispersion coefficient were in agreement with the theoretically calculated values and provided a reasonable approximate of the dispersion in these fibers for areas of their applicability such as ultra-short pulsed lasers. The knowledge of second order dispersion in Germanate-doped fiber, Germanate-Tm and Yb:Tm doped fibers could further be used for development of novel ultra-short pulse fiber lasers operating in the 2µm spectral range.