Dispersion Characterisation of Various Fibres using a Fourier Domain Mode Locked Laser

Abstract

A Fourier Domain Mode Locked (FDML) laser is a new type of fibre based Swept Source laser. FDML laser is capable of changing its wavelength within a large bandwidth (1500 nm to 1600 nm) at a rapid periodic pattern (sweep rate around 50 kHz). It was originally designed for use as the light source in Optical Coherence Tomography (OCT), an imaging technique that can produce 3D tissue images. With the use of FDML laser as the light source, OCT can operate in the spectra domain and allows fast image processing. Recently FDML lasr has found other uses, such as performing dispersion measurements on optical fibres. Optical components such as an optical fibre will always have a dispersion parameter that causes wavelength dependent delay. Using FDML laser, we take advantage of its large bandwidth and determine the dispersion of a broad range of wavelengths. A Mach-Zehnder Interferometer is used to extract the phase information in a specific part of the laser cavity. Using this information, the wavelength pattern of which FDML laser is transmitting can be resolved. By reconstructing the wavelength pattern before and after each optical component, the dispersion of the optical components can be determined. Using this method we can obtain the dispersion of the optical components outside the cavity. For a mode locked laser to operate, the total amount of dispersion after one round trip has to be zero. Using the method above, we wish to determine the dispersion of each optical component in the cavity and how this dispersion is compensated.