This dissertation describes the characteristics and the application of fiber-optic interferometers employing broadband light sources. Optical interferometers applying broadband light source have been widely used in the characterization of optical devices, for one can measure the absolute value of optical path length with their short coherence length.
In this study, we measure the chromatic dispersion of several optical fibers using an optical spectrum analyzer (OSA) and a Michelson interferometer applying a light-emitting diode (LED) as a light source. Additionally, we compose another interferometer employing a wavelength-swept fiber laser (WSFL) as a novel broadband light source and measure the spectral information of several samples with shorter measurement time and higher spatial resolution compared to those of conventional optical frequency-domain reflectometry (OFDR).
A Michelson interferometer composed of a fiber coupler and a LED is used to measure the chromatic dispersions of optical fibers. The dispersions of a dispersion shifted fiber (DSF), a polarization maintaining fiber (PMF), and a two-mode fiber (TMF) are measured respectively as samples. The zero dispersion of the DSF at 1550 nm is confirmed and two polarization states are measured separately in the PMF. In the case of the TMF, the dispersions of the even and the odd LP11 modes are measured respectively.
We compose another Michelson interferometer using a fiber directional coupler and a WSFL. The peak wavelength of the WSFL is continuously swept using the Fabry-Perot (F-P) tunable filter in the laser cavity at the repetition rate of 15 MHz. The output power of 1 mW is achievable with the pumping power of 33 mW by a laser diode at the wavelength of 1.48μm. The cavity length is about 15 m and the pulse width is measured to less than 1 ns, which determines the dynamic range of 5 cm. The spatial resolution of the interferometer is 100 mm, which is limited by the source bandwidth of 20 nm. We introduce the calibrations of a few factors to correct the nonlinear wavelength sweep rates caused by the F-P filter in the cavity, the reduced visibility coming from the optical path difference, and the reduction of measured reflectance originating from the discrete spectral components by Fourier transform. The minimum measurable reflectance is -84 dB after the calibrations. As samples, we measure the attenuation of a conventional attenuator, the reflections from an optical isolator, and the multiple reflections from the structure of slide glasses and spacers. The measurement results are successful when compared to their specification data.
