Citation:
Thesis Type:
MSAbstract:
Optical communications has experienced a rapid development during the last decade. More bandwidth can be acquired by decreasing the spacing of the optical channels or by increasing the data rate. Characterization of the optical components and active monitoring of the network calls for accurate measurement methods. The transfer function of optical components impacts
the performance of communication systems. Analysis and accurate measurement of the transfer function is therefore essential in optimization of the performance of such systems.
Chromatic dispersion of optical bers and frequency chirp of the laser transmitters set limits for the data rate and transmission distance. Measurements of dispersion have traditionally been performed using a Modulation Phase-Shift (MPS) method. When high RF modulation frequencies are applied to achieve high resolution an alias error could be introduced. In this thesis we introduce an apparatus for full complex-amplitude spectral characterization of optical
components and bers. Based on a modication of the MPS method, we introduce a frequency dither to the RF modulation drive, allowing us to detect small phase changes thus overcoming the limitations imposed by the conventional MPS method. Its salient feature is high sensitivity phase detection enabling the use of a low RF driving frequency as necessary for precise measurement of components exhibiting fine spectral features such as microresonators and slow light devices.
We analyze the modied MPS technique using the traditional small signal approximation and compare the results to a full analytic response of the MPS technique. The full analytic response is useful for optimization of the proposed technique. The characterization apparatus has been realized in our lab using commercially available optical and electrical components. We have characterized experimentally the signals passing in the apparatus. Care was taken to prevent higher RF tones (i.e. above 1st order) in the Mach-Zehnder Modulator (MZM) output field, which could interfere with the desired measurement. Moreover, care was taken to prevent RF leakages in the electronic circuitry, which could interfere with the measurement of weak signals. We demonstrate the operation of the modified MPS at two operating points, demodulating with either the same RF carrier or with a doubled one. We measured several component categories and fibers to demonstrate the measurement technique. Finally, we conclude with the advantages and disadvantages of the modified technique.