An Interferometric Auto-Correlator

Electrical engineering

Bett, Norman Macdonald

University:University of Glasgow

关键词: Electrical engineering;   

Others  :  http://theses.gla.ac.uk/78250/1/11007982.pdf

来源: University of Glasgow

【 摘 要 】

This work concerns the design and building of an interferometric auto-correlator for use in the analysis of ultra-short pulses and their sources. The need for such an instrument is explained with particular reference to optical communications. The evidence for the existence of frequency change within ultra-short pulses and methods used to investigate such changes is reviewed. The production of ultra-short pulses is briefly described and the basic theory of mode-locking treated. The relationship between pulse width and bandwidth is established. A brief theoretical treatment of a bandwidth limited pulse is given. Methods used for the detection and measurement of ultra-short pulses are described. Their areas of applicability and their limitations are discussed. Linear and nonlinear correlation techniques are described. Fast and slow correlations are differentiated. Background-free correlation methods for intensity and interferometric scans are described. The necessity for interferometric correlations in the investigation of pulse structure is discussed. The effect of pulse chirp on the correlation obtained is described. The difficulty in interpreting auto-correlations without assumptions regarding the pulse shape and structure, is noted. The construction of an interferometric auto-correlator is described and the functions of the individual components detailed. The mechanical and optical factors affecting instrumental accuracy are discussed. The operation of the instrument is described and its resolution estimated. The results of initial calibration tests are presented and the presence of 'glitch' in the obtained traces is noted. The source of the 'glitch' is identified. The operation of the instrument is demonstrated in three modes. In the first mode it is used as a Michelson interferometer to investigate the output of a semiconductor laser. Visibility curves are presented and several laser parameters estimated from them. Evidence is presented for instability and self-pulsing during cw operation. In the second mode, its use as an intensity auto-correlator is demonstrated. Pulse width measurements are recorded for a mode-locked Nd:YAG laser. In the third mode of operation interferometric auto-correlations are carried out on part of an Nd:YAG pulse and samples of the pulse are taken at different points throughout the pulse length. Indication of chirp within the pulse is demonstrated by the latter.