Monolithically integrated interferometer for optical displacement measurement

Abstract

A monolithically integrated optical displacement sensor in the GaAs/AlGaAs material system has been developed, fabricated and characterized. The device was a double Michelson interferometer with an integrated light source, photodetectors, couplers and phase shifters. A key point of the work was the development of a single growth-step distributed Bragg reflector laser which served as the light source of the interferometer circuit. Special attention was also directed at the establishment of a bandgapengineering technique (vacancy-enhanced disordering) allowing the definition of absorbing areas for the pumped laser section and the photodetector and transparent areas for the waveguiding sections and the grating section of the laser. The combination of the vacancy-enhanced disordering and the laser process enabled the fabrication of a fully integrated optical Michelson interferometer with quadrature signal detection. The maximal measurement distance with this double Michelson interferometer was 25 cm, and a maximal resolution of 20 nm was seen. Although using relatively simple standard processes, complex optical functions could be realized on a single chip. ACKNOWLEDGMENFTSI would like to thank • R. Dändliker for directing this thesis and for many helpful discussions.• H.P. Zappe for supervising this work. He introduced me into the basics of cleanroom work as well as into the field of 111-V-based integrated optics. Without his patience in revising my English manuscripts, I would have managed neither to publish a paper nor to write my PhD thesis.• M.T. Gale and H.W. Lehmann, who created a productive atmosphere in their research groups. Many discussions with them and their co-workers J. Söchtig, H. Teichmann, J.E. Epier, and P. Riel were necessary to animate in me the interest for interferometry, IH-V-processing, and semiconductor laser fabrication.• K. Knop for allowing me to carrying out this PhD work at the Paul Scherrer Institute in Zurich.• H. Schütz, R. Widmer, D. Jeggle, A. Vonlanthen, H. Meier, H.P. Schweizer, R. Stutz,}. Pedersen, and H. Siegwart for their technical and PC support.• N.E de Rooij, H. Heidrich, and H.P. Zappe for their interest in this work and also for being members of the jury.• My family and my friends for their support and patience during my education.Zurich, June 19% Daniel Hofstetter -u- LIST OF PUBLICATIONSThis thesis is an overview of our work in the area of monolithically integrated optical displacement sensing using III-V-semiconductors. Appendix B contains the following reprints of our journal publications. I D. Hofstetter, H.P. Zappe, J.E. Epler and J. Söchtig, Single-growth-step GaAs/AlGaAs distributed Bragg reflector lasers with holographicallydefined recessed gratings, Electron. Lett, vol. 30, no. 22, pp. 1858Lett, vol. 30, no. 22, pp. -1859Lett, vol. 30, no. 22, pp. , 1994 Lett., vol. 67, no. 14, pp. 1978Lett., vol. 67, no. 14, pp. -1980Lett., vol. 67, no. 14, pp. ,1995