Alignment of lines in space (with particular reference to laser-fibre coupling)

• Main Author: Opono-Moyahi-Okello, John A.
• Published: Loughborough University 1987
• Subjects: 621.381045; Automatic production of optoelectronic devices
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292972

The object of this work (featuring the study of alignment of lines in space) is to produce a novel system for automatic production of optoelectronic components. It begins by reviewing the different components associated with optical fibre transmission and examines the existing laser-fibre coupling methods. The manual alignment technique adopted by STC to align a laser beam with a monomode optical fibre is then presented. The various interpretations of alignment are explored. The results obtained from the analysis determine the type of manipulator required for laser to optical fibre coupling. The central axis of a divergent beam emitted by a semi-conductor laser diode is manipulated for alignment with the axis of the fibre. Such an alignment places stringent displacement tolerance and accuracy demands on the manipulator. To construct a manipulator, actuators need to be coupled together. The coWling methods are studied and presented. Prior to this study, commercially available actuators are surveyed leading to the selecticin of the Oriel Encoder Mike actuator. This actuator exhibits some inherent control problems but meets the laser-fibre coupling accuracy demands. Various types of couplings are also examined based on the expansion of the Kelvin coupling for the construction of a four degree of freedom manipulator. A computational algorithm analogous to that used to solve two plane balancing problems is sucessfully tested on this manipulator for alignment of a conventional He-Ne laser beam with the centres of two transparent screens. This algorithm requires linearity for its success. For this reason and for purposes of completeness, spatial displacement characteristics of the manipulator are analysed and confirmed experimentally. This work ends with the ocnstruction. and testing of a program based on a hill climbing technique for the control of a three degree of freedom (Oriel Encoder Mike) manipulator to align a laser beam emitted by a semi-conductor laser diode with a monomode optical fibre.