Coherent optical detection with an emphasis on electronics.
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
In the development of Optical Information Transmission Technology, considerable investigation of the loss mechanisms, in optic fibres, has been made. Subsequently drastic reductions in transmission path loss have been achieved. Somewhat less effort has been spent on methods of improving optical detection efficiencies. By examining the signal-to-noise expressions associated with optical detection schemes, it is clear that by using coherent detection, output signal to noise ratios could be increased by about 3 dB over intensity detection systems. Moreover detection bandwidths could be increased using coherent detection methods. Coherent detection permits the detection of optimum modulation schemes. By exploiting the optical properties of some materials, under the influence of external fields, FSK and PSK modulation can be introduced into a light beam. Using a local oscillator laser, which is added into the beam incident upon the detector, a mixer product, at the detector output, may be generated; either at an intermediate frequency or at the base-band. To recover the information, the mixer product must be amplified. Amplifiers for such applications must produce constant gain over very wide bandwidths (over 8 decades). Moreover if they are to amplify digital signals they must be of linear phase. Such design requirements are difficult to meet, however by applying methods of equalisation, the designer may readily control the gain and phase of such amplifiers over the range of interest. Concepts of broadband equalisation are verified by equalising a number of loads with frequency dependent power gains.