Blanchflower, Ian David; (1993) Optical control techniques for microwave phase locking applications. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

This thesis considers the use of optical control techniques for phase locking of microwave and millimetre wave oscillators. Optical control functions provide a convenient means of controlling high frequency circuits. With the increasing importance of optical techniques in signal distribution applications, there is further advantage to be gained from the use of optically controlled devices as optical-to-electrical transducers. The optical phase locking systems considered are optical injection locking and optical frequency tuning within a phase locked loop. A third system, applying a combination of optical injection locking and optical frequency tuning within a phase locked loop, is considered in detail for the first time. General analytical models for the systems are derived and used to compare the operation. The analysis is effective in deriving new results for the effects of loop delay and differential phase in the novel optical injection locking/phase locked loop combination. Practical systems are demonstrated, employing an optically controlled 1.5 GHz MESFET oscillator. The results of optical frequency tuning and optical injection locking effects are presented, including a frequency tuning modulation response up to 100 MHz, and optical injection locking ranges up to 2 MHz. Measurements performed on the optical phase locking systems confirm the validity of the analysis. The practical implementation of optical phase locking systems is discussed. The analysis shows that phase locked loop bandwidths in excess of 100 MHz are feasible with a moderate optical tuning sensitivity of 10 MHz/mW. The performance of practical systems, however, may suffer from limited tuning modulation bandwidths, frequency tuning range, and poor tuning linearity that are characteristic of some optically tuned oscillators. Optical injection locking is dependent on the operating conditions of the oscillator, and this restricts its application, and that of the combined injection locking/PLL system. Fractional locking bandwidths of up to 1% with a few mW of optical signal power are possible with present devices. Improvements in device design for optical access may allow bandwidths of several hundred MHz in millimetre wave oscillators. The novel optical phase locking schemes are considered as receivers for microwave modulated optical signals in a distribution network for a phased array antenna. Detailed consideration is given to the relative merits with respect to conventional receivers, and the impact of the application of the techniques on the phased array antenna design. The results show the potential for useful performance of optically phase-locked oscillator receivers in applications at millimetre wave ranges.

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