TABLE OF CONTENTS The laser diode provides a compact, reliable, and potentially low-cost method for the optical generation and distribution of mm-wave signals [ [2], [19]]. By large-signal direct modulation of the laser diode, such as gain-switching or mode-locking, harmonic powers can be generated up to millimetre-wave frequencies. Direct modulation is attractive because of its simplicity. In the following large-signal application example, the integrated TLLM model was gain-switched at different subharmonic frequencies to generate a RF signal at 6.6 GHz, useful for locking a GaAs-based monolithic microwave integrated circuit voltage controlled oscillator (MMIC VCO) [ [82]].
A multimoded 1.3 ?m InGaAsP ridge-waveguide laser diode model was used in the simulations, with a comprehensive list of parameter values taken from [ [65]], also listed in Table 15.3. The modulation bandwidth of the laser model is well below 6.6 GHz, hence direct modulation at this frequency is highly inefficient. Therefore, a simple solution is to gain-switch the laser at subharmonic frequencies of 6.6 GHz such as 1.1 GHz, 1.32 GHz, 1.65 GHz, 2.2 GHz, and 3.3 GHz so that the 6.6 GHz component is included as part of the comb of harmonic frequencies. Furthermore, by using subharmonic frequencies, higher drive power is available since RF amplifiers at high frequencies are difficult to realise.
Matching circuits should be used in large-signal modulation of semiconductor lasers to achieve higher RF power and better modulation depth. Matching techniques such as microstrip stub matching circuits [ [64]] and the quarter-wave...
