Optically generation of rapidly tunable millimeter wave subcarrier using microchip lasers.

摘要

There is growing interest in applying photonic techniques to the generation of high fidelity millimeter wave signals. This thesis concerns the optical domain generation of rapidly tunable, very low noise millimeter wave subcarrier signals. Specifically, an optical transmitter employing two heterodyned electro-optically tunable microchip lasers has been designed, fabricated and characterized regarding its tuning range, speed, and noise performance. To explain the fast tuning speed observed in the experiment, a theoretical analysis of the laser dynamics during the intracavity frequency tuning process is advanced using the semi-classic Maxwell-Bloch formulation. The theoretical analysis confirms that microchip laser has a virtually unlimited tuning speed.; The output of the tunable transmitter is contaminated by the optical phase noise initiating in the microchip laser. A novel phase noise control approach, coined an "optical frequency locked loop" (OFLL), is developed to achieve low noise operation. Unlike conventional techniques, this scheme utilizes a long fiber delay in place of an external reference oscillator to correct the phase error. The optical frequency locked loop outperforms conventional phased locks loops, particularly at higher millimeter wave frequencies. The tunable transmitter was successfully evaluated in the context of a broadband fiber radio downlink experiment.