Photonic generation of microwave signals by exploiting fiber birefringence effect in single‐longitudinal‐mode distributed Bragg reflector fiber lazer

Abstract

ratio, even as low as 1.1. This makes the phase shifter ideal in applications involving FET whose capacitance ratio is normally small. However, such an implementation requires that the maximum and minimum capacitances of the varactor of each load are known accurately. Also, because there is no restriction on the type of the switch in a load, it can be a PIN diode, a FET, or a MEMS provided that proper integration with the rest of the phase shifter circuit is observed.By using a varactor diode and a PIN diode for each load, an experimental phase shifter operating at 2.5 GHz was developed. By considering the parasitics of the diodes and peripheral circuits, the need for inductors in the resonant circuits of the phase shifter was eliminated. The measurement confirmed the accuracy of the theoretical design in general. Any disagreements between the measured and predicted values of the insertion and return losses at some bias voltages were believed to be due to the finite resistances of the diodes and lack of accurate manufacturer's specification of the diodes at the desired operating frequency. It was found that the phase shifter has a bandwidth of $7%. The performance of the new phase shifter can be improved significantly using MMIC technology, where losses and parasitics due to the connections, and varactor devices can be controlled and reduced drastically, and where the PIN diodes can be replaced with FET switches easily for higher efficiency. ABSTRACT: A novel all-optical microwave generation technique based on fiber birefringence effect in single-longitudinal-mode (SLM) distributed Bragg reflector (DBR) fiber lazer is presented. Owing to the birefringence-induced mode splitting, the proposed lazer could provide a microwave signal at $1.72 GHz with a 3 dB bandwidth of $30 kHz. Moreover, another microwave signal at 10.96 GHz could also be generated as transverse pressure was applied onto the proposed lazer. Similar phenomenon was observed when another DBR lazer constructed with Er/Yb co-doped fiber was used, and a microwave signal at 11.47 GHz with $33 kHz linewidth have also been achieved.