Traveling-wave microwave fiber-optic links

A traveling-wave microwave fiber-optic link (TW MFL) is proposed and demonstrated for the first time. The structure is electrically equivalent to a traveling-wave microwave amplifier in which the transistors are replaced by individual optical fiber link elements using laser diode (LD)-photodiode (PD) pairs. This results in two transmission-line structures that are periodically loaded with LDs and PDs, respectively, and connected to one another by a fiber array. A three-element TW MFL has been constructed using commercially available components to demonstrate the concept. Over the design bandwidth of 200 MHz-2 GHz, the input and output return loss is better than approximately 10 dB each, while the link gain of -20 dB is in agreement with simulation results. The link gain is seen to increase as the number of link elements is increased. Measured S-parameter results also show the deleterious impact of terminating impedance mismatches and optical delay detuning on the TW MFL´s frequency response.