Hui-Pin Hsu

Analysis Of Low Loss Impedance Matched Fiber-Optic Transceivers For Microwave Signal Transmission

An analysis of fiber-optic link loss and bandwidth based on simple equivalent circuit models for the laser diode and photodiode is presented. The method of modeling the link by defining a transfer coefficient between the current flowing into the active resistance of the laser diode and the current generated at the photodiode allows conventional circuit analysis to be performed. A closed form expression is derived for the link transfer function for both an impedance matched link and an unmatched link. The link loss is shown to be reduced by more than 15 dB by impedance matching the transceiver at microwave frequencies for typical device parameters. The analysis also demonstrates that impedance matched links can actually have a net RF gain with realizable device parameters at frequencies up to X-band. The transfer function for a link with realistic two-element matching circuits is derived. The bandwidth is then determined. These results define a link loss versus bandwidth tradeoff. The analytical results are verified by experiment.

Fiber-Optic Links For Microwave Signal Transmission

The performance and design of fiber-optic links for analog signal transmission at microwave frequencies are discussed. The effect of impedance matching the fiber-optic transceiver using either lossless or lossy circuit elements is presented. In particular, the following performance parameters are examined: link insertion loss, transceiver input and output VSWR, and link bandwidth. The contributions of RF circuit losses as well as optical losses to the overall RF link insertion loss are described. Commercially available fiber-optic links are shown to be unsuitable for most microwave applications. However, fiber-optic links employing lossless impedance matching to the laser diode and photodiode are shown to minimize the link insertion loss and VSWR in a finite frequency band and are therefore practical for many applications involving microwave signal transmission.

Fundamental Gain/Bandwidth Limitations In High Frequency Fiber-Optic Links

The theoretical gain/bandwidth limitations for directly modulated fiber-optic (FO) links are examined. Design curves are presented which enable one to determine the photodiode RC time constant which yields the minimum link loss for a specified receiver bandwidth. The insertion loss characteristics are examined for FO links subject to broadband impedance matching where purely reactive elements are used.

Characterization Of Fiber-Optic Links For Microwave Signal Transmission

The performance of a commercially available 1.3μm, single mode fiber-optic link is characterized in terms of parameters relevant to microwave and RF engineers. In particular, key link performance parameters are evaluated such as insertion loss, input/output VSWR, bandwidth, noise, compression point, intermodulation distortion (IMD) and dynamic range. A description of performance limitation factors is included for each of these parameters.