High-RF-frequency analog fiber-optic links using optical signal processing

Abstract

Wide band phase modulators used with high power laser carriers convert high-frequency RF signals to phase-modulated optical signals. Higher laser optical power to the modulator produces larger RF signal sidebands. A carrier attenuation filter passes the attenuated carrier and non- attenuated RF modulation sidebands. Carrier attenuation leaves the larger RF signal sidebands. A demodulation filter used with a photodetector or a balanced photodetector pair converts the phase-modulated optical signal back to an electrical signal. Carrier-only attenuation allows high power laser use, avoids photodetector damage or saturation, and provides increased RF link gain, low noise figure (NF) and high spurious-free dynamic range (SFDR). Filtered-out carrier power fed back to the laser source increases to overall system efficiency. An additional optical delay filter with dual outputs used with a polarization multiplexer or a coherent combiner coupler combines signal power to a single photodetector to further increase electro-optic signal conversion efficiency.

Description

Background technique [0001] Current analog fiber optic links utilizing intensity modulators are used in both military, aerospace and commercial applications for transmitting analog radio frequency (RF) signals from antennas. Current fiber optic links have limited performance, especially at high RF frequencies (10 to >100 GHz), due to reduced conversion efficiency due to modulator limitations at higher RF frequencies, and damage due to nonlinear saturation Before that happened, small-area high-frequency photodetectors had limited optical power-handling capabilities. These limitations caused by modulators and photodetectors severely limit the performance and implementation feasibility of conventional RF fiber optic links for these high RF frequency signal transmissions. [0002] The present invention is an extension of US Patent No. 7,660,491 filed by EOSapce Corporation on February 9, 2010 and invented by the same inventor, Suwat Thaniyavarn. [0003] Current analog RF fib...

AI Technical Summary

Problems solved by technology

These problems are due to the fact that although optical modulators (used to convert RF electrical signals into optical signals for signal transmission through optical fibers) and photodetectors (used to convert optical signals transmitted through optical return RF signal) can operate at very high RF frequencies, but they are less efficient at higher RF frequencies

In addition, the photodetectors capable of operating at very high RF frequencies are very small in size, which is necessary for operation at higher frequencies, and therefore only capable of limited optical power handling

This limited optical power handling problem of high frequency photodetectors means that higher optical power sources cannot be used

Limiting optical power at the photodetector means limited RF fiber link performance in terms of low link loss, high noise figure, and low dynamic range

These issues limit the current implementation of fiber optic transmission of RF signals at very high RF (20->100GHz) frequencies

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