Optically remoted probe for sensing of RF in aerospace radars
The improvement of radar reliability may require the detection and monitoring of its handled power. For this purpose, a new sensor concept based on an optically remoted RF probe was investigated. This work presents such a dedicated photonic system. The optical probe allows dual-regime operations: testing both radar transmit and receive operations. This monitoring performs not only “Go - No Go” tests, but could also be used for calibration. The paper reports the preliminary demonstrations. A new optoelectronic transducer was realised and a mock-up of probe was assembled and tested.
Design, Fabrication and Characterisation of Normal-Incidence 1.56-µm Multiple-Quantum-Well Asymmetric Fabry-Perot Modulators for Passive Picocells
SUMMARY We have designed and fabricated air-bridged modulators with bandwidths exceeding 10 GHz, the highest yet realised to date for InGaAsP/InGaAsP multiple-quantum-well (MQW) asymmetric Fabry-Perot modulators (AFPMs). Microwave modulation, measurements of intermodulation between the photodetected downlink and modulated uplink signals, and bi-directional broadband data over fibre transmission experiments have been performed to verify the potential of the AFPM as a single electrical/optical transceiver. We also report the first direct integration of this AFPM with a microstrip patch antenna and present results of a preliminary microwave signal transmission experiment over a distance of 1.4 m in free-space at 5.2 GHz
Millimeter-wave asymmetric Fabry-Perot modulators
We have designed, fabricated, and characterized GaAs-AlGaAs (/spl lambda/=864 nm) asymmetric Fabry-Perot modulators with /spl ap/37 GHz modulation frequency response, comparable to the fastest waveguide modulators. The modulation response saturates at high optical powers due to saturation of the excitonic absorption and heating effects, but the frequency response is independent of the incident optical intensity, since it depends only on the RC time constant, and not on the carrier transit time. The device design takes advantage of the fact that the quantum-confined Stark effect is more pronounced at some distance from the absorption edge to achieve a modulator with /spl ges/20 dB contrast and /spl ap/3 dB insertion loss for /spl plusmn/2 V operating voltage, but only 21 fF capacitance. The DC bias used to move the operating point off the absorption edge has the additional benefits of improving the linearity and chirp of the device, as well as the saturation intensity. Here we present measurements of the modulation and photocurrent responses of the modulators, calculate the RC and transit times for the device, analyze the saturation mechanisms, and discuss the linearity and chirp of the device from the perspective of a high-speed digital optical communications system. >