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Abstract:A novel electro-optic (EO) microwave-lightwave converter using a patch antenna embedded with a narrow gap is proposed and experimentally demonstrated. By embedding a narrow gap at the center of the patch antenna and an optical waveguide located under the gap, a wireless microwave signal can be received and converted to an optical signal directly through EO modulation of a lightwave propagating in the optical waveguide. In the experiment, optical sidebands were observed clearly with the irradiation of an 18 GHz wireless signal to the fabricated prototype device. This device operates with no external power supply and no additional modulation electrode. Therefore, it can be operated with low microwave distortion.

Proposed is a new electro-optic microwave-lightwave converter using an optical waveguide and a quasi-phase-matching (QPM) array of patch antennas embedded with a gap. A wireless microwave signal can be received and directly converted to a lightwave signal with low microwave distortion through optical modulation by use of the proposed device. Furthermore, by adopting the QPM structures, the transit-time effect is compensated for and conversion efficiency can be improved. In the experiment using a fabricated device, the conversion efficiency was improved by 10 dB.Introduction: Electro-optic (EO) microwave-lightwave converters are key devices in radio-over-fibre (ROF) systems [1]. EO microwave-lightwave converters can convert wireless microwave signals to lightwave signals through optical modulation adopting microwave antenna technology. Several EO microwave-lightwave converters using antenna-integrated electrodes have been reported [2,3]. The reported devices were composed of an antenna for wireless microwave receiving, an electrode for optical modulation, and their connection line. In these devices, the antenna and the electrode should be tuned precisely to obtain good resonance and impedance matching conditions at the designed frequency. However, some microwave distortion might be still induced through the coupling of them.We have proposed EO microwave-lightwave converters using patch antennas with a gap [4]. The devices are composed of patch antennas only and there is no other planar element on the substrate. They have a simple compact structure and were operated with no precise tuning and no external power supply. The microwave-lightwave conversion with extremely low distortion was demonstrated. However, the conversion efficiency was low owing to the limitation by the lightwave transit-time effect [5].In this Letter, we propose a new EO microwave-lightwave converter utilising an optical waveguide and a quasi-phase-matching (QPM) array of rectangular patch antennas with a narrow gap. The QPM array can compensate for the degradation of conversion efficiency by the transit-time effect. In the experiment, the conversion efficiency of the fabricated device was increased by 10 dB.

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We propose a new electro-optic microwave-lightwave converter using two orthogonal optical waveguides and patch antennas embedded with two orthogonal gaps. Wireless microwave signals can be received, separated and converted directly to lightwave signals through optical modulation using the proposed device. This device operates with no external power supply and with low microwave distortion. In addition, it enables us to measure the magnitude, phase and polarization of the wireless signal simultaneously. Experimental demonstrations of the device were presented at the operation frequency of 26 GHz. The device can be applied for electromagnetic compatibility test in the radio-over-fiber link.

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