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  • April 2012

Optics InfoBase > Spotlight on Optics > Programmable multiple true-time-delay elements based on a Fourier-domain optical processor

Programmable multiple true-time-delay elements based on a Fourier-domain optical processor

Published in Optics Letters, Vol. 37 Issue 4, pp.608-610 (2012)
by Xiaoke Yi, Liwei Li, Thomas X. H. Huang, and Robert A. Minasian

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Spotlight summary: Photonic processing of microwave signals has attracted a huge interest from both the research community and the industrial sector over the last decades. This is due to the fact that photonic processors enable the realization of functionalities in microwave systems that are either complex or even not directly possible in the radiofrequency domain. Reconfigurability, large bandwidth, tuneability, small size and weight are highly desirable features, which are however not straightforward to implement using traditional electronic circuitry. However, photonic processors have been previously based on bulky, expensive and power-consuming architectures. Nevertheless, a bright future for the processing of microwave signals in the photonic domain is envisaged. Recently, more compact solutions have been proposed using photonic integrated circuits based on semiconductor waveguides, ring cavities or photonic crystal waveguides, amongst others.

The authors from the University of Sydney have conducted research on photonic processors using a two-dimensional array of liquid crystal on silicon (LCoS) for years. A LCoS matrix enables the solution of the design of a compact processor with the functionalities of large bandwidth and tuneability. The current paper deals with the implementation of multiple independently controllable True Time Delays (TTDs) using a liquid crystal matrix. TTDs are key elements for the realization of the most common functionalities of microwave photonic processors: phased array antennas, microwave photonic filters, analog-to-digital converters, pulse shapers, radio-over-fiber sytems, etc. Particularly, the authors propose the use of TTDs in the realization of phased array antennas. Photonic TTDs are suitable to avoid the squint beam squint in wideband antennas. The paper is a proof of concept of the generation and independent programmable tuning control of multiple TTD in the microwave domain (up to 20 GHz, in the range from -32ps to +32ps delay) using a LCoS matrix. More information about the performance of LCoS in other applications of the photonic processing of microwave signals can be found in previous papers by the authors, which will help elucidate the potential of the proposed technique. These examples indicate that the realization of compact photonic processors of microwave signals featuring sophisticated functionalities maybe a reality in a not-too-distant future.

--Salvador Sales Maicas

Technical Division: Optoelectronics
ToC Category: Fiber Optics and Optical Communications
OCIS Codes: (060.2360) Fiber optics and optical communications : Fiber optics links and subsystems
(070.1170) Fourier optics and signal processing : Analog optical signal processing
(350.4010) Other areas of optics : Microwaves
(060.5625) Fiber optics and optical communications : Radio frequency photonics

Posted on April 18, 2012

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