Abstract
The use of Spatial Division Multiplexing for Microwave Photonics signal processing is proposed and experimentally demonstrated, for the first time to our knowledge, based on the selective inscription of Bragg gratings in homogeneous multicore fibers. The fabricated devices behave as sampled true time delay elements for radiofrequency signals offering a wide range of operation possibilities within the same optical fiber. The key to processing flexibility comes from the implementation of novel multi-cavity configurations by inscribing a variety of different fiber Bragg gratings along the different cores of a 7-core fiber. This entails the development of the first fabrication method to inscribe high-quality gratings characterized by arbitrary frequency spectra and located in arbitrary longitudinal positions along the individual cores of a multicore fiber. Our work opens the way towards the development of unique compact fiber-based solutions that enable the implementation of a wide variety of 2D (spatial and wavelength diversity) signal processing functionalities that will be key in future fiber-wireless communications scenarios. We envisage that Microwave Photonics systems and networks will benefit from this technology in terms of compactness, operation versatility and performance stability.
Highlights
The use of Spatial Division Multiplexing for Microwave Photonics signal processing is proposed and experimentally demonstrated, for the first time to our knowledge, based on the selective inscription of Bragg gratings in homogeneous multicore fibers
We present in this paper, for the first time to our knowledge, the fabrication and experimental demonstration of the proposed true time delay line (TTDL) based on the inscription of Fiber Bragg Gratings (FBGs) with arbitrary frequency spectra and located at arbitrary points along each core of a homogeneous multicore fibers (MCFs)
Our target is to write complex FBG structures along any core, as the one we propose for the implementation of TTDLs, i.e.: (1) arrays comprising a set of distinct gratings instead of one single grating in each core; (2) a different longitudinal location of the gratings from core to core; (3) high-quality grating featuring a high level of optical power reflection and homogeneity along the inscribed FBGs; (4) a MCF with a higher core density that will require a more precise inscription method and beam control mechanism
Summary
Microwave Signal processing by selective grating inscription in homogeneous multicore fibers received:31August2016 accepted: 03 January 2017. This approach limits the lens effect produced by the round surface of the fiber and improves, as a consequence, the quality of the FBGs inscribed compared when the core is placed in the upper or lower positions[21]. The evolutionary process towards the 2D true time delay line brought us to the following MWP device that allows both spatial-diversity and wavelength-diversity regimes as we described above This second device comprises an array of three uniform gratings that are located in different longitudinal positions along three of the outer cores. A special case is the one related to the central core since it received radiation from the three inscription processes, resulting in a final interference with maximum peak levels 8 dB lower
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