Sergi García

Design of heterogeneous multicore fibers as sampled true-time delay lines

We present a novel procedure for designing a sampled discrete true-time delay line (TTDL) for Microwave Photonics applications based on a heterogeneous MCF. Both simple step-index (SI) and trench-assisted SI profiles are numerically evaluated in terms of physical dimensions and material dopant concentrations in order to individually tailor the group delay and chromatic dispersion of each core. The proposed TTDL features unique properties beyond the current state of the art in terms of record bandwidth, compactness, flexibility, and versatility.

Multi-cavity optoelectronic oscillators using multicore fibers.

We propose the use of both homogeneous and heterogeneous multicore fibers to implement multi-cavity optoelectronic oscillators. We present design equations and examples that show the potential for unique performance in terms of spectral selectivity, tunability and high-frequency operation.

Dispersion-engineered multicore fibers for distributed radiofrequency signal processing.

We report a trench-assisted heterogeneous multicore fiber optimized in terms of higher-order dispersion and crosstalk for radiofrequency true time delay operation. The analysis of the influence of the core refractive index profile on the dispersion slope and effective index reveals a tradeoff between the behavior of the crosstalk against fiber curvatures and the linearity of the propagation group delay. We investigate the optimization of the multicore fiber in the framework of this tradeoff and present a design that features a group delay relative error below 5% for an optical wavelength range up to 100 nm and a crosstalk level below -80 dB for bending radii larger than 103 mm. The performance of the true time delay line is validated in the context of microwave signal filtering and optical beamforming for phased array antennas. This work opens the way towards the development of compact fiber-integrated solutions that enable the implementation of a variety of distributed signal processing functionalities that will be key in future fiber-wireless communications networks and systems.

Experimental demonstration of multi-cavity optoelectronic oscillation over a multicore fiber

We report, for the first time to our knowledge, the experimental demonstration of multi-cavity optoelectronic oscillators where the cavities are provided by the different cores of a multicore fiber. We implemented two multi-cavity architectures over a 20-m-long 7-core fiber link: unbalanced dual-cavity oscillation (the cavity lengths are a multiple of a reference value) and multi-cavity Vernier oscillation (the cavity lengths are slightly different). Since all the cavities are hosted under a single fiber cladding and are subject to the same environmental and mechanical conditions, optoelectronic oscillators built upon multicore fibers benefit from improved performance stability as compared to independent singlemode fiber cavities.

Crosstalk-optimized multicore fiber true time delay lines

We demonstrate the feasibility of implementing 2D sampled discrete true time delay lines built upon crosstalk-optimized heterogeneous multicore fibers. By properly designing the trench-assisted refractive-index profile of each individual core, we assure a crosstalk performance that is insensitive to fiber curvatures for bending radii higher than 158 mm. For regions above that threshold radius, a worst-case intercore crosstalk around -100 dB was achieved, a value much lower than the -70 dB previously reported in the literature.

RF photonic delay lines using space-division multiplexing

We review our last work on dispersion-engineered heterogeneous multicore fiber links designed to act as tunable true time delay lines for radiofrequency signals. This approach allows the realization of fiber-distributed signal processing in the context of fiber-wireless communications, providing both radiofrequency access distribution and signal processing in the same fiber medium. We show how to design trench-assisted heterogeneous multicore fibers to fulfil the requirements for sampled true time delay line operation while assuring a low level of crosstalk, bend sensitivity and tolerance to possible fabrication errors. The performance of the designed radiofrequency photonic delay lines is evaluated in the context of tunable microwave signal filtering and optical beamforming for phased array antennas.

Demonstration of multi-cavity optoelectronic oscillators based on multicore fibers

We report the first experimental demonstration of multi-cavity optoelectronic oscillators where the different cavities are hosted in a single multicore fiber. Different configurations are implemented on the same 20-m 7-core fiber link, exploiting both unbalanced dual-cavity operation (loop lengths are a multiple of a reference value) and multi-cavity Vernier operation (loop lengths are slightly different).

Space-division Multiplexing for fiber-wireless communications

We envision the application of optical Space-division Multiplexing (SDM) to the next generation fiber-wireless communications as a firm candidate to increase the end user capacity and provide adaptive radiofrequency-photonic interfaces. This approach relies on the concept of “fiber-distributed signal processing”, where the SDM fiber provides not only radio access distribution but also broadband microwave photonics signal processing. In particular, we present two different SDM fiber technologies: dispersion-engineered heterogeneous multicore fiber links and multicavity devices built upon the selective inscription of gratings in homogenous multicore fibers.

Fiber-distributed signal processing: Where the space dimension comes into play

We present how to implement fiber-distributed signal processing in the context of fiber-wireless communications by using different multicore fibers, providing both radio access distribution and microwave photonics signal processing in the same fiber medium.

Multi-cavity Microwave Photonics devices built upon multicore fibres

We present novel multi-cavity fibre-based devices built upon the fabrication of cavities along each one of the cores of a homogeneous 7-core fibre. Since the multi-cavity structure is confined in a single optical fiber, this approach translates into optical true time delay lines that offer at the same time 2D operation by exploiting the optical wavelength and the spatial diversity domains. We envisage that multiple Microwave Photonics signal processing systems will benefit from this fibre-integrated technology in terms of compactness, versatility and performance stability.