We review the recent advances reported in the field of integrated photonic waveguide meshes, both from the theoretical as well as from the experimental point of view. We show how these devices can be programmed to implement both traditional signal processing structures, such as finite and infinite impulse response filters, delay lines, beamforming networks as well as more advanced linear matrix optics functionalities. Experimental results reported both in Silicon and Silicon Nitride material platforms will be presented. We will also discuss the main programming algorithms to implement these structures and discuss their applications either as standalone systems or as part of more elaborated subsystems in microwave photonics, quantum information and machine learning.
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.
This paper explores the use of honeycomb lattice waveguide meshes for universal linear operations and photonic
integrated circuit synthesis by programming a common hardware. We discuss the main photonic processor architecture,
the non-ideal effects to be considered and its application to different signal processing functionalities.
Next generation fiber-wireless communication paradigms will require new technologies to address the current limitations
to massive capacity, connectivity and flexibility. Multicore optical fibers, which were conceived for high-capacity digital
communications, can bring numerous advantages to fiber-wireless radio access architectures. Besides radio over fiber
parallel distribution and multiple antenna connectivity, multicore fibers can implement, at the same time, a variety of
broadband processing functionalities for microwave and millimeter-wave signals. This approach leads to the novel
concept of “fiber-distributed signal processing”. In particular, we capitalize on the spatial parallelism inherent to
multicore fibers to implement a broadband tunable true time delay line, which is the basis of multiple processing
applications such as signal filtering, arbitrary waveform generation and squint-free radio beamsteering. We present the
design of trench-assisted heterogeneous multicore fibers composed of cores featuring individual spectral group delays
and chromatic dispersion profiles. Besides fulfilling the requirements for true time delay line operation, the MCFs are
optimized in terms of higher-order dispersion, crosstalk and bend sensitivity. Microwave photonics signal processing
will benefit from the performance stability, 2D operation versatility and compactness brought by the reported fiberintegrated
solution.
The use of multicore optical fibres (MCF) in optical sensing applications has gained increasing interest over the past
years due to the benefits directly brought from their inherent spatial diversity. This property allows measuring either
multiple physical magnitudes at the same time or the same magnitude with slight differences in order to compensate the
cross-sensitivities. We have inscribed Regenerated Fibre Bragg Gratings (RFBGs) in MCFs with the aim of
implementing temperature sensors with an enhanced accuracy and for a very wide temperature range (up to 1000°C). The
sensors have been made in 4-core and 7-core commercially available homogeneous MCFs. The fabrication process has
been designed to create different temperature sensitivities among the identical cores of the MCF. We have obtained
significant wavelength-shift differences up to 1.2 nm at 765°C, what has been used to at least double the temperature
accuracy.
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