Complex-Coefficient Microwave Photonic Filter Based on Orthogonally Polarized Optical Single-Sideband Modulation

A complex-coefficient microwave photonic filter with continuous tunability is proposed and experimentally demonstrated. The filter taps are based on a 360° tunable microwave photonic phase shifter, which is realized by orthogonally polarized optical single-sideband (OSSB) modulation. The experimental results are shown and regarded as good performance for the proposed filter. The phase shift for the two taps covers a full 360° range from 8 GHz to 26 GHz. Frequency responses with different center frequency are measured within 20–21 GHz with the full free spectral ranges (FSRs) of 185 MHz and 285 MHz, respectively.

Photonic RF and Microwave Photonic Channelizers based on Kerr Micro-combs

We review recent work on broadband RF channelizers based on integrated optical frequency Kerr micro-combs combined with passive micro-ring resonator filters, with microcombs having channel spacings of 200GHz and 49GHz. This approach to realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.

Compounding a High Dielectric Constant Thermoplastic Material for Production of Microwave Photonic Crystals through Additive Manufacturing

Additive Manufacturing techniques allow the production of complex geometries unattainable through other traditional technologies. This advantage lends itself well to rapidly iterate and improve upon the design of microwave photonic devices, which are structures with intricate, repeating features. The issue tackled by this work involves compounding a high-dielectric constant material that can be used to produce 3D topological structures using polymer extrusion-based AM techniques. This material was ABS based, and used barium titanate ceramic as the high-dielectric compound of the composite, and involved the use of a surfactant and a plasticizer to facilitate processing. Initial small amounts of material were compounded using an internal batch mixer, and studied using polymer thermal analysis techniques, such as thermogravimetric analysis, rheometry, and differential scanning calorimetry to determine the proper processing conditions. The production of the material was then scaled-up through the use of a twin-screw extruder system, producing homogeneous pellets. Finally, the thermoplastic composite was used with a screw-based, material extrusion additive manufacturing technique to produce a slab for measuring the dielectric constant of the material, as well as a preliminary 3D photonic crystal. The real part of dielectric constant of the composite was measured to be 12.85 in the range of 10GHz to 12GHz, representing the highest dielectric constant ever demonstrated for a thermoplastic AM composite at microwave frequencies. The dielectric loss tangent was equal to 0.046, representing a low-loss dielectric.

Shared-Aperture 24–28 GHz Waveguide Antenna Array

A compact three-element shared-aperture waveguide antenna array for the 24–28 GHz microwave-frequency band is presented as a proof-of-concept of an array with steerable directional beam suitable for 5G telecommunication systems. The array is intended for use in a microwave photonic link and is sufficiently steerable only with the progressively phased excitation signals of equal magnitudes. The mutual interactions between the array elements are minimized to maintain the properties of the individual elements, even if they are embedded and closely spaced in the array. The proposed concept could be simply extended by adding more elements to further increase the directivity and enhance the steering properties of the array.

Multipole resonance and Vernier effect in compact and flexible plasmonic structures

Spoof surface plasmons in corrugated metal surfaces allow tight field confinement and guiding even at low frequencies and are promising for compact microwave photonic devices. Here, we use metal-ink printing on flexible substrates to construct compact spoof plasmon resonators. We clearly observe multipole resonances in the microwave frequencies and demonstrate that they are still maintained even under significant bending. Moreover, by combining two resonators of slightly different sizes, we demonstrate spectral filtering via the Vernier effect. We selectively address a target higher-order resonance while suppressing the other modes. Finally, we investigate the index-sensing capability of printed plasmonic resonators. In the Vernier structure, we can control the resonance amplitude and frequency by adjusting a resonance overlap between two coupled resonators. The transmission amplitude can be maximized at a target refractive index, and this can provide more functionalities and increased design flexibility. The metal-ink printing of microwave photonic structures can be applied to various flexible devices. Therefore, we expect that the compact, flexible plasmonic structures demonstrated in this study may be useful for highly functional elements that can enable tight field confinement and manipulation.