S. Arismar Cerqueira

Recent progress and novel applications of photonic crystal fibers

Photonic crystal fibers present a wavelength-scale periodic microstructure running along their length. Their core and two-dimensional photonic crystal might be based on varied geometries and materials, enabling light guidance due to different propagation mechanisms in an extremely large wavelength range, extending to the terahertz regions. As a result, these fibers have revolutionized the optical fiber technology by means of creating new degrees of freedom in the fiber design, fabrication and applicability. This report aims to provide a detailed statement on the recent progress and novel potential applications of photonic crystal fibers.

Hybrid photonic crystal fiber

We present a hybrid photonic crystal fiber in which a guided mode is confined simultaneously by modified total internal reflection from an array of air holes and antiresonant reflection from a line of high-index inclusions. Experimental results demonstrate that this fiber shares properties of both index-guided and photonic bandgap structures.

Birefringence of Hybrid PCF and Its Sensitivity to Strain and Temperature

The modal and group birefringence of a hybrid photonic crystal fiber (hybrid PCF) and the sensitivities of modal birefringence of hybrid PCF to strain and temperature are investigated. The hybrid PCF composes of air-holes and Ge-doped silica rods surrounding a silica core region and light is confined to the core by hybrid index-guiding and photonic bandgap effects. A theoretical model was established and used to calculate these birefringence properties as functions of Ge concentration and diameter of the Ge-doped region. In experiments, the birefringence properties of a hybrid PCF made by University of Bath were measured by using a Sagnac interferometer. The experimental results show that the sensitivities of fringe minimum of this Sagnac interferometer to strain and temperature, at the wavelength of 1550 nm, were 2.01 nm/m and 0.334 nm/°C, respectively, which agree well with the theoretical predictions. The model may be used to design hybrid PCFs with desired birefringence properties.

Ultra-broadband photonics-based RF front-end toward 5G networks

We propose the concept and report the development of an ultra-broadband photonics-based RF front-end, as well as its experimental digital performance analysis up to 38 GHz. The proposed RF front-end applies optical frequency multiplication based on the external modulation technique and the optical nonlinear effect four-wave mixing for enabling a combination of photonic-assisted RF upconversion and amplification, regardless of frequency operation. We present ultra-broadband operation and frequency tunability from DC to 38 GHz by simultaneously performing RF conversion and amplification in the optical domain. The experimental results of a successful implementation in a real wireless-optical network demonstrate the RF front-end applicability in the three potential frequency bands for 5G networks, namely, 6.0, 28, and 38 GHz. Furthermore, a detailed digital performance investigation using different modulation formats is presented based on diverse RF and optical parameters, including signal-to-noise ratio, RF gain, and error vector magnitude. Low phase noise, spectral purity, and distortion absence are also observed for all frequency bands.

Optically Controlled Reconfigurable Antenna Array for mm-Wave Applications

This letter reports the concept and development of the first optically controlled reconfigurable antenna for millimeter-wave (mm-wave) applications. It is based on a slotted-waveguide antenna array and two photoconductive switches, which are used to control the slot electrical length. This novel photonics-based reconfigurable strategy enables frequency tunability and radiation pattern reconfiguration through the 28- and 38-GHz frequency bands. Numerical simulations and experimental results illustrate its applicability for mm-wave indoor applications. The measured gain is approximately 8.0 and 9.0 dBi at 28 and 38xa0GHz, respectively.

Tri-band RF filters optimization using evolutionary strategy

This paper presents a tri-band RF filter based on T-shape resonators, whose dimensions are determined using evolutionary strategy. The T-shape resonator input impedance has three resonance frequencies with two transmission zeros for improving its passbands isolation. In order to validate the proposed approach, a filter with three poles and center frequencies at 0.75, 1.5 and 2.25 GHz had been designed and numerically evaluated by using the electromagnetic Designer and HFSS from ANSYS. Resonator impedances and lengths are determined by the optimization process performed by a proper adapted evolutionary strategy, which is a computational intelligence approach with biological inspirations from the parents and offsprings relations.

Investigation of noise sources in Radio-over-Fiber systems for Wi-Fi applications

This work presents a experimental and analytical evaluation of Radio-over-Fiber (RoF) systems applied in Wi-Fi networks operating at 2.4 GHz. The performance metrics used were Packet Error Rate (PER), throughput and Relative Signal Strength Indication (RSSI). We used two different commercial RoF systems and verified the impact of each system on these networks. It was observed that Wi-Fi technology can be successfully applied with RoF technology to provide a remote employment up to 3 km from central office.

Convergent and reconfigurable optical-wireless network for LTE and Wi-Fi offloading applications

This work presents the concept and implementation of a convergent and reconfigurable optical-wireless network based on photonic-assisted frequency multiplication for LTE (Long Term Evolution) and Wi-Fi offloading applications. The use of optical external modulation technique for doubling the microwave frequency enables to reconfigure the wireless frequency operation. High quality RF carriers at 2.6 and 5.2 GHz have experimentally obtained using an optical backhaul composed by 2 km of single-mode optical fibers. High spectral purity, distortion absence and low phase noise of the generated RF signal have been observed.

Single-polarization state Hybrid Photonic Crystal Fiber

It is presented a single-polarization operation of a Hybrid Photonic Crystal Fiber with at least 200 nm bandwidth. Experimental results demonstrate polarization dependent loss as high as 23 dB on the photonic bandgap edge. Near field images are also presented.

Temperature response of photonic bandgap fibers based on high-index inclusions

We observed spectral shifts for short heated lengths of photonic bandgap fibers based on high-index rods. Shifts are observed in even shorter lengths if the fiber is bent. Application as alternative distributed sensors is envisaged.