Murilo A. Romero

An analytical model for the photodetection mechanisms in high-electron mobility transistors

The use of microwave high-electron mobility transistors (HEMTs) as photodetectors or optically controlled circuit elements have attracted interest. A model of the optical characteristics of HEMTs, which takes into account carrier transport as well as the quantum mechanical nature of the two-dimensional (2-D) electron gas channel, is presented. It is shown that the effect of illumination is equivalent to a shift in the gate to source bias voltage, referred to as the internal photovoltaic effect. The theoretical model is supported by experimental results that demonstrate that the HEMT photoresponse is a nonlinear function of light intensity with very high responsivity at low optical power levels.

An Extended FDTD Method for the Analysis of Electromagnetic Field Rotators and Cloaking Devices

This paper presents a dispersive finite difference time domain (FDTD) method suitable for the analysis of electromagnetic field rotator (and cloaking) devices. The method employs a coordinate transformation which accurately accounts for the radial dependence of the permittivity and permeability tensors, with Drude material models applied to the respective diagonal elements. The key aspect of the present formulation is the inclusion of the radial dependence of the plasma frequency, which makes this formalism quite attractive for the modeling of a general class of cloaking and field rotator geometries. Firstly, the method is validated by comparing its results with a previously published simulation of a cloaking device. Then, it is applied for the first time to the analysis of dispersive effects on the performance of field rotators.

Temperature Sensing Using Colloidal-Core Photonic Crystal Fiber

We report on a temperature sensor based on the monitoring of the luminescence spectrum of CdSe/ZnS nanocrystals, dispersed in mineral oil and inserted into the core of a photonic crystal fiber. The high overlap between the pump light and the nanocrystals as well as the luminescence guiding provided by the fiber geometry resulted in relatively high luminescence powers and improved optical signal-to-noise ratio (OSNR). Also, both core end interfaces were sealed so as to generate a more stable and robust waveguide structure. Temperature sensitivity experiments indicated a 70 pm/°C spectral shift over the 5°C to 90°C range.

Theoretical analysis of supercontinuum generation in a highly birefringent D-shaped microstructured optical fiber

This paper carries out a rigorous analysis of supercontinuum generation in an improved highly asymmetric microstructured fiber (MF) design. This geometry, defined simply as D-MF, has the advantage of being produced with a regular stacking and drawing technology. We have obtained birefringence values on the order of 4.87x10(-3) at the adopted pump wavelength and a significantly smaller effective area when compared to a whole MF, which makes this fiber quite attractive for SCG. Therefore, this D-MF design is a promising alternative for SCG since it provides new degrees of freedom to control field confinement, birefringence, and dispersion characteristics of MFs.

Hybrid EDFA/Raman Amplification Topology for Repeaterless 4.48 Tb/s (40 x 112 Gb/s DP-QPSK) Transmission Over 302 Km of G.652 Standard Single Mode Fiber

In this work we carry out a comprehensive experimental study on hybrid optical amplification topologies (based on first order Raman and Erbium doped fiber amplifiers) for repeaterless transmission of 112 Gb/s dual polarization-quadrature phase shift keying (DP-QPSK) enabling a 4.48 Tb/s (40 × 112 Gb/s) transmission over 302 km of standard single mode fiber with coherent detection. Hybrid optical amplification was employed for signal boosting and pre-amplification and repeaterless transmission is assured without the use of neither in-line amplification nor remote optical amplifiers. The goal was to achieve the highest bandwidth-distance product for repeaterless DWDM transmission systems over legacy fiber without any in-line amplification technology. The achieved result is a significant milestone, when compared to recent state-of-the-art investigations.

Chaotic Communication Based on the Particle-in-a-Box Electronic Circuit

A secure communication system based on the error-feedback synchronization of the electronic model of the particle-in-a-box system is proposed. This circuit allows a robust and simple electronic emulation of the mechanical behavior of the collisions of a particle inside a box, exhibiting rich chaotic behavior. The required nonlinearity to emulate the box walls is implemented in a simple way when compared with other analog electronic chaotic circuits. A master/slave synchronization of two circuits exhibiting a rich chaotic behavior demonstrates the potentiality of this system to secure communication. In this system, binary data stream information modulates the bifurcation parameter of the particle-in-a-box electronic circuit in the transmitter. In the receiver circuit, this parameter is estimated using Pecora-Carroll synchronization and error-feedback synchronization. The performance of the demodulation process is verified through the eye pattern technique applied on the recovered bit stream. During the demodulation process, the error-feedback synchronization presented better performance compared with the Pecora-Carroll synchronization. The application of the particle-in-a-box electronic circuit in a secure communication system is demonstrated.

Combined Self-Seeding and Carrier Remodulation Scheme for WDM-PON

In this work, we propose a novel self-seeded WDM-PON topology. Unlike previous works, in our case, the self-seeding occurs in RSOAs located at the OLT, allowing upstream transmission based on carrier remodulation at the ONT. Thus, a single wavelength per user can be employed for both traffic directions while eliminating the need for an external broadband light source at the CO. A maximum bidirectional 2.5 dB power penalty for a BER of 10-10 was obtained for an injection power level of -22 dBm into the ONT RSOAs. We also investigate the tolerance of downstream BER to downstream extinction ratio (ERD) and self-seeding power (Pss), as well as analyze the impact of upstream extinction level (ERUP), injection power (Pinj) and ERD levels on upstream BER performance, on symmetric 1.25 Gbps OOK transmission over 20 km without DTLA and FFCI mechanisms. We have successfully demonstrated downstream error free transmission (BER of 10-12) for an as low as 3.5 dB.

Design methodology for multi-pumped discrete Raman amplifiers: case-study employing photonic crystal fibers.

This paper proposes a new design methodology for discrete multi-pumped Raman amplifier. In a multi-objective optimization scenario, in a first step the whole solution-space is inspected by a CW analytical formulation. Then, the most promising solutions are fully investigated by a rigorous numerical treatment and the Raman amplification performance is thus determined by the combination of analytical and numerical approaches. As an application of our methodology we designed an photonic crystal fiber Raman amplifier configuration which provides low ripple, high gain, clear eye opening and a low power penalty. The amplifier configuration also enables to fully compensate the dispersion introduced by a 70-km singlemode fiber in a 10 Gbit/s system. We have successfully obtained a configuration with 8.5 dB average gain over the C-band and 0.71 dB ripple with almost zero eye-penalty using only two pump lasers with relatively low pump power.

Multiplexed fiber optic Bragg grating sensors for strain and temperature measurements in power systems

In Brazil several groups develop Optical Fiber Sensors based on Wavelength Division Multiplexed Optical Bragg Gratings. We present a review of recent results obtained at our groups in the development of Optical Fiber Sensors to measure deformation (strain) or temperature in high voltage power transmission lines.

Novel Sealing Technique for Practical Liquid-Core Photonic Crystal Fibers

In this letter, we describe a simple and effective technique to prevent evaporation in liquid-core photonic crystal fibers (PCFs). The technique consists of using a micropipette to deploy a micro-droplet of an ultraviolet curable polymer adhesive in both core inputs. After it is cured, the adhesive creates sealing polymer plugs with quite satisfactory insertion loss (overall optical transmission of about 15%). Processed fibers remained liquid-filled for at least six weeks. From a practical point of view, we conducted a supercontinuum generation experiment in a water-core PCF to demonstrate a 120-minute spectral width stability and the ability to withstand at least 3-mW average power at the sealed fiber input. Similar experiments carried out with nonsealed fibers produced supercontinuum spectra lasting no longer than 10 minutes, with average powers kept below 0.5 mW to avoid thermally induced evaporation.