Andrés P. L. Barbero

A New Triangulation-Like Technique for the Evaluation of the Refractive Index Structure Constant

A light beam propagating through the atmosphere has its amplitude, phase, and propagation direction changed along the optical path due to atmospheric turbulence. This effect is caused by the randomness of the air refractive index and depends on the local temperature, pressure, and humidity. The physical parameter that quantifies the turbulence strength is well known in the literature as the refractive index structure constant (Cn2). In this paper, a simple and low-cost technique based on a triangulation-like method to measure the Cn2 is presented for the first time to the best knowledge of the authors. Through a novel device comprised of three photodetectors in a triangle-shaped array placed on the receiver plane, it is possible, after power measurements and applying a developed mathematical model, to obtain precisely the position of the beam spot. Therefore, calculates the Cn2 and evaluates the atmospheric turbulence strength. Furthermore, the technique is useful to check the suitability of a free-space optical (FSO) link in a specific geographic region by monitoring the local turbulence. Also, the device will be useful to improve the deployment and maintenance of FSO systems.

(C_{n}^{2})

In this work numerical simulated and experimental results are obtained for a hybrid EDFA-Raman amplifier. Rigorous numerical models of both EDFA and Raman amplifiers are implemented and validated with experimental measurements. Results of ripple smaller than 1 dB are obtained for the hybrid amplifier gain, in 40 nm of bandwidth. The numerical model permits to achieve optimal design and to predict flat amplifier gain using genetic algorithm.

in Free-Space Optical Links

This paper analyzes experimentally the limitations observed in lightwave systems using distributed Raman amplifiers operating under large pump power input conditions. The Brillouin effect is observed as the pump power becomes equal to 1 watt centered in a specific pump wavelength. The presence of Brillouin peaks degrades the system performance. The Raman amplifier is set with singlemode and dispersion compensating fibers and evaluated in a high capacity WDM link at transmission rates up to 40 Gb/s per channel. The dispersion compensation was accomplished by adjusting the length of the dispersion compensating fiber. The system and amplifier characterization were developed in terms of the on-off gain, ripple, optical signal-to-noise ratio, eye diagram and extinction ratio.

Numerical simulations and experimental results of a hybrid EDFA-Raman amplifier

We explore the development of an optoelectronic probe for MF/HF/VHF (up to ~ 37 MHz) radio frequency bands able to display the complete waveforms. It was built from simple, low cost and robust components. A passive loop antenna generates RF current which modulates an ultra-bright LED of display/illumination. The light signals are transmitted along a PMMA plastic optical fibre (POF) to an optical receiver placed in a remote site. All characterization measurements were carried out in the near-field region. Far-field radio transmissions could also be detected. The probe presented at 0.5 MHz tuning-band has shown a 62 dBµV dynamic range and was able to detect down to Hmin ~ 0.8 nA cm−1 magnetic field amplitude. A new technique for loss compensation of the fibre link is proposed and successfully tested.

Brillouin effects in distributed Raman amplifiers under saturated conditions

It is reported a long-period grating (LPG) dynamic interrogation technique based on the modulation of fiber Bragg gratings located in the readout unit of the system. It permits to attenuate the effect of the noise of the electronics in the resolution of the LPG-based sensing head. The concept is tested to detect variations of the external refractive index and a resolution of 2.010 NIR was achieved without system optimization. Additionally, the effect in the sensor resolution when introducing Erbium and Raman optical amplification is experimentally investigated.

An optoelectronic probe with loss compensation for electromagnetic monitoring at low frequencies

It is reported a LPG dynamic interrogation technique based on the modulation of fibre Bragg gratings located in the readout unit that permits to attenuate the effect of the 1/f noise of the electronics in the resolution of the LPG-based sensing head. The concept is tested to detect variations of the external refractive index and a resolution of 2.0×10-4 NIR was achieved without system optimization. Additionally, the effect in the sensor resolution when introducing Erbium and Raman optical amplification is experimentally investigated.

Long-Period Gratings Dynamic Interrogation With Modulated Fiber Bragg Gratings and Optical Amplification

In this paper, we propose a simple and cost-effective bandwidth scalable passive optical network (PON) based on orthogonal frequency division multiplexing (BSOFDM-PON). We report performance analysis in terms of the signal-to-noise ratio (SNR), bit-error-rate (BER) and error vector magnitude (EVM) of a PON system accommodating 32 optical network units (ONUs). Our simulations have successfully demonstrated that throughput of 35.5 and 53.2 Gbps can be achieved using 16 and 64 QAM, respectively, within a total distance ranging from 20 to 30 km. It gives throughputs of 1.10 and 1.66 Gbps per ONU.

Dynamic interrogation of long period gratings with modulated fibre Bragg gratings

In this paper we demonstrate the development of an adjustable and compact polarization mode dispersion (PMD) emulator device, based on piezoelectric actuators that squeezes a defined pieces of an Hi-Bi fiber. Using this device, the first and second order PMD (SOPMD) can be reproduced in a controlled and compact way, allowing its use as a reliable metrological reference for PMD compensators and for the study of several polarizations phenomena that can represent impairments to the high data transmission networks. This emulator was used to perform an analysis of the correlation between the PMD and SOPMD under different climate chamber temperature.

A passive optical network based on centralized wavelength and bandwidth scalable OFDM signals

We describe a simple and inexpensive inline optical power monitor (OPMo) for polymer optical fibre (POF) links that are transmitting visible light carriers. The OPMo is non-invasive in the sense that it does not tap any guided light from the fibre core; rather, it collects and detects the spontaneous side-scattered light. Indeed, the OPMo indicates whether a POF transmission link has dark or live status and measures the average optical power level of the propagating signals without disconnecting the fibre link. This paper demonstrates the proof-of-principle of the device for one wavelength at a time, selected from a set of previously calibrated wavelength channels which have been found in the 45 dB dynamic range, with 50 dBm sensitivity or insensitivity by the use or non-use of a mode scrambler. Our findings are very promising milestones for further OPMo development towards the marketplace.

PMD Emulator based on PZTs attached to pieces of an Hi-Bi fiber

This paper discloses an Analogiser able to carry out digital to analogue conversion of the optically digitised Radio-over-Fibre signals. The Analogiser comprises many interconnected optical circuits based on the Sagnac interferometric rings with an inserted semiconductor optical amplifier. Numerical simulation results are shown for 2.5 GHz sampling rate and 4-bit resolution. The designed circuits are compact, thus enabling optical integration and require optical peak power control in the ~mW range.