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A method for the phase noise characterization of single-loop optoelectronic oscillators (OEO) is presented. Based on the injection-pulling dynamics of OEO under radio frequency (RF) signal injection, this method is used to compute the phase noise spectrum of a free-running single-loop OEO. From the injection locking equation, the expression for the output RF spectrum of single-loop OEO under the influence of a single sinusoidal RF signal injection is derived and this analysis is then utilized to study the RF output power spectrum of the single-loop OEO when injected by two weak and equally strong RF sinusoidal signals with mirror frequencies with respect to the free-running frequency of the OEO. An expression for the far-out phase noise spectrum of a free-running single-loop OEO is presented to capture the far-out phase noise characteristics of the OEO. Also, we derive the expression for the close-in phase noise spectrum of the free-running single-loop OEO by considering the multiplicative noise as the overall loop-gain perturbation in the OEO loop. The experimental results are also given in partial support to the conclusions of the analysis.

Starting with the single-loop optoelectronic oscillator (OEO), it is shown an analysis about the effects of a radio frequency (RF) injected signal on the phase-locked loop OEO. After obtaining the ...

A study on the transient behavior of a single-loop optoelectronic oscillator (OEO) under a single sinusoidal radio frequency (RF) signal injection is presented. Considering only the phase perturbation imposed by the external RF signal, the phase-dynamic equation is solved to analyze the frequency settling behavior of the loop. A closed form expression for the required time of an OEO under RF injection-locking, reaching the steady state condition, is derived in terms of the initial phase difference, beat frequency and injection signal strength. The phase modulated signal, which is responsible for the perturbation of the free running oscillation, is expanded in a Fourier series and the expression for the output RF spectrum of the injection pulled OEO is derived. The injection-pulling dynamics approach is used to describe the phase noise of the OEO and also, the influence of the phase settling time constant on the phase noise of the injection-locked OEO is studied. The experimental results corroborating the theoretical findings are given.

This article presents a detailed study of injection-locking characteristics of a single-loop optoelectronic oscillator (OEO) under strong radio frequency (RF) signal injection. We provide formulas for the steady-state phase-angle after locking, and the locking time for a higher level of a locking signal, considering only the phase perturbation. We also provide a compact expression for the main spectrum components of the pulled OEO in terms of the beat frequency, which is useful to evaluate and quantify the injection-pulling effects in the OEO. The experimental results provide partial support to the conclusion of the analysis. The analytical and experimental results are presented in design curves, which can be used to determine the required properties of an injection-locked OEO for a specific performance of the oscillator.

An optoelectronic oscillator (OEO) configuration with a unique optical fiber length, followed by a dual-loop in the radiofrequency (RF) domain is proposed and studied. Such a configuration with a unique optical delay followed by an RF time delay enables a reduction in the intensity of unwanted frequencies and a remotely fine frequency tuning. The RF output power spectrum was theoretically studied through a formalism that reveals the role of the relative size of optical and RF time delays. The theoretical analyzes were confirmed by the experimental results. An unwanted frequency intensity is 50 dB below RF OEO output frequency after a reduction of 13 dB. A maximum tuning band equal to 94 MHz with a resolution of 250 kHz was achieved without using an RF external source or additional system. Phase noise of − 117 dBc/Hz is measured for an offset frequency of 100 kHz with an optical fiber length equal to 800 m. The phase noise value obtained is compatible with aeronautical and space systems in the S band. All the achieved results are compared with the single loop OEO configuration.

Injection-locking characteristics of a single-loop optoelectronic oscillator (OEO) under an independent sinusoidal RF signal injection are investigated. The mathematical model of the unlocked-driven system is developed to represent phase perturbation of the generated output RF signal caused by the RF injection signal. The closed-form expressions of the output RF spectra distorted due to RF signal injection are derived to formulate the behavior of the injection-pulled OEO. Using the phase dynamics equation, a phase noise model is developed to quantify the influence of RF injection signal on the phase noise performance of the oscillator. It is shown that our analytical model is capable of predicting the injection locking and estimating the injection pulling behavior of the single-loop OEO under RF signal injection. The theoretical results are validated by the experimental results.

This paper describes an analytical model of an injection-synchronized single-loop optoelectronic oscillator (OEO) under the influence of radio frequency (RF) interfering signal to study the performance of the system considering only the phase perturbation imposed by the RF injection signal. We derive the phase dynamic equation of the system, which is used to derive compact expression for the lock-range and investigates the influence of interfering signal on the lock-range considering both weak and strong interfering signal strength. We provide formula for the lock-range of the OEO under RF injection-locking in the presence of interfering signal, to reach the steady-state. It is shown that the injection-synchronized OEO under the influence of strong interfering signal exhibits frequency jump phenomena. The experimental results corroborating the theoretical findings are given.

This paper brings the results of a study of the frequency pulling in a single loop optoelectronic oscillator (OEO) when injected by weak and strong radio frequency (RF) signal. An experiment was performed for three different injection signal powers to study the frequency pulling and the average frequency of the OEO. The analysis is made on the basis of OEO output spectra due to RF signal injection, beat frequency, lock-range and average frequency by extracting the values from the experimental data. It is also illustrated that the spectral components present in the injection signal side are responsible for frequency pulling. The influence of the RF injection signal on the phase noise performance of the free running OEO and injection locked OEO is also studied. The significant improvement in dipping the spurs of the OEO output spectra by injection locking technique is highlighted. Also the effect of Gaussian minimum shift keying signal injection on the injection locked OEO output spectrum has been investigated. The experimental evidence of the pulled OEO output characteristics from fast beat state to locked state is also provided.

This paper analyzes the injection-locking and injection-pulling behavior of two mutually coupled single-loop free-running OEOs with nearby frequencies. We derive the phase dynamics equations of two mutually-coupled OEOs considering weak RF signal injection and the phase stability of the mutually injection-locked system is studied. Also, we present compact closed form expressions for the oscillation frequencies of two mutually injection-pulled OEOs in terms of the injection-ratios and the phase shifts of the mutually injected RF signals. The beat frequency of the mutually injection-pulled system is calculated in terms of the injection ratios. The influence of mutual injection-pulling on the RF output power spectrums of two OEOs are studied. It is shown that the RF output power spectrums of two mutually injection-pulled OEOs are highly asymmetric and strongly depends on the injection ratios. The experimental results corroborating the theoretical findings are given.

This paper presents an analytical model to compute the phase noise spectrum of a self-injection-locked single-loop optoelectronic oscillator (OEO) from the phase dynamics equation of the oscillator. The stability of the self-injection-locked oscillator is also studied. The influence of the feedback coupling network on the phase noise performance of the self-injection-locked OEO is also investigated. The experimental results corroborating the theoretical findings are given. It is shown that the phase noise of the self-injection-locked OEO at the noise offset frequency near the carrier frequency can be reduced by increasing the strength of the self injection signal under stable condition of the loop.

A detailed study of injection-pulling behavior of an injection-locked and phase-locked loop (IL-PLL) single-loop optoelectronic oscillator (OEO) under radio frequency (RF) signal injection is presented. From the locking equation, the expression for the output spectrum of the IL-PLL OEO under RF injection is derived in time domain, to evaluate the spurious performance of the system. The frequency response of the spurious outputs due to RF injection signal is investigated in terms of the injection transfer function. Also, a dual-loop model of the IL-PLL OEO is developed to study the phase noise performance of the system with co-frequency RF injection signal. The experimental results are given in partial support of the conclusions of the analysis.

The different stages carried out in the sizing of a photovoltaic system require a certain degree of technical knowledge, usually carried out by a specialist, which contributes to the high cost of installation of photovoltaic systems. Some sizing software is commercially available, however, usually its value is high, or specialized knowledge in photovoltaic systems is required for its operation, targeting specialized companies in the industry. The present work focuses on the development of a open source tool for the sizing photovoltaic systems, that is easy to use for the user, with the objective of facilitating the sizing and making photovoltaic energy more accessible, especially in developing countries.

This article presents a photonic circuit that achieves direct carrier QPSK modulation of an RF signal from an opto-electronic oscillator (OEO) suitable for satellite data transmitter. The circuit was implemented with three Mach-Zehnder optical modulators. One modulator was used to construct an OEO to generate a carrier with a frequency equal to 2.019 GHz. The others two modulators were used to compose the microwave photonic I/Q modulator. The setup initially achieved a data rate of 50 Mbps in a QPSK scheme with an EVM of 7.5%. Using a root-raised-cosine filter, it was possible to reduce the EVM to 5%. The diagrams of the optoelectronic circuit and the modulation measurements are displayed. After the EVM analysis, the modulated signal was demodulated through an actual satellite receiver. Using the demodulator, it was possible to measure the BER and consequently the degradation analysis. The degradation for a bit rate of 100 Mbps was 0.07 dB using the OEO as RF generator. In this case, the values of Eb/N0 and BER were 11.37 dB and 10-7, respectively.

We present a detailed study of injection-locking (IL) and injection-pulling behavior of an IL single-loop optoelectronic oscillator (OEO) when injected by radio frequency (RF) signal. From the locking equation, the expression for the output spectrum of the IL-OEO under RF injection is derived in the time domain, to evaluate the spurious performance of the system. The frequency response of the spurious outputs due to RF injection signal is investigated in terms of the injection transfer function. Also, a dual-loop model of the IL-OEO is developed to study the phase noise performance of the system with a cofrequency RF injection signal. Also, the effect of Gaussian minimum shift keying signal interference on the IL-OEO output spectrum is investigated. An analytical expression for the side-mode attenuation is presented to describe the influence of IL on the side-modes of free-running OEO. The experimental results corroborating the theoretical findings are given.

This paper addresses the evolution of the photonic QPSK modulator setup previously reported. This second generation setup used two laser sources and the bias tee was replaced by a power combiner. As a result, the second setup enables one to reach higher data rates with better stability and modulated signal quality. The improved setup initially achieved a data rate of 50 Mbps in a QPSK scheme with an EVM of 8%. Using a root-raised-cosine filter, it was possible to reduce the EVM to 4.5%. After the EVM analysis, the modulated signal was demodulated through an actual satellite receiver. Using the demodulator, it was possible to measure the BER and verify if the incoming signal was modulated in the correct order. The QPSK modulator achieved finally a bit rate of 300 Mbps. The degradation analysis of the modulator with QPSK modulation and bit rate of 100 Mbps was 0.06 dB. In this case the values of E b /N 0 and BER were 11.36 dB and 10∼7. The obtained results are a consequence of the photonic technology bandwidth and the improvement made in the input and bias circuit.

This study describes the generation of microwave signals by an optoelectronic oscillator, OEO. The delay of the OEO was made in the optical domain as well in the radio frequency (RF) domain. The constructed OEO was proposed for embedded applications, which requires low components volume, e.g., small size. Aimed at greater thermal stability and the application in embedded systems, a shorter acceptable optical fiber length was used as delay element. This enables to obtain an RF signal with the phase noise values according with the technical specifications. The total value of the OEO delay is completed with a delay in the RF domain. The benefits of this setup include the possibility of using inexpensive components and commercially available bandpass filter. Fiber optic section with length of 200 meters, coaxial cable and a filter with 15MHz of bandwidth were used. The output characteristics of the OEO were a microwave signal at 2.022 GHz, an intensity of 10.5dBm and a phase noise equal to −118.7 dBc/Hz for an offset of 100 KHz and −102.2 dBc/Hz for an offset of 10 KHz.

This article presents a photonic circuit that achieves direct carrier BPSK modulation of a RF signal from an opto-electronic oscillator suitable for satellite telemetry and control. The circuit was implemented with two Mach-Zehnder optical modulators. The optical wavelength is 1550 nm. One modulator was used to construct an optoelectronic oscillator to generate a carrier with frequency equal to 2.5 GHz. The second modulator was used to perform the BPSK direct modulation of the carrier signal. A bit rate of 1 Mbps was used and an EVM of 9.6% was obtained. The diagrams of the optoelectronic circuits and the modulation measurements are displayed.

This paper briefly describes the advantage of Unmanned Aerial Vehicles (UAV) over manned aircraft, listing applications for them also pinpoints the importance of long endurance flight that can be increased by photovoltaic cells integration. A summarized historical overview of solar-powered UAV designs is presented, mentioning improvements required in the past for solar-powered UAV components to achieve a feasible project - achievable nowadays. Also explains the main components of a solar-powered UAV architecture and the concept of energy balance that must be analyzed during design and operation of solar-powered UAV. A methodology to estimate the flight endurance increase of an Electric UAV adapted with photovoltaic cells was proposed and applied to an experimental project, yielding accurate results when compared to an experimental case. This methodology aims to contribute on assess the increasing Electric UAV flight endurance by photovoltaic system integration prior to experimental tests.

In this work, we present an analysis of the influence of the geometrical parameters on the sensitivity and linear range of the fiber optic angular displacement sensor, through computational simulations and experiments. The geometrical parameters analyzed were the lens focal length, the gap between fibers, the fibers cladding radii, the emitting fiber critical angle (or, equivalently, the emitting fiber numerical aperture), and the standoff distance (distance between the lens and the reflective surface). Besides, we analyzed the sensor sensitivity regarding any spurious linear displacement. The simulation and experimental results showed that the parameters which play the most important roles are the emitting fiber core radius, the lens focal length, and the light coupling efficiency, while the remaining parameters have little influence on sensor characteristics. This paper was published in Applied Optics and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-53-36-8436. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law., Comment: 10 pages, 12 figures

In this work we developed a setup to measure the speed of sound in gases using a laser ultrasonics system. The mentioned setup is an all optical system composed by a Q-switched Nd:YAG laser to generate the sound waves, and a fiber optical microphone to detect them. The Nd:YAG provided a laser pulse of approximately 420 mJ energy and 9 ns of pulse width, at the wavelength of 1064 nm. The pulsed laser beam, focused by a positive lens, was used to generate an electrical breakdown (in the gas) which, in turn, generates an sound wave that traveled through a determined distance and reached the fiber optical microphone. The resulting signal was acquired in an oscilloscope and the time difference between the optical pulse and the arrival of the sound waves was used to calculate the speed of sound, since the distance was known. The system was initially tested to measure the speed of sound in air, at room pressure and temperature and it presented results in agreement with the theory, showing to be suitable to measure the speed of sound in gases.

When the electro-optic and acousto-optic effects are combined into a single device, the resulting acousto-electrooptic (AEO) modulator shows improved flexibility to overcome some limitations of the individual modulators or their cascade combinations. By using optical interferometry, it is possible to investigate the AEO modulator behavior as a function of this applied voltage. By this way, a lithium niobate AEO modulator is positioned in one of the arms of a Mach-Zehnder interferometer and operates at 62 MHz frequency, which constitutes the intermediate frequency of the heterodyne interferometer. Operating the AEO modulator in the acousto-optic small diffraction efficiency regime, the photodetected signal amplitude and phase are analyzed, and the induced phase shift, transmission curve and linearity response are obtained. The experimental results show good agreement with that expected from the coupled-mode theory. The possibility of linear control of the optical phase shift by the external voltage, from 0...

The two main constrains on the characteristics of the acousto-optic deflector are the acoustic sound attenuation and velocity. These two parameters will determine the resolution and the radio frequency bandwidth.

It is present da general discussion about acousto-optic and electro-optic interferometric system for RF phase control. After point out the most important problems of such systems it is presented the one arm interferometer based on a collinear acousto-optic modulator and an electro-optic modulator. This proposed setup is compared with the two arms interferometers and its characteristics as insertion loss and bandwidth are discussed.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

After analyzing the combination of the acousto- and electro-optic effects, two applications are presented. The first is the use of that combination to reduce the tilt sensibility of the acousto- optic devices. The second is related to an interaction configuration that is appropriated to wideband spectrometers.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper, we report the development of an intensity modulated fiber optic sensor for angular displacement measurement. This sensor was designed to present high sensitivity, linear response, wide bandwidth and, furthermore, to be simple and low cost. The sensor comprises two optical fibers, a positive lens, a reflective surface, an optical source, and a photodetector. A mathematical model was developed to determine and simulate the static characteristic curve of the sensor and to compare different sensor configurations regarding the core radii of the optical fibers. The simulation results showed that the sensor configurations tested are highly sensitive to small angle variation (in the range of microradians) with nonlinearity less than or equal to 1\%. The normalized sensitivity ranges from $(0.25\times V_{\rm max})$ to $(2.40\times V_{\rm max})$ mV/$\mu$rad (where $V_{\rm max}$ is the peak voltage of the static characteristic curve) and the linear range, from 194 to 1840 $\mu$rad. The unnormalized sensitivity for a reflective surface with reflectivity of 100\% was measured as 7.7 mV/$\mu$rad. The simulations were compared with experimental results to validate the mathematical model and to define the most suitable configuration for ultrasonic detection. The sensor was tested on the characterization of a piezoelectric transducer and as part of a laser ultrasonics setup. The velocity of the longitudinal, shear, and surface waves were measured on aluminum samples as 6.43 mm/$\mu$s, 3.17 mm/$\mu$s, 2.96 mm/$\mu$s, respectively, with an error smaller than 1.3\%. The sensor proved to be suitable to detect ultrasonic waves and to perform time-of-flight measurements and nondestructive inspection, being an alternative to the piezoelectric or the interferometric detectors., Comment: 13 pages, 12 figures

After point out the principles of the acousto-optic spectrometer (AOS) some questions about channels number and the AOS measurements uncertainties are discussed. To overcome the limits imposed by the acoustic attenuation and velocity one low cost LiNbO3 acousto-electro-optic interaction configuration with high channels number possibilities is proposed. Taking the turbulence and temperature effects on measurements uncertainties together it was established a criteria to use the spectroemter during for radio astronomy observations with lower uncertainties and costs.

A laser ultrasonics system was setup to measure the directivity (angular dependence pattern) of the amplitude of ultrasonic waves generated in aluminum samples. A pulsed Nd:YAG laser operating at 1064 nm optical wavelength, with typical pulse width (FWHM) of 8 ns, and energy per pulse of 450 mJ, was used to generate the ultrasound waves in the samples. The laser detection system was a Mach-Zehnder interferometer with typical noise-limited resolution of 0.25 nm (rms), frequency range from 50 kHz to 20 MHz, and measurement range from −75 nm/V to +75 nm/V. Two different optical spot sizes of the Nd:YAG laser were used to generate waves in the ablation regime: one was focused and the other was unfocused. Using the obtained data, the directivity graphics were drawn and compared with the theoretical curves, showing a good agreement. The experiments showed the directivity as a function of the optical spot size. For a point ultrasonic source (or focused optical spot), the directivity shows that the longitudinal waves present considerable amplitude in all directions. For a larger ultrasonic source (or an unfocused optical spot) the directivity shows that the longitudinal waves are generated with the higher amplitudes inside angles around ±10°.

This work reports a theory for the single lens fiber optical microphone. Computational simulation and experimental results were compared presenting good agreement. It is shown that the operating principle of this microphone is based in membrane tilt angle variation rather than membrane longitudinal displacement.

This work is a report bringing the experimental setup and the initial developments to establish a laser ultrasonics system at the Instituto Tecnologico de Aeronautica in Brazil. Present-day development aim to substitute piezoelectric transducer by a high power pulsed laser to generate ultrasound.