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Channel Modelling
Published in Z. Ghassemlooy, W. Popoola, S. Rajbhandari, Optical Wireless Communications, 2019
Z. Ghassemlooy, W. Popoola, S. Rajbhandari
A typical FSO link setup for data communication for different modulation schemes is shown in the Figure 3.35(a). An arbitrary waveform generator (AWG) is used to produce different modulation formats and levels. The data signal is used to directly modulate a laser diode at a range of wavelength (600–1550 nm). To ensure the linearity of the system, the laser is properly biased, and the peak-to-peak voltage of the input signal cannot exceed the specified dynamic range of the laser diode. The optical output from the laser experiences different atmospheric effects, including attenuation (due to absorption and scattering) and intensity fluctuation, before it is collected at the receiver. The receiver front end consists of an optical telescope (or lens) and a photodetector. The electrical signal at the output of the photodetector is amplified using a trans-impedance amplifier and ideally followed by circuitry for clock and timing recovery and regeneration of the transmitted data. The motivation for developing the chamber is to simulate the atmospheric channel effects on an optical signal, traversing it in a controlled environment. Hence, in the experimental setup, data recovery circuitry is not used; rather the raw data at the receiver are analysed.
External Modulators for Coherent Transmission and Reception
Published in Le Nguyen Binh, Digital Processing, 2017
A system arrangement of the OFDM for optical transmission in laboratory demonstration is shown in Ref. [32]. Each individual channel at the input would carry the same data rate sequence. These sequences can be generated from an arbitrary waveform generator. The multiplexed channels are then combined and converted to time domain using the IFFT module and then converted to the analog version via the two digital-to-analog converters (DACs). These orthogonal data sequences are then used to modulate I- and Q-optical waveguide sections of the electro-optica modulator to generate the orthogonal channels in the optical domain. Similar decoding of I and Q channels are performed in the electronic domain after the optical transmission and optical–electronic conversion via the photodetector and electronic amplifier.
Brillouin-Based Distributed Temperature and Strain Sensors
Published in Arthur H. Hartog, An Introduction to Distributed Optical Fibre Sensors, 2017
Experimentally, these comb signals are created from a common laser that is divided into two paths, launched into opposite ends of the sensing fibre. In each path, an intensity EOM is driven by an arbitrary waveform generator. In the probe path, the EOM generates a set of comb lines set around the Brillouin shift with spacing Δfp. In the second path, the EOM generates a pulsed comb at spacing Δfs. It was also found preferable to stagger each line so that in effect, a series of pulses are launched at slightly different times, each providing one line in the comb. This avoids non-linear effects (that could result from interactions between lines in the frequency comb) and it reduces the demands on the optical amplifiers used to boost the power levels prior to launching into the fibre. This is rather similar to the multi-frequency C-OTDR systems discussed in Chapter 3. On collecting the data, of course, the different frequencies must be re-timed to be aligned to the same physical origin in the fibre.
Materials strength and acoustic nonlinearity: case study of CFRP
Published in Research in Nondestructive Evaluation, 2022
Julian Ehrler, Alexander Solodov, Marc Kreutzbruck
The experiment used a piezo-electric actuator manufactured by isi-sys GmbH (Germany). It is driven by a continuous wave voltage generated by the HP 33120A arbitrary waveform generator. The generator is combined with a HVA-B100 amplifier to result in 10–40 V input amplitude for the piezo-actuator. The actuator is vacuum attached to one of the sides of the specimen and nonlinear vibrations produced locally in the area of excitation are measured on the opposite side of the specimen (4.7 mm thick 0°/90° CFRP plate). The exciting tip of the actuator (circular disk of mm) was covered with Al-foil to reduce the contact clapping. The overall level of the instrumental second harmonic was estimated as which permits the measurements in the materials with reasonably high internal nonlinearity. To measure and analyze the frequency content of the vibrations in the excitation area, a scanning laser vibrometer was used. After Fast Fourier Transformation (FFT)the vibration velocities are determined for various harmonics.
Improving the SNR of the phase-OTDR by controlling the carrier in the SOA
Published in Journal of Modern Optics, 2020
Yun Chen, Barerem-Melgueba Mao, Bin Zhou, Changjian Guo, Ziqi Lin
A homodyne coherent phase-OTDR (set-up shown in Figure 4) was used to demonstrate the SNR improvement. A narrow band coherent laser source (RIO Inc., 1550.12 nm, linewidth: 5 kHz) was used in the experiment. The CW output of the laser was divided into two parts through a 9:1 coupler. The laser was modulated into square pulses by the arbitrary waveform generator (AWG)-driven SOA. The pulse duration was 100 ns corresponding to a 10 m spatial resolution and the pulse period was 500 μs. The scattered Rayleigh light was amplified by the local oscillator and detected by the coherent receiver formed by a 90° optical hybrid and four balanced PDs. The two polarization I/Q signals were received by a data acquisition system and demodulated in a personal computer (PC). The 100 G DWDM filters were used to suppress the ASE noise of the EDFAs. A section of 15-m fibre near the end of a 48 km fibre under test was wrapped on a piezoelectric transducer (PZT) to generate sinusoidal vibration for later testing.
Evaluation of Bonding Quality in the Carbon Fiber--Reinforced Polymer (CFRP) Composite Laminates by Measurements of Local Vibration Nonlinearity
Published in Research in Nondestructive Evaluation, 2019
Igor Solodov, Damien Ségur, Marc Kreutzbruck
The technique used in this study is based on the local generation of high amplitude vibrations and detecting the higher harmonics in the excitation area. An option for higher amplitude excitation was found by using piezo-actuators manufactured by Isi-sys GmbH (Germany) with a frequency response extended from low kHz into high kHz range (above 100 kHz). The actuators are vacuum attached to the specimens and can be used for on-site measurements of large aviation components. They are driven by a continuous wave voltage generated by the HP 33120A arbitrary waveform generator. The generator is combined with the HVA-B100 amplifier to result in 10–40 V input amplitude for the piezo-actuator. The actuator is attached (pressed against without any liquid couplant) to one of the sides of the specimen and nonlinear vibrations produced locally in the area of excitation are measured on the opposite side of the specimen (Figure 2).