In this paper the mechanism of reflective fiber-optic vibration sensor has been researched by mathematical modeling and Simulation. Research shows that fiber structure, the numerical aperture and core diameter of fiber, can affect the performance of RIM-FOS. With the increase of the numerical aperture, the peak point and range of detection move forward, received power is not changed, sensitivity is improved; with the increase of core diameter of transmitting fiber, power peak and sensitivity decreases; along with the core diameter of receiving fiber increases, the peak power increases, the slope before sensitivity increased. According to the research results, the best SNR is obtained in an experimental system that the 62.5μm of transmitting fiber and 100μm core diameter of receiving fiber is adopted.
In this paper the mechanism of BBO crystal component for frequency resolved optical gating technique has been researched by mathematical modeling and Simulation. Research shows that thickness of the crystal and the phase matching angle are important parameters affecting the measurement performance. Crystal thickness determines the pulse width limit which this crystal can distinguish; when the phase condition is matched between the fundamental frequency and second-harmonic of light, the SHG efficiency of incident light is highest. According to the calculations, An BBO crystals with 3.5mm thickness, 20.56 degrees phase matching angle is adopted to realize the crystal component for tens to hundreds of femtoseconds pulse width measurement.
With the aim to get harmonic distortion characteristics and frequency components of modulated output signals of a Mach-Zehnder (MZ) intensity modulator, this paper analyzes the optical intensity modulation transfer function by Tailor expandsion method according with the working principle of modulator. From the viewpoint of spectrum, the output signal is mainly comprised of the fundamental harmonic, the second intermodulation harmonic and the third intermodulation harmonic of the input signal and their magnitudes are connected with the bias voltage and Eigen-phase of MZ modulator. The second harmonic distortion and the fundamental harmonic of the modulated output signal are closely related with the drift of the best bias point. When the modulator works at the best DC bias voltage point, the modulated output signals have the minimum second harmonic distortion. If the best bias point drifts, the second harmonic distortion increases and the fundamental harmonic decreases, which changes in proportion to the sine or cosine of the drift voltage. A 1GHz sine signal with 1V amplitude imposed on the modulator, the simulation results by MATLAB presents that the waveform starts distorting along with the drifting of the best bias voltage, which the fundamental wave component starts decreasing and the second harmonic component starts increasing. While at last the fundamental wave component is zero, the frequency of output modulated signal doubles as much the frequency of input signal.
For the echo signals of Satellite laser altimeter, the leading source of noise is the background radiation noise, which mainly comprises the reflection of sunlight by the targets and the atmospheric scattering of sunlight. This paper deals with a theoretical study on the reflection and atmospheric scattering of sunlight. And on the basis, we calculate and simulate the irradiance of extraterrestrial solar spectrum and the respective effects of path zenith angel, solar zenith angle and ground diffuse reflectance on the solar atmospheric radiance, concluding the corresponding relationship between background radiation noise and these parameters, which provides a theoretical basis for the improvement of Satellite laser altimeter.
According to the gridded discrete processing method, the laser echo characteristics in the case of ladder terrain ground are analyzed theoretically, and the ladder-like terrain echo mathematical model are established. We find from the work that these two peaks of ladder terrain echo curve is the reflecting of ladder and ground respectively, the time interval between wave peaks is determined by the mutations height of terrain. The mutations height is higher, pulse shaping is more obvious, it is also shown that ground reflectivity in the laser spot affects the size of the echo peak mainly, and does not affect the peak location on the curve.