A high-performance analog electronic circuit for processing the signal from an absolute distance meter based on a frequency-modulated continuous-wave (FMCW) interferometer is presented. The front-end electronics includes a derivative block followed by a the time-variant baseline restoration of the photodetector current. A high signal-to-noise ratio is ensured by avoiding the use of a resistive transimpedance preamplifier and subsequent voltage processing. The paper details the electrical scheme of the preprocessing chain as well as the experimental results from an actual prototype of a distance meter.
We experimentally prove that glass fibers are efficiently optically poled when inserted in the extended cavity of a microchip laser. Methodical second harmonic measurements confirm the good quality of the poling.
Supercontinuum generation in a multicore fiber in which several uncoupled cores were doped with dissimilar concentrations of germanium was studied experimentally. Germanium doping provided control over the separation between the zero-dispersion wavelength and the 1064-nm wavelength of a Q-switched Nd:YAG pump laser. Supercontinua generated independently in each core of the same piece of fiber displayed clear and repeatable differences due to the influence of germanium doping on refractive index and four-wave mixing. The spectral evolution of the subnanosecond pump pulses injected into the different cores was accurately reproduced by numerical simulations.
A system suitable for the measurement of linear sinusoidal vibration amplitudes is described. The signal beam of a Michelson interferometer is focused on the vibrating target while a suitable phase noise is applied to the reference arm of the interferometer. Signal processing is based on the null adjustment of the Bessel coefficients J/sub 1/ and J/sub 2/ derived from the signal provided by a single photodiode placed in the center fringe of the interference pattern. The system has been shown to be self-calibrating and intrinsically immune to mechanical perturbations induced in the interferometer. The technique proposed has been experimentally demonstrated by measuring the vibration amplitude of a PZT device in the amplitude range from 0.4 to 1.7 mu m and in the frequency range from 8 to 22 kHz.< >
Supercontinuum generation in a multicore Ge-doped microstructured optical fiber is experimentally studied. The output spectral extension and the presence of four-wave mixing peaks are strongly dependent on the level of doping.
In 3-D adaptive profilometry based on structured light projection, the choice of the low-pass filter to he used in the deformed pattern demodulation is crucial. In this paper, we have studied the performance of a typical finite impulse response (FIR) and of an infinite impulse response (IIR) Butterworth low-pass filter. Adaptiveness of the filters to both coarse and small variations of the grating frequency has been investigated. The ability of the filters to adapt to coarse changes of the grating frequency has been quantified in terms of their speed of synthesis, while the ability of the filters to tolerate small variations of the grating frequency has been quantified by measuring the residual phase errors. The analysis shows that the IIR Butterworth filter performs better than the FIR filter both in the coarse and in the fine grating frequency variation cases.< >
An optical continuum was generated in microstructured optical fibre using an incoherent pump generated by stimulated Raman scattering in a step index fibre with normal dispersion. Accelerated spectral broadening to longer wavelengths was observed.
