Amplitude-division two-beam interferometry performed with temporally incoherent light (such as white light, i.e. the path difference is larger than the coherence length) is used to multiplex signals, and applied to the multiplexing of sensors, and for distance measurements. The detection is based on the use of a receiving interferometer tuned to approximately the same path difference. An alternative way to detect path differences in Low Coherent Intensity, by analyzing the output intensity fluctuations with a radio frequency spectrum analyzer (RFSA) is proposed. This is suitable for very long path differences. Experiments have been performed with different lengths from meter to some kilometer of single-mode optical fiber, in a Mach-Zehnder and Michelson configuration.
The fiber optic sensor system, that consists of 6 - 8 fiber sensor heads and can measure the salt-content in the water of near-coastal region of 1 Km2, is presented. The fiber optic sensor head was made by polishing the end of a double fiber in the form of a prism, with reflecting coating on one side, and had a dimension of 250 - 300 microns. The fiber optic sensor with lead-in power of 3 - 15 mW from visible laser diodes was tested for measuring salt content in the seawater from 0 to 4 wt.%. The results are repeatable and the accuracy less than 10-3 is suitable for controlling the salinity degree in the range of 0.5 - 1.7% in the near coastal shrimp farms, especially for the childhood shrimp fields.
A novel method to suppress noise in a high harmonically mode-locked erbium fiber laser with external optical modulator using DFB-laser diodes is presented. The DFB-diode laser played both roles as external-cavity modulator and as stabilizer. The driving frequency is of 2.5 GHz and the wavelength difference between DFB-diode laser emission and fiber laser dominant was adjusted in range of +/- 2 nm. The fiber laser modulation frequencies can be tunable at 2.5; 5 and 10 GHz by the adjusting an external laser diode modulation rounding 2.5 GHz +/- 66 KHz. A fiber laser so stabilized has enabled at 2.5 or 5 GHz remaining error free for more 4 hours with nearly transform-limited pulse width of 25-35 ps.
Radiative transitions in porous silicon (PS) have been studied using a new variant of the time-resolved photoluminescence (TRPL) spectroscopic measurement, in which beside the pulsed light source the sample was irradiated additionally by a continuous light source. With this modification a certain photoluminescence (PL) region in the TRPL spectrum of PS may be quelched, the position and width of which depends strictly on the wavelength range and intensity and the continuous light source. Using different continuous light sources, the quenching of different PL regions has been observed experimentally. The results obtained are discussed with the model of recombination in the core and on the surface of nanocrystallites. It seems that the selective quenching of PL in the TRPL spectrum is helpful to reveal the origin of the light emission for PS.
The sol-gel process has been employed to prepare highly doped Er3+ silica glasses, up to 5-wt% for homogeneous doping distribution. The optical characteristics of the silica glasses including the UV/VIS absorption and fluorescence emission spectra under excitation of 488 nm and 520 nm lights were measured. Micro-Raman spectra of these silica glasses heated at different temperatures from 200 degree(s)C to 1100 degree(s)C under 632.8 nm laser beam excitation of the He-Ne laser also recorded. The green up conversion emission from Er3+ ion doped into the silica glasses heated to 1000 degree(s)C under red light (632.8 nm) excitation has been observed. Two green and weak emission bands, centered at 525 and 550 nm, for the 2H11/2 yields 4I15/2 and 4S3/2 yields 4I15/2 transitions, respectively, have been observed. The blue upconversion emission er3+ at 300 K centered at 460 nm was observed rather strength depends on the He-Ne laser pump powers and the Er3+ concentration. The pump wavelength is far from any electronic absorption from the ground state of the Er3+ ion, but corresponds to the excited state absorption. This upconversion process was interpreted by the excited state absorption and an upconversion mechanisms is proposed.
The fiber-optic refractometer made by the prism-taped fibers is presented. The prism tips of fibers had been making by polishing method and the endface of the load-in fiber was coating by the reflective thin film. The size of the fiber sensor head is of 250-260 microns. The fiber-optic sensor using visible laser diodes of 650-670 nm was performance for the directly distinguish of sugar content in the sugarcanes with accuracy range of 5.10-4. These refractometers are already to use for the sugarcane plantations.
The laser acupuncture equipment using laser diodes of 850, 1300 nm and optical fibers as light needles is presented. The double-frequency modulation of laser beam gives the high efficiency treatment of the low-power laser therapy by the oriental acupuncture method. The laser spot from optical fiber of 50 microns is suitable for the irradiation into special points on body or auricular by the acupuncture treatment schema. The laser intensity in pulse regime of 5 - 40 W/cm2 and irradiation time of 5 - 15 minutes are optimum for treatment of neurosis symptoms and pain-relieving.
The fiber-optic refractometer using visible laser diodes with wavelengths of 650 divided by 670 nm for the liquid refractive-index measurement is presented. The refractive- index measures by fiber-optic sensors of the connected configuration for different liquids with refractive indices from 1.33 to 1.5 have given the accuracy of 5.10-3. The fiber-optic refractometer was performanced for the distinguish of the salt or sugar content in the mixtures with range of 10-3 and 5.10-4, respectively. These refractometers are already to use for the sugar control systems of beverage industry and salt-water environment.
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