Distributed Brillouin sensor system based on offset locking of two distributed feedback lasers

An offset locking technique, which uses an external optical delay line to tune the distributed feedback (DFB) laser frequency and a proportional-integral-derivative (PID) controller to lock the tuned frequency, is proposed for the first time, to the best of our knowledge, in the distributed Brillouin sensor system. This method provides large tuning range (greater than 1 GHz), high tuning speed (less than 100 mus per frequency step), and frequency tuning is independent of the laser frequency and power. The two DFB lasers are phase locked at the Brillouin frequency using a hardware PID controller. Using this offset locking with optical delay line, we demonstrated a high signal-to-noise ratio of 32 dB, which allows 1 m spatial resolution and better than 0.6 MHz frequency measurement accuracy (equivalent to 0.5 degrees C temperature resolution or 8 microepsilon strain resolution) over kilometers sensing length. The bias of the electro-optic modulator is controlled by a lock-in amplifier to provide high temperature or strain measurement accuracy.     

Characteristics of an electrohydrodynamic pump

The head and flow rate characteristics—the dependences of the differential head and the fluid flow rate through an electrohydrodynamic pump (EHDP) on the electric field strength and the properties of the working fluid—have been derived. The head characteristics have been determined in hydrostatic and hydrodynamic modes; a linear dependence of the efficiency of the EHDP on the voltage has been found. The theoretical results are in agreement with the experimental data. Formulas for the calculation of the EHDP have been derived. It has been revealed that silicone fluid exhibits the best performance and can be used in EHD heat exchangers.     

Picosecond-pulse wavelength conversion based on cascaded second-harmonic generation-difference frequency generation in a periodically poled lithium niobate waveguide

The wavelength conversion of picosecond optical pulses based on the cascaded second-harmonic generation-difference-frequency generation process in a MgO-doped periodically poled lithium niobate waveguide is studied both experimentally and theoretically. In the experiments, the picosecond pulses are generated from a 40 GHz mode-locked fiber laser and two tunable filters, with which the lasing wavelength can be tuned from 1530 to 1570 nm, and the pulse width can be tuned from 2 to 7 ps. New-frequency pulses, i.e., converted pulses, are generated when the picosecond pulse train and a cw wave interact in the waveguide. The conversion characteristics are systematically investigated when the pulsed and cw waves are alternatively taken as the pump at the quasi-phase-matching wavelength of the device. In particular, the conversion dependences on input pulse width, average power, and pump wavelength are examined quantitatively. Based on the temporal and spectral characteristics of wavelength conversion, a comprehensive analysis on conversion efficiency is presented. The simulation results are in good agreement with the measured data.