Picosecond optical pulses are widely used in optical communication systems, such as the optical time division multiplexing (OTDM) and photonic analog-to-digital converter (ADC). We have proposed and demonstrated a simple method to generate picosecond optical pulse using the mach-zehnder modulator (MZM), phase modulator (PM) and single model fiber (SMF). The phase modulator is used to generate a frequency chirp which varies periodically with time. The MZM is used to suppress the pedestal of the pulse and improve the performance of the pulse. The SMF is used to compensate the frequency chirp. We have carried out theoretical analysis and numerical simulation for the generation process of the picosecond optical pulse. The influence of phase shift between the modulation signals loaded on the MZM and PM is analyzed by numerical simulation and the conditions for the generation of picosecond optical pulse are given. The formula for calculating the optimum length of SMF which is used to compensate the linear chirp is given. The optical pulses with a repetition frequency of 10 GHz and a pulse width of 8.5 ps were obtained. The time-bandwidth product was as small as 1.09 and the timing jitter is as low as 83 fs.
The paper reports a novel optical fiber fluid flow sensor which is based on the measurement of magnetic-field-induced displacement. This sensor can be used to achieve volumetric flow and mass flow as well. The mechanical part of the sensor is similar as that of conventional turbine flowmeter, except that the single turbine is replaced by a dual-turbine structure. The two turbines are connected with a spring, and their relative position is specially designed that, the rotation phase delay between the two turbines is proportional to the mass flow through the conduit. Two magnets are embedded in the two turbines respectively, and two magnetic field probes are used to measure the rotation phase of turbine by detecting the position of each magnet. The signals from the probes are transformed into light pulses by optical fiber shutter sensors and then transmitted to the central controlling room. A post processing unit receives the light signals, and then calculates out volumetric flow and mass flow value. Compared with other kinds of mass flowmeter, this sensor is rather cheap and inherently safe. Experimental results show that the error of less than I % could he achieved with this sensor.