The Working Point Control In The Integrated Optical Electric Field Sensor System

Integrated optical waveguide electric field sensor system, which is used in themeasurement of electric field due to its ultra-small, strong resistance to electromagneticinterference and so on, has been widely studied. The M-Z modulator and the integratedoptical electric field sensor need a stable offset phase when they are working. But in theactual application, the working point of the M-Z modulator or electric field sensor iseasily affected by external factors such as temperature, the stress and so on and occursdrifting last.Because of the existence phenomenon of working point drift in the LiNbO3electro-optic modulator and the integrated optical electric field sensor system, theworking point automatic control system is designed in this paper. In this control systemthe bias voltage is controlled in time to make the modulator working in the linear region.Then, the control system by tuning the laser’ wavelength is designed to make theelectric field sensor to work in the linear region. The paper’s main research contents areas follows:1. The mechanism of the working point drift of the integrated optical electric fieldsensor has been analyzed in the paper. The working point drift, which impacts theelectric field sensor’s fundamental wave and the second harmonics wave, has beenanalyzed in the paper.2. The working point control system by adopting perturbation signal is designedfor the electro-optical modulator. First the perturbation signal generating circuit、 thecircuits of extracting the amplitude values of the fundamental component and thesecond harmonic component of the detector output、the circuit of power supply and thesingle-chip peripheral circuit are designed and a schematic and PCB figure are drawn.Then the single-chip calculates the actual phase of the modulator and the feedback biasvoltage. Finally, the output optical power of the modulator has been tested. Thefundamental amplitude and the second harmonic amplitude are tested. The bias voltagesare tested when the different frequency modulated signals are input to the modulator. The hardware circuit is tested and so on. Then by analyzing the test values, we knowthat the control system of the working point of the modulator can make the modulatorworking in the linear region well and realize that the maximum drift of the outputoptical power of the modulator is only0.56%of the initial output optical power in15minute and4%of the initial output optical power in5hours.3. When the electric field sensor is used to test the space electric field, in order toavoid the interference of the perturbation signal to the test system, a new method oftuning the light source to control the working point of the electric field sensor is used.First, the circuit of extracting the direct current component in the output signals of thedetector、the circuit of the power supply and the peripheral circuit of the microcontrollerare designed and the schematic and PCB figure are drawn. Then, the software controlsection calculates the best wavelength which can make the electric field sensor work inthe linear region, and set for the best wavelength the laser’s working wavelength torealize controlling the sensor’s working point. Finally, the output optical power of thesensor is tested. When the high voltage pulse signal is input to the sensor, the outputwaveform of the sensor is tested with and without the working point control system. Byanalyzing the test values, we know that the control system has realized to make theelectric field sensor working in the linear region and make the maximum drift of theoutput optical power is6.8%of the initial output optical power.