OPTICAL INTERFEROMETERS FOR SENSING ELECTROMAGNETIC FIELDS

THE OBJECT OF THE PROPOSED EFFORT IS TO ESTABLISH THE FEASIBILITY OF PRODUCING AN ELECTRODE-LESS MACH-ZEHNDER INTERFEROMETER FOR MEASURING ELECTROMAGNETIC FIELDS. AN ELECTRODE-LESS DEVICE IS EXPECTED TO BE MORE ACCURATE THAN A CONVENTIONAL DEVICE DUE TO THE ABSENCE OF ANY METAL ELECTRODES THAT TEND TO DISTURB THE FIELDS. THE KEY TO THE PROPOSED EFFORT IS THE TECHNIQUE OF SELECTIVELY REVERSE POLING A CHANNEL WAVEGUIDE SECTION IN THE CRYSTAL MATERIAL, LITHIUM NIOBATE, BY APPROPRIATE CHOICE OF CRYSTAL ORIENTATION AND TITANIUM DIFFUSION CONDITIONS. A MACH-ZEHNDER WAVEGUIDE INTERFEROMETER IS THEN CREATED USING A LOW TEMPERATURE PROTON EXCHANGE PROCESS IN WHICH ONE LEG OF THE INTERFEROMETER IS SUPERIMPOSED ON TOP OF THE REVERSE POLED CHANNEL CREATED IN THE PREVIOUS TEP. THE EFFECT OF AN EXTERNAL ELECTRI FIELD IN AN ELECTRODE-LESS DEVICE IS EQUIVALENT TO APPLYING VOLTAGES OF OPPOSITE POLARITIE TO THE ELECTRODES IN A CONVENTIONAL DEVICE. A NOVEL COMPLEMENTARY PHOTODETECTION SCHEME IS PROPOSED THAT REPLACES THE OUTPUT Y-BRANCH OF THE INTERFEROMETER WITH A DIRECTIONAL COUPLER. THIS GREATLY REDUCES THE EFFECTS OF LASER INTENSITY NOISE AND THUS LEADS TO TENS OF DB IMPROVEMENT IN DYNAMIC RANGE (>40 DB FOR A 1 GHZ BANDWIDTH). A COMPACT LOW VOLTAGE CALIBRATION SYSTEM IS DECRIBED THAT EXPLOITS THE SMALL SIZE OF THE INTEGRATED OPTICAL DEVICE.