Theoretical research and computer simulations of waveguide sensors for pressure-measuring laser systems

摘要

An original method for measuring pressure (or acceleration) is discussed. The method is based on changes due to pressure in the propagation conditions for guided optical waves in connected waveguides. The design of the waveguide sensor is described. The sensor consists of two optical waveguides, one of which is located a small distance above the other; two (input-output) optical fiber waveguides; and two optical matching units in the form of a channel-horn planar waveguide. Waveguides can be made on the surfaces of substrates of lithium niobate, quartz, or other materials. The bottom substrate is fixed motionlessly (permanently). The upper one is fixed either at both end points or at only one end of the waveguide, in which case it has the opportunity to be bent due to external pressure or acceleration. The optical radiation is fed with an optical fiber to the bottom waveguide and propagates into it. External pressure (acceleration) bends the upper substrate, causing the upper waveguide to approach the bottom one. It results in a change of conditions for waveguide mode propagation. Under definite conditions, optical radiation leaves the bottom waveguide for the upper one. Under a further increase in pressure (a decrease in the distance between the waveguides), optical radiation leaves the upper waveguide for the bottom one, and so on. The amount of optical radiation that passes (jumps) from the bottom waveguide into the upper one and back again depends on the material of the substrates and on their sizes. The optical radiation is outputted from the waveguide via an optical fiber that is connected to a photodetector. The photodetector output signal function is determined by measuring pressure (acceleration) values. Theoretical analyses and computer simulations for several modifications of the integrated optical waveguide sensors have been done.