Study On Key Technologies Of Precise Distance Measurement By Homodyne Interferometry

The research topic of large range, high-precision distance measurement byhomodyne interferometry has important practical significance. The technology hasbroad application prospects in the field of superfinishing, microelectronics, MEMS,nano-measurement, etc. It has great significance for the development of our nationaleconomy and defense industry. The dissertation conducted thorough researchesmainly focus on the measuring theory, optical design, high-frequency signalprocessing and segmentation method of precision distance measurement of the laserinterferometer. The main research contents and concrete work of this dissertation areshown below:1. Based on the theory of the interferometry, the error sources of theinterferometry system and the compensation methods were analyzed. According to thecharacteristics of homodyne interference signal, the conjugate suppression methodswas proposed and used for design the optical path. The noise signal caused by outsideinterference could be suppressed effectively; thereby the measurement accuracy wasimproved greatly. The mathematical model of the homodyne interferometer’s opticalpath was established based on the Jones matrix theory. The analytical calculation ofthe light path was advanced. The variation that the interference signals along with thewaveplates, the polarizing beam splitters or the laser source is numerically analyzed.It has the guiding significance for the optical optimization design.2. According to the required speed of the tracker’s moving target, a low-noiseand wide bandwidth circuit was designed. The result of experiment show that thesystem can achieve the micrometer accuracy when the target moving at a speed of4m/s, which was the same as the measurement accuracy achieved when the targetmoving at a lower speed, that the design met the qualification of the tracker system.3. According to the tracking features of the tracker, a measuring method of thetracking state was proposed. It can distinguish the diffirent state between the light’sbeing interrupted and the light’s departure from the center of the target and the targetis stationary, and transmit the state to the upper computer in real time, thus ensuringthe upper computer’s real-time processing and tracking functions.4. A new method was brought out for subdividing the non-orthogonalinterference signals exactly. By tracking the intersections of the two-channel signals dynamically, the interference signal’s one period was subdivided floatingly, the phasedifference between two signals was tracked accurately, thus ensuring the accuracy ofthe non-orthogonal signals’ counting and subdividing. The influences of the DC levelshift and the high-frequency disturbances can be avoided. The relationgship betweenthe phase difference deviates from orthogonal state and the multiples of thesubdividing or the bit of the ADC was analysed. Using this subdividing technology,the homodyne interferometry distance measuring system could resist strongdisturbance and show sound reliability, and more suitable for using on outdoorengineering site.5. A new correction method, which could remove the cyclic error of thehomodyne interferometer in real-time was introduced. Traditional error correctionmethods require reliable abundant data and time for processing so they corrected thecyclic error off-line. The new method can significantly reduce the calculation amount,so the cyclic error of the interference signal could be removed real-time. Results showthat using the new correction method can make the homodyne interferometry distancemeasurement achieve nanometer accuracy in the natural environment.