Optical Coherence Tomography Signal Detection And Processing Circuit Design And Fabrication

With high resolution and high sensitivity,Optical Coherence Tomography(OCT) can obtain inner tomographic images in real-time non-invasively and non- radiogenicly,and can be applied to a variety fields of biomedicine diagnosis,material analysis,and semiconductor device inspection,etc.The design,fabrication and debugging of the signal detection and processing circuits for the OCT system are carried out in the thesis.The valuable light scattered or reflected from the inner part of a sample to be inspected is generally quite weak and then the useful photocurrent is very small(commonly in the order of microampere-level),at the same time,the noises come from the OCT system itself and outside environment bring much influence to the effective signal.So the key work to design the signal detection and processing circuits is how to effectively filter the noises outside the frequency band and, how to significantly enhance the signal to noise ratio.The principle of OCT and the system hardwares were analyzed in detail,and then the center frequency and the bandwidth of the interference signal were determined.These provided important theoretical bases for the design of signal detection and processing circuits.The signal detection and processing circuits combined the differential signal detecting and narrow-band filtering for maximally suppressing the noises out the band and raising the signal to noise ratio were proposed.Subsequently,the signal detection and processing circuits were designed according to the circuits' specifications and the devices parameters required for the center frequency and the bandwidth of interference signals.Electronic circuit simulation software PSpice was used for the circuit performance simulation tests,and the parameters and sensitivities analysis.So,in this way,the circuit characteristics can be verified,and the processing manner might be also referenced for the post-commissioning.Finally,in order to strengthen the anti-electromagnetic interference ability of the signal detection and processing circuits the PCB was carefully designed from the electromagnetic compatibility.The circuit debugging was carded out in the way of the sub-blocks together with the whole board debugging.After the debugging,the signal detection and processing circuits were applied to our optical fiber-based OCT system to conduct the tomography scanning with the templates and samples tests.The experiments showed that the circuits can not only meet the practical requirements of the OCT system, but also have high signal to noise ratio.The experiments results demonstrate that the signal detection and processing circuits should have a favorable practice value for the volume compactness of conventional photocurrent detection scheme or commercial development of OCT system.