Study Of High Resolution Digital Holography And Image Sensor

With the improvement of image sensor and computer technology,the digital holography has grown rapidly.It records the hologram by using digital image sensor such as charge-coupled device(CCD)or Complementary Metal Oxide Semiconductor(CMOS)instead of photographic plate or film.The image reconstruction and other image process can be done in computer,which has the advantages of numerical and fast.It has wide application in many fields including microscopy,dynamic analysis,micro structure measurement,etc.The contents of this paper focus on resolution of digital holography.This paper analysis the factors which limit the resolution and discusses the resolution improvement methods mainly from reconstruction algorithm and image sensor studying.A resolution improvement method based on extrapolation add with interpolation is proposed by reconstruction algorithm research.Based on the characteristics of the current image sensor,a new high resolution imaging pixel device structure of Vertically-charge-transferring Pixel Sensor(VPS)is proposed,and manufactured the high resolution imaging sensor chip based on integrated circuit techniques.The digital holography imaging system is designed which proves the sensor chip can be used in 3D testing and microscopy successfully.The main contents and achievement are as follows:1.A resolution improvement method based on extrapolation add with interpolation is proposed.Combining with the recording and reconstruction algorithm,the factors which affect the reconstruction image quality of hologram are studied including twin-image term and zero-order term,reconstruction algorithms,the structures of image sensor.Two resolution improvement methods,synthetic aperture and sub-pixel,are studied.Two methods can be done by shifting a single sensor laterally by an amount slightly larger or smaller than the pixel size,which will increase the complexity of system.We propose a iterative algorithm based on extrapolation add with interpolation in which The interpolation process can increase the special sample frequency while the extrapolation can enlarge the numerical aperture.The simulation and experimental results shows that aperture size and sample frequency can be improve simultaneously and the resolution of reconstructed image is improved significantly by using this new method.2.A new high resolution imaging pixel device structure of Vertically-charge-transferring Pixel Sensor(VPS)is proposed.This pixel contains only on floating gate MOSFET whose manufacturing process is compatible with CMOS process.It has advantages of high integration and high resolution.The imaging method and working mechanism are studied in detail.During imaging,a depletion region is generated in the p-type substrate by applying appropriate voltage on the gate,source,drain and substrate.Photoelectrons will be generated after the incident photons are absorbed in the depletion region and driven into floating gate layer by the gate voltage.The simulation and experiment prove that there are two kinds of electron injection mechanism:hot electron injection and F-N tunneling,which depend on the voltage and the charge of channel.3.The NAND and NOR array structure are studied.The pixel devices are in series in NAND structure,so it has high integration.But the series devices will induce signal crosstalk during exposing.In order to solve this problem,an interlacing exposure method is proposed,in which the exposed pixel can be insulated by the two open pixel transistor on each side.For NOR structure,each pixel is independent.It is very convenient to operate each pixel through wordline and bitline.The layout of chip array with 5120×5120 pixels is designed based on NOR structure and 0.13 micron design role.The scale of pixel is 0.95×0.95?m2.4.The testing system based on FPGA is designed and used to study the reset,readout,and imaging property of the developed high-resolution image sensor.It's found that the image shows some vertical write line if using FN erase to reset the chip,which is due to device over erase.A two step reset method of program after erase is presented to solve this issue.The lateral and vertical features of readout image are analyzed and the result shows that the data has lateral seam and vertical descending.It's found that the seam is induced by layout design and the data descending is induced by voltage drop along bitline.The dynamic range is evaluated and a multi-voltage read method is proposed.The experimental result shows that the dynamic range can be increase by using this method.The image method of data difference is proposed in which the difference of pre-exposure and after exposure is used as the image data.This method can eliminate fixed pattern noise such as the seam.The dynamic range is evaluated and a multi-voltage read method is proposed.The experimental result shows that the dynamic range can be increase by using this method.5.Two digital holography experiments are carried out using the high resolution imaging system,which verify that the VPS can be used in digital holography.The first experiment is topography measurement of micro lens array using off-axis holography which proves the imaging system can be used to 3D testing for micro-optic devices.The second experiment is microscopy for a gnat wing using inline holography.By comparing the image recorded by the sensor chip of CMOS-APS,the reconstructed image shows a higher resolution by using VPS which is because a higher sample rate.