Yuejin Zhao

Beijing Institute Of Technology, Peping, Beijing, China

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Publications (96)86.96 Total impact

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    ABSTRACT: The structured light illumination method is applied in an optical readout uncooled infrared imaging system to improve the IR image quality. The unavoidable nonuniform distribution of the initial bending angles of the bimaterial cantilever pixels in the focal plane array (FPA) can be well compensated by this method. An ordinary projector is used to generate structured lights of different intensity distribution. The projected light is divided into patches of rectangular regions, and the brightness of each region can be set automatically according to the deflection angles of the FPA and the light intensity focused on the imaging plane. By this method, the FPA image on the CCD plane can be much more uniform and the image quality of the IR target improved significantly. A comparative experiment is designed to verify the effectiveness. The theoretical analysis and experimental results show that the proposed structured light illumination method outperforms the conventional one, especially when it is difficult to perfect the FPA fabrication.
    Optics Letters 04/2015; 40(7). DOI:10.1364/OL.40.001390 · 3.18 Impact Factor
  • Optical Engineering 04/2015; 54(4):046104. DOI:10.1117/1.OE.54.4.046104 · 0.96 Impact Factor
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    ABSTRACT: Wavefront coding (WFC) technology is adopted in the space optical system to resolve the problem of defocus caused by temperature difference or vibration of satellite motion. According to the theory of WFC, we calculate and optimize the phase mask parameter of the cubic phase mask plate, which is used in an on-axis three-mirror Cassegrain (TMC) telescope system. The simulation analysis and the experimental results indicate that the defocused modulation transfer function curves and the corresponding blurred images have a perfect consistency in the range of 10 times the depth of focus (DOF) of the original TMC system. After digital image processing by a Wiener filter, the spatial resolution of the restored images is up to 57.14 line pairs/mm. The results demonstrate that the WFC technology in the TMC system has superior performance in extending the DOF and less sensitivity to defocus, which has great value in resolving the problem of defocus in the space optical system.
    Applied Optics 04/2015; 54(10). DOI:10.1364/AO.54.002798 · 1.69 Impact Factor
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    ABSTRACT: The structured light illumination method is applied in an optical readout uncooled infrared imaging system to improve the IR image quality. The unavoidable nonuniform distribution of the initial bending angles of the bimaterial cantilever pixels in the focal plane array (FPA) can be well compensated by this method. An ordinary projector is used to generate structured lights of different intensity distribution. The projected light is divided into patches of rectangular regions, and the brightness of each region can be set automatically according to the deflection angles of the FPA and the light intensity focused on the imaging plane. By this method, the FPA image on the CCD plane can be much more uniform and the image quality of the IR target improved significantly. A comparative experiment is designed to verify the effectiveness. The theoretical analysis and experimental results show that the proposed structured light illumination method outperforms the conventional one, especially when it is difficult to perfect the FPA fabrication.
    Optics Letters 04/2015; 40(7):1390-3. · 3.18 Impact Factor
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    ABSTRACT: This letter presents an infrared (IR) focal plane array (FPA) with metamaterial absorber (MMA) integrated to enhance its performance. A glass substrate, on which arrays of bimaterial cantilevers are fabricated as the thermal-sensitive pixels by a polyimide surface sacrificial process, is employed to allow the optical readout from the back side of the substrate. Whereas the IR wave radiates onto the FPA from the front side, which consequently avoids the energy loss caused by the silicon substrate compared with the previous works. This structure also facilitates the integration of MMA by introducing a layer of periodic square resonators atop the SiNx structural layer to form a metal/dielectric/metal stack with the gold mirror functioning as the ground plane. A comparative experiment was carried out on the FPAs that use MMA and ordinary SiNx as the absorbers, respectively. The performance improvement was verified by the evaluation of the absorbers as well as the imaging results of both FPAs.
    Applied Physics Letters 03/2015; 106(11):111108. DOI:10.1063/1.4915487 · 3.52 Impact Factor
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    ABSTRACT: Low order aberration was founded when focused Gaussian beam imaging at Kodak KAI -16000 image detector, which is integrated with lenslet array. Effect of focused Gaussian beam and numerical simulation calculation of the aberration were presented in this paper. First, we set up a model of optical imaging system based on previous experiment. Focused Gaussian beam passed through a pinhole and was received by Kodak KAI -16000 image detector whose microlenses of lenslet array were exactly focused on sensor surface. Then, we illustrated the characteristics of focused Gaussian beam and the effect of relative space position relations between waist of Gaussian beam and front spherical surface of microlenses to the aberration. Finally, we analyzed the main element of low order aberration and calculated the spherical aberration caused by lenslet array according to the results of above two steps. Our theoretical calculations shown that , the numerical simulation had a good agreement with the experimental result. Our research results proved that spherical aberration was the main element and made up about 93.44% of the 48 nm error, which was demonstrated in previous experiment. The spherical aberration is inversely proportional to the value of divergence distance between microlens and waist, and directly proportional to the value of the Gaussian beam waist radius.
    SPIE Optical Engineering + Applications; 09/2014
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    ABSTRACT: For measuring the deflections of the microcantilever biosensor, a reflective grating microcantilevers based on SDI were designed and fabricated, a high precision optical readout approach based on diffraction spectrum balancing feedback control was presented. The diffraction spectrum image was collected by a 12-bit digital area array monochrome CCD. According to the sum gray value of the image which subtracted each other at the balancing position and bending position to control a high precision motorized rotation stage revolve make the sum gray value remained in the balancing position always, then the motorized rotation stage revolving angle is just the cantilever bend angle. The resolution of motorized rotation stage is 35 x 10(-6) deg, the system practical measurement resolution is 1 x 10(-4) deg, that is to say, for a length of 250 mu m microcantilever, the tip measure resolution is up to 0.043 nm. Measurement results clearly demonstrate that this reflective grating microcantilever biosensor and this read out method have a great potential for biological and chemical applications.
    Optik - International Journal for Light and Electron Optics 01/2014; 125(1):84-88. DOI:10.1016/j.ijleo.2013.06.031 · 0.77 Impact Factor
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    ABSTRACT: This paper presents the design, fabrication and performance of a 256×256 bimaterial cantilever focal plane array (FPA) which is able to work in the three infrared (IR) atmospheric windows of 1~2.5μm, 3~5μm and 8~14μm simultaneously. The FPA employs a silicon-framed structure by selectively etching away the substrate with Deep Reactive Ion Etching technique, and a stacked layer of chromium and SiNx serves as the multi-band absorber. The images of short wavelength, middle wavelength and long wavelength infrared were captured successfully with the same FPA by combining the Chromium nano-film with silicon nitride as the multi-band IR absorber. The measured sensitivity of the FPA is 0.18μm/K.
    2014 IEEE 27th International Conference on Micro Electro Mechanical Systems (MEMS); 01/2014
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    ABSTRACT: In the wavefront encoding optical system, a low-resolution sensor is adopted to capture encoded image. Through bi-cubic interpolation and L-R filtering using the PSF as the deconvolution filter, the super-resolution image is achieved.
    Signal Recovery and Synthesis; 01/2014
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    ABSTRACT: The camera lens effects for deflectometry surface measurements are analyzed. The evaluations of aberration induced errors are based on image simulation. Experiments for verification are undergoing.
    Computational Optical Sensing and Imaging; 01/2014
  • Journal of Microelectromechanical Systems 01/2014; DOI:10.1109/JMEMS.2014.2334359 · 1.92 Impact Factor
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    ABSTRACT: An approach based on pixels array matching is proposed for optical readout bimaterial microcantilever focal plane array (FPA) sensing system, by which the CCD's pixel array can match the low resolution FPA properly. Compared with the old method, it has the following three advantages: (1) reduces the impact on the infrared imaging quality due to the bending deformation of the microcantilever pixels; (2) decreases the background noise and lower the infrared imaging system's noise equivalent temperature difference; (3) increases the imaging system's frame rate. A microcantilever FPA infrared imaging system with a programmable smart camera was developed to demonstrate the effectiveness of the approach. In addition, the approach can be applied to a similar optical readout micro-array sensing system whose resolution is lower than the CCD.
    Optik - International Journal for Light and Electron Optics 12/2013; 124(23):6058-6062. DOI:10.1016/j.ijleo.2013.04.074 · 0.77 Impact Factor
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    ABSTRACT: A new method of pulse signal de-noising based on wavelet transform and coherent averaging method is proposed. Pulse signal is complex and weak, generally submerged by the interference of baseline drift, motion artifact and high frequency noise. Consequently, it's difficult to measure the heart rate by processing only one single-channel pulse signal, especially when the noise frequency and the pulse signal frequency are in the same frequency range. In this paper, multichannel pulse signal processing based on wavelet transform and coherent averaging is proposed to solve the above problem. First, the detail coefficients and approximation coefficients of each channel signal are obtained by N layer wavelet decomposition, then reconstructing the signal with high layers coefficients as the high frequency noises always exist in low layers coefficients. In this way we can filter out the high frequency interference. Second, the centerline of the upper and lower envelope curve obtained by cubic spline estimation is subtracted from each reconstructed signal so as to eliminate the baseline drift completely. Finally, the heart rate is acquired with the coherent averaging method which results in the noise being offset each other and the pulse signal being enhanced in the frequency range of pulse wave. The pulse signal and three kinds of noise signals simulated with the superposition of different frequency sin signal were analyzed, besides the experiment of six channel pulse signals measured simultaneously based on PhotoPlethysmoGraphy (PPG) were conducted. The simulation and experiment results showed that this method was superior to the traditional single channel.
    Proceedings of SPIE - The International Society for Optical Engineering 11/2013; DOI:10.1117/12.2034463 · 0.20 Impact Factor
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    ABSTRACT: This paper presents a new optical structure which achieves super-resolution by means of changing the complex amplitude of light wave. It also establishes the numerical simulation of the structure. Placed in front of the aperture of optical system, this new structure can modulate the light wave by changing the amplitude transmittance, and also make the central maximum of the Airy Pattern narrower to achieve super-resolution. We analyze modulation effects of many kinds of transmittance function. The numerical simulated result shows that the central maximum of the Point Spread Function (PSF), modulated by transmittance function whose edge value is greater than central value, becomes narrower than that of the idea optical system. It is also concluded that this optical structure is insensitive to different wavelength compared with the phase shifting apodizer, which brings about less chromatic dispersion. This conclusion is extremely useful to realize the super-resolution.
    Proceedings of SPIE - The International Society for Optical Engineering 11/2013; DOI:10.1117/12.2037242 · 0.20 Impact Factor
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    ABSTRACT: In the optical imaging system, deep depth of focus brings larger imaging space, thereby obtaining more information from object space, but also correcting defocus error caused by variety reasons. Thus deep depth of focus has profound significance in the practical application. The information optical imaging system based on the wave-front coding is a general interest among the current research of focal depth extension area. A special designed phase mask been added in the optical system, which could encode object information obtained from the designed focal depth range. By this mean, the OTF and MTF become insensitive to defocussing. Thus equal blurred middle images could be obtained, being processed by phase mask decided by the optical system which was known both by designing and testing and digital image process technology, the final clear image with extended depth of focus could be acquired. In this paper, the detail of a novel image restoration algorithm for the wave-front coding system was discussed. We aim at a specific designed wave-front coding imaging lens, using the edge condition and wavelet transform for an improved Wiener filtering processing. The result of simulation and experimental shown this algorithm could quickly decode the obtained blurred middle image. In the premise of retain more details, this method could product a good image restoration within with whole range of the designed depth of focus. The peak of signal-to-noise (SNR) ratio and the information entropy have been promoted. So does the control of the blurred edge and the ringing effect.
    Proceedings of SPIE - The International Society for Optical Engineering 11/2013; DOI:10.1117/12.2037489 · 0.20 Impact Factor
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    ABSTRACT: In the development process of satellite control systems and solar sensors, conventional solar simulators can‟t show variations in the solar shape and intensity in the state of solar occultation, so we set up a solar simulation and test platform. A method is put forward to simulate the wavefront error based on deformable mirror (DM). In this paper, the main relevant parameters which describe the atmospheric turbulence are introduced. The statistic characteristics of optical wavefront phase influenced by atmospheric turbulence are presented, and analyzed by the method of Zernike modes. A piezoelectric DM with 109 electrodes manufactured by OKO is used as the wavefront phase modulator. The important technology parameter about the deformable mirror is tested. Owing to the linear superposition, we have a research in the optical influence function and voltage deflection. The method of Karhunen-Loeve function is used in the simulation of optical wavefront, because it is statistically independent and can be expanded into the form of Zernike polynomials. We can get the coefficient matrix of random turbulence wavefront, and then link up with surface of the mirror. According to the relationship between deformation of the mirror and the voltage, we can deduce the voltage control matrix, and change the surface of the mirror as we conceive. The numerical results indicate that wavefront error can be introduced to the distribution maps of solar shape and intensity in different orbital position and any tangent point by DM in the light path.
    Proceedings of SPIE - The International Society for Optical Engineering 11/2013; DOI:10.1117/12.2034356 · 0.20 Impact Factor
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    ABSTRACT: Standard instrumentation for the assessment of respiration rate is large and based on invasive method, and not suitable for daily inspection. An optical, simple and non-contact measurement method to detect human respiration rate using lowend imaging equipment is discussed. This technology is based on the visible light absorption of blood, which contains many important physiological information of the cardiovascular system. The light absorption of facial area can be indirectly reflected to gray value of the corresponding area image. In this paper, we acquire the respiration rate through the video signal captured by low-end imaging equipment. Firstly, the color CCD captures the facial area below the eyes and every frame of the video can be separated into three RGB channels. The blue channel is extracted as the research object. Then, we calculate the mean gray value for each image and draw the mean gray curve along the time. Fourier transform can get the frequency spectrogram of the graph, which is filtered through the Fourier filter. The extreme point is the value of the respiratory rate. Finally, an available interface program is designed and we have some volunteers tested. The correlation coefficient between the experimental data and the data provided by a reference instrument is 0.98. The consistency of the experimental results is very well. This technology costs so low that it will be widely used in medical and daily respiration rate measurement.
    SPIE Optical Engineering + Applications; 09/2013
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    ABSTRACT: A new cardiac rate measurement method is proposed. Through the beam splitter prism, the common-path optical system of transmitting and receiving signals is achieved. By the focusing effect of the lens, the small amplitude motion artifact is inhibited and the signal-to-noise is improved. The cardiac rate is obtained based on the PhotoPlethysmoGraphy (PPG). We use LED as the light source and use photoelectric diode as the receiving tube. The LED and the photoelectric diode are on the different sides of the beam splitter prism and they form the optical system. The signal processing and display unit is composed by the signal processing circuit, data acquisition device and computer. The light emitted by the modulated LED is collimated by the lens and irradiates the measurement target through the beam splitter prism. The light reflected by the target is focused on the receiving tube through the beam splitter prism and another lens. The signal received by the photoelectric diode is processed by the analog circuit and obtained by the data acquisition device. Through the filtering and Fast Fourier Transform, the cardiac rate is achieved. We get the real time cardiac rate by the moving average method. We experiment with 30 volunteers, containing different genders and different ages. We compare the signals captured by this method to a conventional PPG signal captured concurrently from a finger. The results of the experiments are all relatively agreeable and the biggest deviation value is about 2bmp.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2013; DOI:10.1117/12.2022326 · 0.20 Impact Factor
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    ABSTRACT: A method that remotely measures blood oxygen saturation through two cameras under regular lighting is proposed and experimentally demonstrated. Two narrow-band filters with their visible wavelength of 660nm and 520nm are mounted to two cameras respectively, which are then used to capture two photoplethysmographic (PPG) from the subject simultaneously. The data gathered from this system, including both blood oxygen saturation and heart rate, is compared to the output of a traditional figure blood volume pulse (BVP) senor that was employed on the subject at the same time. Result of the comparison showed that the data from the new, non-contact system is consistent and comparable with the BVP senor. Compared to other camera-based measuring method, which requires additional close-up lighting, this new method is achievable under regular lighting condition, therefore more stable and easier to implement. This is the first demonstration of an accurate video-based method for non-contact oxygen saturation measurements by using ambient light with their respective visible wavelength of 660nm and 520nm which is free from interference of the light in other bands.
    Optics Express 07/2013; 21(15):17464-71. DOI:10.1364/OE.21.017464 · 3.53 Impact Factor
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    ABSTRACT: The modified generalized cubic phase mask (GCPM) has recently been applied in wavefront coding systems including infrared imaging and microscopy. In this paper, the stationary phase method is employed to analyze the GCPM characteristics. The SPA of the modulation transfer function (MTF) under misfocus aberration is derived for a wavefront coding system with a GCPM. The approximation corresponds with the Fast Fourier Transform (FFT) approach. On the basis of this approximation, we compare the characteristics of GCPM and cubic phase masks (CPM). A GCPM design approach based on stationary phase approximation is presented which helps to determine the initial parameter of phase mask, significantly decreasing the computational time required for numerical simulation.
    Optics Communications 07/2013; s 298–299:67–74. DOI:10.1016/j.optcom.2013.02.033 · 1.54 Impact Factor