The experiment of volume holographic storage for teaching and training the practical ability of senior students in Applied Physics is introduced. The students can learn to use advanced optoelectronic devices and the automatic control means via this experiment, and further understand the theoretical knowledge of optical information processing and photonics disciplines that have been studied in some courses. In the experiment, multiplexing holographic recording and readout is based on Bragg selectivity of volume holographic grating, in which Bragg diffraction angle is dependent on grating-recording angel. By using different interference angle between reference and object beams, the holograms can be recorded into photorefractive crystal, and then the object images can be read out from these holograms via angular addressing by using the original reference beam. In this system, the experimental data acquisition and the control of the optoelectronic devices, such as the shutter on-off, image loaded in SLM and image acquisition of a CCD sensor, are automatically realized by using LabVIEW programming.
In this paper, a method to measure the flow speed based on microfluidic chip by digital holography in real-time is demonstrated experimentally. The injection pressure of microfluidic device is changed to create different flow rate in microfluidic channels. On this basis, the phase distributions within the microfluidic channels can be reconstructed by using digital holographic microscopy, and then flow rate can be obtain by measuring the phase distributions of cross section. The experiment results show that digital holographic phase image is an effective and real-time detection means for the characteristic parameters of micro-fluid such as flow rate and injection pressure. In addition, the chip calibration is made to ensure the validity of the experimental results.
In this paper, a real-time measurement of liquid concentration changing in a Y-type microfluidic chip by digital holography is presented. In the experiments, the different concentrations of salt solution are injected into two channels of the Y-type microfluidic chip as a target object, and then the digital holograms related to the target solutions are recorded. The refractive index of the solution can be obtained from the reconstructed phase image. The experiment results show that the real-time changing of liquid concentration in microfluidic chip can be effectively measured by digital holographic microscopy.
A method of digital holographic imaging for strong diffuse-reflective metal surface is presented. For a strong diffuse-reflection object, the DC term of Fourier spectrum of the hologram is removed by subtracting the patterns the reference beam and object beam from the hologram, which effectively eliminates the influence of the zero-order of the spectrum image on actual information. In view of the more extensive area of Fourier-spectrum region of the hologram for a diffuse reflection object, the spectrum filtering windows is taken as a half area of the Fourier-spectrum region. According the removal of the zero-order term and the use of the half area of filtering windows, the reconstruction imaging for the surface of an alloy plate is achieved, in which both amplitude and phase images are obtained, respectively.
A segmental dispersion compensation method is proposed to compensate the dispersion in frequency domain optical coherence tomography. Tomographic imaging for epidermal layer of an onion slice is achieved in the experimental setup using optical fiber. The axial resolution of the tomography can be improved by using segmental dispersion compensation, because this dispersion compensation method employs segmental dispersion coefficients for the different lateral positions in one specific layer. Comparing with the traditional dispersion compensation method, segmental dispersion compensation method has the capability of separating the specified layer of sample and eliminating the dispersion broadening effect of specified layer.
In this paper, the simulation experiments both of Abbe-Porter spatial filtering and of optical processing of image addition and subtraction with a grating filter are designed and performed. We realize the design and operation of optical information processing simulation experiments based on information optics theory and the experimental principle by using MATLAB programing language. The spatial filtering of Fourier spectrum, one of the main concepts in information optics, is intuitively described via the simulation experiments, and the experiment process is demonstrated step by step. The results show that the simulation experiments are really helpful for the filter's design and the image processing. These developed virtual experiments have been used in experimental teaching for undergraduate students majored in optics or optical engineering, which effectively assist students to understand concept and principle of optical information processing.
A polarization-multiplexing off-axis dual-wavelength digital holography is presented. The structure of a groove grating is measured by using the polarization-multiplexing dual-wavelength digital holographic system with a co-path optical configuration. Two holograms of the grating is recorded at the wavelengths 671nm and 656nm by using a pair of CCDs, and then their two phase maps are reconstructed by numerical simulation of diffraction process of the holograms, respectively. The synthetic phase image is obtained by subtracting two phase images directly. Thus, the unwrapping phase map of the grating is achieved by using the polarization-multiplexing dual-wavelength digital holography in the off-axis optical setup.
An automatic angular-spectrum filtering for the phase reconstruction of dual-wavelength digital holograms in a common-path configuration is presented. The major procedure of this automatic angular-spectrum filtering consists of excluding the zero-order region of Fourier spectrums and locating the center of order +1 region of the angular spectrums for two individual wavelengths. The phase map of the object is retrieved with the automatic angular spectrum-filtering algorithm in dual-wavelength digital holographic system, which demonstrates that the automatic angular spectrum-filtering algorithm is feasible and effective. It provides an efficient solution for angular-spectrum filtering in real time dual wavelength digital holographic microscopy.
We propose and experimentally demonstrate a shift-multiplexing complex spectral-domain optical coherence tomography (shift-multiplexing CSD-OCT) method, in which the maximum detection depth of SD-OCT can be greatly extended by incorporating the shift-multiplexing of detection positions with CSD-OCT. The tomographic imaging with twofold or threefold microscopic slides as the target sample is performed. The experimental results show that the tomographic imaging with more uniform brightness and clarity for the different depth regions in a thick sample can be achieved by the shift-multiplexing CSD-OCT system. In particular, even while the sample’s depth is beyond the maximum imaging depth of CSD-OCT system, the tomographic imaging of this sample can still be realized by using the shift-multiplexing CSD-OCT method without the need for any replacement of the equipment, such as high spectral capacity grating or high resolution of CCD. The shift-multiplexing CSD-OCT system can perform the imaging with the optimization and less reduction of sensitivity for the deeper detection position in the sample.