A novel method to measure the remaining cladding thickness of side-polished fiber (SPF) was demonstrated by using the digital holography technology. By using angular spectrum method and accurate least-squares phase unwrapping method, the phase distribution of SPF could be reconstructed. Based on the reconstructed phase distribution, the remaining cladding thickness of SPF could be directly measured. It can reduce the errors due to fiber’s asymmetries and edge diffraction. This method could also be used to measure other special optical fibers such as photonic crystal fiber and nano-fiber.
Digital holographic tomography, a computed tomography by use of digital holography, has a huge potential for
three-dimensional imaging of weakly-diffracting phase objects. But the need of multiple angles of illumination weakened
imaging capability of dynamic objects. For cylindrically symmetric object, we can use complex amplitude data of single
hologram under zero incidence angles to replace the other complex amplitude data under different incidence angles.
Therefore, it is possible to achieve the dynamic imaging of cylindrically symmetric objects. The digital holographic
tomography can provide a way for the dynamic imaging of phase-type objects having a cylindrically symmetric structure.
We report an experimental example of the capillary tube having a cylindrically symmetric structure. Tomography of the
capillary tube is performed by filtered back-projection algorithm and Fourier diffraction algorithm respectively to
reconstruct the 3-D map of refractive index. Experimental results show that, comparing with the filtered back-projection reconstruction, diffraction tomography based on the Rytov approximation better respects the dimensions of the capillary tube.
We report the experimental results of geometric parameter measurement of the single-mode fiber by use of digital holographic microtomography technology. Tomography of the single-mode fiber is performed by a filtered back-projection algorithm and a Fourier diffraction algorithm, respectively, to reconstruct the three-dimensional (3-D) map of refractive index. According to this map, we can further get the dimensions of the single-mode fiber by the relate edge detection algorithm of image processing. Experimental results show that compared to the filtered back-projection reconstruction, diffraction tomography based on the Rytov approximation resembles the dimensions of the single-mode fiber. It provides a new way for the nondestructive and on-site measurement of tiny weakly diffracting objects with a cylindrically symmetric structure, such as the single-mode fiber.
There have been many reports on tapered micro-nano optical fiber used in cell monitoring, so it is necessary to discuss
the reverse propagation properties in tapered fiber. In this paper, we use Finite Difference Time Domain (FDTD)
algorithm to simulate the propagation of light wave propagating back and forward in fiber taper, respectively. The results
indicate that most of the light is remain in core in the back way. But little light propagates at a relatively far distance
from core in cladding and most of light energy will back to core at the end part of fiber taper, which is different from
forward propagation. In the subsequent experiment, the conclusion is further proved. Based on this feature, the light
signal in living cell can be easily guided out and the true sense of “endoscopic” for cell detection would be realized.
Phase retrieval techniques have been used for the measurement of 3-D objects. The phase of the transmitted or reflected light beam is modulated by different characteristics of the object and reveals valuable information. The multi-plane diffraction iterative algorithm is a method of phase retrieval with a single beam. Based on numerical phase-error correction system, the method obtains the phase and amplitude of a wavefront with a sequence of intensity patterns recorded at different planes. There are various parameters involved in this method. The parameters impact the retrieval in common. For the optimization in implementation and guidance to experiments, we study six parameters of this method by a series of simulations. The six parameters are the number of sampling planes, the round trip number of iterative, the initial phase, the distance between the object and the first sampling plane, the distance between sampling planes and the wavelength. A discussion on the result of the simulations is also presented.
We present a modified version of the general JPEG encoder for digital holograms. Since digital holograms are characterized by most of their information concentrated at first-order term, to compress digital holograms only with their first-order term is available. The proposed algorithm performs 2D-DCT (discrete cosine transform) on digital holograms as the general JPEG, then quantizes and encodes the low-frequency section extracted with an adaptive mask. Compatible with the general JPEG, the compressed holograms can be directly decoded by the general decoders. Our simulation and experimental results show that this algorithm has higher compression ratio than the general JPEG and more accurate retrieved phase while the compression is equal.
Understanding the evaporation behavior of droplets on a flat substrate is very important for applications of many areas.
In order to obtain quantitative three-dimensional imaging of droplet evaporation process, the dynamic digital holography
has been employed. The off-axis holograms are recorded by a camera and the object waves are numerical reconstructed.
The method can simultaneously provide an amplitude-contrast image and a quantitative phase-contrast image. The
theory of digital holography is introduced and the experiment of water droplet evaporation is presented.
Heavy metal pollution emerges as the industry develops, which threads human health severely. Cd is a kind of
supervirulent heavy metal which needs inspection for food safety. This thesis studies on the immunosensor technology
based on surface plasmon resonance (SPR), successfully detects Cd and introduces the principle of SPR immunosensor
detection system. Cd-iEDTA-BSA (complete antigen of Cd) immunosensor has been made by the methods of
hybridization product and Cd-iEDTA-BSA antibody. There are clear 3*3 arrays on the sensor chip. Two SPR detection
methods of imaging and scanning have been applied to detect the immunoreaction. The picture captured by SPR imaging
system can directly observe the phenomena of the surface plasmon resonance on the sample arrays and the
immunoreaction from the view of the resonance angle. Besides, the excess content of Cd can be found out by finding in
the sample the matched material on the probe of sensor chip. After the immunoreaction the molecular weight of
antigen-antibody compound which forms on the surface of the chip increases, so does the refractive index as well as the
resonance angle. The resonance system can detect the resonance angle and the refractive index of each position on the
sensor chip precisely, and draws the resonance curves. The arrays' resonance curves reflecting the immunocreation have
a clear displacement which indicates the increase of the resonance angle as well as the refractive index. The sensitivity of
the scanning surface plasmon resonance detection system is higher than the imaging one, which is more convenient and
consumes shorter time.
A technique called surface plasmon resonance digital holographic microscopy (SPRDHM) for optical imaging of cell membranes is proposed. The intensity and phase distributions of the reflected light that is modulated by the cell membrane in surface plasmon resonance can be simultaneously obtained. The imaging principle and capability are theoretically analyzed and demonstrated by experiments. In addition, the technique is compared with total internal reflection digital holographic microscopy (TIRDHM) in theory and experiment, respectively. The results show that the SPRDHM technique is better in spatial resolution and phase sensitivity than the TIRDHM technique for imaging of cell membranes
Real time dynamic analysis of micro-object is one of the significant advantages of digital holographic microscopy, but
the process of the spatial filtering limits the application of dynamic and automatic analysis in digital holographic
microscopy. In this paper, a numerical reconstruction technique by means of Gabor wavelet transform (GWT) is
presented for real time dynamic analysis. Appling the GWT to the hologram, the quantitative phase information of the
micro-object is obtained automatically without the process of the spatial filtering. An experiment with a sequence of
holograms of an animalcule is proposed for the dynamic and automatic analysis by employing the GWT method.
The linear integer unconcerned phase-maps fringe projection profilometry has been used to measure the 3-D shape of object with discontinuous height steps. Linear integer unconcerned phase-maps are obtained by changing the angle of grating projected. The technique permits that the frequency of grating is not changed. An automated analysis of the fringe patterns is carried out by the Fourier transform method. Experimental results are presented that demonstrate the validity of the principle.
This paper presents an approach to extract local frequency and phase of interferogram from the ridge of its wavelet transform simultaneously. The principle is introduced. A Morlet wavelet is adopted for the continuous wavelet transform of interferogram. A numerical simulation and an experimental example have shown to verify the validity of the method introduced above.
A new method for analyzing the phase distributions of carrier fringe pattern has been presented. The discontinuities and spurious data has been and still is a cumbersome concern, it is hard to reconstruct the phase by phase demodulation based on phase gradients. The approach that we here introduce to solving this problem is to utilize Gabor transform, a tool excelling for its multiresolution in space-frequency domain, to analyze the phase distributions. The experimental results demonstrate the validity of the proposed method.
It is presented here that the all-digital holography is applied to the digital image hiding. Computer Generated Hologram is generated and reconstructed by numerical method. The secret message and the host message are all still gray-images. The secret image is first transformed into a hologram (CGH), which is called holographic transform and then Arnold transform is performed. DCT is applied in the host image. Then the secret image is embedded into the DCT middle coefficients. The application of the holographic transform improves the transparency of the secret image; by controlling the parameter of the hologram the secrecy of the image is enhanced and add another key to have invisibility and certain robust.
In order to overcome the limitations of conventional Fourier transform and Gabor transform analyzing nonstationary signals, dilating Gabor transform is applied to analyze the optical fringes of 3-D shape measurement. The dilating Gabor transformation is introduced by using a changeable window of Gaussian function in a conventional Gabor transform. This phase analysis method provides more accurate results than Fourier transform and Gabor transform. Simulation and experimental results are presented that demonstrate the validity of the principle.
A new experiment system of three-dimensional shape measurement is presented. The advantages and the disadvantages are analyzed. In this experiment system, using digital light projector replaces traditional projector, and electronical grating replaces traditional grating. Obviously, the system has many advantages such as higher precise, easier to realize, etc. But there still are some disadvantages because of the characteristic of the system. We designed experiments to discuss the errors introduced by the system and look for the best system parameter. From the last result, we can conclude that the system has high practical value.
A new experiment system of three-dimensional shape measurement is presented. The advantages and the disadvantages are analyzed. In this experiment system, using digital light projector replaces traditional mode of projecting, and electronical grating replaces traditional grating. Obviously, the system has many advantages such as higher precise, easier to realize, etc. But there still are some disadvantages because of the characteristic of the system. We create different direction electronical gratings with different period in the system and use the four-step phase-measuring profilometry to get the phase and height of the detected object. According the experiment result, we analyze the errors introduced by the system. Then decrease such errors as much as possible. From the last result, we can conclude that the system has high practical value.
Photonics and photon technology play an important role in information technology and life science in the 21st Century. Jinan University always devotes itself to the training of the technicians in optics and photonics. We have founded the system of undergraduate and postgraduate courses and also built up the photonics technology major lab of Guang Dong Education Bureau. The research involves the optoelectronics detection, the image processing, laser biological effects, optical communications, and so on. Jinan University works hard to promote the industrial application of photonics technology. Jinan University is making its great contribution to the construction of Photon Valley of Guang Dong Province.
A procedure for the measurement of absolute phase values is presented and is used to measure the 3D shape of object with discontinuous height steps. This procedure is based on the linear integer unconcerned phase-maps. Linear integer unconcerned phase-maps are obtained by changing the projecting angle of grating or grating orientation. Experimental results for two kinds of projection optics are presented that demonstrate the validity of the principle.
Fourier transform technique for moire deflectogram is proposed to automatically map the phase object. The moire deflectogram is generate by conventional deflectometer and is analyzed by means of Fourier transform algorithm, in which the fringe phase is retrieved and phase object message is obtained automatically. Theoretical analysis, simulation calculation and application example are presented.
A new technique of the fringe analysis is proposed to automatically measure the 3D object shape. A grating pattern is projected onto an object, and the grating pattern deforms in accordance with the 3D object. This deformed grating image is analyzed by means of subfringe integration algorithm, the phase distribution and the object shape are given at every pixel at measured object. In contrast to FOurier transform profilometry (FTP), this technique processes fringe in its spatial domain instead of the frequency domain, so it is faster and more convenient than FTP.
Moire topography has been used as a noncontact method for grasping the 3D shapes of objects, but it is not easy to judge whether the surface is convex or concave from one moire picture. It is difficult for automatic measurement. In this paper, a new computer-based technique for automatic 3D shape measurement, tracking of carrier coded fringe pattern is proposed. It can accomplish fully automatic distinction between a depression and an elevation of the object shape. Therefore, it can accomplish automatic measurement. Validity of this proposal is experimentally verified.
In this paper, Fourier transform evaluation of fringe phase is proposed for moire deflectometry. Using this method, high-precision and automatic measurement for axisymmetric gas temperature field has been accomplished.