An algorithm is proposed to reconstruct two-dimensional wave-front from phase differences measured by lateral shearing interferometer. Two one-dimensional phase profiles of object wave-front are computed using Fourier transform from phase differences, and then the two-dimensional wave-front distribution is retrieved by use of least-square fitting. The algorithm allows large shear amount and works fast based on fast Fourier transform. Investigations into reconstruction accuracy and reliability are carried out by numerical experiments, in which effects of different shear amounts and noises on reconstruction accuracy are evaluated. Optical measurement is made in a lateral shearing interferometer based on double-grating.
As spatial light modulators (SLMs) are becoming flexible and the preferred device for light steering, the SLM’s modulation calibration still remains challenging. No pixel-addressable measurement of the SLM has yet been practically implemented. We present a quantitative phase measurement and calibration method for a parallel aligned liquid crystal spatial light modulator (PAL-SLM) based on Pancharatnam phase-shifting interferometric microscopy. The pixel-wise phase of SLM can be detected from microscopic interference pattern formed from two orthogonally polarized light waves reflected off the PAL-SLM. The wave phase is modulated or non-modulated depending on its polarization direction parallel or orthogonal to the liquid crystal director. Owing to self-referencing common-path interferometric microscopic imaging, the proposed method is quite robust against environmental disturbance and enables a high-precision pixel-wise characterization of SLM.
With the occurrence of an adding driving field, the properties of the dispersion and the absorption of a four-level system are changed greatly. The system can produce the normal and anomalous dispersion regions with proper parameters. Here, the driving fields can be seemed as knobs to manipulate the group velocity of a weak probe field between subluminal and superluminal.
A generalized phase-shifting method for three-wave shearing interferometry is proposed. The phase-shifting algorithm is derived by an optimal process based on least-squares fitting. With this generalized algorithm, the steps of phase-shifting can be reduced to five, which greatly simplifies the measurement and decreases the burden of computation. Both the numerical simulation and the optical experiment are carried out to demonstrate the adaptability of the method.
A novel multichannel carrier-suppressed return-to-zero (CSRZ) to non-return-to-zero (NRZ) format conversion scheme based on a single custom-designed fiber Bragg grating (FBG) with comb spectra is proposed. The spectral response of each channel is designed according to the algebraic difference between the CSRZ and NRZ spectra outlines. The tailored group delays are introduced to minimize the maximum refractive index modulation. Numerical results show that four-channel 200-GHz-spaced CSRZ signals at 40 Gbits/s can be converted into NRZ signals with high Q-factor and wide-range robustness. It is shown that our proposed FBG is robust to deviations of bandwidth and central wavelength detuning. Another important merit of this scheme is that the pattern effects are efficiently reduced owing to the well-designed spectra response.
A new type of diffractive optical bar code produced by computer-generated holographic technology is proposed. The message in the proposed bar code is hidden in the diffracted light of the bar code element and can be read from the first diffraction order. In contrast to the conventional hidden bar code, which needs a lens to focus the diffracted light, the proposed hidden bar code has a property of self-focusing. This self-focusing ability is achieved by modulating a function of the Fresnel zone plate into the bar code format. Consequently, the read-out process for the information in this hidden bar code avoids the use of a lens. Experiments have shown the feasibility of the proposed bar code and confirmed that it can perform better than the conventional hidden bar code.
Abstract:We designed a multi-software-hybrid-programming digital image processing software for high definition single lens digital imaging system. In this digital image processing software system, LabVIEW ,MATLAB,Quartus ii and C++ are all employed to call DLL library to invoke the CMOS, read data, process image and improve the image quality. Such a software system is specially designed to extend the depth of field in single lens imaging system. Especially, one-button-operation function is designed to reduce the operating time. The results showed that with this software system, even in the large defocus case, the high definition and clear images are ready to output from the single lens imaging system. This system can be used in the fields of biological and medical microscopic imaging, machine vision, etc.
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