Guofan Jin

Compact optical roll-angle sensor with large measurement range and high sensitivity

A simple and effective optical roll-angle sensor based on a magnetic garnet single crystal is demonstrated. The measurement is based on the principle that, when linearly polarized light whose polarization varies alternately in two orthogonal directions passes through a polarization analyzer, the transmitted optical intensity varies. The output voltage from an optical detector located after the analyzer can be used to determine the roll angle. The chief advantages of the sensor are that it is compact, flexible, low cost, and power effective and provides a fast response. Most importantly, the sensor is insensitive to various fluctuations such as optical intensity, photodiode responsivity, and temperature and to vibrations. This performance is most advantageous in long-distance or long-term measurements. Experimental results have shown that the angular resolution is 0.01 degree in a +/-30 degree range.

Phase extraction from interferograms with unknown tilt phase shifts based on a regularized optical flow method

A novel method is presented to extract phase distribution from phase-shifted interferograms with unknown tilt phase shifts. The proposed method can estimate the tilt phase shift between two temporal phase-shifted interferograms with high accuracy, by extending the regularized optical flow method with the spatial image processing and frequency estimation technology. With all the estimated tilt phase shifts, the phase component encoded in the interferograms can be extracted by the least-squares method. Both simulation and experimental results have fully proved the feasibility of the proposed method. Particularly, a flat-based diffractive optical element with quasi-continuous surface is tested by the proposed method with introduction of considerably large tilt phase shift amounts (i.e., the highest estimated tilt phase shift amount between two consecutive frame reaches 6.18λ). The phase extraction result is in good agreement with that of Zygos MetroPro software under steady-state testing conditions, and the residual difference between them is discussed. In comparison with the previous methods, the proposed method not only has relatively little restrictions on the amounts or orientations of the tilt phase shifts, but also works well with interferograms including open and closed fringes in any combination.

Orthogonal-reference-pattern-modulated shift multiplexing for collinear holographic data storage

A novel hybrid shift multiplexing method for collinear holographic data storage (CHDS) by using orthogonal reference patterns (RPs) is proposed, analyzed, and demonstrated. For this method, holograms are multiplexed by not only shifting the media but also using different RPs. Compared with the traditional method, the shift pitch for the hybrid method is substantially reduced because of the selectivity introduced by different RPs. The interpage cross talk due to Bragg mismatch and degeneracy for multiplexing holograms in the same volume by using orthogonal RPs is also attenuated by utilizing the shift selectivity of the hologram. A 1.5 μm shift pitch is experimentally achieved by using three amplitude RPs in a system that would be 4.5 μm with only one RP. This new method offers an alternative to significantly increase the data density and transfer rate of the CHDS system given that the media has ideal properties.

Improvement of photorefractive properties and holographic applications of lithium niobate crystal

Based on analyzing and synthesizing the effects of In doping, Fe doping and oxidation state, we propose an efficient way to improve photorefractive properties of LiNbO3 crystal. According to the proposed way, a sample of In:Fe:LiNbO3 crystal is grown and achieves larger dynamic range, higher sensitivity and better signal-to-noise ratio thanFe:LiNbO3 crystal (Fe:0.03wt.%) that is generally considered as a preferable storage medium for high-density holographic data storage. In a coherent volume 0.074cm3 of this crystal, 2030 holograms have been successfully multiplexed and exactly identified in a compact volume holographic data storage and correlation recognition system.

Improving accuracy of multichannel volume holographic correlators by using a two-dimensional interleaving method.

We introduce a two-dimensional interleaving method to improve the output accuracy of volume holographic correlators. The method redistributes the pattern of every input and stored image without changing their inner products, so it can eliminate the impact of correlation pattern difference on calculated inner product values. Experimental tests show that this method can achieve more accurate output intensity for every channel, which agrees much better with the theoretical value than without this method.

Experiment on parallel correlated recognition of 2030 human faces based on speckle modulation.

In this paper, the experiment on parallel correlated recognition of 2030 human faces in Fe:LiNbO(3) crystal is detailedly presented, a very clear correlation spots array was achieved and the recognition accuracy is better than 95%. According to the experiment, it is proved that speckle modulation on the object beam of volume holographic correlators can well suppress the crosstalk, so that the multiplexing spacing is markedly reduced and the channel density is increased 10 times compared with the traditional holographic correlators without speckle modulation.

Phase-modulated multigroup volume holographic correlator.

We propose a hybrid multiplexing method for volume holographic correlators based on the combination of orthogonal random phase modulation of an object beam and two-dimensional angular multiplexing of a reference beam. This method implements storing multiple groups of library images in a single storage location and outputting multiple groups of correlation spots by switching the modulation phase masks. Three experiments are designed to test the validity of this method.

Reed--Solomon Volumetric Coding with Matched Interleaving for Holographic Data Storage

For various error patterns, including random errors, burst errors, and inhomogeneously distributed errors, in the holographic data storage (HDS) channel, a Reed–Solomon volumetric coding with matched interleaving (RSVC-MI) scheme is proposed in this paper. The RSVC-MI scheme combines the advantages of the RSVC scheme and the matched interleaving scheme, makes full use of the priori knowledge of the error patterns in the HDS channel, distributes errors more uniformly, and decodes data iteratively in three dimensions. It is able to eliminate the influences of non-uniform distribution of errors within a page and across pages, overcome the effects of burst errors, correct random errors, and effectively reduce the symbol error rate (SER) of the HDS channel.

Achromatic generation of radially polarized beams in visible range using segmented subwavelength metal wire gratings

We propose an efficient method to achromatically transform a circularly polarized beam to a radially polarized beam in the visible range using segmented subwavelength metal wire gratings. We present a theoretical analysis of the relationship between the polarization purity of the transmitted beams and the number of segments. To verify our analysis, we fabricate a device composed of four quadrant sectors of subwavelength metal wire gratings and measure the transformation properties of the device at visible wavelengths of 488 nm, 532 nm, and 633 nm, which show a good agreement with theoretical results and the broadband achromatic property of the generation method.

Improving signal-to-noise ratio by use of a cross-shaped aperture in the holographic data storage system

A cross-shaped aperture is proposed to improve signal-to-noise ratio (SNR) in the holographic data storage system (HDSS). Both simulated and experimental results show that higher SNR can be achieved by the cross-shaped aperture than traditional square or circular apertures with the same area. A maximum gain of 20% in SNR is obtained for the optimized cross-shaped aperture. The sensitivities to pixel misalignment and magnification error are also numerically compared.