Phase Mask Research Articles

Selective phase masking to reduce material saturation in holographic data storage systems

Emerging networks and applications require enormous data storage. Holographic techniques promise high-capacity storage, given resolution of a few remaining technical issues. In this paper, we propose a technique to overcome one such issue: mitigation of large magnitude peaks in the stored image that cause material saturation resulting in readout errors. We consider the use of ternary data symbols, with modulation in amplitude and phase, and use a phase mask during the encoding stage to reduce the probability of large peaks arising in the stored Fourier domain image. An appropriate mask is selected from a predefined set of pseudo-random masks by computing the Fourier transform of the raw data array as well as the data array multiplied by each mask. The data array or masked array with the lowest Fourier domain peak values is recorded. On readout, the recorded array is multiplied by the mask used during recording to recover the original data array. Simulations are presented that demonstrate the benefit of this approach, and provide insight into the appropriate number of phase masks to use in high capacity holographic data storage systems.

Inscription of Multiple Bragg Gratings in a Single-Mode Polymer Optical Fiber Using a Single Phase Mask and Its Analysis

Multiple Bragg gratings are inscribed in a photosensitive single-mode polymer fiber using phase mask method and also by applying strain to the fiber. Due to the large strain tuning range of the polymer fiber, multiple Bragg gratings are inscribed with a large peak wavelength separation between adjacent peaks. The effect of hysteresis of the polymer fiber is also considered and its influence on the fabrication of the grating is studied. From this paper, it is found that a fiber elongation up to 0.9% of the total fiber length can be used to inscribe multiple Bragg gratings and give a quality grating array. Fiber elongation ${>}{0.9\%}$ of the total length affects the grating reflectivity and bandwidth due to the creep and hysteresis developed in the polymer fiber from the large strain. Within the 0.9% elongation limit, multiple gratings can be inscribed with a maximum peak wavelength separation of 12 nm between adjacent fiber gratings. The fabricated single-mode polymer fiber Bragg grating array can be used in applications, where temperature and humidity compensations are required, while measuring the strain or as multipoint sensors.

Bragg grating writing in PMMA microstructured polymer optical fibers in less than 7 minutes

We demonstrate fiber Bragg grating (FBG) writing in PMMA microstructured Polymer Optical Fibers (mPOFs) using UV Phase Mask technique with writing times shorter than 10 min. The shortest writing time was 6 minutes and 50 seconds and the longest writing time was 8 min and 50 sec. The FBGs were written in a 125 µm PMMA mPOF having 3-rings of holes, the reflection peaks were centred at 632.6 nm and have a reflectivity as high as 26 dB. We also demonstrate how the writing dynamics depends on the intensity of the writing beam.

一种基于随机相位板复用的光学多二值图像加密系统

一种基于随机相位板复用的光学多二值图像加密系统

3D Hierarchical Architectures Prepared by Single Exposure Through a Highly Durable Colloidal Phase Mask

Three-dimensional hierarchical architectures are fabricated using a simple, cost-effective, durable colloidal phase mask containing a colloidal monolayer embedded in a flexible polydimethylsiloxane (PDMS) membrane. These structures give rise to a photonic bandgap that can be tuned over a wide spectral range from the visible to the near-infrared regions.

Companion search around β Pictoris with the newly commissioned L'-band vector vortex coronagraph on VLT/NACO

AbstractHere we present the installation and successful commissioning of an L'-band Annular Groove Phase Mask (AGPM) coronagraph on VLT/NACO. The AGPM is a vector vortex coronagraph made from diamond subwavelength gratings tuned to the L' band. The vector vortex coronagraph enables high contrast imaging at very small inner working angle (here 0″.09, the diffraction limit of the VLT at L'), potentially being the key to a new parameter space. During technical and science verification runs, we discovered a late-type companion at two beamwidths from an F0V star (Mawet et al. 2013), and imaged the inner regions of β Pictoris down to the previously unexplored projected radius of 1.75 AU. The circumstellar disk was also resolved from ≃ 1″ to 5″ (see J. Milli et al., these proceedings). These results showcase the potential of the NACO L-band AGPM over a wide range of spatial scales.

Hyper Gaussian windows with fractional wavefronts

For reducing the impact of focus errors on the modulation transfer function (MTF), we explore the use of fractional phase power masks combined with either sub Gaussian windows, or super Gaussian windows. We present a sub Gaussian mask combined, with an asymmetric fractional phase profile, which reduces both the variations of the MTF vs. focus errors and the oscillations of the MTF around its tendency curve. However, this mask also reduces the light throughput by a factor of two. Full Text: PDF References M. Mino, Y. Okano, "Improvement in the OTF of a Defocused Optical System Through the Use of Shaded Apertures", Appl. Opt. 10, 2219-2225 (1971). CrossRef J. Ojeda-Castaneda, L. R. Berriel Valdos and E. L. Montes, "Line-spread function relatively insensitive to defocus", Opt. Lett. 8, 458-460 (1983). CrossRef J. Ojeda-Castaneda, L. R. Berriel-Valdos, E. Montes, "Ambiguity function as a design tool for high focal depth", Appl. Opt. 27, 790-795, (1988). CrossRef E. R. Dowski, T. W. Cathey, "Extended depth of field through wave-front coding", Appl. Opt. 34, 1859-1865 (1995). CrossRef N. George, W. Chi, "Extended depth of field using a logarithmic asphere", J. Opt. A - Pure Appl. Opt. 5, 157-163 (2003). CrossRef A. Sauceda and J. Ojeda-Castaneda, "High focal depth with fractional-power wave fronts", Opt. Lett. 29, 560-562 (2004). CrossRef A. Castro and J. Ojeda-Castaneda, "Asymmetric Phase Masks for Extended Depth of Field", Appl. Opt. 43, 3474-3479 (2004). CrossRef S. Mezouari, G. Muyo, A. R. Harvey, "Circularly symmetric phase filters for control of primary third-order aberrations: coma and astigmatism", J. Opt. Soc. Am. A 23, 1058-1062 (2006). CrossRef J. Ares García, S. Bará, M. Gomez García, Z. Jaroszewicz, A. Kolodziejczyk, and K. Petelczyc, "Imaging with extended focal depth by means of the refractive light sword optical element", Opt. Exp. 16, 18371 (2008). CrossRef J. Ojeda-Castaneda, J. E. A. Landgrave and C. M. Gómez-Sarabia, "Conjugate phase plate use in analysis of the frequency response of imaging systems designed for extended depth of field", Appl. Opt. 47, E99 ? E105 (2008). CrossRef J. Ojeda-Casta-eda and Arturo Noyola-Isgleas, "High focal depth by apodization and digital restoration", Appl. Opt. 27, 2583-2586 (1988). CrossRef W. T. Cathey and E. R. Dowski, "New Paradigm for Imaging Systems", Appl. Opt. 41, 6080-6092 (2002). CrossRef J. Ojeda-Castaneda, E. Yépez-Vidal, E. García-Almanza and C. M. Gómez-Sarabia, "Tunable Gaussian mask for extending the depth of field", Photonics Letters of Poland, Vol. 4 (3), 115-117 (2012). DirectLink N. Brenner and C. Rader, "A new principle for fast Fourier transformation", IEEE Acoustics, Speech & Signal Processing 24, 264?266 (1976). CrossRef

Voxel-based Investigations of Phase Mask Effects on Susceptibility Weighted Images

To investigate effects of phase mask on susceptibility-weighted images (SWI) using voxel-based analyses in normal elderly subjects. A three-dimensional (3D) gradient echo sequence ran to obtain SWIs in 20 healthy elderly subjects. SWIs with two (SWI2) and four (SWI4) phase multiplications were achieved with positive (PSWI) and negative (NSWI) phase masks to investigate phase mask effects. The voxel-based comparisons were performed using paired t-tests between PSWI and NSWI and between SWI2 and SWI4. Differences of signal intensities between magnitude images and SWI4 were larger than those between magnitude images and SWI2s. Differences of signal intensities between magnitude images and PSWIs were larger than those between magnitude images and NSWIs. Moreover, the signal intensities from NSWI2s and NSWI4s were greater than those from PSWI2s and PSWI4s, respectively. More differences of signal intensities between NSWI4 and PSWI4s were found than those between NSWI2s and PSWI2s in the whole brain images. The voxel-based analyses of SWI could be beneficial to investigate susceptibility differences on the entire brain areas. The phase masking method could be chosen to enhance brain tissue contrast rather than to enhance venous blood vessels. Therefore, it is recommended to apply voxel-based analyses of SWI to investigate clinical applications.

Robust Technique for Image Encryption and Decryption Using Discrete Fractional Fourier Transform with Random Phase Masking

Abstract Encryption is one of the well known techniques to provide security in transmission of multimedia contents over the internet and wireless networks. There is use of image in all the area so its security is of great concern now a day. To focus on security aspect, In this paper we proposed a novel method of image encryption using discrete fractional Fourier transform (DFRFT) using exponential random phase mask. Encrypting with this technique makes it almost impossible to retrieve the image without using both the right keys. DFRFT is the generalization of the Discrete Fourier transform (DFT). This technique has been implemented and results are discussed in detail with analyzing parameters like Security, sensitivity and MSE.

基于相位掩模板的拉丝塔在线制作光纤布拉格光栅方法及装置研究

基于相位掩模板的拉丝塔在线制作光纤布拉格光栅方法及装置研究

Tunable Gaussian mask for extending the depth of field

We present the use of two asymmetrical amplitude masks, for generating a tunable Gaussian filter. The two masks work as a pair. By introducing a lateral displacement, between the members of the pair, one can tune the width of the Gaussian filter. This tunable mask is useful for controlling unwanted oscillations in the MTFs, which are associated to the use of phase filters extending the depth of field. Full Text: PDF References G. Hauesler, "A method to increase the depth of focus by two step image processing", Opt. Commun. 6, 38 (1972). CrossRef J. Ojeda-Casta?eda, R. Ramos, A. Noyola-Isgleas, "High focal depth by apodization and digital restoration", Appl. Opt. 27, 2583 (1988). CrossRef M. Mino, Y. Okano, "Improvement in the OTF of a Defocused Optical System Through the Use of Shaded Apertures", Appl. Opt. 10, 2219 (1971). CrossRef J. Ojeda-Casta?eda, L.R. Berriel Valdos, E. L. Montes, "Line-spread function relatively insensitive to defocus", Opt. Lett. 8(8), 458 (1983). CrossRef J. Ojeda-Casta?eda, L.R. Berriel-Valdos, E. Montes, "Spatial filter for increasing the depth of focus", Opt. Lett. 10(11), 520 (1985). CrossRef J. Ojeda-Casta?eda, A. Díaz, "High focal depth by quasibifocus", Appl. Opt. 27, 4163 (1988). CrossRef J. Ojeda-Casta?eda, L.R Berriel-Valdos, E. Montes, "Ambiguity function as a design tool for high focal depth", Appl. Opt. 27(4), 790 (1988). CrossRef E.R. Dowski, T.W. Cathey, "Extended depth of field through wave-front coding", Appl. Opt. 34, 1859 (1995). CrossRef H. Wang, F. Gan, "High Focal Depth with a Pure-Phase Apodizer", Appl. Opt. 40, 5658 (2001). CrossRef N. George, W. Chi, "Extended depth of field using a logarithmic asphere", J. Opt. A: Pure Appl. Opt. 5, S157 (2003). CrossRef A. Castro, J. Ojeda-Casta?eda, "Asymmetric Phase Masks for Extended Depth of Field", Appl. Opt. 43(17), 1 (2004). CrossRef Á. Sauceda-Carvajal, J. Ojeda-Casta?eda, "High focal depth with fractional-power wave fronts", Opt. Lett. 29(6), 560 (2004). CrossRef G. Mikula, Z. Jaroszewicz, A. Kolodziejczyk, K. Petelczyc, M. Sypek, "Imaging with extended focal depth by means of lenses with radial and angular modulation", Opt. Exp. 15, 9184 (2007). CrossRef J. Ojeda-Castaneda, J.E.A. Landgrave, C.M. Gómez-Sarabia, "Conjugate phase plate use in analysis of the frequency response of imaging systems designed for extended depth of field", Appl. Opt. 47, E99 ? E105 (2008). CrossRef J. Ares García, S. Bará, M. Gomez García, Z. Jaroszewicz, A. Kolodziejczyk, K. Petelczyc, "Imaging with extended focal depth by means of the refractive light sword optical element", Opt. Exp. 16, 18371 (2008). CrossRef G. Muyo, A. Singh, M. Andersson, D. Huckridge, A. Wood, A.R. Harvey, "Infrared imaging with a wavefront-coded singlet lens", Opt. Exp. 17(23), 21118 (2009). CrossRef J. Ojeda-Casta?eda, E. Yépez-Vidal, E. García-Almanza, "Noncoherent imagery: a novel approach", Phot. Lett. Poland 2(4), 162 (2010). CrossRef H.H. Hopkins, Wave Theory of Aberrations (Oxford, 1950). K.-H. Brenner, A.W. Lohmann, J. Ojeda-Castaneda, "The ambiguity function as a polar display of the OTF", Opt. Comm. 77, 89 (1982). CrossRef

Cylindrical Grating Projection by Single-Shot Normal Exposure of a Radial Phase Mask

A periodic grating is defined at the photoresist-coated wall of a circular cylinder with an integer number of particularly long grooves parallel to the generic lines by the holistic exposure of a radial phase mask to a normally incident collimated laser beam. The single-shot projected element corresponds to the inner grating of a high-resolution miniature shaft encoder.

Color image hiding based on phase-truncation and phase retrieval technique in the fractional Fourier domain

An asymmetric cryptosystem is proposed in this paper for color image hiding and extracting using phase truncated fractional Fourier transforms (FrFTs) and phase retrieval iterative algorithm. The secret image are decomposed into R, G and B channels, and permuted by Arnold transforms (ARTs). The R channel is self-encoded in the manner that the other two channels are separated into three phase masks (PMs) as encryption keys in the following three phase truncated FrFT operations while phase keys for decryption are generated and retained. A phase retrieval iterative algorithm in fractional Fourier domain is employed to hide the self-encoded result in one color channel of host image. The phase keys for decryption are different from those for encryption, which indicates the asymmetry of the proposed method and higher security. Numerical simulations are given to show the validity and robustness of our system.

Improved achromatization of phase mask coronagraphs using colored apodization

For direct imaging of exoplanets, a stellar coronagraph helps to remove the image of an observed bright star by attenuating the diffraction effects caused by the telescope aperture of diameter D. The Dual Zone Phase Mask (DZPM) coronagraph constitutes a promising concept since it theoretically offers a small inner working angle (IWA \sim \lambda_0/D), good achromaticity and high starlight rejection, typically reaching a 1e6 contrast at 5 \lambda_0/D from the star over a spectral bandwidth \Delta\lambda/\lambda_0 of 25% (similar to H-band). This last value proves to be encouraging for broadband imaging of young and warm Jupiter-like planets. Contrast levels higher than 1e6 are however required for the observation of older and/or less massive companions over a finite spectral bandwidth. An achromatization improvement of the DZPM coronagraph is therefore mandatory to reach such performance. In its design, the DZPM coronagraph uses a grey (or achromatic) apodization. We propose to replace it by a colored apodization to increase the performance of this coronagraphic system over a large spectral range. This innovative concept, called Colored Apodizer Phase Mask (CAPM) coronagraph, is defined with some design parameters optimized to reach the best contrast in the exoplanet search area. Once this done, we study the performance of the CAPM coronagraph in the presence of different errors to evaluate the sensitivity of our concept. A 2.5 mag contrast gain is estimated from the performance provided by the CAPM coronagraph with respect to that of the DZPM coronagraph. A 2.2e-8 intensity level at 5 \lambda_0/D separation is then theoretically achieved with the CAPM coronagraph in the presence of a clear circular aperture and a 25% bandwidth. In addition, our studies show that our concept is less sensitive to low than high-order aberrations for a given value of rms wavefront errors.

Fabrication of Fiber Bragg Gratings in High Germania Boron Co-doped Optical Fiber by the Phase Mask Method

Kaedah untuk menghasilkan peranti FBG yang mempunyai peratus pantulan yang tinggi diperkenalkan. Peranti FBG telah dicetak dalam gentian optik khas yang mengandungi germanium dan boron yang tinggi. Kandungan germanium ion di dalam gentian optik teras adalah sebanyak mol 20%. Cara yang digunakan ialah cara percetakan topeng fasa dengan menggunakan cahaya ultra ungu ion yang mempunyai panjang gelombang 244 nm sebagai sumber cahaya. Kami telah berjaya menghasilkan FBG yang mempunyai peratus pantulan setinggi 99.9% dan masa yang diambil untuk cetakan adalah kurang daripada 10 minit. Kata kunci: gentian optik; peranti FBG; laser UV; panjang gelombang Bragg; topeng fasa A technique to fabricate high reflectivity fiber Bragg gratings (FBGs) with minimal optics is presented. The FBG is written in high germania boron co-doped optical fiber using a phase mask with a 244 nm continuous-wave UV light as the printing source. The mol percentage of germania ion in the fiber core is about 20%. We have successfully fabricated FBGs with reflectivity as high as 99.9% in less than 10 minutes of exposure time. Key words: Optical fiber; fiber Bragg grating; UV laser; Bragg wavelength; phase mask

随机间距稀疏三元Toeplitz矩阵相位掩模压缩成像

随机间距稀疏三元Toeplitz矩阵相位掩模压缩成像

Multilayer Collinear Holographic Memory with Movable Random Phase Mask

We proposed a new multilayer collinear holographic memory (MCHM) with a movable random phase mask that can act as an interlayer crosstalk reducer. First, to clarify the feasibility of our proposed device, we showed that it has an extremely sharp shift selectivity along the thickness direction of medium of nearly 5.0 µm when the numerical aperture of the objective lens is 0.60. Next, we demonstrated that the utilization of the movable random phase mask can suppress interlayer crosstalk sufficiently, resulting in the improvement in the quality of reconstructed signals. Moreover, we revealed that the MCHM, in which the parallel use of a multilayered technique and collinear shift multiplexing is performed, brings out the medium potential sufficiently in terms of signal to noise ratio and medium dynamic range consumption. Finally, we verified that the MCHM can achieve a nearly 2 times larger data density at least compared with a conventional collinear holographic memory.

Multilayer Collinear Holographic Memory with Movable Random Phase Mask

We proposed a new multilayer collinear holographic memory (MCHM) with a movable random phase mask that can act as an interlayer crosstalk reducer. First, to clarify the feasibility of our proposed device, we showed that it has an extremely sharp shift selectivity along the thickness direction of medium of nearly 5.0 µm when the numerical aperture of the objective lens is 0.60. Next, we demonstrated that the utilization of the movable random phase mask can suppress interlayer crosstalk sufficiently, resulting in the improvement in the quality of reconstructed signals. Moreover, we revealed that the MCHM, in which the parallel use of a multilayered technique and collinear shift multiplexing is performed, brings out the medium potential sufficiently in terms of signal to noise ratio and medium dynamic range consumption. Finally, we verified that the MCHM can achieve a nearly 2 times larger data density at least compared with a conventional collinear holographic memory.

Design of Reference Pattern and Input Phase Mask for Coaxial Holographic Memory

Design methods of a reference pattern and an input phase mask for a coaxial holographic memory are described. By the proposed method, it is expected that the useless consumption of the dynamic range of a recording medium will decrease, and the light efficiency and the interference efficiency between the signal beam and the reference beam will be improved. A reference pattern and an input phase mask are designed by a simulated annealing. The performance of the proposed design method is confirmed by numerical simulations and optical experiments. Furthermore, the holographic memory system using both the designed reference pattern and the designed input phase mask is also confirmed by numerical simulations and optical experiments.

Design of Reference Pattern and Input Phase Mask for Coaxial Holographic Memory

Design of Reference Pattern and Input Phase Mask for Coaxial Holographic Memory