Nonimaging speckle interferometry for high-speed nanometer-scale position detection

Author(s): E. G. van Putten, A. Lagendijk, and A. P. Mosk

Abstract:

“We experimentally demonstrate a nonimaging approach to displacement measurement for complex scattering materials. By spatially controlling the wavefront of the light that incidents on the material, we concentrate the scattered light in a focus on a designated position. This wavefront acts as a unique optical fingerprint that enables precise position detection of the illuminated material by simply measuring the intensity in the focus. By combining two fingerprints we demonstrate position detection along one in-plane dimension with a displacement resolution of 2.1 nm. As our approach does not require an image of the scattered field, it is possible to employ fast nonimaging detectors to enable high-speed position detection of scattering materials.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 37, Issue 6, pp. 1070-1072 (2012)
doi:10.1364/OL.37.001070

Fabrication of three-dimensional electrospun microstructures using phase modulated femtosecond laser pulses

Author(s): Nathan J. Jenness, Yiquan Wu, Robert L. Clark.

Abstract:

“Electrospun polycaprolactone nanofibers were selectively ablated to form microstructures via the phase modulation of femtosecond laser beams. Ablation width (1–15 μm) and depth (15–110 μm) resolution were dependent upon the selection of pulse energy and microscope objective. Because phase modulation shapes light in a maskless fashion, desired templates were digitally created and physically transferred to electrospun mats within a matter of minutes. Several microarchitectures were formed in parallel by dividing pulse energy between multiple foci, substantially increasing throughput. The data presented herein demonstrates that phase-based laser ablation can be used to rapidly shape and tailor electrospun mats in three dimensions.”

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Publication: Materials Letters, (subscription required)

Issue/Year/DOI: Materials Letters, Volume 66, Issue 1, 1 January 2012, Pages 360–363
doi:10.1016/j.matlet.2011.09.015

Binocular adaptive optics vision analyzer with full control over the complex pupil functions

Author(s): Christina Schwarz, Pedro M. Prieto, Enrique J. Fernández, and Pablo Artal

Abstract:

“We present a binocular adaptive optics vision analyzer fully capable of controlling both amplitude and phase of the two complex pupil functions in each eye of the subject. A special feature of the instrument is its comparatively simple setup. A single reflective liquid crystal on silicon spatial light modulator working in pure phase modulation generates the phase profiles for both pupils simultaneously. In addition, another liquid crystal spatial light modulator working in transmission operates in pure intensity modulation to produce a large variety of pupil masks for each eye. Subjects perform visual tasks through any predefined variations of the complex pupil function for both eyes. As an example of the system efficiency, we recorded images of the stimuli through the system as they were projected at the subject’s retina. This instrument proves to be extremely versatile for designing and testing novel ophthalmic elements and simulating visual outcomes, as well as for further research of binocular vision.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 24, pp. 4779-4781 (2011)
doi:10.1364/OL.36.004779

Fabrication of microscale medical devices by two-photon polymerization with multiple foci via a spatial light modulator

Author(s): Shaun D. Gittard, Alexander Nguyen, Kotaro Obata, Anastasia Koroleva, Roger J. Narayan, and Boris N. Chichkov.

Abstract:

“Two-photon polymerization is an appealing technique for producing microscale devices due to its flexibility in producing structures with a wide range of geometries as well as its compatibility with materials suitable for biomedical applications. The greatest limiting factor in widespread use of two-photon polymerization is the slow fabrication times associated with line-by-line, high-resolution structuring. In this study, a recently developed technology was used to produce microstructures by two-photon polymerization with multiple foci, which significantly reduces the production time. Computer generated hologram pattern technology was used to generate multiple laser beams in controlled positions from a single laser. These multiple beams were then used to simultaneously produce multiple microstructures by two-photon polymerization. Arrays of micro-Venus structures, tissue engineering scaffolds, and microneedle arrays were produced by multifocus two-photon polymerization. To our knowledge, this work is the first demonstration of multifocus two-photon polymerization technology for production of a functional medical device. Multibeam fabrication has the potential to greatly improve the efficiency of two-photon polymerization production of microscale devices such as tissue engineering scaffolds and microneedle arrays.”

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Publication: Biomedical Optics Express, (free download)

Issue/Year/DOI: Biomedical Optics Express, Vol. 2, Issue 11, pp. 3167-3178 (2011)
doi:10.1364/BOE.2.003167

Coaxial holographic encoding based on pure phase modulation

Author(s): Wei Jia, Zhongyu Chen, Fung Jacky Wen, Changhe Zhou, Yuk Tak Chow, and Po Sheun Chung

Abstract:

“We describe a simple technique for coaxial holographic image recording and reconstruction, employing a spatial light modulator (SLM) modified in pure phase mode. In the image encoding system, both the reference beam in the outside part and the signal beam in the inside part are displayed by an SLM based on the twisted nematic LCD. For a binary image, the part with amplitude of “1” is modulated with random phase, while the part with amplitude of “0” is modulated with constant phase. After blocking the dc component of the spatial frequencies, a Fourier transform (FT) hologram is recorded with a uniform intensity distribution. The amplitude image is reconstructed by illuminating the reference beam onto the hologram, which is much simpler than existing phase modulated FT holography techniques. The technique of coaxial holographic image encoding and recovering with pure phase modulation is demonstrated theoretically and experimentally in this paper. As the holograms are recorded without the high-intensity dc component, the storage density with volume medium may be increased with the increase of dynamic range. Such a simple modulation method will have potential applications in areas such as holographic encryption and high-density disk storage systems.”

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Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 50, Issue 34, pp. H10-H15 (2011)
doi:10.1364/AO.50.000H10

Generation of Optical Vortices by Linear Phase Ramps

Author(s): Sunil Vyas

Abstract:

“Generation of optical vortices using linear phase ramps is experimentally demonstrated. When two regions of a wavefront have opposite phase gradients then along the line of phase discontinuity vortices can be generated. It is shown that vortices can evolve during propagation even with the unequal magnitude of tilt in the two regions of the wavefront. The number of vortices and their location depend upon the magnitude of tilt. vortex generation is experimentally realized by encoding phase mask on spatial light modulator and their presence is detected interferometrically. Numerical simulation has been performed to calculate the diffracted intensity distribution from the phase mask, and presence of vortices in the diffracted field is detected by computational techniques.”

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Publication: International Journal of Optics, (free download)

Issue/Year/DOI: International Journal of Optics, Volume 2012, Article ID 794259, 6 pages, (2012)
doi:10.1155/2012/794259

Implementation of phase-shift patterns using a holographic projection system with phase-only diffractive optical elements

Author(s): Wei-Feng Hsu, Yu-Wen Chen, and Yuan-Hong Su

Abstract:

“We proposed a method to implement spatial phase-shift patterns with subdiffraction limited features through a holographic projection system. The input device of the system displayed phase-only diffractive optical elements that were calculated using the iterative Fourier-transform algorithm with the dummy-area method. By carefully designing the target patterns to the algorithm, the diffractive optical elements generated the Fourier-transformed images containing the phase-shift patterns in which the widths of dark lines were smaller than the diffraction limit. With these demonstrations, we have successfully shown that the near-field phase-shift lithographic technique can be realized through an inexpensive maskless lithographic system and can still achieve subdiffraction limited images.”

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Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 50, Issue 20, pp. 3646-3652 (2011)
doi:10.1364/AO.50.003646

Binary-Phase Spatial Light Filters for Mode-Selective Excitation of Multimode Fibers

Author(s): Stepniak, G.; Maksymiuk, L.; Siuzdak, J.;

Abstract:

“In this paper, spatial light modulation is proposed to increase the transmission capacity of graded-index multimode fibers. In the method, selected linearly polarized eigenmodes of the fiber are excited using simple binary-phase spatial filters. Numerical results indicate that the selectivity of the method is very high, also for fibers with perturbed profiles. The excess attenuation of the method is very low. In the experiment, a threefold increase of fiber bandwidth for several filters is obtained.”

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Publication: Journal of Lightwave Technology, (subscription required)

Issue/Year/DOI: Journal of Lightwave Technology, Volume: 29 Issue: 13, P.1980 – 1987 (2011)
doi:10.1109/JLT.2011.2155621

Recursive wavefront aberration correction method for LCoS spatial light modulators

Author(s): J. García-Márquez, J.E.A. Landgrave, N. Alcalá-Ochoa, C. Pérez-Santos

Abstract:

“We present two accurate and relatively simple interferometric methods for the correction of wavefront aberrations of about 3 wavelengths (3λ) in spatial light modulators (SLMs) of the liquid crystal on silicon (LCoS) type. The first is based on a recursive use of a wavefront fitting algorithm in a Wyko™ interferometer, in which Zernike polynomials are employed as the basis functions. We show here that the successive use of only three measurements is required to obtain a peak-to-valley (PV) error as low as λ/10, with an uncertainty of λ/30, in the compensated wavefront. The second method makes use of the actual optical path difference (OPD) computed by the interferometer at each pixel of the image of the interferogram of the LCoS modulator (LCoS-M). From numerical interpolation of these OPD values we were able to assign the required OPD compensation at each pixel of the LCoS-M. With this method, PV errors of the compensated wavefront as low as λ/16, with an uncertainty of λ/30, were obtained for the entire LCoS-M, or of λ/33 for the disk that we used as the domain of the Zernike polynomials in the first method.”

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Publication: Optics and Lasers in Engineering, (subscription required)

Issue/Year/DOI: Optics and Lasers in Engineering, Volume 49, Issue 6, Pages 743-748, (2011)
doi:10.1016/j.optlaseng.2011.01.024

Estimation and Compensation of aberrations in Spatial Light Modulators

Author(s): Augusto Arias and Roman Castaneda

Abstract:

“The spatial light modulator (SLM) Holoeye LC-R720 is based on LCoS (Liquid Crystal on Silicon) technology. Due to the induced curvatures on the silicon plate by the production process, there are static aberrations in the wave-fronts modified by the SLM. In order to calculate the aberrated wave-front we used phase-shifting interferometry, an optimization algorithm for far field propagation, and the geometric characterization of the focal spot along the caustic. Zernike polynomials were used for expanding and comparing the wave-fronts. The aberration compensation was carried out by displaying the conjugated transmittance on the SLM. The complexity of the experimental setup and the requirements of the digital processing of each estimation method were comparatively analyzed.”

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Publication: Journal of Physics: Conference Series, (free download)

Issue/Year/DOI: J. Phys.: Conf. Ser., Volume 274, 012060, (2011)
doi:10.1088/1742-6596/274/1/012060