Phase Mask Research Articles

Efficient Super-resolution of Phase Images Encoded with Random Phase Mask by machine learning techniques

Efficient Super-resolution of Phase Images Encoded with Random Phase Mask by machine learning techniques

Inverse-Designed 3D Laser Nanoprinted Phase Masks to Extend the Depth of Field of Imaging Systems

Inverse-Designed 3D Laser Nanoprinted Phase Masks to Extend the Depth of Field of Imaging Systems

The Designed Phase Mask for Suppressing the Inter-Pixel Crosstalk Noise in Intensity-Modulated Multilevel Holographic Data Storage Systems

Intensity-modulated signals have the advantage of being directly detectable by the image sensor but have the drawback that the signal quality is easily deteriorated by crosstalk noise, in contrast to phase-modulated signals. In order to suppress the crosstalk noise, we propose a new signal arrangement for multilevel intensity-modulated signals. The concept of our method is to reduce the number of adjacent pixels that are a source of inter-pixel crosstalk noise and to minimize intensity modulation owing to interference with crosstalk noise. We have numerically and experimentally demonstrated that our method can reduce the error rate and improve the recording density compared to the conventional signal arrangement. Our proposed method offers a promising solution for achieving higher recording densities in intensity-modulated holographic data storage systems.

Reliability-Based Design Method for Phase Mask With Periodic Array of Tapered Slits

Reliability-Based Design Method for Phase Mask With Periodic Array of Tapered Slits

Deep Unrolled Single Snapshot Phase Retrieval via Non-Convex Formulation and Phase Mask Design

Deep Unrolled Single Snapshot Phase Retrieval via Non-Convex Formulation and Phase Mask Design

Monocular Three-Dimensional Coding Imaging Based on Double Helix Phase Mask

Monocular Three-Dimensional Coding Imaging Based on Double Helix Phase Mask

Interferenceless Incoherent Holography Optimized by Alternate Iteration of Binary Coded Phase Mask

Interferenceless Incoherent Holography Optimized by Alternate Iteration of Binary Coded Phase Mask

Vector Differential Interference Contrast Microscopy Based on a 3-in-1 Phase Mask through a Dynamic Diffractive Optical Element

Vector Differential Interference Contrast Microscopy Based on a 3-in-1 Phase Mask through a Dynamic Diffractive Optical Element

Spatio-temporal coherent snapshot compressed imaging with time-varying composite phase masks

Snapshot compressed imaging (SCI) can encode an image sequence into a single-frame measurement and has the advantages of low requirements for physical sensors, low bandwidth/ memory requirements, and a fast acquisition speed. However, existing snapshot compressed imaging mainly focuses on incoherent imaging, such as video/hyperspectral imaging, and research on coherent imaging is rare. In this paper, snapshot compressed sensing is introduced for coherent imaging conditions, and a spatio-temporal coherent snapshot compressed imaging method with time-varying composite phase masks is proposed. Numerical experiments demonstrate the effectiveness and superiority of our proposed spatio-temporal coherent snapshot compressed imaging with time-varying composite phase masks method (CSCI-CPM) in terms of the reconstruction quality and robustness for both self-sparse and complex cases.

Single-Frequency Erbium Laser Based on Random Distributed Feedback Based on Inhomogeneities of Phase Mask

Single-Frequency Erbium Laser Based on Random Distributed Feedback Based on Inhomogeneities of Phase Mask

Phase Mask Pinholes as Spatial Filters for Laser Interference Lithography

Laser resonators have outputs with Gaussian spatial beam profiles. In laser interference lithography (LIL), using such Gaussian‐shaped beams leads to an inhomogeneous exposure of the substrate. As a result, dimensions of lithography‐defined features vary significantly across the substrate. In most LIL setups, pinholes are used as filters to remove optical noise. Following a concept proposed by Hariharan et al., a phase mask can be added to these pinholes. In theory, this modification results in a more uniform beam profile, and, if applied as spatial filters in LIL, in improved exposure and hence feature size uniformity. Here, the first successful fabrication of such elements is reported on and their use in an LIL setup is demonstrated to reduce feature dimension variations in fabricated devices.

Phase Mask Design Based on an Improved Particle Swarm Optimization Algorithm for Depth of Field Extension

Phase mask optimization is one of the critical steps in designing a wavefront coding system to extend the depth of field (DoF). As a classical phase mask, a cubic phase mask was taken as an example. An improved particle swarm optimization (PSO) algorithm was applied to calculate the parameters of the cubic phase mask by introducing the modulation transfer function as the optimization criterion and a threshold as a constraint. The quality of the subsequent image restoration is guaranteed on the premise of the extended DoF. Finally, the improved PSO was proved to be faster, more efficient, and more accurate compared to the simulated annealing algorithm and the traditional PSO. The experimental results verify that the cubic phase mask optimized by the improved PSO can achieve DoF extension in the wavefront coding system. The improved PSO can also be applied to other phase masks of wavefront coding systems.

Through-The-Coating Fabrication of Fiber Bragg Grating Relative Humidity Sensors Using Femtosecond Pulse Duration Infrared Lasers and a Phase Mask

Fiber Bragg grating (FBG) relative humidity (RH) sensors are fabricated in commercially available polyimide (PI)-coated optical fibers with diameters of 50 and 125 μm. Infrared (800 nm) femtosecond pulse duration laser pulses and a phase mask are used to inscribe Type-I and Type-II FBGs directly through the protective polyimide coatings of both 50 and 125 μm diameter fibers without typical fiber processing such as hydrogen loading, cryogenic storage, stripping, recoating or annealing. The devices are then evaluated for their performance as humidity sensors. At telecom wavelengths, the 50 μm diameter fiber devices with a 10 μm thick PI coating had a wavelength shift of the Bragg resonance at a constant temperature of 2.7 pm/%RH, whereas the 125 μm diameter fiber devices with a 17 μm thick PI coating had a wavelength shift of 1.8 pm/%RH. The humidity sensors in the 50 µm diameter fiber demonstrated a more rapid response time to small changes in humidity and a weaker hysteresis when compared to the 125 µm diameter fiber devices. No modification to the PI coatings was observed during fabrication. No difference in RH sensitivity was observed for Type-I devices when compared with Type-II devices with the same fiber. The applicability of this approach for fabricating distributed RH sensing arrays with hundreds of sensing elements on a single fiber is discussed.

Femtosecond Inscription of a Fiber Bragg Grating Spectral Array in the Same Spatial Location.

A five fiber Bragg grating (FBG) array is inscribed at the same spot with a single uniform phase-mask (PM). The inscription setup consists of a near-infrared femtosecond laser, a PM, a defocusing spherical lens and a cylindrical focusing lens. The tunability of the center Bragg wavelength is achieved by a defocusing lens, and by translating the PM, which results in a different magnification of the PM. A first FBG is inscribed, followed by four cascading FBGs, which are inscribed exactly at the same spot only after the translation of the PM. The transmission and reflection spectra of this array are measured, showing a second-order Bragg wavelength at ~1.56 µm with a transmission dip of ~-8 dB. The spectral wavelength shift between each consecutive FBG is ~2.9 nm, and the total wavelength shift is ~11.7 nm. The reflection spectrum of the third-order Bragg wavelength is measured at ~1.04 µm, showing a wavelength separation of ~1.97 nm between neighboring FBGs, and the total spectral span between the first FBG and the last one is ~8 nm. Finally, the wavelength sensitivity to strain and temperature is measured.

Reflection Spectral Characteristics of Bragg Gratings Fabricated via Femtosecond Laser Phase Mask Technique

Reflection Spectral Characteristics of Bragg Gratings Fabricated via Femtosecond Laser Phase Mask Technique

Concurrent Optimization of Diffraction Fields from Binary Phase Mask for Three-Dimensional Nanopatterning

Obtaining a high resolution of a three-dimensional (3D) nanostructure is crucial in nanoengineering. For proximity-field nanopatterning (PnP), a type of nanostructure fabrication with a continuous transfer of interference, the geometry of the phase mask primarily determines the resolution of a fabricated nanostructure by modulating the phase shift of coherent lights. Currently, phase masks for PnP are limited to the intuitive design focusing on reducing zeroth (0th) order efficiency with a single variable design. Herein, the concurrent optimization method, using particle swarm optimization, calculates the optimum phase mask with an improved figure of merit for maximizing the electric field intensity contrast. For the high-contrast 3D nanopatterning, we inversely designed the desired electric-field intensity map and calculated the required phase mask. The calculated optimum phase mask for PnP fabricates the hexagonal nanochannel array with high uniformity in lattice and pore shape owing to its selective intensity control. In contrast to the minimized zeroth diffraction design, which cannot modify the intensity in a specific region, the inverse design can selectively maximize or minimize the intensity in the target regions. This concurrent optimization using the inverse design method increases the degree of freedom for the nanostructure of PnP, and it can fabricate the proper nanostructure applicable to various fields such as energy devices, structural materials, and semiconductor devices.

Femtosecond inscription of chirped fiber Bragg gratings and fiber Bragg grating arrays using a single uniform phase-mask

Chirped fiber Bragg gratings (CFBGs) and arrays of fiber Bragg gratings (FBGs) are inscribed with femtosecond pulses and a single uniform phase-mask (PM). The inscription setup includes an 800 nm NIR femtosecond laser, a PM, a defocusing spherical lens and a cylindrical focusing lens. The wavelength tunability is achieved by a defocusing lens, and movement of the PM. A first FBG is inscribed, followed by nine cascading FBGs, where each one is inscribed only after the movement of the PM and a movement of the fiber, thus allowing inscription on a fresh fiber section without overlapping. The transmission and reflection spectra of these ten cascaded FBGs are measured showing a spectral shift of ∼0.9 nm between each one, and a total shift of ∼8 nm. The transmission dip of each FBG is roughly −10 dB. The CFBG is inscribed with the same single uniform PM and with the same setup, but with different movement increments of the PM and fiber. The transmission and reflection spectra of the resulting CFBG are measured with a strength of ∼20 dB and a continuous bandwidth of ∼4.7 nm at FWHM. This yields a chirp rate of ∼1 nm/cm, while the full length of the CFBG is ∼45 mm.

Optimal design of the annular groove phase mask central region.

Vortex phase masks have been shown to be an efficient means to reduce the blinding stellar light in high-contrast imaging instruments. Once placed at the focal plane of the telescope, the helical phase ramp of a vortex phase mask diffracts the light of a bright on-axis source outside the re-imaged telescope pupil, while transmitting the light of a faint off-axis companion nearly unaffected. The Annular Groove Phase Mask (AGPM) is a broadband metasurface implementation of a vector vortex phase mask using the artificial birefringence of a circular subwavelength grating etched onto a diamond substrate. To date, the AGPM design has been optimized using rigorous coupled-wave analysis (RCWA), which is a valid tool to simulate periodic straight gratings. However, we have now reached a performance level where the curvature of the grating lines at the center becomes a limiting factor. Here, we use a finite-difference time-domain (FDTD) method to correctly describe the AGPM performance, including the effect of the curved grating close to its center. We confirm the validity of this simulation framework by comparing its predictions with experimental results obtained on our infrared coronagraphic test bench, and we show that RCWA fails at reproducing correctly the central AGPM performance, confirming the need for a full 3d simulation tool such as FDTD. Finally, we use FDTD to optimize the grating parameters at the AGPM center, and conclude with a new optimal design.

Use of Phase Masks to Construct the Required Spatial Pattern of an Ultrasonic Field

Use of Phase Masks to Construct the Required Spatial Pattern of an Ultrasonic Field

ISPY – NaCo Imaging Survey for Planets around Young stars

Context.Direct imaging has made significant progress over the past decade, in part thanks to a new generation of instruments and excellent adaptive optic systems, but also thanks to advanced post-processing techniques. The combination of these two factors allowed the detection of several giant planets with separations as close as 0.2 arcsec with contrasts typically reaching 9–10 magnitudes at nearinfrared wavelengths. Observing strategies and data rates vary depending on the instrument and the wavelength, withL-andM-band observations yielding tens of thousands of images to be combined.Aims.We present a new approach, tailored for VLT/NaCo observations performed with the Annular Groove Phase Mask (AGPM) coronagraph, but that can be applied to other instruments using similar coronagraphs. Our pipeline aims to improve the post-processing of the observations on two fronts: identifying the location of the star behind the AGPM to better align the science frames and performing frame selection.Methods.Our method relies on finding the position of the AGPM in the sky frame observations, and correlating it with the circular aperture of the coronagraphic mask. This relationship allows us to retrieve the location of the AGPM in the science frames. We are then able to model the torus shape visible in the sky-subtracted science frames, as a combination of negative and positive 2D Gaussian functions. The model provides additional information that is useful to design our frame selection criteria.Results.We tested our pipeline on three targets (βPictoris, R CrA, and HD 34282), two of which have companions at intermediate and close separations, and the third hosts a bright circumstellar disk. We find that the centering of the science frames has a significant impact on the signal-to-noise ratio (S/N) of the companions. Our results suggest that the best reduction is achieved when performing the principal component analysis centered on the location of the AGPM and derotating the frames centered at the location of the star before collapsing the final datacube. We improved the S/N of companions aroundβPictoris and R CrA by 24 ± 3% and 117 ± 11% respectively, compared to other state-of-the-art reductions. We find that the companion position for all the centering strategies are consistent within 3σ. Finally, we find that even for NaCo observations with tens of thousands of frames, frame selection yields just marginal improvement for point sources, but may improve the final images for objects with extended emission such as disks.Conclusions.We propose a novel approach to identify the location of the star behind a coronagraph even when it cannot easily be determined by other methods. We led a thorough study on the importance of frame selection, concluding that the improvements are marginal in most cases, but may yield better contrast in some specific cases. Our approach can be applied to the wealth of archival NaCo data and, assuming that the field of view includes the edges of the coronagraphic mask, its implementation can be adapted to other instruments with coronagraphs similar to the AGPM used on NaCo (e.g., Keck/NIRC2, LBT/LMIRCam).