New partially coherent unidirectional imaging system enhances visual data transmission

Phys.org  October 28, 2024 Unidirectional imagers form images of input objects only in one direction. Researchers at UCLA reported unidirectional imaging under spatially partially coherent light and demonstrated high-quality imaging only in the forward direction (A → B) with high power efficiency while distorting the image formation in the backward direction (B → A) along with low power efficiency. Their analyses revealed that when illuminated by a partially coherent beam with a correlation length of ≥∼1.5λ, where λ was the wavelength of light, diffractive unidirectional imagers achieved robust performance, exhibiting asymmetric imaging performance between the forward and backward directions. A […]

Researchers reveal quantum advantage that could advance future sensing devices

Phys.org  October 16, 2024 Quantum metrology takes advantage of quantum correlations to enhance the sensitivity of sensors and measurement techniques beyond their fundamental classical limit. The use of both temporal and spatial correlations present in quantum states of light can extend quantum-enhanced sensing to a parallel configuration that can simultaneously probe an array of sensors or  independently measure multiple parameters. Researchers at the University of Oklahoma used multispatial-mode bright twin beams of light to probe a four-sensor quadrant plasmonic array. They showed that it is possible to independently and simultaneously measure local changes in refractive index for all four sensors […]

Silicon metasurfaces unlock broad-spectrum infrared imaging

Phys.org  October 16, 2024 Nonlinear metasurfaces are used for infrared imaging and spectroscopy. However, due to their low conversion efficiencies several strategies have been adopted to enhance their performances. Using resonances at signal or nonlinear emission wavelengths results in a narrow operational band of the nonlinear metasurfaces, which has bottlenecked many applications, including nonlinear holography, image encoding, and nonlinear metalenses. An international team of researchers (UK, Australia) introduced a new nonlinear imaging platform to overcome this issue. They demonstrated broadband nonlinear imaging for arbitrary objects using metasurfaces. A silicon disk-on-slab metasurface was introduced with an excitable guided-mode resonance at the […]

Proof-of-concept study demonstrates mid-infrared computational temporal ghost imaging

Phys.org  August 26, 2024 Ghost imaging in the time domain allows for reconstructing fast temporal objects using a slow photodetector. The technique involves correlating random or pre-programmed probing temporal intensity patterns with the integrated signal measured after modulation by the temporal object. However, the implementation of temporal ghost imaging necessitates ultrafast detectors or modulators for measuring or pre-programming the probing intensity patterns, which are not available in all spectral regions especially in the mid-infrared range. An international team of researchers (China, Finland) demonstrated a frequency down conversion temporal ghost imaging scheme that enables to extend the operation regime to arbitrary […]

Pyramid optical networks for unidirectional image magnification and demagnification

Phys.org  August 1, 2024 Researchers at UC California developed a pyramid-structured diffractive optical network design (P-D2NN), optimized specifically for unidirectional image magnification and demagnification. The diffractive layers were pyramidally scaled in alignment with the direction of the image magnification or demagnification, to inhibit image formation in the opposite direction, thus achieved the desired unidirectional imaging operation using a much smaller number of diffractive degrees of freedom within the optical processor volume. The design maintained its unidirectional image magnification/demagnification functionality across a large band of illumination wavelengths. It allowed a unidirectional magnifier and a unidirectional demagnifier operation simultaneously in opposite directions, […]

High-speed electron camera uncovers new ‘light-twisting’ behavior in ultrathin material

Phys.org  July 10, 2024 Manipulating the polarization of light at the nanoscale is key to the development of next-generation optoelectronic devices. This is typically done via waveplates using optically anisotropic crystals, with thicknesses on the order of the wavelength. A team of researchers in the US (Stanford, SLAC Nation Acceleration Laboratory, Harvard University, Columbia University, Florida State University, UCLA) used a novel ultrafast electron-beam-based technique sensitive to transient near fields at THz frequencies to observe a giant anisotropy in the linear optical response in Tungsten ditelluride (WTe2). They demonstrated that it is possible to tune THz polarization using a 50 […]

Researchers leverage shadows to model 3D scenes, including objects blocked from view

Phys.org  June 18, 2024 Existing methods for single-view 3D reconstruction with Neural radiance fields (NeRF) rely on either data prior to hallucinate views of occluded regions which may not be physically accurate, or shadows observed by RGB cameras which are difficult to detect in ambient light and low albedo backgrounds. A team of researchers in the US (MIT, industry) proposed using time-of-flight data captured by a single-photon avalanche diode to overcome these limitations models two-bounce optical paths with NeRF using lidar transient data for supervision. By leveraging the advantages of both NeRF and two-bounce light measured by lidar they reconstructed […]

Researchers unveil single-shot and complete polarization imaging system using metasurfaces

Phys.org  May 2, 2024 When light scatters off an object, its polarization, in general, changes—a transformation described by the object’s Mueller matrix. Mueller matrix imaging is an important technique in science and technology to image the spatially varying polarization response of an object of interest, to reveal rich information otherwise invisible to traditional imaging. An international team of researchers (USA – UC San Diego, Germany) conceptualized, implemented, and demonstrated a compact Mueller matrix imaging system—composed of a metasurface to produce structured polarization illumination and a metasurface for polarization analysis—that could, in a single shot, acquire all 16 components of an […]

Pushing back the limits of optical imaging by processing trillions of frames per second

Phys.org  March 25, 2024 Despite real-time femtophotography advantages over conventional multi-shot approaches, existing techniques confront restricted imaging speed or degraded data quality by the deployed optoelectronic devices application scope, acquisition accuracy, and hindered by the limitations in the acquirable information imposed by the sensing models. An international team of researchers (Canada, France) overcame these challenges by developing swept coded aperture real-time femtophotography (SCARF). This enables all-optical ultrafast sweeping of a static coded aperture during the recording of an ultrafast event, bringing full sequence encoding of up to 156.3 THz to every pixel on a CCD camera. They demonstrated SCARF’s single-shot ultrafast […]

Holographic message encoded in simple plastic

Phys.org  March 18, 2024 Researchers in Austria produced a sub-terahertz holographic image of a two-dimensional 576-bit data code using a diffractive phase-plate element. The phase plate was designed to encode a focused image of the data code into a phase modulation profile. The complex phase plate structure is fabricated from polylactic acid using fused deposition modeling, a common three-dimensional-printing technique. The simplified optical setup, consisted of a 0.14 THz diverging source, the holographic phase plate, and a scanning detector, without the need for additional optical elements. The information stored in the data code was an example of a cryptographic private […]