Phase Shift Of Light Research Articles

Far-Field Phase-Shifting Structured Light Illumination Enabled by Polarization Multiplexing Metasurface for Super-Resolution Imaging.

The phase-shifting structured light illumination technique is widely used in imaging but often relies on mechanical translation stages or spatial light modulators, leading to system instability, low displacement accuracy, and limited integration feasibility. In response to these challenges, we propose and demonstrate an approach for generating far-field phase-shifting structured light using a polarization multiplexing metasurface. By controlling the polarization states of incident and transmitted light, the metasurface creates a three-step displacement of structured light, eliminating the need to move samples or illumination sources. As a proof of concept, we experimentally demonstrate microscopic imaging using structured light illumination generated by metasurfaces, extracting high-frequency information from objects, and surpassing the diffraction limit. The proposed metasurface platform offers a promising approach for developing compact and robust phase-shifting imaging systems, with broad prospects in quantitative detection, machine vision, and beyond.

Novel Optical Modulator Photonic Device Based on TiN/Ti3C2 Heterojunction.

Due to the ability of optical modulators to achieve rapid modulation of optical signals, meeting the demands of high-speed data transmission, modulators based on different novel nanomaterials have become one of the research hotspots over the past dacade. Recently, TiN/Ti3C2 heterojunction exhibits highly efficient thermo-optic performance and extremely strong stability. Therefore, we have demonstrated an all-optical modulator based on the principle of Michelson interference and the thermo-optic effect in this paper. The modulator employs a TiN/Ti3C2 heterojunction-coated microfiber (THM) and further demonstrates its ability to generate phase shifts through an ASE light source. The modulator, with a phase shift slope of 0.025π/mW, can also convert the phase shifts of signal light into amplitude modulation through Michelson interference. The fixed signal light wavelength is 1552.09 nm, and the modulation depth is stable at about 26.4 dB within a wavelength detuning range of -10 to 6 nm; The waveforms of signal light at modulation rates of 500 Hz, 1000 Hz, 2000 Hz, and 3000 Hz were tested, and a 3 dB modulation bandwidth of 2 kHz was measured. The all-optical modulator based on THM has the advantages of high efficiency and stability and has broad application prospects in the fields of all-optical signal processing and high-speed optical communication.

Flat lens–based subwavelength focusing and scanning enabled by Fourier translation

Abstract We demonstrate a technique for flexibly controlling subwavelength focusing and scanning, by using the Fourier translation property of a topology-preserved flat lens. The Fourier transform property of the flat lens enables converting an initial phase shift of light into a spatial displacement of its focus. The flat lens used in the technique exhibits a numerical aperture of 0.7, leading to focusing the incident light to a subwavelength scale. Based on the technique, we realize flexible control of the focal positions with arbitrary incident light, including higher-order structured light. Particularly, the presented platform can generate multifocal spots carrying optical angular momentum, with each focal spot independently controlled by the incident phase shift. This technique results in a scanning area of 10 μm × 10 μm, allowing to realize optical scanning imaging with spatial resolution up to 700 nm. This idea is able to achieve even smaller spatial resolution when using higher-numerical-aperture flat lens and can be extended to integrated scenarios with smaller dimension. The presented technique benefits potential applications such as in scanning imaging, optical manipulation, and laser lithography.

On‐Chip Light Polarization Management by Mapping the Polarization Information to Phase Shift

AbstractThe comprehensive management of light polarization states has significantly advanced various fields into a new era. With the advent of photonic integration, there has been a persistent desire to replace the bulky optical components with compact chip‐scale circuits. Nonetheless, the complete integration of polarization‐dependent systems has not yet been accomplished due to the absence of a mature polarization management scheme that possesses a tiny form factor and high foundry process compatibility meanwhile maintaining low operation complexity. Here, to overcome these limitations a novel concept called polarization phase mapping, which encodes the information between the light polarization in one waveguide and the relative light phase shift in another two waveguides, is proposed. With this bi‐directional mapping approach, the fundamental basis of polarization management has shifted from polarization adjustment to phase regulation. All essential polarization‐related functions including synthesizing, stabilizing, measuring, rotating, splitting, and mixing are demonstrated with the standard process in foundries. The size of the polarization rotating unit is pushed down to a few light wavelengths while keeping a competitive performance. Moreover, the proposed concept can be readily applied to other integrated photonics platforms. It is expected to unlock new opportunities for complex polarization‐related applications.

Phase-domain modulated hybrid phase-shifting structured light based efficient 3D measurement

Phase-shifting profilometry (PSP) measurement technology remains a research hotspot in 3D imaging. However, existing PSP methods require projecting additional patterns, which limits measurement space, or involves compressing fringe amplitudes to eliminate phase ambiguity. These practices result in reduced measurement efficiency and robustness. To overcome these challenges, we present a novel phase-domain modulated hybrid phase-shifting (PDM-HPS) structured light 3D measurement approach to solve the phase error of existing spatial-domain modulated phase-shifting (SDM-PS) methods without imposing additional pattern or space constraints. The method integrates phase-shifting speckle and phase-shifting fringe methodologies to create a hybrid phase-shifting coding pattern. In the decoding phase, the offset speckle phase is detected and corrected by the low-precision phase extracted in the frequency domain. The separation of binary speckle and high-precision wrapped phase is realized. Ultimately, an efficient binary speckle-aided stereo phase matching process is employed to achieve unambiguous phase unwrapping. We test the PDM-HPS method in multiple complex real-world scenarios using binocular structured light systems, and compare its accuracy and efficiency with three existing advanced methods. The qualitative and quantitative results show that the proposed method can achieve the measurement accuracy similar to that of the multi-frequency (MF) method by using only 1/3 projection patterns.

Polarizing white light interferometry for phase measurements using two simultaneous interferograms.

Our research introduces a design for a polarization phase-shifting white light interferometric system (PPS-WLIS) that operates in a transmissive mode for measuring the slope phase of transparent objects. It comprises a cyclic path interferometer (lateral shear interferometer) coupled with a multiplexing Michelson interferometer. The system uses polarization to produce two parallel interferograms with polarization modulated with relative shifts simultaneously. To determine the optical phase, we used a two-step algorithm for phase demodulation that does not necessitate precise phase shifts, making the system more straightforward to operate. As a result, we could observe variations in the object associated with optical phase changes. Furthermore, our method simplifies the phase-shift interferometry process by requiring only one capture, making it an effective way to examine objects at dynamic events. As an illustration, we demonstrated the temperature measurement generated by a section of a candle flame.

Thickness-dependent optical characteristics of WS2 flakes prepared by Au- and Ag-assisted exfoliation

WS2 flakes with a number of layers (N WS2) ranging from 1 to 10 are exfoliated on ultraflat template-stripped Au and Ag layers. The apparent colors of WS2/Au and WS2/Ag strongly depend on the underlying metal layers as well as N WS2. The measured and calculated optical reflectance spectra are in good agreement, confirming the identification of N WS2 for each flake. The absorption in the WS2 flake for WS2/Au (A WS2–Au) and WS2/Ag (A WS2–Ag) is calculated: the maximum value of A WS2–Ag for N WS2 = 10 (∼0.93) is much larger than that of A WS2–Au (∼0.5). As expected, the local maxima of A WS2–Au and A WS2–Ag for each N WS2 are found near the exciton resonance wavelengths of WS2. The largest peak of A WS2–Ag is located close to the C exciton resonance wavelength, and the peak position shows a redshift with increasing N WS2. Despite the extremely small flake thickness, the optical resonant modes can appear in WS2/Au and WS2/Ag, according to the anticipated phase shifts of light. These resonant modes can explain how N WS2 and the metal layer affect the optical characteristics of the WS2/metal structures.

Light-induced thermoelastic spectroscopy by employing the first harmonic phase angle method

A highly sensitive gas sensor based on light-induced thermoelastic spectroscopy (LITES) with the first harmonic phase angle(1f-PA) wavelength modulation technique is reported. In this research, methane (CH4) is selected as the target gas, and the detection target wavelength is close to 1653.72 nm. Modulated laser beam passes through a 35 cm absorption cell and is focused on the root of the quartz tuning crystal fork (QCTF). The retrieved in-phase and out-of-phase first harmonic (1f) components are processed with 1f-PA method. With this detection method, the amplitudes of the 1f-PA have demonstrated immunity to light intensity dithering as well as demodulation phase shift. The fluctuation of 1f-PA amplitudes is less than 0.5% while the light intensity varies between 2.11 mW and 10.20 mW. Also, the 1f-PA amplitudes have ranged within 0.4% while the demodulated phase shifted from 0° to 360°. In addition, the system also demonstrates an excellent linear response. While the concentration varies from 200 ppm to 10,000 ppm, the linearity coefficient (R2) is 0.999. According to Allan deviation analysis, the lowest detection limit is 2.85 ppm, and the corresponding normalized noise equivalent absorption coefficient (NNEA) is 3.24 × 10−8 cm−1WHz. With the 1f-PA method, the precise gas concentration which is immune to both light intensity dithering and phase shift can be obtained conveniently for LITES. It has shown great advantages and application prospects in long-term field applications.

Circadian Disruption and Consequences on Innate Immunity and Inflammatory Response.

Circadian rhythms control almost all aspects of physiology and behavior, allowing temporal synchrony of these processes between each other, as well as with the external environment. In the immune system, daily rhythms of leukocyte functions can determine the strength of the immune response, thereby regulating the efficiency of defense mechanisms to cope with infections or tissue injury. The natural light/dark cycle is the prominent synchronizing agent perceived by the circadian clock, but this role of light is highly compromised by irregular working schedules and unintentional exposure to artificial light at night (ALAN). The primary concern is disrupted circadian control of important physiological processes, underlying potential links to adverse health effects. Here, we first discuss the immune consequences of genetic circadian disruption induced by mutation or deletion of specific clock genes. Next, we evaluate experimental research into the effects of disruptive light/dark regimes, particularly light-phase shifts, dim ALAN, and constant light on the innate immune mechanisms under steady state and acute inflammation, and in the pathogenesis of common lifestyle diseases. We suggest that a better understanding of the mechanisms by which circadian disruption influences immune status can be of importance in the search for strategies to minimize the negative consequences of chronodisruption on health.

Quantitative Phase Imaging: Recent Advances and Expanding Potential in Biomedicine.

Quantitative phase imaging (QPI) is a label-free, wide-field microscopy approach with significant opportunities for biomedical applications. QPI uses the natural phase shift of light as it passes through a transparent object, such as a mammalian cell, to quantify biomass distribution and spatial and temporal changes in biomass. Reported in cell studies more than 60 years ago, ongoing advances in QPI hardware and software are leading to numerous applications in biology, with a dramatic expansion in utility over the past two decades. Today, investigations of cell size, morphology, behavior, cellular viscoelasticity, drug efficacy, biomass accumulation and turnover, and transport mechanics are supporting studies of development, physiology, neural activity, cancer, and additional physiological processes and diseases. Here, we review the field of QPI in biology starting with underlying principles, followed by a discussion of technical approaches currently available or being developed, and end with an examination of the breadth of applications in use or under development. We comment on strengths and shortcomings for the deployment of QPI in key biomedical contexts and conclude with emerging challenges and opportunities based on combining QPI with other methodologies that expand the scope and utility of QPI even further.

Optimal photonic crystal slabs for modulators based on transitions between photonic bands

The real part of refractive index is important for the phase shift of light propagating in a dielectric medium. Modulation of the refractive index can be used for electro-optic modulators based on Mach–Zehnder interferometer. In this study we simulate Si-based 2D photonic crystal slabs and by comparing the performance of different lattice types and structure of holes, in respect to the value of effective refractive index change when modulating the refractive index of Si, we find the most promising structures for Si photonics electro-optic modulators based on transition between photonic bands.

Self-Hybridized Exciton-Polaritons in Sub-10-nm-Thick WS2 Flakes: Roles of Optical Phase Shifts at WS2/Au Interfaces.

Exciton–polaritons (EPs) can be formed in transition metal dichalcogenide (TMD) multilayers sustaining optical resonance modes without any external cavity. The self-hybridized EP modes are expected to depend on the TMD thickness, which directly determines the resonance wavelength. Exfoliated WS2 flakes were prepared on SiO2/Si substrates and template-stripped ultraflat Au layers, and the thickness dependence of their EP modes was compared. For WS2 flakes on SiO2/Si, the minimum flake thickness to exhibit exciton–photon anticrossing was larger than 40 nm. However, for WS2 flakes on Au, EP mode splitting appeared in flakes thinner than 10 nm. Analytical and numerical calculations were performed to explain the distinct thickness-dependence. The phase shifts of light at the WS2/Au interface, originating from the complex Fresnel coefficients, were as large as π/2 at visible wavelengths. Such exceptionally large phase shifts allowed the optical resonance and resulting EP modes in the sub-10-nm-thick WS2 flakes. This work helps us to propose novel optoelectronic devices based on the intriguing exciton physics of TMDs.

Anisotropic Goos–Hänchen shift in few-layer two-dimensional materials

We study the Goos–Hänchen (GH) effect in mechanically exfoliated anisotropic two-dimensional (2D) black phosphorus and rhenium disulfide by using a beam displacement amplification technique. We observed anisotropic GH shifts along different crystal orientations of two 2D materials, and they exhibit different anisotropy characteristics. It is because the GH shift is mainly affected by the phase shift of light in the 2D materials, which is related to the real part of the refractive index, while the absorption effect related to the imaginary part of the refractive index has negligible influence on the GH shift. The GH shift can be applied to explore the anisotropy of the real part of the refractive index of a 2D material. Our results provide an important way to reveal the anisotropy mechanism of 2D materials.

High-efficiency and large light-receiving area superconducting nanowire single-photon detector integrated with high-contrast grating

By using a high-contrast grating (HCG, high transmittance > 90 % ) to control the phase shift of incident light, we theoretically designed a novel-structured HCG-integrated superconducting nanowire single-photon detector (HCG-SNSPD) with a high-efficiency and large light-receiving area. Without enlarging the typical single-pixel SNSPD nanowire area ( 10 μm × 10 μm ), the effective detection area is expanded to 115 μm, while the absorption efficiency of the nanowire reaches 84.9% at a wavelength of 1550 nm. The effective detection area of HCG-SNSPD is increased by 11.5 times compared to that of conventional single-pixel SNSPDs. Moreover, the absorption efficiencies of HCG-SNSPD exceed 70% at wavelengths ranging from 1460 nm to 1650 nm, indicating high-efficiency broadband detection. This study promotes new possibilities for the application of SNSPDs.

Evaluation of SLE arthritis using frequency domain optical imaging

ObjectivesSystemic lupus erythematosus (SLE) affects the joints in up to 95% of patients. The diagnosis and evaluation of SLE arthritis remain challenging in both practice and clinical trials. Frequency domain...

Semiconductor nanopillars for programmable directional lasing emissions

Mie resonances facilitate an efficient manipulation of light on the subwavelength scale in high-refractive-index metasurfaces. These ultra-thin high-refractive-index nanostructures have been utilized in wave-front engineering devices for amplitude and phase modulation on the subwavelength scale in dielectric metasurfaces with high transmission efficiencies. We seek to establish a guideline for the desired phase modulation of each element in the metasurfaces integrated with light-emitting devices. Numerical simulations of gallium arsenide (GaAs) nanopillar metasurfaces are carried out over the visible and near-infrared spectral ranges. We analyze the scattering properties of the nanopillars of various sizes along with reflection, transmission, absorption, and phase-change spectra of the nanopillar arrays. We study phase-change properties of nanopillars of varied radii along the spectrum and elaborate on the scattering features of the metasurfaces to create a library of phase-change characteristics. The results indicate that the nanostructures respond with strong resonances and the corresponding phase-change features in the visible and near-infrared frequencies. By the variation of the nanopillar dimensions, one can control the light phase change and shift the features along the spectrum.

Method for the differential measurement of phase shifts induced by atoms in an optical ring cavity

We demonstrate a new method of light phase shift measurement using a high-finesse optical ring cavity which exhibits reduced phase noise due to cavity length fluctuations. Two laser beams with a frequency difference of one cavity free spectral range are simultaneously resonant with the cavity, demonstrating noise correlations in the error signals due to the common-mode cavity length fluctuations. The differential error signal shows a 30 dB reduction in cavity noise down to the noise floor in a frequency range up to half the cavity linewidth ($\delta\nu/2 \simeq 30$ kHz). Various noise sources are analyzed and their contributions to the noise floor are evaluated. Additionally, we apply this noise-reduced phase shift measurement scheme in a simulated spin-squeezing experiment where we have achieved a factor of 40 improvement in phase sensitivity with a phase resolution of 0.7 mrad, which may remove one important barrier against attaining highly spin-squeezed states. The demonstrated method is the first reported measurement using an optical ring cavity and two independent beams, a flexible situation. This method can find direct application to non-destructive measurements in quantum systems, such as for the generation of spin-squeezed states in atom interferometers and atomic clocks.

Quantifying Subcellular Growth Dynamics using Quantitative Phase Imaging

Unregulated growth has a drastic effect on the health of organisms. Unbalanced biomass production and degradation within cells can lead to diseases including diabetes, cancer, and organ hypertrophy. Understanding such growth dysregulations and the development of treatments requires understanding growth. Average growth of cell populations can be measured based on proliferation, while more advanced growth measurement approaches study single cells and can extract cell-to-cell heterogeneity information. We have developed a technique that extends further to measure localization of growth within single cells, using quantitative phase imaging (QPI) microscopy technique.QPI measures the phase shift of light as it passes through a sample, which is linearly proportional to cell biomass in the light path. As a result, QPI data show the changing biomass distribution within cells. Cell growth is commonly measured by QPI as the rate of change of biomass in whole cells over time. This approach has previously been shown to rapidly measure single cell growth and growth inhibition by drugs or therapies. Our work expands the scope of QPI further with an algorithm that utilizes the biomass distribution data to output a discretized subcellular growth map.Our approach is based on solution of a mass balance that considers biomass advection in subcellular regions. Observed changes in mass within each region of the cell can be caused by either advection of mass or biosynthesis/degradation. We can directly measure the change in biomass in each subcellular volume using QPI. We then measure the velocity of mass movement using particle image velocimetry on QPI images. Combining these two allows us to measure the amount of biosynthesis in each subcellular region. Our approach visualizes subcellular growth dynamics in real-time and quantify intracellular growth inhibition in response to drug treatments targeting cell growth mechanisms.

Error self-correction method for phase jump in multi-frequency phase-shifting structured light.

Among 3D measurement approaches, multi-frequency phase-shifting structured light has advantages such as high resolution and high sampling rate owing to its point-to-point calculation method. However, there is always phase jump in the measurement process, which greatly reduces measurement accuracy. This paper proposes an error self-correction method for phase jump based on the multi-frequency heterodyne approach. The method uses redundant measurement data to implement self-correction and does not require additional data acquisition steps. We perform both simulations and experiments using the proposed error self-correction method and the classical heterodyne approach to compare the results. The experiment results verify both the accuracy and suitability of the proposed method.

Phase Imbalance Optimization in Interference Linear Displacement Sensor with Surface Gratings.

In interferential linear displacement sensors, accurate information about the position of the reading head is calculated out of a pair of quadrature (sine and cosine) signals. In double grating interference schemes, diffraction gratings combine the function of beam splitters and phase retardation devices. Specifically, the reference diffraction grating is located in the reading head and regulates the phase shifts in diffraction orders. Measurement diffraction grating moves along with the object and provides correspondence to the displacement coordinate. To stabilize the phase imbalance in the output quadrature signals of the sensor, we propose to calculate and optimize the parameters of these gratings, based not only on the energetic analysis, but along with phase relationships in diffraction orders. The optimization method is based on rigorous coupled-wave analysis simulation of the phase shifts of light in diffraction orders in the optical system. The phase properties of the reference diffraction grating in the interferential sensor are studied. It is confirmed that the possibility of quadrature modulation depends on parameters of static reference scale. The implemented optimization criteria are formulated in accordance with the signal generation process in the optical branch. Phase imbalance and amplification coefficients are derived from Heydemann elliptic correction and expressed through the diffraction efficiencies and phase retardations of the reference scale. The phase imbalance of the obtained quadrature signals is estimated in ellipticity correction terms depending on the uncertainties of influencing parameters.