Diffraction Compensation Research Articles

Fast phase distortion identification and automatic distortion compensated reconstruction for digital holographic microscopy using deep learning

Digital holographic microscopy (DHM) is a quantitative phase measurement technique with full-field, contactless, and fast. The technique provides accurate micro-surface morphology of samples. These steps are essential for accurate phase reconstruction, such as holographic focusing, numerical diffraction, phase unwrapping and distortion compensation. Performing these processes manually is time-consuming and is not conducive to the general application of the technology. In order to improve the detection efficiency, this paper proposes a deep learning model that can achieve fast identification of DHM phase distortion and automatic phase distortion compensation reconstruction. The model can be preprocessed for holographic phase to accurately identify the type of phase distortion present in the phase. And adaptively adjust the network weight parameters for phase distortion compensation reconstruction. The experimental results show that the method proposed in this paper achieves fast and accurate identification of multiple phase distortions. The model has high accuracy and strong generalization ability. The reconstructed holographic phase map has PSNR of 35.2743dB and RMSE as low as 10-2 level in the face of complex mixed aberrations. The identification and reconstruction processes took 0.005s and 0.058s, both in milliseconds, respectively. The evaluation indexes SSIM, FSIM and NC can reach above 0.99. It is shown that the method in this paper is not only capable of reconstructing holograms, but also able to effectively retain the detailed features of the original image.

High-harmonic diffractive lens color compensation.

Large diameter, high-harmonic diffractive lenses could find applications in future space telescopes. Residual chromatic aberrations from these lenses can cause significant blurring. Solutions to reduce chromatic dispersion and other aberrations to diffraction-limited performance are discussed. A design example based on a 240-mm-diameter, 1-m focal length multi-order diffractive engineered lens operating over the astronomical R-Band (589-727 nm) is presented. The design example uses a relay subsystem with four times smaller diameter than the primary. This color corrector includes both refractive and diffractive optical elements and reduces the longitudinal chromatic aberrations by more than a factor of 30 compared to the primary lens alone, while maintaining the effective focal length and numerical aperture of the system.

Under Display Camera Image Recovery through Diffraction Compensation

Under Display Camera(UDC) technology is being developed to eliminate camera holes and place cameras behind display panels according to full display trend in mobile phone. However, these camera systems cause attenuation and diffraction as light passes through the panel, which is inevitable to deteriorate the camera image. In particular, the deterioration of image quality due to diffraction and flares is serious, in this regard, this paper discusses techniques for restoring it. The diffraction compensation algorithm in this paper is aimed at real-time processing through HW implementation in the sensor for preview and video mode, and we've been able to use effective techniques to reduce computation by about 40 percent.

Fast method for calculating a curved hologram in a holographic display.

A curved hologram can increase the view angle in a holographic display. The huge data processing and curved computer-generated hologram (CCGH) computation time is still a challenge for real-time display. Here, we propose two fast methods to accelerate the computation. The first one is a diffraction compensation (DC) method where the diffraction calculation is from the wave-front recording plane (WRP) to a CCGH. The other is an approximate compensation (AC) method that adds a phase difference distribution to the WRP to obtain the CCGH. Numerical simulations and optical experiments are performed, which demonstrate that the two methods are feasible and the computation time is dramatically reduced. The AC method can further reduce time significantly compared with the DC method. And the image quality for proposed methods is similar. It is expected that these fast methods can be combined with curved display screen and flexible display materials in the future.

Investigation of influence incoherent background illumination on the nonlinear response of a lithium niobate crystal sample at low light intensity

The total compensation of nonlinear diffraction of coherent laser beams of He-Ne laser (wavelengths 633 nm) with diameters on full width of half maximum near to 15 - 20 μm due of assistance of incoherent background have been experimentally demonstrated. Incoherent background had a shorter wavelengths (455 – 465) nm and much lower intensity compared with coherent signal beam with wavelengths 633 nm. Obtained the dependences of the refractive index change in the LiNbO3:Fe crystal under the conditions of such incoherent background.

Theoretical description and design of nanomaterial slab waveguides: application to compensation of optical diffraction.

Planar optical waveguides made of designable spatially dispersive nanomaterials can offer new capabilities for nanophotonic components. As an example, a thin slab waveguide can be designed to compensate for optical diffraction and provide divergence-free propagation for strongly focused optical beams. Optical signals in such waveguides can be transferred in narrow channels formed by the light itself. We introduce here a theoretical method for characterization and design of nanostructured waveguides taking into account their inherent spatial dispersion and anisotropy. Using the method, we design a diffraction-compensating slab waveguide that contains only a single layer of silver nanorods. The waveguide shows low propagation loss and broadband diffraction compensation, potentially allowing transfer of optical information at a THz rate.

Diffraction Effects and Compensation in Passive Acoustic Mapping.

Over the last decade, a variety of noninvasive techniques have been developed to monitor therapeutic ultrasound procedures in support of safety or efficacy assessments. One class of methods employs diagnostic ultrasound arrays to sense acoustic emissions, thereby providing a means to passively detect, localize, and quantify the strength of nonlinear sources, including cavitation. Real array element diffraction patterns may differ substantially from those presumed in existing beamforming algorithms. However, diffraction compensation has received limited treatment in passive and active imaging, and measured diffraction data have yet to be used for array response correction. The objectives of this paper were to identify differences between ideal and real element diffraction patterns, and to quantify the impact of diffraction correction on cavitation mapping beamformer performance. These objectives were addressed by performing calibration measurements on a diagnostic linear array, using the results to calculate diffraction correction terms, and applying the corrections to cavitation emission data collected from soft tissue phantom experiments. Measured diffraction patterns were found to differ significantly from those of ideal element forms, particularly at higher frequencies and shorter distances from the array. Diffraction compensation of array data resulted in cavitation energy estimates elevated by as much as a factor of 5, accompanied by the elimination of a substantial bias between two established beamforming algorithms. These results illustrate the importance of using measured array responses to validate analytical field models and to minimize observation biases in imaging applications where quantitative analyses are critical for assessment of therapeutic safety and efficacy.

Solitons generated by self-organization in bismuth germanium oxide single crystals during the interaction with laser beam

We present here the experimental, theoretical, and numerical investigations of Kerr solitons generated by self-organization in black and yellow high quality bismuth germanium oxide (Bi12GeO20) single crystals. A picosecond laser beam of increasing power induces competing cubic and quintic nonlinearities. The numerical evolution of two-dimensional complex cubic-quintic nonlinear Schrodinger equation with measured values of nonlinearities shows the compensation of diffraction by competing cubic and quintic nonlinearities of opposite sign, i.e., the self-generation and stable propagation of solitons. Experiments as well as numerical simulations show higher nonlinearity in the black Bi12GeO20 than in the more transparent yellow one.

Affordable real-time diffraction compensation in the spatial domain

Diffraction is a source of distortion in optical imaging, and can be nearly eliminated by linear compensating components such as lenses. However, in many applications such components are impractical, and thus the ongoing interest in simple low-cost solutions. Since standard detection is based on power measurements (rather than coherent field measurements) a simple linear filter cannot compensate for the distortions. However, if the variations in the image are relatively small the process is approximately linear and can be compensated by applying a linear filter. This approach has been developed, however, the analysis was always done in the spectral domain, in which case electrical spectral filters cannot be easily implemented on a 2D matrix without digital processing. We present a spatial filter for diffraction compensation in the spatial domain, based on a filter which was originally developed by us for dispersion mitigation. To the best of our knowledge, this is the first time that an analytical expression is derived for a diffraction compensating filter in the spatial domain. Moreover, in previous works a small imaginary parameter was introduced to eliminate divergence. In the present paper a simple analytical evaluation of this parameter is given, which eliminates the need for iterative computations.

Self-structuring of stable dissipative breathing vortex solitons in a colloidal nanosuspension.

The self-structuring of laser light in an artificial optical medium composed of a colloidal suspension of nanoparticles is demonstrated using variational and numerical methods extended to dissipative systems. In such engineered materials, competing nonlinear susceptibilities are enhanced by the light induced migration of nanoparticles. The compensation of diffraction by competing focusing and defocusing nonlinearities, together with a balance between loss and gain, allow for self-organization of light and the formation of stable dissipative breathing vortex solitons. Due to their robustness, the breathers may be used for selective dynamic photonic tweezing of nanoparticles in colloidal nanosuspensions.

협대역 초음파 신호를 이용한 시간 영역에서의 감쇠 지수 예측

The VSA(Video Signal Analysis) method is the time-domain approach for estimating ultrasonic attenuation which utilizes the envelop signals from backscattered rf signals. The echogenicity of backscattered ultrasonic signals, however, from deeper depths are distorted when the broadband transmit pulse is used and it degrades the estimation accuracy of attenuation coefficients. We propose the modified VSA method using adaptive bandpass filters according to the centroid shift of echo signals as a pulse propagates. The technique of dual-reference diffraction compensation is also proposed to minimize the estimation errors because the difference of attenuation properties between the reference and sample aggravates the estimation accuracy when the differences are accumulated in deeper depth. The proposed techniques minimize the distortion of relative echogenicity and maximize the signal-to-noise ratio at the given depth. Simulation results for numerical tissue-mimicking phantoms show that the Rectangular-shaped filter with the appropriate center frequency exhibits the best estimation performance and the technique of the dual-reference diffraction compensation dramatically improves accuracy for the region after the beam focus.

Anomalous diffraction in hyperbolic materials

We demonstrate that light is subject to anomalous (i.e., negative) diffraction when propagating in the presence of hyperbolic dispersion. We show that light propagation in hyperbolic media resembles the dynamics of a quantum particle of negative mass moving in a two-dimensional potential. The negative effective mass implies time reversal if the medium is homogeneous. Such property paves the way to diffraction compensation, spatial analogue of dispersion compensating fibers in the temporal domain. At variance with materials exhibiting standard elliptic dispersion, in inhomogeneous hyperbolic materials light waves are pulled towards regions with a lower refractive index. In the presence of a Kerr-like optical response, bright (dark) solitons are supported by a negative (positive) nonlinearity.

Continuous Solitons in a Lattice Nonlinearity.

We study theoretically and experimentally the propagation of optical solitons in a lattice nonlinearity, a periodic pattern that both affects and is strongly affected by the wave. Observations are carried out using spatial photorefractive solitons in a volume microstructured crystal with a built-in oscillating low-frequency dielectric constant. The pattern causes an oscillating electro-optic response that induces a periodic optical nonlinearity. On-axis results in potassium-lithium-tantalate-niobate indicate the appearance of effective continuous saturated-Kerr solitons, where all spatial traces of the lattice vanish, independently of the ratio between beam width and lattice constant. Decoupling the lattice nonlinearity allows the detection of discrete delocalized and localized light distributions, demonstrating that the continuous solitons form out of the combined compensation of diffraction and of the underlying periodic volume pattern.

Manipulation of orbital angular momentum beams based on space diffraction compensation

We put forward a technique to manipulate the size of orbital angular momentum (OAM) beams based on space diffraction compensation. Paraxial Fresnel diffraction which carries a negative spatial quadratic phase distribution can be regarded as a negative diffractive effect. To compensate the negative diffraction, we employ a 4f Fourier lens system containing a phase mask to generate an inverse quadratic phase. The size of OAM beams can be easily controlled by designing the phase mask profile without changing the OAM. The applications of space diffraction compensation in OAM demultiplexing, ring fiber coupling for OAM beams and optical manipulation of micro particles are also discussed.

Ultrasound time-reversal MUSIC imaging with diffraction and attenuation compensation

Time-reversal imaging with multiple signal classification (TR-MUSIC) is an algorithm for imaging point-like scatterers embedded in a homogeneous and non-attenuative medium. We generalize this algorithm to account for the attenuation in the medium and the diffraction effects caused by the finite size of the transducer elements. The generalized algorithm yields higher-resolution images than those obtained with the original TR-MUSIC algorithm. We evaluate the axial and lateral resolutions of the images obtained with the generalized algorithm when noise corrupts the recorded signals and show that the axial resolution is degraded more than the lateral resolution. The TR-MUSIC algorithm is valid only when the number of point-like targets in the imaging plane is fewer than the number of transducer elements used to interrogate the medium. We remedy this shortcoming by dividing the imaging plane into subregions and applying the TR-MUSIC algorithm to the windowed backscattered signals corresponding to each subregion. The images of all subregions are then combined to form the total image. Imaging results of numerical and phantom data show that when the number of scatterers within each subregion is much smaller than the number of transducer elements, the windowing method yields super-resolution images with accurate scatterer localization. We use computer simulations and tissue-mimicking phantom data acquired with a real-time synthetic-aperture ultrasound system to illustrate the algorithms presented in the paper.

Multifokalität in Kombination mit Aberrationskorrektur: ein neues Konzept einer Presbyopie korrigierenden IOL

Further developments in the field of intraocular lenses have resulted in improvements of multifocal lenses (MIOL) which enable spectacle-free vision at near and far distance under most conditions. In our prospective study we investigated a new aberration-corrected MIOL, whereby 31 eyes of 19 patients, aged between 40 and 81 years, received a Tecnis ZMB00 MIOL (Abbott Medical Optics). Postoperative visual results were documented. Patients were enrolled if they were at least 40 years old and if they were scheduled for cataract surgery or presbyobic lens exchange. Exclusion criteria were any other visually relevant pathologies and a corneal astigmatism of 1.5 D or more. After 6 months, 94.7 % of the patients had a binocular uncorrected distance vision of 0.1 LogMAR or better, 67.7 % of eyes could read Jaeger 1+ (0.0 LogMAR) and 93.6 % could read Jaeger 1 (0.1 LogMAR) or better. There was no correlation between the power of the implanted lens and the postoperative distance or near vision or between IOL power and best-corrected distance vision. The aspheric diffractive multifocal IOL Tecnis ZMB00 provides a restoration of far and near visual function after cataract surgery or presbyopia correction. The correction provided by the IOL is predictable and independent from the optical power of the IOL implanted. The combination of diffractive multifocality and compensation for corneal spherical aberration is an effective alternative for cataract surgery and presbyopia correction.

Determining the Spectral Resolution of a Charge-Coupled Device (CCD) Raman Instrument

A new method based on dispersion equations is described to express the spectral resolution of an applied charge-coupled device (CCD) Czerny-Turner Raman instrument entirely by means of one equation and principal factors determined by the actual setup. The factors involved are usual quantities such as wavenumber values for the laser and the Raman band, the diffraction grating groove density, the second focal length, the angle between the incident and the diffracted light, and the full width at half-maximum (FWHM) value of the signal on the detector. A basic formula is derived to estimate the spectral resolution of the Raman instrument. An essential feature of the new method is a proposed way to compensate for non-ideality (diffractions, aberrations, etc.) by use of a hyperbola model function to describe the relationship between the width of the entrance slit and the image signal width on the CCD. The model depends on the spectrometer magnification and a diffraction and aberration compensation factor denoted as A. A could be approximated as a constant that can be determined by the experimental method. The validity of the new expression has been examined by measuring the band width of the 1332.4 cm−1 diamond Raman fundamental band, excited with two quite different wavelengths (a deep ultraviolet 257.3 nm laser line and a visible green 514.5 nm line). A low pressure mercury line at 265.2042 nm also was applied to give further verification of the given expression. A useful method to find true Raman band widths is also provided. A final finding was that the known significant changes in spectral resolution along the Raman shift axis make static recording and synchronous (extended) scanning modes differ significantly with respect to their resolution properties; this feature has been often overlooked in many contemporary works reporting Raman spectra. A reason for this is that many Raman bands are too wide to show the effect.

Dispersion-accumulated diffraction-compensated superprism with two cascaded photonic crystals

The benefits of unusual dispersive properties of photonic crystals are often mitigated by unwanted phenomena like spatial broadening of propagating beams. This problem is usually faced using millimeter long conditioning regions to precompensate for beam spreading. A new approach is explored here to manage the strong diffraction of photonic superprisms without preconditioning regions. Unconventional photonic crystal lattice cells are engineered using plane wave expansion calculations, and two photonic crystals having both positive dispersions but diffraction properties of opposite signs are selected. Light propagation in the combined photonic structure is studied using finite difference time domain simulation to validate the predicted dispersion accumulation and diffraction compensation approach.

Reflective Heterostructure Photonic Crystal Superprism Demultiplexer

A new design for a wideband and compact demultiplexer for coarse wavelength-division-multiplexing applications is proposed. This is based on the superprism effect, using diffraction compensation in a stratified hetero-lattice photonic crystal (PhC) operating in reflective mode. Modeling the variation of the beam envelope within the hetero-lattice, an optimum eight-channel design with 20-nm wavelength spacing is feasible within 42000 μm2 of PhC area. The design results in almost diffraction-limited output beams, and provides a size reduction of 2.6 to 7 times when compared to the PhC area required in the homo-lattice SP design.

Composite superprism photonic crystal demultiplexer: analysis and design

We present the analysis and design of a superprism-based demultiplexer that employs both group and phase velocity dispersion of the photonic crystal (PhC). Simultaneous diffraction compensation and spatio-angular wavelength channel separation is realized in a slab region that divides the PhC. This avoids the excessive broadening of the beams inside the PhC and enhances the achievable angular dispersion of the conventional superprism topology. As a result, a compact demultiplexer with a relaxed requirement for low divergence input beams is attained. The dynamics of the beams envelops are considered based on the curvature of the band structure. Analysis shows at least 36-fold reduction of the PhC area and much smaller propagation length in slab compared to the preconditioned superprism, based on the same design model. PhC area scales as Δω(-2.5) with Δω being the channel spacing.