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To achieve a substantial retroreflection reduction accompanied with a superior anti-laser blinding property without suffering significant degradations in imaging quality, we design a novel imaging system based on the wavefront coded light-field rendering. Relevant studies have been carried out around its mechanism in both anti-laser reconnaissance and blinding. According to the Fresnel-Kirchhoff diffraction theory, the laser propagation through the composite imaging system is theoretically modeled. By comparison among the conventional, the wavefront coding, the light-field, and the composite imaging systems with different defocus parameters and phase modulation coefficients, the spot profiles and intensity distributions on both the imaging and observation planes are further studied, according to which the optimization principle is proposed. The results show that compared with the conventional one, the composite imaging system could not only increase the interference and blinding thresholds by nearly one order of magnitude but also attenuate the retroreflection peak intensity and the echo-detector receiving power by even more than one order of magnitude, achieving the superior properties of anti-laser reconnaissance and blinding.

We present a method that simultaneously increases the aperture and depth of field (DOF). A novel, to the best of our knowledge, method called lens-combined wavefront coding (WFC) is proposed for optical design. By rationally balancing rather than minimizing the aberrations, the DOF enhances instead of reduces with expansion of the aperture size. Two optical systems by traditional design and lens-combined WFC are designed to demonstrate our concept. Experiments are conducted using the manufactured lenses to show the extension of the DOF both in the laboratory and the real scene. A spatially invariant deconvolution algorithm is exploited to further suppress the aberrations regarding the field of view. The results show that the aperture and the DOF can be successfully enhanced at the same time.

The modified generalized cubic phase mask (GCPM) has recently been applied in wavefront coding systems including infrared imaging and microscopy. In this paper, the stationary phase method is employed to analyze the GCPM characteristics. The SPA of the modulation transfer function (MTF) under misfocus aberration is derived for a wavefront coding system with a GCPM. The approximation corresponds with the Fast Fourier Transform (FFT) approach. On the basis of this approximation, we compare the characteristics of GCPM and cubic phase masks (CPM). A GCPM design approach based on stationary phase approximation is presented which helps to determine the initial parameter of phase mask, significantly decreasing the computational time required for numerical simulation.

The point spread function (PSF) is a non-rotational symmetric for the wavefront coding (WFC) system with a cubic phase mask (CPM). Antireflective boundary conditions (BCs) are used to eliminate the ringing effect on the border and vibration on the edge of the image. The Kronecker product approximation is used to reduce the computation consumption. The image-formation process of the WFC system is transformed into a matrix equation. In order to save storage space, biconjugate gradient (Bi-CG) and biconjugate gradient stabilized (Bi-CGSTAB) methods are used to solve the asymmetric matrix equation, which is a typical iteration algorithm of the Krylov subspace using the two-side Lanczos process. Simulation and experimental results illustrate the efficiency of the proposed algorithm for the image deconvolution. The result based on the Bi-CGSTAB method is smoother than the classic Wiener filter, while preserving more details than the Truncated Singular Value Decomposition (TSVD) method.

We propose in this paper an introduction to the wavefront coding technique for incoherent imaging. Wavefront coding introduces image processing in the conception of an imaging system. It consists in introducing controlled aberrations in the optics able to reduce, after processing, some defaults of the optical system such as defocus, chromaticity. We present the basis of wavefront coding and illustrate them on two images with different characteristics: a spoke pattern and a galaxy image.

As the light travels through the wavefront coding (WFC) system, the modulation transfer function(MTF) of the WFC system was very low, consequently the intermediate blurred image has been received by the detector. However, there is no zero point in the passband of the MTF of the WFC imaging system, and the target information cannot be saved very well. An appropriate filter can be used to restore the sampled intermediate image. The noise of the system is enlarged in the restoration process where the signal be amplified by the filter, and the signal to noise ratio(SNR) of the image is reduced. In order to solve the above issues, an improved algorithm has been proposed in this paper. The noise is controlled by the wavelet in the reconstruction process, and the intermediate blurred image is restored by the wiener filter algorithm with a prior knowledge of the degradation function. Thus, the wavelet de-noising and wiener filter algorithm are combined to restore the middle blurred image of the WFC system. Finally, the restoration image with the diffraction limit level is acquired in image detail restoration and noise control.

In this paper, it presents a new wavefront coding (WFC) technology that we call lens-combined modulated wavefront coding (LM-WFC). Based on the LM-WFC design method, we establish a large depth of field and large aperture system. Simulation results indicate that the modulation transfer function of the system has a defocus invariant characteristic, which all typical WFC systems have, with a large depth of field. Experimental results for comparing the LM-WFC imaging system and a traditional imaging system are presented. The comparative results demonstrate that the LM-WFC system has an imaging performance invariant over a wide depth of field range.

The quality of X-ray optics on beamline is a key factor that limits the performance of the beam line to play. For X-ray mirror surface characterization with high accuracy, long trace profiler and NOM for flat or slight curved mirror have been developed. However, these two kind of instruments cannot measure the highly curved mirror since requirement of high precision and that of large range contradict each other. In this paper, we proposed a novel wavefront-coding-based surface slope metrology technique. Four-dimension information of the optics under test, including x-y position and sagittal/tangential angle, is provided. Due to the focused beam used and the high speed DMD (Digital Mirror Device), high spatial resolution of the measurement is obtained. In experiment, we demonstrated this technique by measuring bend-based high energy monochromator developed in BSRF.

Wavefront coding can extend the depth of field of traditional optical system by inserting a phase mask into the pupil plane. In this paper, the point spread function (PSF) of wavefront coding system with annular aperture are analyzed. Stationary phase method and fast Fourier transform (FFT) method are used to compute the diffraction integral respectively. The OTF invariance is analyzed for the annular aperture with cubic phase mask under different obscuration ratio. With these analysis results, a wavefront coding system using Maksutov-Cassegrain configuration is designed finally. It is an F/8.21 catadioptric system with annular aperture, and its focal length is 821mm. The strength of the cubic phase mask is optimized with user-defined operand in Zemax. The Wiener filtering algorithm is used to restore the images and the numerical simulation proves the validity of the design.

Wavefront Coding is a new method to extend the depth of field, which combines optical design and signal processing together. By using optical design software ZEMAX ,we designed a practical wavefront coded imaging system based on a conventional Cooke triplet system .Unlike conventional optical system, the wavefront of this new system is modulated by a specially designed phase mask, which makes the point spread function (PSF)of optical system not sensitive to defocus. Therefore, a series of same blurred images obtained at the image plane. In addition, the optical transfer function (OTF) of the wavefront coded imaging system is independent of focus, which is nearly constant with misfocus and has no regions of zeros. All object information can be completely recovered through digital filtering at different defocus positions. The focus invariance of MTF is selected as merit function in this design. And the coefficients of phase mask are set as optimization goals. Compared to conventional optical system, wavefront coded imaging system obtains better quality images under different object distances. Some deficiencies appear in the restored images due to the influence of digital filtering algorithm, which are also analyzed in this paper. The depth of field of the designed wavefront coded imaging system is about 28 times larger than initial optical system, while keeping higher optical power and resolution at the image plane.

Wavefront coding (WFC) is a hybrid technology designed to increase depth of field of conventional optics. The goal of our research is to apply this technology to the short-focus and ultra-wide-angle lens which suffers from the aberration related with large field of view (FOV) such as coma and astigmatism. WFC can also be used to compensate for other aberration which is sensitive to the FOV. Ultra-wide-angle lens has a little depth of focus because it has small F number and short-focus. We design a hybrid lens combing WFC with the ultra-wide-angle lens. The full FOV and relative aperture of the final design are up to170° and 1/1.8 respectively. The focal length is 2 mm. We adopt the cubic phase mask (CPM) in the design. The conventional design will have a wide variation of the point spread function (PSF) across the FOV and it is very sensitive with the variation of the FOV. The new design we obtain the PSF is nearly invariant over the whole FOV. But the result of the design also shows the little difference between the horizontal and vertical length of the PSF. We analyze that the CPM is non-symmetric phase mask and the FOV is so large, which will generate variation in the final image quality. For that reason, we apply a new method to avoid that happened. We try to make the rays incident on the CPM with small angle and decrease the deformation of the PSF. The experimental result shows the new method to optimize the CPM is fit for the ultra-wide-angle lens. The research above will be a helpful instruction to design the ultra-wide-angle lens with WFC.

Wavefront coding system can realize defocus invariance of PSF/OTF with a phase mask inserting in the pupil plane. Ideally, the derivative of the PSF/OTF with respect to defocus error should be close to zero as much as possible over the extended depth of field/focus for the wavefront coding system. In this paper, we propose an analytical expression for the computation of the derivative of PSF. With this expression, the derivative of PSF based merit function can be used in the optimization of the wavefront coding system with any type of phase mask and aberrations. Computation of the derivative of PSF using the proposed expression and FFT respectively are compared and discussed. We also demonstrate the optimization of a generic polynomial phase mask in wavefront coding system as an example.

In this work, a wavefront encoded (WFE) imaging system built using a squared cubic phase mask, designed to reduce the sensitivity of the imaging system to spherical aberration, is investigated. The proposed system allows the use of a space-invariant image restoration algorithm, which uses a single PSF, to restore intensity distribution in images suffering aberration, such as sample–induced aberration in thick tissue. This provides a computational advantage over depth-variant image restoration algorithms developed previously to address this aberration. Simulated PSFs of the proposed system are shown to change up to 25% compared to the 0 µm depth PSF (quantified by the structural similarity index) over a 100 µm depth range, while the conventional system PSFs change up to 84%. Results from experimental test-sample images show that restoration error is reduced by 29% when the proposed WFE system is used instead of the conventional system over a 30 µm depth range.

High resolution and fast dynamic visualization in 3D can be achieved by combining light sheet and wavefront coding. This results in a system that allows the light sheet to be positioned at different distances from the focus plane. By scanning the light sheet through the sample, it is possible to produce high-resolution volumetric images of living samples at unprecedented speeds.

International audience; Increasing the capture volume of visible cameras while maintaining high image resolutions, low power consumption and standard video-frame rate operation is of utmost importance for hand-free night vision goggles or embedded surveillance systems. Since such imaging systems require to operate at high aperture, their optical design has become more complex and critical. Therefore new design alternatives have to be considered. Among them, wavefront coding changes and desensitizes the modulation transfer function (MTF) of the lens by inserting a phase mask in the vicinity of the aperture stop. This smart filter is combined with an efficient image processing that ensures optimal image quality over a larger depth of field. In this paper recent advances are discussed concerning design and integration of a compact imaging system based on wavefront coding. We address the design, the integration and the characterization of a High Definition (HD) camera of large aperture (F/1.2) operating in the visible and near infrared spectral ranges, endowed with wavefront coding. Two types of phase masks (pyramidal and polynomial) have been jointly optimized with their deconvolution algorithm in order to meet the best performance along an increased range of focus distances and manufactured. Real time deconvolution processing is implemented on a Field Programmable Gate Array. It is shown that despite the high data throughput of an HD imaging chain, the level of power consumption is far below the initial specifications. We have characterized the performances with and without wavefront coding through MTF measurements and image quality assessments. A depth-of- field increase up to x2.5 has been demonstrated in accordance with the theoretical predictions.

We propose the use of two asymmetrical phase masks combined with the subtracted imaging method to enhance the signal-to-noise ratio in wavefront coding systems. This subtracted imaging technique is similar to the variable pinhole diameter in confocal microscopy. Two different phase modulations of same phase masks are employed to promote the magnitude of the optical transfer function (OTF). The ratio factor is used to control the phase variation between two phase masks. The noise of decoded images is suppressed owing to the higher magnitude of the OTF than the wavefront coding systems with a phase mask. A tangent phase mask as an example is used to demonstrate our concept. Simulated results show that the performance promotion controls noise amplification of decoded images while maintaining a depth-of-field extension.

Decoupling the illumination from the detection optics in microscopy can be achieved by combining light sheet and wavefront coding. This results in a system that allows the light sheet to produce optical sections from out of focus planes. By scanning the light sheet through the sample, it is possible to produce high-resolution volumetric images of living samples at unprecedented speeds.

Hybrid optical–digital imaging involves a combination of optical coding during image formation and digital decoding and image reconstruction. This process offers enhanced functionality beyond what is possible using conventional purely optical imaging, for example, in the fields of miniaturization, cost reduction, extended depth of field and three-dimentional imaging. This article focuses on one of the most important hybrid imaging techniques namely, wavefront coding, which was proposed principally as a means to extend the depth of field of an imaging system. A review of the theory behind wavefront coding, the manufacturing of wavefront-coding elements and various applications for which it has been proposed is provided.

In this work we explore the use of the wavefront coding technique for obtaining high resolution images of the retina of human eyes. The numerical analysis pretends to show the robustness of the technique under changes in pupil diameter and wavefront shape including intersubject and intrasubject variability, using always the same restoration filter or image decoder. The results show that it is possible to obtain high resolution images under different ocular aberrations and pupil diameters with the same decoder, opening the possibility of real time high resolution images with this low-cost and robust technique.

A focusing-free and multispectral three-dimensional endoscope based on a compact compound-eye camera is proposed. A prototype TOMBO endoscope with 3 ×2 aspherical lenses using a wavefront coding technique and a 640 ×480-pixel color imager demonstrates extended depth of field and registration of multispectral images based on an estimated depth map. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(11): 14–27, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11431

A simple graphical interpretation at the pupil of an optical system is proposed to analyse the properties of the cubic-phase wavefront-coding function. The approach explains the invariance achieved against optical defocus of wavefront coding imaging systems with simplicity and clarity. Next, an analytical approximation of the modulation-transfer function of general wavefront coding systems is derived and used, in combination with the graphical interpretation, for selecting the optimal strength of the cubic-phase encoding function.

This article describes the principle of wavefront coding (WFC) technology and the role it plays in optical system. The infrared optical system in tokamak includes three parts: (1) the combination of the concave aspheric mirror and flat mirror; (2) the Cassegrain system; (3) the relay group lenses. Because of the application of wavefront coding, the optical system is less sensitive to the change of the temperature and the depth of field is enlarged. Comparing the modulation transfer function (MTF) of the original optical system and the improved system in different temperatures, the results show that the new system can be used in a larger range of temperature. (C) 2012 Elsevier B.V. All rights reserved.

The wavefront coding technology is an effectively method for extending the depth of field. However, the phase delayed by the phase mask changes with light wavelength, and the chromatic aberration is caused by chromatic dispersion of the optical elements. The modulation transfer function (MTF) of the cubic phase mask (CPM) system is derived with considering the axial chromatic aberration and optical path difference variation with wavelength, and the wavelength behavior of CPM system is analyzed in details. We yield that the MTF is approximately wavelength invariant within a certain frequency bandwidth, and the bandwidth is nearly inverse proportional to wavelength and varies with axial chromatic aberration. The effect induced by dispersion of the CPM material is very weak. If the CPM system is illuminated by wideband spectral light and the ACA exists, then the frequency bandwidth may become narrower than the monochromatic case, and the position of image sensor can be relocated to balance frequency bandwidth among all wavelengths.

The wavefront coding technique is used to enlarge the depth of field (DOF) of incoherent imaging systems.The key to wavefront coding lies in the design of suitable phase masks. To date, numerous kinds of phase masks are proposed. However, further understanding is needed regarding phase mask with its phase function being in a standard sinusoidal form. Therefore, the characteristics of such a phase mask are studied in this letter. Deriving the defocused optical transfer function (OTF) analytically proves that the standard sinusoidal phase mask is effective in extending the DOF, and actual experiments confirm the numerical results. At the same time, with the Fisher information as a criterion, the standard sinusoidal phase mask shows a higher tolerance to focus errors (especially severe focus errors) than the classical cubic phase mask.

Wavefront coding system is a new type of optical-digital two-step imaging system.The cubic phase mask is used to get asymmetric point spread function and the intermediate blurred image which nearly the same in a considerable depth of field.Combined with spatial domain optical imaging modeland kronecker product,an image restoration algorithm which based on the Bi-CGSTAB(BiConjugate Gradient Stabilized) and antireflective boundary conditions was used in the digital decoding part of the wavefront coding system.This algorithm have advantages such as small computing amount,high computing speed and nearly no boundary effect.The new algorithm was optimized and transplanted with the characteristics of parallel computing for the platform of TMS320DM642.The whole platform consists of image capture module,image display module and external memory module.By a specially designed optical system,the experiment imaging the human and object with the object distance of 1 m,5 m and 10 m.From the experimental result of middle blurred images,the effect of this new algorithm on the platform of TMS320DM642 is good,and it gives the possibility to realization of the truly portable and practical of the wavefront coding system.

Iris recognition has gained increasing popularity over the last few decades; however, the stand-off distance in a conventional iris recognition system is too short, which limits its application. In this paper, we propose a novel hardware–software hybrid method to increase the stand-off distance in an iris recognition system. When designing the system hardware, we use an optimized wavefront coding technique to extend the depth of field. To compensate for the blurring of the image caused by wavefront coding, on the software side, the proposed system uses a local patch-based super-resolution method to restore the blurred image to its clear version. The collaborative effect of the new hardware design and software post-processing showed great potential in our experiment. The experimental results showed that such improvement cannot be achieved by using a hardware-or software-only design. The proposed system can increase the capture volume of a conventional iris recognition system by three times and maintain the system’s high recognition rate.

Certain optical aberrations of imaging systems yield low resolution images. Wavefront coding has proven to minimise this problem by means of hybrid optical-digital imaging systems. The optical part usually involves a phase plate described in terms of cubic polynomials whose shape is a linear combination of ( x 3 + y 3 ) and ( x 2 y + xy 2 ). Optimization is achieved by seeking the most appropriate linear combination with respect to the optical system's constraints. Here, we propose the shape of two pairs of phase plates such that by means of relative rotations they allow for variation of the linear combination of the cubic terms. This will enable adaptive optimization of the cubic phase to the optical system's constraints when these vary in time. Results will be illustrated with numerical simulations.

Wavefront coding is a technique that makes use of aspheric phase masks and image processing to greatly increase the depth of focus and/or reduce the cost of imaging systems. The phase mask adds a controlled amount of aberrations to the optical system in such a way that invariant imaging properties are achieved over a wide range of defocus. When aspheric phase plates are fabricated, their shape has to be carefully designed to avoid introducing other aberrations into the optical system, which could reduce its performance. In this work, we will show how inherent spherical aberration for trefoil-shaped phase plates reduces the quality of color images. Results will be illustrated with numerical simulations. We will show that a fourth-order polynomial added to a trefoil shaped phase mask can avoid the plate generating undesired spherical aberration that will affect the final quality of the decoded color images.

A method for optimizing the strength of a parametric phase mask for a wavefront coding imaging system is presented. The method is based on an optimization process that minimizes a proposed merit function. The goal is to achieve modulation transfer function invariance while quantitatively maintaining final image fidelity. A parametric filter that copes with the noise present in the captured images is used to obtain the final images, and this filter is optimized. The whole process results in optimum phase mask strength and optimal parameters for the restoration filter. The results for a particular optical system are presented and tested experimentally in the laboratory. The experimental results show good agreement with the simulations, indicating that the procedure is useful.

A wavefront-coded imaging system employing a spatial light modulator (SLM) for the agile implementation of phase masks is presented. The SLM is a liquid crystal display that can be modulated to implement cubic phase masks of variable coding strength. These phase masks produce broad point spread functions insensitive to defocus aberration and are used in combination with post-detection digital image processing to extend the depth-of-field of an imaging system. A detailed description of the calibration process of the SLM in phase mode is presented together with experimental results which include wavefront-coded modulation transfer functions and increased depth-of-field images. The most interesting feature is the versatility provided by the imaging system, as compared to conventional (fixed phase mask) designs, and the agility in which it is done.

Iris recognition can offer high-accuracy person recognition, particularly when the acquired iris image is well focused. However, in some practical scenarios, user cooperation may not be sufficient to acquire iris images in focus; therefore, iris recognition using camera systems with a large depth of field is very desirable. One approach to achieve extended depth of field is to use a wavefront-coding system as proposed by Dowski and Cathey, which uses a phase modulation mask. The conventional approach when using a camera system with such a phase mask is to restore the raw images acquired from the camera before feeding them into the iris recognition module. In this paper, we investigate the feasibility of skipping the image restoration step with minimal degradation in recognition performance while still increasing the depth of field of the whole system compared to an imaging system without a phase mask. By using a simulated wavefront-coded imagery, we present the results of two different iris recognition algorithms, namely, Daugman's iriscode and correlation-filter-based iris recognition, using more than 1000 iris images taken from the iris challenge evaluation database. We carefully study the effect of an off-the-shelf phase mask on iris segmentation and iris matching, and finally, to better enable the use of unrestored wavefront-coded images, we design a custom phase mask by formulating an optimization problem. Our results suggest that, in exchange for some degradation in recognition performance at the best focus, we can increase the depth of field by a factor of about four (over a conventional camera system without a phase mask) by carefully designing the phase masks.

The development of nanoscale single-molecule localization and tracking technology for multiple bio-molecules in intact cells has important significance for studying the dynamic process in life process. Since most of cells are several microns in depth, but the focal depth of traditional optical microscopes are less than one micron, the limited depth of field is the main drawback of conventional single molecular localization microscopy that prevents observation and tracking of multiple molecules in intact cells. In this paper, based on the wavefront coding technique, a new type of holographic phase plate with high efficiency is proposed and designed to extend the depth of field of single molecular localization microscopy, which combines the distorted multi-value pure-phase grating (DMVPPG) with the double-helix point spread function (DH-PSF). The DMVPPG can be used to realize multiplane imaging of several tens of layers of a sample in a single detection plane. And the DH-PSF is an engineered point spread function which encodes the lateral and axial position with high precision of a molecule in the center of its two lobes and the angle between them respectively. Using the combined holographic phase plate, the molecules in dozens layers of a whole cell can be simultaneously imaged on the same detection plane with DH-PSF. Not only can the axial resolving power be improved, but the imaging depth can also be extended without scanning. Adding such a holographic phase plate to the imaging path, the limited imaging depth problem in single-molecule-localization microscopy can be solved without sacrificing the localization accuracy. The proposed new type of holographic phase plate can also be implemented with a spatial light modulator. In the following numerical simulation experiments, the designed holographic phase plate is composed of 600×600 pixels with a pixel size of 10 μm. The distance between two adjacent focal planes is designed to be 0.5 μm. Such a holographic phase plate is placed on the Fourier transform plane of the detection light path. When an emitter is located on the focal plane, it can be imaged as two lobes without rotation in a center area of the field of view. If an emitter is -6 μm away from the focal plane, the DH-PSF appears in the upper-left area of the field of view. Simulation results demonstrate that a total of 25 sample layers can be simultaneously imaged on the single detection plane and the 12 μm detection range can be achieved, thus proving the feasibility of this method.

We propose a novel optical design method for small F/number (F/#) compact camera module using wavefront coding. Decreasing the F/# decreases the focus depth of the optical system, which can result in manufacturing tolerances so tight that fabrication is impossible. To obtain reasonable tolerances for easy fabrication and alignment of compact camera module, we designed the final imaging system to have a target wavefront with an extended focus depth. Because additional optical elements, such as phase plates, are not available for compact camera modules, target wavefront should be the combination of the wavefront errors of all lenses in the optical system. Wavefront-coded compact camera modules have higher tolerances and an extended focus depth, so that the images obtained from them have high resolution over a broad defocus range. Images simulated by a wavefront-coded optical system can be restored to much higher resolution using deconvolution of images and a point spread function given by the coded target wavefront.

The analyses of the imaging performance of the wavefront coding system are always based on the Fourier optics. In this paper, geometrical optics is used to analyze the imaging characteristics of arbitrary phase mask in the wavefront coding system. The characteristics of the spot diagrams created by odd and even symmetrical phase masks, including the size, upper and lower boundaries, ray structure, and the stability, are analyzed by the ray aberration theory. These characteristics are also compared with those obtained by Fourier optics, and the two sets of characteristics are proved to be consistent with each other quite well.

By applying the wavefront coding technique to an optical system, the depth of focus can be greatly increased. Several complicated methods, such as Fisher Information on based method, have already been taken to optimize for the best pupil phase mask in ideal condition. Here one simple point spread function (PSF) based method with only the standard deviation method used to evaluate the PSF stability over the depth of focus is taken to optimize for the best coefficients of pupil phase mask in practical optical systems. Results of imaging simulations for optical systems with and without pupil phase mask are presented, and the sharpness of image is calculated for comparison. The optimized results showed better and much more stable imaging quality over the original system without changing the position of the image plane.

Artefacts and noise degrade the decoded image of a wavefront coding infrared imaging system, which usually results in the decoded image being inferior to the in-focus infrared image of a conventional infrared imaging system. The previous letter showed that the decoded image fell behind the in-focus infrared image. For comparison, a bar target experiment at temperature of ﹢20°C and two groups of outdoor experiments at temperatures of ﹢28°C and ﹢70°C are respectively conducted. Experimental results prove that a wavefront coding infrared imaging system can achieve the decoded image being approximating to its corresponding in-focus infrared image.

The cubic phase mask is known to cause significant changes of point spread function (PSF) as the angle of view increases. view. Instead of the conventional on-axis PSF in the best focal plane, we utilized the arithmetic-average of PSFs at various angles of view to generate the deconvolution filter for wavefront coding, and confirmed that the effective angle of view was successfully expanded about 1.6 times than conventional.

Wavefront coding[1] is the most commonly used method of extending the depth of field (DOF). In this method, the DOF is extended by phase modulation of the pupil function using a cubic phase mask and digital processing using a deconvolution filter. We propose a new aperture for the system that extends the DOF and suppresses artifacts.

We achieved a significant extension of the depth of field for a laser-scanning barcode reader by wavefront coding with a cubic phase mask. If the present method is adopted in a laser-scanning barcode reader, a decrease in the frequency of reading failure is expected.

Imaging samples with a depth in excess of the depth of field of the objective poses a serious challenge in microscopy. The available techniques such as focus-stacking accomplish the task; however, besides necessitating complicated optical and mechanical arrangements, these techniques often exhibit very long acquisition times. As a result, their applicability is limited to static samples. We describe a simple and practical hybrid 3D imaging technique which permits the acquisition of 3D images in a single snapshot. Additionally, the proposed method solves the post-recovery artefact formation problem which plagues hybrid imaging systems; thus, enabling high-quality, artefact-free images to be obtained. Experimental results indicate that this method can yield an image quality comparable to that given by a focus-stack (which can require up to a few hundred snapshots) from a single snapshot.

While the performance of optical imaging systems is fundamentally limited by diffraction, the design and manufacture of practical systems is intricately associated with the control of optical aberrations. The fundamental Shannon limit for the number of resolvable pixels by an optical aperture is generally therefore not achieved due to the presence of off-axis aberrations or large detector pixels. We report how co-called computational-imaging (CI) techniques can enable an increase in imaging performance using more compact optical systems than are achievable with traditional optical design. We report how discontinuous lens elements, either near the pupil or close to the detector, yield complex and spatially variant PSFs that nevertheless provide enhanced transmission of information via the detector to enable imaging systems that are many times shorter and lighter than equivalent traditional imaging systems. Computational imaging has been made possible and attractive with the trend for advanced manufacturing of aspheric, asymmetric lens shapes at lower cost and by the exploitation of low-cost, high-performance digital computation. The continuation of these trends will continue to increase the importance of computational imaging.

Wavefront coding, a technique of optical-digital hybrid image, can be used to extend the depth of the field. However, it sacrifices the signal-to-noise ratio (SNR) of system at a certain degree, especially on focus situation. The on-focus modulation transfer function (MTF) of wavefront coding system is much lower than that of generally traditional optical system. And the noise will be amplified in the digital image processing. This paper analyzes characteristics of the SNR of the wavefront coding system in the frequency domain and calculates the rate of noise amplification in the digital processing. It also explains the influence of the image detector noise severely reducing the restored quality of images. In order to reduce noise amplification in the process of image restoration, we propose a modified wiener filter which is more suitable for restoration in consideration of noise suppression. The simulation experiment demonstrates that the modified wiener filter, compared with traditional wiener filter, has much better performance for wavefront coding system and the restored images having much higher SNR in the whole depth of the field.

A novel method for broadband imaging of using a diffractive photon sieves is proposed and experimentally demonstrated. Unlike conventional photon sieves imaging in which clear imaging is only valid at a single designed wavelength due to the strong wavelength-dependent nature of diffractive elements, broadband photon sieves imaging is implemented with wavefront coding of a simple cubic phase mask without complicated optical system to compensate large chromatic aberration. Experimental validation was performed using an UV-lithography fabricated photon sieves of a focal length of 500mm and a diameter of 50mm at designed wavelength 632.8nm and a diamond-turning fabricated cubic phase mask of a phase parameter α=20π. Results show that extension of the working bandwidth of the proposed photon sieves imaging system is at least 88 times that of a conventional one with almost the same optical resolution and much increased energy efficiency. The proposed method suggests a new concept of extending the applications of photon sieves to work in a broadband wavelength range with a simple method in contrast to conventionally work at a single wavelength only.