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Based on the radiation pattern of a spatial uniform magnetic current line source (UMLS) antenna, we propose a method for creating a spatial optical tube with a variable length and arbitrary orientation for a 4 π focusing system. A virtual spatial UMLS antenna situated at the foci of two high numerical aperture objectives is used to obtain the required illumination at the entrance pupil plane. Numerical results demonstrate that the length of the created optical tube is approximately equal to that of the UMLS antenna. Its orientation is consistent with that of the line source. Its polarization is pure azimuthal, and the transverse size of the optical tube shell and the dark tunnel is uniform over the entire depth of focus. This optical tube can be customized according to application requirements. The generated optical tube can be used for such applications as arbitrary orientation particle trapping and guiding, micromanipulation, and optical microscopy.

Ruby is one of the best solids for generation of slow light at room temperature. Ultraslow light propagation to ∼ 2.8 m/s has been demonstrated experimentally in ruby rod of length 7.6 cm. The systematic variation of optical delay with the modulation frequency, laser power and depth of focus has been studied. Fine tuning from ∼ 12 ms to ∼ 20 ms has been achieved by using laser power and depth of focus as a knob, at a modulation frequency of 1.8 Hz. These studies suggest that ruby rod may find potential applications in developing the tunable optical delay-based devices.

We study the optimum design of traditional integral imaging (InI) display system based on an improved view analysis. Human eyes are fully modeled and aberration of lens array is considered. We show that aperture of the elemental lens should be small enough (i.e. F-number>1.7) to prevent the optics aberration decreasing the display performance. Combining with the requirements on an InI system for reconstructing three-dimensional images with a continuous pattern, parallax, and no gap, we introduce an optimum design method aiming to enlarge the depth of focus. The feasibility of the proposed design method is demonstrated with numerical simulation. To the best of our knowledge, this is the first time that the effects of both aperture and aberration on InI performance have been quantitatively analyzed.

The halo effect is a very problematic visual artifact occurring in extended depth of focus or multi-focal ophthalmic lenses such as e.g. intra-ocular (after cataract surgery) or contact lenses when used in dark illumination conditions. This artifact is generated due to surface structures added on top of those lenses in order to increase their depth of focus or to realize multiple focal lengths. In this paper we present novel solution that can resolve this major problem of ophthalmic lenses. The proposed solution involves modification to the surface structure that realizes the extended depth of focus. Our solution is fabricated and numerically and experimentally validated also in preliminary in-vivo trials.

A longitudinally polarized optical chain is generated in a proposed 4π focusing system. The radially polarized Bessel–Gaussian incident beam is modulated by a complex amplitude filter. Their focusing performance is investigated using the Debye integral. Longitudinally polarized focusing spots with uniform intensity, high axial resolution and small spot volume are achieved in the proposed scheme. The number of the focusing spots in the optical chain is controllable by adjusting the complex amplitude filter. As an example, a longitudinally polarized optical chain with seven uniform intensity focusing spots is obtained. The volume of each focusing spot is reduced by about seven times and the axial resolution is only one-fourth of that in a single lens system with the same parameters. The influence of optical axes mismatching and foci shifting on the focusing performance is also investigated. The focusing system with the complex amplitude filter permits a large foci shifting because of the elongated depth of focus. It is expected that the research results can be used in the field of confocal microscopy, optical trapping and manipulating.

Special kinds of eye models are constructed by means of optical system design to quantitatively investigate impacts of longitudinal chromatic aberration (LCA), transverse chromatic aberration (TCA) and LCA+TCA on retina image quality and on depth of focus (DOF), as well as interaction between chromatic and higher-order aberrations. Results show that LCA plays a main role in enhancement of DOF and higher-order aberrations further increase DOF. For most of the eyes the impact of higher-order aberrations on vision is much smaller than that of LCA+TCA and the presence of LCA+TCA further reduces the impact of higher-order aberrations. The impact of LCA approximates to that of LCA+TCA, and the impact of TCA approximates to that of normal level of higher-order aberrations and is negligible.

Maskless laser direct writing lithography has been applied in the fabrication of optical elements and electric-optical devices. With the development of technology, the feature size of the elements and devices is required to reduce down to nanoscale. Increasing the numerical aperture of converging lens and shortening the laser wavelength are good methods to obtain the small spot and reduce the feature size to nanoscale, while this will cause the reduction of the depth of focus. The reduction of depth of focus will lead to some difficulties in the focusing and tracking servo controlling during the high speed laser direct writing lithography. In this work, the combination of the diffractive optical elements and the nonlinear absorption inorganic resist thin films cannot only extend the depth of focus, but also reduce the feature size of the lithographic marks down to nanoscale. By using the five-zone annular phase-only binary pupil filter as the diffractive optical elements and AgInSbTe as the nonlinear absorption inorganic resist thin film, the depth of focus cannot only extend to 7.39 times that of the focused spot, but also reduce the lithographic feature size down to 54.6 nm. The ill-effect of sidelobe on the lithography is also eliminated by the nonlinear reverse saturable absorption and the phase change threshold lithographic characteristics.

With the continuous development of the field of information technology, there has been a demand for recording mark size of optical data storage, optical imaging resolving power, and characteristic linewidth of photolithography to reach nanoscale. However, it is very difficult to realize the goal due to the optical diffraction limit restrictions. Much interest has focused on the study of optical far-field super-resolution spot by using pupil filters. However, common concerns have continued to plague super-resolving pupil filters based on either scalar diffraction theory or vector diffraction theory. These concerns include the fact that the side lobe becomes non-negligible when the central lobe is squeezed to a certain extent. Moreover, it is difficult to reduce the super-resolving spot to nanoscale. In this work, we proposed a novel method to combine the super-resolving pupil filters with nonlinear saturable absorption thin films to reduce the central spot size to nanoscale, lower the intensity ratio of side lobe to central lobe, and elongate the depth of focus or tunable tolerance distance between the superresolving spot and sample. The simulated results indicate that by using the three-zone annular binary phase filter as the super-resolving pupil filter and Sb 2 Te3 as the nonlinear saturable absorption thin films, the central spot size can be reduced to nanoscale, the side lobe intensity is squeezed to about 10% of the central lobe intensity, and the tunable tolerance distance between the super-resolving spot and the sample is about two times that of the depth of focus of the diffraction limited spot at the incident laser wavelength of 405 nm and the numerical aperture of focusing lens of 0.95. The combination of the super-resolving pupil filters with the nonlinear saturable absorption thin films is very useful for nanooptical data storage, maskless nanolithography, and nano-optical imaging. It is also easy to use in actual applications because of the operation in the far-field range.

Vectorial properties of light have significant effects on the focusing properties, especially for the case of tightly focusing, where the requirements on the ratio of the longitudinal field to the traverse fields (RLT) are different for various applications, such as particle acceleration, micronano-fabrication, fluorescent imaging, determination of three dimensional orientation of individual molecules and so on. Here, utilizing inhomogeneous polarization modulation (IPM) method, we demonstrate how to adjust the numbers of focal spots, the RLT, and the depth of focus (DOF) in terms of requirements and create successfully single or multiple focal spots with dominant transverse or longitudinal fields and small size. In terms of this method, not only the asymmetry of the focal spot for linearly polarized illumination with IPM can be obviously decreased, but also its size is the same as that of the short axis of the elliptical focusing spot for the case without IPM. Moreover, it can not only produce the focal spot with dominant transverse field, low sidelobe, and size slightly smaller than that of the radial polarization, but also can realize the identical resolutions in the transverse direction. In addition, for a focal spot with dominant transverse or longitudinal field, both the subdiffraction sizes (0.4 λ or 0.5 λ ) and the DOF of 6.92 λ are also achieved.

In Optical Coherence Tomography (OCT), both high axial and lateral resolutions are desired. While axial ( z- axis) resolution is achieved by a broadband source, lateral ( x–y axes) resolution is achieved by high NA lenses. However, high NA objectives result in decreased depth of focus (DOF). The small DOF makes it difficult to obtain single shot imaging of biological samples having large lateral dimension. In this work we incorporate special interfering phase mask allowing to extend the DOF of an OCT system and to allow imaging of samples without axial scanning.

We propose a novel system allowing remote control of the location of the extended focal depth region. This system may find applications in situations where controllable optical access to an enclosure is needed and it is desirable to minimize the movement of the focusing lens. Our scheme uses three axicons, two external ones generating a ring and an internal one producing the focal region. We present a proof of concept of this system, consisting of measurements of the longitudinal and transverse intensity distributions, for a reference configuration and one with a displaced position of the extended depth of field focus.

Imaging of small objects such as single molecules, DNA clusters and single bacterial cells is problematic not only due to the lateral resolution that is obtainable in currently existing microscopy but also, and as much fundamentally limiting, due to the lack of sufficient axial depth of focus to have the full object focused simultaneously. Extension in depth of focus is helpful also for single molecule steady state FRET measurements. In this technique it is crucial to obtain data from many well focused molecules, which are often located in different axial depths. In this paper we present the implementation of an all-optical and a real time technique of extension in the depth of focus that may be incorporated in any high NA microscope system and to be used for the above mentioned applications. We demonstrate experimentally how after the integration of special optical element in high NA 100× objective lens of a single molecule imaging microscope system, the depth of focus is significantly improved while maintaining the same lateral resolution in imaging applications of incorporated groups of molecules, DNA constructs and clusters inside bacterial cells.

A method based on double imaging is proposed for three-dimensional focus manipulation. A thin birefringent plate placed behind a focusing lens was applied to generate two foci with a separation smaller than the original DOF. Depth of focus enlargement of 227% was achieved without serious degradation in lateral resolution. Experimental results obtained by using a confocal arrangement were in good agreement with theory. Both theoretical considerations and experimental results showed that in non-paraxial case the ordinary and extraordinary foci could not be excited independently.

A defocusing exposure dose distribution model is established with the integral effect of light intensity on time taken into account for laser direct writing on a thin photoresist with total reflection substrate. Exposure dose distribution curves are established using the established model for different photoresist depths. A side slope angle is established for each defocusing amount in accordance with the exposure dose distribution curves, and so depth of focus can be estimated by simply checking to see if the maximum side slope angle with the horizontal is in the range of 80–100°. Simulation results indicate that when laser direct writing is done on a thin photoresist with total reflection substrate using a laser with wavelength equal to 442 nm and a lens with numerical aperture equal to 0.5, the depth of focus estimated using the proposed method is 1 μm, which is just 1/3 of the depth of focus estimated using the method based on intensity distribution. It is therefore concluded that it is the integral effect of light intensity on time that causes the depth of focus estimation error, and the proposed method can be used to achieve a more accurate depth of focus estimation compared to the intensity distribution based method.

We have reshaped the TEM00 beam emitted by a diode-pumped Nd-Yag laser by means of an optical homogenizer with zoom. The laser beam, first enlarged up to a size of (100 × 37.5) mm2, is homogenized and resized to a final dimension continuously adjustable from (130 × 4.5) mm2 up to (130 × 52) mm2. We measured the plateau uniformity, the root mean square fluctuation and the edge steepness of the beam according to the ISO standard definitions, showing a poor reliability of the above parameter values due to the definitions themselves, and propose an amendment to overcome this problem. We obtained a very sharp edge steepness, but the spatial coherence of the laser beam put a lower limit to the high-frequency intensity fluctuations on the plateau region of the homogenized beam. Finally, we discuss the optimum homogenizer design for spatially coherent laser beams, including the depth of focus issue.

See-through head-mounted displays, which allow to overlay virtual information over the user’s real view, suffer normally from a limited depth of focus (DOF). To overcome this problem we discuss in this paper the use of a fast oscillating, variable-focus lens in a retinal projection display. The evaluation is based on a schematic eye model and on the partial coherence simulation tool SPLAT which allows us to calculate the projected retinal images of a text target. Objective image quality criteria demonstrate that the use of an oscillating lens is promising provided that partially coherent illumination light is used. In this case, psychometric measurements reveal that the depth of focus for reading text can be extended by a factor of up to 2.2. For fully coherent and incoherent illumination, however, the retinal images suffer from structural and contrast degradation effects, respectively.

This paper presents a novel coherent head mounted display (HMD) which provides nearly accommodation-free images. It is based on a liquid crystal display (LCD) illuminated by coherent light from a laser diode which projects the LCD-image directly onto the eye’s retina. The paper describes the theoretical considerations involved in optimizing the above display for the best possible depth of focus. The theoretical analysis is verified through modulation transfer function (MTF) and readability measurements using an optical bench model of the proposed system. It is shown that the MTF-values are larger than 0.5 for eye power changes up to 5 diopters (D) and for spatial frequencies up to 32 cyc/mm. This value corresponds to the maximum resolution of today’s state of the art microdisplays used in HMD systems. In addition, text readability measurements indicated that text targets, which correspond to 15-pt-sized arial font text viewed from a distance of 50 cm, can be read for eye accommodation ranging from 0 up to 5 D. As the normal adult human eye has a range of accommodation of about 5 D, the proposed coherent display can be considered quasi-accommodation-free.

A binary (π/2−0) two-zone phase filter is proposed to optimize the optical distribution of solid immersion lens (SIL). The analysis using angular spectrum method shows that the phase filter can not only decrease the full-width at half maximum (FWHM) of the optical distribution but also increase the depth of focus of the SIL system. Furthermore, the lateral distribution profile is also optimized.

A simple analytic expression describing the field of various orders of Bessel light beams produced by an axicon is obtained. The focusing properties of an axicon are discussed. The focal length of an axicon as well as the depth of focus for various orders of Bessel beams are determined.

An optical pickup using the combination of an objective lens and a diffractive optical element for a high-density optical disk is proposed in this paper. The new system will enhance the resolution and extend the depth of focus as required in high-density compact disc (CD) pickup systems. Optimisation algorithms are used to synthesise the diffractive optical element (DOE) to meet a detailed specification of the point spread function (PSF) of the system. The theoretical simulation and experimental results show that the system produces good resolution enhancement, extended depth of focus, high diffraction efficiency and moderate sidelobe level.

We present a method for the design of a binary phase-only diffractive optical element for use in a lens, diffractive element combination. It is based on iterative optimisation of the intensity point spread function of the combination. Increase in the depth of focus and control over the sidelobe level is demonstrated. It is shown that the lens, diffractive element combination designed by this method can reproduce its favourable performance when incorporated into a typical high-resolution photolithography system, increasing depth of focus without significant undesirable proximity effects.

Faultless multi-pinhole masks are generated by a spatial filtering process using very simple intensity filters. In particular, in the case of hexagonal multi-pinhole masks, filters with only one hexagonal ring of pinholes are used yielding two interesting features of the filtered images: the depth of focus of the images is increased to centimeters, and the number of holes within the masks can very easily be increased by a factor 4 or 9.

The method to obtain an increased depth of field consists of two steps. The first step is to produce a modified incoherent image of the three dimensional object which, though degraded, has the same degradation for all object planes. The second step is to filter this modified image in a coherent image processor to obtain un undegraded image with increased depth of focus.