This PDF file contains the front matter associated with SPIE Proceedings Volume 9131 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Monte Carlo ray tracing is an important simulation tool in applications where fluorescence is present, e.g. in bio-medical applications and in the design of luminaires and luminescent solar concentrators. A frequently used ray tracing procedure for fluorescence is the ‘dual stage’ approach. In this approach, first, all sources are traced through the system and the rays absorbed in the fluorescent components are stored. Next, the emission from the fluorescent components is traced. This approach does not allow for subsequent re-absorption and re-emission effects in fluorescent materials with a spectral overlap between excitation and emission spectra. In this work, a ‘multi stage’ ray tracing procedure for the simulation of luminescence is presented. Herein, wavelengths are traced from short to long separately and no distinction is made regarding the origin of emission (either a fluorescent component or a source). The presented approach can be easily implemented in existing commercial ray tracing software thus reducing the programming efforts for the new ray tracing algorithm and taking advantage of the strength of the selected ray tracing package concerning the modelling of complex geometrical systems. Both techniques are compared to investigate the influence of the selected ray tracing approach on the efficiency and colour prediction of a remote phosphor LED module.

Luminaires are conventionally modeled using a far-field representation. To calculate this representation, a photometer revolves a light source at fixed distance and illuminances are measured in a set of angular directions. Using the inversesquare- law, the far-field intensity, also termed luminous intensity distribution is then calculated. For Lambertian sources, the far-field starts from a distance of five times the maximal dimension of a light source; which is called the limiting photometric distance. The advent of luminaires composed of LED arrays with narrow beams have shown that this limit is no longer valid and far larger distances (up to 15 times the maximal diameter) are suggested by the lighting community. This problem is even more outspoken when the individual LEDs are focused at close distance, as in e.g. surgical luminaires. To overcome these problems, we exploit the use of a near-field representation to describe an array of two narrow-beam LEDs focused at close distance. For such a test source, this paper shows how a near-field luminance goniometer is able to construct ray-data. Ray files can be used to calculate a near-field representation and far-field representation of a light source. These measurements are validated by a theoretical derivation of the intensity of an array, using a simple analytical model to describe the emission of the individual LEDs. This near-field approach makes discussions to determine the far-field photometric distance superfluous.

A Gaussian laser beam is reshaped to have specific irradiance distributions in many applications in order to ensure optimal system performance. Refractive optics are commonly used for laser beam shaping. A refractive laser beam shaper is typically formed by either two plano-aspheric lenses or by one thick lens with two aspherical surfaces. Ray mapping is a general optical design technique to design refractive beam shapers based on geometric optics. This design technique in principle allows to generate any rotational-symmetric irradiance profile, yet in literature ray mapping is mainly developed to transform a Gaussian irradiance profile to a uniform profile. For more complex profiles especially with low intensity in the inner region, like a Dark Hollow Gaussian (DHG) irradiance profile, ray mapping technique is not directly applicable in practice. In order to these complex profiles, the numerical effort of calculating the aspherical surface points and fitting a surface with sufficient accuracy increases considerably. In this work we evaluate different sampling approaches and surface fitting methods. This allows us to propose and demonstrate a comprehensive numerical approach to efficiently design refractive laser beam shapers to generate rotational-symmetric collimated beams with a complex irradiance profile. Ray tracing analysis for several complex irradiance profiles demonstrates excellent performance of the designed lenses and the versatility of our design procedure.

Obsidianus lapis is a volcanic rock that has been worked into tools for cutting or weaponry by Teotihuacan people for hundreds of years. Currently it is used in jewelry or for house decorative items such as elaborated sculptures. From the physico-chemical properties point of view, obsidianus lapis is considered a glass as its composition is 80% silicon dioxide. In México there are different kinds of obsidianus lapis according to its colour: rainbow, black, brown, red, silver, golden and snowflake. The traditional grinding process for working with obsidianus lapis includes fixed grinders and sandpaper for the polishing process, where the craftsman grinds the rock manually obtaining a variety of shapes. Laser processing of natural stones is a relatively new topic. We propose the use of an Yb^3+-doped fibre laser for cutting and ablating obsidianus lapis into spherical, rectangular and oval shapes. By means of a theoretical analysis of roughness and hardness, which affect the different surfaces and final shapes, and considering the changes in material temperature during laser interaction, this work will focus on parameter determination such as: laser fluence, incidence angle, laser average power and peak pulse energy, from the proposed Q-switched fibre laser design. Full optical, hardness and rugosity, initial and final, characterization will be included in the presentation.

We present a theoretical design study concerning compact freeform lens array for laser beam splitting. In our approach beam splitting optical element is designed as a compact element combining both functions of collimation and beam splitting into one component. Main emphasis of our paper is on the design methodology and subsequent theoretical analysis of design approach for such elements using examples of regular and irregular beam splitting elements. We use multi-parameter optimization method in conjunction with custom merit function implemented in ray-tracing software to implement our designs. In our design approach, we introduce a novel pupil sampling method based on Fibonacci grid. First, we deal with examples using regular lens arrays designed independently. Next, we evaluate some of standard and readily available freefrom surface representations that can replace usual description of lens array by compact continuous freeform surface. As a final example, we consider example design of irregular beam splitter with potential for control of power distribution between spots in focal plane. Some of designed structures are initially produced by optimization with some discontinuities that need to be removed to enforce smoothness of final design. We demonstrate application of local filtering techniques to produce smoothed versions of surfaces with discontinuities. Possible applications of similar designs are in laser fiber coupling and off-axis multi-spot generation where power splitting ratio can be arbitrarily predefined.

Optical freeform surfaces are gaining importance in different optical applications. A huge demand arises e.g. in the fields of automotive and medical engineering. Innovative systems often need high-quality and high-volume optics. Injectionmoulded polymer optics represents a cost-efficient solution. However, it has to be ensured that the tight requirements with respect to the system’s performance are met by the replicated freeform optics. To reach this goal, it is not sufficient to only characterise the manufactured optics by peak-to-valley or rms data describing a deviation from the nominal surface. Instead, optical performance of the manufactured freeform optics has to be analysed and compared with the performance of the nominal surface. This can be done by integrating the measured surface data of the manufactured freeform optics into the optical simulation model. The feedback of the measured surface data into the model allows for a simulation of the optical performance of the optical subsystem containing the real freeform optics manufactured. Hence, conclusions can be drawn as to whether the specifications with respect to e.g. imaging quality are met by the real manufactured optics. This approach will be presented using an Alvarez-Humphrey optics as an example of a tuneable optics of an ophthalmological application. The focus of this article will be on design for manufacturing the freeform optics, the integration of the measured surface data into the optical simulation model, simulation of the optical performance, and analysis in comparison to the nominal surface.

The performance of optical components is usually improved by optical coatings. Some of these optical components exhibit complex geometrical shapes and are therefore very difficult to coat in a homogeneous way. The spectral performance of the optical coatings on such substrates will vary as a function of its geometry making it very difficult to keep the spectral performance within customer specifications all over the substrate. Examples for optics with complex geometries are half sphere lenses, freeform surfaces, diffraction gratings, microlense arrays, large substrates etc. We developed a simulation tool that can calculate and optimize the spectral performance of a given multilayer stack on arbitrarily shaped optics as a function of the processing parameters of the coating plant. This tool will obviously reduce the risk and the development costs. The spectral performance of a multilayer stack is given in general by the coating design, that means by the individual layer thicknesses and the refractive indices of the different layer materials. On curved optics different coating materials exhibit different thickness and refractive index distributions. Consequently the optical layer stack will exhibit varying spectral performance at different positions on the substrate. Empirical models for thickness and refractive index distributions have been developed as a function of the most important processing parameters (e.g., deposition rate, deposition angle, ion impingement rate and temperature).

Many commercial, medical and scientific applications of the laser have been developed since its invention. Some of these applications require a specific beam irradiance distribution to ensure optimal performance. Often, it is possible to apply geometrical methods to design laser beam shapers. This common design approach is based on the ray mapping between the input plane and the output beam. Geometric ray mapping designs with two plano-aspheric lenses have been thoroughly studied in the past. Even though analytic expressions for various ray mapping functions do exist, the surface profiles of the lenses are still calculated numerically. In this work, we present an alternative novel design approach that allows direct calculation of the rotational symmetric lens profiles described by analytic functions. Starting from the example of a basic beam expander, a set of functional differential equations is derived from Fermat's principle. This formalism allows calculating the exact lens profiles described by Taylor series coefficients up to very high orders. To demonstrate the versatility of this new approach, two further cases are solved: a Gaussian to at-top irradiance beam shaping system, and a beam shaping system that generates a more complex dark-hollow Gaussian (donut-like) irradiance profile with zero intensity in the on-axis region. The presented ray tracing results confirm the high accuracy of all calculated solutions and indicate the potential of this design approach for refractive beam shaping applications.

In this work, novel imaging designs with a single freeform optical surface (either refractive or reflective) are presented. In these designs, not only the mapping is obtained in the design process, but also the shape of the object is found. In the examples considered, the image is virtual and located at infinity and is seen from known pupil, which can emulate a human eye. In the first introductory part, 2D designs and 3D designs by rotation using the differential equation method for the limit case of small pupil have been reviewed. Furthermore, the differential equation method is used to provide the freedom to control the tangential rays and sagittal rays simultaneously. In the second part, according to the study of astigmatism of different types of design with rotational symmetry, the differential equation method for 3D rotational design without astigmatism (at the small pupil limit) on a curved object surface has been extended to 3D freeform design. The result of this extended method has been proved to coincide with the former 3D design by rotation which is a special case of 3D freeform design. Finally, the initial condition has been used as an additional freedom to control the shape of the object surface. As a result, a reflective design with a much flatter object surface has been obtained.

During the last years, the average power of commercial ultra-short pulsed laser sources increased significantly. The efficient utilization of the high average laser power in the field of material processing requires an effective distribution of the laser power onto the work piece. One approach to increase the efficiency is the application of beam splitting devices to enable parallel processing. But the shaping and steering of multiple beams requires particular optical systems which are not state of the art today. Limitations for large spot arrays are evaluated and considered for the design concept of appropriate optical systems. For the purpose of micro structuring with high demands on the spatial accuracy, an optical system based on a diffractive 14×14 beam splitter (DOE) is designed and set up. All partial beams are coupled into a scanner device by using a relay lens system. Furthermore, this relay lens system offers a practicable solution to remove higher diffraction orders of the DOE. Due to the scanner a highly dynamic, simultaneous deflection of all partial laser beams can be achieved. For the alignment and the experimental evaluation of the complex optical system appropriate measurement devices are necessary. The simultaneous determination of several spot positions is realized by a camera system and adapted evaluation software. First experiments of large-area processing metal foils show promising results.

Choppers are optomechatronic devices used for the modulation of light: to attenuate or eliminate certain wavelength ranges or to generate series of laser impulses with different profiles. We have previously made a detailed study on choppers with rotating wheels with different configurations (with windows with linear and with non-linear margins) – and for different types of laser beams (i.e., top-hat, Gaussian and Bessel). In this paper we report a novel configuration of optical choppers with fast rotating elements (patent pending). The possible configurations of the device are discussed, and several chopper types are presented. The modulation functions of one of the types of choppers newly introduced (i.e., the functions of the transmitted flux) are deduced and studied with regard to the geometry of the device. Comparison with other types of choppers – classical and eclipse (the latter introduced by us) – are being made. Aspects like chop frequency, attenuation coefficient, and profile of the light impulses transmitted by the device are taken into account.

The compensation of thermal lensing in laser optics for application in the high power domain is an up-to-date topic and discussed in literature multiple times. This paper combines distinct published approaches with own contributions to enhance current methodologies for the simulation, the measurement and the compensation of thermally induced optical effects. Particularly, a thermal time constant is introduced to characterize the time until steady state is reached. Moreover, a metrological setup is described for thermal lens measurement at high power. Finally, methods for thermal lens compensation and material data acquisition are discussed on the basis of an experimental example.

Nonlinear laser processing of dielectrics with ultrafast lasers has been extensively studied over the last years and successfully applied to the production of photonics and micro-fluidic devices. Still, problems related to the presence of strong optical nonlinearities make it difficult to optimize the spatial intensity distribution in the focal region (SIDFR) in some cases. Methods providing a rapid estimate of the latter, even approximately, can be of great help for optimizing processing strategies and in other applications conditioned by nonlinear propagation like spatial soliton shaping. We have developed a numerical method for estimating the SIDFR inside a dielectric material, considering nonlinear absorption, nonlinear refraction and spherical aberration for laser beams with arbitrarily shaped wavefront. It is based on a generalized adaptive fast-Fourier evolver and has been successfully tested for flat wavefronts in subsurface processing. In this work we demonstrate its applicability to complex wavefronts, like those that can be generated with spatial light modulators (SLM). For this purpose the beam wavefront is described using Zernike polynomials before being propagated inside the material for different depths, pulse parameters. The results obtained show that under certain conditions, nonlinearities can be not only controlled and pre-compensated but also exploited for producing tailored SIDFRs.

With the catalog of 1992 SCHOTT introduced two formulae each with six parameters for a better representation of the refractive index of optical glasses. The Sellmeier-equation improved the characterization of dispersion at room temperature and the Hoffmann equation that of its temperature dependence. Better representation had been expected because both formulae were derived from general dispersion theory. The original publication of Hoffmann et al. from 1992 contains first results on the accuracy of the fits. The extended use of the formulae has led to a collection of data allowing reviewing the adequacy of the Sellmeier-equation approach on a much broader basis. We compare fitted refractive index values with measured values for all wavelengths used at our precision refractive index goniometer. Data sets are available for specific melts of the four representative glass types N-BK7, N-FK5, LF5 and IRG2. For some materials, the optical glass N-LAF21, the IR glass IRG2 and the crystal CaF2, several sets of data for the temperature dependence of the refractive index are available thus giving evidence for the variation of these properties among melts of the same material.

Light pipes are key optical components used in projection systems to transport and homogenize light from the source towards the light valve. They can provide a uniform light distribution at their output as a result of multiple internal reflections. In laser projection systems, such light pipes are useful in combination with a laser-light module consisting of one or more single-mode lasers and a rotating diffuser. The partially coherent light emanating from the rotating diffuser is transported and homogenized towards the end of the light pipe. Consequently, propagation through the light pipe will also modify the coherence properties of the laser light. In this paper, a computationally efficient simulation model is presented to propagate partially coherent light through a homogenizing rectangular light pipe. The resulting coherence function clearly differs from that of free-space propagation over the same optical path length. The implications of these results on, for example, the appearance of speckle are discussed in further detail. The simulation results are experimentally verified using a reversing wavefront Michelson interferometer. The approach described in this paper can be extended further to investigate other types of light pipes, such as tapered light pipes or even more complex ones.

Modern laser technology demands powerful numerical tools to predict the efficiency of laser configurations. Birefringence has a strong influence on the beam quality and output power of a laser amplifier. We developed a complex physical model for simulating laser amplifiers and analyzing the birefringence effects. This model includes pump configuration, thermal lensing effects, birefringence, and beam propagation in the laser amplifier. The pump configuration is simulated using a complete three-dimensional ray tracing or by an approximation based on super-Gaussian functions. For an accurate modeling of the thermal lensing effect, the deformation of the end faces and the polarization dependent index of refraction was taken into account. Temperature, deformation and stress inside the laser crystal were calculated by a three-dimensional finite element analysis (FEA). In particular, the refractive index was accurately calculated by considering its temperature dependency and the photo elastic effect. This refractive index was used in the simulation of laser beam propagation through an amplifier. These simulations were performed by a complete three-dimensional vectorial beam propagation method (VBPM). The advantage of VBPM is that it can be applied to a polarization dependent index of refraction. This is important when taking into account the birefringence obtained by the photo elastic effect inside the laser crystal. The beam propagation method is based on finite elements on block structured grids as well as a Crank-Nicolson approximation in the propagation direction (FE-BPM). Reflecting boundaries were eliminated by introducing a perfect matching layer (PML). Simulation results show that a complete three-dimensional simulation model was useful in analyzing and optimizing high power laser amplifiers. The value of our model lies in the fact that it can take into account the crystal cut direction. Based on this the birefringence for simulating the laser beam quality and output power can be calculated.

Designing a novel optical system is a nested iterative process. The optimization loop, from a starting point to final system is already mostly automated. However this loop is part of a wider loop which is not. This wider loop starts with an optical specification and ends with a manufacturability assessment. When designing a new spectrometer with emphasis on weight and cost, numerous iterations between the optical- and mechanical designer are inevitable. The optical designer must then be able to reliably produce optical designs based on new input gained from multidisciplinary studies. This paper presents a procedure that can automatically generate new starting points based on any kind of input or new constraint that might arise. These starting points can then be handed over to a generic optimization routine to make the design tasks extremely efficient. The optical designer job is then not to design optical systems, but to meta-design a procedure that produces optical systems paving the way for system level optimization. We present here this procedure and its application to the design of TROPOLITE a lightweight push broom imaging spectrometer.

TMA, or three mirror anastigmats, have already been used successfully for various space missions. In the frame of earth observation, ProbaV satellite uses 3 TMAs to cover a total 102.4° field-of-view; ground sampling distance is about 100m at the center of field-of view and 370m at the edge. For future earth observation missions, the goal would be to reach 100m spatial resolution all over the 102.4° FOV. This would require to up-scale optical specifications, thus increasing geometrical aberrations. FMA, or four mirror anastigmats, could thus be a good candidate for future missions, as a fourth mirror would allow better correction of optical aberrations. In this work, TMA and FMA have been optimized over different fields-of view. Performance limitations are then derived, which show that FMA seems promising for future missions. Radiometry aspects are discussed and preliminary tolerance analysis is carried out.

The concept of three-dimensional (3D) optical addressing based on low one-photon absorption (LOPA) microscopy is theoretically and experimentally studied in detail. The numerical calculation results show that the intensity distribution of focused light beam strongly depends on the absorption of studied materials and on the numerical aperture of employed objective lenses. Obviously, in the case of LOPA based miscroscopy, with a significant low linear absorption and tight focusing conditions, the light intensity is not affected by absorption and the focused beam shape and intensity remain almost the same everywhere inside the absorbing material. This allows to use LOPA microscopy to perform a highly resolved focusing spot in three dimensions as achieved by the two-photon absorption (TPA) technique. The theoretical calculations were then experimentally verified by focusing different light sources with different objective lenses into a Rhodamine 6G (Rh6G) solution. The experimental results show that it is impossible to realize a deep focusing inside the Rh6G solution when using a laser wavelength at 532 nm (high absorption), even if the light beam is tightly focused. In contrast, by using a light source (coherent or incoherent), emitting a wavelength located in the low absorption range of the Rh6G solution, for example, at 633 nm, the light beam can be focused deeply inside the solution, similar to the result obtained by using a pulsed laser at 1064 nm (TPA). The LOPA based microscopy presents therefore a great advantage over conventional OPA and TPA methods. Indeed, since it operates on the basis of a one-photon absorption mechanism, it does not require an expensive pulsed light source, but only a simple setup and a low-cost, low power continuous laser source, as in the case of standard OPA. It, however, allows to deal with submicrometric 3D imaging and 3D fabrication, as well as 3D data storage, with similar performances as those obtained with TPA microscopy.

In this paper we present a three dimensional numerical model, based on a Pseudo-Spectral Time Domain algo- rithm (PSTD), that simulates the propagation of light carrying an image through a scattering medium and the back propagation of the scattered light which is re ected back by a phase conjugate mirror, modelled thanks to the nonlinear optical process of three-wave-mixing. We show how the phase conjugate wave retraces the scattering path and retrieves the spatial information of the input image with a signal to noise ratio that depends on the lateral dimensions of the phase conjugate mirror and of the number of realizations cumulated. Moreover, we show that the image restoration is not precluded by the polarization change between the phase conjugate wave and the scattered light exiting the complex medium.

We present a numerical study on the spatial distribution of fluorescence and photobleaching occurring in samples subject to multi-photon excitation. We developed a simulation model and implemented a simulator program. Its quantitative predictions can help to find the optimal operating parameters (such as laser power, pulse length, pulse repetition rate) of the two-photon microscope to reach higher image quality, to reduce undesired photobleaching, and to pave the way for optimized photoswitching-based super-resolution imaging. Conversely, the simulator might also be useful when photodynamic parameters are searched for. Furthermore, such simulations can promote the evaluation of the results of other fluorescence-based techniques [e.g. fluorescence recovery after photobleaching (FRAP) measurements]. The photodynamic model of the fluorophore contains a ground state, an excited state, a triplet state, and several photobleached states; the state transitions are characterized by absorption cross sections and lifetimes. The sample is modeled as a fluorophore solution divided into cubic cells among which diffusion takes place. The illumination is simulated as a focused laser pulse train described by a pulsed Gaussian beam. As a demonstration of the capabilities of the simulator, an example is presented that reveals the spatial distribution of photon emission in the sample investigated by a two-photon microscope in the case of different laser and photobleaching parameters, assuming one-photon absorption induced photobleaching. The simulation demonstrates quantitatively how photobleaching affects the spatial distribution of fluorescence and the resolution of the microscope.

In the past decade there has been significant interest in image processing for brightfield cell microscopy. Much of the previous research on image processing for microscopy has focused on fluorescence microscopy, including cell counting, cell tracking, cell segmentation and autofocusing. Fluorescence microscopy provides functional image information that involves the use of labels in the form of chemical stains or dyes. For some applications, where the biochemical integrity of the cell is required to remain unchanged so that sensitive chemical testing can later be applied, it is necessary to avoid staining. For this reason the challenge of processing images of unstained cells has become a topic of increasing attention. These cells are often effectively transparent and appear to have a homogenous intensity profile when they are in focus. Bright field microscopy is the most universally available and most widely used form of optical microscopy and for this reason we are interested in investigating image processing of unstained cells recorded using a standard bright field microscope. In this paper we investigate the application of a range of different autofocus metrics applied to unstained bladder cancer cell lines using a standard inverted bright field microscope with microscope objectives that have high magnification and numerical aperture. We present a number of conclusions on the optimum metrics and the manner in which they should be applied for this application.

Numerical modeling Optical Coherence Tomography (OCT) systems is needed for optical setup optimization, development of new signal processing methods and assessment of impact of different physical phenomena inside the sample on OCT signal. The Monte Carlo method has been often used for modeling Optical Coherence Tomography, as it is a well established tool for simulating light propagation in scattering media. However, in this method light is modeled as a set of energy packets traveling along straight lines. This reduces accuracy of Monte Carlo calculations in case of simulating propagation of dopeds. Since such beams are commonly used in OCT systems, classical Monte Carlo algorithm need to be modified. In presented research, we have developed model of SD-OCT systems using combination of Monte Carlo and analytical methods. Our model includes properties of optical setup of OCT system, which is often omitted in other research. We present applied algorithms and comparison of simulation results with SD-OCT scans of optical phantoms. We have found that our model can be used for determination of level of OCT signal coming from scattering particles inside turbid media placed in different positions relatively to focal point of incident light beam. It may improve accuracy of simulating OCT systems.

We present an advanced simulation tool for optical time-domain reflectometry (OTDR) with the ability to incorporate any OTDR pulse shape. According to our knowledge, the proposed OTDR simulator is the first one with this feature, thus progressing beyond the existing state of the art of OTDR simulations. Starting from a mathematical formalism, we develop the numerical implementation of the simulation tool. To include the effects of the OTDR pulse shape, the optical fiber network under test is treated in our approach as a linear time-invariant single-input/single-output system. Furthermore, the limitations of current OTDR equipment such as (nonlinear) power saturation of the OTDR detector, and limited dynamic range due to detector noise are also incorporated into the simulation model. Our simulation results are experimentally verified with OTDR measurements, and we show an excellent agreement between the simulated traces and the measured traces. The advanced OTDR simulation tool has proven to correctly reproduce measured traces of systems for various pulse widths, and is thus very valuable to evaluate the usability of OTDR measurements for a certain application, without the need to run actual OTDR measurements.

In recent years, several groups have investigated the use of Proximal Spatial Light modulation (PSML) as an alternative fiber optic imaging technique. In PSLM, the light exiting the distal end of the fiber optic endoscope can be focused, without any distal micro-optics or micro-mechanics, on any point within the Field Of View (FOV) via spatial modulation of the light before it is coupled in at the endoscope’s proximal end. In previous work, we reported on the custom design of a Coherent Fiber Bundle made with soft glasses (as opposed to the commercially available optical fibers used by other groups) to be used with PSLM. In this paper we present the results of the numerical characterization of the Coherent Fiber Bundle fabricated according to our design. We investigate the CFB’s modal propagation characteristics as well as its imaging properties (FOV and point spread function). Our numerical characterization also takes into account fabrication induced defects such as variations in core size, core shape (ellipticity) and lattice constant. Realistic values for the defects were obtained via SEM images of the fabricated CFB’s cross section. We find that noise on the wave front of the field exiting the distal end of the CFB causes a much larger deterioration of the point spread function than amplitude noise. And while we find that variations in core shape have the largest impact on the CFB’s propagation characteristics, our results indicate that this negative impact could be negated if the elliptical cores were aligned along a common axis.

We propose a new and versatile design of a directional coupler able to generate and multiplex high order modes in few mode fibers. The designed device can selectively generate five high order modes and multiplex them in a few mode fiber with an overall insertion loss not exceeding 3dB at the telecommunication wavelength λ = 1550 nm. The mode dependent loss is found to be weakly dependent to the wavelength. The proposed device is very promising for high order mode multiplexing and suitable for high bit-rate optical communication systems.

Long-haul optical communications links based on space-division multiplexing use space as the final degree of multiplexing freedom, possibly exploring the modal orthogonality in a few-mode fiber (FMF). However, if conventional EDFAs are used, each mode will experience a different value of optical gain, on account of distinct field profile configurations. This lack of gain equalization imposes difficulties for mode demultiplexing and may impair the system performance. The FMF-EDFA designer should define Er doping and/or refractive index profiles, as well as the pumping configuration, to provide the best possible mode equalization of optical gain and noise figure. In the case of the FMFEDFA, the problem is involved because each mode contributes with its own set of coupled differential equations. To use this approach to carry out a rigorous optimization procedure is not feasible and typical FMF-EDFAs designs proposed in the literature are empirical. A novel optimization method is proposed here. The definition of a figure of merit related to the equalization of the pump-mode signal overlap integral significantly reduces computation time, allowing the implementation of a multiobjective optimization approach. The results obtained were validated against the solution provided by the full set of rate and propagation equations and we conducted a FMF-EDFA optimization case study. Our double-ring Er doping profile design requires a single 350 mW LP_11,p pump to provide a mean gain of 21.6 dB, within 0.6 dB of equalization for each of the four modes considered.

We present a general analytical synthesis method to design quarter-wave dielectric multilayers exhibiting reflection properties which approximate a given reflection spectrum. We show that the method can be used as a design procedure for N-band antireflection coatings. Examples confirming the effectiveness of our procedure in designing dual- and three-band antireflection coatings are illustrated.

Focusing the light onto nanostructures thanks to spherical lenses is a first step to enhance the field, and is widely used in applications needing strong light matter interactions. Nonetheless, the electromagnetic response of such nanostructures, which have subwavelength patterns, to a focused beam can not be described by classical optics. Here, we describe a formalism to efficiently compute the behavior of nanostructures under a focused beam based on an apodized decomposition on plane waves. Besides, each computation of a plane wave is done on only one period thanks to a conical B-spline modal method. Various examples illustrating the focusing are detailed, and in particular the possibility to move the focal spot and to tilt the focus beam.

The two-dimensional non-separable linear canonical transform (2D-NS-LCT) involves a significant generalization of the separable LCT (S-LCT), since it can represent orthogonal and non-orthogonal first order optical systems. Thus the availability of a discrete numerical approximation of the 2D-NS-LCT is important as it permits the modelling of a broad class of optical systems. The continuous 2D-NS-LCTs are unitary, but discretization can destroy this property. In this paper, we discuss the condition on the sampling chosen in the discretization, under which some special cases of the discrete 2D-NS-LCTs are unitary. The results presented here provide a basis for the discussion of the general condition for the discrete 2D-NS-LCT to be unitarity.

The thin element approximation is an efficient algorithm to analyze diffractive optical elements (DOEs), whose feature size is large enough compared with the working wavelength. However, the thin element approximation is only valid under the condition of normal illumination. We hereby extend an algorithm, which is called the parabasal thin element approximation, to include the non-perpendicular illumination. More specifically, the thin element approximation is valid for paraxial incident beam, while the parabasal thin element approximation is valid for parabasal beam^∗. In this article, we present the algorithm of the parabasal thin element approximation and compare the result with that of rigorous method. All the simulations are based on field tracing1 and done with the optical software VirtualLab^TM.²

We present a new numerical method for the analysis of second-harmonic generation (SHG) in one- and twodimensional (1D, 2D) diffraction gratings with arbitrary profile made of non-centrosymmetric optical materials. Our method extends the generalized source method (GSM), which is a highly efficient alternative to the conventional Fourier modal method, to quadratically nonlinear diffraction gratings. The proposed method consists of a two-stage algorithm. Initially, the electromagnetic field at the fundamental frequency is computed in order to obtain the second-harmonic polarization using the known second-order nonlinear susceptibility. Then the optical field at the second-harmonic frequency is computed using this polarization as an additional source term in the GSM. We show how to integrate this source term into the GSM framework without changing the structure of the basic algorithm. We use the proposed algorithm to investigate a doubly resonant mechanism that leads to strong enhancement of SHG in a nonlinear 2D circular GaAs grating mounted on top of a GaAs slab waveguide. We design this optical device such that slab waveguide modes at the fundamental and second-harmonic are simultaneously excited and phase matched by the grating. The numerically obtained resonance frequencies show good agreement with analytically computed resonance frequencies of the unperturbed slab waveguide.

We introduce a numerically feasible method for rigorous modeling of crossed diffraction gratings with isotropic third order nonlinear materials. The approach is based on an iterative solution of the crossed grating problem with anisotropic linear materials. Several numerical experiments are performed to demonstrate the versatility and numerical stability of our computation scheme. Resonance waveguide gratings made of isotropic cubic nonlinear materials are investigated numerically using this newly developed technique. A polarization-sensitive shift of resonance peak with variation of light intensity is numerically demonstrated.

Photopolymerizable nanoparticle-polymer composites (NPCs) have thus far shown their excellent performance in various applications, such as holographic data storage, nonlinear optics and neutron optics. Specifically, for such applications, a high spatial frequency material response is necessary, as it is the response to high spatial frequencies that determines their spatial resolution and diffraction properties. However, it is known that the spatial frequency response of a recorded hologram in multi-component photopolymers including NPCs and holographic polymer-dispersed liquid crystals exhibits a reduction in refractive index modulation at high spatial frequencies. In order to overcome this drawback, an addition of chain transfer agents (CTAs) may be useful as done for all-organic photopolymers to modify their nonlocal response and phase separation characteristics. In our work, we investigate the effect of CTAs on the spatial frequency response in NPCs. Here we employ various chain-transfer agents with three different thiol groups in a photopolymerizable ZrO₂ NPC film. A range of CTA concentration is carried out, in order to explore the most effective material combination used in the examination of spatial frequency response. The significant improvement in spatial frequency response of NPCs through the addition of a CTA with the most appropriate concentration is presented.

We report on volume holographic recording in thiol-ene based nanoparticle-polymer composites (NPCs) at a wavelength of 404 nm by using a highly coherent blue diode laser. We study the photopolymerization dynamics of two types of thiol-ene based NPCs doped with different blue-sensitive initiator/sensitizer systems (Darocur ® TPO and Irgacure ® 784/BzO₂) at various doping concentrations. We also characterize a volume holographic grating recorded in these two types of thiol-ene based NPCs. Such material characterization includes the refractive index modulation, the material recording sensitivity and polymerization shrinkage. It is shown that Darocur R _ TPO provides larger refractive index modulation and higher material recording sensitivity than those with Irgacure ® 784/BzO₂ but these two blue-sensitive initiator/sensitizer systems amount to meeting the requirements of the refractive index modulation and the material recording sensitivity for holographic data storage. However, it is found that shrinkage reduction of a volume grating recorded in these two types of thiol-ene based NPCs at 404 nm is not as effective as the same thiol-ene based NPC doped with Irgacure ® 784/BzO₂ at 532 nm.

Digital holographic microscopy is suitable for the detection of microbial particles in a rapidly flowing fluid since in this technique the focusing can be carried out as post-processing of a single captured image. This image, known as a digital hologram, contains the full complex wave front information emanating from the object which forms an interference pattern with a known reference beam. Post-processing is computationally intense and it constitutes a bottleneck for real time inspection of fast moving scenes. In the current work, GPU computation is used to accelerate the post-processing of the holographic images captured by digital holographic microscopy. Efficiency and reliability of a pre-processing step in order to eliminate low information content holographic images is also investigated.

Holographic sight was successfully recorded and observed. All necessary properties of recorded sight were confirmed. Optimal parameters for holographic sight recording were calculated. Were shown advantages of PTR glass application as a holographic medium for holographic gun sights. Obtained holograms have high visibility, diffraction efficiency, spectral selectivity and transparency.

We present a new method to calculate wavefront pre-compensation of the thermal deformation aberrations based on the finite element method (FEM) and Zernike polynomials. The thermal deformation aberrations of a plat circular Si mirror are theoretically analyzed in detail. Model of the beam path with 4 reflective mirrors and a uniform incident laser source is established. With the above model, performances of the outgoing laser with and without wavefront pre-compensation are calculated, respectively. The results show that the Strehl ratio of the outgoing laser beam is increased from 0.13 to 0.66 with wavefront pre-compensation using the new method. The influence of Fresnel number on the ability of wavefront pre-compensation was also studied. The value of SR increases to 0.83 as the Fresnel number is 257. The ability of wavefront pre-compensation is limited when the Fresnel number is small.

The slow light effect in SOAs has many applications in microwave photonics such as phase shifting and filtering. Models are needed to predict slow light in SOAs and its dependence on the bias current, optical power and modulation index. In this paper we predict the slow light characteristics of a tensile-strained SOA by using a detailed time-domain model. The model includes full band-structure based calculations of the material gain, bimolecular recombination and spontaneous emission, a carrier density rate equation and travelling wave equations for the input signal and amplified spontaneous emission. The slow light effect is caused by coherent population oscillations, whereby beating between the spectral components of an amplitude modulated lightwave causes carrier density oscillations at the beat frequency, leading to changes in the group velocity. The resulting beat signal at the SOA output after photodetection, is phase shifted relative to the SOA input beat signal. The phase shift can be adjusted by controlling the optical power and bias current. However the beat signal gain is low at low frequencies, leading to a poor beat signal output signal-to-noise ratio. If the optical input and SOA drive current are simultaneously modulated, this leads to forced population oscillations that greatly enhance the low frequency beat signal gain. The model is used to determine the improvement in gain and phase response and its dependency on the optical power, bias current and modulation index. Model predictions show good agreement with experimental trends reported in the literature.

It is common for many companies to use multiple LEDs to enhance the brightness of a LED lamp and, in general, four LEDs are used in the LED lamp systems. Moreover, the second-lens must be used to obtain a straight uniform illumination from LED lights. Where four LEDs are used, four second-lenses are also assembled conventionally and those four units of second-lenses are manufactured from a single mold and assembled together with the LEDs. However, this study introduces a new method of using the Least Square Method to get a uniform illumination with the divergence angle of 40 degrees with a new single injection molded lens. Thanks to this optical design with a single lens, the assembling process of LED lamp system was simplified by eliminating the complicated assembly procedure. Also, the uniformity of illumination of this newly designed lamp system was less than 14.1%.

The phase shifting algorithms are a widespread method in the technical and scientific literature for relatively noninvasive measurements of a variety physical variables. PSI (phase-shifting interferometry) techniques consist in acquiring at least three interferograms to obtain the wrapped phase. It is important to emphasize that if these acquired intensity images are inadequate, the measurement would have an error associated. The presence of miscalibration or mechanical vibrations in an interferogram can cause an inaccurate measurement; it is possible to design a phase shifting algorithm with a better performance. The present work proposes a novel methodology in order to determine the existence of a miscalibrated interferogram in a four steps phase shifting algorithm by applying the Radon transform.

Photopolymers are often used as a base of holographic memories displays. Recently the capacity of photopolymers to record diffractive optical elements (DOE’s) has been demonstrated. To fabricate diffractive optical elements we use a hybrid setup that is composed by three different parts: LCD, optical system and the recording material. The DOE pattern is introduced by a liquid crystal display (LCD) working in the amplitude only mode to work as a master to project optically the DOE onto the recording material. The main advantage of this display is that permit us modify the DOE automatically, we use the electronics of the video projector to send the voltage to the pixels of the LCD. The LCD is used in the amplitude-mostly modulation regime by proper orientation of the external polarizers (P); then the pattern is imaged onto the material with an increased spatial frequency (a demagnifying factor of 2) by the optical system. The use of the LCD allows us to change DOE recorded in the photopolymer without moving any mechanical part of the set-up. A diaphragm is placed in the focal plane of the relay lens so as to eliminate the diffraction orders produced by the pixelation of the LCD. It can be expected that the final pattern imaged onto the recording material will be low filtered due to the finite aperture of the imaging system and especially due to the filtering process produced by the diaphragm. In this work we analyze the effect of the visibility achieved with the LCD and the high frequency cut-off due to the diaphragm in the final DOE recorded into the photopolymer. To simulate the recording we have used the fitted values parameters obtained for PVA/AA based photopolymers and the 3 dimensional models presented in previous works.

The Wigner distribution function (WDF) has been used as a tool in wave optics for more than forty years. It is desirable to numerically simulate the WDF for a variety of situations; we argue that the reasons this is not more commonly done are the difficulty in defining the discrete transform appropriately and the size of the computation. In this paper, we examine a number of software packages freely available online, each purporting to calculate the WDF. We present results on their speed and accuracy. Optical engineers desiring to make use of the WDF in optical analysis and design will find our results useful in choosing which package to use in their simulations.

Subpixel methods increase the accuracy and efficiency of image detectors, processing units, and algorithms and provide very cost-effective systems for object tracking. A recently proposed method permits micropixel and submicropixel accuracies providing certain design constraints on the target are met. In this paper, we explore the use of Costas arrays - permutation matrices with ideal auto-ambiguity properties - for the design of such targets.

We apply two-wavelength phase shifting interferometry to generate 3D surface profile maps of spent bullet cartridge cases. From the captured interferograms, an optimized algorithm was used to calculate a phase profile from which a precise digital surface map of the cartridge casing may be produced. This 3D surface profile is used to enhance a firearms examiner's ability to uniquely identify distinct features or toolmarks imprinted on the casing when the weapon is fired. These features play a key role in the matching process of ballistic forensic examination.

Autocollimation measurement devices have very wide applications in produce of instrument, machine and metrical technology. They are used for ensuring status of details, units and planes, for the control of optical details and straightforwardness directing, and for the control of the displacement of revolving converters, in the national standard planar angle. Autocollimation methods have different errors in the most status. The main systematic error in autocollimation measurement methods is an error caused by vignetting. The analytic research of function describing this error was made. The survey considers vignetting in autocollimation systems and algorithmic methods of errors’ compensation caused by vignetting; also it's considered construction principles of the program model using computer simulation.

A novel 4 × 4 multimode interference couplers based phase-shifted photonic quantization scheme using multiwavelength mode locked pulse lasers as sampling source for all-optical analog-to-digital converter is proposed. Numerical analysis indicates that 8-bit quantization resolution operating at 40 GHz bandwidth could be achieved with an incident average optical power of 1.932 mW to each photodiode. The whole scheme can be integrated on a InP-based chip.

In article is described the method of the «angle photometric resection» and the definition of the parameters of the external orientation (spatial coordinates of the points of shooting and the angular position of the shooting plane) and his use for the optic-electronic system that determinates the position of counter-reflector.

Problems of automated hartmanogramm processing while controlling optical systems using Hartmann technique are considered. Examined a separation phase and shown algorithms elaborated for locating the spots.

To raise the speed of characterizing wafer-level LEDs, simultaneous measurement for both electrical and optical properties in parallel is a necessity. A non-imaging concentrator array is designed to concentrate as much light as possible from LEDs for optical characterization of multiple points on the wafer. For the sake of meeting the requirements between the numerical aperture of the sensing fiber and the emitting half-cone angle from a Lambertian source, a reversed angle transformer (RAT) is used in this study. The simulation is conducted using the commercial software LightTools® , based on the Monte-Carlo ray-tracing method. According to the simulation, the entrance port can collect approximately 94% of radiance from a Lambertian source, and the concentration ratio of RAT is approximately 99%. Finally a design prototype is demonstrated in this paper to validate our design.

Problems of designing of systems for virtual display systems for augmented reality placed near the observers eye (so called head worn displays) with the light guide prismatic elements are considered. Systems of augmented reality is the complex consists of the image generator (most often it’s the microdisplay with the illumination system if the display is not self-luminous), the objective which forms the display image practically in infinity and the combiner which organizes the light splitting so that an observer could see the information of the microdisplay and the surrounding environment as the background at the same time. This work deals with the system with the combiner based on the composite structure of the prism elements. In the work three cases of the prism combiner design are considered and also the results of the modeling with the optical design software are presented. In the model the question of the large pupil zone was analyzed and also the discontinuous character (mosaic structure) of the angular field in transmission of the information from the microdisplay to the observer’s eye with the prismatic structure are discussed.

The dimensional relationships in a two-components zoom lenses are obtained. Application of analytical expressions relationship between the main aberration parameters and aberration parameters of the arbitrary position components allows to make an analysis of change the value of aberrations when you change transverse magnification image in the particular case where the distance between axial object and image points is equal to zero.

In this paper, we implement a WDM-Nyquist transmission system with 12.5 GHz channel spacing generated through an Optical Flat Comb Source (OFCS). Each channel could carry one of four different modulation format as Polarization Multiplexing-Quadrature Phase Shift Keying (POLMUX-QPSK), Polarization Multiplexing-Differential Quadrature Phase Shift Keying (POLMUX-DQPSK), Polarization Multiplexing-Quadrature Amplitude Modulation based on 16 (POLMUX-16QAM) and 64 (POLMUX-64QAM) with Return-to-Zero (RZ) pulse carving and 33% duty cycle. Numerical simulations of 1 Tbit/s superchannel have been carried out, in order to evaluate the performances of the different modulation format using appropriate metrics. We discuss their back-to-back receiver sensitivity and the required Optical-to-Noise Signal Ratio (OSNR) for 3.8•10^-3 and 10^-9 Bit Error Rate (BER). We find that POLMUXQPSK has the best receiver sensitivity and the lower OSNR penalty compared to the other modulation formats. With POLMUX-QPSK sensitivity as reference, we can observe a power penalty of 13.4 dB (for a BER equal to 3.8•10^-3) for POLMUX-64QAM. In addition, we can observe an OSNR penalty of 21 dB in OSNR for POLMUX-64QAM compared to POLMUX-QPSK modulation format for a BER equal to 3.8•10^-3. However, it is important to mention that POLMUX- 64QAM presents higher Spectral Efficiency (SE). We study also the robustness of these four optical modulation formats for transmission of 1 Tbit/s in dispersion compensated WDM-Nyquist systems using two kinds of transmission fibers: SMF (Single Mode Fiber) and NZDSF (Non-Zero Dispersion Shifted Fiber). We find that POLMUX-QPSK is the suitable modulation format in dispersion compensated WDM-Nyquist systems using NZDSF fiber. We simulate the nonlinear effect tolerance by considering self-phase modulation (SPM), cross-phase modulation (XPM) and four-wave mixing (FWM) for the different modulation format. We observe that POLMUX-QPSK has the best robustness against the cited nonlinear fiber effects in NZDSF fiber.

The main advantages and disadvantages of using autoreflection and autocollimation schemes for constructing the measuring channel, which is designed to control the relative position of the elements of the optical system Space Telescope are described in this paper. Results of modeling in the Zemax software complex are given. Methods of determining the autocollimation images coordinates for calculate the error relative position of the optical system are described.

The possibility of a stigmatic and aplanatic correction of third-order aberrations in the image, which is formed by the positive lens system is showed and the conditions for such a correction are determine. The relations defining the position of the entrance pupil of a thin lens, in which the image formed in the absence of primary coma and astigmatism, was obtained.

In this paper, we consider the influence of various factors and interference invariant transformations measuring information on autoreflection schemes alignment control. Theoretical and experimental studies of an error for biprizm scheme. Shown that the main influencing factors are non-linear transformations in optical systems and the impact of the air path. Experimental studies were conducted based on two alignment control opto- electronic systems in which the control element (CE) is configured as one or two corner-cube retroreflectors.

We present numerical investigation of noise properties of lasers for telecommunication purposes with emphasis on widely used distributed feedback (DFB) lasers and its influence on multi-level modulation formats. DFB lasers can be used in optical transmitters with internal and external modulation, as well as in optical receivers employing coherent detection, where they act as local oscillator. The main noise factors influencing signal characteristics of semiconductor-based lasers are intensity and phase noise. These random impairments cause degradation of fundamental output laser characteristics such as power and phase fluctuation, which are directly related to the optical signal-to-noise ratio and the laser linewidth. In case of implementation of new modulation formats into the transmission system, these stochastic processes are of main importance and significantly impact the transmission properties of modulated signals and total performance of fiber-optic transmission systems. Throughout this paper, the noise influence on the multi-level modulation formats is evaluated by effective signal-to-noise ratio (SNR) algorithms in combination with bit-error ratio (BER) formulas for appropriate type of modulation format. The obtained results have shown that the noise of DFB laser is serious restriction for multi-level modulation formats and can be improved by higher power levels, yielding to higher SNR, as required for better values of BER.

High spatial frequencies in holographic gratings are difficult to obtain by limitations of the recording material. In this work, the results obtained after storing holographic transmission gratings with a spatial frequency of 2656 lines/mm in a material based on PVA/AA are presented. A chain transfer agent, the 4,4 '-azobis (4-cyanopentanoic acid) (ACPA) has been incorporated in the material composition to improve the spatial resolution. The concentration of the ACPA in the different compositions of the material has been modified in order to find the optimal concentration which gets obtain the maximum diffraction efficiency for high spatial frequencies.

The optical switching phenomena have been contemplated and the Mach-Zehnder interferometer (MZI) structure is used for the implementation of the optical AND gate. The cogitation of various factors such as crosstalk, extinction ratio, power imbalance and transition loss has been presented. The contemplation is carried out by simulating the proposed device with Beam propagation method and using the observed results to study the characteristics of influencing parameters in consideration with the device parameters.

Spiral laser beams is a family of laser beams that preserve the structural stability up to scale and rotate with the propagation. Properties of spiral beams are of practical interest for laser technology, medicine and biotechnology. Researchers use a spiral beams for movement and manipulation of microparticles. Spiral beams have a complicated phase distribution in cross section. This paper describes the results of analytical and computer simulation of Hermite-Gaussian beams with self-forming spiral phase distribution. In the simulation used a laser beam consisting of the sum of the two modes HG TEMnm and TEMn₁m₁. The coefficients n₁, n, m₁, m were varied. Additional phase depending from the coefficients n, m, m1, n1 imposed on the resulting beam. As a result, formed the Hermite Gaussian beam phase distribution which takes the form of a spiral in the process of distribution. For modeling was used VirtualLab 5.0 (manufacturer LightTrans GmbH).

Time-delay of transmitted pulses with respect to the incident pulse in bacteriorhodopsin films has been studied without the use of a pump beam. Based on a modified saturable absorber model, analytical expressions of the transmitted pulse have been obtained. As a result, time delay, distortion and fractional delay have been theoretically analyzed for sinusoidal pulses with a low background.

Kinoform is synthesized phase diffractive optical element which allows to reconstruct image by its illumination with plane wave. Kinoforms are used in image processing systems. For tasks of kinoform synthesis iterative methods had become wide-spread because of relatively small error of resulting intensity distribution. There are articles in which two or three iterative methods are compared but they use only one or several test images. The goal of this work is to compare iterative methods by using many test images of different types. Images were reconstructed in Fourier plane from synthesized kinoforms displayed on phase-only LCOS SLM. Quality of reconstructed images and computational resources of the methods were analyzed. For kinoform synthesis four methods were implemented in programming environment: Gerchberg-Saxton algorithm (GS), Fienup algorithm (F), adaptive-additive algorithm (AA) and Gerchberg-Saxton algorithm with weight coefficients (GSW). To compare these methods 50 test images with different characteristics were used: binary and grayscale, contour and non-contour. Resolution of images varied from 64×64 to 1024×1024. Occupancy of images ranged from 0.008 to 0.89. Quantity of phase levels of synthesized kinoforms was 256 which is equal to number of phase levels of SLM LCOS HoloEye PLUTO VIS. Under numerical testing it was found that the best quality of reconstructed images provides the AA method. The GS, F and GSW methods showed worse results but roughly similar between each other. Execution time of single iteration of the analyzed methods is minimal for the GS method. The F method provides maximum execution time. Synthesized kinoforms were optically reconstructed using phase-only LCOS SLM HoloEye PLUTO VIS. Results of optical reconstruction were compared to the numerical ones. The AA method showed slightly better results than other methods especially in case of gray-scale images.

At present time methods of optical encryption are actively developed. The majority of existing methods of optical encryption use not only light intensity distribution, easily registered with photosensors, but also its phase distribution which require application of complex holographic schemes in conjunction with spatially coherent light. This leads to complex optical schemes and low decryption quality. To eliminate these disadvantages it is possible to implement optical encryption using spatially incoherent illumination which requires registration of light intensity distribution only. However this applies new restrictions on encryption keys: Fourier spectrum amplitude distribution of encryption key should overlap Fourier spectrum amplitude distribution of image to be encrypted otherwise loss of information is unavoidable. Therefore it seems that best key should have white spectrum. On the other hand due to fact that only light intensity distribution is registered, spectra of image to be encrypted and encryption key always have peaks at zero frequency and their heights depend on corresponding total energy. Since encrypted image contains noise, ratio of its average spectrum energy to noise average energy determines signal to noise ratio of decrypted image. Therefore ratio of amplitude at zero frequency to average spectrum amplitude (RZA) of encryption key defines decrypted images quality. For generation of encryption keys with low RZA method of direct search with random trajectory (DSRT) was used. To estimate impact of key RZA on decrypted images error numerical experiments were conducted. For experiments keys with different RZA values but with same energy value were generated and used. Numerically simulated optical encryption and decryption of set of test images was conducted. Results of experiment demonstrate that application of keys with low RZA generated by DSRT method leads to up to 20% lower error in comparison to keys generated by means of uniform random distribution.

There is an increasing demand for optical elements having the functionalities of hybrid devices, such as the combination of a Fresnel lens and a diffraction grating. These new devices can be used in many applications, such as in optical spectrometers, optical precision measurement systems and diffractive optical systems for enhancing the efficiency of third generation photovoltaic solar cells. There is also a growing need for developments of a cost-effective technology to fabricate compact optical devices. Therefore the motivation of our project is to find a new model of the G-Fresnel (i.e. grating and Fresnel lens) taking into account the utilization of the electromagnetic theory for the rigorous analysis of its behavior. In this paper, a novel method is proposed and employed to design a G-Fresnel device that has only one structure layer with subwavelength features, and that focuses and separates different bands of light spectra in the same focal plane. The device performance has been studied through the use of rigorous electromagnetic theory, by using the Finite Difference Time Domain (FDTD) for the study of the near field and the Angular Spectrum Method (ASM) for the study of the propagation in the far field. The optimal design of the G-Fresnel profiles depends on the profile of the Fresnel lenses that minimize the longitude chromatic aberration, and also on the diffraction grating with high first order diffraction efficiency. The verification of the G-Fresnel model that we propose shows high diffraction efficiency and a good performance in separation for a broadband light spectrum. This promising G-Fresnel model could be used to increase the efficiency of third generation photovoltaic cells.

In this paper we investigate limits of intensity and phase modulation formats used in optical communications. Non- Return to Zero, Return to Zero, Chirped Return to Zero, Carrier-Suppressed Return to Zero, Binary Phase Shift Keying, and Quadrature Phase Shift Keying including the most actual solutions, such as Polarization Division Multiplexing Quadrature Phase-Shift Keying, are investigated in terms of spectral efficiency, Bit Error Rate to find the limits for selected topologies and spectral grids in Dense Wavelength Division Multiplexing. Differential Phase-Shift Keying and mainly Differential Quadrature Phase-Shift Keying offer improvements in Bit Error Rate and transmission reach, among others. There are practical conclusions about transition from 10 Gb•s^-1 to much higher bit rates. We study the potential increase of efficiency of Wavelength Division Multiplexing. We investigate the performance of Polarization Division Multiplexing Quadrature Phase-Shift Keying in very high speed optical systems that are promising even for terabit transmission.

In this work we numerically investigate and analyse the properties of an optical structure comprised of successive thin film layers that can possess high values of nonlinear susceptibility, affecting the refractive index and/or the absorption coefficient. By applying the Transmission Line Method (TLM), properly modified to resolve the inclusion of third order nonlinearity, the spectral reflectivity and transmission of such a device are presented. Specifically, the method is applied for the case of conceptual design of a Distributed Bragg Reflector (DBR). Optical bistability can be observed, which translates not only to a change in the value of reflectivity, as the input power increases, but also to a shift of the Bragg wavelength.

The wavefront reconstruction diagram has come to supply the need in literature of an ampler vision over the many methods and optronic devices used for the reconstruction of wavefronts and to show the existing interactions between those. A computational platform has been developed using the diagram’s orientation for the taking of decision over the best technique and the photo sensible and electronic structures to be implemented. This work will be directed to an ophthalmological application in the development of an instrument of help for the diagnosis of optical aberrations of the human eye.

In backlight modules, the light guide plate (LGP) is a key component for performance and also facilitates access to develop LGPs on its own. In this research, we propose a newly developed method: LEDs with freeform as a lighting source, are employed to integrate and manipulate the specially designed and optimized 3D-like pattern distribution of the micro features in order to obtain the required optical characteristics at maximal performance. In this research propose the concept of Light Guide Film(LGF) at the back side of Back Light Unit(BLU). This new design may induce the exterior light ,then improve the power-saving of existent BLU. Two design models are reseated: One is design for 14 inch LCD monitor of notebook computer, which might improve 21% compared to traditional one. Another is designed for 3.5 inch LCD for mobile phone display ,which might improve 15% compared to traditional one.