Search

We present a low-cost terahertz wave plate based on form birefringence fabricated using ordinary paper. Measurements of the transfer function of the wave plate between polarizers closely agree with predictions based on the measured complex indices of refraction of the effective medium. For the design frequency, the dependence on wave plate angle also agrees with theory.

In situ ablation of thin metal films on fused silica substrates by picosecond class lasers was investigated as a method of characterizing the beam at the sample plane. The technique involved plotting the areas enclosed by constant fluence contours identified in optical microscope images of the ablation sites versus the logs of the pulse energies. Inconel films on commercially available neutral density filters as well as magnetron sputtered gold films were used. It was also shown that this technique could be used to calibrate real-time beam profile diagnostics against the beam at the sample plane. The contours were shown to correspond to the boundary where part or all of the film was ablated.

Segment-edges for extremely large telescopes are critical for observations requiring high contrast and SNR, e.g. detecting exo-planets. In parallel, industrial requirements for edge-control are emerging in several applications. This paper reports on a new approach, where edges are controlled throughout polishing of the entire surface of a part, which has been pre-machined to its final external dimensions. The method deploys compliant bonnets delivering influence functions of variable diameter, complemented by small pitch tools sized to accommodate aspheric mis-fit. We describe results on witness hexagons in preparation for full size prototype segments for the European Extremely Large Telescope, and comment on wider applications of the technology.

The measurement of the bonded area of pulp fibers has been an unsolved issue in paper science for more than 40 years. By the use of an established pulp fiber model, and a 4 × 4 transfer matrix formalism we simulated the optical behavior of pulp fibers in a modified imaging ellipsometer, and we demonstrate that there are rather strong symmetries in the ellipsometric angles Ψ and Δ when comparing single fibers, unbonded fiber crossings, and fiber-fiber bonds. Based on these symmetries we propose and test an algorithm that allows to distinguish the three cases (single fibers, unbonded fiber crossings, and fiber-fiber bonds) in the analysis of ellipsometric data.

International audience; We show that conventional paper can be cut using a 1W laser diode, provided the cutting lines are first traced using a proper ink. The ink should absorb the laser light, and penetrate deep into the paper. An " invisible ink " that is transparent in the visible range and absorbing in the infrared has been successfully tested. The paper is tidily cut. The laser power required to cut the paper is proportional to the displacement speed of the paper. Cutting speeds exceeding 3 cm.s-1 .W-1 have been demonstrated. At higher speeds, the paper is not cut through, but easy-tearable lines and easy-folding lines are obtained. The whole inking and laser cutting process may be integrated into next generations of personal inkjet printers and expand document creation abilities.

A long plasma channel, formed due to the dynamic balance between the nonlinear self-focusing and the plasma defocusing in the propagation of intense femtosecond laser pulses in air, is demonstrated to be able to continuously propel a paper airplane without complicated focusing optics. The maximum coupling coefficient generated by the plasma channel is found to be more than 8.5 dyne/W. In the plasma channel, the detonation wave generation with the air ionization is found to be the propulsive source.

High detector efficiency has broad appeal and includes such diverse fields as quantum optics and solar energy. An optical resonator can improve detector efficiency by employing multiple re-reflections to the detector. This short paper uses geometric ray tracing to examine-for a given entry port size-the probability that a photon will escape from an ideal perfectly reflective two-dimensional cavity.

Graphene and its derivative graphene oxide (GO) have been the focus of attention in the field of chemical and biological sensing. In this paper, we report a fiber-optic sensor for chemical gas sensing by using graphene oxide coated microfiber knot resonator (GMKR). The refractive index of GO was changed when the gas molecules were adsorbed to the surface of GO, and the gas concentration varying induced refractive index change can be detected by measuring the interference fringes shift of the GMKR. The experimental results show the sensitivities of ~0.35pm/ppm for NH3 and ~0.17pm/ppm for CO detection, due to the different adsorption energy and charge transfer ability between the gas molecules and GO. Experimental results show GO is a promising candidate for gas sensing and can be combined with various fiber-optic devices due to the easy transfer process.

Chemical modification of the graphene is emerging as a promising approach in producing graphene devices for electronics and nano/biotechnology applications. The electronic and chemical properties of graphene can be modified by Diels-Alder chemistry via formation of sp3 centers on the graphene lattice. Here we develop an approach of creating –COOH functional groups on CVD graphene using Diels-Alder reaction with hydrolysis. Conventionally, –COOH functional groups on graphene was often created using graphene oxide. In our approach, we functionalized a CVD graphene sheet and –COOH groups can be conjugated to fluorophores and proteins. This allows visualization of a graphene layer and estimation of functional group density using XPS with efficiency and convenience.

A comparative research on the near infrared performance of three kinds of widely used graphene saturable absorbers, namely, graphene polymer composite films, neat graphene films and graphene dispersions, was performed by using Z-scan technique with 340 fs pulses at 1030 nm. The polymer films and graphene films were fabricated through solution cast method and vacuum filtration technique based on the liquid-phase exfoliated graphene dispersions, respectively. The polymer films reveal the best saturable absorption (SA) response and the lowest saturation intensity Is, in comparison with the neat films and dispersions. The graphene films show the largest SA coefficient and figure of merit due to its highest linear absorption coefficient and refractive index. By employing slow SA modeling, the excited state and ground state absorption cross sections were estimated to be ~10−17 cm2, and the ratio were 0.61, 0.57 and 0.71 for the dispersions, polymer films and neat films, respectively.

The dense packing of two dimensional flakes by van der Waals forces has enabled the creation of new metamaterials with desirable optical properties. Here we assemble graphene oxide sheets into a three dimensional metamaterial using a microfluidic technique and confirm their ordering via measurements of ellipsometric parameters, polarized optical microscopy, polarized transmission spectroscopy, infrared spectroscopy and scanning electron microscopy. We show that the produced metamaterials demonstrate strong in-plane optical anisotropy (Δn≈0.3 at n≈1.5-1.8) combined with low absorption (k

We studied the optimization of common-path optical coherence tomography (CP OCT) sensitivity through an angled fiber probe. The magnitude of reference power derived from the tip of the fiber was optimized through careful selection of the polishing angle. We experimentally measured the signal-to-noise ratio (SNR) at different polishing angles to validate the effectiveness of this technique. We also obtained OCT images with the reference optimized CP OCT with more than 8 dB improvement in SNR.

The polarization state of infrared emission from water at large viewing angles is explained mathematically by a polarization-dependent emissivity. To provide polarized emissivity values for a wind-roughened water surface in a convenient format, this electronic paper provides interactive tables and plots of polarized water emissivity for the spectral range of 3-15 microm. The rough surface is modeled as a collection of specular facets with slopes given by a Gaussian distribution. The interactive electronic format provides a tutorial on emission polarization and it allows readers to copy the desired numbers and paste them into their electronic applications without the difficulty of transcribing numbers from printed tables.

We show that reflectivity measurements enable the determination of the thickness of multilayered graphene on a metal substrate. The developed technique is based on comparison of the substrate reflectance with and without graphene and relies on the strong absorbance of graphene and high refractive index contrast. We demonstrate the technique by measuring the thickness of the CVD graphene film grown on a copper substrate.

We report a graphene-based transparent conductive electrode for use in ultraviolet (UV) GaN light emitting diodes (LEDs). A few-layer graphene (FLG) layer was mechanically deposited. UV light at a peak wavelength of 368 nm was successfully emitted by the FLG layer as transparent contact to p-GaN. The emission of UV light through the thin graphene layer was brighter than through the thick graphene layer. The thickness of the graphene layer was characterized by micro-Raman spectroscopy. Our results indicate that this novel graphene-based transparent conductive electrode holds great promise for use in UV optoelectronics for which conventional ITO is less transparent than graphene.

Glare and visual discomfort are important factors that should be taken into account in illumination design. Conventional freeform lenses offer perfect control over the outgoing intensity distribution, thereby allowing optical radiation patterns with sharp cut-offs in order to optimize the unified glare rating index. However, these freeform lenses do not offer control over the near-field luminance distribution. Observing the emitted light distribution from a high-brightness LED through a freeform lens gives a high peak luminance that can result in glare. To reduce this peak luminance, freeform lenses should be used in conjunction with light diffusing structures. However, this diminishes the control over the outgoing intensity distribution what is the main benefit of a freeform lens. Another approach to reduce the observed peak luminance, is by spreading the emitted light over multiple optical channels via freeform lens arrays. This paper proposes a novel method to design luminance spreading freeform lens arrays that offer perfect control over the resulting intensity pattern. The method is based on a non-invertible mapping of a 2D parameter space. This results in a source-target mapping in which multiple ingoing ray directions are mapped onto every position of the target distribution. The case of continuous and discontinuous mappings are both discussed in this paper. Finally, the example of a discontinuous freeform lens array with 7x 7 individual lenses is designed and experimentally demonstrated. ispartof: Optics Express vol:27 issue:23 pages:32994-33004 ispartof: location:United States status: published

A novel architecture of a visible light communication (VLC) network that can provide bidirectional transmission for multiple users is proposed in this paper. Multiple users can exchange data asynchronously and simultaneously thanks to the use of analog network coding (ANC) and optical code division multiple access (OCDMA) with the support of a coordinator, which plays a role as a relay node. We derive the mathematical expressions for bit error rate (BER) and network throughput of an indoor VLC network with multiple users located in a room and one coordinator mounted on the ceiling. Many physical layer impairments are considered in our analysis, including shot noise, thermal noise, multiuser interference (MUI), and optical beat noise. BER and throughput performance are investigated versus the transmitted optical power, the number of users, and the VLC transceiver’s parameters. The numerical results obtained in this paper will provide useful information for designing the indoor multiuser VLC networks.

The ability of optical whispering gallery mode (WGM) resonators to store energy in a very small volume for a long time enables their use in practical applications as low-threshold lasers, high-sensitivity sensors, and tunable add-drop filters. In this paper, we express in detail the tapered fiber asymmetric coupling mechanism to multimode microsphere resonators in order to selectively excite or collect WGMs. It is shown that due to the close effective refractive indices of degenerate spherical WGMs, depending on the amount of phase matching and overlap of fiber and resonator modes, a combination of WGMs with certain intrinsic losses is excited. By precisely designing the taper dimensions, critical coupling to one or a group of modes can be satisfied. This paper provides a general figure of merit for designing taper-coupled microresonators that can be employed in nonlinear optics and lasers in which the intra-cavity field distribution determines the characteristics of the device.

In a previous paper by Cebrian et al. [Opt. Eng.53, 092006 (2014)OPEGAR0091-328610.1117/1.OE.53.9.092006], the knife-edge interferometer (KEI) was used for testing lenses with a collimated beam illuminating the lens. In this paper, a 2f scheme is used to test lenses, eliminating the use of a collimation beam, and testing, for the first time, concave reflecting (spherical and parabolic) surfaces at the center of curvature with KEI.

This paper presents a method to design a monolithic complete-light modulator (MCLM) that fully controls the amplitude, phase, and polarization of incident light. The MCLM is made of birefringent materials that provide different refractive indices to orthogonal eigen-polarizations, the ordinary o and extraordinary e states. We propose an optimization method to calculate the two relief depth distributions for the two eigen-polarizations. Also, a merging algorithm is proposed to combine the two relief depth distributions into one. The corresponding simulations were carried out in this work and the desired light distribution, including information on amplitude, phase, and four polarization states, was obtained when a laser beam passed through a 16-depth-level micro-structure whose feature size is 8 μm. The structure was fabricated by common photolithography. An experimental optical system was also set up to test the optical effects and performances of the MCLM. The experimental performance of the MCLM agrees with the simulation results, which verifies the validity of the algorithms we propose in this paper.

An optical-see-through augmented reality (AR) system assists our daily work by augmenting our sense with computer-generated information. Two of optical challenges of AR are image registration and vision correction due to fixed optical properties of the optical elements of AR systems. In this paper, we demonstrated an AR system with optical zoom function as well as a function of image registration via two LC lenses in order to help people see better by magnifying the virtual image and adjusting the location of virtual image. The operating principles are introduced, and experiments are performed. The concept demonstrated in this paper could be further extended to other electro-optical devices as long as the devices exhibit the capability of phase modulations.

Three of the headings of Table 1, which have been switched by mistake in our paper, are corrected here. The rest of the paper, including all results and conclusions, remain intact.

The photovoltaic-thermoelectric (PV-TE) hybrid system can achieve full-spectrum utilization of the solar spectrum, but surface reflection has always been an important reason to suppress its power conversion efficiency. Therefore, a novel composite nanostructure (CN) is proposed by the finite-difference time-domain (FDTD) simulation method to reduce the surface reflection in the spectral range of 0.3-2.5 μm, which consists of a pyramid and grating structure. For the sake of generality, this paper studies the spectral reflectance of the CN under multiple parameters. The results show that the CN integrated pyramid and grating correspond to excellent anti-reflection performance in the short wavelength range and long wavelength range, respectively, compared to a unitary structure, achieving anti-reflection in the full spectral range. In addition, the CN expresses the insensitivity to the structural parameters, and has lower reflectivity compared with a commercial battery. The mechanism for achieving this full-spectrum anti-reflection is mainly to enhance the path of light in the medium to enhance absorption and achieve high transmission under the action of the waveguide. This paper implements ultra-broadband anti-reflection of a compound nanostructure for full-spectrum utilization of solar energy, and provides a solution to improve the power conversion efficiency of PV-TE hybrid systems.

Due to the interference of excitation lights and the perturbation of spattered particles, it is very difficult to detect the real-time evolution of ceramics damaged by pulsed laser. In this paper, a metrology "on-line detection of damage identification via the polarization spectrum imaging" is proposed to realize the real-time observation for damage evolution of ceramic composite irradiated by the laser. In this metrology, the detection principle is based on a mathematical model of polarization bidirectional reflectance distribution function. According to the Stokes vector analysis method, the damage law of the material surface under the continuous activating illuminations of multiple laser pulses and the increase of pulse energy is theoretically deduced and analyzed first, then the measured polarization spectra are compared with the microscopic imaging method to extract the edge texture information, and further the damage details are characterized with this metrology under the typical polarization parameters: I, Q, U, V, DOP and AOP. As a result, the damaging degree of ceramic composite irradiated by the 1064nm nanosecond pulsed laser, which is changed from the pulse power of 155.54 mJ and 14 pulses to 217.94 mJ and 1 pulse, can be identified with a series of polarization parameters in the different polarization spectrum images. These polarization parameters and their derived results reflect the physical and chemical evolutive properties including of texture orientation of the target surface that is different from other methods of damage detection. Finally, it can be concluded that this paper provides a new method for real-time detection of laser damage and lays a foundation for detection and identification under other strong light interference.

The pistons of sparse aperture systems need to be controlled within a fraction of a wavelength for the system's optimal imaging performance. In this paper, we demonstrate that deep learning is capable of performing piston sensing with a single wide-band image after appropriate training. Taking the sensing issue as a fitting task, the deep learning-based method utilizes a deep convolutional neural network to learn complex input-output mapping relations between the broadband intensity distributions and corresponding piston values. Given a trained network and one broadband focal intensity image as the input, the piston can be obtained directly and the capture range achieving the coherence length of the broadband light is available. Simulations and experiments demonstrate the validity of the proposed method. Using only in-focused broadband images as the inputs without defocus division and wavelength dispersion, obviously relaxes the optics complexity. In view of the efficiency and superiority, it's expected that the method proposed in this paper may be widely applied in multi-aperture imaging.

In this paper, the absorptivity of a tungsten ($W$W) based metamaterial absorber has been studied. The paper revolves around the spectral characteristics of the nano-holed $W$W film coated over silicon oxide (SiO${_2}$2) substrate. The anisotropic effective permittivity of the nanoholed W film has been deduced by employing the effective medium theory. The light-plasmon coupling at $W$W-$SiO_{2}$SiO2 interface has been investigated by the eigenvalue equation. The effect of the nanoholed radii on coupling and absorptivity has been analyzed. As such, absorption features of the absorber have been studied in the visible and near-infrared (NIR) regimes by finite difference time domain(FDTD) simulation under the excitation of fundamental transverse electric(TE)- and transverse magnetic (TM)-mode. It has been observed that absorptivity can be altered by tailoring the holes radii of tungsten nanolayer. Further, the effects of the incidence angle of the light on the absorptivity have been studied. Observations reveal that absorptivity depends on the nanohole radius of $W$W, and angle of incidence of excited light. Also, wideband absorptivity has been attained using $W$W thin film. Such an absorber would be useful for solar cell, solar heating and integrated optics related applications.

This paper presents a modeling approach of a laser varifocal system for longitudinal Gaussian beam waist shifting. The developed approach is based on laser optics theory, which is considered to be classical optics generalized for coherent radiation. A basic optical system, consisting of two components, was developed using this theory. Components have fixed focal lengths and specific movements. An automated modeling algorithm was proposed, and an example was provided in text. Various systems shown in this paper form a Gaussian beam with required waist parameters and provide its longitudinal shifts, which exceed the length of the near-zone of a focused Gaussian beam. Such systems can be used in laser technologies, including micro- and nano-sized objects manipulation.

This paper presents the Fantatrope, an improvement of the pre-cinematographic devices such as the zoetrope, which creates a comfortable 3D display with the addition of ultra-realistic full-color holograms. The Fantatrope is built with a set of holograms of 3D-printed figurines mounted on a cylinder rotating at constant speed. A stroboscopic RGB LED lamp synchronized with the rotation successively illuminates the different frames and the recorded character is animated like in a stop-motion movie. All principal functions of this new device can be adjusted and this paper evaluates its performances. The operation of the Fantatrope is successfully demonstrated and shows the effect of a true 3D display without the need for special glasses or other viewing aids.

As a saturable absorption material, the heterostructure with the van der Waals structure has been paid much attention in material science. In general, the heterogeneous combination is able to neutralize, or even exceed, the individual material's advantages in some aspects. In this paper, which describes the magnetron sputtering deposition method, the tapered fiber is coated by the MoS2-WS2 heterostructure, and the MoS2-WS2 heterostructure saturable absorber (SA) is fabricated. The modulation depth of the prepared MoS2-WS2 heterostructure SA is measured to be 19.12%. Besides, the theoretical calculations for the band gap and carrier mobility of the MoS2-WS2 heterostructure are provided. By employing the prepared SA, a stable and passively erbium-doped fiber laser is implemented. The generated pulse duration of 154 fs is certified to be the shortest among all fiber lasers based on transition mental dichalcogenides. Results in this paper provide the new direction for the fabrication of ultrafast photon modulation devices.

Three dimensional (3D) body scanning has been of great interest to many fields, yet it is still a challenge to generate accurate human body models in a convenient manner. In this paper, we present an accurate 3D body scanning system based on structured light technology. A four-step phase shifting combined with Gray-code method is applied to match pixels in camera and projector planes. The calculation of 3D point coordinates are also derived. The main contribution of this paper is twofold. First, an improved registration algorithm is proposed to align point clouds reconstructed from different views. Second, we propose a graph optimization algorithm to further minimize registration errors. Experimental results demonstrate that our system can produce accurate 3D body models conveniently.

This paper presents a proposal of an optically reconfigurable gate array using a colored configuration. The optically reconfigurable gate array consists of a very-large-scale integration (VLSI), a holographic memory, and four lasers with different wavelengths. The optically reconfigurable gate array VLSI includes a fine-grained programmable gate array as well as field programmable gate arrays. Four configuration contexts can be stored on the holographic memory and can be programmed onto the programmable gate array VLSI addressed by the four lasers. This paper presents the demonstration of the optically reconfigurable gate array using a colored configuration.

A novel microwave waveform generator based on a dual-polarization quadrature phase-shift-keying (DP-QPSK) modulator is proposed and experimentally demonstrated in this paper. The X-QPSK modulator is modulated by a local oscillator signal. For XI Mach-Zehnder modulator (MZM), odd sidebands are eliminated; for XQ-MZM, even sidebands are eliminated, while the Y-QPSK modulator is not modulated. Triangular or square waveforms can be generated by biasing the X-QPSK and adjusting the polarization controller properly. 3 GHz and 6 GHz triangular and square waveforms are successfully generated by experiment. The scheme does not need a high modulation index (m=1.25 in this paper). In addition, it features low cost and a simple structure without a filter or phase shifter.

Electron accumulation in transparent conductive oxides (TCOs), when driven by a gate voltage, is capable of inducing extremely strong electro-optic absorption at the telecommunication wavelength window due to the epsilon-near-zero (ENZ) effect and various waveguide modulators have been proposed in recent years. This paper conducts a comparative analysis of TCO modulators by reviewing several representative designs based on the uniform concentration accumulated carrier model and the classical continuous carrier distribution model. We also apply the quantum moment model to analyze the free carrier distribution of the TCO based metal-oxide-semiconductor (MOS) capacitor for the first time, and reveal significantly different device physics compared with previous simulation models. The quantum moment model predicts a much higher driving voltage in order to turn the TCO materials into ENZ and a stronger modulation strength compared with the classical model. Especially, the requirement of the higher gate voltage brings a great challenge to the insulator layer as the electric field in the insulator is exceeding the breakdown strength, which raises the concern of reliability. In order to evaluate the accuracy of different models, we compare the simulation results with two of the most recent experimental papers and show that the quantum model has a better match in terms of the electro-absorption rate and the differential driving voltage. However, the quantum moment model still cannot explain some other experimental results, which may be induced by different modulation mechanisms.

Computer-generated holography (CGH) is a technique for converting a three-dimensional (3D) object scene into a two-dimensional (2D), complex-valued hologram. One of the major bottlenecks of CGH is the intensive computation that is involved in the hologram generation process. To overcome this problem, numerous research works have been conducted with the aim of reducing arithmetic operations involved in CGH. In this paper, we shall review a number of fast CGH methods that have been developed in the past decade. These methods, which are commonly referred to as point-based CGH, are applied to compute digital Fresnel holograms for an object space that is represented in a point cloud model. While each method has its own strength and weakness, trading off conflicting issues, such as computation efficiency and memory requirement, they also exhibit potential grounds of synergy. We hope that this paper will bring out the essence of each method and provide some insight on how different methods may crossover into better ones.

It has been shown in [ J. A. Hoffnagle C. M. Jefferson , Opt. Eng.42, 3090, (2003)] that a pair of plano-aspheric lenses can be used to transform a radially symmetric, Gaussian beam to a radially symmetric flat-top beam. In this paper it is shown that a pair of plano-freeform lenses can be used to transform a collimated light beam of arbitrary (including, non-radially symmetric) intensity profile to a collimated output beam of constant phase and a priori specified intensity pattern over a given flat region. The curved surfaces of both lenses can be chosen strictly convex which should facilitate fabrication. The required pair of plano-freeform lenses is designed using the supporting quadric method (SQM) [ V. I. Oliker in Trends in Nonlinear Analysis, (Springer-Verlag, 2003)] combined with ideas from optimal mass transport [ V. I. Oliker , Arch. Rational Mechanics and Analysis201, 1013 (2011)]. Such approach provides a rigorous methodology for designing freeform optics for irradiance redistribution. In this paper, this approach is applied to design of a laser beam shaping system with two lenses.

A smooth end face is the critical factor for the application of photonic crystal fiber (PCF) to enhance coupling efficiency. A number of air holes distributed on the cladding make the surface a discontinuous structure. For the sake of acquiring a high-quality end surface of PCF, this paper proposes a detailed study first on dynamics simulation of the grinding process of PCF using a finite element model with a verification experiment later. To facilitate the calculation, the grinding is simplified as a single grain to cut the material on the location between two holes. The process of material removal is analyzed on the basis of force curve obtained by changing the cutting depth and position, respectively. Theoretical and experimental results illustrate that the earliest material collapse occurs on the rim of the air hole, and brittle cracks extend along circumferential and axial direction of the hole; the damage on the edge of the hole is more severe with the increment of grain tip radius and cutting depth. Keeping the grinding force stable can achieve the process in the ductile regime, and a smooth surface can be obtained by polishing with abrasive paper of fine grit.

Ultrafast fiber laser light sources attract enormous interest due to the booming applications they are enabling, including long-distance communication, optical metrology, detecting technology of infra-biophotons, and novel material processing. In this paper, we demonstrate 175 fs dispersion-managed soliton (DMS) mode-locked ytterbium-doped fiber (YDF) laser based on single-walled carbon nanotubes (SWCNTs) saturable absorber (SA). The output DMSs have been achieved with repetition rate of 21.2 MHz, center wavelength of 1025.5 nm, and a spectral width of 32.7 nm. The operation directly pulse duration of 300 fs for generated pulse is the reported shortest pulse width for broadband SA based YDF lasers. By using an external grating-based compressor, the pulse duration could be compressed down to 175 fs. To the best of our knowledge, it is the shortest pulse duration obtained directly from YDF laser based on broadband SAs. In this paper, SWCNTs-SA has been utilized as the key optical component (mode locker) and the grating pair providing negative dispersion acts as the dispersion controller.

Front side pyramids are the industrial standard for wafer based monocrystalline silicon solar cells. These pyramids fulfill two tasks: They act as anti-reflective structure on the one hand and as a light-trapping structure on the other hand. In recent development smaller pyramids with sizes below 1 µm attract more and more interest. In this paper an optical analysis of periodically arranged front side pyramids is performed. The impact on the reflectance as well as on the useful absorption within the solar cell is investigated depending on the pyramids size, the amount of additional scattering in the system and the quality of the rear side reflector. In contrast to other investigations not only the solar cell, but the full photovoltaic (PV) module stack is considered. This can strongly influence results, as we show in this paper. The results indicate that in a PV module stack with realistic assumptions for the amount of scattering as well as for the rear side reflectance only small differences for pyramids with sizes above 600 nm occur. Preliminary conclusions for random pyramids deduced from these results for periodically arranged pyramids indicate that these differences could become even smaller.

This paper provides the results of work on a new method for metrological laser beam steering for the purpose of angular stabilization. Frequency stabilized metrological lasers are used for interference measurements of length and angle. Angular deviation of the beam may cause cosine errors when measuring displacements. This paper presents a method for metrological laser beam deflection with an air wedge of variable refractive index. The change in the index is achieved by changing the air pressure in the wedge volume. The implemented system produced a range of angular displacements of the 0.1 mrad (10−4 rad; 100 μrad) beam with a resolution of 10−7 rad.

The traditional approach of a star tracker for reducing the dynamic error concentrates on a single frame of star images. Through correlating adjacent star images together with their angular relations sensed by a gyroscope unit (GU), the attitude-correlated frames (ACF) approach expands the view from one single frame to frame sequences. However, the star centroid is shifted from the star true position at the center time of the exposure period under complex dynamic conditions, which is called the complex motion induced error (CMIE) in this paper. The CMIE has a large effect on the performance of the ACF approach. This paper presents a method to compensate the CMIE through reconstructing the star trajectory with the angular velocity of the star tracker sensed by a GU, which achieves effective compensation of the CMIE crossing the boresight direction. Since the observation sensitivity to the CMIE along the boresight direction is low, the attitudes from two different fields of view (FOVs) are combined to improve its compensation accuracy. Then the ACF approach is applied to the obtained results where the CMIE has already been compensated completely. Simulations under shipboard dynamic conditions and experiments under oscillating conditions indicate that the proposed method is effective in improving the performance of the ACF approach and reducing the dynamic error of a star tracker under complex dynamic conditions.

A thought-provoking proposal by Tsakmakidis et al. [Science 356, 1260 (2017)] suggests that nonreciprocal optics can break a time-bandwidth limit to passive resonators. Here I quantize their resonator model and show that quantum mechanics does impose a limit, or requires extra noise to be added in the same fashion as amplified spontaneous emission in an active resonator. I also use thermodynamics to argue that extra dissipation or noise must be present in their proposed device., Comment: 4 pages, 3 figures. v2: expanded and submitted; v3: updated and published. Copyright 2018 Optical Society of America. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modifications of the content of this paper are prohibited

Calculations on the influence of compressible gas effects on the performances of exciplex pumped alkali vapor lasers (XPALs) with supersonic flow system are made. Modified configuration of experimental apparatus for XPALs is designed in this paper as well. On the basis of fluid mechanics and thermodynamics, theoretical derivations for the boundary of temperature gradient which actually is the position of shock wave plane are firstly deduced and presented. And our simulated results show that XPALs have broadband of not only in absorption spectrum but also in pump power, which will be helpful for researchers to find the way to make very high-power gas lasers. In addition, the simulating method to obtain the operating temperature of XPALs is given, and predicted the value, at the conditions of this paper, is 1500K with optimized parameters of Pp = 3×106 W, Tstag=513 K, initial Mach number = 2.5.

Optical lithography is extensively used in micro and nano scale semiconductor fabrication. However, the information transmission mechanism in lithography systems is not yet completely understood. This paper studies and analyzes the lithography imaging process from an information theory perspective. The optical lithography system is regarded as an information channel, an approximate statistical model is built to depict the imaging process, and information theoretical aspects of coherent optical lithography systems are studied. Based on that, we derive the mutual information between the mask pattern and print image, as well as the maximum information transfer (MIT) of the coherent lithography system. This paper also reveals and discusses the physical meaning of MIT in the lithography imaging process. Finally, a method to calculate the theoretical limit of image fidelity using the MIT is proposed and verified by a set of simulations.

This paper aims to develop and analyze the design method of multifocal contact lenses to obtain curvature continuity in the optical surfaces with the high addition (Add) powers by adjusting non-uniform rational B-spline (NURBS) curves. The paper has developed mathematical formulae to generate the optical power distributions in which the powers continuously change from either near or distant center to the opposite focal length in the periphery of the optical region with different change rates and Add power values. This developed method can efficiently adjust and optimize three parameters, including control points, weight, and knots of the NURBS, to be anterior optical lens surface profiles to adapt for these given power profiles. The result shows that the proposed contact lenses not only achieve smooth and continuous anterior optical surfaces, but also satisfy various optical power distributions with high Add power values for different pupil diameters. Then, these designs of contact lenses can be feasibly converted to the computer-aided design format for analysis and manufacture for molding or single-point diamond turning. Experimental results of this method have been tested and proven when both the power distributions of simulation of lenses and the actual machined samples match the original specified powers provided by clinical demands of a multifocal contact lens. Future integration with variant clinical demands and optimization rules of lens design can be explored for a progressive contact lens.

In this paper, we numerically investigate the fluorescence decay of Tm-doped tellurite glasses with different dopant concentrations. The aim is to find a set of data that allows the prediction of material performance over a wide range of doping concentrations. Among the available data, a deep investigation of the reverse cross-relaxation process (F,F,→H,H) was not yet available. The numerical simulation indicates that the reverse cross-relaxation process parameter can be calculated by fitting the slow decaying H fluorescence tails emitted when the pump level is almost depopulated. We also show that the floor of the H decay curve is indeed related to a second exponential constant, half the F lifetime, kicking in once the H level depopulates. By properly fitting the whole set of decay curves for all samples, the proposed value for the reverse cross-relaxation process is 0.03 times the cross-relaxation parameter. We also comment on the measurement accuracy and best set-up. Excellent agreement was found between the simulated and experimental data, indicating the validity of the approach. This paper therefore proposes a set of parameters validated by fitting experimental fluorescence decay curves of both the H and F levels. To the best of our knowledge, this is the first time a numerical simulation has been able to predict the fluorescence behavior of glasses with doping levels ranging from 0.36 mol% to 10 mol%. We also show that appropriate calculations of the reverse cross-relaxation parameter may have a significant effect on the simulation of laser and amplifier devices., This article is based upon work from H2020 COST Action MP1401 on “Fiber Lasers and Their Applications” supported by COST “(European Cooperation in Science and Technology)”. M. Ferrari acknowledges CNRS support, part of this research has been supported during his visit at UMR7010 INPHYNI - Institute de Physique de Nice.

This paper presents a model to design bi-aspherical catadioptric lenses with limited image diffraction. A first refractive Cartesian oval surface that does not introduce any spherical aberration is used. When total internal reflection occurs, this surface can also be simultaneously used as a mirror. The reflective characteristics of Cartesian ovals are also well described in this paper. The theoretical work described here can considerably reduce computing time in optical system design. This model is applied to examples of antennae design for visible light communications (VLC).

Various existing target ranging techniques are limited in terms of the dynamic range of operation and measurement resolution. These limitations arise as a result of a particular measurement methodology, the finite processing capability of the hardware components deployed within the sensor module, and the medium through which the target is viewed. Generally, improving the sensor range adversely affects its resolution and vice versa. Often, a distance sensor is designed for an optimal range/resolution setting depending on its intended application. Optical triangulation is broadly classified as a spatial-signal-processing-based ranging technique and measures target distance from the location of the reflected spot on a position sensitive detector (PSD). In most triangulation sensors that use lasers as a light source, beam divergence-which severely affects sensor measurement range-is often ignored in calculations. In this paper, we first discuss in detail the limitations to ranging imposed by beam divergence, which, in effect, sets the sensor dynamic range. Next, we show how the resolution of laser-based triangulation sensors is limited by the interpixel pitch of a finite-sized PSD. In this paper, through the use of tunable focus lenses (TFLs), we propose a novel design of a triangulation-based optical rangefinder that improves both the sensor resolution and its dynamic range through adaptive electronic control of beam propagation parameters. We present the theory and operation of the proposed sensor and clearly demonstrate a range and resolution improvement with the use of TFLs. Experimental results in support of our claims are shown to be in strong agreement with theory.

This paper proposes a fast source optimization (SO) method for lithography systems to improve the imaging performance of different hotspots on the fullchip layout. Hotspots are referred to as the critical locations on the layout that are difficult to print. A fullchip layout usually includes numerous hotspots with different geometric characteristics. Current SO approaches collect all of the data from different hotspots before the optimization, and then try to calculate the common optimal source for all hotspots. If any new data from unaccounted hotspots become available, the optimal source has to be recalculated. This paper first develops a batch-processing sequential least square estimator, and then uses it to iteratively modify the source pattern based on the ongoing hotspot data. The optimized source for one hotspot can be updated to suit others without redundant computation. Simulations show that the proposed method can significantly accelerate the SO procedure, while improving the imaging performance of multiple hotspots.

Although the diode pumped alkali laser (DPAL) works in a three-level scheme, higher energy-state excitation and ionization processes exist during operation, which may lead to deleterious effects on laser performance. In this paper, we report the ionization degree measurement in the gain medium of an operational hydrocarbon-free Rb DPAL by using the optogalvanic method. The results show that, at the pulsed mode with a duration of ~1 ms, a maximal ionization degree of ~0.06% is obtained at a pump power of 140 W. While in the CW mode, the plasma reaches an ionization degree as high as ~2% at a pump power of 110 W, which is mainly due to the enough time for sufficient plasma development. A comparison with our previous work [Opt. Lett.39, 6501 (2014)] as well as modeling results is made and discussed. The influences of different population transfer channels on laser performance are simulated and analyzed. The results show that, for a typical hydrocarbon-free Rb laser (pump intensity of 15 kW/cmsup2/sup, helium pressure of 10 atm and cell temperature of 438 K), all the high-energy excitation effects give an overall negative influence on laser efficiency of ~3.78%, while the top two influencing channels are the photoionization (~1.8%) and the energy pooling (~1.53%). The work in this paper experimentally reveals the influence of the macroscopic ionization evolution process on an operational DPAL for the first time, which would be helpful for a more comprehensive understanding of the physics in DPALs.

We report the use of a phase retrieval procedure based on maximum likelihood estimation (MLE) to produce an improved, experimentally calibrated model of a point spread function (PSF) for use in three-dimensional (3D) localization microscopy experiments. The method estimates a global pupil phase function (which includes both the PSF and system aberrations) over the full axial range from a simple calibration scan. The pupil function is used to refine the PSF model and hence enable superior localizations from experimental data. To demonstrate the utility of the procedure, we apply it to experimental data acquired with a microscope employing a tetrapod PSF with a 6 micron axial range. The phase-retrieved model demonstrates significant improvements in both accuracy and precision of 3D localizations relative to the model based on scalar diffraction theory. The localization precision of the phase-retrieved model is shown to be near the limits imposed by estimation theory, and the reproducibility of the procedure is characterized and discussed. Code which performs the phase retrieval algorithm is provided., 14 pages, 4 figures. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: https://doi.org/10.1364/OE.25.007945