Optical Design for the Off-axis Reflective Optics with Wide Field

Reflective optics with wide field of view has been applied more and more widely in EUVL or space optics, and also plays an important role in promoting scientific and technological research. Among the reflective optics, the off-axis reflective optics is the most hopeful solution to the ever-highest demands of these applications. This paper gives the requirements of both the above mentioned applications and the similarities and differences between these two kinds of optical systems. Finally, a design example of off-axis reflective optics with wide field of view is presented and described.

10-Gb/s Transmission in WDM PON Employing Reflective Semiconductor Optical Amplifier and Fibre Bragg Grating Equaliser

We propose a 10-Gb/s Wavelength- Division-Multiplexed Passive Optical Network （WDM-PON） scheme with upstream transmi- ssion employing Reflective Semiconductor Op- tical Amplifier （RSOA） and Fibre Bragg Gra- ting （FBG） optical equaliser. Transmissions of 10-Gb/s non return-to-zero signals using a 1.2- GHz RSOA and FBG optical equaliser with different setups are demonstrated. Significant performance improvement and 40-kin standard single mode fibre transmission are achieved using FBG optical equaliser and Remotely Pum- ped Erbium-Doped Fibre Amplifier （RP-EDFA）, where they are used to equalise the output of the band-limited RSOA and amplify the seed light and upstream signal, respectively.

A Method for Spaceborne Synthetic Remote Sensing of Atmospheric Aerosol Optical Depth and Vegetation Reflectance

Spaceborne synthetic remote sensing of atmospheric aerosol optical depth and vegetation reflectance is very significant, but it remains to be a question unresolved yet. Based on the property of vegetation reflectance spectra from near ultra violet to near infrared and the sensitivity of outgoing radiance to vegetation reflectance and atmospheric aerosol optical depth, a new method for spaceborne synthetic remote sensing of the reflectance and the depth is proposed, and an iteration correlation inversion algorithm is developed in this paper. According to numerical experiment, effects of radiance error, error in aerosol imaginary index and vegetation medium inhomogeneity on retrieved result are analyzed. Inversion results show that the effect of error in aerosol imaginary index is very important. As the error of aerosol imaginary index is within 0.01, standard errors of aerosol optical depth and vegetation reflectance solutions for 14 spectral channels from 410 nm to 900 nm are respectively less than 0.063 and 0.023. And as the radiance error is within 2%, the standard errors are less than 0.023 and 0.0056.

Photon counts modulation in optical time domain reflectometry

The quantum fluctuation of photon counting limits the field application of optical time domain reflection. A method of photon counts modulation optics time domain reflection with single photon detection at 1.55 μm is presented. The influence of quantum fluctuation can be effectively controlled by demodulation technology since quantum fluctuation shows a uniform distribution in the frequency domain. Combined with the changing of the integration time of the lock-in amplifier, the signal to noise ratio is significantly enhanced. Accordingly the signal to noise improvement ratio reaches 31.7 dB compared with the direct photon counting measurement.

Optical anisotropy of black phosphorus by total internal reflection

Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.

Investigation of optical reflectance from different animal vertebra along the fixation trajectory of pedicle screw in frequency domain

Accurate placement of pedicle screw(PS)is crucial in spinal surgery.Developing new real-time intra-operative monitoring and navigation methods is an important direction of clinical appli-cation research.In this paper,we studied the spectrum along the fixation trajectory of PS in frequency domain to tackle the accuracy problem.Fresh porcine vertebrae,bovine vertebrae and ovine vertebrae were measured with the near-infrared spectrum(NIR)device to obtain the reflected spectrum from the vertebrae.Along the fixation trajectory of PS,average energy from different groups was calculated and used for identifying different tissues and compared to achieve the optimal recognition factor.Compared with the time domain approach,the frequency domain method could divide the spectra measured at different tissue points into different groups more stably and accurately,which could serve as a new method to assist the PS insertion.The results gained from this study are significant to the development of hi-tech medical instruments with independent intellectual property rights.

Artifcial eur ral networks based estimation of optical parameters by diffuse reflectance imaging under in vitro conditions

Optical parameters(properties)of tissue-mimicking phantoms are determined through nonin-vasive optical imaging.Objective of this study is to decompose obtained difuse reflectance into these optical properties such as absorption and scattering coefficients.To do so,transmission spectroscopy is firstly used to measure the coefficients via an experimental setup.Next,the optical properties of each characterized phantom are input for Monte Carlo(MC)simulations to get diffuse reflectance.Also,a surface image for each single phantom with its known optical properties is obliquely captured due to reflectance-based geometrical setup using CMOS camera that is positioned at 5°angle to the phantoms.For the illumination of light,a laser light source at 633 nm wavelength is preferred,because optical properties of different components in a biological tissue on that wavelength are nonoverlapped.During in vitro measurements,we prepared 30 different mixture samples adding clinoleic intravenous lipid emulsion(CILE)and evans blue(EB)dye into a distilled water.Finally,all obtained difuse reflectance values are used to estimate the optical coefficients by artificial neural networks(ANNs)in inverse modeling.For a biological tissue it is found that the simulated and measured values in our results are in good agreement.

Evaluation of Correction Algorithm for the Reflectance Measured with Optical Glass

The proposed algorithm for reflectance measured with optical glass has been verified with materials of various forms. The reflectances measured with optical glass ( raw), without glass (true) and corrected by the algorithm are compared. The results show that the corrected reflectance agrees very well with true one and their color differences fall below the acceptable limit, which indicates the validity of the correction algorithm. The algorithm could be used not only for fiber-forming materials, but also for powder-forming, granulate-forming, etc.

Research progress of cholesteric liquid crystals with broadband reflection characteristics in application of intelligent optical modulation materials

Cholesteric liquid crystals（CLCs） have recently sparked an enormous amount of interest in the development of soft matter materials due to their unique ability to self-organize into a helical supra-molecular architecture and their excellent selective reflection of light based on the Bragg relationship.Nowadays,by the virtue of building the self-organized nanostructures with pitch gradient or non-uniform pitch distribution,extensive work has already been performed to obtain CLC films with a broad reflection band.Based on authors＇ many years＇ research experience,this critical review systematically summarizes the physical and optical background of the CLCs with broadband reflection characteristics,methods to obtain broadband reflection of CLCs,as well as the application in the field of intelligent optical modulation materials.Combined with the research status and the advantages in the field,the important basic and applied scientific problems in the research direction are also introduced.

Reflectivity and thickness analysis of epiretinal membranes using spectral-domain optical coherence tomography

AIM：To compare thickness and reflectivity spectral domain optical coherence tomography（SD-OCT）findings in patients with idiopathic epiretinal membranes（ERMs）,before and after ERM peeling surgery,with normal controls.·METHODS：A retrospective study analyzing SD-OCTs of eyes with ERMs undergoing ERM peeling surgery by one surgeon from 2008 to 2010 and normal control eyes.SD-OCTs were analyzed using a customized algorithm to measure reflectivity and thickness.The relationship between the SD-OCT findings and best corrected visual acuity（BCVA）outcomes was also studied.·RESULTS：Thirty-four ERM eyes and 12 normal eyes were identified.Preoperative eyes had high reflectivity and thickness of the group of layers from the internal limiting membrane（ILM）to the retinal pigment epithelium（RPE）and the group of layers from the ILM to the external limiting membrane（ELM）.The values of reflectivity of these two groups of layers decreased postoperatively,but were still higher than normal eyes.In contrast,preoperative eyes had lower reflectivity of two10×15 pixel regions of interest（ROIs）incorporating：1）ELM＋outer nuclear layer（ONL）and 2）photoreceptor layer（PRL）＋RPE,compared to controls.The values of reflectivity of these ROIs increased postoperatively,but were still lower than normal controls.A larger improvement in BCVA postoperatively was correlated with a greater degree of abnormal preoperative reflectivity and thickness findings.·C ONCLUSION：Quantitative differences in reflectivity and thickness between preoperative,postoperative,and normal SD-OCTs allow assessment of changes in the retina secondary to ERM.Our study identified hyperreflective inner retina changes and hyporeflective outer retina changes in patients with ERMs.SD-OCT quantitative measures of reflectivity and/or thickness of specific groups of retinal layers and/or ROIs correlate with improvement in BCVA.

REAL-TIME OPTICAL MONITORING OF CAPILLARY GRID SPATIAL PATTERN IN EPITHELIUM BY SPATIALLY RESOLVED DIFFUSE REFLECTANCE PROBE

We developed a novel method for real-time monitoring of alteration of the local epithelium vessel/capillary and blood oxygenation spatial pattern in epithelium exploiting a compact fibre sensor system based on spatially and spectrally resolved diffuse reflectance.The method is based on collection of spatially resolved diffuse reflectance Re(λ)by fiber sensors.The spatial resolution is provided as a dependence of Re(λ)on a set of distancesρbetween the source and detector(attenuation curve).It is expected that the new method can reasonably extract the minor spatial deviations of oxygenation and local blood volume fraction-parameters,directly related to the local vessel density and capillary spatial patterns in the epithelium.Light scattering in visible range is naturally taken into account in the proposed method.

Review of reflective fiber optic sensors for surface topography measurement

Different from the traditional contact surface topography measurement,reflective intensity-modulated fiber optic sensor(RIM-FOS)has the unique advantages of non-contact nondestructive detection.This paper briefly introduces the principle and performance of RIM-FOS for surface topography measurement and compares with several other methods of topography measurement.Based on the review of its development process,this paper summarizes and analyses the hot issues of RIM-FOS in the surface topography measurement,then predicts the future trend for a guidance of the further study.

Analysis of reflection coefficient for coated optical waveguide devices

From an ordinary condition,using a full three-dimensional model theory and an infinite perturbation expansion method,an exact solution of the reflection coefficient for the coated narrow stripe-geometry optical waveguide devices has been derived.All six components and the vector property of the electromagnetic field have been considered.The results are suitable for the symmetric and asymmetric waveguides.

Determination of the Deep Optical Properties of Healthy and Diseased Skin Using Diffuse Reflectance Spectroscopy

In this study, we focused on diffuse reflectance spectroscopy, a rapid and noninvasive spectroscopy technique that has considerable potential for medical diagnosis. In order to better understand and analyze the signals induced by this method, we performed a series of in vivo measurements on healthy and diseased skin. Measurement sites on a human hand and feet were chosen. Some preliminary results obtained on these sites show the feasibility of this technique in clinics.

Precise Optical Fiber Length Measurement System Based on Fresnel Reflection

In this study, a precise optical fiber length measurement system is proposed. The measurement technique is based on the measurement of relative Fresnel reflected light intensity in a test fiber. Time delayed optical reflected pulses are obtained from a single nanosecond pulse injected at the input due to the difference in lengths of the reference and test fibers. The lengths of the different optical fibers have been measured with this technique with high resolution and fast response time. The measured results show that, the proposed technique has a comparable performance with the well-known length measurement systems.

Reflective Ladder Topology Network Based on White Light Fiber-Optic Mach-Zehnder Interferometer

In order to improve the multiplexing capability of the optical sensors based on the lower interferential optic fiber sensing technology and the white light fiber-optic Mach-Zehnder interferometer,reflective ladder topology network ( RLT) with tailored formula was proposed. The topology network consists of 6 rungs sensing elements linked by 5 couplers. Two cases with different choices of couplers were contrasted: one is equal coupling ratio,and the other is tailored coupling ratio. Through the simulation of these two cases,the detailed multiplexing capability was analyzed,and accordingly the experiments were also carried out. The simulation results showed that,the tailored formula enhances the multiplexing capability of the structure. In the first case, the maximum number of sensors which can be multiplexed is 8,and in the other case is 12 fiber optic sensors. The experimental results have a good agreement with numerical simulation results. Thus,it is considered expedient to incorporate RLT into large-scale building,grounds,bridges,dams,tunnels,highways and perimeter security.

Retrieval of Aerosol Optical Properties over the Beijing Area Using POLDER/PARASOL Satellite Polarization Measurements

Aerosol optical properties over Beijing and Xianghe under several typical weather conditions （clear sky, light haze, heavy pollution and dust storm） are derived from POLDER （POLarization and Directionality of the Earth＇s Reflectances）/PARASOL （Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar） multi-directional, multi-spectral polarized signals using a more reliable retrieval algorithm as proposed in this paper. The results are compared with those of the operational retrieval algorithm of POLDER/PARASOL group and the ground-based AERONET （AErosol RObotic NETwork）/PHOTONS （PHOtometrie pour le Traitement Operational de Normalisation Satellitaire） measurements. It is shown that the aerosol optical parameters derived from the improved algorithm agree well with AERONET/PHOTONS measurement. The retrieval accuracies of aerosol optical thickness （AOT） and effective radius are 0.06 and 0.05 μm respectively, which are close to or better than the required accuracies （0.04 for AOT and 0.1 μm for effective radius） for estimating aerosol direct forcing.

Single‑Layer ZnO Hollow Hemispheres Enable High‑Performance Self‑Powered Perovskite Photodetector for Optical Communication

The carrier transport layer with reflection reduction morphology has attracted extensive attention for improving the utilization of light.Herein,we introduced single-layer hollow ZnO hemisphere arrays(ZHAs)behaving light trapping effect as the electron transport layer in perovskite photodetectors(PDs).The singlelayer hollow ZHAs can not only reduce the reflection,but also widen the angle of the effective incident light and especially transfer the distribution of the optical field from the ZnO/FTO interface to the perovskite active layer confirmed by the 3D finitedifference time-domain simulation.These merits benefit for the generation,transport and separation of carriers,improving the light utilization efficiency.Finally,our optimized FTO/ZHA/CsPbBr3/carbon structure PDs showed high self-powered performance with a linear dynamic range of 120.3 dB,a detectivity of 4.2×10^(12) Jones,rise/fall time of 13/28μs and the f_(−3) dB of up to 28 kHz.Benefiting from the high device performance,the PD was demonstrated to the application in the directional transmission of encrypted files as the signal receiving port with super high accuracy.This work uniquely utilizes the features of high-performance self-powered perovskite PDs in optical communication,paving the path to wide applications of all-inorganic perovskite PDs.

Optical Absorption Enhancement Effects of Silver Nanodisk Arrays in the Application of Silicon Solar Cell

Surface plasmon resonance of noble metal nanoparticles leads to the optical absorption enhancement effects,which have great potential applications in solar cell.By using the general numerical method of discrete dipole approximation （DDA）,we study the absorption and scattering properties of two-dimensional square silver nanodisks （2D SSN） arrays on the single crystal silicon solar cell.Based on the effective reflective index model of the single crystal silicon solar cell,we investigate the optical enhancement absorption of light energy by varying the light incident direction,particle size,aspect ratio,and interparticle spacing of the silver nanodisks.The peak values and position of the optical extinction spectra of the 2D square arrays of noble metal nanodisks are obtained with the different array structures.

Accuracy design of ultra-low residual reflection coatings for laser optics

Refractive index inhomogeneity is one of the important characteristics of optical coating material, which is one of the key factors to produce loss to the ultra-low residual reflection coatings except using the refractive index inhomogeneity to obtain gradient-index coating. In the normal structure of antireflection coatings for center wavelength at 532 nm, the physical thicknesses of layer H and layer L are 22.18 nm and 118.86 nm, respectively. The residual reflectance caused by refractive index inhomogeneity（the degree of inhomogeneous is between -0.2 and 0.2） is about 200 ppm, and the minimum reflectivity wavelength is between 528.2 nm and 535.2 nm. A new numerical method adding the refractive index inhomogeneity to the spectra calculation was proposed to design the laser antireflection coatings, which can achieve the design of antireflection coatings with ppm residual reflection by adjusting physical thickness of the couple layers. When the degree of refractive index inhomogeneity of the layer H and layer L is-0.08 and 0.05 respectively, the residual reflectance increase from zero to 0.0769% at 532 nm. According to the above accuracy numerical method, if layer H physical thickness increases by 1.30 nm and layer L decrease by 4.50 nm, residual reflectance of thin film will achieve to 2.06 ppm. When the degree of refractive index inhomogeneity of the layer H and layer L is 0.08 and -0.05 respectively, the residual reflectance increase from zero to 0.0784% at 532 nm. The residual reflectance of designed thin film can be reduced to 0.8 ppm by decreasing the layer H of 1.55 nm while increasing the layer L of 4.94 nm.