C-band three-port tunable band-pass thin film optical filter with low polarization-sensitivity

According to the oblique incidence characteristics of thin film narrowband filter, the stack of 100 GHz DWDM four cavities angle-tuned thin film filter has been designed and optimized. The two polarization modes’ central wavelengths of the thin film filter can be centered at the same one in oblique incidence, and it has a stable tuning range of 20 nm without the phenomenon of polarization central wavelength separation. Using this kind of angle-tuned thin film filter and the polarization beam-splitters, the tuning range of the angle-tuned thin film filter can be further expanded due to the reason that it can transmit only the s-polarization light. In this paper we also developed a three-port bandpass tunable filter device with new structure, which tuning range can cover the whole C-band and its adjacent channel isolation degree is high. The experiments show that the three-port tunable filter has an effective tuning range of 33 nm, and its adjacent channel isolation degree is more than 35 dB. It has a bright application opportunity for its flexibility and effective performance.     

800 mW/1484 nm highly efficient two-cascaded phosphosilicate Raman fiber laser pumped by Nd:YVO4 solid-state laser

Using 1064 nm CW Nd:YVO₄ solid-state laser as a pump, 1-km phosphosilicate fiber and cascaded cavities with two pairs of fiber Bragg grating mirrors for 1239 and 1484 nm, we obtained a CW 800 mW/1484 nm Raman fiber laser (RFL) for an actual incident pump power of about 2 W (Nd:YVO₄ power of 6.90 W). The conversion efficiency is as high as 40%. To the best of our knowledge, this is the highest conversion efficiency of RFL pumped by solid-state laser. The output power instability at 1484 nm in half an hour is less than 3%. In addition, the numerical simulations are also performed. Good agreement between the results of numerical simulation and the results of the experiment has been demonstrated.     

A new standing-wave-type linear ultrasonic motor based on in-plane modes

This paper presents a new standing-wave-type linear ultrasonic motor using combination of the first longitudinal and the second bending modes. Two piezoelectric plates in combination with a metal thin plate are used to construct the stator. The superior point of the stator is its isosceles triangular structure part of the stator, which can amplify the displacement in horizontal direction of the stator in perpendicular direction when the stator is operated in the first longitudinal mode. The influence of the base angle θ of the triangular structure part on the amplitude of the driving foot has been analyzed by numerical analysis. Four prototype stators with different angles θ have been fabricated and the experimental investigation of these stators has validated the numerical simulation. The overall dimensions of the prototype stators are no more than 40 mm (length) × 20 mm (width) × 5 mm (thickness). Driven by an AC signal with the driving frequency of 53.3 kHz, the no-load speed and the maximal thrust of the prototype motor using the stator with base angle 20° were 98 mm/s and 3.2 N, respectively. The effective elliptical motion trajectory of the contact point of the stator can be achieved by the isosceles triangular structure part using only two PZTs, and thus it makes the motor low cost in fabrication, simple in structure and easy to realize miniaturization.     

Effect of surface steps on sputtering and surface defect formation: molecular-dynamics study of 5 keV Xe bombardment of Pt(1 1 1) at glancing incidence angles

Using molecular-dynamics simulation, we study sputtering and defect formation induced by 5 keV Xe⁺ ion impact on a Pt(1 1 1) surface at oblique and glancing incidence angles. Impact on a terrace produces yield maxima at ?=60-65° incidence angle towards the surface normal. Beyond 75-80°, no damage is produced due to projectile ion reflection. Impact on a dense-packed step, however, produces defects in sizeable numbers up to glancing incidence, ?=85°. The dependence of the yields on the incidence angle and distance of the impact point of the projectile to the step are discussed.     

Investigation of irradiance efficiency for LED phototherapy with different arrays

Red and yellow light emitting diodes (LEDs) are currently utilized as lighting sources during LED phototherapy. These LEDs were arranged on a disk with an external diameter of 70 mm with different arrays — radial, rhombus, square radial, and square rhombus arrays. The radial and square radial arrays had better irradiance efficiency than rhombus and square rhombus arrays by optical simulation. Additionally, the radial array had 76 sets of LEDs, but the square radial array had 100 sets. Thus, a mockup sample of radial array phototherapy was constructed for performance tests. The mixture efficiency of the radial array was observed at distances of 1-100 mm and lighting was well mixed when distance exceeded 50 mm by optical simulation. Irradiance variation with angle was approximated by experiment and theory at a treatment distance of 50 mm and 100 mm using the phototherapy mockup. The radial array was one good choice for LED phototherapy.     

Design of non-polarization angle-tuned narrowband thin film filter

Angle-tuned thin film bandpass filter is widely used in DWDM system. In oblique incidence, the bandwidths and central wavelengths of the P-polarization and S-polarization light will separate obviously, which will cause serious polarization dependent loss. These phenomena of the polarization sensitivities are analyzed and a novel non-polarization 100 GHz four-cavity narrowband dielectric thin film stack used in oblique incidence is proposed. The simulation results show that it can eliminate the polarization bandwidths and central wavelengths separation within the incident angle from 0° to 25°, and its tunable range can cover the whole C-band.     

Absolute calibration of Hartmann-Shack wavefront sensor by spherical wavefronts

A method for absolute calibration of Hartmann-Shack wavefront sensor (HSWFS), in which the wavefront differences of several spherical wavefronts are used to determine parameters of HSWFS, is proposed in this paper. The calibration method is introduced and the experiment results and error analysis are presented. Across a pupil with diameter of 2.6 mm, a lenslet array of 20 × 20 sub-apertures with square configuration, and focal length 4 mm, is used to sample the incident wave. The results indicate the uncertainty of the Hartmann-Shack wavefront sensor calibrated by the proposed method, is improved to less than λ/60 PV value and λ/500 RMS value (λ = 635 nm) with modal reconstruction method. Furthermore, the factors affected the results are analyzed. The error analysis suggested that the influences of the factors on the accuracy of reconstruction can be controlled to an accept level.     

Optical performance of a versatile illumination system for high divergence LED sources

An efficient flat-top illuminating optical system optimized for an extended light source is presented. The source is a high-brightness high divergence light emitting diode (LED), sized 1 mm × 1 mm, producing monochromatic emission (525 ± 5 nm) with viewing angle of 130°. The design is based on a rotationally symmetrical catadioptric system, developed on a geometrical optics basis, and modelled with ZEMAX^® software. The device consists of two optical systems: (i) a collimating system which, in turn, is formed by an aspheric lenses system (low numerical apertures, NA < 0.26) and two-mirror system (0.26 < NA < 0.86), and (ii) an external mirror (NA > 0.86) designed and optimized for each purpose. By itself, the collimating system works with a residual divergence of θ_C = 1.46°. The external mirror can be adequately designed to produce some given conditions. For instance, a flat-top profile is obtained in the selected focusing plane, with a maximum transversal intensity variation of 2.5% over 18 mm. In addition, when the focusing mirror is allowed to move along the optical axis in a ±1 mm range, other interesting profiles can be reached for a given working distance, therefore increasing the versatility of the system.     

The path to stoichiometric composition of III-V binary quantum dots through plasma/ion-assisted self-assembly

Semiconductor III-V quantum dots (QDs) are particularly enticing components for the integration of optically promising III-V materials with the silicon technology prevalent in the microelectronics industry. However, defects due to deviations from a stoichiometric composition [group III: group V = 1] may lead to impaired device performance. This paper investigates the initial stages of formation of InSb and GaAs QDs on Si(1 0 0) through hybrid numerical simulations. Three situations are considered: a neutral gas environment (NG), and two ionized gas environments, namely a localized ion source (LIS) and a background plasma (BP) case. It is shown that when the growth is conducted in an ionized gas environment, a stoichiometric composition may be obtained earlier in the QD as compared to a NG. Moreover, the stoichiometrization time, t_st, is shorter for the BP case compared to the LIS scenario. A discussion of the effect of ion/plasma-based tools as well as a range of process conditions on the final island size distribution is also included. Our results suggest a way to obtain a deterministic level of control over nanostructure properties (in particular, elemental composition and size) during the initial stages of growth which is a crucial step towards achieving highly tailored QDs suitable for implementation in advanced technological devices.     

The research on semi-active muffler device of controlling the exhaust pipe’s low-frequency noise

In order to control low frequency noise in exhaust pipe, this paper puts forward a new concept of H-Q tube based semi-active muffler device. The semi-active muffler device and bench testing system have been designed and operated. Finite element simulation study on semi-active muffler and experimental study on semi-active muffler and passive muffler have been carried on. The effect of simulation and experiment are consistent. The semi-active muffler device acts well in low frequency band, especially between 50 Hz and 150 Hz. The average level of noise reduction is around 35 dB, which is much better than passive muffler. Between 150 Hz and 350 Hz, semi-active muffler has a better performance than passive muffler; above 350 Hz, it has worse performance compared with the passive muffler.     

Designing a plano-convex aspheric lens for fiber optics collimator

A plano-convex aspheric lens is designed to collimate the emitted light of the fiber optics. In this paper even orders of general aspheres are used to describe the aspheric surfaces sag. To determine the aspheric coefficient, the even asphere polynomial are fitted on the computed sag data. The surface sag data is determined using genetic algorithm method. The surface sag was analyzed by the commercial optical software package ZEMAX. For typical fiber optics, the numerical aperture (NA) of 0.22 was assumed. With this specification, the expected output spot diagram of 20 mm and the maximum aperture of 25.4 mm have been obtained. A comparison between here presented lens and the similar type of conventional lens has been carried out; the proposed aspheric lens corrected the spherical aberration, which led to increase in the collimated distance.     

Molecular dynamics simulation of low-energy bombardment of Pt (1 1 1) surface by Cu atoms with various incident angles

The low-energy bombardment of Pt (1 1 1) surface by Cu atoms with various incident angles (θ) is studied with MD simulations. In the case of near-normal incidence (θ≤20°), the result of energy deposition is similar to that of θ=0°. In contrast, in the case wherein the incident angles are higher than 60°, the incident atom cannot penetrate through the first layer and is scattered directly on the surface. The low-energy deposition has no obvious effect on the substrate. For 20°≤θ≤60°, the oblique incidence contributes to uniformity of nucleation and layer-by-layer growth of film as well as the layer-by-layer removal of atoms in the surface layers. Based on our MD simulations, the mechanism behind the deposition and thin film formation is related to the horizontal component and the vertical component of the impact momentum.     

Experimental and numerical study on aeroacoustic sound of axial flow fan in room air conditioner

Fan is one of the main noise sources of the room air-conditioners. Axial flow fans are widely used in the outdoor unit of split type air-conditioners. The interaction between the fan and the heat exchanger should be taken into consideration. However, only a few researches have been carried out on predicting the aeroacoustic noise because of the difficulty in obtaining detailed information of the flow field. This paper is to understand the generation mechanism of sound and to develop a prediction method for the flow field and the acoustic pressure field of the outdoor unit. Acoustic measurement is performed in a semi-anechoic chamber. Effects of each components is analyzed. Based on commercial computational fluid dynamics (CFD) code, Fluent, Fukano’s model is used to predict the overall sound pressure level of broadband noise. The predicted sound pressure levels based on original Fukano’s model are 7.66 dB and 7.42 dB lower than measurement results at 780 rpm and 684 rpm, respectively. And the errors are about 13%. However, when wake width and relative velocity are both calculated by numerical simulations and the distance to blade trailing edge is taken into consideration, the difference of sound pressure level between measurement and prediction is less than 3.4 dB and errors less than 5.5% while the distance is less than 10 mm. Thus, the distance to blade trailing edge should also be an important parameter for Fukano’s model. In comparison with experimental results, it is clearly shown that the Fukano method based on numerical simulation can provide more accuracy than the original Fukano model and numerical results are in a reliable level.     

Effects of measurement errors on refractive outcomes for pseudophakic eye based on eye model

With the Gullstrand-Le Grand eye model, the effects of various measurement errors on refractive outcomes for pseudophakic eye are studied. An equation to calculate the postoperative refractive error for pseudophakic eyes is derived. The accuracy to get a refractive error less than ca. 25 D is ±0.1 mm for the axial length, ±0.03 mm for the radius of the corneal anterior surface, ±0.12 D for the corneal power and ±0.16 mm for the postoperative anterior chamber depth (ACD). An error of 1 D in intraocular lens (IOL) power leads to a postoperative refractive error of −0.69 D. K-reading leads to a postoperative hyperopia from 0.18 to 0.74 D for eye with different refractive errors previously corrected. The constant velocity in ultrasound biometry assumption overestimates the axial length from 0.17 to 0.31 mm with actual axial length ranging from 21.31 to 32.31 mm. Errors in axial length, corneal power or radius of the corneal anterior surface and postoperative ACD play critical roles in determining the refractive outcomes. The constant-velocity assumption tends to overestimate the axial length. The change of the ratio of corneal anterior to the posterior surface is of minor importance for the overestimation of K-reading.     

Effect of angle of incidence on self-mixing laser Doppler velocimeter and optimization of the system

Based on the theory of speckle and self-mixing interference in laser-diode, three-facet cavity model is introduced to analyze laser Doppler effect based on self-mixing interference in the case of a rough surface, and numerical solution of the signal is obtained. Simulation results of speckle-modulated Doppler signal based on self-mixing effect and tracking accuracy at different incident angles are given using parameters employed in the experiment. Simulation results indicate incident angle of around 30° is most suitable when both tracking accuracy and signal amplitude are considered. Experimental waveforms agree well with simulation results, and similar conclusions as simulation predictions about changing trend of tracking accuracies of the system at different incident angles can be made. Combining with difference frequency analog phase-lock loop (PLL) technique and appropriate sampling time, a laser Doppler velocimeter with tracking accuracy better than 1.3% in the range of 10-470 mm/s is realized.     

Analysis of motion tracking in echocardiographic image sequences: Influence of system geometry and point-spread function

This paper focuses on motion tracking in echocardiographic ultrasound images. The difficulty of this task is related to the fact that echographic image formation induces decorrelation between the underlying motion of tissue and the observed speckle motion. Since Meunier’s seminal work, this phenomenon has been investigated in many simulation studies as part of speckle tracking or optical flow-based motion estimation techniques. Most of these studies modeled image formation using a linear convolution approach, where the system point-spread function (PSF) was spatially invariant and the probe geometry was linear. While these assumptions are valid over a small spatial area, they constitute an oversimplification when a complete image is considered. Indeed, echocardiographic acquisition geometry relies on sectorial probes and the system PSF is not perfectly invariant, even if dynamic focusing is performed.This study investigated the influence of sectorial geometry and spatially varying PSF on speckle tracking. This was done by simulating a typical 64 elements, cardiac probe operating at 3.5 MHz frequency, using the simulation software Field II. This simulation first allowed quantification of the decorrelation induced by the system between two images when simple motion such as translation or incompressible deformation was applied. We then quantified the influence of decorrelation on speckle tracking accuracy using a conventional block matching (BM) algorithm and a bilinear deformable block matching (BDBM) algorithm. In echocardiography, motion estimation is usually performed on reconstructed images where the initial sectorial (i.e., polar) data are interpolated on a cartesian grid. We therefore studied the influence of sectorial acquisition geometry, by performing block matching on cartesian and polar data.Simulation results show that decorrelation is spatially variant and depends on the position of the region where motion takes place relative to the probe. Previous studies did not consider translation in their experiments, since their simulation model (spatially invariant PSF and linear probe) yields by definition no decorrelation. On the opposite, our realistic simulation settings (i.e., sectorial probe and realistic beamforming) show that translation yields decorrelation, particularly when translation is large (above 6 mm) and when the moving regions is located close to the probe (distance to probe less than 50 mm).The tracking accuracy study shows that tracking errors are larger for the usual cartesian data, whatever the estimation algorithm, indicating that speckle tracking is more reliable when based on the unconverted polar data: for axial translations in the range 0-10 mm, the maximum error associated to conventional block matching (BM) is 4.2 mm when using cartesian data and 1.8 mm for polar data. The corresponding errors are 1.8 mm (cartesian data) and 0.4 mm (polar data) for an applied deformation in the range 0-10%. We also show that accuracy is improved by using the bilinear deformable block matching (BDBM) algorithm. For translation, the maximum error associated to the bilinear deformable block matching is indeed 3.6 mm (cartesian data) and 1.2 mm (polar data). Regarding deformation, the error is 0.7 mm (cartesian data) and 0.3 mm (polar data). These figures also indicates that the larger improvement brought by the bilinear deformable block matching over standard block matching logically takes place when deformation on cartesian data is considered (the error drops from 1.8 to 0.7 mm is this case).We give a preliminary evaluation of this framework on a cardiac sequence acquired with a Toshiba Powervision 6000 imaging system using a probe operating at 3.25 MHz. As ground truth reference motion is not available in this case, motion estimation performance was evaluated by comparing a reference image (i.e., the first image of the sequence) and the subsequent images after motion compensation has been applied. The comparison was quantified by computing the normalized correlation between the reference and the motion-compensated images. The obtained results are consistent with the simulation data: correlation is smaller for cartesian data, whatever the estimation algorithm. The correlation associated to the conventional block matching (BM) is in the range 0.45-0.02 when using cartesian data and in the range 0.65-0.2 for polar data. The corresponding correlation ranges for the bilinear deformable block matching are 0.98-0.2 and 0.98-0.55. In the same way these figures indicate that the bilinear deformable block matching yield a larger improvement when cartesian data are considered (correlation range increases from 0.45-0.02 to 0.98-0.2 in this case).     

LES-FEM coupled analysis and experimental research on aerodynamic noise of the vehicle intake system

To thoroughly explore the aerodynamic noise in order to achieve a more efficient engineering application for a vehicle intake system, the large eddy simulation and the finite element method were employed in numerical simulations, and the aeroacoustic characteristics were validated through the experimental data. In this research, the k-ε model was adopted to simulate the steady state fluid dynamic, and the static pressure loss was consistent with the bench test data, indicating the computational fluid dynamics model was valid. After acquiring the data from the steady state simulation, the fluctuating pressure of the inner wall was calculated based on the transient state calculation results from the large eddy simulation. Thereafter, the finite element method was used to determine the acoustic performance of the intake system. By comparing the experiment data, the noise reduction indicated that the intake system performed well at various frequencies, e.g. 320 Hz, 520 Hz and 770 Hz, but poorly at 140 Hz, 210 Hz, 420 Hz and 600 Hz. Finally, the far-field aerodynamic noise was calculated based on FW-H equation, and the output showed that the noise of each measuring point agreed well with the test results in trend. In particular, the inlet sound pressure spectrum almost fit the test data with the airflow of 300 m³/h, and several amplitude peaks appeared at 210 Hz, 420 Hz and 600 Hz, corresponding to the low-attenuation region of the noise reduction curve. Moreover, the specific frequencies were not shifted with the airflow changing. In conclusion, the numerical simulation method proves to be effective in calculating the aerodynamic noise accurately.     

Optical absorption by surface plasmons in deep sub-wavelength channels

The interaction of visible light with surface plasmons in a periodic array of silver channels is studied experimentally and theoretically. Channels of width 130 nm and depth 280 nm on a pitch of 468 nm were fabricated using electron beam lithography. Measurements of the reflectance of the channels show strong absorption for a specific angle of incidence at a given wavelength of the light. It is shown using a simple geometric model that this is consistent with the excitation and propagation of surface plasmons in the deep sub-wavelength channels. A numerical simulation of the electromagnetic fields excited in the channels confirms this result.     

Wide band gain flattening Yb-doped fiber amplifier

The gain flattening of Yb³⁺-doped fiber amplifier of 1053 nm band has been realized in experiment using three cascade 1 × 2 fused tapered fiber coupler. The gain flattening band is about 20 nm with less than 1 dB power fluctuation around 1053 nm, which is agree with our numerical stimulation results very well.     

Space radiation effect on EDFA for inter-satellite optical communication

The erbium-doped fiber (EDF) has been irradiated by electron with a dose of 1000 krad to analyse the space radiation effect on EDF amplifier (EDFA) in inter-satellite optical communication. This is the first work to analyse the effect on actually applied systems. Three critical parameters of EDFA, most important for external module subsystems, have been tested. The output power comes down to −57.21 dBm and the noise figure (NF) climbs up to 18.14 dB at dose 1000 krad, when the input power is −2.00 dBm. Although there is a strong ability to recover after the radiation experiment, EDFA deterioration is really huge. Apart from that, the central wavelength of EDFA never changes. To guarantee the accuracy of analysis of the radiation effect on EDFA, WDM coupler and isolator are also irradiated with the EDF at the same time. According to the results of all the tests, the EDFA could be directly used in the low-radiation dose orbits if doses are less than 20 krad. And the radiation experiment data will also be a good reference for the design of the actual systems in inter-satellite optical communication with different dose orbits.