Mirror Tilt Angle Research Articles

Long-range frequency-domain optical delay line based on a spinning tilted mirror for low-cost ocular biometry.

Optical biometers are routinely used to measure intraocular distances in ophthalmic applications such as cataract surgery planning or myopia monitoring. However, due to their high cost and reduced transportability, access to them for screening and surgical planning is still limited in low-resource and remote settings. To increase patients' access to optical biometry we propose a novel low-cost frequency-domain optical delay line (FD-ODL) based on an inexpensive stepper motor spinning a tilted mirror, for integration into a time-domain (TD)-biometer, amenable to a compact footprint. In the proposed FD-ODL, the axial scan range and the A-scan rate are decoupled from one another, as the former only depends on the spinning mirror tilt angle, while the A-scan rate only depends on the motor shaft rotational speed. We characterized the scanning performance and specifications for two spinning mirror tilt angles, and compared them to those of the standard, more expensive FD-ODL implementation, employing a galvanometric scanner for group delay generation. A prototype of the low-cost FD-ODL with a 1.5 deg tilt angle, resulting in an axial scan range of 6.61 mm and an A-scan rate of 10 Hz was experimentally implemented and integrated in a dual sample beam optical low-coherence reflectometry (OLCR) setup with a detour unit to replicate the measurement window around the anterior segment and the retina. The intraocular distances of a model eye were measured with the proposed low-cost biometer and found to be in good agreement with those acquired by a custom swept-source optical coherence tomography (SS-OCT) system and two commercial biometers, validating our novel design.

Transmission structured illumination microscopy with tunable frequency illumination using tilt mirror assembly

We present experimental demonstration of tilt-mirror assisted transmission structured illumination microscopy (tSIM) that offers a large field of view super resolution imaging. An assembly of custom-designed tilt-mirrors are employed as the illumination module where the sample is excited with the interference of two beams reflected from the opposite pair of mirror facets. Tunable frequency structured patterns are generated by changing the mirror-tilt angle and the hexagonal-symmetric arrangement is considered for the isotropic resolution in three orientations. Utilizing high numerical aperture (NA) objective in standard SIM provides super-resolution compromising with the field-of-view (FOV). Employing low NA (20X/0.4) objective lens detection, we experimentally demonstrate sim (0.56 mmtimes0.35 mm) size single FOV image with sim1.7- and sim2.4-fold resolution improvement (exploiting various illumination by tuning tilt-mirrors) over the diffraction limit. The results are verified both for the fluorescent beads as well as biological samples. The tSIM geometry decouples the illumination and the collection light paths consequently enabling free change of the imaging objective lens without influencing the spatial frequency of the illumination pattern that are defined by the tilt-mirrors. The large and scalable FOV supported by tSIM will find usage for applications where scanning large areas are necessary as in pathology and applications where images must be correlated both in space and time.

Two-mirror aerial mapping camera design with a tilted-aplanatic secondary mirror for image motion compensation.

The optical compensation method is a promising method to compensate the image motion by driving the optical element of the system. However, the tilt motion of the optical element could induce the degradation of the image quality. Based on the Nodal Aberration Theory (NAT), this paper proposes a novel optical image motion compensation design with a secondary tilt-aplanatic two-mirror optical system (STATOS), which achieves the insensitivity on the image quality of the optical system. First, the properties of coma-free pivot point depending on the location of stop at primary mirror or secondary mirror have been analyzed respectively. Then the calculating method about construction parameters in terms of STATOS is developed. Further, the maximum tilt angle of secondary mirror could be solved using NAT under ordered specific restriction. Finally, a prototype is designed with SM-tilting result of MTF value maintain above 0.32 at the cut-off frequency of detector, where the principal distance could remain stable and the changed distortion is better than 0.03%. A test flight has been carried out to prove the desired results and feasibility of STATOS used in an aerial mapping camera.

Кинематический расчет элементов микрозеркал микроэлектромеханических систем (MEMS)

Currently, the development and application of micro machines is an important direction in the development of microelectromechanical systems (MEMS) technologies. In these devices, electromechanical energy conversion occurs, as a result of which forces arise that carry out mechanical work within the dimensions of the microcircuit case. The paper considers the kinematic calculation of the design of a micromirror with a reflective layer of high optical quality of the surface for deflecting the reflected laser beam. By changing the angle of inclination of the micromirror, the laser beam enters the various input channels of the optical sensor. In this case, a control signal is generated for the further operation of the microcircuit. Thus, the micromirror performs the function of a switch of input optical channels, connecting in various combinations certain input or output elements of the microcircuit for further processing. The article presents the calculation of the kinematic parameters of the mechanical structure of the micro mirror. Practical recommendations are given for choosing the optimal range of variation of the micro mirror tilt angles in order to increase the strength of its structure, as well as to reduce the power of the mechanical drive of the micro machine required to change the micro mirror tilt angles

Influence of Dust Accumulation on the Solar Reflectivity of a Linear Fresnel Reflector

Solar reflecting and heat collecting systems are generally operated outdoors year-round, and the optical performance of the reflector is reduced by dust accumulation on the surface. In this study, the dust accumulation on a linear Fresnel reflector was investigated. The relative reflectivity of the mirror before and after dust accumulation and the physical and chemical characteristics of the dust were measured using an ultraviolet spectrophotometer, scanning electron microscope, and X-ray diffractometer. The results showed that the dust density on the mirror increased, and the relative reflectivity decreased with an increase in the dust accumulation time. During 48 days of dust accumulation, the average relative reflectivity decreased 9.4% for a 1 g/m2 increase in the dust density. Additionally, the dust density on the mirror increased while the relative reflectivity decreased with a decrease in the mirror tilt angle. The rate of decrease of the relative reflectivity was higher for the aluminum mirror than that of the silver mirror after dust accumulation. The main component of the dust particles in the test area was SiO2, and the particle size range of the dust was 0.9 um to 87 µm. According to the physical and chemical properties of the dust and the shielding effect of the dust on the mirror, a model to predict the influence of natural dust accumulation on the relative reflectivity of the linear Fresnel reflector was proposed. The predicted results deviated about 1% from the test results.

Optofluidic microbubble Fabry-Pérot cavity.

An optofluidic microbubble Fabry-Pérot (OMBFP) cavity was investigated. In contrast to plane-plane FP (PPFP) cavities, the optical mode confinement and stability in an OMBFP were significantly enhanced. The optical properties of the OMBFP cavity, including the quality (Q) factor, effective mode area, mode distribution as a function of the core refractive index, microbubble position, and mirror tilt angle, were investigated systematically using the finite element method. In optofluidic lasing experiments, a low lasing threshold of 1.25 µJ/mm2, which was one order magnitude lower than that of the PPFP, was achieved owing to improved modal lateral confinement. Since the microbubble acts as a micro-lens and microfluidic channel in the parallel FP cavity, mode selection and cell-dye laser were easily realized in the OMBFP cavity.

Effects of the Mirror Tilt Angle on the Growth of LiCoO2 Single Crystals by the Traveling Solvent Floating Zone (TSFZ) Technique Using a Tilting-Mirror-type Image Furnace

The effects of the mirror tilt angle on the molten zone shape during the growth of LiCoO2 crystals were investigated for the first time for the TSFZ technique using a tilting-mirror-type image furn...

Design of diffractive imaging optical system based on off-axis four-mirror

According to the Schupmann's achromatic theory, a calculation method of off-axis four-mirror diffractive imaging optical system is introduced. By using the method, an optical system which has an aperture of 1 m, F-number of 8, full field of view of 0.12°, waveband of 582.8 nm~682.8 nm is designed. The results show that the chromatic aberration is corrected effectively. The modulation transfer function (MTF) is more than 0.53 in the range of 50 lp/mm, and the RMS radius of diffusion spot is less than the airy radius. It demonstrates that the image quality of this system is close to the diffraction limit. It is analyzed that the processing of diffractive primary lens and diffractive correct mirror can be realized by traditional lithography and diamond turning, respectively. Monte-Carlo simulation of tolerance analysis is carried out, it determined that the tolerance error mainly originates from the tilt angle of relay mirror, which provides guidance for the process of assembling and adjusting. This system has the advantages of broadband, high image quality, which can provide references for the development of reflective diffractive imaging optical system.

Stable High-Q Bouncing Ball Modes inside a Fabry–Pérot Cavity

We discover that stable high-Q bouncing ball modes with tight lateral confinement and whole-body light–matter interaction can exist in an imperfectly aligned, wedged plano–plano FP (WFP) cavity by simply introducing a vertical dielectric interface (DI) between two media with different refractive indices. Compared to a pure WFP cavity without the DI, which is known to have a low-Q factor and a finesse of 10–300 due to the large diffraction and geometrical walk-off losses, our WFP-DI cavity exhibits a high-Q factor of ∼105, a finesses of ∼3000, and a mode size (or diameter) down to 2 μm. Furthermore, optical properties of our WFP-DI cavity, including stability, loss, dependences of the Q-factor, and the effective mode area on the DI refractive index contrast and the mirror tilt angle are systematically investigated using numerical methods. Finally, we experimentally demonstrate WFP-DI dye lasers in the total internal reflection (TIR) and non-TIR cases. A lasing threshold of 1–2 μJ/mm2 is achieved, which is 7–40× lower than the pure WFP laser without the DI and agrees well with the theoretical predications. Our results suggest that the WFP-DI cavity provides a promising technology platform for miniaturized photonic devices, optofluidic lasers, and microfluidics for biological/chemical analysis.

A detailed investigation and performance optimization of a photovoltaic panel integrated with a reflecting mirror

In this paper, the performance of a photovoltaic panel integrated with a reflecting mirror is investigated. In this regard, the effects of panel and mirror tilt angles, and the mirror length on the system performance are modeled. The cell temperature rises have also been considered. Moreover, by a 3D model, the lighting and shading statuses are studied in detail, and all the possible conditions are presented and modeled. The resulting model can calculate the amount of incident solar energy on the panel and the generated electrical power in every moment during a year. This amount is dependent on the system configuration and capacity and its location. A 250-W photovoltaic panel and the city of Tehran have been considered the basics of calculations to assess the model results. By employing the genetic algorithm method, the optimum configuration has been found to have 69.084° and 0° tilt angles for the panel and the mirror, respectively, at the mirror length of 2 m. This configuration can generate 2.38 GJ (613.89 kWh) of electrical energy annually. It was also found that the optimum configuration had 0.024 GJ of annual energy losses due to the effects of cell temperature rise.

Principle of a two-output-difference interferometer for removing the most important interference distortions

ABSTRACTThis paper presents a two-output-difference interferometer for removing the most important interference distortions caused by nonlinear detectors. These distortions can be removed not only because the resulting interferogram is composed of the difference between the signals of the two detectors, but also because the modulated signals at each output have the same amplitude and opposite phases. Due to the use of two corner-cube mirrors fixed as a single moving element, the tilt and shearing problem will disappear. The effect of the corner-cube mirror deviation angle and the plane mirror tilt angle are investigated in detail, and the formulas of their tolerance are derived by means of modulation depth and phase error. The advantage of the interferometer enables it to be suitable for Fourier transform spectrometers.

Measurement of absolute gravity based on cold atom gravimeter at large tilt angle

The tilt angle of a cold atom gravimeter (CAG) could have a significant influence on the measurement of absolute gravity. The measurement, manipulation, and compensation of the tilt for CAG need to be conducted in order to obtain a high-accuracy absolute gravity measurement. In this paper, firstly, the influences of tilt on absolute gravity measurement under four different conditions are analyzed theoretically by taking into account the position of vacuum system relative to Raman retro-reflection mirror. Then, the experimental investigation is carried out and it is found that the measured results agree well with the theoretical prediction curves. According to the analysis above, we design a scheme for absolute gravity measurement based on two inclinometers, mainly to solve the problem of long-term tilt drift of CAG especially in harsh measurement environment. In this scheme, a high-resolution inclinometer is used to record the tilt angle of Raman retro-reflection mirror, which is fixed on a passive vibration isolation platform. Besides, another inclinometer is utilized to monitor the tilt angle of vacuum chamber of the CAG. By doing so, the vibration noise can be suppressed and the tilt data can be measured with a high precision. Finally, the experimental verification of this proposal is carried out based on our homemade compact cold atom gravimeter, and the high accuracy absolute gravity measurement is realized in a complex workshop environment. Since the vibration noise of Raman mirror is improved by using the vibration isolation platform, the sensitivity of our CAG can reach 319 μGal √Hz. Besides, we measure the long-term changes of gravity with time and find that the experimental results are consistent with the curves calculated by theoretical tidal model. Moreover, due to the precise measurement and compensation for the tilt drift, the accuracy of our CAG is estimated at 12.3 μGal. In order to evaluate this system accuracy, a comparison between our CAG and the FG5 at the same measured site is made. The absolute gravity values determined by both gravimeters coincide with each other. In this paper, we provide a feasible scheme for measuring the absolute gravity in the complex environment. The experimental demonstration of this measurement scheme is performed thereby acquiring some valuable reference data for the practical use of CAG.

Modeling and analysis for the image mapping spectrometer**Project supported by the National Natural Science Foundation of China (Grant Nos. 61635002 and 61307020) and the Changjiang Scholars and Innovative Research Team in University (PCSIRT) Program, China.

The snapshot image mapping spectrometer (IMS) has advantages such as high temporal resolution, high throughput, compact structure and simple reconstructed algorithm. In recent years, it has been utilized in biomedicine, remote sensing, etc. However, the system errors and various factors can cause cross talk, image degradation and spectral distortion in the system. In this research, a theoretical model is presented along with the point response function (PRF) for the IMS, and the influence of the mirror tilt angle error of the image mapper and the prism apex angle error are analyzed based on the model. The results indicate that the tilt angle error causes loss of light throughput and the prism apex angle error causes spectral mixing between adjacent sub-images. The light intensity on the image plane is reduced to 95% when the mirror tilt angle error is increased to (). The prism apex error should be controlled within the range of 0–36 (0.01 ) to ensure the designed number of spectral bands, and avoid spectral mixing between adjacent images.

Bistability Controlled by Convection in a Pattern-Forming System.

We analyze the transition from convective to absolute dynamical instabilities in a nonlinear optical system forming patterns, i.e., a photorefractive crystal in a single feedback configuration. We demonstrate that the convective regime is directly related to the bistability area in which the homogeneous steady state coexists with a pattern solution. Outside this domain, the system exhibits either a homogeneous steady state or an absolute dynamical regime. We evidence that the bistability area can be greatly increased by adjusting the mirror tilt angle and/or by applying an external background illumination on the photorefractive crystal.

Research on beam characteristics in a large-Fresnel-number unstable-waveguide hybrid resonator with parabolic mirrors.

Large-Fresnel-number unstable-waveguide hybrid resonators employing spherical resonator mirrors suffer from spherical aberration, which adversely affects beam quality and alignment sensitivity. In this paper, we present experimental and numerical wave-optics simulations of the beam characteristics of a negative-branch hybrid resonator having parabolic mirrors with a large equivalent Fresnel number in the unstable direction. These results are compared with a resonator using spherical mirrors. Using parabolic mirrors, the output beam has a smaller beam spot size and higher power density at the focal plane. We found that the power extraction efficiency is 3.5% higher when compared with a resonator using spherical mirrors as the cavity length was varied between -1 and 1 mm from the ideal confocal resonator. In addition, the power extraction efficiency is 5.6% higher for mirror tilt angles varied between -6 and 6 mrad. Furthermore, the output propagating field is similar to a converging wave for a spherical mirror resonator and the output beam direction deviates 3.5 mrad from the optical axis. The simulation results are in good agreement with the experimental results.

Effects of tilt angle of mirror–lamp system on shape of solid–liquid interface of silicon melt during floating zone growth using infrared convergent heating

The tilt effects of the mirror–lamp (M–L) system on the shape of the interface of the silicon molten zone formed during growth using the infrared convergent heating floating zone method were studied at various positions of the M–L system. The stability and the interfaces of the molten zone formed in the tilted condition were compared with those in the no tilt condition. The molten zone appeared to be more stabilized in the tilted condition than in the no tilt condition. However, the conventional parameters characterizing the interface shape such as convexities (h/r), gap and zone length (L) were almost independent of the tilt angle (θ) of the M–L system and insufficient to discuss the tilting effects on the molten zone shape. The curvature of the solid–liquid interface was affected by the θ. New characterizing parameters such as the growth interface and triple point angles (δ and TPA, respectively) were effective to quantitatively describe the tilting effects on the interface shape. With increase of the θ, the δ was decreased and the TPA was increased in both the feed and crystal sides. A silicon crystal of 45mm in diameter was grown successfully in the tilted condition.

Design method of off-axis extreme ultraviolet lithographic objective system with a direct tilt process

An off-axis extreme ultraviolet (EUV) lithographic objective can achieve a high numerical aperture (NA) beyond 0.33 with only six mirrors due to the efficient separation of the ray path, which greatly improves the resolution and energy utilization. A method is developed to design an off-axis lithographic objective with six mirrors. The method starts with a coaxial system with ray vignetting caused by increase of the NA. To avoid the ray vignetting, a reasonable range of solution for the tilt angle of each mirror is determined by real ray calculation. A set of optimal solutions for tilt angles of mirrors, which corresponds to the minimal composite root-mean-square wavefront error, is found from the reasonable ranges of solutions by a search program. In this way, an initial off-axis configuration without ray vignetting can be directly obtained and it is suitable for further optimization. To demonstrate the practicability of the method, an off-axis design example is given which shows that the presented method provides an efficient process to get to initial configuration for off-axis EUV lithographic objective with six mirrors.

Hybrid approach for the design of mirror array to produce freeform illumination sources in immersion lithography

Source and mask optimization (SMO) has emerged as a key resolution enhancement technique (RET) for 45nm technology node and below in lithography. The design method of freeform illumination sources predicted by SMO is significant for the scanner development. We present a hybrid approach combining simultaneous and sequential approaches to optimize the tilt angles of the mirrors to produce multi target freeform illumination sources accurately and quickly. The size of spot reflect by plane mirror can be easily controlled by changing different microlens arrays with appropriate focal length, which reduce the complexity of the system and makes it more flexible to produce the specific freeform sources compared to curving the mirrors used in previous work. The relationship between the tilt angles of plane mirrors and the positions of the spots in the pupil is obtained by chief ray tracing. Using the hybrid approach the freeform illumination sources required by SMO can be designed by merely adjusting the tilt angles of mirrors without changing other parameters of optical elements, which is most effective for both lithography tool manufacture and its applications. The real ray tracing results demonstrate that our design method is capable of creating multi freeform illumination sources with high transmittance, and confirm that the effectiveness of the hybrid approach for optimized design and control of mirror array in immersion lithography system.

High-Throughput and Low-Cost Fabrication of Polymer Microscanner for Lighting Applications

A high-throughput and low-cost fabrication process for an optical microscanner is proposed for lighting applications. The process utilizes mold replication and transfer of printed functional layers to form a film. We confirmed that a high-throughput fabrication lasting less than 30 s could be obtained by using a mold with a knife edge. A polymer microscanner with feature size of 0.6×2 mm2 was successfully fabricated using our process. The scanner was actuated by magnetic forces generated by an external coil, and the mirror tilt angle was successfully measured by a strain gauge formed by the functional layer transfer. By synchronizing the LED input signal and the polymer scanner tilt angle, the illuminance distribution could be controlled. For example, this distribution could be expanded from 10 to 50° or divided into two separated spots. We believe that our developed process can address new MEMS applications such as commercial lighting.

Torque Measurement Device Using an Integrated Microdisplacement Sensor

In this paper, we propose a torque measurement device embedded in robot arms. The device uses an integrated microdisplacement sensor and trapezoidal frame. The sensor tip of 3 mm area and 0.7 mm thickness measures the mirror tilt angle on the underside of the frame caused by a torque applied to the frame. We have successfully measured a linear output change for the torque and found that the gradient of the output change differed largely from the material and the corner angle of the frame.