Collimator Lens Research Articles

Positioning control effectiveness of optical knife edge displacement sensor-embedded monolithic precision stage

This paper presents positioning control effectiveness of optical knife edge sensors (OKES) for compact nanopositioning stage applications. The OKES performance was characterized in terms of precision, dynamic characteristics, working range and control effectiveness. The OKES consists of the laser diode, collimation lens, beam splitter, mirror, double-side sharp knife edge, and two lensed photodiodes. The double compound notch type flexure stage was fabricated by additive manufacturing process, stereolithography, and the OKES was successfully embedded into the flexure stage to control the positioning in a compact and efficient configuration. The voice coil motor was aligned along the moving axis of the stage without offset to mitigate Abbe error, and the OKES was setup at the center perpendicular to the moving axis. The positioning of flexure stage was proportional-integral-derivative feedback controlled. As a result, the AM flexure mechanism was successfully position controlled to a margin of 50nm within a 500μm range. It was also found that the OKES is sensitive to torsional motion and it can be used for angular motion measurement such as parasitic motions with high sensitivity. Therefore, the OKES and voice coil actuator can be a good alternative to the capacitive sensors and piezoelectric transducers in terms of performance: measuring and actuation range, positioning accuracy, resolution, bandwidth and control effectiveness.

Cell depth imaging by point laser scanning fluorescence microscopy with an optical disk pickup head

A compact, cost-effective, and position-addressable digital laser scanning microscopy (DLSM) instrument is made using a commercially available Blu-ray disc read-only memory (BD-ROM) pickup head. Fluorescent cell images captured by DLSM have resolutions of 0.38 µm. Because of the position-addressable function, multispectral fluorescence cell images are captured using the same sample slide with different excitation laser sources. Specially designed objective lenses with the same working distance as the image-capturing beam are used for the different excitation laser sources. By accurately controlling the tilting angles of the sample slide or by moving the collimator lens of the image-capturing beam, the fluorescence cell images along different depth positions of the sample are obtained. Thus, z-section images with micrometer-depth resolutions are achievable.

Microbolometer Terahertz Focal Plane Array and Camera with Improved Sensitivity in the Sub-Terahertz Region

A pixel in an uncooled microbolometer terahertz (THz) focal plane array (FPA) has a suspended structure above read-out integrated circuit (ROIC) substrate. An optical cavity structure is formed between a thin metallic layer deposited on the suspended structure and a thick metallic layer deposited on the ROIC surface. The geometrical optical cavity length for our previous pixel structure, 3–4 μm, is extended three times, so that responsivity can be increased in the sub-THz region. This modification is carried out by depositing a thick SiN layer on the thick metallic layer. The modified pixel structure is applied to 640 × 480 and 320 × 240 THz-FPAs with 23.5 μm pixel pitch. Minimum detectable powers per pixel (MDP) are evaluated for these FPAs at 4.3, 2.5, 0.6, and 0.5 THz, and the MDP values are found to be improved by a factor of ten at 0.6 and 0.5 THz. The MDP values of the THz-FPAs developed in this work are compared with those of other THz detectors, such as uncooled antenna-coupled CMOS (complimentary metal-oxide semiconductor) THz-FPAs and cooled bolometer arrays. It is found that our THz-FPAs are more sensitive in the sub-THz region than the CMOS THz-FPAs, while they are much less sensitive than the cooled bolometer arrays. These THz-FPAs are incorporated into a 640 × 480 THz camera and 320 × 240 THz camera, and imaging equipment is developed. The equipment consists of a linearly polarized sub-THz source, a collimator lens, a beam homogenizer, two wire grids, a quarter-wave plate, and two THz cameras, and sub-THz images are demonstrated. It should be mentioned for the equipment that imaging of transmission and reflection is realized by moving only the quarter-wave plate, and the reflection image is taken along a direction normal to a sample surface so that the reflection image is hardly deformed.

Enhanced transmission and beaming of light from a photonic crystal waveguide via two collimation lenses

Directional emission of light passing through a subwavelength photonic crystal waveguide (PCW) with the help of two collimation lenses is researched. The collimation lens is another photonic crystal with a self-collimation effect. Four different configurations of PCW and collimation lens are studied by the finite-difference time-domain (FDTD) method. Simulation results show that this collimation lens method can not only achieve a high transmission and low divergence light beam but also provide a wide band width of Δω/ω=5% (where, ω is the angular frequency), which is better than the mechanism of interference of surface modes.

High power high efficiency fiber coupled diode laser module

The high coupling-efficiency fiber coupled diode laser module is obtained by beam shaping. The wavelength of the CW diode laser bar is 976 nm, and five bars are collimated by a fast axis collimation lens. Then the beams are transformed and collimated by slow axis collimation optics. Then all the beams are combined in space, and focused into a multimode fiber (400 m core diameter, the numerical aperture (NA) is 0.22). Experimental results show that the laser output from fiber could reach 327 W, and the coupling-efficiency is more than 93.6%. Experimental results demonstrate that this module lays a foundation for multi-wavelength, polarization beam combining and the high beam quality, high coupling efficiency diode laser module with CW thousands watts class output power can be developed.

A novel inlet system for online chemical analysis of semi-volatile submicron particulate matter

Abstract. We herein present a novel modular inlet system designed to be coupled to low-pressure gas analyzers for online chemical characterization of semi-volatile submicron particles. The "chemical analysis of aerosol online" (CHARON) inlet consists of a gas-phase denuder for stripping off gas-phase analytes, an aerodynamic lens for particle collimation combined with an inertial sampler for the particle-enriched flow and a thermodesorption unit for particle volatilization prior to chemical analysis. The denuder was measured to remove gas-phase organics with an efficiency > 99.999% and to transmit particles in the 100–750 nm size range with a 75–90% efficiency. The measured average particle enrichment factor in the subsampling flow from the aerodynamic lens was 25.6, which is a factor of 3 lower than the calculated theoretical optimum. We coupled the CHARON inlet to a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) which quantitatively detects most organic analytes and ammonia. The combined CHARON-PTR-ToF-MS setup is thus capable of measuring both the organic and the ammonium fraction in submicron particles in real time. Individual organic compounds can be detected down to levels of 10–20 ng m−3. Two proof-of-principle studies were carried out for demonstrating the analytical power of this new instrumental setup: (i) oxygenated organics and their partitioning between the gas and the particulate phase were observed from the reaction of limonene with ozone and (ii) nicotine was measured in cigarette smoke particles demonstrating that selected organic target compounds can be detected in submicron particles in real time.

Analysis and minimization of spacing error of holographic gratings recorded with spherical collimation lenses.

This research proposes a feedback method to adjust the dual-beam exposure system with spherical collimation lenses to achieve gratings with low spacing error. Through theoretical analysis and numerical calculation, it is proved that the interference aberration can be analyzed with the Zernike polynomials and the adjustment errors can be estimated according to the linear relationship between the errors and the polynomial coefficients. Moreover moving the substrate along its normal is proposed to decrease the spacing error but keep the grating's period unchanged. In the experiments, the wavefront measurement results of the ± 1st orders are used to deduce the spacing error. Based on the feedback adjustment method, the grating with a spacing error of 0.03 λ within 70 mm × 70 mm is fabricated with the collimation lenses of 0.6 λ spherical aberration.

Nonuniform grid target tessellation method for the design of lens group with rectangular uniform illumination

A nonuniform grid target tessellation method is proposed for designing a lens group with rectangular uniform illumination, a small screen incident angle, and high collection efficiency. A collimation lens is first designed to collimate the source rays preliminarily. Second, the source collected solid angle is tessellated so that each source ray encompasses the same flux. Third, the source rays are traced to the first surface of lens 2. Finally, the nonuniform grid target tessellation iteration is applied to find the integrability mapping. The freeform surface constructed with this method can exactly refract the rays to their corresponding target location, and the rectangular uniform illumination is accomplished. To verify the effectiveness of the proposed method, a design example is presented with a rectangular figuration and a high uniformity, the incident angle is smaller than 12° and the collection efficiency reaches 96% with Lambertian point source.

Influence on the recovered spectrum caused by thermal optics effect of the collimation lens used in static Fourier transform infrared spectrometer

In a stepped-mirror-based static Fourier transform infrared spectrometer, the collimation lens is located adjacent to the light source and the thermal radiation would lead to the partial temperature increase, and the refractive index of the infrared material unavoidably changes. Then the light beam passing through the collimation lens will induce a divergence angle, directly affecting the resolution of the recovered spectrum. Meanwhile, the angular divergence results in a displacement in the interference signal, making increasing difficulties in the interferogram processing and the spectrum recovery. In this paper, the distribution of temperature in different areas of the collimation lens is studied under the working condition, and the defocusing value of the collimation lens is 0.153 mm that is caused by the refractive index gradient of the infrared material along with the temperature. In addition, the divergence angle induced by defocusing is calculated, its distribution being nonuniform but symmetrical within the sample area. Moreover, the divergence angle brings about additional optical path difference, its effect on the recovered spectrum is analyzed. Compared with the ideal recovered spectrum, much noise emerges and the peak value is reduced in the real recovered spectrum. The spectrum-construction error of the real recovered spectrum is 18.72%, indicating that the recovered spectrum is seriously distorted, and the resolution at the center wavelength in the ideal recovered spectrum and the real spectrum are 4.71 cm-1 and 5.57 cm-1, respectively. This indicates that the spectrum resolving power is weakened. Furthermore, the reasonable temperature range is obtained by analyzing the curve of spectrum-construction error versus temperature of the collimation lens. When a spectrum-construction error of less than 5% is demanded, the temperature difference between the front len of collimation and the ambient must be less than 8 ℃. Finally, experiments are performed using a SiC rod as the light source, and interferograms are made by four steps including dark current electric noise elimination, spatial gain correction, image signal averaging, and spectrum recovery. Results show that the spectrum-construction errors (SCE) from the cold light source and non-cold light source are 8.48% and 21.51%, respectively. Although they are all larger than the theoretical value, the SCE of cold light source decreases by 13.03% compared to cooling-free light source. Hence, it is necessary to reduced the thermal radiation influence on collimation lens from the light source. This result is helpful in solving the analogous problems.

基于大功率LED扩展光源的均匀光斑光辐射模拟器设计

Based on principle of edge ray and etendue conservation ideas,the compound parabolic concentrator and freeform lens collimator were designed for high power Light Emitting Diode extended source.By using TracePro software for ray tracing simulation and experimental guidance,a light radiation simulator with uniform illumination output was developed.The divergence angle of simulator output light beam is measured as ±0.2rad.In the lightscreen of 50 cm distance the beam horizontal uniformity is measured better than 4.1%,and longitudinal uniformity better than 3.8%,within 14cm×14cm size illuminated area.

LED Collimation Module for Time Sequential Back Light System

Collimation lenses for light-emitting diode (LED) light sources have been widely used in lighting engineering. In this paper, a collimated LED light source was developed for a color liquid-crystal display backlight, which is driven using a two-field driving scheme to display color. A color-separation backlight that involves using the designed collimation modules possesses several advantages such as low volume, elimination of dye color filters, high feasibility with conventional ultra-precision machining processes, and a wide color gamut.

A study on the optical parts for a semiconductor laser module

A semiconductor laser module consists of a LD (laser diode) chip that generates a laser beam, two cylindrical lenses to collimate the laser beam, a high-reflection mirror to produce a large output by collecting the laser beam, a collimator lens to guide the laser beam to an optical fiber and a protection filter to block reflected laser light that might damage the LD chip. The cylindrical lenses used in a semiconductor laser module are defined as FACs (fast axis collimators) and SACs (slow axis collimators) and are attached to the system module to control the shape of the laser beam. The FAC lens and the SAC lens are made of a glass material to protect the lenses from thermal deformation. In addition, they have aspheric shapes to improve optical performances. This paper presents a mold core grinding process for an asymmetrical aspheric lens and a GMP (glass molding press), what can be used to make aspheric cylindrical lenses for use as FACs or SACs, and a protection filter made by using IAD (ion-beam-assisted deposition). Finally, we developed the aspheric cylindrical lenses and the protection filter for a 10-W semiconductor laser module.

Compact LED projector design with high uniformity and efficiency.

The aim of this study is to design a compact LED projector that is divided into two systems: an illumination system and an imaging optical system. The illumination system consists of an RGB LED light source with a collimator lens group and a mirror with a color filter and a lens array integrator instead of an integrated rod so as to improve the uniformity of the light intensity. By using a new total internal reflection prism and projection lens, the whole optical engine is smaller in size and has a higher contrast ratio for image quality. The imaging optical system consists of a total of eight lenses (six spherical lenses and two aspherical lenses), for a total length of 52 mm; a tolerance analysis is conducted. Optical simulation software is used for the system analysis in order to determine the efficiency and uniformity of the light intensity. In this design, the uniformity of the screen reaches more than 82%, and the efficiency increases by more than 44%.

A Simple Design Approach of a Fresnel Lens for Creating Uniform Light-Emitting Diode Light Distribution Patterns

Devising an efficient method for distributing high-radiance light-emitting diode emissions onto target surfaces is a continuing challenge. Most current design methods are mathematically complex and require intricate optimizations. In this article, a simple and highly accurate geometric optics analysis is described for creating a free-form total internal reflection collimator lens and a Fresnel exit lens, which can be fabricated easily for producing a specific intensity distribution. A powerful application is the ability to create various high-efficiency and uniform illumination patterns from a standard widely used MR16 light bulb by simply attaching a Fresnel exit lens onto the face of the bulb.

Full spectral and angular characterization of highly directional emission from nanocrystal quantum dots positioned on circular plasmonic lenses.

We design a circular plasmonic lens for collimation of light emission from nanocrystal quantum dots at room temperature in the near IR spectral range. We implement a two-dimensional k-space imaging technique to obtain the full spectral-angular response of the surface plasmon resonance modes of the bare plasmonic lens. This method is also used to map the full spectral-angular emission from nanocrystal quantum dots positioned at the center of the circular plasmonic lens. A narrow directional emitting beam with a divergence angle of only ∼4.5° full width at half-maximum is achieved with a spectrally broad bandwidth of 30 nm. The spectrally resolved k-space imaging method allows us to get a direct comparison between the spectral-angular response of the resonant surface plasmon modes of the lens and the emission pattern of the quantum dots. This comparison gives a clear and detailed picture of the direct role of these resonant surface waves in directing the emission. The directional emission effect agrees well with calculations based on the coupled mode method. These results are a step toward fabricating an efficient room-temperature single photon source based on nanocrystal quantum dots.

Note: Longitudinally excited N₂ laser with low beam divergence.

We developed a longitudinally excited N2 laser (337 nm) with low beam divergence without collimator lenses. The N2 laser consisted of a 30 cm long Pyrex glass tube with an inner diameter of 2.5mm, a normal stable resonator formed by flat mirrors, and a simple, novel driver circuit. At a N2 gas pressure of 0.4 kPa and a repetition rate of 40 Hz, the N2 laser produced a circular beam with an output energy of 2.6 μJ and a low full-angle beam divergence of 0.29 mrad due to the uniform discharge formed by the longitudinal excitation scheme, the long cavity with the small aperture, and the low-input energy oscillation.

Stable-wavelength and narrow-bandwidth high-power external-cavity laser diode stack

We demonstrated a simple external-cavity configuration to effectively suppress the spectral bandwidth of a high-power laser diode (LD) stack. The external cavities consisted of a set of microcylindrical lenses for fast-axis collimation and a single volume Bragg grating. On the basis of this configuration, we reduced the bandwidth from 2.34 to 0.36 nm (6.5-fold reduction) and achieved a peak power output of 335 W. The external-cavity LD stack showed very good spectrum stability in the entire current and wide temperature ranges considered.

Miniaturized reflectance devices for chemical sensing

This effort seeks to evaluate the potential of the TAOS TCS3200 RGB sensor chip in a reflectance configuration for use in target detection based on color changes in porphyrin indicators using alcohols as model targets. The chip was evaluated as provided by Parallax, Inc as a component of the TCS3200-DB which includes white LEDs, collimator lens, and standoffs for optimization of sensing distance. Nonlinearity in the response of the daughter board to color standards was observed. Signal noise levels were determined to be less than 1% within a given measurement and measurement-to-measurement variations of ~9% were observed. The device proved effective for detection of the color change in several porphyrins upon target exposure and for monitoring the time dependence of changes following exposure. An array of six porphyrins was used for demonstration of differential changes in response to specific targets. Proof-of-concept use of the porphyrin indicators onboard two types of unmanned aerial vehicles (UAVs) is described.

Gradient index collimator lens for high pressure applications.

A modified gradient index (GRIN) lens is optimised for use in a liquid-type high pressure cell. It was found that high pressure changes the optical power of the gradient-index lenses by changing the index profile of the glass. In this paper, we present a modified GRIN lens in which these changes are compensated by the pressure-induced changes of the refraction index of the liquid used as a pressure medium. New lens was used for the collimation of the pressure tuned tapered laser working in external resonator. The lens proved to have the optical power almost independent of the pressure up to 1.6 GPa, as it allowed to obtain tuning range almost independent on pressure without the need of any modification of the optical setup.

Measuring Parallelism for Two Thin Parallel Beams Based on Autocollimation Principle

In order to measure the parallelism of two thin parallel beams in multi-axis interferometers and differential interferometers, the autocollimation principle was used by locating a CCD at the focal plane of collimation lens, the two beams converge on CCD image plane at different points when they are not parallel, and the distance between the two converging points is used to calculate the parallelism of the two beams. To achieve high accuracy and low system error, the CCD defocus and tilt should be strictly controlled according to the accuracy requirement. A centroid algorithm with grey threshold was used to reduce the influence of image noise. A beam-selected structure was designed to let the two beams converge to the CCD image plane in sequence to avoid superposition of beam spots. An experimental setup is built to verify the validity of the method. Experimental results show that the system has a centroid position resolution of 0.05 arcsec and a centroid position stability of 0.4 arcsec. It is therefore concluded that the method can be used to measure parallelism that is more than few arcsecs for two thin beams. Moreover, the measuring accuracy of this method can be improved when higher centroid position stability is achieved.