Illumination Optics Research Articles

351nm Excimer Large-Area Lithography by Scanning and Projection

For the system of a large-area laser projection image exposure using 351nm XeF excimer, its constitution, optical design parameters, and manufacturing process are introduced. The system is capable of patterning in photoresists for large-format products, with feature sizes ranging from 10 µm to below 1µm and substrate sizes ranging from 100×100mm to 600×900mm. 351nm excimer is used in this system because of its capability for exposure of conventional photoresists. Large-area lithography refers to the patterning on such areas with the desired resolution and seamless scanning. Along with the demands for lithography equipment that can provide high-resolution imaging capability, high-precision alignment performance and lower manufacturing costs, it is important for us to design and manufacture such equipment. Some key problems such as laser illumination optics, projection optics, positioning and controlling machinery, are described here. The existing problem and solutions in the optics and machinery are analyzed and discussed.

Hyperspectral Shack–Hartmann test

A hyperspectral Shack-Hartmann test bed has been developed to characterize the performance of miniature optics across a wide spectral range, a necessary first step in developing broadband achromatized all-polymer endomicroscopes. The Shack-Hartmann test bed was used to measure the chromatic focal shift (CFS) of a glass singlet lens and a glass achromatic lens, i.e., lenses representing the extrema of CFS magnitude in polymer elements to be found in endomicroscope systems. The lenses were tested from 500 to 700 nm in 5 and 10 nm steps, respectively. In both cases, we found close agreement between test results obtained from a ZEMAX model of the test bed and test lens and those obtained by experiment (maximum error of 12 μm for the singlet lens and 5 μm for the achromatic triplet lens). Future applications of the hyperspectral Shack-Hartmann test include measurements of aberrations as a function of wavelength, characterization of manufactured plastic endomicroscope elements and systems, and reverse optimization.

Design and fabrication of a fingerprint imager with compact LED illumination and compact imaging optics

In this study, we presented a light-emitting diode-based (LED) miniaturized optical pattern imager for slim mobile phone application. To meet volume constraints, we designed a miniaturized compact illuminating and imaging optical component. The objective was to minimize optical loss using several nano- and micro-fabrication methods. After integration into a single optical body, the prototype imager-with dimensions of 6.8 × 2.2 × 2.5 mm and a weight of 0.4 g-demonstrated clear feasibility in measuring 2D micropatterns with widths of 50 and 10 μm.

Three-Dimensional Display System Based on Integral Imaging with Viewing Direction Control

We propose a three-dimensional display system based on integral imaging with viewing direction control. In the proposed method, 4-f illumination optics with a dynamic aperture are used to direct the displayed three-dimensional images to the viewer. It is also possible to control the divergence or convergence of the illumination for an optimized display of real or virtual images. The principle of the proposed method was verified experimentally.

78.1: Ultra Compact Polarization Recycling System for White Light LED based Pico‐Projection System

AbstractAn ultra compact polarization recycling system, for white light LED based projectors, is proposed. White light LED is applied as the light source, which is composed of blue LED die and yellow phosphor. By optimizing the illumination optics and properly placing a reflective type polarization film, the light with non‐useable polarization state will be reflected back and concentrated right on to the phosphor surface. The yellow phosphor will be reexcited by the blue spectrum component of the reflected light. More light energy will be recycled by attaching a piece of quarter wave plate before the reflective type polarization film. Experimental results show more than 30% light efficiency improvement.

Focus on lasers and imaging

Focus on lasers and imaging

レーザ光源プロジェクタ向け高輝度・超短焦点投写光学系および色再現処理技術の開発

Our newly developed ultra-short throw distance laser light source projector is composed of triple rod illumination optics, mirror-lens hybrid ultra-wide angle projection optics and laser color processing. This projector has achieved the highest brightness of 7,000lm, the shortest throw distance of 60 cm at 100-inch image size and wider color gamut of 190% compared with sRGB by making full use of the advantages of laser such as high luminance, small etendue and high color purity. These specifications improve the visibility, convenience of installation and vividness of the image. In this paper, we describe our original developed technology such as the triple-rod illumination optical system, ultra-short projection optical system and laser color processing.

Photoacoustic and high-frequency power Doppler ultrasound biomicroscopy: a comparative study

Both photoacoustic imaging and power Doppler ultrasound are capable of producing images of the vasculature of living subjects, however, the contrast mechanisms of the two modalities are very different. We present a quantitative and objective comparison of the two methods using phantom data, highlighting relative merits and shortcomings. An imaging system for combined photoacoustic and high-frequency power Doppler ultrasound microscopy is presented. This system uses a swept-scan 25-MHz ultrasound transducer with confocal dark-field laser illumination optics. A pulse-sequencer enables ultrasonic and laser pulses to be interlaced so that photoacoustic and power Doppler ultrasound images can be coregistered. Experiments are performed on flow phantoms with various combinations of vessel size, flow velocity, and optical wavelength. For the task of blood volume detection, power Doppler is seen to be advantageous for large vessels and high flow speeds. For small vessels with low flow speeds, photoacoustic imaging is seen to be more effective than power Doppler at the detection of blood as quantified by receiver operating characteristic analysis. A combination of the two modes could provide improved estimates of fractional blood volume in comparison with either mode used alone.

Micro Lens Array Milling on Large Wafers

AbstractMicro Lens Arrays (MLA) containing thousands of lenses with an aspheric shape and a precise position on large substrates are used in sensor devices directly or as master moulds for the low‐cost replication of micro lenses in an array. They have to fulfill the high requirements in wafer scale manufacturing of small optics. This high volume manufacturing method for low‐cost but effective micro optics relies on the sandwich‐like assembly of the sensors and optical components like lenses as well as mechanical components like apertures and spacers on wafer level. After joining all components the dicing results in a batch of wafer level cameras for the use in cellular phones or webcams.Micro Lens Arrays are also a centrepiece of today's sensor products, either to raise the fill factor and collect more light on each pixel or to deflect the incoming beam to measure the aberrations of the wavefront, the working principle of the Hartmann‐Shack sensor. Within illumination optics, MLA are commonly used for beam homogenization in projection systems. In all fields of application ranging from automotive, medical, consumer and industrial optics to high‐end sensors for space instrumentation, high quality lens arrays for direct use or replication must be provided.

가간섭 영역 외의 배경 잡음성 간섭무늬 신호 필터링을 통한 백색광 주사간섭계의 성능 향상

본 논문에서는 백색광 간섭계(White Light Interferometry, WLI)의 데이터 처리 과정에서 가간섭 영역 외의 배경 잡음성 신호 필터링을 통하여 백색광 주사 간섭계의 성능을 향상시켰다. 광학계의 개구수(Numerical Aperture, NA)가 유한한 백색광 간섭계의 경우, 단차가 크고 표면 굴곡이 심한 시료를 측정하게 되면 유한한 초점심도(Depth Of Focus, DOF)에 의하여 배경 잡음이 발생하며, 반사가 심한 경면의 경우에는 간섭무늬 신호보다 배경 잡음의 영향을 많이 받게 된다. 따라서 배경 잡음을 제거하기 위하여 간섭무늬 신호 자체 형상에 영향을 주지 않으면서 효율적으로 배경 잡음 필터링이 가능한 전후 구간 평균법을 제시하였다. 전후구간 평균법은 원 데이터와 그 이동평균과의 차이를 이용하는 방법으로, 고속으로 대략적인 정점의 위치를 파악한 후 정밀도가 높은 가시도 정점 검출 알고리즘으로 처리하여 측정 속도와 정밀도를 높였다. 전후구간 평균법을 이용하여 배경 잡음을 제거한 경우, 제거하지 않은 경우와 비교하여 잡음 화소가 약 1/4로 감소되었다. In order to enhance the background noise filtering performance of the white light interferometry(WLI), we demonstrate the noise filtering performance of preprocessing of the measured fringe signals. The WLI was realized through a mirau interferometer which was equipped with a green LED. When measuring large-height and rough surface objects, the illumination optics are considered the numerical aperture(NA) and the depth of focus(DOF). In this case, the limited NA of the illumination optics has a considerable impact on the interference fringe. Therefore, we propose a preprocessing method that uses the intensity difference between the measured intensity and the moving average intensity. The performance is demonstrated by measuring an array of metal solder balls fabricated on printed circuit board(PCB). The proposed method reduces the noise pixels by 15 percent.

Signal limitations in tip-enhanced Raman scattering: the challenge to become a routine analytical technique

The fundamental parameters and limitations that determine the signal strength in tip-enhanced Raman scattering (TERS) are discussed. A semiquantitative analysis of the Raman signal expected in different experimental geometries and with different sample systems is presented, taking into account experimental parameters including Fresnel factor, numerical aperture of the illumination and collection optics, detection efficiency, and the Raman scattering cross section of the material. A top/side-on illumination geometry is essential for the study of nontransparent samples. It can yield the highest signal levels when strong tip-sample coupling using a metallic substrate provides large field enhancement. In contrast, axial/through-sample illumination is limited to transparent sample materials. Although conceptually simpler in experimental implementation and despite high numerical aperture signal collection efficiency, signals are generally weaker due to limited field enhancement. Crystalline solids with small Raman cross sections and dense molecular/biological systems with unavoidable far-field background provide the biggest challenge for TERS analysis yet at the same time hold the most exciting outstanding scientific questions TERS has the potential to answer.

Optical design and extended multi-objective optimization of miniature L-type optics

In ordinary optical design and optimization, it is difficult to strike a balance between relative illuminance (RI) and the modulation transfer function (MTF); this is even more difficult for special fold optical zoom lenses. We propose a thinning L-type zoom lens design that exploits the reflecting and refracting surfaces that constitute a prismatic lens. However, in L-type designs, the lens RI is comparatively low compared with that in its coaxial counterparts. Attempts to improve the RI also cause MTF degradation. We propose a combination of the Taguchi method and principal component analysis to improve both the RI and MTF in L-type zoom systems. We analysed an orthogonal array L9 using the Taguchi method. The resulting experimental values of the orthogonal array L9 were used as inputs for principal component analysis to obtain the total point value. The total point value was then analysed by variance, revealing that the two most significant factors were (1) the semi-aperture of the front element and (2) the surface 7 to image length. Our proposed method increased the MTF and RI by 0.16% and 0.44%, respectively, in system wide-angle ends.

Application of Matrix Projection Exposure Using a Liquid Crystal Display Panel to Fabricate Thick Resist Molds

The patterning characteristics of matrix projection exposure using an analog liquid crystal display (LCD) panel in place of a reticle were investigated, in particular for oblique patterns. In addition, a new method for fabricating practical thick resist molds was developed. At first, an exposure system fabricated in past research was reconstructed. Changes in the illumination optics and the projection lens were the main improvements. Using fly's eye lenses, the illumination light intensity distribution was homogenized. The projection lens was changed from a common camera lens to a higher-grade telecentric lens. In addition, although the same metal halide lamp was used as an exposure light source, the central exposure wavelength was slightly shortened from 480 to 450 nm to obtain higher resist sensitivity while maintaining almost equivalent contrast between black and white. Circular and radial patterns with linewidths of approximately 6 µm were uniformly printed in all directions throughout the exposure field owing to these improvements. The patterns were smoothly printed without accompanying stepwise roughness caused by the cell matrix array. On the bases of these results, a new method of fabricating thick resist molds for electroplating was investigated. It is known that thick resist molds fabricated using the negative resist SU-8 (Micro Chem) are useful because very high aspect patterns are printable and the side walls are perpendicular to the substrate surfaces. However, the most suitable exposure wavelength of SU-8 is 365 nm, and SU-8 is insensitive to light of 450 nm wavelength, which is most appropriate for LCD matrix exposure. For this reason, a novel multilayer resist process was proposed, and micromolds of SU-8 of 50 µm thickness were successfully obtained. As a result, feasibility for fabricating complex resist molds including oblique patterns was demonstrated.

Polarization property of light guide surface with bilayered nanostructure

The surface of a solid plate light guide patterned with nanostructure composed of bilayered dielectric and metallic stripes is capable of partially transmitting only one of two orthogonal polarizations while reflecting most of the other, and therefore performs as a reflective polarizer. The polarization dependent transmittance, polarization efficiency and extinction ratio of both parallel and cross stacking of the bilayered nanostructure have been analyzed for all radial and azimuthal light incident angles. Both configurations have shown overall polarization efficiency above 98% over the visible spectrum, and exhibit an extinction ratio above 1,000 within a specific range of light incident angle. Accompanied by a proper polarization converter and light extraction pattern, the polarized light guide can provide a high efficiency or even a polarizer free illumination optics for an application where a planar illuminator with polarized light is required.

High-resolution OCT balloon imaging catheter with astigmatism correction

We report new optics designs for an optical coherence tomography (OCT) balloon imaging catheter to achieve diffraction-limited high resolution at a large working distance and enable the correction of severe astigmatism in the catheter. The designs employed a 1 mm diameter gradient-index lens of a properly chosen pitch number and a glass rod spacer to fully utilize the available NA of the miniature optics. Astigmatism caused by the balloon tubing was analyzed, and a method based on a cylindrical reflector was proposed and demonstrated to compensate the astigmatism. A catheter based on the new designs was successfully developed with a measured diffraction-limited lateral resolution of approximately 21 microm, a working distance of approximately 11-12 mm, and a round-shape beam profile. The performance of the OCT balloon catheter was demonstrated by 3D full-circumferential imaging of a swine esophagus in vivo along with a high-speed, Fourier-domain, mode-locked swept-source OCT system.

41.1: Viewing Direction Controllable Three‐Dimensional Display Based on Integral Imaging

AbstractA novel method to control the viewing direction of the integral imaging based three‐dimensional display using the 4‐f illumination optics is proposed. Based on integral imaging principle, the light from the point light source array is modulated by the spatial light modulator, displaying three‐dimensional images. The viewing direction of the three‐dimensional image is determined by the diverging direction of the light emanating from each relayed point light source. In the proposed method, a 4‐f optics with a dynamic aperture in the Fourier plane relays the point light source array to the spatial light modulator. The dynamic aperture acts as a band‐pass filter in the Fourier plane, effectively controlling the diverging direction of the light from the point light sources. Resultantly, the proposed system can control the viewing direction of the three‐dimensional image dynamically. The proposed method can be combined with the head tracking system, providing the three‐dimensional image over large viewing angles.

Actinic Mask Blank Inspection and Signal Analysis for Detecting Phase Defects Down to 1.5 nm in Height

The capability of an actinic (at-wavelength) inspection system for extreme ultraviolet lithography (EUVL) mask blank has been analyzed by experiment and simulation. The actinic inspection optics, that we developed to obtain a two-dimensional dark field image, consists of illumination optics, Schwarzschild optics with concave and convex mirrors as dark-field imaging optics, and a back-illuminated charge-coupled-device (BI-CCD). A test mask blank with programmed bump defects of smaller sizes and lower heights compared to those used in a previous work was fabricated and the bump defects were detected by the tool. The inspection experiments demonstrated that fabricated multilayer defects down to 1.5 nm in top height and 60 nm in width can be successfully detected. The simulation further indicated that the inspection optics performed well in detecting phase defects of 1.5 nm in height and 40 nm in width.

Free-form optics for illumination

Illumination optics has been the first to benefit from advances in free-form tooling mainly because of its looser requirements (on surface accuracy and finishing). In the last decade, advances in free-form surface tooling have offered the designer possibilities for which there are few theoretical design tools. The available free-form design tools are reviewed with special attention to the most powerful: the SMS 3D design method. Examples of designs done with this method are given.

A Flexible Anti-Brownian Electrokinetic (ABEL) Trap for Single-Molecule Immobilization in Solution

We demonstrate our ability to trap and probe individual fluorescent particles in solution using an improved anti-Brownian electrokinetic (ABEL) trap. Traditional single-molecule immobilization techniques include surface attachment and laser tweezers; the former technique often disrupts fragile biochemical systems, while the latter requires that molecules be conjugated to large beads. The ABEL trap circumvents these issues by tracking the motion of a particle via fluorescence, and applying electrokinetic feedback forces to cancel its Brownian motion.Our ABEL trap suppresses the Brownian motion of a fluorescent particle as follows. A laser beam is rapidly steered in a small scan pattern near the center of a microfluidic cell. An avalanche photodiode detects fluorescence photons from the molecule. A field-programmable gate array compares the precise arrival time of each photon with the known position of the laser, and generates a corresponding feedback voltage. The feedback voltages is amplified and applied to the trap. We use a broadband supercontinuum laser with an acousto-optic tunable filter to enable fluorescent tracking in any part of the visible spectrum, and we scan the laser using electro-optic deflectors that can function at up to 100 kHz. This combination of hardware enables precise spatial, temporal, and spectral control of our illumination and detection optics and can apply feedback at a latency of 2 μs, a better-than-tenfold improvement over previous trap designs. We hope that these improvements will enable us to trap single small-molecule fluorophores in solution.The flexibility of the ABEL trap makes it amenable for a wide variety of biophysical studies. Work is currently underway to apply the ABEL trap to study the dynamics of DNA in solution. In the future, we hope to apply the trap to study the kinetics of proteins such as proteorhodopsin.

High extinction ratio polarized light guide with layered cross stacking nanostructure

Cross stacking of aluminum and PMMA strip nanostructure has been proposed as a reflective polarizer on the top surface of a solid light guide plate for polarization recycling in order to increase the efficiency of a side edge type backlight module for liquid crystal display. In order to exploit the range of light incident angle on the layered nanostructure with high extinction ratio, a dedicated backlight illumination optics for LED light source has been designed for controlling the light propagation direction within the light guide while achieving satisfactory uniformity in the meantime. The illumination optics features a reflective cup in front of the LED source and one-dimensional V-groove on the bottom surface of the light guide as the light extraction pattern. Ray tracing simulation has shown that a 4 in. diagonal light guide with proposed architecture has achieved uniformity of 75% while having the extracted light well constrained within the range of incident angle on the layered nanostructure where extinction ratio above 1000 can be obtained.