二元位相匹配衍射透镜的研究与应用

针对大数值孔径衍射透镜制作难、衍射效率低的问题，探讨了用位相匹配原理对元件结构参数优化设计的方法，研制出８台阶二元衍射位相匹配透镜列阵，达到了预期的效果。采用该方法设计的大数值孔径红外锗透镜和为光聚能器，应用在提高红外探测器性能的实验中。     

Back-focal-plane position detection with extended linear range for photonic force microscopy

In photonic force microscopes, the position detection with high temporal and spatial resolution is usually implemented by a quadrant position detector placed in the back focal plane of a condenser. An objective with high numerical aperture (NA) for the optical trap has also been used to focus a detection beam. In that case the displacement of the probe at a fixed position of the detector produces a unique and linear response only in a restricted region of the probe displacement, usually several hundred nanometers. There are specific experiments where the absolute position of the probe is a relevant measure together with the probe position relative the optical trap focus. In our scheme we introduce the detection beam into the condenser with low NA through a pinhole with tunable size. This combination permits us to create a wide detection spot and to achieve the linear range of several micrometers by the probe position detection without reducing the trapping force.     

Collection efficiency of a single optical fiber in turbid media

If a single optical fiber is used for both delivery and collection of light, two major factors affect the measurement of collected light: (1) the light transport in the medium that describes the amount of light that returns to the fiber and (2) the light coupling to the optical fiber that depends on the angular distribution of photons entering the fiber. We focus on the importance of the latter factor and describe how the efficiency of the coupling depends on the optical properties of the medium. For highly scattering tissues, the efficiency is well predicted by the numerical aperture (NA) of the fiber. For lower scattering, such as in soft tissues, photons arrive at the fiber from deeper depths, and the coupling efficiency could increase twofold to threefold above that predicted by the NA.     

Addressing Factors Affecting Fluorescent Signal Collection of a Multimode Photonic Crystal Fiber Fluorometer

A multimode photonic crystal fiber (PCF) fluorometer interrogated by a spectrometer is investigated. By adding a glass tip at the end of the PCF, we found that this fluorometer significantly enhances the fluorescent light collection efficiency (CE). Factors associated with the CE and stray light rejection are addressed. The experimental study verifies the proposed PCF probe based on the consideration of solely meridian rays. However, our further study in this paper shows the significance of skew rays under total internal reflection (TIR), which in fact carry 53% of the total guidable fluorescent signal power and are blocked in our experiment. We highlight that this missing power is strongly associated with the numerical aperture (NA) of each optical component in the system and suggest further improvement on the components in the system. The proposed PCF fluorometer is particularly efficient and cost effective for an immersion medium with a high attenuation.      

Effects of source shape on the numerical aperture factor with a geometrical-optics model

We study the effects of an extended light source on the calibration of an interference microscope, also referred to as an optical profiler. Theoretical and experimental numerical aperture (NA) factors for circular and linear light sources along with collimated laser illumination demonstrate that the shape of the light source or effective aperture cone is critical for a correct NA factor calculation. In practice, more-accurate results for the NA factor are obtained when a linear approximation to the filament light source shape is used in a geometric model. We show that previously measured and derived NA factors show some discrepancies because a circular rather than linear approximation to the filament source was used in the modeling.     

Near-field optical apertured tip and modified structures for local field enhancement

We present experimental measurements and simulation of the spatial distribution of near-field light at the aperture of a Si micromachined near-field scanning optical microscopy (NSOM) probe. A miniature aperture at the apex of a SiO(2) tip on a Si cantilever was fabricated with the low temperature oxidation and selective etching technique. An optical transmission efficiency (optical throughput) of the fabricated probe was determined to be approximately 10(-2) when the aperture size was approximately 100 nm, which is several orders of magnitude higher than that for conventional optical fibers. A three-dimensional finite difference time domain (FDTD) simulation shows that the near-field light is well confined within the aperture area with a throughput of 1% for a 100-nm aperture, which is in good agreement with the measurement. The spatial distribution of the near-field light at an aperture of 300-nm diameter shows a full width at half-maximum of 250 nm with a sharp peak that is nearly 60 nm wide. The 2.4% throughput for a 300-nm aperture was estimated based on the measured spatial distribution of the near-field light that is almost the same as the experimental result. We also present the initial results of the fabrication of high throughput coaxial and surface plasmon enhancement NSOM probes.     

Inorganic immersion fluids for ultrahigh numerical aperture 193 nm lithography

Immersion lithography has become attractive since it can reduce critical dimensions by increasing numerical aperture (NA) beyond unity. Among all the candidates for immersion fluids, those with higher refractive indices and low absorbance are desired. Characterization of the refractive indices and absorbance of various inorganic fluid candidates has been performed. To measure the refractive indices of these fluids, a prism deviation angle method was developed. Several candidates have been identified for 193 nm application with refractive indices near 1.55, which is approximately 0.1 higher than that of water at this wavelength. Cauchy parameters of these fluids were generated and approaches were investigated to tailor the fluid absorption edges to be close to 193 nm. The effects of these fluids on photoresist performance were also examined with 193 nm immersion lithography exposure at various NAs. Half-pitch 32 nm lines were obtained with phosphoric acid as the immersion medium at 1.5 NA. These fluids are potential candidates for immersion lithography technology.     

Ultrathin cameras using annular folded optics

We present a reflective multiple-fold approach to visible imaging for high-resolution, large aperture cameras of significantly reduced thickness. This approach allows for reduced bulk and weight compared with large high-quality camera systems and improved resolution and light collection compared with miniature conventional cameras. An analysis of the properties of multiple-fold imagers is presented along with the design, fabrication, and testing of an eightfold prototype camera. This demonstration camera has a 35 mm effective focal length, 0.7 NA, and 27 mm effective aperture folded into a 5 mm total thickness.     

Two-fiber spectroscopic probe with improved scattered light rejection

Our angled two-fiber probe design for in situ spectroscopic measurements (e.g., fluorescence, phosphorescence, or Raman) through a sapphire window has been modified to provide improved rejection of scattered excitation light while maintaining good efficiency of collection of the desired signal. The improvement is achieved by changing the probe axis to an off-normal configuration to minimize back reflection from window surfaces while maximizing the overlap of the light cones of the excitation and collection fibers at the outer window surface where the sample is in contact with the window. The results of laser-induced fluorescence measurements on phenol solution and sand samples, demonstrating the improved performance of the new probe, are reported. Up to 90-fold improvement in the fluorescence/scattered light ratio has been observed with the new probe.     

Experimental study of near-field light collection efficiency of aperture fiber probe at near-infrared wavelengths

We examined the near-field collection efficiency of near-infrared radiation for an aperture probe. We used InAs quantum dots as ideal point light sources with emission wavelengths ranging from 1.1 to 1.6 μm. We experimentally investigated the wavelength dependence of the collection efficiency and compared the results with computational simulations that modeled the actual probe structure. The observed degradation in the collection efficiency is attributed to the cutoff characteristics of the gold-clad tapered waveguide, which approaches an ideal conductor at near-infrared wavelengths.     

Novel Near-Field Millimeter-Wave Differential Probe Using a Loaded Modulated Aperture

Near-field millimeter-wave techniques have effectively been used for nondestructive testing (NDT) and imaging applications for over a decade. The interaction of the fields and a structure under test (SUT) in the near field of a probe is more complex than that of the far-field interaction. In the near field, the distance between the probe and the SUT, which is referred to as the standoff distance, is an important measurement parameter, and when optimally chosen, it can significantly improve detection sensitivity. However, undesired changes in this parameter can adversely influence the detection outcome to the extent that a target may be totally masked. Consequently, in the past, several different methods and remedies have been proposed to eliminate or drastically reduce this adverse influence, each with its own limitations. In this paper, a novel method involving a probing waveguide aperture loaded with two small modulated antennas is introduced, which operates in a differential mode and is capable of automatically eliminating undesired changes in the standoff distance during testing. In addition, this differential probe efficiently overcomes the limitations of the previously developed methods. The proposed probe is based on electronic modulation of the dominant aperture field of the rectangular waveguide using p-i-n diode-loaded dipoles symmetrically placed in the aperture. This paper presents the design of this unique probe, and the results show that the adverse effect of the standoff distance variation can be eliminated or otherwise significantly reduced by noncoherently subtracting the signals measured at two different aperture modulation states.     

Synthetic aperture interferometry: in-process measurement of aspheric optics

A scanning probe consisting of a source and receive fiber pair is used to measure the phase difference between wave fronts scattered from the front and rear surfaces of an aspheric optic. This system can be thought of as a classical interferometer with an aperture synthesized from the data collected along the path of the probe. If the form of either surface is known, the other can be deduced. In contrast with classical interferometers, the method does not need test or null plates and has the potential to be integrated into the manufacturing process.     

Multiple-fiber probe design for fluorescence spectroscopy in tissue

The fiber-optic probe is an essential component of many quantitative fluorescence spectroscopy systems, enabling delivery of excitation light and collection of remitted fluorescence in a wide variety of clinical and laboratory situations. However, there is little information available on the role of illumination--collection geometry to guide the design of these components. Therefore we used a Monte Carlo model to investigate the effect of multifiber probe design parameters--numerical aperture, fiber diameter, source--collection fiber separation distance, and fiber-tissue spacer thickness--on light propagation and the origin of detected fluorescence. An excitation wavelength of 400 nm and an emission wavelength of 630 nm were simulated. Noteworthy effects included an increase in axial selectivity with decreasing fiber size and a transition with increasing fiber-tissue spacer size from a subsurface peak in fluorophore sensitivity to a nearly monotonic decrease typical of single-fiber probes. We provide theoretical evidence that probe design strongly affects tissue interrogation. Therefore application-specific customization of probe design may lead to improvements in the efficacy of fluorescence-based diagnostic devices.     

光纤探针型近场光镊光强分布特性的数值模拟

光纤探针型近场光镊是近场光学领域中的新型技术,因其可对纳米尺度微粒直接进行捕获和操纵而受到广泛关注,其光纤探针尖端的近场分布特性影响着纳米粒子捕获及操纵的成败探针金属膜外侧电磁场由光波在针尖小孔处衍射而成,根据夫朗和费衍射公式分析了圆形纳米小孔的光波衍射图样,运用时域有限差分法（FDTD）研究了均匀平面波垂直入射于镀膜光纤探针的近场分布,比较了不同锥角、不同出射孔径、不同金属膜厚度及不同入射波长的近场分布情况,并对不同情况下的通光效率进行了分析。通过对各参数的计算与比较,结果表明,当锥角越大、孔径越大、镀合适膜厚并且入射波长越小时,探针尖端的出射光强越大并具有较大的通光效率     

Silicon planar-apertured probe array for high-density near-field optical storage

We propose a novel, to our knowledge, silicon planar-apertured probe array as an optical head for high-density near-field optical storage. In comparison with a conventional fiber probe employed for near-field optical storage the apertured probe array has a higher readout data-transmission rate and better mechanical durability. A probe array with an aperture size of 100 nm was fabricated by use of photolithography and wet etching of a silicon wafer. Subwavelength-readout capability was demonstrated by use of one aperture of the probe array. Furthermore, we achieved a 16 times increase in the light-transmission efficiency of the probe array by installing glass-sphere microlenses on each aperture. The increase was confirmed by measurement of the near-field optical intensity.     

无源多通道神经硅微电极的设计方法

为了探讨一种用于神经信号测量的无源多通道硅微电极的设计方法,基于电极的结构和制造工艺,提出了硅微电极用于测量神经信号的电路模型．从大脑皮层及脑膜的结构、互连线的干扰噪声和探针的机械特性3个方面讨论了神经微电极探针的几何参数确定方法,并提出了在满足一定负载能力以穿透硬度较大的脑膜的前提下,尽量减小探针体积的设计原则．     

PSTM中不同探针扫描成像的模拟分析

金属纳米粒子或薄膜在可见光的激励下产生表面增强效应。尝试在光子扫描隧道显微镜(PSTM)中应用带铝的光纤探针来提高成像的分辨率和灵敏度。采用二维时域有限差分法(FDTD)模拟计算了裸光纤、尖端镀铝颗粒光纤、孔径镀铝膜光纤和全镀铝膜光纤探针的成像。结果显示,采用带铝探针后的灵敏度均比裸光纤提高两个数量级;尖端镀铝颗粒光纤探针的分辨率最好,可优于20nm;全镀铝膜和孔径镀铝膜光纤探针的分辨率分别可达到20nm和60nm。结果可供探针制备及实验参数设置参考。     

Ultrahigh interference spatial compression of light inside the subwavelength aperture of a near-field optical probe

Spatial effects of interference and interaction of light modes in the subwavelength part of the near-field optical microscopy probe have been theoretically studied. It was found that the mode interference can lead to higher spatial compression of light (wavelength is equal to 500 nm in free space) within the transverse size of 25 nm inside the probe output aperture of 100 nm in diameter. The results predict a principal possibility of higher spatial resolution in the near-field optical microscopy technique.     

四发射单接收光学非接触测头

研究开发了一种具有4个发射光源和1个CCD摄像机作为接收装置的光学非接触测头．测头可以用来测量包括具有强反射表面的曲面．测头基于三角法工作原理．在恰当设计的情况下,至多只有1路从工件表面反射回来的光,能够进入CCD摄像机．通过将相应通道切断,很容易消除镜面反射光的影响．这时测头就相当于1个三发射单接收光学非接触测头．测头可以同时用来测量表面的位置和方向．对于具有很大倾斜的表面具测头仍能正常工作,采用干涉滤光片消除了环境光的影响．提出了一种系统的标定方法．通过对量块的测量证实了系统工作的正确性和有效性并给出了实验结果．     

Analytic solutions for the optical and radiative properties of nonaccepted light radiation of V-trough concentrators

Knowledge of optical and radiative properties is often essential for the design and evaluation of V-trough solar energy collectors. Using the concept of reflection modes, we derived a set of functions associated with each mode; this allowed us to calculate the optical and radiative properties for rejected light radiation. These expressions, together with those for accepted light radiation published previously, were used to calculate the optical efficiency for beam radiation and the exchange factors (diffuse radiation) between aperture and absorber (accepted light) and between aperture and aperture (rejected light). Numerical results of these factors were obtained for various combinations of concentration ratio and vertex angle. Results are compared between a case in which the reflectivity is constant and one in which the reflectivity varies with incidence angle; the difference does not exceed 1% for a reflectivity of 0.8. Considering the reflectivity as a constant allows us to obtain analytic solutions for the exchange factors, expressed as a sum of trigonometric functions.