Two-dimensional array self-assembled quantum dot sub-diffraction waveguides with low loss and low crosstalk

We model and demonstrate the behavior of two-dimensional (2D) self-assembled quantum dot (QD) sub-diffraction waveguides. By pumping the gain-enabled semiconductor nanoparticles and introducing a signal light, energy coupling of stimulated photons from the QDs enables light transmission along the waveguide. Monte Carlo simulation with randomized inter-dot separation reveals that the optical gain necessary for unity transfer is 3.1 × 10(7)?m(-1) for a 2D (2?μm length by 500?nm width) array compared to 11.6 × 10(7)?m(-1) for a 1D (2?μm length) given 8?nm diameter quantum dots. The theoretical results are borne out in experiments on 2D arrays by measurement of negligible crosstalk component with as little as 200?nm waveguide separation and is indicative of near-field optical coupling behavior. The transmission loss for 500?nm wide structures is determined to be close to 3?dB/4?μm, whereas that for 100?nm width is 3?dB/2.3?μm. Accordingly, higher pump power and gain would be necessary on the narrower device to create similar throughput. Considering existing nanoscale propagation methods, which commonly use negative dielectric materials, our waveguide shows an improved loss characteristic with comparable or smaller dimensions. Thus, the application of QDs to nanophotonic waveguiding represents a promising path towards ultra-high density photonic integrated circuits.     

Two-color medium-infrared scanning interferometer for the Frascati tokamak upgrade fusion test device

A scanning beam interferometer installed on the Frascati tokamak upgrade (FTU) experiment is presented. The scanning beam scheme combined with the small dimensions of the beams produces a system with very high spatial resolution: more than 30 adjacent (nonoverlapping) chords sample most of the plasma cross section. A good time resolution is achieved by the use of a proper scanning device, with a scanning frequency >or=8 kHz. Very fast events are measured by three additional fixed lines of sight providing a time resolution >or=100 kHz. The instrument is a two-color medium-infrared-compensated-type interferometer; two wavelengths (colors) are used to measure both the density and the mechanical vibrations of optical components. A CO2 laser (lambda=10.6 microm) is the main light source, and a CO laser (lambda=5.4 microm) is the compensation one. The optical scheme is a double pass Mach-Zehnder type. All the retroreflector mirrors are mounted directly on the FTU mechanical structure thanks to the compensation system that allows for large vibration amplitudes of optical components. Heterodyne detection at 30 and 40 MHz is obtained by frequency shifting the reference beams with two acousto-optic modulators (Bragg cells). Many features are implemented to achieve high measurement accuracy and reliability. A real-time system computes the integral density measured on one of the fixed lines of sight and provides an analog signal for density feedback control. The interferometer was used to measure density profiles both in medium-density discharges (n(e) approximately 10(20) m(-3)) and in high-density pellet injected discharges (n(e) approximately 7-8 x 10(20) m(-3)). The measurement error is approximately 2 x 10(18) m(-2) under optimal conditions but can be higher in some cases, mainly because of the large tilt of the retroreflector mirrors.     

F⁃P干涉仪差分锁频系统研究

为解决法布里?珀罗（Fabry?Perot, F?P）干涉仪锁频方法响应速度、抗干扰能力、长期稳定性方面存在不足的问题,提出了F?P干涉仪差分锁频方案,将存在频差的双频激光耦合入F?P谐振腔,当激光频差足够小时,两光强信号曲线存在交叉,以两光强信号的差值作为被控量,在交叉点附近构建单调过零函数,作为闭环控制系统的反馈量,实现动态差分锁频控制。基于该方案,搭建了一套F?P干涉仪微位移测量装置并开展实验验证,结果表明该装置能够实现0 ~ 300 nm范围内的微位移测量,位移测量分辨力达到23 pm,验证了F?P干涉仪差分锁频方案的有效性,为推动微位移测量领域的发展提供了重要借鉴。     

Wavenumber scanning-based Fourier transform white-light interferometry

Fourier transform white-light interferometry recovers the optical path difference of an interferometer by measuring the phase change caused by scanning wavelength. However, the optical spectrum, obtained by wavelength scanning method (λ-method), contains a chirp in period. The chirp would induce deviation and decrease the measurement accuracy. An improved method, the wavenumber scanning method (k-method), is proposed and experimentally demonstrated, in which there is no chirp in the optical spectrum. The measurement results using the k-method and the λ-method are compared experimentally. The experimental results show that the standard deviation of the measurement results decreases from 0.015 to 0.004?μm, when an extrinsic Fabry-Perot interferometer with a cavity length of 387?μm is interrogated.     

Automated determination of best focus and minimization of optical path difference in Linnik white light interferometry

It is difficult to search for interference fringes in Linnik white light interferometry with an extremely short coherence length because of the optical path mismatch of two interference arms and the defocus of the reference mirror and the test surface. We present an automated method to tackle this problem in this paper. The determination of best foci of the reference mirror and the test surface is implemented by the astigmatic method based on a modified commercial DVD pickup head embedded in the interference system. The astigmatic method is improved by setting a threshold value in the sum signal to truncate the normalized focus error signal (NFES). The truncated NFES has a monotonic relationship with the displacement of the test surface, which removes the position ambiguity of the test surface during the autofocus process. The developed autofocus system is confirmed experimentally with a dynamic range of 190?μm, average sensitivity of 70 mV/μm, average standard deviation of 0.041?μm, displayed resolution of 4.4 nm, and accuracy of 55 nm. The minimization of the optical path difference of two interference arms is carried out by finding the maximum fringe contrast of the image captured by a CCD camera with the root mean square fringe contrast (RMSFC) function. The RMSFC function, combined with a 4×4 pixel binning of the CCD camera, is recommended to improve the computational efficiency. Experimental tests show that the automated method can be effectively utilized to search for interference fringes in Linnik white light interferometry.     

1 550 nm全光纤激光多普勒测振系统研制

针对目前国内激光测振系统价格昂贵、使用不便的问题,采用1 550 nm波段成熟的窄线宽光源和光纤元器件研制了一套低成本的全光纤激光测振系统原理样机。此原理样机光路部分采用马赫?泽德干涉仪结构,搭建了外差式激光干涉光路,参考光被40 MHz的声光调制器调制,与测量光在光电探测器表面发生干涉,产生原始的激光多普勒信号;信号解调部分采用相位解调法对原始激光多普勒信号进行解调,得到振动目标的运动特性,包括位移、速度和加速度信息。采用本单位的振动标准装置对其性能进行了测试,实验结果表明：在10 ~ 2 000 Hz的中低频振动范围内,1 550 nm全光纤激光多普勒测振系统峰值位移、速度和加速度的测量误差在-0.6% ~ 0.7%内。该系统在中低频段具有较高的测量准确度,且成本相对较低、操作便捷,具有技术借鉴价值。     

Instrumental noise effect in an optical heterodyne profiler

An optical heterodyne profiler has been developed for measuring surface roughness at Brookhaven National Laboratory. The height measurement sensitivity and lateral resolution are 1.1 ? and 4 μm, respectively, when a 40× objective is used. A Zeeman-split He-Ne laser is the light source. A noncontact measurement system is designed as an optical common-path interferometer. Optical and electronic common-mode rejection techniques are employed to minimize the effects of environmental conditions. The effect of the system noise is analyzed in detail. The effect of varying the number of samples at each sampling point is shown. The comparisons of the system noises with different objectives, 5×, 10×, 20×, and 40×, are presented.     

Study of a dual-frequency laser interferometer with unique optical subdivision techniques

A dual-frequency laser interferometer has been developed based on a low-performance commercial interferometer. An optical resolution of 1.24 nm and a nanometer-scale accuracy have been achieved by using unique techniques to obtain an optical subdivision factor of 1/8. A method for reducing static positioning errors was also shown. The measurement of a free-falling body was performed to test the maximum achievable target velocity of the device. The experimental setup for measuring the static positioning errors was also given. The new interferometer could be widely used in nanometer-scale fabrications and measurements.     

Axial-scanning low-coherence interferometer method for noncontact thickness measurement of biological samples

We investigated a high-precision optical method for measuring the thickness of biological samples regardless of their transparency. The method is based on the precise measurement of optical path length difference of the end surfaces of objects, using a dual-arm axial-scanning low-coherence interferometer. This removes any consideration of the shape, thickness, or transparency of testing objects when performing the measurement. Scanning the reference simplifies the measurement setup, resulting in unambiguous measurement. Using a 1310?nm wavelength superluminescent diode, with a 65?nm bandwidth, the measurement accuracy was as high as 11.6?μm. We tested the method by measuring the thickness of both transparent samples and nontransparent soft biological tissues.     

Portable Fourier transform infrared spectroradiometer for field measurements of radiance and emissivity

A hand-held, battery-powered Fourier transform infrared spectroradiometer weighing 12.5 kg has been developed for the field measurement of spectral radiance from the Earth's surface and atmosphere in the 3-5-μm and 8-14-μm atmospheric windows, with a 6-cm(-1) spectral resolution. Other versions of this instrument measure spectral radiance between 0.4 and 20 μm, using different optical materials and detectors, with maximum spectral resolutions of 1 cm(-1). The instrument tested here has a measured noise-equivalent delta T of 0.01 °C, and it measures surface emissivities, in the field, with an accuracy of 0.02 or better in the 8-14-μm window (depending on atmospheric conditions), and within 0.04 in accessible regions of the 3-5-μm window. The unique, patented design of the interferometer has permitted operation in weather ranging from 0 to 45 °C and 0 to 100% relative humidity, and in vibration-intensive environments such as moving helicopters. The instrument has made field measurements of radiance and emissivity for 3 yr without loss of optical alignment. We describe the design of the instrument and discuss methods used to calibrate spectral radiance and calculate spectral emissivity from radiance measurements. Examples of emissivity spectra are shown for both the 3-5-μm and 8-14-μm atmospheric windows.     

3D characterization of microstructured poly(methacrylic acid) thin films via Mach-Zehnder interference microscopy

We demonstrate the adaption of a further developed Mach-Zehnder interference (MZI) microscope for the rapid 3D characterization of transparent microstructured polymer thin films. In order to quantify the accuracy of the Mach-Zehnder interferometer, comparative film thickness measurements of photolithographically patterned poly(methacrylic acid) polymer brushes are performed employing two alternative techniques: white light profilometry (WIM) and atomic force microscopy (AFM). When the refractive index of the polymer brushes is calculated from MZI data, we obtain a good agreement with results received from an independent method (ellipsometry).In contrast to surface probing techniques such as AFM or WIM, Mach-Zehnder interferometry is a transmitted light method that measures both surface height profiles and refractive index distributions. MZI thus enables the quantification of film homogeneity with respect to height and density variations at the lateral resolution of a refraction limited microscope. We conclude that MZI is an adequate tool for the rapid and non-destructive characterization of structured polymer thin films. This method should be particularly useful for production quality control of microstructured polymer thin films which possess great potential in electronic device fabrication and biotechnology.     

绝对重力仪落体光心与质心空间距离测量

为了准确测量重力仪落体光心与质心距离,减少落体光心与质心不重合引起的旋转对重力加速度测量的影响,设计了落体光心与质心空间距离测量装置。提出了1种光心与质心间距的计算方法,并仿真验证了计算方法的可行性。使用设计的测量装置对落体进行测试,结果表明:激光干涉仪在信号频率为0.3~0.5Hz时的测量精度为0.1nm,提出的计算方法可以使测量系统的A类不确定度优于10μm,最大调校测量误差为1μm。     

Surface displacement imaging by interferometry with a light emitting diode

We present an imaging technique to measure static surface displacements of electronic components. A device is supplied by a transient current that creates a variation of temperature, thus a surface displacement. To measure the latter, a setup that is based on a Michelson interferometer is used. To avoid the phenomenon of speckle and the drawbacks inherent to it, we use a light emitting diode as the light source for the interferometer. The detector is a visible CCD camera that analyzes the optical signal containing the information of surface displacement of the device. Combining images, we extract the amplitude of the surface displacement. Out-of-plane surface-displacement images of a thermoelectric device are presented.     

Optical assessment of nonimaging concentrators

An optical measurement method for nonimaging radiation concentrators is proposed. A Lambertian light source is placed in the exit aperture of the concentrator. Looking into the concentrator's entrance aperture from a remote position, one can photograph the transmission patterns. The patterns show the transmission of radiation through the concentrator with the full resolution of the four-dimensional phase space of geometric optics. By matching ray-tracing simulations to the measurement, one can achieve detailed and accurate information about the geometry of the concentrator. This is a remote, noncontact measurement and can be performed in situ for installed concentrators. Additional information regarding small-scale reflector waviness and surface reflectivity can also be obtained from the same measurement with additional analysis.     

一种新型单频激光干涉系统的研究

这种单频激光干涉系统采用共光路设计布局,通过偏振分束器以及1/4波长片等光学器件对干涉条纹进行空间移相,提取相位依次相差90°的三路干涉输出信号,进行比较放大,解决了常规单频激光干涉仪中的光强“零漂”问题。利用共模抑制技术,提高了干涉系统的测量稳定性和重复性。采用光程差放大技术,提高了干涉系统的分辨力。     

Real-time polarization state measurement based on a birefringent crystal wedge

Abstract

We present a method of single-shot polarization state measurement based on a birefringent crystal wedge. The phase delay and amplitude angle of detected light are encoded into two groups of fringes through the interference in a crystal wedge and further decoded by fringe position locations. This method has the merit of real-time measurement, a compact set-up and simple calibration. The principle, set-up, calibration and error analysis are presented in details. In the end, a single-shot measurement set-up with 80 kHz temporal resolution is demonstrated to investigate the molecule dynamic behaviour in a TN liquid crystal under a rectangular voltage.     

激光干涉仪在纳米测量中的典型应用

激光干涉仪具有测量分辨力高、测量结果可溯源等优点,在纳米测量中的应用日益广泛。介绍纳米测量机和低膨胀材料线膨胀系数测量装置中应用的迈克尔逊型激光干涉仪以及在高准确度位移测量装置中应用的法布里-珀罗型激光干涉仪,并结合这些实例对激光干涉仪光学系统设计、测量环境控制、迈克尔逊干涉仪非线性误差补偿以及法布里-珀罗干涉仪量程扩展等方面的关键问题进行分析和总结。所述原则和方法对实现纳米级测量准确度具有重要意义,可为高准确度激光干涉仪的研制及其在纳米测量中的更广泛应用提供技术参考。     

Electronic speckle pattern interferometry based on spatial information using only two sheets of speckle patterns

Abstract

Speckle interferometry is an important deformation measurement method for an object with a rough surface. In this paper, a novel fringe analysis method is proposed that uses a new optical system, which uses a plane wave as the reference beam of the speckle interferometer. When the optical system is employed in fringe analysis, the deformation information and the bias components of the speckle patterns are clearly separated in the frequency domain. Therefore, the deformation information can be readily extracted using a Fourier transform, which gives a pair of real and imaginary components concerning the information. The specklegram is calculated using such a pair of components, and the phase map is obtained from the specklegram. Experimental results confirmed that the resolution power of this measurement method is higher than 1/261 of the wavelength of the light source of the optical system.     

外差干涉仪中光路调整的分析

分析了共光路外差干涉仪光路中几个组成元件的调整方法 ,包括入射光位置的调整、渥拉斯顿棱镜位置的调整、被测表面位置的调整等。     

大量程纳米级光栅干涉位移测量

针对传统光栅干涉仪中测量范围和分辨率难以同时提高的问题,提出利用单根大长度、低线数光栅实现大量程、高分辨率位移测量的方法.首先利用长度400mm,栅距10μm计量光栅的±5级衍射光生成条纹图,实现了条纹的10倍光学细分.然后提出一种基于傅里叶变换时移特性的条纹细分新方法,利用相邻两帧条纹图同一位置处相位的变化实现了高达1000倍的条纹电子细分.在此过程中,针对能量泄漏对傅里叶变换法相位提取精度的影响,提出条纹图整周期裁剪的方法,使条纹细分精度至少可达到1/1000条纹周期.仿真和实验结果表明,系统具有纳米级的分辨率和优于10nm的测量精度.