Confocal reflectance theta line scanning microscope for imaging human skin in vivo

A confocal reflectance theta line scanning microscope demonstrates imaging of nuclear and cellular detail in human epidermis in vivo. Experimentally measured line-spread functions determine the instrumental optical section thickness to be 1.7 +/- 0.1 microm and the lateral resolution to be 1.0 +/- 0.1 microm. Within human dermis (through full-thickness epidermis), the measured section thickness is 9.2 +/- 1.7 microm and the lateral resolution is 1.7 +/- 0.1 microm. An illumination line is scanned directly in the pupil of the objective lens, and the backscattered descanned light is detected with a linear array, such that the theta line scanner consists of only seven optical components.     

基于多级组合棱镜提高激光中心波长检测精度的研究

为了在保证抗干扰能力不下降的条件下提高对激光中心波长的检测精度,设计了多级组合棱镜系统,并提出了多级组合棱镜的干涉条纹拼接处理方法及相位耦合的计算公式.通过计算多级组合棱镜的干涉图强度、光程差函数及光谱分辨率,分析了采用三块子棱镜的组合结构的光谱获取,给出了用于分段干涉条纹拼接的处理方法及步骤,最终光谱分辨率可达2.8...     

Fourier domain optical coherence tomography using optical demultiplexers imaging at 60,000,000 lines/s

We describe high-speed Fourier domain optical coherence tomography (OCT) using optical demultiplexers (ODs) for spectral dispersion. The OD enables separation of a narrow spectral band of 14 GHz (0.11 nm) from a broadband incident light at 256 different frequencies in 25.0 GHz intervals centered at 192.2 THz (1559.8 nm). OCT imaging of 60,000,000 axial scans per second was achieved through parallel signal acquisition using 256 balanced photoreceivers to simultaneously detect all the output signals from the ODs in a Fourier domain OCT system. OCT imaging at a 16 kHz frame rate, 1100 A-lines per frame, 3 mm depth range, and 23 microm resolution was demonstrated using a resonant scanner for lateral scanning.     

基于Dyson同心光学系统的消色差Féry棱镜高光谱成像仪的设计

为实现高光谱成像系统小型化、轻量化和高成像质量的要求,并使全工作波段具有更高的光学效率,提出以Féry棱镜组合作为分光元件的Dyson高光谱成像仪系统,系统中引入消色差棱镜组合以减小光谱的非线性色散,使棱镜系统色散的线性度达到较高。结果表明,可见近红外（VNIR）光谱通道的光学调制传递函数（MTF）达到0.9以上,光谱分辨率为4.2～6.8 nm。短波红外（SWIR）光谱通道的MTF达到0.73～0.87,光谱分辨率为6.4～12.5 nm。通过消色差Féry棱镜组合的设计,该光学成像系统两个光谱通道内的相对谱线弯曲均小于0.05%,色畸变小于0.13%。     

Wollaston棱镜阵列干涉光谱仪的研制及其光通量的分析

利用空间调制干涉光谱技术研制了基于双层Wollaston棱镜组的干涉仪原理样机,用该样机进行了干涉光谱实验,采集了He-Ne激光器干涉图像,通过对图像进行数据处理,获得了光源的归一化光谱图。并对样机系统做了光通量分析。它与传统的使用单个Wollaston棱镜测量光谱的方法相比,光谱分辨率和光通量可以提高一倍以上。     

Extended focus depth for Fourier domain optical coherence microscopy

We report on a new detection scheme for Fourier domain optical coherence microscopy that exhibits high transverse resolution along an axially extended focal range. Nearly constant transverse resolution of approximately 1.5 microm along a focal range of 200 microm is experimentally verified with a maximum sensitivity of 105 dB. A broad-bandwidth Ti:sapphire laser allowed for an axial resolution of 3 microm in air.     

潜望式瞄准镜中消像旋棱镜的装调工艺技术

当潜望式光学系统中反射镜绕机械轴转动时,影像会在视场中绕光轴旋转严重影响观瞄。消像旋棱镜可以使像产生反向转动从而消除这种影响。从探索潜望式瞄准镜中消像旋棱镜的装调工艺出发,通过对2种常用消像旋棱镜在光学系统中对光线折转的分析,提出了其光机装调过程的判断依据,总结了2种消像旋棱镜应用的装调工艺方法,并提出了在平行光路中检测消像旋棱镜固定前后的分辨率以保证成像质量。经过多个项目的验证,此方法能有效降低消像旋棱镜的装调难度,装调后消像旋棱镜光轴与系统基准轴偏差控制在30以内。     

一种新型静态成像光谱系统的研究

静态干涉系统具有稳定性好、抗干扰能力强的优势,但其缺点是光谱分辨率低并且光谱测试范围不易调整。针对静态干涉型成像光谱系统光谱分辨率低且不可调等问题,设计了一种新型静态成像光谱系统。系统由光束整形模块、新型静态干涉调制模块以及成像模块构成。光束整形模块将入射光缩束并整形为平行光,进而保证入射干涉具后可以获得较好的干涉效果;新型静态干涉调制模块对入射光进行相干处理。在双折射干涉结构的基础上进行了改进,在不改变原有静态干涉具尺寸的基础上提高了系统的光谱分辨率,并实现了光谱分辨率的静态调制;成像模块完成对目标区域二维可见光图像的采集。系统核心部件由两组光轴相互正交的Wollaston棱镜作为分光器件,在两棱镜间放置电光调制模块,实现光程的静态扫描。分析了新型静态成像光谱系统的工作原理,给出了入射角、折射角等主要参数的函数表达式,并构建了系统的数据模型。通过绘制系统光线追迹图的方式,得到了该系统横向剪切量的函数方程,并对影响横向剪切量的各个参数进行了分析与讨论。通过仿真计算了改变结构角、晶体厚度以及调制度等参数对横向剪切量的影响程度,并定量计算了两个参数对系统光谱分辨率的影响程度。由仿真分析结果可知,增大结构角与加宽调制晶体厚度都可以为系统提供更大的光程差。故通过电光调制的方式实现横向剪切量的静态扫描是可行的,可以实现静态光谱图像的获取。在实验中对660 nm激光进行了测试。新型静态干涉模块采用孔径20 mm×20 mm,厚度10 mm的两块光轴相反的Wollaston棱镜与厚度10 mm的电光调制晶体构成。当调制度分别是0.000 2和0.000 6时,成像模块采集得到干涉条纹具有明显差异。当调制度增大时,其干涉条纹密度增大,说明采用越大的调制度,系统对应的光谱静态扫描能力越强,对光谱分辨率的控制越好。由此可见,本静态成像光谱系统在控制电光晶体调制度的条件下具有光谱分辨率可调的特性,验证了系统的可行性。     

Profiles with microscopic resolution by single-sided NMR

A single-sided NMR sensor to produce depth profiles with microscopic spatial resolution is presented. It uses a novel permanent magnet geometry that generates a highly flat sensitive volume parallel to the scanner surface. By repositioning the sensitive slice across the object one-dimensional profiles of the sample structure can be produced with a space resolution better than 5 microm. The open geometry of the sensor results in a powerful testing tool to characterize arbitrarily sized objects in a non-destructive way.     

Electric Field Enhancement of Nano Gap of Silver Prisms

Using numerical calculation, we examine the effects of gap distance of a pair of nano gap silver prisms with rounded corners on the local light intensity enhancement. Two peaks due to localized surface plasmon （LSP） excitation are observed in a wavelength range from 900nm to 300nm. The results demonstrate that peaks at a longer and a shorter wavelength corresponded to dipole-like and quadrupole-like LSP resonances, respectively. It is found that a gap distance up to 20 nm provides larger light intensity enhancement than that of a single silver nano prism with rounded corners. Furthermore, nano gap silver prisms are fabricated by direct focused ion beam processing, and we measure the scattering light spectrum of a pair of nano prisms by a confocal optical system. However, the two LSP peaks are not observed in visible range because the sizes of the nano gap and prisms are too large.     

Phase-resolved optical coherence tomography and optical Doppler tomography for imaging blood flow in human skin with fast scanning speed and high velocity sensitivity

We have developed a novel phase-resolved optical coherence tomography (OCT) and optical Doppler tomography (ODT) system that uses phase information derived from a Hilbert transformation to image blood flow in human skin with fast scanning speed and high velocity sensitivity. Using the phase change between sequential scans to construct flow-velocity imaging, this technique decouples spatial resolution and velocity sensitivity in flow images and increases imaging speed by more than 2 orders of magnitude without compromising spatial resolution or velocity sensitivity. The minimum flow velocity that can be detected with an axial-line scanning speed of 400 Hz and an average phase change over eight sequential scans is as low as 10 microm/s, while a spatial resolution of 10 microm is maintained. Using this technique, we present what are to our knowledge the first phase-resolved OCT/ODT images of blood flow in human skin.     

Linear-to-circular polarization transformation upon optical tunneling through an embedded low-index film

Quarter-wave retardation can be achieved in optical tunneling through a low-index thin film that is surrounded by a medium of higher refractive index, for any index ratio N>2.414, over a range of incidence angles that is determined by N. A novel frustrated-total-internal-reflection circular polarization beam splitter (CPBS) is proposed that uses an adjustable air gap between two Ge prisms. This tunable CPBS operates over a broad (2-12 microm) IR spectral range by controlling the air-gap thickness to match one-tenth of the wavelength of light by use of a piezoelectric transducer.     

Fiber-optic-bundle-based optical coherence tomography

A fiber-optic-bundle-based optical coherence tomography (OCT) probe method is presented. The experimental results demonstrate this multimode optical fiber-bundle-based OCT system can achieve a lateral resolution of 12 microm and an axial resolution of 10 microm with a superluminescent diode source. This novel OCT imaging approach eliminates any moving parts in the probe and has a primary advantage for use in extremely compact and safe OCT endoscopes for imaging internal organs and great potential to be combined with confocal endoscopic microscopy.     

振镜扫描光学多道谱仪

以平面光栅单色仪和光学扫描振镜为基础研制一套具有高时间分辨能力的光学多道分析系统,并利用计算机进行实时控制与数据采集。实验表明：本系统在保持谱分辨的同时,时间分辨率达到１０ｍｓ以内。     

Geometrical optics analysis for reduction of trapezoidal image distortion in a single prism-based optical fingerprint scanner

A single prism-based optical fingerprint scanner structure is mathematically analyzed by using geometrical optics approach. Important parameters including a tilting angle of the fingerprint accepting plane, a geometrical-optic distant difference, a trapezoidal image distortion, an object compression ratio, and an orientation of a two-dimensional image sensor are formulated for the first time in terms of all three angles of the prism and the prism material. In addition, based on our mathematical model, we propose to design all three angles of the prism in such a way that the plane accepting the fingertip observed from one side of the prism is normal to the optical axis of the system. In this way, the imaging plane is perpendicular to the optical axis, eliminating the trapezoidal image distortion and leading to ease of implementation. Experimental verification using three commercially available dispersion prisms made from three different glass materials and one prism based on our design concept shows that a prism with higher refractive index provides lower trapezoidal image distortion. The experimental data generally obeys our theoretical analysis.     

Extended continuous-wave supercontinuum generation in a low-water-loss holey fiber

We report on the development of a 2.5 microm core photonic crystal fiber with a substantially reduced water-peak loss around 1.38 microm, which allows extended Raman-soliton supercontinuum generation up to 1.55 microm with a cw ytterbium fiber laser pump source. The resulting broadband, high-spectral-power-density, low-coherence light source can be employed for advanced, submicrometer resolution optical coherence tomography.     

Local coupling-coefficient characterization in fiber Bragg gratings

We propose a new method for characterizing the local parameters of fiber Bragg gratings. This method combines measurement of the complex impulse response by optical low-coherence reflectometry and reconstruction of the complex coupling coefficient by layer peeling. Application of the method to a nonhomogeneous grating shows that the local coupling coefficient can be precisely determined with an axial resolution below 20 microm and a maximum error of less than 5% for amplitude and phase, respectively.     

Laminar optical tomography: demonstration of millimeter-scale depth-resolved imaging in turbid media

Laminar optical tomography (LOT) is a new technique that combines the advantages of diffuse optical tomography image reconstruction and a microscopy-based setup to allow noncontact imaging with 100-200-microm resolution effective over depths of 0-2.5 mm. LOT is being developed primarily for multispectral imaging of rat cortex, for which resolving functional dynamics in various layers of the brain's cortex (to depths of 1500 microm) is of increasing interest to neurophysiologists. System design and image reconstruction techniques are described, along with simulation and phantom results that demonstrate the characteristics and limitations of system accuracy and resolution.     

High-resolution ultrasound-modulated optical tomography in biological tissues

We present a novel implementation of high-resolution ultrasound-modulated optical tomography that, based on optical contrast, can image several millimeters deep into soft biological tissues. A long-cavity confocal Fabry-Perot interferometer, which provides a large etendue and a short response time, was used to detect the ultrasound-modulated coherent light that traversed the scattering biological tissue. Using 15-MHz ultrasound, we imaged with high-contrast light-absorbing structures placed >3 mm below the surface of chicken breast tissue. The resolution along the axial and the lateral directions with respect to the ultrasound propagation direction was better than 70 and 120 microm, respectively. The resolution can be scaled down further by use of higher ultrasound frequencies. This technology is complementary to other imaging technologies, such as confocal microscopy and optical-coherence tomography, and has the potential for broad biomedical applications.     

Broadband light generation by noncollinear parametric downconversion

Broadband light generation is demonstrated by noncollinear spontaneous parametric downconversion with a cw pump laser. By use of a suitable noncollinear phase-matching geometry and a tightly focused pump beam, downconverted signals that feature a bell-shaped spectral distribution with a bandwidth approaching 200 nm are obtained. As an application of the generated broadband light, submicrometer axial resolution in an optical coherence tomography scheme is demonstrated; a free-space resolution down to 0.8 microm was achieved.