从迈克耳孙干涉仪到光学相干层析术

介绍了迈克耳孙干涉仪在物理学发展史上的重要作用及生物医学成像技术的发展状况．从迈克耳孙干涉仪的发展过程出发,讨论了光学相干层析术的原理、特性及其在生物医学成像、物理学、材料科学中的应用,并将频谱光学相干层析术与傅里叶变换光谱术作了比较,最后讨论了它在教学上的意义．     

Optimal interferometer designs for optical coherence tomography

We introduce a family of power-conserving fiber-optic interferometer designs for low-coherence reflectometry that use optical circulators, unbalanced couplers, and (or) balanced heterodyne detection. Simple design equations for optimization of the signal-to-noise ratio of the interferometers are expressed in terms of relevant signal and noise sources and measurable system parameters. We use the equations to evaluate the expected performance of the new configurations compared with that of the standard Michelson interferometer that is commonly used in optical coherence tomography (OCT) systems. The analysis indicates that improved sensitivity is expected for all the new interferometer designs, compared with the sensitivity of the standard OCT interferometer, under high-speed imaging conditions.     

Performance analysis of a swept-source optical coherence tomography system with a quadrature interferometer and optical amplification

A performance analysis of signal to noise ratio for an optical coherence tomography system with quadrature detection and a semiconductor optical amplifier in the sample arm is discussed. The results are compared and discussed in relation to a conventional OCT system (without optical amplification). An increase of the signal to noise ratio up to 14 dB at a depth of 0.5 mm is obtained compared to the system without the optical amplifier. Overall, an improvement was demonstrated for signal coming from deeper regions within the samples. Arterial plaque from a myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbit is visualized and characterized using this system. Improvement of signal to noise ratio increases the penetration depth possible for OCT images, from 1 mm to 2 mm within the vessel wall of an artery. Preliminary results show that vulnerable plaque with fibrous cap, macrophage accumulations and calcification in the arterial tissue are measurable with this OCT system.     

What type of coherence of the optical field is observed in the Michelson interferometer

The types and corresponding coherence functions of the optical field are considered depending on the frequency and angular spectra of the field. The main concepts of the theory of coherence effects in the interference experiment with the amplitude splitting of the initial field are discussed. It is shown that, in strict correspondence with the theory of coherence of the random wave fields, the Michelson interferometer reveals manifestations of the transverse and longitudinal spatial (rather than temporal, as it is commonly adopted) coherence of the optical field; the purely temporal coherence of the optical field is revealed only under special conditions of the interference experiment. Beyond these conditions, either spatial or spatiotemporal coherence is revealed.     

Vibration-displacement measurements with a highly stabilised optical fiber Michelson interferometer system

A highly stabilised vibration-displacement measurement system, which employs fiber Bragg gratings (FBGs) to interleave two fiber Michelson interferometers that share the common-interferometric-optical path, is presented. The phase change in the interferometric signals of the two fiber Michelson interferometers have been tracked, respectively, with two electronic feedback loops. One of the fiber interferometers is used to stabilise the system by the use of an electronic feedback loop to compensate the environmental disturbances. The second fiber interferometer is used to perform the measurement task and employs another electronic feedback loop to track the phase change in the interferometric signal. The measurement system is able to measure vibration-displacement and provide the sense of direction of the displacement. The frequency range of the measured vibration-displacement is from 0.1 to 200 Hz and the measurement resolution is 10 nm.     

Double-grating interferometer with a one-to-one correspondence with a Michelson interferometer

We describe a double-grating interferometer that has a one-to-one correspondence with a Michelson interferometer. The half spatial periods of the gratings are equivalent to the wavelengths of the interferometer. The widths of the interference fringes can be changed easily. The intensity distribution of the interference pattern is independent of the wavelength of the light source used. The surface profile of an object can be measured because two interference beams can coincide precisely on the image plane of the object. The measuring range is much larger than that of a Michelson interferometer.     

基于迈克耳孙干涉仪的近场光学实验

介绍了一种以迈克耳孙干涉仪作为操作平台的近场光学实验系统.该系统可以测量棱镜内表面全内反射产生的隐失场,观察两维光栅样品的近场光学结构,还可以用于光子扫描隧穿显微镜(PSTM)的原理性实验,有助于学生深入了解隐失场的结构和近场光学显微镜的基本工作原理.该装置具有结构简单可靠,操作简便等特点,十分适用于物理实验教学.     

Power-efficient nonreciprocal interferometer and linear-scanning fiber-optic catheter for optical coherence tomography

A nonreciprocal fiber-optic interferometer is demonstrated in an optical coherence tomography (OCT) system. The increased power efficiency of this system provides a 4.1-dB advantage over standard Michelson implementations. In addition, a new linear-scanning fiber-optic catheter is demonstrated that avoids the rotary optical junction that is required in circumferential scanning systems. These advancements have permitted the clinical implementation of OCT imaging in the human gastrointestinal tract.     

全光纤频域光学相干层析成像系统优化研究

针对频域光学相干层析(SD-OCT)系统特有硬件(线阵CCD及分光光栅)参数对成像质量造成的影响,展开了对基于光纤的频域OCT系统中硬件参量的模拟和优化工作,分析了分光计中CCD线列阵像素数及数字化深度、CCD安装偏差等因素对OCT成像质量的影响,并对光谱像素图定位进行了修正.研究表明:纵向分辨率不受CCD线列阵像素数的影响,CCD线列阵像素数的增多将线性地增大最大测量深度;CCD数字化深度小于6 bit将直接导致系统纵向分辨率的锐减;线阵CCD偏离聚焦透镜焦面将导致点扩展函数的强度减弱、系统分辨率降低;在较小角度内转动CCD,将使纵向分辨率得到提高;采用氖灯光谱进行像素图定位校正之后,可以相应地提高系统分辨率.部分模拟结论得到实验验证.采用此模拟优化结果,可根据OCT成像的具体要求对系统硬件参量进行优化选择.     

偏振迈克耳孙干涉仪(POLMINT)及其在光学教学中的应用

详细介绍了国际上新近发展的迈克耳孔干涉仪的一种变形－－偏振迈克耳孙干涉仪（POLMINT）的原理,并对其在光学教学中的应用进行了讨论。     

Spectral-domain optical coherence tomography with a Fresnel spectrometer

We propose a novel spectral-domain optical coherence tomography (SD-OCT) equipped with a Fresnel spectrometer, which utilizes a Fresnel zone plate (FZP) as both dispersion and focusing optics and thus spreads the spectral interferogram evenly in wavenumber domain because of the proportional relation between the focal length of the FZP and the wavenumber. With no need of the conversion calculation from wavelength to wavenumber in conventional SD-OCT, this new design is favorable for fast imaging with high resolution. As only a FZP and CCD are used, the Fresnel spectrometer is simple and compact. It is experimentally shown that its performance is as good as that of numerical interpolation in conventional SD-OCT. Imaging of bio-tissue by Fresnel SD-OCT is also demonstrated.     

Enhanced phase-shifting measurement with a double-passed Michelson interferometer

Optical Review - A double-passed Michelson interferometer for enhanced phase-shifting measurement is described in this paper. Two interference signals concerning measurement and reference beams are...     

Spectroscopic optical coherence tomography

Spectroscopic optical coherence tomography (OCT), an extension of conventional OCT, is demonstrated for performing cross-sectional tomographic and spectroscopic imaging. Information on the spectral content of backscattered light is obtained by detection and processing of the interferometric OCT signal. This method allows the spectrum of backscattered light to be measured over the entire available optical bandwidth simultaneously in a single measurement. Specific spectral features can be extracted by use of digital signal processing without changing the measurement apparatus. An ultrabroadband femtosecond Ti:Al(2)O(3) laser was used to achieve spectroscopic imaging over the wavelength range from 650 to 1000 nm in a simple model as well as in vivo in the Xenopus laevis (African frog) tadpole. Multidimensional spectroscopic data are displayed by use of a novel hue-saturation false-color mapping.     

Second-harmonic optical coherence tomography

Second-harmonic optical coherence tomography, which uses coherence gating of second-order nonlinear optical responses of biological tissues for imaging, is described and demonstrated. Femtosecond laser pulses were used to excite second-harmonic waves from collagen harvested from rat tail tendon and a reference non-linear crystal. Second-harmonic interference fringe signals were detected and used for image construction. Because of the strong dependence of second-harmonic generation on molecular and tissue structures, this technique imparts contrast and resolution enhancement to conventional optical coherence tomography.     

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.     

Holoscopy--holographic optical coherence tomography

Scanning optical coherence tomography (OCT) is limited in sensitivity and resolution by the restricted focal depth of the confocal detection scheme. Holoscopy, a combination of holography and Fourier-domain full-field OCT, is proposed as a way to detect photons from all depths of a sample volume simultaneously with uniform sensitivity and lateral resolution, even at high NAs. By using the scalar diffraction theory, as frequently applied in digital holographic imaging, we fully reconstruct the object field with depth-invariant imaging quality. In vivo imaging of human skin is demonstrated with an image quality comparable to conventionally scanned OCT.     

Fourier domain optical coherence tomography with a linear-in-wavenumber spectrometer

We describe Fourier domain optical coherence tomography equipped with a novel linear-in-wavenumber spectrometer. The presented device linearizes the spectral dispersion of the spectrometer in wavenumber using a specifically designed prism. The spectral linearity in wavenumber makes numerical interpolation into wavenumber unnecessary, reduces computing time, and furthermore results in improvement of the falloff of signal with image range inherent to frequency-domain optical coherence tomography imaging. Experiments demonstrate the improvement of the falloff and agree with the expected results from simulation.     

Two-wavelength optical coherence tomography

We present the results of studies of the basic principles and describe the design of a low-coherence two-wavelength interferometer based on polarization-maintaining fiber. The interferometer was developed for optical coherence tomography (OCT) imaging of the internal structure of living biological tissue simultaneously at two wavelengths, 830 and 1300 nm. Images of several sites of living biological tissue are presented and analyzed.     

Tracking optical coherence tomography

An experimental tracking optical coherence tomography (OCT) system has been clinically tested. The prototype instrument uses a secondary sensing beam and steering mirrors to compensate for eye motion with a closed-loop bandwidth of 1 kHz and tracking accuracy, to within less than the OCT beam diameter. The retinal tracker improved image registration accuracy to <1 transverse pixel (<60 microm). Composite OCT images averaged over multiple scans and visits show a sharp fine structure limited only by transverse pixel size. As the resolution of clinical OCT systems improves, the capability to reproducibly map complex structures in the living eye at high resolution will lead to improved understanding of disease processes and improved sensitivity and specificity of diagnostic procedures.     

Feasibility study of phase-sensitive imaging based on multiple reference optical coherence tomography

Multiple reference optical coherence tomography(MR-OCT) is a recently developed, low-cost and compact time-domain OCT solution for primary care and consumer level applications. A combination of a voice coil actuator and a partial mirror(PM) extends the scan range for imaging depths of approximately 1 mm in biological samples. Our previous research on MR-OCT is based only on intensity information obtained from the depth-resolved interference signal. In this Letter, we extract the phase information from the MR-OCT signal and, hence, provide an additional contrast modality. The phase sensitivity of the system is measured to be approximately 0.2 and 1.5 rad for the first and twelfth orders of reflection when using a mirror as the sample.This Letter describes first results of phase-sensitive data measured on a phantom obtained with MR-OCT. Data from a chick embryo chorioallantoic membrane(CAM) is used to demonstrate the feasibility of MR-OCT for in vivo phase-sensitive imaging.