Simultaneous dual-wavelength-band common-path swept-source optical coherence tomography with single polygon mirror scanner

We report a novel (to the best of our knowledge) simultaneous 1310/1550 two-wavelength band swept laser source and dual-band common-path swept-source optical coherence tomography (SS-OCT). Synchronized dual-wavelength tuning is performed by using two laser cavities and narrowband wavelength filters with a single dual-window polygonal scanner. Measured average output powers of 60 and 27 mW have been achieved for the 1310 and 1550 nm bands, respectively, while the two wavelengths were swept simultaneously from 1227 to 1387 nm for the 1310 nm band and from 1519 to 1581 nm for the 1550 nm band at an A-scan rate of 65 kHz. Broadband wavelength-division multiplexing is used for coupling two wavelengths into a common-path single-mode GRIN-lensed fiber probe to form dual-band common-path SS-OCT. Simultaneous OCT imaging at 1310 and 1550 nm is achieved. This technique allows for in vivo high-speed OCT imaging with potential application in functional (spectroscopic) investigations.     

Multiscale multimodal imaging with multiphoton microscopy and optical coherence tomography

A multiscale multiphoton microscopy (MPM) and optical coherence tomography (OCT) system has been developed using a sub-10 fs Ti:sapphire laser. The system performs cross-sectional OCT imaging over millimeter field-of-view and en-face high-resolution MPM imaging with submicrometer resolution from the same sample location. With fish cornea, we have demonstrated cross-sectional imaging of cornea tissue layers using OCT, and the zoom-in imaging of cells and collagen fibers in each layer using MPM. The multiscale MPM/OCT system shows the potential of a rapid coarse scan to search for abnormal regions and the subsequent fine zoom-in imaging for diagnosis.     

Fiber-optic Fourier-domain common-path OCT

We experimentally and theoretically investigated the performance of a fiber-optic based Fourier-domain common-path optical coherence tomography （OCT）. The fiber-optic common-path OCT operated at the 840-nm center wavelength. The resolution of the system was 8.8 μm （in air） and the working depth using a bare fiber probe was approximately 1.5 mm. The signal-to-noise ratio （SNR） of the system was analyzed. OCT images obtained by the system were also presented.     

Investigation of gold-coated bare fiber probe for in situ intra-vitreous coherence domain optical imaging and sensing

We have investigated the usage of gold-plated bare fiber probes for in situ imaging of retinal layers and surrounding ocular tissues using time-domain common-path optical coherence tomography. The fabricated intra-vitreous gold-plated micro-fiber probe can be fully integrated with surgical tools working in close proximity to the tissue to provide subsurface images having a self-contained reference plane independent to the Fresnel reflection between the distal end of the probe and the following medium for achieving reference in typical common-path optical coherence tomography. We have fully characterized the probe in an aqueous medium equivalent to the vitreous humor in the eye and were able to differentiate various functional retinal tissue layers whose thickness is larger than the system’s resolution.     

Optical Coherence Tomography Premiere in Korea

Optical Coherence Tomography (OCT) is considered as fundamentally new image modality having advantages such as high-speed, real-time cross sectional imaging with non-invasive in vivo investigation of biological tissue and its potential for clinical application is highly evaluated. In spite of these merits, the research activity in OCT has not taken much attention until recently. However the situation in Korea is gradually changing due to understanding of its versatile applications. Active research and commercialization are underway. Bulk optics-based OCT system is changed into alignfree fiber-optics system. With our expertise in the fabrication of fiber grating devices and strong background in control of fiber based system, we hope to contribute in developing simplified all-fiber OCT system with better performance. As a leading research group, working on OCT, we have firstly implemented fiber-based OCT system in Korea and demonstrated the imaging performance with glass plate and onion.     

MR in vivo imaging of oxygen suppression effect of soft contact lens on the human cornea

The O(2) suppression effect of a soft contact lens on the human cornea was measured using dynamic magnetic resonance imaging (MRI) of the anterior chamber transcorneally exposed to O(2). Dynamic T(1)-weighted fast spin echo imaging of anterior chambers (TR = 2 s, TE = 15 ms, 5-mm slice) was performed both before and during oxygen supply to a full goggle placed on the face of volunteers wearing a soft contact lens on one eye and nothing on the other eye as a control. Within 15 min after O(2) administration, significantly lower intensity changes were obtained in the anterior chambers of the eyes with the contact lens than in those of the eyes without one, suggesting that dynamic MRI of the anterior chamber transcorneally exposed to O(2) can be used to evaluate the O(2) suppression effect of a soft contact lens on the cornea.     

Common-path phase-shift interferometry surface plasmon resonance imaging system

Surface plasmon resonance (SPR) and common-path phase-shift interferometry (PSI) techniques are integrated in a biosensing imaging system for measuring the two-dimensional spatial phase variation caused by biomolecular interactions on a sensing chip without the need for additional labeling. The common-path PSI technique has the advantage of long-term stability, even when it is subjected to external disturbances. Hence the system meets the requirements of the real-time kinetic studies involved in biomolecular interaction analysis. The proposed SPR-PSI imaging system demonstrates a detection limit of a 2 x 10(-7) refractive-index change, a long-term phase stability of 2.5 x 10(-4) pi rms for 4 h, and a spatial phase resolution of 10(-3) pi with a lateral resolution of 100 microm.     

Measurement of absolute flow velocity vector using dual-angle, delay-encoded Doppler optical coherence tomography

Single-beam laser Doppler measurements of flow velocity are only sensitive to the velocity component parallel to the optical axis. We describe a simple modification to a standard Doppler optical coherence tomography (OCT) system using a single sample beam that provides velocity information from multiple angles within the beam. By introducing a glass plate midway into the OCT beam path, the sample beam is divided into several components, each with a different group delay and each providing a separate interferogram with its own effective Doppler angle. By combining the Doppler shift measured in each of these component interferograms, the flow velocity vector is fully determined.     

Sinusoidal fringe projection system based on compact and non-mechanical scanning low-coherence Michelson interferometer for three-dimensional shape measurement

We report a sinusoidal fringe projection system based on superluminiscent diode (SLD) as a broad-band light source in conjunction with an acousto-optic tunable filter (AOTF) as frequency tuning device for three-dimensional shape measurement. The present system is based on a compact low-coherence Michelson interferometer system. The conventional interferometric system was modified in which one side of the beam splitter was coated with aluminum oxide which is used as reference mirror. With this modified version, interference fringes can easily be obtained by simply placing the external mirror in contact on the other side of beam splitter. Sinusoidal fringes with multiple spatial-carrier frequency can be generated in real-time using the present system by means of changing the radio-frequency signal to AOTF electronically without mechanically moving any component in the system. The present system was tested by projecting the sinusoidal fringes on a step-like object and 3D shape of the object was reconstructed using Fourier transform fringe analysis technique. The main advantages of the proposed system are completely non-mechanical scanning, easy to align, high stability because of its nearly common-path geometry and compactness.     

基于谱域相位分辨光学相干层析的纳米级表面形貌成像

提出了一种基于谱域相位分辨光学相干层析的纳米级表面形貌成像方法,由干涉光谱计算样品相邻两点的相位差,得到样品表面相位差分图,经过积分,重建样品表面形貌的定量分布.当相邻两点相位差的绝对值小于π,不产生相位包裹,避免了目前的干涉法相位解包裹存在的问题,将干涉法相邻两点相位差绝对值的限制条件由目前的π扩大到2π,提高了干涉法表面形貌成像的适用范围.参考面和样品置于同一平台之上,消除环境干扰及系统振动的影响,噪声幅度小于0.3 nm.通过对光学分辨率片及表面粗糙度标准样板的表面形貌成像,对本方法进行了验证,系统的轴向分辨率优于1 nm.     

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.     

The modelling of the influence of a corneal geometry on the pupil image of the human eye

In normal conditions, a pupil of the eye is observed through the optical system of the cornea. The cornea is the anterior surface of the eye and is the major refractive element of the human eye. The influence of the corneal shape should not be neglected in measurements of the pupil size. The purpose of this study was to estimate the influence of the corneal geometry, the diameter of the pupil and its position in the anterior chamber on the magnification and position of the image of the pupil. The numerical calculations presented in the paper assume infinitely thin cornea, and the corneal topography was approximated by the elongated ellipsoid. The ray tracing procedure was used in our numerical modelling. The magnification of the pupil image amounted to about 10% and increases with decrease of radius of curvature and eccentricity of the corneal profile and decreases for the largest pupil. The results show also that the pupil image is placed nearer the corneal apex than the real pupil. The image of the pupil is always blurred, which limits the sharp observation of the pupil.     

Real-time quadrature projection complex conjugate resolved Fourier domain optical coherence tomography

We present a novel algorithm for full-range imaging by suppression of the complex conjugate artifact in phase-shifting Fourier domain optical coherence tomography. This technique utilizes the projection of multiple phase-shifted interferograms onto an orthogonal basis set to reconstruct the complex interferogram. Full-range imaging with >30 dB suppression of the symmetric artifact is demonstrated using a 3 x 3 fiber coupler swept source OCT system, providing a depth range of 6.6mm with -8 dB roll-off in sensitivity at the depth boundaries relative to DC. Real-time display of full-range images of the anterior segment of the human eye acquired in vivo at a line rate of 6.67 kHz are presented.     

Electrostatic force of dust deposition originating from contact between particles and photovoltaic glass

Charged photovoltaic glass produces an electrostatic field. The electrostatic field exerts an electrostatic force on dust particles, thus making more dust particles deposited on the glass. In this paper, the contact electrification between the deposited dust particles and the photovoltaic glass is studied. Meanwhile, the surface charge density model of the photovoltaic glass and the electrostatic force of charged particles are analyzed. The results show that with the increasing of the particle impact speed and the inclination angle of the photovoltaic panel, the charges on particles increase to different degrees.Under a given condition, the electrostatic forces acting on the charged particles at different positions above the glass plate form a bell-shaped distribution at a macro level, and present a maximum value in the center of the plate. As the distance between the particle and the charged glass decreases, the electrostatic force exerted on the particle increases significantly and fluctuates greatly. However, its mean value is still higher than the force caused by gravity and the adhesion force,reported by some studies. Therefore, we suggest that photovoltaic glass panels used in the severe wind-sand environment should be made of an anti-static transparent material, which can lessen the dust particles accumulated on the panels.     

Electrostatic micromachine scanning mirror for optical coherence tomography

Compact electrostatic micromirror structures for use in the scanning arm of an optical coherence tomography (OCT) system are described. These devices consist of millimeter-scale mirrors resting upon micrometer-scale polyimide hinges that are tilted by a linear micromachine actuator, the integrated force array (IFA). The IFA is a network of deformable capacitor cells that electrostatically contract with an applied voltage. The support structures, hinges, and actuators are fabricated by photolithography from polyimide-upon-silicon wafers. These devices were inserted into the scanning arm of an experimental OCT imaging system to produce in vitro and in vivo images at frame rates of 4 to 8 Hz.     

适合于内窥成像的共路型光学相干层析成像系统

提出了一种采用光纤型迈克耳孙干涉仪进行光程补偿的菲佐型光学相干层析成像(OCT)系统.该系统的传感探头为共路干涉结构,以解决现有内窥光学相干层析成像系统中存在的探头运动导致图像失真、以及更换使用不同探头时需进行色散和偏振态调节等问题.光程补偿和振动干扰实验结果表明,光程补偿方法正确可行,系统对环境干扰不敏感.利用研制的系统对反射镜和近红外卡进行了成像实验,验证了系统的有效性.提出的方法非常适合于内窥成像,并给出了把系统扩展为内窥光学相干层析成像系统的具体实现过程.     

Use of a scanner to modulate spatial interferograms for in vivo full-range Fourier-domain optical coherence tomography

We report a new yet simple method to achieve full-range complex Fourier-domain optical coherence tomography (OCT) for in vivo imaging. The method utilizes a scanner that is dedicated for lateral scanning in the system to introduce a constant carrier frequency into the OCT spectral interferograms during the scanning. This is achieved by simply offsetting the sampling beam spot away from the pivot point of the scanning mirror. We demonstrate the method experimentally for in vivo full-range imaging of the anterior segment of a human eye. The method is free from complex conjugate mirror image and self-cross-correlation image artifacts.     

Optically deviated focusing method based high-speed SD-OCT for in vivo retinal clinical applications

The aim of this study is to provide accurately focused, high-resolution in vivo human retinal depth images using an optically deviated focusing method with spectral-domain optical coherence tomography (SD-OCT) system. The proposed method was applied to increase the retinal diagnosing speed of patients with various values of retinal distances (i.e., the distance between the crystalline eye lens and the retina). The increased diagnosing speed was facilitated through an optical modification in the OCT sample arm configuration. Moreover, the optical path length matching process was compensated using the proposed optically deviated focusing method. The developed system was mounted on a bench-top cradle to overcome the motion artifacts. Further, we demonstrated the capability of the system by carrying out in vivo retinal imaging experiments. The clinical trials confirmed that the system was effective in diagnosing normal and abnormal retinal layers as several retinal abnormalities were identified using non-averaged single-shot OCT images, which demonstrate the feasibility of the method for clinical applications.     

Polarization Fizeau interferometer based on birefringent thin film

A polarization Fizeau interferometer based on birefringent thin film is presented. The interferometer adopts a birefringent thin film to obtain orthogonally polarized and strictly common-path reference and test beams. Advantages include ease of implementation on large-aperture interferometer, measuring test optics from long distance, and achieving high fringe visibility. The phase shift is obtained by combining a quarterwave plate and an analyzer. The concepts illustrated are verified experimentally.     

Simultaneous swept source optical coherence tomography of the anterior segment and retina using coherence revival

We report on an implementation of coherence revival-based heterodyne swept source optical coherence tomography that is capable of simultaneously imaging the anterior and posterior eye. A polarization-encoded sample arm was used to efficiently focus orthogonal polarizations on the anterior segment and retina. Depth encoding was achieved using coherence revival, which allows for multiple depths within a sample to be simultaneously imaged and frequency encoded by carefully controlling the optical pathlength of each sample path. This design is a significant step toward whole-eye optical coherence tomography (OCT), which would enable customized ray-traced modeling of patient eyes to improve refractive surgical interventions and eliminate optical artifacts in retinal OCT diagnostics. We demonstrated the feasibility of this system for in vivo imaging by simultaneously acquiring images of the anterior segments and retinas in healthy human volunteers.