Rapid Scanning Optical Delay Line Research Articles

Rapid scanning optical delay line based on a diffraction grating pair for a low-coherence reflectometer.

We present a simple low-coherence time-domain interferometric reflectometer with a rapidly scanning optical delay line (RSODL) based on a non-parallel diffraction grating (DG) pair. The novelty of the solution is that the lightwave in the reference channel is focused on a galvo-mirror in a sub-mm static spot, which allows implementation of fast microelectromechanical systems scan optics. It is shown that the DG pair can be operated as a non-dispersive element that provides dynamic group delay of a reference lightwave. The DG pair system is also capable of tuning the RSODL dispersion from negative to positive values. The experimental depth range in air was obtained as large as 2.5mm for axial resolution of 20μm.

Stimulated Raman scattering microscopy and spectroscopy with a rapid scanning optical delay line.

Stimulated Raman scattering (SRS) microscopy that is capable of both high-speed imaging and rapid spectroscopy will be advantageous for detailed chemical analysis of heterogeneous biological specimens. We have developed a system based on spectral focusing SRS technology with the integration of a rapid scanning optical delay line, which allows continuous tuning of SRS spectra by scanning a galvo mirror. We demonstrate SRS spectral measurements of dimethyl sulfoxide solution at low concentrations and multi-color imaging of rice pollens and HeLa cells with line-by-line delay tuning to reduce motion artifacts, as well as fast acquisition of SRS spectra at specific regions of interest.

An improved algorithm of structural image reconstruction with rapid scanning optical delay line for Optical Coherence Tomography

A new algorithm of structural image reconstruction in Optical Coherence Tomography is described. The modified rapid scanning optical delay (RSOD) line, low numerical aperture, small angle raster scanning with consecutive averaging and multilevel digital filtering have been used to obtain high quality structural images of an onion and the nail bed of a human thumb. The proposed method significantly improves image contrast and allows visualization of small blood capillaries under the nail plate.

1F35 1400帯低コヒーレンス光干渉計を用いたヒト皮膚における含水率分布マイクロ断層可視化システムの基礎的検討

Visco-elastic properties of skin tissue is strongly dependent on moisture content around epidermal tissue, which should cause skin wrinkles Therefore, an in vivo quantitative measurement of moisture content is necessary to clarify skin mechanics. In this paper, we propose OCM (Optical Coherence Moisturegraphy), which is a method of tomographic micro-visualizing moisture content using low coherence interferometer with 1400 nm band light source. The tomographic detection of the intensity attenuation due to light absorption of water can determine moisture content profile inside skin tissue. The rapid scanning optical delay line was implemented as a reference arm so as to visualize video-rate tomography of moisture content field. In order to verify the proposed system, respective OCT system with 1300 nm and 1400 nm light source were applied separately to a pig skin tissue covered with a moisturizing sheet. Consequently, the interference signal intensity of 1400 nm band, comparing with 1300 nm band, was observed tomograpically to be decreasing exponentially with water diffusion inside skin. It was concluded that OCM has promising potential of diagnosing tomographic moisture content inside skin tissue.

Optical Coherence-domain Imaging of Subcutaneous Human Blood Vessels in vivo

Experimental methods of Optical Coherence Tomography (OCT) are applied for two-dimensional mapping of subcutaneous human blood vessels. Structural images of in vivo human finger and human palm macro vessels (0.2-1.0 mm) before and after optical clearing using the modified low power rapid scanning optical delay line are presented. Images are scanned with 12 µm minimum spatial resolution. The described modifications enable to apply low power (0.4-0.5 mW), low noise broadband near infrared light source and to obtain structural images with detection of not only reflected but also multiply scattered coherence-gated photons. The achieved transcutaneous probing depth is about 1.6-1.8 mm.

치석 진단용 소형 프로브 기반 광간섭단층촬영 시스템

Optical coherence tomography(OCT) is a noninvasive optical imaging tool for biomedical applications. OCT can provide depth resolved two/three dimensional morphological images on biological samples. In this paper, we integrated an OCT system that was composed of an SLED(Superluminescent Light Emitting Diode, <TEX>${\lambda}_0$</TEX>=1305 nm bandwith= 141 nm), a reference arm adopting a rapid scanning optical delay line(RSOD) to get high speed imaging, and a sample arm that used a micro electro mechanical systems(MEMS) scanning mirror. The sample arm contained a compact probe for imaging dental structures. The performance of the system was evaluated by imaging in-vivo human teeth with dental calculus, and the results indicated distinct appearance of dental calculus from enamel, gum or decayed teeth. The developed probe and system could successfully confirm the presence of dental calculus with a very high spatial resolution(<TEX>$6{\mu}m$</TEX>).

Noninvasive monitoring of glucose concentration using differential absorption low-coherence interferometry based on rapid scanning optical delay line

A non-invasive method of detecting glucose concentration using differential absorption low-coherence interferometry (DALCI) based on rapid scanning optical delay line is presented. Two light sources, one centered within (1625 nm) a glucose absorption band, while the other outside (1310 nm) the glucose absorption band, are used in the experiment. The low-coherence interferometry (LCI) is employed to obtain the signals back-reflecting from the iris which carries the messages of material concentration in anterior chamber. Using rapid scanning optical delay line (RSOD) as the reference arm, we can detect the signals in a very short time. Therefore the glucose concentration can be monitored in real-time, which is very important for the detection in vivo. In our experiments, the cornea and aqueous humor can be treated as nearly non-scattering substance. The difference in the absorption coefficient is much larger than the difference in the scattering coefficient, so the influence of scattering can be neglected. By subtracting the algorithmic low-coherence interference signals of the two wavelengths, the absorption coefficient can be calculated which is proportional to glucose concentration. To reduce the speckle noise, a 30 variation of signals were used before the final calculation of the glucose concentration. The improvements of our experiment are also discussed in the article. The method has a potential application for noninvasive detection of glucose concentration in vivo and in real-time.

In vivo investigation of human cone photoreceptors with SLO/OCT in combination with 3D motion correction on a cellular level

We present a further improvement of our SLO/OCT imaging system which enables to practically eliminate all eye motion artifacts with a correction accuracy approaching sub-cellular dimensions. Axial eye tracking is achieved by using a hardware based, high speed tracking system that consists of a rapid scanning optical delay line in the reference arm of the interferometer. A software based algorithm is employed to correct for transverse eye motion in a post-processing step. The instrument operates at a frame rate of 40 en-face fps with a field of view of approximately 1 degrees x 1 degrees. Dynamic focusing enables the recording of 3D volumes of the human retina with cellular resolution throughout the entire imaging depth. Several volumes are stitched together to increase the total field of view. Different features of the three dimensional structure of cone photoreceptors are investigated in detail and at different eccentricities from the fovea.

In-vivo retinal imaging by optical coherence tomography using an RSOD-based phase modulator

Fourier-domain rapid scanning optical delay line (RSOD) was introduced for phase modulation and depth scanning in a time-domain optical coherence tomography (TD-OCT) system. Investigation of parameter optimization of RSOD was conducted. Experiments for RSOD characterization at different parameters of the groove pitch, focal length, galvomirror size, etc. were performed. By implementing the optimized RSOD in our established TD-OCT system with a broadband light source centered at 840 nm with 50 nm bandwidth, in vivo retina imaging of a rabbit was presented, demonstrating the feasibility of high-quality TD-OCT imaging using an RSOD-based phase modulator.

Imaging Depth-Resolved Tissue Birefringence With a Single Detector

We report a novel frequency multiplexed optical coherence tomography (FM-OCT) system that is capable of measuring depth-resolved tissue birefringence from a single record of a single detector. The FM-OCT system utilizes polarization-maintaining-fiber based components. The orthogonal channels of the polarization-maintaining-fiber and the cross-terms are frequency multiplexed. After recording the interference signal, a set of digital band-pass filters extract the polarization information. A rapid scanning optical delay line in the reference arm compensates for dispersion and allows a real-time display of tissue birefringence. The axial resolution provided by a superluminescent diode working at 855nm with 28nm bandwidth is 12μm. The accuracy and sensitivity measurements suggest that the FM-OCT system is suitable for depth-resolved birefringence characterization of biological tissue.

基于快速扫描延迟线相位调制的光纤型光学相干层析系统

基于快速扫描延迟线相位调制的光纤型光学相干层析系统

Wide dynamic range detection of bidirectional flow in Doppler optical coherence tomography using a two-dimensional Kasai estimator

We demonstrate extended axial flow velocity detection range in a time-domain Doppler optical coherence tomography (DOCT) system using a modified Kasai velocity estimator with computations in both the axial and transverse directions. For a DOCT system with an 8 kHz rapid-scanning optical delay line, bidirectional flow experiments showed a maximum detectable speed of >56 cm/s using the axial Kasai estimator without the occurrence of aliasing, while the transverse Kasai estimator preserved the approximately 7 microm/s minimum detectable velocity to slow flow. By using a combination of transverse Kasai and axial Kasai estimators, the velocity detection dynamic range was over 100 dB. Through a fiber-optic endoscopic catheter, in vivoM-mode transesophageal imaging of the pulsatile blood flow in rat aorta was demonstrated, for what is for the first time to our knowledge, with measured peak systolic blood flow velocity of >1 m/s, while maintaining good sensitivity to detect aortic wall motion at <2 mm/s, using this 2D Kasai technique.

Dispersion Compensation in Optical Coherence Tomography with a Prism in a Rapid-Scanning Optical Delay Line

We demonstrate the theoretical and experimental results of using a single prism in the rapid-scanning optical delay line of an optical coherence tomography (OCT) system for compensating the mismatches of the first- and second-order group delay dispersion (GDD) between the reference and sample arms. The analytical expressions for the first- and second-order GDD are derived based on the typically designed system configuration. Numerical results in varying various parameters are shown. An optimized set of parameters for efficient dispersion compensation in a practical fiber-based OCT system is obtained. The numerical result of the dispersion compensation is demonstrated. Also, the experimental implementation of such a dispersion compensation method is illustrated with the conditions similar to the numerical calculations. The compensation result is quite satisfactory

Power-efficient grating-based scanning optical delay line: time-domain configuration

A power-efficient, grating-based, time-domain rapid scanning optical delay line (TD-RSOD) suitable for optical coherence tomography (OCT) is presented. The 6 dB power efficiency of this TD-RSOD over conventional double-pass Fourier-domain RSOD (FD-RSOD) provides approximately 4 dB SNR advantage in a typical balanced-detection OCT. The scanning performance of TD-RSOD is comparable to that of FD-RSOD.

Spectral Shaping in Rapid Scanning Optical Delay Line ofOptical Coherence Tomography

A small spatial optical filter is put into the rapid-scanning opticaldelay line (RSOD) to shape the spectrum of the reference beam in opticalcoherence tomography (OCT). The experimental results show thatthe longitudinal resolution can be improved by a factor of 81% withthis method, while at the same time, the signal-to-noise ratio of theOCT system is not much affected. This method can be used in OCT systemsthat use RSOD as the reference arm with a light source ofsuperluminescent diodes, femtosecond lasers and crystal fibre as well.

Extended range, rapid scanning optical delay linefor biomedical interferometric imaging

A new configuration of a rapid scanning optical delay line for use in the interferometric optical imaging of macroscopic biological specimens, in vivo is presented. A linear delay of 2.3 cm in air, scanned at a velocity of 1 m/s, with uniform intensity and near 100% duty cycle is demonstrated.

High-speed phase- and group-delay scanning with a grating-based phase control delay line

A rapid-scanning optical delay line that employs phase control has several advantages, including high speed, high duty cycle, phase- and group-delay independence, and group-velocity dispersion compensation, over existing optical delay methods for interferometric optical ranging applications. We discuss the grating-based phase-control delay line and its applications to interferometric optical ranging and measurement techniques such as optical coherence domain reflectometry and optical coherence tomography. The system performs optical ranging over an axial range of 3 mm with a scanning rate of 6m/s and a repetition rate of 2 kHz. The device is especially well suited for applications such as optical coherence tomography that require high-speed, repetitive, linear delay line scanning with a high duty cycle.