All-fiber Optical Coherence Tomography Research Articles

Sagnac interferometer based optical coherence tomography

We present in this paper an all-fiber Optical Coherence Tomography OCT system in the time domain by employing a Sagnac fiber loop. The optical fiber version of TD-OCT uses directional couplers to construct a Michelson interferometer instead of a beam splitter which is used in the bulk optics version. Instead of implementing the optical delay by an external movable mirror, we present a new configuration that employs a Sagnac interferometer. Avoiding the use of an external movable mirror, eliminates the problems of alignment to couple back the optical signal into the fiber after being delayed by the external mirror. Moreover, this all-fiber system has the advantage of being compact and having large values of optical path difference.

Study on an all-fiber optical coherence tomography (OCT) probe

An all-fiber probe is proposed to meet the requirements of small size and strong light-collection capability for optical coherence tomography (OCT) probes for in vivo human detection. It consists of a single-mode fiber, a coreless fiber and a gradient refractive index (GRIN) fiber. The coreless fiber is fused into a spherical shape to focus the beam and the GRIN fiber is added to the microsphere probe to optimise the resolution. The optical transmission model of the probe is developed, and then the structural design of the probe is modelled and simulated to determine the optimal parametric structure of the probe. Moreover, apply the probe to the OCT system for the imaging experiments to obtain grey-scale interior images of three- layer of slides, which can verify the feasibility of the probe. The diameter of the probe is 300 μm, which meets the size requirements for in vivo human detection and provides a highly compact, high-resolution option for the field of in vivo detection.

Study on the structure and optical imaging characteristics of an all-fiber OCT probe

Aiming at small size, compact structure, strong light-collecting ability, and low loss requirements of optical coherence tomography (OCT) probes used for human body detection, we design an all-fiber OCT probe, which is composed of a single-mode fiber and a multimode fiber (MMF) with spherical lens. By measuring the optical performance of these probes, we found that, when the length of the MMF of the composite probe is 372 μm and the diameter of the ball lens is 300 μm, it has the strongest focusing effect and a large reflected light signal receiving angle. Furthermore, the OCT probe studied was applied to a self-made spectral domain OCT system for validation. The results show that our probe can obtain a clear two-dimensional grayscale image of three layers of glass and fish scales, i.e., the probe manufacturing scheme can be used. Furthermore, it meets the needs of miniature OCT probes, which provides more effective options for measuring human blood vessels or other biological tissues.

Common-path all-fiber optical coherence tomography probe based on high-index elliptical epoxy-lensed fiber

We propose and demonstrate high-index elliptical epoxy-lensed fiber probes designed specifically for endoscopic common-path (CP) swept-source optical coherence tomography (OCT) imaging inside wet tissues. The high-index epoxy lens uses a beam expansion region of a few hundred microns, which is capped with a spherical surface mounted at the end of an optical fiber. The probe is designed to operate inside wet tissues and shows improved performance over a long imaging depth, compared to bare or simple half-ball-lensed fiber probes. It allows optimal CP-OCT imaging in wet tissues by providing a stable reference power level and optimal beam waist for a long imaging depth. We have fabricated an array of these probes and one with a beam expansion region length of 288 μm and with a lens surface radius of 61 μm exhibiting 25-dB signal-to-noise ratio improvement compared to a bare fiber probe at 1.5-mm distance in water. The proposed probe is tested using a phantom sample comprising several layers of tape in water. The OCT images show that the probe is capable of high-resolution imaging over a distance of 1.5 mm.

All-fiber probe for optical coherence tomography with an extended depth of focus by a high-efficient fiber-based filter

Although methods have been proposed to maintain high transverse resolution over an increased depth range, it is not straightforward to scale down the bulk-optic solutions to minimized probes of optical coherence tomography (OCT). In this paper, we propose a high-efficient fiber-based filter in an all-fiber OCT probe to realize an extended depth of focus (DOF) while maintaining a high transverse resolution. Mode interference in the probe is exploited to modulate the complex field with controllable radial distribution. The principle of DOF extension by the fiber-based filter is theoretically analyzed. Numerical simulations are conducted to evaluate the performances of the designed probes. A DOF extension ratio of 2.6 over conventional Gaussian beam is obtainable in one proposed probe under a focused beam diameter of 4.6μm. Coupling efficiencies of internal interfaces of the proposed probe are below −40 dB except the last probe–air interface, which can also be depressed to be −44 dB after minor modification in lengths for the filter. Length tolerance of the proposed probe is determined to be −28∕+20μm, which is readily satisfied in fabrication. With the merits of extended-DOF, high-resolution, high-efficiency and easy-fabrication, the proposed probe is promising in endoscopic applications.

Dual-fiber stretcher as a tunable dispersion compensator for an all-fiber optical coherence tomography system

We present an all-fiber tunable dispersion compensator based on a pair of fiber stretchers made with different fiber types in which the group delay and the second-order dispersion can be tuned independently. Its efficiency is demonstrated in a fiber-based optical coherence tomography (OCT) system operating in the 800 nm wavelength range. The average sample dispersion in OCT imaging or the dispersion of transmission lines could also be compensated by our system.

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.