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Park KS, Park E, Lee H, Lee HJ, Lee SW, Eom TJ. Phase stable swept-source optical coherence tomography with active mode-locking laser for contrast enhancements of retinal angiography. Sci Rep 2021; 11:16636. [PMID: 34404853 PMCID: PMC8371173 DOI: 10.1038/s41598-021-95982-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 07/30/2021] [Indexed: 11/23/2022] Open
Abstract
Swept-source optical coherence tomography (SS-OCT) is an attractive high-speed imaging technique for retinal angiography. However, conventional swept lasers vary the cavity length of the laser mechanically to tune the output wavelength. This causes sweep-timing jitter and hence low phase stability in OCT angiography. Here, we improve an earlier phase-stabilized, akinetic, SS-OCT angiography (OCTA) method by introducing coherent averaging. We develop an active mode-locking (AML) laser as a high phase-stable akinetic swept source for the OCTA system. The phase stability of the improved system was analyzed, and the effects of coherent averaging were validated using a retina phantom. The effectiveness of the coherent averaging method was further confirmed by comparing coherently and conventionally averaged en face images of human retinal vasculature for their contrast-to-noise ratio, signal-to-noise ratio, and vasculature connectivity. The contrast-to-noise ratio was approximately 1.3 times larger when applying the coherent averaging method in the human retinal experiment. Our coherent averaging method with the high phase-stability AML laser source for OCTA provides a valuable tool for studying healthy and diseased retinas.
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Affiliation(s)
- Kwan Seob Park
- Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, 123 Cheomdan-gwagiro, Buk-gu, Gwangju, 61005, South Korea
| | - Eunwoo Park
- Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, 123 Cheomdan-gwagiro, Buk-gu, Gwangju, 61005, South Korea
| | - Hwidon Lee
- Harvard Medical School, Boston, MA, 02115, USA.,Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, 40 Blossom Street, Boston, MA, 02114, USA
| | - Hyun-Ji Lee
- Safety Measurement Institute, Korea Research Institute of Standards and Science, 267 Gajeong-ro, Yuseong-gu, Daejeon, 34113, South Korea.,Department of Medical Physics, University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon, 34113, South Korea
| | - Sang-Won Lee
- Safety Measurement Institute, Korea Research Institute of Standards and Science, 267 Gajeong-ro, Yuseong-gu, Daejeon, 34113, South Korea.,Department of Medical Physics, University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon, 34113, South Korea
| | - Tae Joong Eom
- Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, 123 Cheomdan-gwagiro, Buk-gu, Gwangju, 61005, South Korea.
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LEE HWIDON, KIM GYEONGHUN, VILLIGER MARTIN, JANG HANSOL, BOUMA BRETTE, KIM CHANGSEOK. Linear-in-wavenumber actively-mode-locked wavelength-swept laser. OPTICS LETTERS 2020; 45:5327-5330. [PMID: 33001885 PMCID: PMC7574329 DOI: 10.1364/ol.397715] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 07/20/2020] [Indexed: 06/11/2023]
Abstract
We report on an akinetic actively-mode-locked wavelength-swept laser (ASL) with a sweep that is highly linear in wavenumber. By tailoring the drive waveform of the intracavity modulator, the wavenumber sweep was further linearized to enable high fidelity frequency-domain interferometric ranging without resampling of the acquired data. Used for catheter-based optical coherence tomography, the ASL showed comparable imaging performance to a state-of-the-art polygon-based wavelength-swept source at a matching sweep rate of 103.6 kHz, a duty cycle of 95%, and a bandwidth of 100 nm, centered at 1330 nm.
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Affiliation(s)
- HWI DON LEE
- Harvard Medical School, Boston, Massachusetts (MA) 02115, USA
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, 40 Blossom Street, Boston, MA 02114, USA
| | - GYEONG HUN KIM
- Harvard Medical School, Boston, Massachusetts (MA) 02115, USA
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, 40 Blossom Street, Boston, MA 02114, USA
- Department of Cogno-Mechatronics Engineering, Pusan National University, 2 Busandaehak-ro 63beon-gil, Busan, 46241, South Korea
| | - MARTIN VILLIGER
- Harvard Medical School, Boston, Massachusetts (MA) 02115, USA
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, 40 Blossom Street, Boston, MA 02114, USA
| | - HANSOL JANG
- Department of Cogno-Mechatronics Engineering, Pusan National University, 2 Busandaehak-ro 63beon-gil, Busan, 46241, South Korea
| | - BRETT E. BOUMA
- Harvard Medical School, Boston, Massachusetts (MA) 02115, USA
- Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, 40 Blossom Street, Boston, MA 02114, USA
- Institute for Medical Engineering and Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
| | - CHANG-SEOK KIM
- Department of Cogno-Mechatronics Engineering, Pusan National University, 2 Busandaehak-ro 63beon-gil, Busan, 46241, South Korea
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Lee HD, Kim GH, Shin JG, Lee B, Kim CS, Eom TJ. Akinetic swept-source optical coherence tomography based on a pulse-modulated active mode locking fiber laser for human retinal imaging. Sci Rep 2018; 8:17660. [PMID: 30518926 PMCID: PMC6281618 DOI: 10.1038/s41598-018-36252-z] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2018] [Accepted: 11/15/2018] [Indexed: 01/09/2023] Open
Abstract
Optical coherence tomography (OCT) is a noninvasive imaging modality that can provide high-resolution, cross-sectional images of tissues. Especially in retinal imaging, OCT has become one of the most valuable imaging tools for diagnosing eye diseases. Considering the scattering and absorption properties of the eye, the 1000-nm OCT system is preferred for retinal imaging. In this study, we describe the use of an akinetic swept-source OCT system based on a pulse-modulated active mode locking (AML) fiber laser at a 1080-nm wavelength for in-vivo human retinal imaging. The akinetic AML wavelength-swept fiber laser was constructed with polarization-maintaining fiber that has an average linewidth of 0.625 nm, a spectral bandwidth of 81.15 nm, and duty ratio of 90% without the buffering method. We successfully obtained in-vivo human retinal images using the proposed OCT system without the additional k-clock and the frequency shifter that provides a wide field of view of 43.1°. The main retina layers, such as the retinal pigment epithelium, can be distinguished from the OCT image with an axial resolution of 6.3 μm with this OCT system.
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Affiliation(s)
- Hwi Don Lee
- Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju, 61005, South Korea
| | - Gyeong Hun Kim
- Department of Cogno-Mechatronics Engineering, Pusan National University, Busan, 46241, South Korea
| | - Jun Geun Shin
- Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju, 61005, South Korea
| | - Boram Lee
- Department of ophthalmology, Korea University college of medicine, Seoul, 02841, South Korea
| | - Chang-Seok Kim
- Department of Cogno-Mechatronics Engineering, Pusan National University, Busan, 46241, South Korea.
| | - Tae Joong Eom
- Advanced Photonics Research Institute, Gwangju Institute of Science and Technology, Gwangju, 61005, South Korea.
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Takubo Y, Shirahata T, Yamashita S. Optimization of a dispersion-tuned wavelength-swept fiber laser for optical coherence tomography. APPLIED OPTICS 2016; 55:7749-55. [PMID: 27661607 DOI: 10.1364/ao.55.007749] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
We optimized parameters of a dispersion-tuned wavelength-swept fiber laser by numerically analyzing dynamic characteristics. The optimized laser is experimentally demonstrated and applied to the swept-source optical coherence tomography (SS-OCT) system. The dispersion-tuned wavelength-swept laser (DT-WSL) is a unique tunable fiber laser, whose lasing wavelength can be tuned rapidly without any mechanical tunable filters. Although the wavelength of a DT-WSL can be swept rapidly and widely, the broadening of the instantaneous spectral width at a high sweep rate has been a critical drawback for SS-OCT applications. Numerical simulations have shown that higher modulation frequencies for active mode-locking lead to narrower instantaneous spectral widths. However, a lower modulation frequency is needed to achieve a wider wavelength tuning range. Pulse modulation is employed to solve the trade-off between instantaneous spectral width and wavelength tuning range. In this paper, the characteristics of a sinusoidally modulated and a pulse-modulated DT-WSL are compared numerically and experimentally. The numerical simulation results show that a pulse-modulated laser can achieve spectral widths as narrow as that of the sinusoidally modulated laser with >5 GHz modulation frequency, even when the pulse modulation frequency is as low as 500 MHz. We also study the difference in the laser characteristics with different sweep directions and discover that a positive wavelength sweep leads to a narrower instantaneous spectral width. We also experimentally confirmed that pulse modulation can indeed achieve a narrower spectral width, as expected from our numerical simulation results. The pulse-modulated DT-WSL is then used in an SS-OCT system and successfully achieves a coherence length of 1.3 mm, whereas that of a sinusoidally modulated DT-WSL is limited to only 0.7 mm. Furthermore, we experimentally compare the performance difference in OCT imaging with different wavelength sweep directions, and the results proved that it is advantageous to apply a positive wavelength sweep, as predicted by our numerical simulation.
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Takubo Y, Yamashita S. High-speed dispersion-tuned wavelength-swept fiber laser using a reflective SOA and a chirped FBG. OPTICS EXPRESS 2013; 21:5130-9. [PMID: 23482047 DOI: 10.1364/oe.21.005130] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
We present a high-speed wavelength-swept fiber laser based on a dispersion tuning method using a reflective semiconductor optical amplifier (RSOA) and a chirped fiber Bragg grating (CFBG). By using these devices, the cavity length can be shortened drastically. The short cavity improves the laser performance at high sweep rates over 200 kHz. We achieve a sweep range of 60 nm and an output power of 8.4 mW at 100 kHz sweep. We applied the dispersion-tuned fiber laser to the swept-source OCT system and successfully obtained OCT images of an adhesive tape at up to 250 kHz sweep rate.
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Affiliation(s)
- Yuya Takubo
- Department of Electrical Engineering and Information Systems, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
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