Akademik Veri Yönetim Sistemi
Tozburun S. (Yürütücü), İlday F. Ö.
TÜBİTAK Projesi, 2017 - 2020
The aim of the project is to develop a rapid, wavelength-swept laser source with a sweep range of over a 90-nm for Optical Coherence Tomography (OCT). We envision that the source will achieve wavelength sweeping at a sweep repetition rate of 20 MHz through incorporation of positive and negative chromatic dispersion within the ring laser cavity and the use of a fast intensity modulator. Additionally, because there is no dedicated mechanical moving mirror/scanner within the laser cavity, this is an intrinsically phase-stable wavelength-swept source.
In 1991, Optical Coherence Tomography was introduced as a new technology in optical imaging field. This imaging modality shows similarities with ultrasound imaging in principle (measuring back-scattered light from the sample instead of back-scattered sound wave to provide an image) however; it uses light rather than using sound wave as source. Real-time cross sectional images in resolutions of 1-15 mm were successfully provided. Due to the intense demands of high speed imaging with high resolution (3D imaging) and potentials in clinical application sites, Swept-source OCT, which is capable of producing 3D and high sensitive imaging, took more attention from the researchers in the field. One of the key points in Swept-source OCT is the laser source, which is defining the axial resolution, A-line rate, and coherence length of the system. Many technologies have been used in the development of wavelength-swept sources for Swept-source OCT and it is still an active field of research. In the recently developed laser sources, spectral-tuning was achieved with either a mechanical actuators placed in the cavity or dispersion mode-locking techniques. Here, the proposed research study offers a novel laser design, which produces rapidly wavelength swept laser output for Swept-source OCT imaging modality. The specific novelties of the project are to: i) enable very fast laser wavelength-swept configuration, ii) have very low high-frequency relative intensity noise (RIN) in laser, and iii) provide intrinsically phase-stability between optical pulses for a long period of time.
One technical challenge associated with the performance of the laser is the laser wavelength tuning mechanism using two chromatically dispersive elements for stretching and compressing optical pulses in time along with a 10-GHz lithium-niobate intensity modulator. To achieve dispersion matching, the group delay for each dispersive element will be measured separately and in combination. The dispersion matching must be sufficient to maintain a constant cavity round trip time across a large optical bandwidth and the variation in cavity round trip time across the lasing bandwidth should be less than the intensity modulator pulse width for providing wide sweeping range. In addition, the significance of polarization mode dispersion in the laser performance will be investigated. The source relative intensity noise (RIN) will be also measured at around 500 MHz with the use of a RF analyzer. Lastly, the laser outputs including axial resolution, coherence length, phase stability between optical pulses and phase contrast sensitivity will be characterized with a variable-delay Mach-Zehnder interferometer.
There are mainly three goals of the proposed research project. Firstly, fiber Bragg grating (FBG) based intracavity stretching and compression of an optical pulse generated by an intensity modulator wavelength scanner will be built and characterized. Secondly, the laser cavity will be customized and laser outputs will be optimized for the best performance. Thirdly, the newly developed laser source will be characterized for actively Swept-source Optical Coherence Tomography applications.