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7B-I-27
BIOMEDICAL PHOTONICS
Non-obvious features of low-coherence interferometry
G.V. Glikonov
Institute of Applied Physics Russian Academy of Sciences e-mail address: grgel@ipfran.ru
Low-coherence interferometry has occupied a special niche not only in measurements of physical quantities, but also in sensor and diagnostic systems and devices. The most striking example of such an application is Optical Coherence Tomography. Despite its apparent simplicity, the measurement of low-coherence interference is associated with a number of features that significantly affect the result. Often these features are not obvious. We will discuss the issues of the observed optical noise and achieving its minimum values, calculating the dispersion characteristics of an object when direct measurement is impossible, and the influence of the spectrometer resolution on the attenuation of the spectral OCT signal with depth.
Optical noise contains fundamental and technical parts. Technical noise has multiple sources and can be eliminated. Fundamental noises consist of shot and beat noises of the spectral components, due to the incoherent nature of the radiation sources for low-coherence interferometry. In the case of weak reflection or scattering from the observed object, the intensity of the reference radiation in the Michelson interferometer has an optimum, which is achieved by attenuating this radiation in the reference arm while maintaining the division ratio of 50/50. [1, 2]
When using a tandem scheme with a measuring interferometer and an additional interferometer that compensates for the difference in the path of the measuring one, both waves of the compensating interferometer must have the same intensity. In this case, the excess noise cannot be completely subtracted, and its value will differ by times from the original one. [3]
In the case of impossibility of directly measurement the dispersion characteristics of the object of study (for example, when examining the retina), they can be calculated from the registered interference signal. [4]
In spectral optical coherence tomography, the signal decay with depth, in addition to the general scattering and absorption factors, is also determined by the resolution of the measuring spectrometer. An improved model of the spectrometer is presented, which more accurately describes the signal decay with depth. [5] The work was supported under IAP RAS State financing, project #0030-2021-0013
[1] Feldchtein F., Bush J., Gelikonov G., Gelikonov V., Piyevsky S. Cost effective, all-fiber autocorrelator based 1300 nm OCT system // Progress in Biomedical Optics and Imaging - Proceedings of SPIE. V. 5690. P. 349-355 (2005)
[2] Bush J., Feldchtein F., Gelikonov G., Gelikonov V., Piyevsky S. Cost effective, all-fiber autocorrelator for Optical Coherence Tomography imaging // Proceedings of SPIE - The International Society for Optical Engineering. V. 5855 PART I. P. 254-257 (2005)
[3] Gelikonov V.M., Romashov V.N., Gelikonov G.V. Excess broadband noise at equal intensities in the interferometer arms. // Quantum Electronics. V.51, №.5, P. 377-382.(2021)
[4] Gelikonov G.V., Gelikonov V.M. Measurement and Compensation for the Amplitude and Phase Spectral Distortions of an Interference Signal in Optical Coherence Tomography for the Relative Optical-Spectrum Width Exceeding 10%. // Radiophysics and Quantum Electronics. V.61, №.2, P. 135-145.(2018)
[5] Sherstnev E.P., Shilyagin P.A., Terpelov D.A., Gelikonov V.M., Gelikonov G.V. An Improved Analytical Model of a Spectrometer for Optical Coherence Tomography. // Photonics. V.8, №.12, P. 1-10. (2021)
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