Experimental proof-of-concept is presented for a quasi-holographic solution to polarization-sensitive optical coherence tomography (PS OCT). Due to decoupling between the reference and sample beams by polarization, the solution seems acceptable to acquisition and communication of optical data in the nonlaboratory environment. The nonlab environment implies uncontrollable disturbances, e.g., temperature changes and mechanical effects happening under shop testing in industry or routine examinations in common clinics and hospitals. For mapping the collagen-related depolarization ratio of light backscattered from the human dermis, a phenomenological model is evolved from the theory of light depolarization in crystalline polymers. The model yielded a simplified intensity-based estimation algorithm. The design concept and the model rely on a submillimeter tumor thickness as a proofed prognostic factor and an important criterion for complementary functional diagnostics of skin cancers in their early phase. Choice of the model is inspired by similarity of structural and optical properties between liquid-crystal collagen fibers in the dermis and birefringent crystalline lamellae in some polymer materials. The model gives a plausible interpretation of a peculiarity of cumulative birefringence in the abnormal skin dermis. Following a top-down approach to design, the authors attempt to contribute to bridging the gap between practitioners' concerns and academic studies.
We demonstrate a novel implementation of spectral domain OCT by using a proposed sweeping detector at 1320 nm
wavelength range. A fiber pigtailed Fabry-Perot tunable filter is newly adapted to receive spectral interferometer
information using a photo-receiver instead of using charged couple detector arrays. In order to show a possibility of the
scheme in other view point, we have changed the position of the Fabry-Perot tunable filter of the interferometer. The
combination of a super luminescent LED and a semiconductor optical amplifier was used as an optical source. Its output
power is about 10 mW and the spectral bandwidth is about 60 nm. The filtered light after passing thorough the Fabry-
Perot tunable filter has 0.15 nm instantaneous spectral linewidth with 1.3 mW average output power. The system with an
axial resolution of 12 μm performed OCT imaging of a cornea of a rat eye proving potential about the application of the
proposed sweeping detector OCT.
There have been several technologies to enable high resolution cross-sectional images of biological tissues in optical coherence tomography (OCT) method. Optical frequency comb (OFC) source has been proposed to overcome the crosstalk problem among the CCD detector pixels of the continuous spectrum of light source. Recently, a passive-type OFC is demonstrated simply placing a Fabry-Perot interferometer filter right after the broadband light source, but it shows a high loss of output light power and limited tenability of channel spacing of multi-wavelength. In this work, we experimentally demonstrate a spectral comparison of a novel multi-wavelength source based on a fiber Sagnac interferometer. The channel spacing is flexibly tuned by the effective length control of polarization-maintaining fiber (PMF). The uniform and stable multi-wavelength spectral distribution is also helpful to obtain the higher sensitivity from the lower exposure intensity source to get a better quality spectral OCT image.
A further insight into the prior concept of polarization sensitive optical coherence tomography system intended for non-laboratory
conditions is brought forward and an experimental proof-of-concept is presented. A phenomenological model
is adopted from the theory of light depolarization in crystalline polymers and modified to yield a simplified algorithm for
mapping depolarization ratio in dermis. The algorithm could distinguish between dermal layers with depleted collagen
content and normal dermis of normal perilesional skin. Dermis is simulated by bireringent lamellae of collagen arranged
chaotically in multiple layers parallel to the skin surface. Both the design concept and the model imply the sub-millimeter
tumor thickness as a proofed prognostic factor and an important criterion for complementary functional
diagnostics of skin cancers at their early phase of vertical growth. Choice of the model is inspired by similarity of
structural and optical properties between liquid-crystal collagen fibers in dermis and birefringent crystalline lamellae in
polymer materials. The numerical computation based on the model allowing for real characteristics of dermis gives
plausible interpreting of depolarization peculiarities caused by collagen depletion. Feasibility is discussed of exploiting
fiber optic analogs of achromatic retarders. Fabrication of the fiber retarders is shown to be realistic by making use of the
photonics technology possessed by the authors.
A challenge is accepted to identify depth resolved optical birefringence of turbid media, particularly human skin using
polarization sensitive optical coherence tomography under external environmental perturbations, e.g. under application
conditions in clinics and hospitals. A novel concept is advanced and respective design is elaborated for a system which
comprises a source of low-coherence light, a tandem of a readout interferometer and a sensing interferometer with reference
and sample arms, and a handheld probe integrated into the sensing interferometer through polarization-maintaining fibers.
The system provides fast electro-optic switching over orthogonal polarization components of a measurand light beam at the
same output from the sensing interferometer. At said output either of the aforementioned components remains perpendicular
to the polarization plane of light in the reference arm. For either of the components the readout interferometer compensates
optical path length differences in the sensing interferometer within a given interval of depth in the sample, and evolves
spatial fringes which are read out by optoelectronic means without any mechanical scanning in depth. The fringes are devoid
of cross-correlation artifacts inasmuch as the readout interferometer recombines coherently the measurand beam and the
reference beam having mutually orthogonal polarizations only.
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