(a) Schematic of the polarization sensitive optical low-coherence reflectometry setup: SLD – superluminescent diode, P – polarizer, W – quarter wave plate, BS – non-polarizing beam splitter, S – sample, R – reference mirror with scanning assembly, PBS – polarizing beam splitter, D, D⊥, D∥ – photo diodes, DAQ – data acquisition system, ED – envelope detector, PC – laptop, and other electronic processing units. The lower corner shows the photograph of the compact experimental setup developed and used by the authors. (b) The schematic shows the unfolded view of light propagation in the reference arm. The state of polarization of light after each optical components is also shown. (c) The unfolded view of light propagation in the sample arm is shown here. The sample is assumed to behave as an optical rotator, accordingly, it is shown as a combination of mirror and a waveplate. Hence, the backscattered light from the sample may have mixed state of polarization due to additive nature, while the reflected light from the sample retains the state of polarization.
Estimated values of ellipticity against the angle of optical rotation in the sample arm. These estimations were made using Jones matrix calculation using the schematic of Figs. 1(b) and 1(c) . The inset showing linear change is a magnified view.
OLCR signals obtained from the reference plate (cover-slip of thickness μm) and sample are shown. The complete signal is shown in (a) at top, where a-g and g-t represent the air-glass and glass-tissue interface, respectively. The planes from the signal obtained are shown schematically. The signal obtained from the tissue-glass interface is magnified and shown in (b). The signal is integrated (shaded region) up to a distance of 400 μm ignoring the coherent signal obtained for the glass surface is shown in (c) at bottom corner. The integrated signal is used while estimating ellipticity of the polarized light.
Measured values of ellipticity with angular position of waveplate. The results matches with the theoretical values as shown in Figure 2 .
Change in refractive index with concentration of glucose (a) and other electrolytes (b-d). The boxed regions show the normal body values of human subjects. 23
Theoretical (solid line) and experimental (filled dots) observations of ellipticity with increasing glucose concentration using tissue phantom is exhibited. The fluctuations in experimental data is attributed to the size distribution of scatterers in the tissue phantom.
The value of ellipticity measured using the device developed by the authors group (Y axis) and the simultaneous measurement of glucose concentration using commercial grade glucometer (X axis) are shown. The data obtained from subjects 1 and 2 are shown in (a) and (b). The filled circle corresponds to first set of measurements while the open circles, second set of measurements. (c) The ellipticity values obtained with six subjects. The lines are drawn to fit the experimental data.
Measured values of ellipticity of polarized light (with error bar) and glucose concentration (solid squares) with time after a glucose drink is exhibited here. Both the curves follow closely.
Statistics and slope values of the subjects.
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