THORLABS OCT-LK Series, Руководство пользователя

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OCTP Series Scanner Chapter 5: Description
Page 24 MTN003971
Chapter 5 Description
5.1. Theory
5.1.1. Signal Generation
Optical coherence tomography (OCT) generates cross-sectional images up to several millimeters deep into
tissue. The images are assembled by a series of adjacent depth profiles, allowing 2D and 3D reconstruction of
the specimen.
Therefore the interference between the light coming back from the specimen and from a reference is sampled
for a broad range of different wavelengths. This is performed either by using a broadband light source divided
into separate wavelengths using a spectrometer or by a laser with small bandwidth quickly tuned over a broad
wavelength range.
The phase delay of the back-reflected and back-scattered light (with respect to the stationary reference) is
recorded as a function of wavenumber, and a Fast Fourier Transform (FFT) yields the cross-sectional images
as a function of sample depth.
5.1.2. Limitations
The spatial resolution and sensitivity of the OCTP depends on several parameters, including the following:

Wavelength Range:
The optical components within the OCTP are optimized for a specific wavelength
range, depending upon the model. For the usable wavelength range please refer to Table 2.

Optical Power:
The sensitivity of the OCTP is directly related to the intensity of the light returning from
the sample. Factors that can reduce the collected light intensity from the sample fiber include: dirty
fibers, blocked/cropped beams, and condensed water in the environment.

Physical Movements:
OCT systems use a camera to detect the phase relation of the light returning
from the sample. Even small movements of the specimen in relation to the optical reference arm can
”wash out” the wavenumber-resolved phase contrast, affecting the image.

Imaging:
In a fiber-based OCT setup, the light returning from the sample is focused into the core of an
optical fiber. Hence, the fiber can be thought of as a spatial filter for the light. This filter has an effective
diameter, referred to as the “mode field diameter. For single mode propagation, mode field diameter is
larger than the fiber core diameter. Poor focusing, caused by optical aberration or misalignment,
therefore leads to loss of contrast and sensitivity.