Editing Optical coherence tomography (section)

====Spectral-domain OCT====
Spectral-domain OCT (spatially encoded frequency domain OCT) extracts spectral information by distributing different optical frequencies onto a detector stripe (line-array CCD or CMOS) via a dispersive element (see Fig. 4). Thereby the information of the full depth scan can be acquired within a single exposure. However, the large signal-to-noise advantage of FD-OCT is reduced due to the lower dynamic range of stripe detectors with respect to single photosensitive diodes, resulting in an SNR advantage of ~10 [[decibel|dB]] at much higher speeds. This is not much of a problem when working at 1300&nbsp;nm, however, since dynamic range is not a serious problem at this wavelength range.<ref name="ReferenceA"/>

The drawbacks of this technology are found in a strong fall-off of the SNR, which is proportional to the distance from the zero delay and a [[Sinc function|sinc]]-type reduction of the depth-dependent sensitivity because of limited detection linewidth. (One pixel detects a quasi-rectangular portion of an optical frequency range instead of a single frequency, the Fourier transform leads to the sinc(z) behavior). Additionally, the dispersive elements in the spectroscopic detector usually do not distribute the light equally spaced in frequency on the detector, but mostly have an inverse dependence. Therefore, the signal has to be resampled before processing, which cannot take care of the difference in local (pixelwise) bandwidth, which results in further reduction of the signal quality. However, the fall-off is not a serious problem with the development of new generation CCD or [[photodiode]] array with a larger number of pixels.

[[Optical heterodyne detection|Synthetic array heterodyne detection]] offers another approach to this problem without the need for high dispersion.