Optical coherence tomography (OCT)

Optical coherence tomography (OCT) is a noncontact, three-dimensional imaging modality. Based on broadband light sources, interferometric detection, and confocal gating, OCT provides cross-sectional images with a resolution of a few microns.

Swept-Source OCT

The concept of OCT using a narrowband tunable laser is based on the electronic beat signal detected at the output of a Michelson interferometer, where one arm detects the back reflected light from the sample. A Fourier transformation of the detected signal from one frequency sweep yields the desired axial reflectivity/scattering profile. The concept is equivalent to optical frequency domain reflectometry (OFDR), where only a surface profile or the depth resolved reflection characteristic of a fiber is detected. The terms swept source OCT (ss-OCT) or optical frequency domain imaging (OFDI) are used.

Michelson 585

Typical Michelson-interferometer setup for swept-source OCT. An interference signal is formed between ligth returning from sample and reference arms.

fringe generation 585

In both sample and reference arms, the optical frequency changes over time due to the swept laser input. Each pathlength difference leads to a unique time delay between those sweeps. Hence, the radio-frequency (RF) beat signal frequency is directly proportional to the axial position in the sample.

Literature

Read more about OCT in the following publications:

  1. The fundamental paper on OCT by David Huang at Jim Fujimotos' MIT group.
  2. FDML laser for multi-MHz OCT at 1300nm.
  3. Multi-MHz OCT at 1060nm for retinal imaging, based on FDML technology.