Louisiana State University 




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    MEMS-based optical probes for endoscopic optical coherence tomography (EOCT)

  • OCT is analogous to ultrasonography. Figure 1 shows the schematic block diagram of an OCT system.

    • OCT uses light (typically near-infrared or NIR) instead of acoustic wave.

    • Axial focusing is achieved by interference of short-coherent-length light.

    • Axial scanning is obtained by scanning optical delay.

    • OCT is useful as an in vivo imaging tool, when combined with endoscopy.

    • There are two types of configurations depending on the imaging orientation of the probe relative to its guiding direction.

      • Forward-looking probes are suitable for hollow organs.

      • Side-looking probes are for luminal structures.

          Fig. 1. Schematic block diagram of a typical OCT system.

  • MEMS microscanner for transversal scanning

    • There are various ways to implement transversal scanning in OCT.

      • Mechanical rotation of probe with external motor

      • Scanning a mirror with an internal galvanometric motor

      • Fiber tip swing with a piezoelectric cantilever

      • Proximal scanning with relay lenses

      • Fused multimode fiber bundles

      • Grin rod lens array

    • MEMS microscanners bring following advantages.

      • Compact probe

      • Minimal vibration

      • No intermediate mechanical devices necessary, such as links

  • A narrow, forward-looking optical probe (Figure 2)

    • Light passes a GRIN lens three times for one direction.

    • Scanning mirror reflects the light almost parallel to the optical axis.

    • Light stays more or less parallel to the optical axis, resulting in small probe diameter.

          Fig. 2. Schematic diagram of the narrow, forward-looking optical probe.