In most biophotonic systems a beam of light must be scanned across a sample; often achieved via the use of macro-scale galvanometers. The size of these devices prohibits their use in compact or endoscopic systems. AdvancedMEMS' technologies allow biophotonic systems to achieve their full potential today.
More information about the basics of optical coherence tomography can be found on the biophotonic science page. Our probes have been used in time-domain, spectral-domain and Fourier-domain systems. Here a schematic diagram of a simplified 3D Time-Domain OCT system shows the incorporation of an AdvancedMEMS probe into a typical clinical OCT system. Light from a low coherence source (nominally at a wavelength of 1310nm with a 70nm bandwidth and a power level of 10mW for endoscopic imaging) is coupled into a fiber-optic Michelson interferometer. A visible aiming beam (generally a 633nm laser) is also coupled into the interferometer in order to allow simultaneous imaging and visual identification of the area of tissue being imaged.
In the reference arm of the interferometer a rapid scanning optical delay line (RSOD) is utilized to provide a variable optical path length. In a time-domain (TD-OCT) system the RSOD line utilizes a galvanometer to scan a grating, allowing separate control of the phase and group delays. In addition, an electro-optical phase modulator is incorporated into the reference arm to generate a stable carrier frequency.
The MEMS based probe is placed at the end of the sampling arm of the interferometer. The MEMS scan-head is used to direct a focused beam onto the sample as well as to provide beam scanning during image acquisition.
The reflected beam entering the sample arm of the interferometer is recombined with the beam from the reference path and the interference signal is detected using a high speed photo-detector. The sampled signal is then processed and displayed as an image to the operator.
As previously described the AdvancedMEMS imaging probe serves as a means of delivering light to the sample being imaged as well as a beam steering and optical focusing device. The optical elements in the probe determine the lateral resolutions of the imaging system while the coherence length of the source determines the axial (depth) resolution.
Our typical 3-D OCT endoscopic imaging probes range from 3.9mm to 5.0mm in outer diameter and achieve resolutions between 10μm×10μm×10μm and 20μm×20μm×10μm with the ability to achieve scan rates of several kHz.
While we've attempted to provide a brief and informative introduction to AdvancedMEMS imaging probe technology, with OCT as an example, this is simply an overview. Please refer to our publications or contact us for additional information.