Control and Synthesis of 3-D Spatial Coherence Function

Existing techniques of OCT (optical coherence tomography) and low coherence interferometry are all based on the temporal coherence characteristic of broadband light. Shown in the top figure below is a schematic illustration of OCT that uses an optical frequency comb as a tunable light source. By changing the comb frequency interval, one can generate a high temporal coherence peak at the desired location of image sectioning. However, because of the broadband spectrum of the source, these techniques suffer from a dispersion problem in many practical applications such as biological applications, where dispersion of the object and/or the light propagation medium is unavoidable.

Control and Synthesis of 3-D Spatial Coherence Function of Optical Fields with Applications to Photonic Sensing and Metrology Department of Information and Communication Engineering Professor Mitsuo TAKEDA takeda@ice.uec.ac.jp
	Existing techniques of OCT (optical coherence tomography) and low coherence interferometry are all based on the temporal coherence characteristic of broadband light. Shown in the top figure below is a schematic illustration of OCT that uses an optical frequency comb as a tunable light source. By changing the comb frequency interval, one can generate a high temporal coherence peak at the desired location of image sectioning. However, because of the broadband spectrum of the source, these techniques suffer from a dispersion problem in many practical applications such as biological applications, where dispersion of the object and/or the light propagation medium is unavoidable.

	We are developing a new technique of OCT and profilometry that is based on spatial coherence, rather than temporal coherence. Instead of a point source with a broad spectrum, an extended source with a narrow spectrum is used in our technique. We synthesize a desired longitudinal coherence function by controlling the spatial structure of an extended quasi-monochromatic spatially incoherent light source with SLM (spatial light modulator). In our scheme, the optical frequency comb is replaced with a spatial frequency chirped comb generated by a zone-plate-like source. Besides solving the dispersion problem, the technique opens up a new possibility of OCT through an extremely narrow spectral absorption window, and enables a fast longitudinal coherence scan and phase shift with SLM without mechanical moving components.

Control and Synthesis of 3-D Spatial Coherence Function of Optical Fields with Applications to Photonic Sensing and Metrology