ASE swept source with self-tracking filter for OCT medical imaging

#Optical coherence analysis relies on the use of the interference phenomena between a reference wave and an experimental wave or between two parts of an experimental wave to measure distances and thicknesses, and calculate indices of refraction of a sample. Optical Coherence Tomography (OCT) is one example technology that is used to perform usually high-resolution cross sectional imaging. It is often applied to imaging biological tissue structures, for example, on microscopic scales in real time. Optical waves are reflected from an object or sample and a computer produces images of cross sections of the object by using information on how the waves are changed upon reflection.

#The original OCT imaging technique was time-domain OCT (TD-OCT), which used a movable reference mirror in a Michelson interferometer arrangement. More recently Fourier domain OCT (FD-OCT) has been developed. Two related FD-OCT techniques are time encoded and spectrum encoded OCT. These Fourier domain techniques use either a wavelength swept source and a single detector, sometimes referred to as time-encoded FD-OCT (TEFD-OCT) or swept source OCT, or, alternatively, a broadband source and spectrally resolving detector system, sometimes referred to as spectrum-encoded FD-OCT or SEFD-OCT. These three OCT techniques parallel the three spectroscopy approaches implemented by Fourier transform spectrometers, tunable laser spectrometers, and dispersive grating with detector array spectrometers.

#These various OCT techniques offer different performance characteristics. FD-OCT has advantages over time domain OCT (TD-OCT) in speed and signal-to-noise ratio (SNR). Of the two Fourier Domain OCT techniques, swept-source OCT or TEFD-OCT has distinct advantages over SEFD-OCT because of its capability of balanced and polarization diversity detection; it has advantages as well for imaging in wavelength regions where inexpensive and fast detector arrays are not available.

#In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings:

#FIG. 1 is a block diagram of a swept optical source with a contra-directional self-tracking filter using polarization diversity and a double-pass reflective amplification stage according to a first embodiment of the present invention;

#FIG. 2 is a block diagram of a swept optical source with a contra-directional self-tracking filter using polarization diversity and a double-pass reflective amplification stage using an isolator according to a second embodiment of the present invention;

#In the following description similar components in the different embodiments are given the same or similar reference numerals to indicate similar construction and functionality.

#FIG. 1 shows a first embodiment swept optical source 100a with contra-directional self-tracking filter using polarization diversity and a reflective, double-pass amplification stage, which has been constructed according to the principles of the present invention.

#Preferably, the source 100a is entirely implemented on a single bench 110 with free space optics coupling the optical beams between the optical elements. In the coordinate system of the figure, the bench extends in the x-z plane and the y-axis extends vertically from the plane of the bench.