The speed improvement is a game-changer in optical coherence tomography (OCT) imaging because it opens up for new and very exciting applications. The frame rate of an OCT system is limited by the speed of the camera or the sweep rate of the light source. This problem can be overcome by multiple-beam imaging, in which different locations on the sample are illuminated by an array of light simultaneously. This technique allows parallel imaging from multiple sample locations and therefore improves OCT axial scan rate by a factor equal to the number of beams used simultaneously which can go up to very high frequency ranges (e.g. MHz) easily. In this work, we introduce a compact integrated-optics based multiple-beam illumination design in which several waveguides with certain length differences are combined with wavelength-independent couplers for space-division multiplexing. Electrodes will be placed on each beam path in order to separate desired signal from unwanted reflections at the optical surfaces or tissue. The imaging speed will be improved by the number of the beam paths used. In addition to fast imaging, the proposed design will be very compact which makes it very suitable to be used in endoscopic probes. The proof-of-concept of this idea was experimentally demonstrated using a design which consists of 2 times 4 parallel OCT channels that are realized with a total of 6 Y-couplers. Each individual OCT channel has an optical path length delay with respect to the other channels.
In this work, two different integrated-optics based spectrometer designs are presented. The first one is called interleaved arrayed waveguide grating (AWG) spectrometer provides large bandwidth (i.e. 30 nm) and high resolution (i.e. 0.1 nm) for a compact size (i.e. 2.4 cm × 3 cm). The second spectrometer is called ultra-high resolution Fourier transform (FT) spectrometer provides 1 pm of resolution for only 2 cm × 0.5 cm (1 cm2) device size at 1.3 μm. For the interleaved AWG spectrometer, the primary AWG has narrow closely spaced passbands (that equal the final desired channel spacing) that repeat N times in the desired wavelength range, using the frequency-cyclic nature of the AWG. The channel spacing of the secondary AWGs should be equal to the free spectral range (FSR) of the primary AWG. In this configuration, the FSR of the secondary AWGs defines the FSR of the overall configuration whereas the channel spacing (resolution) of the primary AWG defines the overall system resolution. The ultra-high resolution FT spectrometer is formed by sequentially-activated 60 Mach-Zehnder interferometers that are connected to photodetectors through very-low-loss beam combiners based on two-mode interference. The long optical delays are provided by tapping the propagating light out at certain locations on the optical waveguides by using electro-optically-controlled directional couplers. A design example with a spectral resolution of 500 MHz (~1 pm) and bandwidth of 15 GHz is presented for a device size of only 2 cm × 0.5 cm (1 cm2).
Optical coherence tomography (OCT) has enabled clinical applications that revolutionized in vivo medical diagnostics.
Nevertheless, its current limitations owing to cost, size, complexity, and the need for accurate alignment must be
overcome by radically novel approaches. Exploiting integrated optics, the central components of a spectral-domain OCT
(SD-OCT) system can be integrated on a chip. Arrayed-waveguide grating (AWG) spectrometers with their high spectral
resolution and compactness are excellent candidates for on-chip SD-OCT systems. However, specific design-related
issues of AWG spectrometers limit the performance of on-chip SD-OCT systems. Here we present advanced AWG
designs which could overcome the limitations arising from free spectral range, polarization dependency, and curved
focal plane of the AWG spectrometers. Using these advanced AWG designs in an SD-OCT system can provide not only
better overall performance but also some unique aspects that a commercial system does not have. Additionally, a
partially integrated OCT system comprising an AWG spectrometer and an integrated beam splitter, as well as the in vivo
imaging using this system are demonstrated.
We review our recent results on integrating biomedical optical systems onto a silicon chip. Light collection by integrated
waveguides has been investigated. Confocal light delivery and collection by a combination of two arrayed-waveguide
gratings has been achieved. Using an arrayed-waveguide grating as an integrated spectrometer, Raman spectroscopy and
spectral-domain optical coherence tomography have been demonstrated.
Conference Committee Involvement (2)
Emerging Technologies for Cell and Tissue Characterization
28 June 2023 | Munich, Germany
Emerging Technologies for Cell and Tissue Characterization
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