A high-speed linear wavelength-swept laser source working at center wavelength of 1309 nm is demonstrated.
Wavelength tuning is performed using a compact polygon filter in Littrow telescope-less configuration. The repetition
frequency of the wavelength-swept laser source is up to 50 kHz with the polygon scanned at a speed of 694 rotations per
second. The turning range is 130 nm and full width at half maximum (FWHM) is 61 nm. The average output power can
reach to 7 mW. The developed swept laser source can be implemented in optical frequency domain imaging, optical
reflectometry, and other test or measurement applications.
Current analysis for spectroscopic optical coherence tomography (SOCT) signals is limited by an uncertainty
relationship between time (depth) and frequency (wavelength). Various joint time-frequency distributions (TFDs)
can meliorate the limits to obtain the best information. Synthesized signals which correspond to three typical
SOCT signals in the Fourier-domain under different SOCT imaging schemes, were generated and validate several
different TFDs, including short time Fourier transform (STFT), continuous wavelet transform (CWT),
Wigner-Villy distribution (WVD), and smoothed pseudo WVD (SPWVD). We found that different SOCT
imaging scheme requires different optimal TFDs. STFT offers the most reliable and fast time-frequency (TF)
analysis, which is appreciate for retrieving the absorption spectra from a homogeneously absorbing media; WT
offers the best spatial resolution or the best spectral resolution locally; WVD generate the most compact TF
analysis, but suffers from the artifacts due to the cross terms. SPWVD is applied to yields high spectral and
spatial resolution and be free from the artifacts and limitations commonly observed with WVD.
Wavelength-encoded imaging uses wavelength division multiplexing to produce cross-sectional images without
mechanical scanning, and could be of a great interest in endoscope applications. In this paper, a scheme for
wavelength-encoded imaging using time-encoded Frequency-domain optical coherence tomography (swept-source
optical coherence tomography, SS-OCT) is presented. This approach implements swept broadband source with
narrow instantaneous spectral width and low dispersion diffraction grating to simultaneously produce depth-lateral
imaging of the sample. Compared to previous spectral-domain wavelength-encoded endoscope, the proposed
method enables high-speed and high dynamic range detection. System design such as image resolvable points,
imaging resolution as well as theoretical analysis of the interference signal pattern are developed.
We present a high-speed spectral domain optical coherence tomography (SD-OCT) system at 830
nm wavelength which is consisted of a fiber based Michelson interferometer and a custom-built
spectrometer. The designed resolution of the spectrometer is about 67.4pm which limits the
maximum detection depth 2.56mm in air. And the 35us exposure time of the high speed line scan
CCD makes real-time imaging possible. Furthermore, a novel method of spectrometer calibration
is put forward. The method can remove the influence of dispersion mismatch, thus accurately
determine the distribution of wavelength on the line scan CCD, which leads to a precise
interpolation and a subsequent better contrast image.
Dual-wavelength optical low-coherent interferometry is proposed in this paper to measure the oxygen saturation in
human retinal blood vessel. Wavelength consideration is made from the standpoint of eye safety and system
sensitivity. Principle of oxygen saturation measurement based on dual-wavelength low-coherence interferometer is
thoroughly developed. Numerical simulation on interference signal versus oxygen saturation corresponding to the
oxygen sensitive wavelength and the isobestic wavelength is conducted.
KEYWORDS: Optical coherence tomography, Phase modulation, Scanners, Demodulation, Signal detection, Heterodyning, Modulation, Modulators, Numerical analysis, Signal to noise ratio
Optical coherence tomography (OCT) is an emerging technology for high-resolution bio-medical imaging. The rapid
scanning optical delay line (RSOD) has developed basically for depth scanning and dispersion compensation. If the
pivot center of the galvamirror in RSOD is offset, phase modulation can be realized, providing a high carrier frequency
required for heterodyne detection. However, the size of galvamirror should be increased, leading to lower response for
its oscillation and hence a low scanning rate. In this paper we propose to apply a sinusoidal waveform (resonant scan)
instead of a triangle waveform (linear scan) to the galvamirror. Numerical analysis on phase modulation by RSOD and
successive envelop demodulation under different driving waveform is conducted. We demonstrate that it is possible to
improve OCT frame rate by resonant scan without compromising the signal-to-noise performance if complete and
accurate envelope demodulation and appropriate signal processing are adopted.
Accurate measurement of tissue optical properties becomes more and more important in biomedical applications such as
diagnostic imaging for tissue pathology. Taking account of multiple scattering effects in OCT model, an algorithm is
developed to extract depth-resolved tissue optical properties including scattering coefficient and anisotropy factor. By
adding absorption coefficient as the third fitting parameter in the algorithm, it is possible to reduce fitting errors
introduced by sample absorption. With an adapted algorithm based on the extended model, absorption coefficient can
also be extracted. The validity of those algorithms is verified by sample model of solution of polyethylene sphere (PS).
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