Automatic spectral calibration for polarization-sensitive optical coherence tomography

Continuous Hue-Based Self-Calibration of a Smartphone Spectrometer Applied to Optical Fiber Fabry-Perot Sensor Interrogation

Smartphone-based optical spectrometers allow the development of a new generation of portable and cost-effective optical sensing solutions that can be easily integrated into sensor networks. However, most commonly the spectral calibration relies on the external reference light sources which have known narrow spectral lines. Such calibration must be repeated each time the fiber and diffraction grating holders are removed from the smartphone and reattached. Moreover, the spectrometer wavelength scale can drift during the measurement because of the smartphone temperature fluctuations. The present work reports on a novel spectral self-calibration approach, based on the correspondence between the light wavelength and the hue features of the spectrum measured using a color RGB camera. These features are caused by the nonuniformity of camera RGB filters' responses and their finite overlap, which is a typical situation for RGB cameras. Thus, the wavelength scale should be externally calibrated only once for each smartphone spectrometer and can further be continuously verified and corrected using the proposed self-calibration approach. An ability of the plug-and play operation and the temperature drift elimination of the smartphone spectrometer was experimentally demonstrated. Conducted experiments involved interrogation of optical fiber Fabry-Perot interferometric sensor and demonstrated a nanometer-level optical path difference resolution.

Single input state polarization-sensitive optical coherence tomography with high resolution and polarization distortion correction

In single input state polarization-sensitive optical coherence tomography (PS-OCT) with high resolution, the imperfections of quarter-wave plate (QWP) and the sensitivity roll-off mismatch between the two detection channels cause unpredictable polarization distortion. We present a correction method based on the Jones matrix modeling of the system. In a single input PS-OCT system working at 840 nm with an axial resolution of ~2.3 μm, the method yielded better estimation of retardation and optic axis orientation with significantly reduced noise level, especially in weakly birefringent samples. Numerical simulations and quantitative imaging of a sample of known birefringence were performed to validate the performance. We further demonstrate the advantages of our approach with birefringence imaging of swine retina, rat aortic wall, and rat esophageal mucosa for potential clinical applications.

Characterization of spectral-domain OCT with autocorrelation interference response for axial resolution performance

We present a class of novel system characterization methods for spectral-domain optical coherence tomography (SD-OCT) particularly on getting optimized axial resolution performance. Our schemes uniquely utilize the autocorrelation interference response, also known as the self-interference product, which is generated by the optical fields from the imaging sample in automatic interferences. In our methods, an autocorrelation-inducing calibration sample was prepared which was made by sandwiching glass plates. OCT images of the calibration sample were captured by an SD-OCT system under testing. And the image data were processed to find various system characteristics based on the unique properties of autocorrelation interferograms, free of dispersion- and polarization-involved modulations. First, we could analyze the sampling characteristic of the SD-OCT's spectrometer for spectral calibration that enables accurate linear-k resampling of detected spectral fringes. Second, we could obtain the systematic polarization properties for quantifying their impact on the achieved axial resolutions. We found that our methods based on the autocorrelation response provide an easy way of self-characterization and self-validation that is useful in optimizing and maintaining axial resolution performances. It was found very attractive that a variety of system characteristics can be obtained in a single-shot measurement without any increased system complexity.