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For the first time we applied the maximum entropy method (MEM) to spectral domain optical coherence tomography to enhance axial resolution (AR). The MEM estimates the power spectrum by fitting. For an onion with optimization of M = 70, the AR of 18.8 microm by discrete Fourier transform (DFT) was improved three times compared with peak widths. The calculation time by the MEM with M = 70 was 20 times longer than that of DFT. However, further studies are needed for practical applications, because the validity of the MEM depends on the sample structures.

We experimentally demonstrated that the technique to stabilize the output signal by harmonic intensities is useful in heterodyne detection with an incoherent light source such as a halogen lamp. The relation between the relative standard deviation of an output signal and the fluctuation of the light intensity is analyzed and simulated. Using the fundamental to sixth harmonics increases the stabilities of output signal approximately 3 times, and subtracting the relative standard deviation of the intensity of light source enhances the stabilities 49 times. The fluctuating phase that is due to the fluctuating frequency and temperature and its power spectrum density for an interferometer is also calculated with the Allan variance.

We report a quasi-single-shot wide-field optical coherence tomography system that enables to measure the reflection, phase and en- face OCT images from the same setup using the glass jig. The jig consisting of a wedge glass substrate and a glue dot is contacted to the tissue surfaces, and the data within glue dot is used to reduce the phase noise of the interference signal. The reconstructed image size of the object was 4.0 mm × 4.3 mm. The standard deviation (STD) of the phase variation was minimized by 54 % and obtained to be 0.027 rad for the poke tissue. The corresponding STD in optical path length change was measured to be 1.4 nm. The refractive index of the water and poke tissue at the surface is also evaluated as 1.36 and 1.39, respectively, using reflection intensity images. Further, the en- face sectional images of the tissue sample are also measured. [ABSTRACT FROM AUTHOR]

Abstract: We propose and demonstrate quadrature fringes wide-field optical coherence tomography (QF WF OCT) to expand an optical Hilbert transformation to two-dimensions. This OCT simultaneously measures two quadrature interference images using a single InGaAs CCD camera to obtain en face OCT images. The axial and lateral resolutions are measured at 29μm in air and 70μm limited by a pixel size of camera using a superluminescent diode with a wavelength of 1.3μm as the light source; the system sensitivity is determined to be −90dB. The area of the en face OCT images is 4.0mm×4.0mm (160×160 pixels). The OCT images are measured axially with steps of 10μm. The en face OCT images of a in vivo human fingertip and a in situ rat brain are three-dimensionally measured up to the depth of about 3mm with some degradations of a lateral resolution. [Copyright &y& Elsevier]

We propose a new technique for processing the heterodyne heal signals obtained in interferometry by sinusoidal modulation of the optical path difference. This technique achieves a high degree of signal stabilization with respect to phase drifts, while removing earlier restrictions imposed on the modulation index. Four Fourier harmonics of the interference signal allow the determination of the current modulation index, and then the coherent component of the intensity can he calculated. The method was tested both numerically and experimentally, and compared to a previous technique that uses the same input data. The effects of phase drifts are canceled on a wide range of the modulation index, values, while the reference method achieves the same performance only for particular isolated values. A simplified version of the method is proposed for cases when the signal-to-noise ratio is low. [ABSTRACT FROM AUTHOR]

Proposes a continuous two-step method (CTSM) to obtain an image from two interference images for the measurement time reduction of optical coherence tomography. Image processing performed for each pixel in CTSM; Calculated signal intensity; Assumption that the heterodyne beat signal contains the random noise in simulations and calculate the influence of the normalized standard deviation on the random noise intensity for both CTSM and the conventional three-step method.

Presents information on a study which described the development of detection schemes for optical coherence tomography (OCT). Factors that affect the performance of an interferometer-based OCT; Causes of phase drift in an interferometer; Conclusions.

Abstract: We demonstrate the feasibility of a compact single-shot full-field time domain optical coherence tomography (OCT) for imaging dynamic biological sample in real-time. The system is based on a Linnik type polarization Michelson interferometer and a four-quadrature phase-stepper optics, which can simultaneously capture four quadraturely phase-stepped interferograms on a single CCD. Using a superluminescent diode as light source with center wavelength of 842nm and spectral width of 16.2nm, the system yields an axial resolution of 19.8μm, and covers a field of view of 280×320μm2 (220×250 pixels) with a transverse resolution of 4.4μm by using a 10× microscope objective (0.3NA). Three-dimensional OCT images of biological samples such as an onion slice and a diaptomus were obtained without any image averaging or pixel binning. In addition, in vivo depth resolved dynamic imaging was demonstrated to show the beating internal structure of a diaptomus with a fame rate of 5fps. [Copyright &y& Elsevier]

Abstract: We describe the performance of a compact single-shot low-coherence interferometric scheme that can be capable of measuring three-dimensional surface profiles and shape. This technique utilizes a polarizing Michelson interferometer and a four-channel polarization phase-stepper optics, which is based on a paired wedge prism, a combined wave plate and a Wollaston prism. The coherence gated surface image can be calculated by the simultaneous acquisition of two interferograms and a DC image on a single CCD camera. The image calculation is based on a novel algorithm to calibrate the imbalanced intensity as well as the deviated arbitrary relative phase of each of the imaging channels. The system can display the transverse cross-sectional images in real-time. To demonstrate the feasibility of this system, a Japanese coin is presented as a 3-D shape measurement example with an image size of 4mm (horizontal)×4mm (vertical)×160μm (depth). [Copyright &y& Elsevier]