Pavel A. Shilyagin

Linear-wavenumber spectrometer for high-speed spectral-domain optical coherence tomography

An equidistant (in the wavenumber) spectrometer based on a diffraction grating, a compensation prism, and a CCD linear array is developed and implemented for spectral-domain optical coherence tomography. A criterion is introduced for estimating the level of residual nonequidistance. This criterion allows one to determine the threshold compensation level necessary for obtaining the spectrally limited spatial resolution. The method is tested in spectral-domain optical coherent tomography systems at wavelengths of 1270 and 830 nm.

Coherent noise compensation in Spectral-Domain optical coherence tomography

An efficient technique for the separation of and compensation for coherent noise in spectral optical coherence tomography with parallel spectrum detection is proposed and validated. The coherent noise is separated during one exposure by modulating the mutual delay of the signal and reference waves by a certain law. It is shown that the influence of internal motions in an object on the quality of the coherent noise separation can be reduced by the modulation frequency increasing. The technique has been numerically and experimentally validated with the help of an optical coherence tomography (OCT) setup with a radiation source operating at a wavelength of 1277 nm and a width of the recorded spectrum of about 100 nm.

A control system for the optical-fiber piezoelectric modulator of the optical path

The operating principle of an optical-fiber piezoe lectric modulator of the optical path in all-opti-cal-fiber interferometers is described. The control system of the optical-fiber piezoelectric modulator is composed of a controller based on a field programmable gate array, a digital-to-analog converter, an analog low-pass filter, and a power amplifier. A 4.4-m/s speed of chan ge in the optical length of the fiber has been attained with an error of 0.1% at a modulation length of the optical path of >1 mm.

Noniterative method of reconstruction optical coherence tomography images with improved lateral resolution in semitransparent media

A method of OCT imaging with a resolution throughout the investigated volume equal to the resolution in the best-focused region is described. It is based on summation of three-dimensional scattered field distributions at the wavelengths determined by OCT source spectral decomposition. A method of finding parameters needed for algorithmic realization of the summation is also proposed. The proposed approaches are tested on several model media, including biological ones.

Digital refocusing in optical coherence tomography

The problem of restoration Optical Coherence Tomography (OCT) images, acquired with tightly focused probing beam, in out-of-focus region for improving lateral resolution of the OCT has been considered. Phase stability issue has been discussed and phase equalization algorithm has been proposed. After phase equalization, the algorithm of digital refocusing, based on some methods from the DH, have been applied to the simulated as well as to experimental OCT data, acquired with tightly focused scanning beam to restore micrometer lateral resolution in the whole investigated volume.

Linear wave-number spectrometer for spectral domain optical coherence tomography

The linear wave-number spectrometer for spectral domain optical coherence tomography (SD-OCT) is proposed. Compensation by optical glass prism is used to make optical frequency readouts equidistant in diffraction grating based spectrometer. We demonstrate that selection of only two optical prism parameters almost completely eliminates non-equidistance of optical frequency readouts. Proposed optically linearized spectrometer allows reconstructing OCT image without any numerical resampling.

Electronic interface systems for goals of spectral domain optical coherence tomography

A setup for visualizing the internal structure of media, which partially scatter radiation, using the spectral domain optical coherence tomography (OCT) method is described. The special complex of electron interface systems, ensuring the operating speed of the spectral domain OCT system at a level of 10000 A-scans (longitudinal scans along the depth) per second, high dynamic imaging range, and complete suppression of coherent noise peculiar to the spectral method has been designed to eliminate artifacts characteristic of this method.

Correction of aberrations in digital holography using the phase gradient autofocus technique

We propose a method for correcting aberrations in digital holography based on the principles of computational adaptive optics using the phase gradient autofocus technique that demands no reference measurements. The method requires a priori information on the relative positions of the elements of the optical setup. It is applicable for sufficiently smooth optical aberrations. This technique does not impose any restrictions on the magnitude of the scattered optical field phase distortions caused by the object structure. The efficacy of the proposed method is demonstrated through numerical simulation and experimental verification.

Single-shot full complex spectrum spectrometer-based OCT with a single-line photodiode array

An efficient technique of simultaneous obtaining of quadrature spectral components of interference signal in spectrometer-based OCT using a single-line linear photodiode array is proposed. The components are obtained in air-spaced non-polarization interferometer by partition of reference beam onto two parts and using an achromatic phase shifter. Several setups are described and compared.

Linear in-wavenumber optical spectrum registration in SD-OCT

An efficient technique of linear in-wavenumber optical spectrum registration in SD-OCT is proposed. Methods of partial phase correction of registered optical spectrum for in-wavenumber linearization are described and investigated. The decrease sensitivity decay with depth increasing degeneration is presented. The experimental results for sample media are presented.