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The problem of recognising single sparsely located scatterers against the noise background in the image obtained by the method of optical coherence tomography (OCT) is considered. An identification method based on the use of specific scanning features upon OCT image registration and on the statistical analysis of image fragments is proposed. The efficiency of the method is demonstrated experimentally in the diagnosis of otitis media with effusion. The approach can be used in the development of automated algorithms for determining the presence of highly transparent effusion in the middle ear cavity of a human with acute otitis media with effusion, including postoperative one.

We report a theoretical and experimental study of the excess photocurrent noise in the detection of low-coherence radiation caused by the beats of the random components of the optical spectrum at equal intensities in the interferometer arms. It is shown that, in this case, the spectral density of photocurrent fluctuations is times higher than when detecting radiation without interference. This result makes it possible to clarify the value of the limiting level of the total fundamental noise of low-coherence radiation during interference. Excess noise cannot be completely subtracted in balanced detection.

The paper describes the design of an optical coherence tomograph adapted for studying the state of the tympanic cavity of the human middle ear. We present the images obtained by the method of optical coherence tomography, which are characteristic of the norm and of the case of pathology – otitis media with effusion.

Methods for determining the dependence of the lateral-scan coordinate on the A-scan number from tomographic images of test samples are investigated and techniques for compensating for horizontal distortions of tomographic images caused by uneven speed of the probing-beam displacement are proposed. An opal-glass Ronchi ruling and an inclined flat surface of the volume-scattering plate were used as test samples.

The application of computational methods to correct distortions in spectral-domain optical coherence tomography due to fast probe movements relative to a studied object is described. This technique is intended for use in endoscopy or in the study of external biological tissues using a handheld probe. The effectiveness of the method was confirmed experimentally.

We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in optical coherence tomography. The method is based on the analysis of phase shifts of the neighboring scans, which are due to microscale displacements, and further compensation for these displacements by using phasefrequency correction in the spectral domain. Unlike the known correlation methods, the proposed method does not distort the represented shape of the object surface. Its operability is demonstrated in model experiments in the cases of harmonic and random types of the motion of the scattering object, as well as in vivo imaging of the structures of the human middle ear.

We study the causes of artifact appearance in the images obtained by the method of spectral domain optical coherence tomography with parallel reception of the optical-spectrum components, which are manifested in repetition and overlay of the structural elements of the images of the studied medium with a shift in depth. It is shown that nonidentity of the transfer characteristics of the channels of the multichannel photoreceiving elements is one of the sources of such artifacts. A numerical method for eliminating such artifacts is proposed and experimentally verified. This method is based on using the models whose parameters are estimated by the recorded signal and does not require a priori information on the transfer characteristics of the channels. The method efficiency is demonstrated during the experiments on the in vivo visualization of the human middle-ear elements.

The method for displacement correction along the slow axis of Optical Coherence Tomography (OCT) data volumes is presented. The method is based on the recursive replacement of the next displaced OCT measurements by the weighted summation of itself and the previous OCT measurement in the slow axis dimension already corrected for the displacement. The values of the appropriate weight multipliers were defined from the local correlation of the two measurements. The proposed method was used as a preprocessing step for Optical Coherence Angiography processing of the OCT data. Substantial reduction of the motion-induced stripe artifact was demonstrated.

We describe a universal method of compensating for the arbitrary dispersion in the spectral and time domain optical coherence tomography systems. In combination with the amplitude method of correcting the optical-spectrum irregularities, this approach allows one to obtain the spectrally determined resolution if the instrument function is close to the Gaussian one. The efficiency of the method is demonstrated in the time and spectral domain optical coherence tomographies with the fully fiber-type optical systems for the relative optical-spectrum width exceeding 10%.

We consider a cross-polarization optical coherence tomography system with a common path for the sounding and reference waves and active maintenance of the circular polarization of a sounding wave. The system is based on the formation of birefringent characteristics of the total optical path, which are equivalent to a quarter-wave plate with a 45° orientation of its optical axes with respect to the linearly polarized reference wave. Conditions under which any light-polarization state can be obtained using a two-element phase controller are obtained. The dependence of the local cross-scattering coefficient of light in a model medium and biological tissue on the sounding-wave polarization state is demonstrated. The necessity of active maintenance of the circular polarization of a sounding wave in this common path system (including a flexible probe) is shown to realize uniform optimal conditions for cross-polarization studies of biological tissue.

We develop an effective method for reducing nonequidistance when recording the spectral components of an interference signal in ultra-wideband spectral-domain optical coherence tomography. For this purpose, a corrector consisting of two identical prisms is used in a diffraction-grating spectrometer. The corrector rotation with respect to the diffraction-grating plane and a variation in the angle between the corrector elements allow one to adjust the equidistant spatial distribution of the spectral components in the photoreceiver array. It is shown experimentally that the developed method substitutes digital correction and leads to a significant reduction of the computational load in the optical coherence tomography device.

We describe a system of optical spectrum registration at the output of an interferometer with controlled phase shifts for an experimental device intended for visualizing the internal structure of an optically turbid specimen, using the method of spectral domain optical coherence tomography. A device for spectral domain optical coherence tomography based on a common-path optical scheme with a USB 3.0 interface for inputting data into a computer has been developed. An imaging speed of 91 912 A-scans/s has been attained. At the achieved speed, a series of live experiments were carried out to visualize the internal structure of skin tissues from a finger and front segments of an eye.

A method for determining and correcting distortions in spectral-domain optical coherence tomography images caused by medium dispersion was developed. The method is based on analysis of the phase distribution of the interference signal recorded by an optical coherence tomography device using an iterative approach to find and compensate for the effect of a medium’s chromatic dispersion on point-spread function broadening in optical coherence tomography. This enables compensation of the impact of medium dispersion to an accuracy of a fraction of a radian (units of percent) while avoiding additional measurements and solution of the optimization problem. The robustness of the method was demonstrated experimentally using model and biological objects.

A method of numerical compensating of OCT image distortion provided by fluctuations of the distance to the object has been proposed and verified experimentally. The method is based on the analysis of inter A-scan phase shifts caused by micrometer-scale displacements, and the subsequent compensation of the displacements by phase-frequency correction in the spectral space. The efficiency of the method is demonstrated in model experiments with harmonic and random movements of a scattering object, as well as during in vivo imaging of the retina of the human eye.

We propose a new method of compensating for the wavefront aberrations during the image processing. The method employs the digital-holography potential. The developed algorithms allow one to find the wavefront distortions caused by the optical-path nonuniformities during the interference recording of images without additional measurements (i.e., without using the reference point source and measuring the wavefront distortions). The possibility of decreasing the wavefront aberrations from tens to several radians using digital methods is demonstrated.

We report realizations of OCT combining conventional structural imaging, polarization-sensitive one, as well as allowing for real-time angiographic, elastographic and lymphangiographic modalities with manual-operation capabilities. Among the main features of the developed device one can point out on-flight imaging of microvascular network with feedback for clinicians when performing angiography; in elastography - robust "vector" method of interframe phasevariation gradient estimation and stiffness quantification using reference silicone layers; lymphangiography utilizing pixel statistics beyond conventional amplitude thresholding, etc. These capabilities are ensured by the developed optical schemes of the probe, signal receiving parts, as well as computationally efficient signal processing methods. Examples of the developed device usage in preclinical and clinical applications are discussed (efficient criteria for PDT success; angiographic monitoring of complications during radiotherapy; elastographic classification of tumor and non-tumor regions; detailed imaging of fairly rapid transient and slowly varying deformations in laser-assisted reshaping of collagenous tissues; lymphangiography-based diagnostics in gynecology; otolaryngologic applications for diagnosing inner ear diseases, etc.)

To investigate the morphometric and optical coherence tomography (OCT) characteristics of the microstructure of retroperitoneal peripancreatic adipose tissue during passive drainage and active perfusion-aspiration drainage for infected pancreatic necrosis.The authors analyzed 74 samples of peripancreatic adipose tissue obtained from 37 patients with passive (Group 1) and active perfusion-aspiration drainage (Group 2) of a focus of peripancreatitis. The tissues were examined with OCT, then fixed in a formalin solution and underwent histological examination, including morphometric one.The examined groups showed qualitative and quantitative differences in the tissue microstructure. In Group 1 samples, the proportion (median (upper quartile; lower quartile)) of interlobular connective tissue was 5.6 (3.9; 6.1)%; and that of adipocytes was 44.6 (41.2; 51.6)%. Necrotic tissue occupied 46.2 (35.6; 56.1)% of the area of specimens. The OCT images of necrotic tissue displayed a preponderance of unstructured regions with a high signal level while the parenchymal areas showed a cellular structured pattern. In Group 2 samples, the proportion of interlobular connective tissue was 16.2 (11.4; 19.7)%, and that of adipocytes was 68.5 (59.7; 71.2)%. At the same time, Group 2 exhibited necrosis - 14.4 (11.5; 19.2%) that was 3.2 times less than in Group 1. The OCT images of Group 2 samples showed a preponderance of cellular structured regions characteristic of the parenchyma, with pronounced stromal elements, which corresponded to the histological pattern.Active perfusion-aspiration drainage of peripancreatic adipose tissue versus passive drainage is associated with a smaller proportion of necrotic tissue (14.4% versus 46.2%; p≤0.05) and a larger proportion of a stromal vascular component (16.2% vs. 5.6%; p≤0.05). OCT could qualitatively distinguish viable fat tissue parenchyma from necrotic areas, without specially preparing the samples, which was confirmed by histomorphometric results.Цель исследования - изучить особенности морфометрических и полученных при оптической когерентной томографии (ОКТ) характеристик микроструктуры забрюшинной парапанкреатической жировой клетчатки при пассивном дренировании и в условиях активного перфузионно-аспирационного дренирования инфицированного панкреонекроза. Материал и методы. Проведен анализ 74 образцов парапанкреатической жировой клетчатки, полученной у 37 пациентов с пассивным (1-я группа) и активным (2-я группа) перфузионно-аспирационным дренированием очага парапанкреатита. Ткани исследовали с помощью ОКТ, после чего фиксировали в растворе формалина и проводили гистологическое исследование, включая морфометрию. Результаты. В микроструктуре ткани исследуемых групп выявлены качественные и количественные различия. В образцах из 1-й группы доля (медиана (верхний квартиль; нижний квартиль)) междольковой соединительной ткани составила 5,6 (3,9; 6,1)%, жировых клеток - 44,6 (41,2; 51,6)%. Некротизированная ткань занимала 46,2 (35,6; 56,1)% площади препаратов. На ОКТ-изображениях некротизированной ткани преобладали бесструктурные участки с высоким уровнем сигнала, а на участках с паренхимой визуализировался ячеистый структурированный рисунок. В образцах из 2-й группы доля междольковой соединительной ткани составила 16,2 (11,4; 19,7)%, а адипоцитов - 68,5 (59,7; 71,2)%. При этом выявлено 14,4 (11,5; 19,2)% некроза, что в 3,2 раза меньше, чем в 1-й группе. На ОКТ-изображениях образцов из 2-й группы преобладали зоны ячеистой структуры, характерной для паренхимы, с выраженными элементами стромы, что соответствовало гистологической картине. Заключение. Активное перфузионно-аспирационное дренирование парапанкреатической клетчатки по сравнению с пассивным дренированием ассоциировано с меньшей долей некротизированной ткани (14,4% против 46,2%; p≤0,05) и большей долей сосудисто-стромального компонента (16,2% против 5,6%; p≤0,05). Метод ОКТ позволил качественно отличать паренхиму жизнеспособной жировой клетчатки от участков некроза без специального приготовления образцов, что было подтверждено результатами гистоморфометрии.

Aperture synthesis techniques such as Interferometric Synthetic Aperture Microscopy (ISAM) and digital refocusing allow to restore Optical Coherence Tomography (OCT) images in out-of-focus regions and obtain increased spatial resolution. Since these techniques are phase sensitive, they require object stability during OCT data acquisition. Since these techniques are manipulate volumetric data as well, application of the techniques to in vivo measurements require some motion correction procedure. In this work we will show that some of these correction procedures can obliterate not only local phase variations caused by the objects motion during the acquisition but local phase variations caused by defocusing, thus erasing information necessary for OCT image restoration. Ways of overcoming the problem are presented and discussed.

This work is dedicated to development of the OCT system capable to visualize blood vessel network for everyday clinical use. Following problems were solved during the development: compensation of specific natural tissue displacements, induced by contact scanning mode and physiological motion of patients (e.g. respiratory and cardiac motions) and on-line visualization of vessel net to provide the feedback for system operator.

Modern methods for diagnosis of exudative otitis media (EOM) have great potential, however, the problem of diagnosis of EOM is still relevant. The article describes the methods of modern diagnostics that are widely used in the daily practice of an otolaryngologist. The basic principles, advantages and disadvantages of generally accepted diagnostic methods for EOM are presented. The method of optical coherence tomography (OCT) is described as a method of studying biological tissues, which is used in many fields of medicine. Information is provided on the possibilities of OCT in the diagnosis of diseases of the ENT organs and, in particular, of the middle ear. The results of studies of the tympanic cavity structures in various inflammatory conditions, the possibilities of intrasurgery use of OCT, as well as the possibilities and perspectives of introducing OCT into the practice of an otorhinolaryngologist in the diagnosis of exudative otitis media are described.Современные методы диагностики экссудативного среднего отита (ЭСО) обладают широкими возможностями, однако проблема диагностики ЭСО все еще актуальна. В работе описаны методы современной диагностики, получившие широкое распространение в ежедневной практике оториноларинголога. Представлены основные принципы, преимущества и недостатки общепринятых методов диагностики ЭСО. Метод оптической когерентной томографии (ОКТ) описан как метод исследования биологических тканей, применяющийся во многих сферах медицины. Представлена информация о возможностях ОКТ в диагностике заболеваний лор-органов, в частности среднего уха. Описаны результаты исследований структур барабанной полости при различных воспалительных состояниях, возможности интраоперационного использования ОКТ, а также возможности и перспективы внедрения ОКТ в практику оториноларинголога при диагностике экссудативного среднего отита.

Otitis media with effusion (OME) accounts for 15-17% of the total number of recorded diseases of the middle ear. Surgical methods have become much more common. One of the factors affecting the tactics and effectiveness of treatment OME is the degree of viscosity of the effusion. Modern diagnostic methods do not allow to reliably identify cases of OME with high effusion viscosity.To study the possibilities of optical coherence tomography (OCT) in the diagnosis of OME and a non-invasive study of effusion viscosity.An analysis of the results of the examination of 29 patients who underwent surgical treatment for OME - tympanostomy. A control group of 30 patients without middle ear pathology. The study used a spectral OCT with a non-contact probe designed specifically for studies of the structural middle ear. Quantitative analysis of the results using open source ImageJ. Objectification of the degree of viscosity of the effusion was carried out by means of viscometry. A comparative analysis of the intensity of the optical signal in the external auditory canal (EAC) and in the tympanic cavity (TC) was performed, as well as a comparison of the signal from viscous and fluid effusion.In all patients with OME, during the OCT study, an optical signal with a higher intensity was recorded in TC than in the EAC. In all cases, in the control group in the TC, an optical signal was recorded that was identical in intensity with the signal in the EAC. When measuring the degree of viscosity of the effusion, 17 cases of OME were characterized as effusion of a low degree of viscosity, 12 cases - effusion of extreme viscosity. When comparing the average intensity of the optical signal of the OCT images of viscous and liquid effusion, a statistically significant difference was revealed,OCT makes it possible to detect light scattering from large scatterers - cell structures characteristic of low viscosity effusion. In addition, OCT allows you to register an optical signal from small scatterers - high molecular weight structures that are present in large quantities in viscous effusion. A correlation was found between the intensity of the optical signal in the TC and the degree of viscosity of the middle ear effusion.Based on OCT data, it is possible to determine the indications for surgical treatment of OME by detecting viscous exudate.Экссудативный средний отит (ЭСО) занимает 15—17% от общего количества регистрируемых заболеваний среднего уха. В течение последних десятилетий изменились подходы к лечению ЭСО, хирургические методы стали применяться значительно чаще. Одним из факторов, влияющих на тактику и эффективность лечения ЭСО, является степень вязкости экссудата. Современная комплексная диагностика не позволяет достоверно выявить случаи ЭСО с высокой вязкостью выпота.Изучение возможностей оптической когерентной томографии (ОКТ) в диагностике ЭСО и неинвазивном определении вязкости экссудата.Проведен анализ результатов обследования 29 пациентов, которым было проведено хирургическое лечение по поводу ЭСО — тимпаностомия. Контрольную группу составили 30 пациентов без патологии среднего уха. В исследовании использовалась спектральная ОКТ с бесконтактным зондом, разработанным специально для исследования структур среднего уха. Количественный анализ полученных ОКТ-изображений производился с помощью программного обеспечения с открытым кодом ImageJ. Объективизация степени вязкости экссудата осуществлялась путем проведения вискозиметрии. Был проведен сравнительный анализ интенсивности оптического сигнала в наружном слуховом проходе (НСП) и в барабанной полости (БП), а также сравнение сигнала от вязкого и жидкого экссудата.У всех пациентов с ЭСО при ОКТ-исследовании в БП регистрировался оптический сигнал большей интенсивности, чем в НСП. Во всех случаях в контрольной группе в зоне БП был зарегистрирован оптический сигнал, идентичный по интенсивности сигналу в НСП. При измерении степени вязкости экссудата 17 случаев ЭСО были охарактеризованы как выпот низкой степени вязкости, 12 образцов — как экссудат крайней степени вязкости. При сравнении величины средней интенсивности оптического сигнала ОКТ-изображений вязкого и жидкого экссудата было выявлено статистически сверхзначимое различие,ОКТ позволяет регистрировать рассеяние света от крупных рассеивателей — клеточных структур, характерных для выпота низкой степени вязкости. Кроме того, ОКТ позволяет регистрировать оптический сигнал от мелких рассеивателей — высокомолекулярных структур, которые присутствуют в большом количестве в вязком экссудате. Выявлена корреляция между интенсивностью оптического сигнала в БП и степенью вязкости выпота среднего уха.На основании данных ОКТ возможно определение показаний к хирургическому лечению ЭСО путем выявления вязкого экссудата.

An analogy between spectral-domain optical coherence tomography (SD OCT) data and broadband digital holography data is considered. Based on this analogy, a method for processing SD OCT data, which makes it possible to construct images with a lateral resolution in the whole investigated volume equal to the resolution in the in-focus region, is developed. Several issues concerning practical application of the proposed method are discussed. (laser biophotonics)

The second part of this paper continues the discussion of possibilities for combining functionally different types of biomedical characterization of tissues using optical coherence tomography (OCT). In the first part, polarization-sensitive imaging and conventional approaches to elastographic mapping in OCT were considered. Here, we consider an unconventional approach to elastographic mapping based on the analysis of variability of OCT images of the deformed tissue, omitting the stage of the displacement-field reconstruction. We also discuss methods for quantification of blood flow and visualization of microvasculature, some of which have much in common with the elastographic approach based on the analysis of temporal variability of OCT frames. This similarity looks especially promising in the context of combining multiple contrast mechanisms to enable prospective multimodal OCT scanners, as is essential for biomedical progress given the complex and heterogeneous nature of real biological tissues.

We have thoroughly investigated the method of simultaneous reception of spectral components with the achromatised quadrature phase shift between two portions of a reference wave, designed for the effective suppression of the 'mirror' artefact in the resulting image obtained by means of spectral domain optical coherence tomography (SD OCT). We have developed and experimentally tested a phase-shifting element consisting of a beam divider, which splits the reference optical beam into the two beams, and of delay lines being individual for each beam, which create a mutual phase difference of π/2 in the double pass of the reference beam. The phase shift achromatism over a wide spectral range is achieved by using in the delay lines the individual elements with different dispersion characteristics. The ranges of admissible adjustment parameters of the achromatised delay line are estimated for exact and inexact conformity of the geometric characteristics of its components to those calculated. A possibility of simultaneous recording of the close-to-quadrature spectral components with a single linear photodetector element is experimentally confirmed. The suppression of the artefact mirror peak in the OCT-signal by an additional 9 dB relative to the level of its suppression is experimentally achieved when the air delay line ismore » used. Two-dimensional images of the surface positioned at an angle to the axis of the probe beam are obtained with the correction of the 'mirror' artefact while maintaining the dynamic range of the image. (laser biophotonics)« less

We discuss physical principles of obtaining polarization-sensitive images, elastographic mapping and visualization of blood circulation/vasculature in optical coherence tomography (OCT). Along with the general overview of the respective methods, we perform comparative critical analysis of some of them from the viewpoint of their feasibility and requirements to OCT systems destined for combining the above-mentioned different image modalities.

Experimental results on observation of the light scattering in optically anisotropic transparent media are presented. During observation at angles close to the normal to the light beam in the crystal, a periodic trace line, which reflects the light-scattering dependence on the polarization of the laser light beam passing through the medium, is seen. Generalization of the well-known Umov experiment to more complex optically anisotropic media is presented. A simple theoretical model for a qualitative interpretation of the experimental data is proposed.

We present an approximate method of performing the Fourier transform of the data sampled in nonequidistant readouts. It is shown that the data can be recalculated as equidistant readouts by using a nonuniform convolution, i.e., convolution of a certain function whose form depends on the calculated element and the character of nonequidistance. Thus, this recalculation does not require calculation of the values of the initial data in intermediate readouts (unlike the linear approximation, spline, or other recalculations). Since the size of the kernel of this nonuniform convolution is about 9, the proposed method can be the basis for an efficient computational algorithm. Applicability of the proposed approach to spectral optical coherence tomography is demonstrated.

To construct a Stochastic Optical Reconstruction Microscopy (STORM) image one should collect sufficient number of localized fluorophores to satisfy Nyquist criterion. This requirement limits time resolution of the method. In this work we propose a probabalistic approach to construct STORM images from a subset of localized fluorophores 3-4 times sparser than required from Nyquist criterion. Using a set of STORM images constructed from number of localizations sufficient for Nyquist criterion we derive a model which allows us to predict the probability for every location to be occupied by a fluorophore at the end of hypothetical acquisition, having as an input parameters distribution of already localized fluorophores in the proximity of this location. We show that probability map obtained from number of fluorophores 3-4 times less than required by Nyquist criterion may be used as superresolution image itself. Thus we are able to construct STORM image from a subset of localized fluorophores 3-4 times sparser than required from Nyquist criterion, proportionaly decreasing STORM data acquisition time. This method may be used complementary with other approaches desined for increasing STORM time resolution.

Based on the fact that spectral domain (SD) optical coherence tomography (OCT) data can be treated as digital holography (DH) data acquired pointwise, we develop a spectral refocusing algorithm and show its ability to shift the focal region of OCT images obtained from SD OCT data acquired with a tightly focused scanning beam. Although refocusing itself depends on the refractive index of the studied media, we propose a procedure capable of restoring images with resolution equal to the resolution in the focal plane in the whole volume even in case of unknown refractive index of the media. As the proposed refocusing method operates with phases of the 3D Fourier spectrum of the SD OCT signal, it is very sensitive to the object motion during data acquisition. Thus, we also propose phase equalization preprocessing, which allows compensating the influence of such motions.

An improved method for suppressing image artefacts in spectral domain optical coherence tomography (SD OCT) and multiwave digital holography, caused by the influence of coherent noise in the course of successive registration of an autocorrelation component and informative signal is reported. The method allows complete suppression of all types of coherent noises, provided that the sample of values used to record the autocorrelation component satisfies the conditions of Kotelnikov's theorem: in SD OCT — for the transverse structure of the studied medium, in multiwave digital holography — for the envelop function of the radiation source frequency tuning spectrum.

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.

We consider specific features of optical-circuit operation in the presence of radiation which is returned to the source after having passed an optical path exceeding the initial coherence length of the reference wave when, as was previously assumed, the delay modulation should not influence the oscillation mode. However, experiments with the Michelson and Sagnac fiber interferometers showed that intensity modulation of the interference signal and, therefore, intensity modulation of the source radiation related to the active-medium nonlinearity appear when the interfering waves with the phase-difference modulation return. The revealed effect leads to distortion of a signal at the interferometer output irrespectively of the delay time and can be removed by placing an optical isolator at the source output.

The method of spectral selection based on weak coupling between a tilted short Fabry-Perot interferometer and a semiconductor optical amplifier has been proposed. An unusual effect was discovered at a certain inclination. Narrowband spectral maxima are observed in the light backreflected from a tilted short base Fabry-Perot interferometer at natural resonances. To demonstrate possible use of this effect for creation of selective feedback in a laser, a semiconductor laser with wavelength tuning range of ±10 nm at central wavelength 1290 nm and coherence length 8 mm has been developed.

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.

In this paper, we review methods for obtaining in vivo optical images of bio-objects with the resolution ranged from several units to tens of micrometers, namely, the methods of spectral-domain optical coherence tomography. We focus on problems that are specific of the spectral-domain optical coherence tomography, namely, the presence of coherent noise and mirror-symmetric phantoms in the image. On the basis of the most important relevant publications, we analyze possibilities of eliminating these drawbacks in modern devices.

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 complete theoretical interpretation of the experimental data on the transformation of the polarization state of a weak wave in a layer of resonant medium (methane) depending on the intensity of high-power counterpropagating wave is presented in terms of the vector theory of radiation-matter interaction. A method for the experimental determination of the coefficients of rotational and translational gas diffusion is developed based on the theoretical calculation of two types of dichroism and birefringence and the use of experimental data on the change in the probe wave polarization at saturation of the resonant transition by the intensity of a counterpropagating wave with two different (linear and circular) field polarizations. This method also takes into account low backscattering of the strong wave field from optical path inhomogeneities.

During the last years, an increased misuse of doping substances in sport has been observed. The action of doping substances characterized by the stimulation of blood flow and metabolic processes is also reflected in the hair structure. In the present study it was demonstrated that optical coherent tomography is well suited for the analysis of hair parameters influenced by doping. Analyzing 20 patients, systemically treated with steroids which also represent doping substances, it was found that in all cases a significant increase in the cross-section of the hairs could be detected. The results obtained in the study are not only important for the screening of doping substances but also for medical diagnostics and control of compliance of patients.

Using the method of nonlinear polarization spectroscopy in the oppositely propagating laser beams of different power at a wavelength of 3.39 µm, we study, both theoretically and experimentally, the mechanisms of the formation of dichroism and birefringence during the interaction of arbitrarily polarized fields of resonant radiation with gaseous methane under conditions of low pressure of the gas in the cell and saturation of the operating transition F 2 (2) by the field of a strong wave. Spectral forms of the polarization resonances of the test-wave intensity at the output of the polarization spectrometer are studied experimentally. Based on the vector theory of light interaction with matter, we present an exhaustive theoretical interpretation of the experimental data on the dependence of the polarization state of a weak wave on the intensity of a linearly or circularly polarized high-power counterpropagating wave. A new technique of measuring the induced nonlinear anisotropy for test-field waves and the macroscopic parameters of the resonant gas is developed.

The problem of designing a two-wave single-mode-fibre 3-dB coupler is considered. The method is proposed for adjusting the parameters of the coupler for simultaneous use of radiation at 0.83 and 1.3 μm in one fibre interferometer. The dependence of the coupling efficiency on the wavelength is studied experimentally for different angle mismatches of fibres in the coupler. The results of experiments and numerical calculations are presented.

We give a retrospective review of studies performed by a joint team of researchers from the Institute of Applied Physics of the Russian Academy of Sciences and the Nizhny Novgorod State Medical Academy and related to practical implementation of optical coherence tomography and its use as a novel method for biomedical diagnostics.

We have developed new methods of IR ultrabroadband interferometry for increasing the limiting capabilities of optical coherent tomography (OCT). In particular, this permitted us to create an optical coherent microscope combining the principles of confocal microscopy and OCT. To increase the longitudinal resolution, we synthesized an ultrabroadband optical spectrum based on two superluminescent diodes with separated radiation spectra. The resulting longitudinal resolution was 3.4 μm and the transverse resolution was 3.9 μm. Images of the inner structure of biological tissues are obtained at the cellular level. Experimental results of a study of biological tissue by the cross-polarization OCT are described.

The propagation of polarised low-coherent radiation is studied in an anisotropic single-mode glass fibre with imperfections of anisotropy. These imperfections are typical for interferometers used in devices for optical coherence tomography and can be caused by an inaccurate splicing of fibres or by their compression. The appearance of parasitic interference peaks due to anisotropic inhomogeneities is considered theoretically. The subtraction of parasitic peaks with orthogonal polarisations is studied theoretically and experimentally. The obtained experimental data well agree with theoretical estimates. The results of the paper are important for improving the methods for calculating interference schemes and for diagnostics of their defects.