A broadband quantum noise source based on detection of shot noise of a balanced photodetector is demonstrated. Precise electro-optical tuning of the balanced photodetector circuit was carried out by an integrated optical beam splitter constructed in the form of the dual output Mach-Zehnder interferometer on a lithium niobate substrate. The classical component of the detected noise related to the relative intensity noise of a laser diode was suppressed by more than 15 dB. At the maximum laser power of 100 mW, the power spectral density of detected shot noise was 12 dB higher than the level of technical noise of the measuring system in the frequency band above 3 GHz. Keywords: quantum random number generator, vacuum fluctuations, shot noise measurements, integrated optics, lithium niobate

Subject of study. A system of an integrated electro-optical modulator and a fiber circulating loop is studied. Aim of study. The study aims to maximize the nonlinearity of the response of an integrated electro-optical modulator while obtaining a stable output frequency spectrum. Method. Experimental studies of the spectra of optical (1550 nm) and radio-frequency (1 GHz) waves' collinear interaction under various conditions of the back coupling system are made. Main results. It is experimentally demonstrated that, to maximize the nonlinearity of the electro-optical modulator response in a fiber circulating loop, it is necessary to achieve not only in-phase wave propagation within the interaction region but also phase coincidence at the beginning of the interaction region during each pass of the system. In this case, the main contribution to the number of peaks of the emerging optical frequency comb comes from the matching of the radio-frequency wave with itself. The stability of the output spectrum over time is primarily ensured by the self-consistency of the optical radiation phase. Practical significance. The scheme described in the article enables the creation of discretely tunable sources of optical frequency combs, which maybe used in the future for fiber communication systems with frequency multiplexing. (c) 2024 Optica Publishing Group

Subject of study. The optical losses in waveguides designed for creating quantum photon gates at a wavelength of 810 nm were investigated. Aim of study. The aim of the study was to create integrated optical single-mode waveguides for quantum photon gates at a wavelength of 810 nm and to estimate optical losses acceptable for maintaining the necessary degree of photon-pair entanglement. Method. The waveguides were manufactured through thermal diffusion of titanium ions into a substrate composed of an X-slice of nominally pure lithium niobate (LiNbO3). Optical losses were estimated by experimentally measuring the loss per unit length of the waveguide. Optical radiation was coupled into and out of the waveguide using fiber segments, with one end connected and the other cleaved. A drop of immersion liquid was applied between the cleaved fiber and waveguide end, and measurements were performed for both polarization modes. Main results. Six groups of samples were produced, each containing waveguides with strip widths of d= 3.0, 2.0, and 1.5 mu m. The measured optical losses in the manufactured waveguides indicated that those with a titanium strip width of d approximate to 3 mu m exhibited the lowest losses. The estimated minimum optical losses for transverse magnetic and transverse electric polarization were approximately 0.20-0.25 and 0.1 dB/cm, respectively. Practical significance. The waveguides manufactured with a strip width of approximately 3 mu m can be used to create quantum photonic gates in an integrated optical design. The chosen wavelength of 810 nm offers potential for near-future development of photonic gates, as one of the most accessible methods for generating entangled photon pairs involves using a 405-nm laser followed by wavelength doubling through a nonlinear beta-barium borate crystal. (c) 2024 Optica Publishing Group

This research discusses the influence of the parameters of the traveling wave electrodes on the efficiency of RF control. It was demonstrated that for more efficient collinear interaction, it is necessary to use electrodes of a travelling wave with a refractive index close to the refractive index of the optical waveguide. Moreover, when refractive indices coincide, bandwidth width is limited mainly by the attenuation of the signal in the electrodes.

For the first time, the theory and practical realization of a broadband quantum noise generator based on original integrated optical beam splitter in the form of a Mach-Zehnder interferometer is demonstrated. The beam splitter with a double output, made on a lithium niobate substrate, provided accurate electro-optical balancing of the homodyne quantum noise detection circuit. According to our knowledge, the experimentally obtained excess of quantum noise over classical noise by 12 dB in the frequency band over 4 GHz, which is the best parameters of quantum noise generators known from the literature.

The laser source with dual wavelengths, with tunable distance between them simultaneously generating is demonstrated. The possibility of using it for a two wavelength holography is shown. Dual wavelengths at 890.7 nm and 906.7 nm provides measured accuracy of 3d surface profile at 25 µm,

The comparison of the influence of intra-cavity spectral selectors: static Bragg gratings and dynamic gain gratings, has been presented. It has been shown that their effect on the spectral properties of the laser radiation with a loop resonator is similar. The performed statistical study of the mode composition of the groups of the generation pulses at the Q-factor modulation mode allows us to conclude that the rewriting of the grating by the subsequent group pulse does not prevent radiation at the same frequency. This opens up the possibility of frequency stabilization of the radiation. The presence of an intra-cavity Bragg grating causes an increase in the probability of preserving the radiation frequency in neighboring pulses of the radiation group. It has been shown that there is a narrowing of the pulse generation spectrum in the group, despite the fact that the spectral width of the grating exceeds the spectral width of the generation pulse. The combined operation of static and dynamic intra-cavity gratings makes it possible to create a line of lasers with high pulse energy, radiation quality close to the diffraction limit, high peak power, and a narrow radiation spectrum.

This research discusses the leaking modes as an important optical noise factor, that limits dynamic range and contrast in the electro-optic modulators. The simulation demonstrates that the power of leaking modes at the output port of a common Mach-Zehnder modulator consists a 10-15% of the main waveguide mode even for the open state. When it is closed the leaking modes power increases due to the energy conservation law, so even after a Fresnel reflection from the modulator crystal's border the crosstalk can reach about 0,1-1% of the input power.

Subject of study. A digital holographic system for layer-by-layer control of component quality in additive manufacturing able to determine the size and depth of defects on the surface of each layer was investigated. Method. The digital holographic system for layer-by-layer control of component quality in additive manufacturing operates based on a two-wavelength holographic interferometry method. The digital holographic system is based on a Michelson interferometer. The considered method involves recording holograms of the surface of each component layer at two adjacent wavelengths. As a result of hologram reconstruction, the complex amplitudes of the object wave in the reconstruction plane are determined, which, in turn, define the phases of the waves and their difference. The wave phase difference allows the depth of the defect on the component layer surface to be determined. A tunable diode laser and camera based on a CCD matrix are used as the radiation source and detector, respectively. Main results. The results of the investigation of the surfaces of additively manufactured components using the two-wavelength holographic interferometry method are presented. The recognition of large irregularities is possible through expansion of the phase pattern. The detection of surface defects with the size of 25 mu m is demonstrated. The reconstructed surface of a component manufactured by laser sintering of successive layers using the M250 additive setup for selective laser sintering and the reconstructed surface of a millimeter-scale macroscopic object are presented. Practical significance. The possible use of the digital holographic system for component quality control in industrial settings, including those applying additive technologies, is demonstrated. The component quality criterion is the absence of defects (cavities or protrusions) with size larger than 25 mu m. (C) 2022 Optica Publishing Group

The experimental setup, based on a two-wavelength holography method is described. The possibility of recognizing defects of the order of 25 μm are demostrated. The ability of pulsed two- wavelength holography with 0 new inexpensive laser source is demonstrated.

Subject of study. The lasing spectra of a pulsed laser based on a Cr:LiSrAlF6 active medium are studied. Method. An intracavity transmission volume Bragg grating was used as the lasing mode on two aliquant wavelengths and wavelength tuning. The grating was recorded in a photo-thermo-refractive glass. Main results. For the first time in Russia, simultaneous narrowband lasing was demonstrated at two aliquant wavelengths in the band of 795-895 nm in a Cr:LiSrAlF6 crystal. The use of a volume transmission Bragg grating for continuous tuning of the central wavelength of the generated laser emission was demonstrated using additional feedback through a mirror with a high reflection coefficient positioned in the first diffraction order. Practical significance. Pulsed lasers with tunable wavelengths are applied in various scientific and practical applications including ecological monitoring of atmosphere conditions. The lasing at two aliquant wavelengths investigated in this study enables the design of high-power pulsed sources of terahertz radiation in the range of 15.5-27.1 THz. (C) 2022 Optica Publishing Group

Holographic interferometry is a well-established field of science and optical engineering. It has a half-century history of successful implementation as the solution to numerous technical tasks and problems. However, fast progress in digital and computer holography has promoted it to a new level of possibilities and has opened brand new fields of its application. In this review paper, we consider some such new techniques and applications.

Subject of study. The electrical properties of traveling wave electrodes positioned on a lithium niobate surface are investigated in this study. Method. The investigation methods included the analytical calculation, numerical modeling, and experimental investigation of the amplitude-frequency response and spectra of collinear interaction at the wavelength of 1552 nm. Main results. We demonstrated that traveling wave electrodes with a refractive index close to the refractive index of the optical waveguide should be used when grating periods are shorter than the length of the interaction area. Moreover, in the case of an exact match of the refractive indices, the minimum grating period is mostly limited by frequency-dependent signal attenuation in the electrodes. The effective phase modulation of light at the wavelength of 1552 nm by an electric signal in the band up to 40 GHz was demonstrated. Practical significance. This study determines the parameters of integrated optical circuits, which allow the fabrication of highly effective phase and amplitude light modulators. (C) 2022 Optica Publishing Group.

Исследовано влияние мод утечки на работу СВЧ интегрально-­оптических амплитудных модуляторов и квантовых генераторов шума, построенных по схеме интерферометра Маха-­Цендера. Показано, что рассеяние оптической мощности через моды утечек приводит к уменьшению динамического диапазона амплитудного модулятора, и, что самое главное, к возможности атаки нарушителем на квантовую линию связи. Для квантовых генераторов шума, построенных по схеме интерферометра Маха-­Цендера, моды утечки обеспечивают проникновение в схему генератора шума вакуумных флуктуаций, что необходимо для работы генератора.

A detailed statistical analysis was carried out, as a result of which the probability of retention the frequency of radiation of successive pulses was experimentally obtained. We demonstrate the effect of retention the frequency of radiation of Nd:YAG phase conjugate laser and determine the probability of retention the frequency of neighboring pulses in train.

Broadband quantum noise source based on the shot noise detection of a balanced photodetector is demonstrated. Precise electro-optical tuning of the balanced photodetector circuit was carried out by an integrated optical beam splitter in the form of the dual output Mach-Zehnder interferometer on a lithium niobate substrate. The classical component of the detected noise related to the relative intensity noise of a laser diode was suppressed by more than 15 dB. At the maximum laser power of 100 mW, power spectral density of detected shot noise was 12 dB higher than the level of technical noise of the measuring system in the frequency band above 3 GHz.

Broadband integrated optical modulators are key elements of modern optical information systems. The three main technological material platforms for their manufacture are considered: lithium niobate, III-V semiconductors, and silicon. Progress achieved in the development of integrated optical modulators is analyzed, and the main parameters of modulators obtained for various materials are compared with requirements for practical applications. Directions in the further development of the technology of modulators related to new problems in optical information systems are discussed.

Представлен обзор оригинальных результатов исследования оптических и голографических свойств двух видов фоточувствительных материалов, используемых в современной оптической голографии: легированных кристаллов ниобата лития и фото-терморефрактивных стекол. Приведен сравнительный анализ основных голографических характеристик этих материалов. Показаны преимущества и недостатки фото-терморефрактивных стекол и кристаллов ниобата лития, а также наиболее значимые примеры их практических применений в фотонике. Ключевые слова: ниобат лития, фото-терморефрактивное стекло, объемные брэгговские решетки, голографические оптические элементы.

We demonstrate electro-optic Q-switched solid state laser with Cr:LiSAF active medium. A single 50 ns pulse with 14 mJ of output energy is demonstrated. Simultaneous generation of several peaks with a step of 1.4 nm within the spectrum envelope with a full width at half maximum of 10.3 nm is demonstrated. For an electro-optic Q-switched mode a Pockels cell is used. Demonstrated laser can be used in differential absorption lidar systems.