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The UV-LED controlled phase shifter of an RF signal based on a GaN-sapphire surface-acoustic-wave (SAW) filter has been implemented. At the optical wavelength of 298 nm and SAW frequency of 307 MHz, the UV-induced relative change in SAW velocity per unit optical power density is 2 x 10^sup -6^ (μW/mm^sup 2^)^sup -1^ corresponding to 3.7 degrees phase shift. The phase modulation of an RF signal by rectangular UV pulses has been demonstrated. The efficiency of the phase shifter can be considerably improved by proper selection of sheet-resistivity of the GaN layer.

The UV-LED controlled phase shifter of an RF signal based on a GaN-sapphire surface-acoustic-wave (SAW) filter has been implemented. At the optical wavelength 298nm and SAW frequency 307MHz, the UV-induced relative change in SAW velocity per unit optical power density is 2*10-6 (muW/mm2)-1 corresponding to 3.7 deg phase shift. The phase modulation of an RF signal by rectangular UV pulses has been demonstrated. The efficiency of the phase shifter can be considerably improved by proper selection of sheet-resistivity of the GaN layer.

Soliton microcombs constitute chip-scale optical frequency combs, and have the potential to impact a myriad of applications from frequency synthesis and telecommunications to astronomy. The demonstration of soliton formation via self-injection locking of the pump laser to the microresonator has significantly relaxed the requirement on the external driving lasers. Yet to date, the nonlinear dynamics of this process has not been fully understood. Here, we develop an original theoretical model of the laser self-injection locking to a nonlinear microresonator, i.e., nonlinear self-injection locking, and construct state-of-the-art hybrid integrated soliton microcombs with electronically detectable repetition rate of 30 GHz and 35 GHz, consisting of a DFB laser butt-coupled to a silicon nitride microresonator chip. We reveal that the microresonator’s Kerr nonlinearity significantly modifies the laser diode behavior and the locking dynamics, forcing laser emission frequency to be red-detuned. A novel technique to study the soliton formation dynamics as well as the repetition rate evolution in real-time uncover non-trivial features of the soliton self-injection locking, including soliton generation at both directions of the diode current sweep. Our findings provide the guidelines to build electrically driven integrated microcomb devices that employ full control of the rich dynamics of laser self-injection locking, key for future deployment of microcombs for system applications. Self-injection locking of the pump laser for a soliton microcomb has significantly relaxed the requirements for laser drives. Here the authors study self-injection locking in experiment and theory and reveal that the soliton formation is feasible with detunings unreachable according to previous theories.

The stabilization and manipulation of laser frequency by means of an external cavity are nearly ubiquitously used in fundamental research and laser applications. While most of the laser light transmits through the cavity, in the presence of some back-scattered light from the cavity to the laser, the self-injection locking effect can take place, which locks the laser emission frequency to the cavity mode of similar frequency. The self-injection locking leads to dramatic reduction of laser linewidth and noise. Using this approach, a common semiconductor laser locked to an ultrahigh- Q microresonator can obtain sub-Hertz linewidth, on par with state-of-the-art fiber lasers. Therefore it paves the way to manufacture high-performance semiconductor lasers with reduced footprint and cost. Moreover, with high laser power, the optical nonlinearity of the microresonator drastically changes the laser dynamics, offering routes for simultaneous pulse and frequency comb generation in the same microresonator. Particularly, integrated photonics technology, enabling components fabricated via semiconductor CMOS process, has brought increasing and extending interest to laser manufacturing using this method. In this article, we present a comprehensive tutorial on analytical and numerical methods of laser self-injection locking, as well a review of most recent theoretical and experimental achievements.

This work reflects many years of experience in the development and implementation of an automated process control system at traditional power units with a capacity of 300 to 800 MW. It is part of a series of articles devoted to multiply connected automatic control systems, their development in accordance with modern requirements for maintaining the frequency and power of the power system. The interrelations of the main circuits of automatic control of power units and ways to neutralize the negative interrelations between them are described in detail. The problems of regulating the frequency and power of power units and solving power system problems are considered. A simplified matrix of the power unit control object is presented. Three types of autonomy (autonomy I, II, and III) and the relationship between the main leading and driven operating parameters of the power unit are considered. The advantages of the combined variant of the implementation of the Standard unit load control systems (LCS) are shown, which makes it possible to use each technological solution regardless of the current mode of operation of the power unit. A method for neutralizing the interconnections between local automatic control systems (LACS) both in the LCS-1 structure and in the combined LCS is described in detail by switching on compensation devices with the implementation of the invariance of the main controlled variables during disturbances in the boiler’s operation. Methods have been developed and improved to improve the dynamics of regulation of important technological parameters. The developed structural solutions for equipment automation are widely used in the implementation of distributed automated control systems. The schemes of the main channels of automatic control of the power units considered in the article are given, in the process of adjusting the process control systems of which positive results were obtained. The implementation of the optimal settings for the main control loops ensures an increase in the quality of the control processes of the power unit as a whole.

This article considers problems of construction and theoretical substantiation of computational algorithms for analyzing generalized V. M. Glushkov integral models based on the V. K. Dzyadyk approximation method.

The authors propose, theoretically substantiate, and programmatically implement high-precision numerical-analytical algorithms for approximation of problems solutions in inhomogeneous media on the basis of linear polynomial operators.

Micro- and nanofibers are the universal elements of the optical schemes for solving wide variety of experimental tasks. One usually uses the commercial optical fiber tapering in the burner’s flame to produce such nanofibers. Such tapers are actively used for production of highly sensitive sensors, experiments with the cold atoms and coupling to optical microresonators. The theoretical model of geometrical shape altering during the fiber tapering and heating was adapted in this publication for use in the algorithm with universal adjustment of the tapering modes to get a fiber with the desired set of parameters. One of the innovations was the implementation of the computer vision to control the tapering process. As a result, the nanofibers with the optimal waist diameter of about 700 nm for the radiation wavelength of 1.55 μm were obtained. The optimized methodic of tapering allows the production of the nanofibers with the transmittance of up to 80%. The produced nanofibers were successfully used for coupling to the crystalline whispering gallery mode microresonator. As a result, the optical combs with the spectrum range up to 200 nm were obtained in IR range.

Result are presented from an experimental investigation of nonstationary fluctuations in the intensity and aiming of a stabilized continuous-wave Model 126 Lightwave laser. We discuss mechanisms of their emergence, ways of describing them, and procedeures for suppressing them.

Microcombs, formed in optical microresonators driven by continuous-wave lasers, are miniaturized optical frequency combs. Leveraging integrated photonics and laser self-injection locking (SIL), compact microcombs can be constructed via hybrid integration of a semiconductor laser with a chip-based microresonator. While the current linear SIL theory has successfully addressed the linear coupling between the laser cavity and the external microresonator, it fails to describe the complicated nonlinear processes, especially for dark-pulse microcomb formation. Here, we investigate -- theoretically, numerically and experimentally -- the Kerr-thermal dynamics of a semiconductor laser self-injection-locked to an integrated silicon nitride microresonator. We unveil intriguing yet universal dark-pulse formation and switching behaviour with discrete steps, and establish a theoretical model scrutinizing the synergy of laser-microresonator mutual coupling, Kerr nonlinearity and photo-thermal effect. Numerical simulation confirms the experimental result and identifies the origins. Exploiting this unique phenomenon, we showcase an application on low-noise photonic microwave generation with phase noise purified by 23.5 dB. Our study not only adds critical insight of pulse formation in laser-microresonator hybrid systems, but also enables all-passive, photonic-chip-based microwave oscillators with high spectral purity.