arXiv subjects

Nikita Yu. Dmitriev

Publications and source records attributed to Nikita Yu. Dmitriev.

8 recordsLinked to original sources

arXiv2026

Low-confinement silicon nitride waveguides manufactured via direct glass bonding

Reducing the fabrication cost of photonic integrated circuits while maintaining low optical losses and technological simplicity is essential for their wider implementation. In conventional manufacturing methods, the dielectric cladding thickness around waveguides is usually limited to $\sim20$~$μ$m, which complicates suppression of radiative losses and parasitic scattering in low-confinement geometries. In this paper, we propose and experimentally demonstrate an alternative technology for forming low-confinement waveguides in Borofloat~33 glass by thermal fusion bonding of two glass wafers. The waveguide pattern is formed by etching trenches with depths on the order of tens of nanometers into the glass, filling them with silicon nitride, removing the excess layer, and bonding the planarized glass surfaces, thereby forming a thick, symmetric dielectric cladding. As a proof of concept, we fabricated straight waveguides with a core height of 50~nm and widths from 1.3 to 3.5~$μ$m. With butt coupling to standard SMF-28 single-mode fiber at 1550~nm, we obtained chip transmissions up to 60\%, corresponding to input/output coupling losses of $\sim1$~dB per facet and consistent with numerical estimates. Fabry--Perot analysis of high-resolution spectra measured with AR-coated lensed fibers gave effective propagation losses down to $0.62\pm0.36$ dB/cm, depending on waveguide width and polarization. The proposed approach provides a simple and scalable route to low-confinement glass-encapsulated photonic circuits with passive butt coupling, promising for long delay lines, external-cavity laser feedback circuits, and ring-resonator sensors.

physics.optics↗

arXiv2025

Microring resonator as a Rayleigh mirror for broadband laser-cavity comb generation

High-quality microring resonators (MRRs) have proven to be promising sources of optical combs generated from continuous-wave radiation. In addition to the primary comb that propagates along with the pump, Rayleigh scattering creates a comb that travels in the opposite direction. Normally, the scattering is a very weak, however, in the high-quality-factor MRR the power transferred to the backward-propagating comb can be quite significant. We demonstrate that the backward-propagating comb can be used as a feedback source for a fiber laser, effectively creating a nonlinear mirror for the laser cavity. By assembling a simple laser cavity comprising only active fiber and two mirrors, one of which is an integrated MRR, we show a robust self-starting comb generation with width exceeding 500 nm. We confirm the universal character of this approach for other types of microresonators, including whispering gallery mode resonators, by launching self-starting laser cavity combs with the crystalline toroidal cavity, coupled with a tapered fiber. This method provides significant simplification for the filter-driven laser cavity soliton generation, especially when free-space coupling is applied.

physics.optics↗

arXiv2025

Stokes microcombs in silicon nitride microresonators

Silicon nitride microresonators have become an ubiquitous platform for cutting-edge photonics applications. Improvement in silicon nitride fabrication techniques, providing ultra-high quality-factor values up to $10^7$, has opened up new possibilities for nonlinear effects realizations in such structures. Here we report for the first time to our knowledge on the observation of the Stokes microcombs in silicon nitride on-chip microresonators exhibiting normal group velocity dispersion. Moreover, using different pump schemes, namely, a tunable laser with an isolator and a stabilized diode laser, we demonstrate on-chip stimulated Raman frequency combs including dark-pulse Raman states. We reveal a complex interplay between Kerr and Raman nonlinearities and elaborate effective method of controllable switching between predominantly Kerr-comb and predominantly Raman-comb operation. We prove the Raman-induced platicon formation by numerical model which shows perfect agreement with experimental results. These findings are of special importance for silicon nitride photonics and provide a basis for novel photonic devices.

physics.optics↗

arXiv2025

Universal Kerr-thermal dynamics of self-injection-locked microresonator dark pulses

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.

physics.optics↗

arXiv2022

Recent Advances in Laser Self-Injection Locking to High-$Q$ Microresonators

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.

physics.optics↗

arXiv2021

A hybrid integrated dual-microcomb source

Dual-comb interferometry is based on self-heterodyning two optical frequency combs, with corresponding mapping of the optical spectrum into the radio-frequency domain. The dual-comb enables diverse applications, including metrology, fast high-precision spectroscopy with high signal-to-noise ratio, distance ranging, and coherent optical communications. However, current dual-frequency-comb systems are designed for research applications and typically rely on scientific equipment and bulky mode-locked lasers. Here we demonstrate for the first time a fully integrated power-efficient dual-microcomb source that is electrically driven and allows turnkey operation. Our implementation uses commercially available components, including distributed-feedback and Fabry--Perot laser diodes, and silicon nitride photonic circuits with microresonators fabricated in commercial multi-project wafer runs. Our devices are therefore unique in terms of size, weight, power consumption, and cost. Laser-diode self-injection locking relaxes the requirements on microresonator spectral purity and Q-factor, so that we can generate soliton microcombs resilient to thermal frequency drift and with pump-to-comb sideband efficiency of up to 40\% at mW power levels. We demonstrate down-conversion of the optical spectrum from 1400 nm to 1700 nm into the radio-frequency domain, which is valuable for fast wide-band Fourier spectroscopy, which was previously not available with chip-scale devices. Our findings pave the way for further integration of miniature microcomb-based sensors and devices for high-volume applications, thus opening up the prospect of innovative products that redefine the market of industrial and consumer mobile and wearable devices and sensors.

physics.optics↗

arXiv2021

Numerical study of solitonic pulse generation in the self-injection locking regime at normal and anomalous group velocity dispersion

We developed an original model describing the process of the frequency comb generation in the self-injection locking regime and performed numerical simulation of this process.Generation of the dissipative Kerr solitons in the self-injection locking regime at anomalous group velocity dispersion was studied numerically. Different regimes of the soliton excitation depending on the locking phase, backscattering parameter and pump power were identified. It was also proposed and confirmed numerically that self-injection locking may provide an easy way for the generation of the frequency combs at normal group velocity dispersion. Generation of platicons was demonstrated and studied in detail. The parameter range providing platicon excitation was found.

physics.optics↗

arXiv2020

Dynamics of soliton self-injection locking in a photonic chip-based microresonator

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 requirement on external driving lasers has been significantly relaxed with the demonstration of soliton formation via self-injection locking of the pump laser to the microresonator. Yet to date, the dynamics of this process has not been fully understood. Prior models of self-injection locking were not able to explain sufficiently large detunings, crucial for soliton formation. Here we develop a theoretical model of self-injection locking to a nonlinear microresonator (nonlinear self-injection locking) for the first time and show that self- and cross-phase modulation of the clockwise and counter-clockwise light enables soliton formation. Using an integrated soliton microcomb of directly detectable 30 GHz repetition rate, consisting of a DFB laser self-injection-locked to a Si3N4 microresonator chip, we study the soliton formation dynamics via self-injection locking, as well as the repetition rate evolution, experimentally. We reveal that Kerr nonlinearity in microresonator significantly modifies locking dynamics, making laser emission frequency red detuned. We propose and implement a novel technique for measurements of the nonlinear frequency tuning curve and concurrent observation of microcomb states switching in real time.

physics.optics↗