Shun Fujii

Abstract Designing and engineering microresonator dispersion are essential for generating microresonator frequency comb. Microresonator frequency combs (microcombs, Kerr frequency combs) offer the potential for various attractive applications as a new type of coherent light source that is power efficient and compact and has a high repetition rate and a broad bandwidth. They are easily driven with a continuous‐wave pump laser with adequate frequency tuning; however, the resonators must have a hig

Abstract Microresonator-based optical frequency combs emitted from high-quality-factor microresonators, also known as microcombs, have opened up new horizons to areas of optical frequency comb technology including frequency metrology, precision sensing, and optical communication. To extend the capability of microcombs for such applications, large and reliable tunability is of critical importance. Here, we show broad spectral tuning of Kerr soliton microcombs in a thermally controlled crystalline

We demonstrated the deterministic generation of blue light emission (438 nm) via the third-harmonic process from an infrared pump by carefully engineering the dispersion of a high-quality-factor whispering gallery mode microcavity. We present two different approaches to obtaining broad bandwidth light. One is based on a clustered comb and the other employs a dispersive wave, and a broad Kerr comb spanning a half-octave is obtained. This allowed frequency conversion over a broad bandwidth ranging

We theoretically and experimentally investigated the transition between modulation instability and Raman gain in a small silica microcavity with a large free-spectral range, which reveals that we can selectively switch from a four-wave mixing dominant state to a stimulated Raman scattering dominant state. Both the theoretical analysis and the experiment show that a Raman-dominant region is present between transitions of Kerr combs with different free-spectral range spacings. We can obtain a stab

In this Letter, we report phase-matched four-wave mixing separated by over one octave in a dispersion-engineered crystalline microresonator. Experimental and numerical results presented here confirm that primary sidebands were generated with a frequency shift up to 140 THz, and that secondary sidebands formed a localized comb structure, known as a clustered comb in the vicinity of the primary sidebands. A theoretical analysis of the phase-matching condition validated our experimental observation

The development of ultrahigh-quality-factor ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mtext class="MJX-tex-mathit" mathvariant="italic">Q</mml:mtext> </mml:mrow> </mml:math> ) microresonators has been driving such technologies as cavity quantum electrodynamics (QED), high-precision sensing, optomechanics, and optical frequency comb generation. Here we report ultrahigh <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathM

By using nonlinear coupled mode equations, we numerically investigated the generation of a Kerr comb in a normal dispersion microcavity system, where mode coupling between two cavity modes is present. In contrast to previous studies, our model is rigorous in which we fully considered the mode coupling between two modes. We investigated the phase matching condition to obtain the suitable parameters needed to form a free-spectral-range (FSR)-selectable comb. Our calculations are in good agreement

A high-Q silica whispering gallery mode microresonator is an attractive platform on which to demonstrate a broad and phase-locked Raman comb in various wavelength regimes. Raman combs can be used for applications such as compact pulse laser sources, sensors, optical clocks, and coherence tomography. However, the formation dynamics of a Raman comb has not been well exploited. Here we study the dynamics of the Raman comb formation in silica rod microresonators, which have cavity-free spectral rang

Abstract Mode‐locked ultrashort pulse sources with a repetition rate of up to several tens of gigahertz greatly facilitate versatile photonic applications such as frequency synthesis, metrology, radar, and optical communications. Dissipative Kerr soliton microcombs provide an attractive solution as a broadband, high‐repetition‐rate compact laser system in this context. However, its operation usually requires sophisticated pump laser control to initiate and stabilize the soliton microcombs, parti

Optical nonlinear processes are indispensable in a wide range of applications, including ultrafast lasers, microscopy, and quantum information technologies. Among the diverse nonlinear processes, second-order effects usually overwhelm the higher-order ones, except in centrosymmetric systems, where the second-order susceptibility vanishes to allow the use of the third-order nonlinearity. Here we demonstrate a hybrid photonic platform whereby the balance between second- and third-order susceptibil

Platinum(II) complexes with salophen ligands bearing carboxy substituents at different positions, [Pt{(COOH)_<i>n</i>-salophen}] (<i>n</i> = 2 (1), 3 (2), 1 (3)), were synthesized and characterized by acquiring UV-vis and luminescence spectra. These complexes exhibited systematic variations in absorption spectra depending on the number of carboxy groups, and this effect was attributed to metal-ligand charge transfer with support from density functional theory calculations. The luminesc

We made a CNT-PDMS composite and measured reverse saturable absorption (RSA) with a lifetime of 76 µs. We achieved mode-locking even in the presence of RSA thanks to the fast response of the SA property.

We demonstrate the all-precision-machining fabrication of ultrahigh-quality-factor (Q) crystalline optical microresonators. The obtained Q exceeds 100 million for both magnesium fluoride (MgF₂) and calcium fluoride (CaF₂) materials. This constitutes the highest Q factor obtained for whispering gallery mode crystalline microresonators fabricated solely by ultra-precision machining. We also achieve octave-wide optical parametric oscillation using an MgF₂ resonator

Mode-locked ultrashort pulse sources with a repetition rate of up to several tens of gigahertz greatly facilitate versatile photonic applications such as frequency synthesis, metrology, radar, and optical communications. Dissipative Kerr soliton microcombs provide an attractive solution as a broadband, high-repetition-rate compact laser system in this context. However, its operation usually requires sophisticated pump laser control to initiate and stabilize the soliton microcombs, particularly i