arXiv subjects

Minhao Pu

Publications and source records attributed to Minhao Pu.

11 recordsLinked to original sources

arXiv2026

Harnessing thermo-optic dynamics for frequency-agile soliton microcombs

Dissipative Kerr soliton microcombs enable compact and scalable frequency comb sources for precision metrology, spectroscopy, communications and coherent LiDAR, where broad and reliable frequency tuning is essential. Thermo-optic response can support thermal locking during soliton operation, enabling resonance tracking and thereby extending the tuning range, albeit modestly. However, it also induces pronounced thermal instability during soliton initiation, hindering reliable access to this extended operating regime and limiting practical deployment in applications requiring frequency agility. Here we show that strong mode coupling reshapes the effective detuning trajectory governing soliton formation, establishing a distinct operating regime in which thermo-optic response is significantly reinforced and constructively harnessed. In this regime, soliton formation proceeds without the thermal instability inherent to conventional operation, enabling robust soliton generation in material platforms previously limited by strong thermal effects. Importantly, the enhanced thermo-optic response strengthens thermal locking during soliton operation, enabling more effective resonance tracking and substantially extending the tuning range. Leveraging this regime in AlGaAs-on-insulator multimode microresonators, we demonstrate soliton generation with a tuning range approaching 100 GHz at a pump power of 32 mW. The same mechanism further enables frequency-agile operation through direct pump-frequency tuning without auxiliary stabilization, allowing massively parallel chirped comb generation with more than 90 channels exhibiting frequency excursions exceeding 10 GHz. These results establish a general operating principle for transforming thermo-optic effects from a limiting factor into an active resource, enabling robust and frequency-agile integrated soliton microcombs.

physics.optics↗

arXiv2026

Broadband parametric amplification in AlGaAs-on-insulator nanowaveguides

Optical amplification is critical for optical signal transmission. While the emergence of erbium-doped fiber amplifiers has revolutionized optical communications in fiber-based systems, on-chip amplification remains essential for integrated optics. Nanoscale waveguides enhance nonlinearity by several orders of magnitude, making them promising candidates for optical parametric amplification. Using a pulsed pump at 1550 nm, broadband optical parametric amplification based on four-wave mixing is investigated in AlGaAs-on-insulator nanowaveguides. The strong nonlinearity enables an on-off gain as high as 58.4 dB. Meanwhile, the low propagation loss leads to a net on-chip gain of 56.2 dB. With further dispersion engineering, the net on-chip gain bandwidth extends beyond 415 nm, which is 2.3 times larger than previous reports pumped in the telecom band in integrated optics. These results represent the largest parametric gain and bandwidth reported for on-chip parametric amplifiers.

physics.optics↗

arXiv2026

Thermally accessible broadband soliton microcombs in silicon carbide enabled by dynamic polarization control

Optical microcombs generated in high-Q microresonators are promising chip-scale light sources for applications ranging from optical communications to spectroscopy and metrology. However, thermo-optic instabilities remain a major obstacle to reliable soliton access. Self-cooling using auxiliary modes can stabilize the intracavity power, yet part of the power is continuously allocated to thermal compensation rather than comb generation, thereby limiting comb power and bandwidth. Here we propose a thermal compensation scheme based on dynamic polarization control. During soliton initiation, a fraction of the pump is coupled to an orthogonally polarized mode to provide self-cooling and ensure reliable soliton access. After soliton formation, polarization rotation and pump tuning transfer this cooling power to the comb-generating mode, enabling efficient single-soliton operation. Using this approach, we experimentally demonstrate a broadband 108-GHz-FSR single-soliton microcomb spanning over 450 nm, together with approximately 39% improvement in the 20-dB bandwidth and 60% increase in comb power relative to the static self-cooling configuration. This dynamic polarization-based thermal compensation enables efficient use of available laser power and provides a practical route to high-performance soliton microcombs in platforms with strong thermo-optic effects.

physics.optics↗

arXiv2025

Octave-spanning, deterministic single soliton generation in 4H-silicon carbide-on-insulator microring resonators

The miniaturization of self-referencing frequency comb systems enables emerging applications in metrology and spectroscopy. One major challenge in realizing the chip-scale self-referencing function is to generate octave-spanning soliton microcombs with low operation power. Accessing soliton states is also not trivial due to the thermal effect. Though an auxiliary laser was utilized to compensate for the thermal effect, deterministic single soliton generation is still elusive, especially for broadband operation. In this work, dispersion management is performed for a 4H-silicon carbide-on-insulator (SiCOI) multi-mode microring resonator, benefiting from the submicron-confinement waveguide layout. The fundamental transverse electric (TE) mode is engineered to anomalous dispersion for two dispersive waves generation over an octave span. While a higher order TE mode is engineered to normal dispersion to accommodate the auxiliary light for thermal compensation. The normal dispersion prevents modulation-instability Kerr comb generation, allowing for a large soliton existence range. We achieve microring resonators with Q up to 5.8 million and sub-milli-watt-threshold Kerr comb generation. Combining the dispersion-managed design and high Q device, we demonstrate the deterministic generation of a single soliton comb spanning beyond an octave with a low on-chip power of 60 mW. Our demonstration paves the way to realize chip-scale, turn-key, self-referenced frequency combs.

physics.optics↗

arXiv2025

Breaking the bandwidth-efficiency trade-off in soliton microcombs via mode coupling

Dissipative Kerr solitons in optical microresonators have emerged as a powerful tool for compact and coherent frequency comb generation. Advances in nanofabrication have allowed precise dispersion engineering, unlocking octave-spanning soliton combs that are essential for applications such as optical atomic clocks, frequency synthesis, precision spectroscopy, and astronomical spectrometer calibration. However, a key challenge hindering their practical deployment is the intrinsic bandwidth-efficiency trade-off: achieving broadband soliton generation requires large pump detuning, which suppresses power coupling and limits pump-to-comb conversion efficiencies to only a few percent. Recent efforts using pulsed pumping or coupled-resonator architectures have improved efficiency to several tens of percent, yet their bandwidths remain below one-tenth of an octave, inadequate for applications demanding wide spectral coverage. Here, we overcome this limitation by harnessing mode interactions between spatial modes within a single microresonator. The mode hybridization creates an additional power-transfer channel that supports large pump detuning while maintaining strong pump-to-resonator coupling, enabling broadband soliton formation at substantially reduced pump power. Using this approach, we demonstrate an octave-spanning soliton microcomb with a record pump-to-comb conversion efficiency exceeding 50%. These results resolve the fundamental bandwidth-efficiency dilemma in soliton microcombs and paves the way toward fully-integrated, high-efficiency, ultrabroad comb sources for next-generation photonic systems.

physics.optics↗

arXiv2025

Engineered mode coupling in high-Q microresonators enables deterministic low-repetition-rate soliton microcombs

Soliton optical frequency combs have become key enablers for a wide range of applications, including telecommunications, optical atomic clocks, ultrafast distance measurements, dual-comb spectroscopy, and astrophysical spectrometer calibration, many of which benefit from low repetition rates. However, achieving such low-repetition-rate soliton microcombs is nontrivial as long cavities require substantially higher pump power, which induces stronger thermal effects that, in turn, exacerbate thermal instability and complicate access to stable soliton states. The dual-mode pumping scheme, in which a continuous-wave pump couples to both the comb-generating mode and an auxiliary mode, has proven simple and effective for mitigating thermal instability and enabling thermally accessible soliton generation. Yet, in long-cavity devices, the standard bus-to-resonator coupling conditions for these two modes diverge substantially, resulting in insufficient pump coupling to the auxiliary mode, which makes dual-mode pumping particularly challenging for low-repetition-rate microcombs. In this work, we overcome this limitation by coupling the pump to the auxiliary mode via inter-modal coupling, which can be introduced in racetrack microresonators and engineered by tailoring the cavity bend design. We validate this approach in a high-Q (>$10^7$) silicon nitride microresonator and demonstrate thermally accessible, deterministic single-soliton generation at a repetition rate of 33 GHz. This work provides a simple and robust pathway for generating low-repetition-rate soliton microcombs.

physics.optics↗

arXiv2025

Silicon Nitride Microresonator Raman Lasers

Silicon nitride (SiN) has emerged as a promising platform for integrated nonlinear photonics because of its low propagation loss, wide transparency window, and CMOS compatibility. Nonlinear processes arising from photon-electron interactions, such as Kerr frequency comb generation and second harmonic generation, have been extensively explored. In contrast, photon-phonon interaction-based nonlinearities, such as stimulated Raman scattering, remain largely unexplored in this integrated platform, despite their potential for broadband frequency conversion. Here, we demonstrate efficient Raman lasing in ultra-high-Q SiN microresonators by harnessing the strong intracavity field enhancement and engineering the optical mode to overlap with the Raman-active silica cladding. Through dispersion engineering and waveguide geometry optimization, we suppress competing Kerr nonlinearities while enhancing Raman gain, achieving lasing with sub-2 mW thresholds. We further investigate the trade-off between optical confinement and quality factor, revealing its impact on the overall nonlinear efficiency. Moreover, we also demonstrate broadband tunability of the Raman shift exceeding 120 inverse centimeters, enabled by the wide Raman gain spectrum of silica, offering new flexibility in designing integrated tunable Raman lasers. These results position SiN as a viable platform for chip-scale Raman lasers, expanding the nonlinear optics toolbox of the SiN platform and enabling compact, power-efficient light sources for applications in spectroscopy, optical communications, and quantum photonics.

physics.optics↗

arXiv2023

Post-2000 Nonlinear Optical Materials and Measurements: Data Tables and Best Practices

In its 60 years of existence, the field of nonlinear optics has gained momentum especially over the past two decades thanks to major breakthroughs in material science and technology. In this article, we present a new set of data tables listing nonlinear-optical properties for different material categories as reported in the literature since 2000. The papers included in the data tables are representative experimental works on bulk materials, solvents, 0D-1D-2D materials, metamaterials, fiber waveguiding materials, on-chip waveguiding materials, hybrid waveguiding systems, and materials suitable for nonlinear optics at THz frequencies. In addition to the data tables, we also provide best practices for performing and reporting nonlinear-optical experiments. These best practices underpin the selection process that was used for including papers in the tables. While the tables indeed show strong advancements in the field over the past two decades, we encourage the nonlinear-optics community to implement the identified best practices in future works. This will allow a more adequate comparison, interpretation and use of the published parameters, and as such further stimulate the overall progress in nonlinear-optical science and applications.

physics.optics↗

arXiv2022

Integrated Optical Vortex Microcomb

The explorations of physical degrees of freedom with infinite dimensionalities, such as orbital angular momentum and frequency of light, have profoundly reshaped the landscape of modern optics with representative photonic functional devices including optical vortex emitters and frequency combs. In nanophotonics, whispering gallery mode microresonators naturally support orbital angular momentum of light and have been demonstrated as on-chip emitters of monochromatic optical vortices. On the other hand, whispering gallery mode microresonators serve as a highly efficient nonlinear optical platform for producing light at different frequencies - i.e., microcombs. Here, we interlace the optical vortices and microcombs by demonstrating an optical vortex comb on an III-V integrated nonlinear microresonator. The angular-grating-dressed nonlinear microring simultaneously emits spatiotemporal light springs consisting of 50 orbital angular momentum modes that are each spectrally addressed to the frequency components (longitudinal whispering gallery modes) of the generated microcomb. We further experimentally generate optical pulses with time-varying orbital angular momenta by carefully introducing a specific intermodal phase relation to spatiotemporal light springs. This work may immediately boost the development of integrated nonlinear/quantum photonics for exploring fundamental optical physics and advancing photonic quantum technology.

physics.optics↗

arXiv2016

Octave-spanning supercontinuum generation in a silicon-rich nitride waveguide

We experimentally show octave-spanning supercontinuum generation in a non-stoichiometric silicon-rich nitride waveguide when pumped by femtosecond pulses from an erbium fiber laser. The pulse energy and bandwidth are comparable to results achieved in stoichiometric silicon nitride waveguides, but our material platform is simpler to manufacture. We also observe wave-breaking supercontinuum generation by using orthogonal pumping in the same waveguide. Additional analysis reveals that the waveguide height is a powerful tuning parameter for generating mid-infrared dispersive waves while keeping the pump in the telecom band.

physics.optics↗

arXiv2015

AlGaAs-On-Insulator Nonlinear Photonics

The combination of nonlinear and integrated photonics has recently seen a surge with Kerr frequency comb generation in micro-resonators as the most significant achievement. Efficient nonlinear photonic chips have myriad applications including high speed optical signal processing, on-chip multi-wavelength lasers, metrology, molecular spectroscopy, and quantum information science. Aluminium gallium arsenide (AlGaAs) exhibits very high material nonlinearity and low nonlinear loss when operated below half its bandgap energy. However, difficulties in device processing and low device effective nonlinearity made Kerr frequency comb generation elusive. Here, we demonstrate AlGaAs-on-insulator as a nonlinear platform at telecom wavelengths. Using newly developed fabrication processes, we show high-quality-factor (Q>100,000) micro-resonators with integrated bus waveguides in a planar circuit where optical parametric oscillation is achieved with a record low threshold power of 3 mW and a frequency comb spanning 350 nm is obtained. Our demonstration shows the huge potential of the AlGaAs-on-insulator platform in integrated nonlinear photonics.

physics.optics↗