arXiv subjects

Haoyang Tan

Publications and source records attributed to Haoyang Tan.

4 recordsLinked to original sources

arXiv2026

Featurized Occupation Measures for Structured Global Search in Numerical Optimal Control

Numerical optimal control has long been split between globally structured but dimensionally intractable Hamilton--Jacobi--Bellman (HJB) methods and scalable but local trajectory optimization. We introduce Featurized Occupation Measures (FOM), a finite-dimensional primal--dual interface for coupling numerical optimal control solvers with explicit HJB subsolutions: the certificate guides the primal search, while primal residuals tighten the certificate in a primal-dual language. Two realizations are developed. The explicit realization uses finite weak-form Liouville tests, and the implicit realization couples rollout-based search with sampled primal--dual residuals. Both are proved asymptotically consistent with the exact occupation-measure linear program under refinement, separating primal expressiveness from dual accuracy in the limit. The framework also gives structural conditions under which HJB-type certificates avoid full state-space representation. For factor graphs induced by compatible passivity-based interconnections, blockwise HJB inequalities assemble into globally feasible OM-dual certificates, and the decomposition is preserved under blockwise approximation. The curse of dimensionality is then shifted from state space to interconnection topology. Approximate certificates remain reusable under time shifts and bounded model perturbations, with explicit degradation bounds. On a static obstacle-avoidance benchmark, certificates of increasing tightness guide a sample-based optimizer toward global optima, confirming that even a coarse certificate carries useful global information.

math.OC↗

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

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↗