Cavities with high quality (Q) factors and small mode volumes are crucial for realizing high-performance nanolasers suitable for optical interconnects. In this work, we propose a novel one-dimensional photonic crystal nanobeam cavity design with fins for controlled electrical injection into the active region. An effective optimization algorithm based on the first-order perturbation theory of quasinormal modes is implemented and shown to significantly enhance the cavity quality factor. The one-dimensional geometry of the cavity lends itself to unidirectional coupling of the resonant mode into the waveguide by introducing asymmetry in the mirror. The resulting design is shown to achieve high extraction efficiencies ( > 90 % ) while maintaining a high Q-factor ( > 10 & sdot; 10(3 )) . Through an analysis of the cavity's decay channels, we find that the introduced asymmetry induces unexpected interactions between these channels. Passive InP cavities are fabricated and experimentally characterized, demonstrating record-high quality factors exceeding 170 & sdot; 10(3) for designs without fins and exceeding 70 & sdot; 10(3) for designs with fins, confirming the efficacy of the optimization method and the quality of the fabrication process.

This paperfocuses on the design and optimization of high contrast grating (HCG) used in tunable micro-electromechanical system - vertical-cavity surface emitting laser (MEMS-VCSEL). The optimization consists of mitigating reflectivity dips, that can present when incidence angle effects are not considered, to obtain a broad reflectivity bandwidth. Two new designs are proposed, low-duty-cycle and focusing HCG. These designs are verified using FDTD 3D simulations and then fabricated. From the characterization, the best result was obtained with a low-duty-cycle design, that achieved a maximum tuning range of 67.8 nm and an average tuning range of 55.8 nm surpassing the standard design where we obtained 62.2 nm and 50.2 nm respectively. Furthermore, the new designs displayed better performance in the maximum output power and a better far-field profile compared to the standard design, indicatingimproved light extraction efficiency. These findings demonstrate the promise of optimized HCG, although further fabrication refinement is crucial to consistently achieve and maximize their performance for swept-source optical coherence tomography (SS-OCT) applications.

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 is still needed for integrated optics. Since nanoscale waveguides enhance nonlinearity by several orders of magnitude, they are 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 intense nonlinearity enables an on-off gain as large as 58.4 dB. Meanwhile, the low propagation loss leads to a 56.2-dB net on-chip gain. Combined 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. The demonstrated results represent the largest parametric gain and bandwidth reported for on-chip parametric amplifiers.

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.

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.

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

We report lasing from a lithographically defined buried heterostructure with an estimated lateral footprint of (107 nm)2, embedded in an InP photonic-crystal nanobeam cavity. This represents the smallest laterally confined buried heterostructure gain region from which lasing has been observed. Despite etching of the active region during cavity definition and the associated risk of surface-related nonradiative recombination, optically pumped devices exhibit a clear lasing threshold and a narrow linewidth. By systematically varying the buried heterostructure size, we investigate how the lasing threshold depends on the active volume under optical pumping. The estimated intrinsic threshold under ideal carrier injection is 57 nW, comparable to values reported for single quantum-dot nanolasers, highlighting the potential of quantum-dot-scale buried heterostructures as deterministic, scalable gain media for nanophotonic lasers.

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.

We demonstrate frequency comb generation in a 108 GHz-FSR SiC microresonator using an obliquely polarized pumping. A portion of the pump couples to an orthogonally polarized auxiliary mode for thermal compensation, enabling stable generation of broadband single soliton microcombs.

The demand for advanced photonics technology is increasing rapidly, fueled by the necessity for high‐performance, cost‐effective optical information processing systems extending into the quantum domain. Silicon, benefiting from its mature fabrication processes, stands as an ideal platform. However, its inherent indirect bandgap leads to inefficient light emission. The integration of III‐V materials is essential to overcome this drawback. These materials are recognized for their efficient light emission and superior bandgap engineering, making them indispensable in photonics and beyond. Here, we present the monolithic integration of small‐volume III‐V nano‐heterostructures with silicon via selective area epitaxy in pyramidal openings etched in (100)‐oriented silicon substrate. Precise positioning of the nano‐heterostructures is achieved using electron beam lithography. Atomic resolution imaging and chemical analysis confirm the epitaxial nature of InP growth, revealing well‐defined heterointerfaces. Each structure incorporates an InAsP quantum dot‐like active medium, and the correlation of the growth parameters with the nanoscale structure is analyzed using advanced electron microscopy. Eight‐band k·p calculations demonstrate energy level quantization in three spatial dimensions. Optical characterization shows that heterostructure emission can be engineered to cover the entire telecom wavelength range. These InAsP/InP nano‐heterostructures can serve as gain medium for silicon‐based hybrid nano‐lasers, nano‐LEDs, and quantum light sources in telecom wavelength range.

Silicon nitride (Si3N4), among other materials, is particularly attractive for linear and nonlinear optics because of its ultra-low loss properties, enabling advances in various fields, including narrow linewidth lasers [1], Kerr frequency comb [2], quantum photonics [3], etc. One of the important examples is stimulated Raman scattering. It is an efficient approach to extend the available spectral coverage of conventional laser sources [4], [5], enabling applications including molecular spectroscopy, environmental analysis, and biological detection [6]. Intrapulse Raman scattering is broadband in nature in amorphous materials such as silica and Si3N4, which relates to the vibrational material response of the cubic nonlinearity. This work presents the on-chip continuous-wave (CW) Raman laser generation in Si3N4 platform, which is benefited from the enhanced intracavity power of ultra-high quality factor (Q) microresonators.

We designed a silicon nitride racetrack microresonator that introduces a proper mode coupling for generating single soliton microcomb through manual tuning. With the proposed design, high quality factor is sustained and we demonstrate thermally accessible 30-GHz soliton microcomb. (c) 2025 The Author(s)

Integrated octave-spanning frequency combs are crucial for portable precision metrology, yet existing methods face major hurdles1. Integrated Kerr combs in microresonators struggle with bandwidth and repetition rates incompatible standard RF electronics2. While supercontinuum generation (SCG) in waveguides achieve octave spans, it demands high-peak-power (up to kW) femtosecond pulses, far exceeding capabilities of chip-scale sources (~W, ps)3. This pump mismatch blocks progress towards fully integrated systems. Here, we introduce a new SCG paradigm in highly nonlinear aluminum-gallium-arsenide-on-insulator (AlGaAsOI) waveguides using cascaded four-wave mixing (CFWM) mediated by parametrical amplification. This enables coherent octave-spanning combs driven by watt-level picosecond pulses, drastically reducing requirements and bridging the gap to integrated laser compatibility.

We experimentally demonstrate broadband 30 GHz soliton combs, optimized by a fabricationaware design framework that incorporates the critical loss-dispersion relationship. Using this design principle, we show that over 300 usable lines are achievable in a microcomb-supporting the development of ultra-dense optical transceivers.

The integration of Lithium Niobate (LN) on low-loss, CMOS-compatible SiN platforms combines the high Pockels effect of LN with SiN's low loss and CMOS compatibility, enabling efficient modulation and processing. Micro transfer printing ($\mu$ TP) facilitates the integration of functional materials such as LN, III-V, and BTO, enabling the creation of compact, multifunctional chips. LN-SiN Mach-Zehnder Modulators (MZMs) require long interaction lengths (in the cm range) for low-voltage operation, necessitating $\mu$ TP of em-long LN coupons. These coupons should ideally cover the MZM arms, including signal and ground electrodes $(\sim 100\mu \mathrm{m}$ wide). However, $\mu$ TP of long coupons faces challenges such as limited rotational alignment accuracy, especially if the electrode incorporated on the LN coupon. Additionally, hybrid SiN-LN modulators encounter mode transition loss and reflections at the SiN-LN interface, which are typically mitigated with long tapers. However, tapering LN coupons for $\mu$ TP often causes cracks and fabrication complexities [1]. This work presents design (Fig. 1(a)) and fabrication of LN-SiN modulator with simulated $\mathrm{V}\pi\mathrm{L}=3.6\mathrm{V}$ -cm (Fig. 1(b)) and 3-dB bandwidth of over 100 GHz (Fig. 1(d)). The design features bi-layer SiN waveguides (750 nm and 200 nm thick) for adiabatic optical mode coupling [2], achieving ultra-low transition loss, and minimal reflection without LN tapers thereby alleviating the alignment accuracy requirement for $\mu$ TP [3]. We also present the fabrication of the device, including the high-yield fabrication and $\mu$ TP of LN coupons up to 1 cm long, 100 $\mu\mathrm{m}$ wide.

Dissipative Kerr soliton (DKS) microcombs, known for generating broadband and highly coherent frequency combs in miniature and scalable integrated platforms, have revolutionized various fields. Among integrated nonlinear material platforms, AlGaAs-on-Insulator (AlGaAsOI) stands out due to its ultra-high nonlinearity, enabling efficient frequency comb generation [1]. Accessing the DKS in the red-detuned regime is challenging because of significant thermo-optic instability while tuning the pump across the resonance. AlGaAs exhibits significant thermo-optic coefficient, complicating the soliton formation in AlGaAsOI platform [2]. Although approaches such as cryogenic cooling, high-dispersion design, and dual-pump schemes [3] have been proposed to mitigate thermal instability, they introduce additional complexity or impose limitations on DKS operation.

The interaction between light and matter can be enhanced by spatially concentrating the light field and extending photon dwell time. Plasmonic structures can provide strong light confinement but suffer from ohmic losses. Recent advances in dielectric nanostructures enable strong light localization without metallic losses. However, previous studies primarily focused on minimizing the optical mode volume without adequately addressing light-matter interactions. Here, we demonstrate a nanolaser that colocalizes photons and excited carriers within a dielectric nanobridge. This extreme dielectric confinement of both light and matter yields a subdiffraction-limited mode volume and a subwavelength carrier volume without lateral quantum confinement. We observe a strong correlation between the mode field and carrier distribution, where enhanced mode localization produces stronger carrier confinement. By suppressing carrier surface recombination, this platform not only enables continuous-wave lasing at room temperature but also achieves a substantially reduced lasing threshold. We quantify the intensified interaction with an interaction volume, generalizing mode volume to a broad class of active media.

We leverage dark-soliton microcombs to demonstrate optical arbitrary waveform generation (OAWG) at unprecedented bandwidths of more than 400 GHz. We use the scheme for 16QAM and 32QAM transmission at 400 GBd - a record-high symbol rate for fully coherent QAM signalling. (c) 2025 The Author(s)