Juanjuan Lu

The development of large-scale quantum networks requires scalable interconnects operating from cryogenic to ambient temperatures. While conventional electrical interconnects pose thermal management and system complexity challenges, photonic interconnects enable efficient optical modulation and fiber transmission. Here, we present temperature-dependent characterization of a modified uni-traveling carrier photodetector (MUTC-PD) for quantum network applications. The $28~\mu $ m device exhibits stable responsivity (> 0.56 A/W), > 9 GHz bandwidth at–5 V bias, and good linearity from 5 K to 300 K. These robust characteristics identify the MUTC-PD as a promising candidate for scalable quantum photonic interconnects and provide design insights for next-generation cryogenic photodetectors.

On-chip carrier-envelope offset (f_CEO) detection establishs a new benchmark for scalable, power-efficient, self-referenced frequency combs and quantum-enabled photonic systems. In this work, we demonstrate amplification-free f_CEO detection in parabolically width-modulated z-cut thin-film lithium niobate (TFLN) waveguide. With 116 fs pulses at 1560 nm, the device generates more than two octaves broadband supercontinuum generation (SCG) spanning 600nm to beyond 2400 nm, enabling spectral overlap be-tween dispersive wave and second-harmonic generation near 780 nm for robust f–2f self-referencing. Most notably, we achieve the first fully amplification-free f_CEO detection—without optical or electronic amplifiers—directly on-chip, obtaining 34 dB SNR at 100 kHz RBW and 57 dB at 100 Hz RBW, the highest reported to date under such conditions.

Optical spectrometers are indispensable tools across various fields, from chemical and biological sensing to astronomical observations and quantum technologies. However, the integration of spectrometers onto photonic chips has been hindered by the low spectral resolution or large device footprint with complex multiple channel operations. Here, we introduce a chip-integrated spectrometer by leveraging the acoustically-stimulated Brillouin scattering in a hybrid photonic-phononic chip. The Brillouin interaction provides a dynamic reflection grating with a high reflectivity up to 50% and a fast switching time on the microsecond scale, achieving a spectral resolution of 0.56 nm over a 110 nm bandwidth using just a single 1 mm-long straight waveguide. This performance approaches the fundamental limit of resolution for a given device size, validating the potential of the hybrid photonic-phononic device for efficient and dynamically-reconfigurable spectral analysis, and thus opens up the avenues for advanced optical signal processing and sensing applications.

The second harmonic generation (SHG) technology based on quasi-phase matching in periodically poled lithium niobate (PPLN) has reached a high level of maturity. However, the generated second harmonic signal is often overwhelmed by pump light, making direct application challenging. In this paper, we have designed and fabricated, for the first time, to the best of our knowledge, an integrated second harmonic generation device with on-chip wavelength division demultiplexing (WDDM). The device achieves a second harmonic conversion efficiency of 1200% W⁻¹cm⁻² and provides approximately 20 dB attenuation in the telecom C-band near 1550 nm, while introducing about 4 dB insertion loss in the visible light near 775 nm, significantly improving the signal-to-noise ratio. The WDDM section employs a cascaded linearly tapered waveguide design, which offers broadband coupling efficiency. This result shows promise as a foundation for fully integrated quantum photonic chips.

We demonstrate amplification-free carrier-envelope offset (fCEO) detection in parabolically width-modulated z-cut thin-film lithium niobate (TFLN) waveguide that simultaneously engineers dispersion and enhances nonlinear interactions. With 116 fs pulses at 1560 nm, the device generates more than two octaves broadband SCG spanning 600 to beyond 2400 nm, enabling spectral overlap between dispersive waves and second-harmonic generation near 780 nm for robust f-2f self-referencing. Most notably, we achieve the first fully amplification-free, on-chip fCEO detection without optical or electronic amplifiers, obtaining 34 dB SNR at 100 kHz RBW and 57 dB at 100 Hz RBW, the highest reported to date under such conditions. These results establish a new benchmark for scalable, power-efficient, self-referenced frequency combs and quantum-enabled photonic systems.

Thin‐film lithium tantalate (TFLT) has recently emerged as a promising photonic platform for chip‐scale nonlinear optics due to its weaker photorefraction, higher optical damage threshold, broader transparency window, and lower birefringence compared to that of thin‐film lithium niobate. Here we report the first functional second harmonic generator achieved through high‐fidelity poling of z‐cut TFLT waveguides, based on a low‐loss lithium tantalate integrated photonic platform. As a result, quasi‐phase matching is performed between telecom (1,550 nm) and near‐visible (775 nm) wavelengths in a straight waveguide and prompts strong second‐harmonic generation with a normalized efficiency of 229 %/(W·cm ² ). An absolute conversion efficiency of 5.5 % is achieved with a pump power of 700 mW in the waveguide. Such a second‐harmonic generator exhibits stable temperature tunability (−0.44 nm/°C), which is important for applications that require precise frequency alignment such as atomic clocks and quantum frequency conversion.

Thin-film lithium tantalate (TFLT) has recently emerged as a promising photonic platform for chip-scale nonlinear optics due to its weaker photorefraction, higher optical damage threshold, broader transparency window, and lower birefringence compared to that of thin-film lithium niobate. Here we develop an ultralow-loss lithium tantalate integrated photonic platform and report the first functional second harmonic generator based on high-fidelity poling of z-cut TFLT. As a result, quasi-phase matching (QPM) is performed between telecom (1550 nm) and near-visible (775 nm) wavelengths in a straight waveguide and prompts strong second-harmonic generation with a normalized efficiency of 229 %/W/$cm^2$. An absolute conversion efficiency of 5.5 % is achieved with a pump power of 700 mW. Such a second-harmonic generator exhibits stable temperature tunability (-0.44 nm/$^\circ C$) which is important for applications that require precise frequency alignment such as atomic clocks and quantum frequency conversion.