Yuqing Jiao

We present a tri-wavelength integrated photonic interferometer for nanometer-resolution displacement sensing in semiconductor metrology. The device integrates large-area waveguide hologram couplers optimized for 635 nm, 780 nm, and 850 nm to illuminate and receive light from a reflective target, forming a Mach–Zehnder interferometer. A novel design method enables scalable intensity control, achieving an average focusing efficiency of −12.8 dB , the highest reported for tri-wavelength couplers, to our knowledge. Interferometric operation was verified at 633 nm and 775 nm. Displacement measurements were demonstrated down to 16 nm, currently limited by the resolution of the external translation stages. Picometer-scale resolution is feasible using commercially available signal processing systems. These results demonstrate a path toward compact, solid-state, high-resolution optical metrology systems.

Heterogenous integration of lasers combining with low-loss dielectric waveguides is a promising approach to realize on-chip lasers with enhanced functionalities such as narrow linewidth, tunability, and stable lasing performance. Visible-wavelength lasers, due to their shorter wavelengths and hence the compact footprint, are particularly vital for emerging applications in quantum computing, biosensing, atomic clocks, and AR/VR displays which demand high-performance laser sources. Despite significant advancements in near-infrared (NIR) III-V lasers, the development of true heterogeneous blue lasers remains limited due to technological challenges associated with InGaN/GaN as the gain material. In this work we report our progress towards the development of a III-nitride heterogenous blue laser on SiN passive photonic platform. We have designed the SiN waveguide geometry suitable for III-nitride to SiN heterogenous integration. Optical coupling is also discussed in detail, and we have designed a fabrication-tolerant coupler, that exhibits very low coupling loss of 0.28 dB over a total length of 266 μm. We also studied the effect of bonding layer thickness and fabrication induced deviations of the taper tip width on the coupling efficiency. We show experiments with GaN and Si wafer-scale bonding to integrate these materials. We propose a novel double-flip fusion bonding technique to transfer GaN epitaxial layer onto a silicon substrate with oxide-oxide fusion bonding to preserve the original growth orientation as on the growth substrate. The proposed process flow can be tailored to different GaN epitaxial growth substrates. Our initial results establish a foundational framework for future development of high-performance heterogeneous blue laser platforms.

Quantum key distribution (QKD) makes use of the principles of quantum mechanics to enable provably secure communication^1,2. One substantial challenge persists in building large-scale QKD networks with many clients over long communication distances³. Although quantum relays continue to pose practical difficulties⁴, existing trusted-node networks^5,6,7,8,9, point-to-multipoint networks^10,11 and wavelength-multiplexed entanglement networks^12,13 encounter issues such as reliance on trusted intermediaries or limited distances. Twin-field quantum key distribution (TF-QKD) provides a compelling architecture that can overcome those issues while enhancing communication distance¹⁴. Although long-distance point-to-point TF-QKD has been achieved^{15,16,17,18,19,20,21}, realizing large-scale networks requires scalable quantum devices. Here we report a proof-of-principle demonstration of an integrated-photonics TF-QKD network with exceptional scalability and reliability. This network includes 20 independent client-side QKD transmitter chips with one server-side optical microcomb chip. The microcomb generates a broad range of ultralow-noise coherent frequency combs with Hz-level linewidths, which serve as seeds and references for all client chips. Each client chip regenerates ultralow-noise light phase-locked to microcombs and prepares quantum keys. We sequentially implement pairwise QKD across 20 client chips through ten wavelength-multiplexed channels, with each surpassing the repeaterless bound at 370 km in spooled fibre, achieving a networking capability (client pairs × communication distance) of 3,700 km. We further demonstrate the wafer-scale reproducibility of both server-side microcomb chips and client-side QKD transmitter chips, together establishing system-level scalability. Combining mass-manufacturability, cost-effectiveness and high scalability of integrated photonics with long-distance quantum communication represents a viable path to large-scale quantum networks.

We present a monolithically integrated indium phosphide photonic chip that provides a broadband, tunable two-tone optical source for terahertz beat-note generation. The device combines a widely tunable sampled-grating (SG) laser with a stable distributed-feedback laser, enabling compact and robust optical operation. To address the multi-parameter bias-control challenge in SG lasers, we develop a fully automated tuning framework that integrates database-assisted initialization, machine-learning-based prediction, and particle swarm optimization (PSO). This approach achieves efficient convergence toward optimal bias conditions, yielding single-mode tuning over 41 nm (1520–1561 nm) with side-mode suppression ratios above 20 dB across the full range and exceeding 30 dB in the 1523–1561 nm region, while maintaining linewidths below 90 kHz. Optical measurements confirm two-tone operation with tunable frequency spacing from 1.02 to 5.93 THz. These results establish a compact, scalable platform for integrated broadband THz sources with strong potential for wireless communications, spectroscopy, and sensing.

The fast-maturing photonic integration technology is calling for a versatile platform that supports both active and passive functions as well as high scalability through component miniaturization. Indium phosphide (InP) has long been recognized for its ability to deliver a comprehensive suite of photonic components. InP membrane technology has emerged as a next-generation solution that could unite the functional completeness with high scalability. This paper describes recent advancements in the InP-membrane-on-Si (IMOS) platform, which supports high-performance passives, polarization and mode handling, native light sources, amplifiers, modulators and detectors, and novel material integration.

Indium–phosphide membrane on silicon is a nanophotonics platform which allows for monolithic integration of sub-micron nanophotonic waveguide circuits with native and efficient amplifiers and lasers. Active devices such as amplifiers have a high topography that requires a thick dielectric layer for planarization and wafer bonding, which poses challenges in thermal dissipation. Herein, we comprehensively analyzed the performance of distributed feedback lasers (DFBs) bonded on Si using a 2 µm-thick benzocyclobutene (BCB) layer, and with and without a 5 µm-thick gold thermal shunt to the substrate for efficient thermal dissipation. The thermal resistance of shunted devices is 176 and 115 K W⁻¹ for 0.5 mm and 0.75 mm lengths, respectively, which is a 2× improvement compared to reference membrane devices with no thermal shunt. This thermal resistance is maintained across various BCB thicknesses up to 30 µm, ensuring the possibility of using such devices for scalable 3D integration on other platforms or with electronics. Moreover, we showed that the thermal resistance value is around 110–120 K W⁻¹ for 0.75 mm-long shunted DFBs having array density values in the range of 40–200 µm, and that the temperature rise at the end of the DFB contact is as low as 1.3 °C at 8 kA cm⁻² driving current. Both of these characteristics demonstrate the density scaling potential of these nanophotonic devices.

InP membrane directly modulated semiconductor lasers (DMLs) with photon-photon resonance (PPR) have a lot of potential to be used in short-range telecommunication systems due to their small footprint, high energy efficiency, and high modulation bandwidth. However, the stability of the S21 response in PPR-based devices is sensitive to precise phase-matching between the lasing mode and PPR mode. We designed, fabricated, measured, and analyzed a C-band DML with active phase-tuning achieved by a thermal phase shifter on top of a long passive waveguide. The phase shifter enables tuning of the PPR frequency in the range of 5 GHz resulting in the PPR peak power enhancement of 16 dB. We study the small-signal responses at different combinations of bias current and phase shifter current and show, that in some cases the phase shifter enables a bandwidth that cannot be achieved by sweeping the bias current. The laser dynamic behavior is simulated and the influence of the most important design and processing parameters on bandwidth is studied in detail.

We present the design, fabrication, and characterization results of a compact, widely tunable laser realized on an indium phosphide membrane-on-silicon (IMOS) platform. The laser features a compact Mach–Zehnder interferometric structure as the wavelength-selective intracavity filter with a footprint of 0.13 mm2. The filter design is optimized to ensure narrow filter transmission and high side-mode-to-main-mode-ratio, enabling single-mode operation for the laser. The high optical confinement on the IMOS platform can support tight waveguide bends. Leveraging this, the laser achieves a short cavity length, further enhancing the single-mode operation. Measurement results indicate a threshold current of 29 mA and a maximum on-chip output power of approximately 3.6 dBm and wall plug efficiency of 1.8%. The side-mode suppression ratio ranges from 30 to 44 dB, with a tuning range spanning 40 nm, from 1555 to 1595 nm. A complete tuning lookup table is generated via an automated setup incorporating a stochastic search algorithm.

Heterogeneous integration helps to maximize the performance of photonics or electronics devices by leveraging the strengths of diverse material platforms within a unified process flow. A promising approach is the 3D integration of InP photonic or electronic membranes to other substrate materials containing photonics or electronics ICs via adhesive bonding. However, wafer-scale spatial distortions arising from the bonding process can compromise fabrication. Herein, we used electron-beam metrology to investigate the distortion of InP membranes resulting from wafer-scale bonding with benzocyclobutene (BCB). We measured both the linear and residual components of distortions across the tested wafers. First, bonding of InP substrate with BCB on various carrier substrates (Si, InP, SiC, and glass) was realized, which unveiled post-bonding membrane expansion factors in the range of ~0-325 ppm and beyond that for the glass carrier. The diversion of these values from theoretical estimations was linked to the adhesive bonding process. Next, we examined the effect of BCB thickness in the ranges of 1-12μm, residual mechanical stress, and the impact of defects on distortions. Using these findings, we experimentally verified that the largest part of distortions can be efficiently pre-compensated to overcome the challenges of multilayer overlay errors in the fabrication of heterogeneously integrated photonic and electronic devices.