Yu Zhang

Thermo-optic phase shifters are cornerstones in large-scale silicon photonic systems, yet their practical deployment is hindered by a persistent trade-off between power efficiency and compact broadband operation. Here, we break this trade-off using an artificial-gauge-field (AGF) design that permits dense waveguide folding without incurring crosstalk penalties—a key enabler for high-density photonic integration. Fabricated on a standard 220-nm SOI platform, our devices achieve π -phase-shift powers of 3.4 mW (7-fold) and 4.2 mW (5-fold) within a footprint of only 200 × 10 μm ² . Across the S + C + L band (1480–1600 nm), the phase shifters maintain >15 dB extinction ratio with flat tuning response, ensuring wavelength-independent operation for multi-band systems. Moreover, devices tolerate ±20 nm fabrication variations without performance degradation, demonstrating CMOS-compatible manufacturability.

Free-space optical (FSO) communication offers high capacity, license-free spectrum, and immunity to electromagnetic interference, making it a promising solution for future wireless links. However, practical deployment of FSO systems remains challenged by issues of link security and reliable transmission under atmospheric turbulence. In this work, we investigate the use of nonseparability encoding based on vectorial structured light as a turbulence-resilient and secure transmission approach. Through simulations and experiments, we compare multi-level nonseparability encoding with conventional amplitude modulation under various turbulence strengths and eavesdropping scenarios. The results demonstrate that vectorial structured light exhibits inherent security advantages, imposing higher optical signal-to-noise ratio penalties on eavesdroppers and making information recovery from partial interception significantly more difficult. These findings confirm the potential of nonseparability-based encoding for enhancing both security and robustness in FSO communication systems.

The significant birefringence in 220 nm silicon-on-insulator (SOI) silicon waveguides makes polarization diversity essential in silicon photonic integrated circuits. To address this, we propose a broadband polarization splitter-rotator (PSR) based on a silicon-nitride-on-silicon (SiN-on-SOI) hybrid integration platform. The device consists of a polarization rotator (PR) unit and an asymmetrical directional coupler (ADC). The PR unit is formed by a double-layer silicon taper coupled with a single-layer silicon nitride taper, while the ADC is implemented using a shallow-etched ridge waveguide. During operation, the TM₀ mode is adiabatically converted to the TE₁ mode, which is then coupled via the ADC into the narrow waveguide, propagating as the TE₀ mode. Meanwhile, the input TE₀ mode passes through the original waveguide without conversion. Through systematic optimization of the width parameters in the three-layer taper structure, efficient mode mixing is achieved across the entire 1260–1675 nm band, resulting in excellent broadband performance. Theoretical analysis indicates that the PSR operates effectively over the full optical communication band, with an insertion loss (IL) below 0.34 dB and an extinction ratio (ER) exceeding 17 dB. Experimental results demonstrate a 1dB bandwidth of 190 nm and an ER greater than 14.5 dB, representing the widest operational bandwidth reported for a silicon PSR to date. Furthermore, a comprehensive fabrication tolerance analysis reveals the device's high robustness to silicon nitride dimensional variations, while identifying the silicon slab thickness as the critical parameter for maintaining high extinction ratios. The device is fully compatible with standard silicon photonic foundry processes and holds strong potential for large-scale production.

L-Band on-chip heterogeneous integration lasers and semiconductor optical amplifiers (SOA) are important silicon photonics components in many applications such as light detection and ranging (LiDAR) and optical communications in data center interconnects. In this work, we demonstrate an L-band widely tunable laser and a high gain SOA on a III-V/Si integration platform. The laser gives a tuning range of 43 nm with side-mode suppression ratio > 45 dB, and output power of 9.15 mW, while the SOA shows a small-signal gain of 21 dB and a saturation output power of 13 dBm. The SOA and laser share the same III-V epitaxial wafer structure and a common fabrication process, which benefits the high-density components integration and reduces costs greatly in many applications.

The rising demand for high-bandwidth, energy-efficient interconnects in artificial intelligence (AI) and cloud-scale data centers has driven the development of Co-Packaged Optics (CPO) and optical input/out (I/O) technologies. These architectures require compact, high-speed modulators with dense wavelength-division multiplexing (DWDM) capability. Nevertheless, conventional micro-ring modulators (MRMs) suffer from the constraints of free spectral range (FSR) and extinction ratio (ER). Here we propose a slot waveguide-assisted asymmetric add-drop micro-ring modulator with a view to simultaneously realizing a large FSR and a high ER. Our design achieves an ER of 33 dB—approaching critical coupling and exceeds the 15 dB typical of single-bus configurations. The device features a 4 μm radius and operates in the C-band with a 22.5 nm FSR, supporting high channel density. Under a –6 V bias, it demonstrates a 95 GHz electro-optic bandwidth at 0.4 nm detuning, extended to 110 GHz via optical peaking at 0.5 nm. At 110 Gb/s non-return-to zero (NRZ) modulation, the MRM achieves a signal-to-noise ratio (SNR) of 2.70 and consumes only ∼7.19 fJ/bit at 2.2 V drive. The combination of compact footprint, high bandwidth, and low power consumption makes this device well suited for integration into DWDM-based optical I/O and CPO systems, offering a scalable path toward multi-terabit optical interconnects.

Optical frequency combs (OFCs) have emerged as versatile tools for diverse applications. In this work, we demonstrated a high quality factor (Q) silicon nitride ( $\text{Si}_{\mathbf {3}}$ $\text{N}_{\mathbf {4}}$ ) micro-ring resonator (MRR) fabricated via a stress-release pre-etching process for large-scale integrated $\text{Si}_{\mathbf {3}}$ $\text{N}_{\mathbf {4}}$ photonic integrated circuits (PICs). By pre-etching deep trenches prior to $\text{Si}_{\mathbf {3}}$ $\text{N}_{\mathbf {4}}$ deposition, crack propagation is suppressed, enabling a single-step deposition of stoichiometric $\text{Si}_{\mathbf {3}}$ $\text{N}_{\mathbf {4}}$ films with thicknesses exceeding 800 nm. The fabricated waveguides exhibit a propagation loss of ~0.1 dB/cm, measured via the cutback method. Using I-line stepper lithography, we design anomalous-dispersion MRR with width gradient, achieving an intrinsic Q-value of $2.83\times 10 ^{\mathbf {6}}$ . Further, modulation-instability (MI) frequency combs are generated through rapid laser tuning.

Waveguide grating antennas (WGAs) are key transmitting components for integrated optical phased arrays (OPAs). However, the typical WGAs in 220 nm silicon-on-insulator (SOI) platform suffer from high perturbation loss for TE₀ mode. In this letter, we experimentally demonstrated two ultra-long silicon multimode WGAs by TE₁ and TM₁ modes. We also fabricated two high-performance mode (de)multiplexers for generating TE₁ and TM₁ modes input. The optimized TE₁-WGA and TM₁-WGA losses are 3.58 dB/mm and 1.10 dB/mm at 1550 nm wavelength, while the measured losses are as low as 3.22 dB/mm and 1.59 dB/mm. The corresponding beam divergences with 3 mm antenna lengths are 0.0286° and 0.0267° at 1550 nm wavelength, respectively. To the best of our knowledge, this is the first demonstration of high-order mode multiplexed WGAs.

A high modulation efficiency depletion mode silicon micro-ring modulator with NRZ modulation rate up to 128 Gb/s has been demonstrated. The MRM utilizes a meandering doping structure to enhance the overlap factor between the carrier variation region and light field to improve modulation efficiency at 33.5 pm/V, ∼38% improvement from a conventional doping design. It has a quality factor of ∼5200, a high electro-optical bandwidth above 67 GHz, and can reach 110 GHz under the optical peaking effect. The drive voltage of the MRM loading a 128 Gb/s signal is 1.36 V; the corresponding power consumption is ∼8.54 fJ/bit.

An ultra compact add-drop silicon micro-ring modulator with free spectrum range of 22.9 nm and modulation efficiency of 30.4 pm/V has been demonstrated. The electrooptical bandwidth of the modulator is greater than 90 GHz and can reach 110 GHz under the optical peaking effect. The modulator can achieve 128 Gb/s NRZ signal transmission at 1.36 V drive voltage with an extinction ratio of 3.28 dB, the corresponding power consumption is $\sim$4.93 fJ/bit. The calculated back-to-back bit error ratio (BER) of 128 Gb/s NRZ signal is 2.1×10^-3 at -3 dBm receiving optical power lower than harddecision forward error correction (HD-FEC) assumption threshold and 1.5×10^-2 at -5.5 dBm receiving optical power lower than soft-decision forward error correction (SD-FEC) assumption threshold.