Jia Xu Brian Sia

Photonic isolation is an essential on-chip function needed to stabilize laser operation and prevent cross-talk between different components within a communication system. Monolithically integrated isolator designs incorporate magneto-optical cladding consisting of doped yttrium iron garnet (YIG), such as cerium-doped YIG (Ce:YIG) and bismuth-doped YIG (Bi:YIG), where a YIG seedlayer is required prior to the deposition and subsequent crystallization of doped YIG. This adversely impacts isolator performance through reduced mode overlap with the doped YIG layer. Furthermore, the Faraday rotations of YIG and Ce:YIG have opposing signs such that they partially cancel out. This work demonstrates a seedlayer-free, monolithic nonreciprocal photonic platform based on an alternative garnet formulation, bismuth-doped terbium iron garnet (Bi:TbIG). We further realize on-chip integration of electromagnets to obviate the requirements of external magnets. An isolator based on the asymmetric Mach-Zehnder interferometer (MZI) architecture is implemented, which records a π nonreciprocal phase shift with a power consumption of 52 mW. Optical isolation as high as 24 dB is achieved.

Optical phase modulators are critical components in integrated photonics, but conventional designs suffer from a trade-off between modulation efficiency and optical loss. Two-dimensional materials like graphene offer strong electro-optic effects, yet their high optical absorption at telecom wavelengths leads to significant insertion losses. Although monolayer transition metal dichalcogenides (TMDs) provide exceptional telecom-band transparency for low-loss electro-refractive response, their practical implementation in phase modulators requires top electrodes to enable vertical electric field tuning, which typically introduces parasitic absorption. Here, we address this challenge by developing hybrid tungsten oxyselenide/graphene (TOS/Gr) electrodes that minimize optical loss while enabling efficient phase modulation in TMD-based devices. The UV-ozone-converted TOS (from WSe ₂ ) acts as a heavy p-type dopant for graphene, making the graphene transparent in the NIR region while enhancing its conductivity. Our complete device integrates a hybrid TOS/graphene transparent electrode with a hexagonal boron nitride dielectric spacer and monolayer WS ₂ electro-optic material on a SiN microring platform. This achieves a high modulation efficiency of 0.202 V·cm while maintaining an exceptionally low extinction ratio change of just 0.08 dB, demonstrating superior performance compared to modulators employing conventional electrodes. Our breakthrough in near-lossless phase modulation opens new possibilities for energy-efficient optical communications, photonic computing, and fault-tolerant quantum networks.

Quantum cascade lasers (QCLs) are essential for a wide range of mid-infrared (mid-IR) applications. Achieving wavelength beam combining (WBC) of QCLs on a chip scale is highly desirable for power scaling and/or broadband emission multi-wavelength output while maintaining a single output beam. We propose a straightforward architecture that monolithically integrates five distributed feedback (DFB) QCLs with an arrayed waveguide grating (AWG), using III–V semiconductor waveguides. The AWG channel wavelengths are carefully designed to align with the corresponding DFB emissions. An amplifier is also incorporated at the output to boost the total power. After the deposition of anti-reflection coatings on the output facet, the best-performing laser element achieved a peak power of 3 W under pulsed operation, with at least 1.75 W from the other channels. These results mark a significant step toward the realization of on-chip high-power WBC QCLs.

We observed tunable characteristics of optical frequency combs (OFCs) generated from InGaAs/GaAs double quantum wells (DQWs) asymmetric waveguide two-section mode-locked lasers (TS-MLLs). This involves an asymmetric waveguide mode-locked semiconductor laser (AWML-SL) operating at a center wavelength of net modal gain of approximately 1.06 µm, which indicates a stable pulse shape, with the power-current(P-I) characteristic curve revealing a small difference between forward and reverse drive currents in the gain region. Under different operating conditions, the laser exhibits the characteristics of OFCs. And the pulse interval in the timing and the peak interval in the frequency domain show a periodic alternating change trend with the increase in the gain current. This tunable characteristic is reported for the first time. The study demonstrates the feasibility of generating tunable optical combs using a monolithic integrated two-section mode-locked semiconductor laser (MI-TS-MLL). This has important reference value for the application of OFCs generated from MI-TS-MLLs or integrated optical chips.

Chalcogenide optical phase change materials (PCMs) have garnered significant interest for their growing applications in programmable photonics, optical analog computing, active metasurfaces, and beyond. Limited endurance or cycling lifetime is however increasingly becoming a bottleneck toward their practical deployment for these applications. To address this issue, a systematic study elucidating the cycling failure mechanisms of Ge ₂ Sb ₂ Se ₄ Te (GSST) is performed, a common optical PCM tailored for infrared photonic applications, in an electrothermal switching configuration commensurate with their applications in on‐chip photonic devices. Further a set of design rules building on insights into the failure mechanisms is proposed, and successfully implemented them to boost the endurance of the Ge ₂ Sb ₂ Se ₄ Te (GSST) device to over 67 000 cycles.

An optoelectronic oscillator (OEO) system is built up with a high-speed silicon microring modulator. The modulator is based on a p-n doped ring resonator with a radius of 10 μm. Its electro-optic (EO) 3 dB bandwidth is ∼31.7 GHz, which makes it suitable for generating multi-GHz radio frequency signals. By using this modulator, one of the essential components of an OEO, the EO converter, has been dramatically miniaturized. At the same time, assisted by the ring resonator, the phase noise of the generated 10 GHz signal (nearly −90 dBc/Hz at 10 kHz offset) is not compromised compared to other integrated OEOs with mm footprint modulators. This is an important step toward a compact, scalable, and fully integrated silicon photonics-based OEO system together with our existing integrated light sources and photodetectors.

Ferrimagnetic iron garnets enable magnetic and magneto‐optical functionality in silicon photonics and electronics. However, garnets require high‐temperature processing for crystallization which can degrade other devices on the wafer. Here bismuth‐substituted yttrium and terbium iron garnet (Bi‐YIG and Bi‐TbIG) films are demonstrated with good magneto‐optical performance and perpendicular magnetic anisotropy (PMA) crystallized by a microheater built on a Si chip or by rapid thermal annealing. The Bi‐TbIG film crystallizes on Si at 873 K without a seed layer and exhibits good magneto‐optical properties with Faraday rotation (FR) of −1700 deg cm⁻¹. The Bi‐YIG film also crystallizes on Si and fused SiO₂ at 873 K without a seed layer. Rapidly cooled films exhibit PMA due to the tensile stress caused by the thermal expansion mismatch with the substrates, increasing the magnetoelastic anisotropy by 4 kJ m⁻³ versus slow‐cooled films. Annealing in the air for 15 s using the microheater yields fully crystallized Bi‐TbIG on the Si chip.

Silicon photonics, compatible with large-scale silicon manufacturing, is a disruptive photonic platform that has indicated significant implications in industry and research areas (e.g., quantum, neuromorphic computing, LiDAR). Cutting-edge applications such as high-capacity coherent optical communication and heterodyne LiDAR have escalated the demand for integrated narrow-linewidth laser sources. To that effect, this work seeks to address this requirement through the development of a high-performance hybrid III-V/silicon laser. The developed integrated laser utilizes a single microring resonator (MRR), demonstrating single-mode operation with a side mode suppression ratio (SMSR) exceeding 45 dB, with laser output power as high as 16.4 mW. Moving away from current hybrid/heterogeneous laser architectures that necessitate multiple complex controls, the developed laser architecture requires only two control parameters. Importantly, this serves to streamline industrial adoption by reducing the complexity involved in characterizing these lasers, at-scale. Through the succinct structure and control framework, a narrow laser linewidth of 2.79 kHz and low relative intensity noise (RIN) of -135 dB/Hz are achieved. Furthermore, optical data transmission at 12.5 Gb/s is demonstrated where a signal-to-noise ratio (SNR) of 10 dB is measured.

Silicon photonics, compatible with large-scale silicon manufacturing, is a disruptive photonic platform that has indicated significant implications in industry and research areas (e.g., quantum, neuromorphic computing, LiDAR). Cutting-edge applications such as high-capacity coherent optical communication and heterodyne LiDAR have escalated the demand for integrated narrow-linewidth laser sources. To that effect, this work seeks to address this requirement through the development of a high-performance hybrid III-V/silicon laser. The developed integrated laser, utilizes a single microring resonator (MRR), demonstrating single-mode operation with a side mode suppression ratio (SMSR) exceeding 40 dB, with laser output power as high as 16.4 mW. Moving away from current hybrid/heterogeneous laser architectures that necessitate multiple complex control, the developed laser architecture requires only two control parameters. Importantly, this serves to streamline industrial adoption by reducing the complexity involved in characterizing these lasers, at-scale. Through the succinct structure and control framework, a narrow laser linewidth of 2.79 kHz and low relative intensity noise (RIN) of -135 dB/Hz are achieved. Furthermore, optical data transmission at 12.5 Gb/s is demonstrated where a signal-to-noise ratio (SNR) of 10 dB is measured.