Hybrid Silicon Microring Lasers Research Articles

Hybrid quantum-dot microring laser on silicon

Future high-performance computers demand highly dynamic data rates, e.g., a few terabytes per second communication bandwidth between switch hubs, and hundreds of gigabytes per second bandwidth between nodes and hubs, in order to overcome the challenges to rapidly growing traffic. Integrated photonic interconnect on silicon is believed to be one of the best solutions for low-cost, energy efficient, and high-speed data communications because of its fundamental advantages in high-volume throughput and dense integration. Applied with signal multiplexing techniques, e.g., wavelength division multiplexing (WDM), large bandwidth data links have been proved to be achievable on silicon. In such a system, an on-chip, robust, low-power consumption laser source is the key component as well as one of the fundamental limits to the silicon platform. In this work, we report the first hybrid silicon microring lasers with quantum-dot (QD) gain material to show great potential for uncooled, highly energy efficient, and isolator-free operation. The hybrid silicon QD lasers have a microring cavity with a 50 μm diameter that incorporates InAs/GaAs QD gain material at a 1.3 μm emission wavelength. The threshold current is as low as 0.7 mA under continuous wave (CW) operation at room temperature, and the laser operates at stage temperatures of up to 70°C. We demonstrate, to the best of our knowledge, a hybrid QD laser with non-return-to-zero (NRZ) communication at a record-high direct modulation rate of 15 Gb/s with energy efficiency of 1.2 pJ/bit. We believe this work shows huge benefits from superior QD lasing material and hybrid photonic integration not only for data communications but also optical memory and many other emerging applications.

Teardrop Reflector-Assisted Unidirectional Hybrid Silicon Microring Lasers

We study directional bistability in hybrid silicon microring lasers and demonstrate a unidirectional laser. Unidirectional emission is achieved by integrating a passive reflector that feeds laser emission back into the laser cavity to introduce an extra unidirectional gain. We show that the length of the passive reflector is a critical parameter in determining the lasing behavior.

Low Threshold Electrically-Pumped Hybrid Silicon Microring Lasers

We report on significantly improved performance of a compact hybrid silicon microring lasers obtained by selectively reducing the volume of active region. This is done by appropriately undercutting the multiple quantum well (MQW) region to force carriers to flow toward the outer edge of the microring for better gain/optical mode overlap. We observe a reduction of the threshold of over 20% and up to 80% output power enhancement. These are primarily due to the improved injection efficiency. We developed a diode laser model that includes nonradiative recombination. The model and the experimental results highlight the benefits, as well as the negative effects from excessive undercutting, including lower MQW confinement, higher modal loss, and higher thermal impedance. A design rule for MQW undercutting is, therefore, provided.

Optimization of Hybrid Silicon Microring Lasers

In this paper, we review the recent optimization work in hybrid silicon microring lasers. Device structure and fabrication procedures are discussed first, followed by two major improvements in carrier injection and thermal management. A simple, well-controlled quantum well undercut leads to about 20% enhancement of injection efficiency. A silicon-on-diamond (SOD) substrate is demonstrated to fundamentally solve the device heating issue for silicon-on-insulator (SOI)-based active devices. SOD rib waveguides show low propagation loss of 0.74 dB/cm, which is 0.2 dB/cm higher than SOI counterparts. More than 22× reduction of device heating in hybrid silicon microring lasers is projected by simulations.

Recent progress in lasers on silicon

Silicon lasers have long been a goal for semiconductor scientists. This Progress Article reviews the most recent developments in this field, including silicon Raman lasers, the first germanium-on-silicon lasers operating at room temperature, and hybrid silicon microring and microdisk lasers. Challenges and opportunities for the present approaches are also discussed.

Electrically-pumped compact hybrid silicon microring lasers for optical interconnects

We demonstrate an electrically-pumped hybrid silicon microring laser fabricated by a self-aligned process. The compact structure (D = 50 microm) and small electrical and optical losses result in lasing threshold as low as 5.4 mA and up to 65 degrees C operation temperature in continuous-wave (cw) mode. The spectrum is single mode with large extinction ratio and small linewidth observed. Application as on-chip optical interconnects is discussed from a system perspective.