High-Efficiency and Polarization-Independent Waveguide-Integrated Graphene Plasmonic Photodetectors Operating at 2 μm

As the operating wavelength of silicon photonics extends from near-infrared to mid-infrared, today's photonic-integrated circuit calls for high-performance waveguide-integrated mid-infrared photodetectors. A plasmonic-enhanced graphene photodetector (GPD) offers a promising way and has brought about widespread attention. However, the reported devices always suffer from serious metallic absorption loss and polarization-sensitive photoelectric response. Here, we propose and demonstrate two types of plasmonic GPDs operating at a 2 μm band with ultralow metallic loss and polarization-independent photodetection. Through a low-loss periodic metallic nanostructure with a deep-subwavelength cycle, a high-efficiency GPD enabled by Bloch surface plasmon mode is obtained, exhibiting a responsivity of 122 mA/W and bandwidth >14 GHz (setup-limited). A polarization-independent GPD is also realized utilizing metallic dual-strips on top of the waveguides, which shows similar responsivity for transverse electric (TE) and transverse magnetic (TM) modes (84 and 76 mA/W, respectively). We believe that these GPDs hold great potential for integrated ultrafast, highly efficient, and polarization-independent photodetection and pave the way for the practical application of graphene-based optoelectronics devices in the future.