100 Gbps PAM4 ultra-thin photodetectors integrated on SOI platform by micro transfer printing.

The integration of compact high-bandwidth III-V active devices in a scalable manner is highly significant for Silicon-on-insulator (SOI) photonic integrated circuits. To address this, we demonstrate the integration of pre-fabricated 21 × 57 µm2 InGaAs photodetector (PD) coupons with a thickness of 675 nm to a 500 nm SOI platform using a direct bonding micro-transfer printing process. The common devices are coupled to the Si waveguides via butt, grating and evanescent coupling schemes with responsivities of 0.13, 0.3 and 0.6 A/W respectively, in line with simulations. The thin device facilitates simplified high-speed connections without the need for an interlayer dielectric. A back-to-back data communication rate of 50 Gb/s is achieved with on-off keying and with post processing of four-level pulse-amplitude modulation (PAM4) 100 Gb/s is realized. Potentially, around 1 million devices per 75 mm InP wafer can be attained. The integration of compact PDs exhibited in this work can be extended to modulators and lasers in the future.

Nonvolatile programmable silicon photonics using an ultralow-loss Sb2Se3 phase change material.

The next generation of silicon-based photonic processors and neural and quantum networks need to be adaptable, reconfigurable, and programmable. Phase change technology offers proven nonvolatile electronic programmability; however, the materials used to date have shown prohibitively high optical losses, which are incompatible with integrated photonic platforms. Here, we demonstrate the capability of the previously unexplored material Sb2Se3 for ultralow-loss programmable silicon photonics. The favorable combination of large refractive index contrast and ultralow losses seen in Sb2Se3 facilitates an unprecedented optical phase control exceeding 10π radians in a Mach-Zehnder interferometer. To demonstrate full control over the flow of light, we introduce nanophotonic digital patterning as a previously unexplored conceptual approach with a footprint orders of magnitude smaller than state-of-the-art interferometer meshes. Our approach enables a wealth of possibilities in high-density reconfiguration of optical functionalities on silicon chip.

High-speed silicon Michelson interferometer modulator and streamlined IMDD PAM-4 transmission of Mach-Zehnder modulators for the 2 µm wavelength band.

We demonstrate high-speed silicon modulators optimized for operating at the wavelength of 2 µm. The Mach-Zehnder interferometer (MZI) carrier-depletion modulator with 2 mm phase shifter has a single-arm modulation efficiency (Vπ ·Lπ) of 2.89 V·cm at 4 V reverse bias. Using a push-pull configuration it operates at a data rate of 25 Gbit/s OOK with an extinction ratio of 6.25 dB. We also proposed a mathematically-analysed streamlined IMDD PAM-4 scheme and successfully demonstrated a 25 Gbit/s datarate PAM-4 with the same 2 mm modulator. A Michelson interferometer carrier-depletion modulator with 0.5 mm phase shift length has also been shown with modulation efficiency (Vπ ·Lπ) of 1.36 V·cm at 4 V reverse bias and data rate of 20 Gbit/s OOK. The Michelson interferometer modulator performs similarly to a Mach-Zehnder modulator with twice the phase shifter length.

Experimental demonstration of an apodized-imaging chip-fiber grating coupler for Si3N4 waveguides.

A silicon nitride waveguide is a promising platform for integrated photonics, particularly due to its low propagation loss compared to other complementary metal-oxide-semiconductor compatible waveguides, including silicon-on-insulator. Input/output coupling in such thin optical waveguides is a key issue for practical implementations. Fiber-to-chip grating couplers in silicon nitride usually exhibit low coupling efficiency because the moderate index contrast leads to weak radiation strengths and poor directionality. Here, we present the first, to the best of our knowledge, experimental demonstration of a recently proposed apodized-imaging fiber-to-chip grating coupler in silicon nitride that images an in-plane waveguide mode to an optical fiber placed at a specific distance above the chip. By employing amplitude and phase apodization, the diffracted optical field of the grating is matched to the fiber mode. High grating directionality is achieved by using staircase grating teeth, which produce a blazing effect. Experimental results demonstrate an apodized-imaging grating coupler with a record coupling efficiency of -1.5 dB and a 3 dB bandwidth of 60 nm in the C-band.