Ultralow-power, High-speed Integrated Si Photonic Switch Enabled by III–V/Si Hybrid MOS Optical Phase Shifters

This paper presents an integrated Si photonic switch based on III–V/Si hybrid MOS optical phase shifters, aiming to achieve ultralow-power, high-speed switching for next-generation data centers. The proposed switch exhibits sub-femtowatt static power consumption and nanosecond-order switching speed, addressing the challenges of high data traffic and energy efficiency in data center interconnects.

Key Contributions:

1. Motivation and Challenges:

• Conventional electrical switches used in data centers suffer from optical-electrical-optical (O-E-O) conversion, which leads to high energy dissipation and latency. Optical switches, which bypass O-E-O conversion, are needed for faster, more energy-efficient signal routing.

• Traditional Si photonic switches using thermo-optic (TO) phase shifters face high power consumption, slow switching speeds, and thermal crosstalk. The paper addresses these challenges by introducing III–V/Si hybrid MOS phase shifters.

2. Hybrid MOS Phase Shifters:

• The III–V/Si hybrid MOS optical phase shifters are based on an InGaAsP/Si structure, where an InGaAsP layer is bonded to SiO₂-embedded Si waveguides. These phase shifters enable efficient optical phase modulation via the plasma dispersion effect and band-filling effect in InGaAsP.

• The key advantage of this approach is the ultralow power consumption of the phase shifters, which are over 10¹⁰ times lower than traditional thermo-optic phase shifters due to minimal gate leakage current.

3. Design and Fabrication:

• The photonic switch is based on a Clements configuration, which allows for arbitrary unitary transformations of input signals. The switch is fabricated using 300mm wafer-scale CMOS-compatible techniques, where III-V epitaxial layers are bonded onto Si waveguides and patterned to create phase shifters.

• InGaAsP/Si hybrid MOS phase shifters were fabricated using wet etching for the InGaAsP region, followed by the deposition of SiO₂ cladding and metal contacts (Au/Ni) for electrical access.

4. Experimental Results:

• The insertion loss of the optical tapers was measured to be 0.19 dB/taper, with the modulation efficiency of the phase shifters reaching 0.13 Vcm and an optical attenuation of 0.22 dB at a π phase shift.

• The switching speed was characterized using a Mach-Zehnder Interferometer (MZI) setup, demonstrating a rise time of 4.73 ns and a fall time of 4.78 ns, achieving nanosecond-order switching.

• The total static power consumption of the switch was found to be 352 fW at a gate voltage of 3 V, indicating ultralow power consumption for the entire switch.

5. Switching Performance:

• The I-V characteristics of the phase shifters were measured, and the total static power consumption was dominated by the worst-case phase shifter. The device showed a low leakage current and minimal power dissipation, making it highly energy-efficient.

• Bit error rate (BER) measurements with a 10 Gbps NRZ signal demonstrated a BER of < 10⁻⁹ at an average received power of −30.5 dBm, confirming the suitability of the switch for high-speed data transmission.

6. Comparison and Future Work:

• The performance of the proposed Si photonic switch was compared with other types of switches (e.g., TO, MEMS, Si PIN switches). The III–V/Si hybrid MOS phase shifter-based switch showed significantly lower power consumption and faster switching compared to other technologies, making it a promising solution for high-speed, energy-efficient optical switching.

• Future work includes optimizing the fabrication process to improve static power consumption and switching speed, as well as extending the technology to enable scalable, high-resolution optical switching architectures for AI data centers.

Conclusion:

This paper demonstrates a breakthrough in integrated Si photonic switches using III–V/Si hybrid MOS phase shifters, achieving ultralow power consumption and fast switching speeds. The proposed switch has significant potential for use in next-generation data centers, providing a scalable, energy-efficient solution for high-speed optical switching, particularly for AI applications and high-throughput data interconnects.