Ge-on-insulator Platform for Mid-infrared Photonic Integrated Circuits

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Ge-on-insulator Platform for Mid-infrared Photonic Integrated Circuits.pdf

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The paper "Ge-on-insulator Platform for Mid-infrared Photonic Integrated Circuits" by Mitsuru Takenaka et al. explores the development of a germanium-on-insulator (GeOI) platform for mid-infrared (MIR) photonic integrated circuits (PICs).

Key Highlights:

1. Motivation & Background:

• Mid-infrared (MIR) wavelengths are crucial for optical communication, sensing, and quantum information applications.

• Silicon (Si) photonics is widely used for near-infrared (NIR) applications, but its transparency range is limited to 1.2–8 μm, restricting its use in MIR.

• Germanium (Ge) is fully transparent in the 2–14 μm range, making it a promising alternative for MIR PICs.

2. Ge-on-Insulator (GeOI) Platform Development:

• The paper introduces a GeOI platform where a thin Ge membrane is bonded onto a buried oxide (BOX) layer, enabling strong optical confinement.

• Wafer bonding & Smart-cut techniques were used to fabricate GeOI wafers.

3. Key Devices Developed on GeOI:

• Low-loss waveguides: Fabricated using optimized hydrogen ion implantation and annealing processes to minimize defects.

• Thermo-optic (TO) phase shifters: Leveraging Ge’s higher thermo-optic coefficient (compared to Si) for efficient modulation.

• Optical modulators: Utilizing free-carrier absorption in Ge for intensity modulation in the MIR range.

• Photodetectors (PDs): A sub-bandgap Ge PD was developed, achieving high responsivity for MIR detection.

4. Performance & Applications:

• Demonstrated compact and efficient PICs using GeOI for MIR optical sensing and communication.

• The platform allows the integration of both passive and active components (waveguides, modulators, detectors) with low loss and high efficiency.

Conclusion:

The GeOI platform provides a highly integrated and scalable solution for MIR photonics, leveraging existing silicon photonics technologies. The work demonstrates various essential photonic devices on GeOI, paving the way for next-generation MIR PICs for applications in sensing, communication, and computing.

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