Low-voltage silicon photonics modulator with CMOS-compatible driving for compact quantum key distribution...

Area of Science:

• Quantum Information Science
• Integrated Photonics
• Semiconductor Device Engineering

Background:

• Quantum key distribution (QKD) systems often utilize silicon photonic chips.
• Carrier depletion modulators (CDMs) are common in QKD but require high driving voltages (>5 V) due to low modulation efficiency.
• High operating voltages limit the compactness and energy efficiency of QKD transmitters.

Purpose of the Study:

• To investigate the use of a carrier injection modulator (CIM) for quantum bit encoding in QKD.
• To demonstrate a CIM with significantly lower operating voltages compared to CDMs.
• To confirm the CIM's suitability for compact and energy-efficient QKD transmitters.

Main Methods:

• Structural optimization of a silicon photonic carrier injection modulator (CIM).
• Characterization of the CIM's half-wave voltage and modulation depth.
• Demonstration of intensity and polarization state modulation for quantum bit encoding.

Main Results:

• The optimized CIM achieved a low half-wave voltage of 1.1 V (DC) and 1.28 V (at 100 MHz).
• A high modulation depth exceeding 24 dB was recorded under both DC and 100 MHz conditions.
• Successful demonstrations of intensity and polarization state modulation were performed.

Conclusions:

• Carrier injection modulators (CIMs) offer superior modulation efficiency for QKD.
• Optimized CIMs enable significantly lower operating voltages, compatible with CMOS technology.
• CIMs are a promising technology for developing compact and energy-efficient QKD transmitters.