Monolithic 850 nm VCSEL array for quantum key distribution applications via the polarization-based BB84 and...

Area of Science:

• Optics and Photonics
• Quantum Information Science
• Semiconductor Device Physics

Background:

• Quantum cryptography offers physics-based security but relies on complex single-photon sources.
• Decoy state protocols often use weak coherent pulses and external optics for polarization control.
• Existing setups require multiple lasers and optical elements, limiting efficiency and increasing complexity.

Purpose of the Study:

• To develop a compact, integrated laser source for quantum cryptography.
• To simplify sender configurations in polarization-based quantum key distribution (QKD).
• To enhance signal rates and reduce the complexity of QKD systems.

Main Methods:

• Demonstration of a monolithic Vertical-Cavity Surface-Emitting Laser (VCSEL) array.
• Integration of subwavelength gratings within the VCSELs for intrinsic polarization control.
• Precise adjustment of individual VCSEL operating points for wavelength matching.

Main Results:

• Achieved high Orthogonal Polarization Suppression Ratios (OPSRs) up to 19.7 dB (rectilinear) and 19.1 dB (diagonal).
• Demonstrated wavelength matching of all eight VCSELs at 851.2 nm.
• Developed a compact, room-temperature operating VCSEL array eliminating the need for external state preparation.

Conclusions:

• The monolithic VCSEL array provides a simplified and efficient solution for quantum cryptography sender modules.
• Integrated polarization control and wavelength matching enable higher signal rates and practical QKD implementations.
• This technology advances the development of robust and scalable quantum communication systems.