1-MHz linewidth VCSEL enabled by monolithically integrated passive cavity for high-stability chip-scale atomic clocks

Area of Science:

• Photonics and Quantum Technologies
• Laser Physics and Engineering

Background:

• Conventional vertical-cavity surface-emitting lasers (VCSELs) have limitations for precision applications due to short cavity lengths and spontaneous emission, leading to broad linewidths.
• Narrow-linewidth lasers are crucial for chip-scale atomic clocks and quantum sensors, but achieving this in compact VCSELs remains a challenge.

Purpose of the Study:

• To demonstrate a monolithically integrated VCSEL with intrinsic linewidth compression for enhanced frequency stability.
• To develop a VCSEL architecture suitable for next-generation quantum-enabled frequency references and sensing platforms.

Main Methods:

• Designed and fabricated a VCSEL with an adjacent passive cavity to extend photon lifetime and suppress unwanted modes.
• Characterized the VCSEL's optical performance, including linewidth, single-mode operation, side-mode suppression ratio (SMSR), and polarization suppression ratio (OPSR).
• Integrated the VCSEL into a Cesium vapor-cell atomic clock to evaluate its performance in a real-world application.

Main Results:

• Achieved intrinsic linewidth compression to approximately 1 MHz at the Cesium D1 line (894.6 nm) without external feedback.
• Demonstrated robust single-mode operation with SMSR > 35 dB and OPSR > 25 dB over a wide range of current and temperature.
• Observed a beam divergence of approximately 7°.
• Integrated VCSEL enabled a Cesium atomic clock frequency stability of 1.89 × 10^-12 τ^-1/2.

Conclusions:

• The novel VCSEL architecture with an embedded passive cavity successfully achieves significant linewidth reduction.
• The demonstrated VCSEL is a compact, scalable, and high-performance solution for chip-scale atomic clocks and quantum sensors.
• This technology paves the way for next-generation portable and robust quantum-enabled devices.