High-temperature operating 894.6nm-VCSELs with extremely low threshold for Cs-based chip scale atomic clocks.

Area of Science:

• Optoelectronics
• Laser Physics
• Atomic Clocks

Background:

• Vertical-cavity surface-emitting lasers (VCSELs) are crucial components in chip-scale atomic clocks.
• High operating temperatures often increase threshold current in VCSELs, limiting their application.
• Optimizing active region structures and gain-cavity detuning is key to improving VCSEL performance.

Purpose of the Study:

• To design and fabricate 894.6nm VCSELs with exceptionally low threshold currents at elevated temperatures.
• To investigate a novel design method for reducing transparent current density in VCSELs.
• To suppress the increase in threshold current with rising temperatures for enhanced device stability.

Main Methods:

• Proposed a new design methodology analyzing threshold gain and carrier density for active regions.
• Implemented large gain-cavity detuning in VCSEL design to mitigate temperature-induced threshold current increase.
• Fabricated 894.6nm VCSELs utilizing the developed design principles.

Main Results:

• Achieved a minimum threshold current of 0.23mA at 70 °C by detuning the gain-cavity mode to -11nm.
• Demonstrated stable operation at 110 °C for the 894.6nm emission wavelength.
• Obtained a single mode suppression ratio (SMSR) exceeding 25dB with a threshold current of 0.32mA at the operating temperature.

Conclusions:

• The proposed design method effectively reduces transparent current density, leading to lower threshold currents.
• Large gain-cavity detuning successfully suppresses threshold current increase at high temperatures.
• The fabricated VCSELs are suitable for chip-scale atomic clock applications due to their low threshold and stable high-temperature operation.