Methods and evaluation of frequency aging in distributed-feedback laser diodes for rubidium atomic clocks

Area of Science:

• Atomic, Molecular, and Optical Physics
• Laser Technology
• Metrology

Background:

• Distributed-feedback laser diodes (DFB-LDs) are crucial for laser-pumped rubidium atomic clocks.
• The stability of the injection current is vital for maintaining atomic resonance and clock accuracy.
• Understanding laser diode aging is essential for predicting clock performance over time.

Purpose of the Study:

• To evaluate the aging characteristics of DFB-LDs operating at 780 nm.
• To quantify the change in injection current needed to reach the rubidium D2 resonance line over time.
• To assess the implications of this aging on rubidium atomic clock performance.

Main Methods:

• DFB-LDs emitting at 780 nm were operated under controlled temperature conditions in both air and vacuum.
• The injection current required to lock onto the rubidium D2 resonance line was monitored over a 9-month period.
• Aging rates were calculated based on the observed current drift.

Main Results:

• A consistent decrease in the required injection current was observed for DFB-LDs.
• The current drift ranged from 50 to 80 μA per month.
• This drift was observed in lasers operated in both air and vacuum environments.

Conclusions:

• The aging of DFB-LDs, characterized by a decreasing current requirement, is a significant factor affecting rubidium atomic clocks.
• This current drift necessitates recalibration or adjustments to maintain clock accuracy.
• The findings provide critical data for estimating the operational lifetime and long-term stability of laser-pumped rubidium atomic clocks.