Analysis of broadly tunable coupled-cavity semiconductor lasers

Area of Science:

• Semiconductor diode lasers
• Quantum well physics
• Optical engineering

Background:

• Broadly tunable lasers are crucial for applications like optical coherence tomography (OCT).
• Asymmetric multiple quantum well (AMQW) coupled-cavity lasers offer wide tuning ranges but often suffer from multimode operation.
• Controlling spectral properties is essential for optimizing laser performance in specific applications.

Purpose of the Study:

• To investigate the spectral properties of AMQW coupled-cavity lasers.
• To understand mode selection mechanisms in these lasers.
• To evaluate the impact of a short external cavity (SXC) on laser performance, particularly for OCT.

Main Methods:

• Development of a traveling wave model to analyze mode selection.
• Experimental measurement of spectral properties of AMQW coupled-cavity lasers.
• Integration and testing of an SXC with the AMQW lasers.
• Evaluation in a synthesized optical coherence tomography setup.

Main Results:

• A traveling wave model successfully explained the observed mode selection.
• The addition of a weak, short external cavity (SXC) enabled single-frequency operation across a ~100 nm tuning range.
• The SXC reduced the coherence length of the AMQW lasers.
• Enhanced performance of the AMQW lasers in OCT applications was demonstrated.

Conclusions:

• A short external cavity is an effective method for achieving single-frequency operation in broadly tunable AMQW lasers.
• Reducing coherence length via SXC significantly enhances AMQW laser suitability for optical coherence tomography.
• The findings provide a pathway for optimizing tunable semiconductor lasers for advanced optical sensing.