Linewidth reduction of a broad-area laser diode array in a compound external cavity

Area of Science:

• Optics and Photonics
• Semiconductor Lasers
• Laser Diode Arrays

Background:

• Broad area laser diodes often exhibit inhomogeneous spectral distribution due to manufacturing imperfections like the 'smile' effect.
• Narrowing the spectral linewidth is crucial for applications requiring high spectral purity.

Purpose of the Study:

• To design and implement a compound external cavity for homogeneous spectrum distribution.
• To narrow the spectral linewidth of a broad area laser diode array.

Main Methods:

• A compound external cavity integrating an optical coupler and a Littrow external cavity with a fast-axis telescope was developed.
• The telescope corrects for spectral inhomogeneity caused by the 'smile' effect.
• The optical coupler enhances transverse coupling between laser emitters.

Main Results:

• The 'smile' effect-induced spectral inhomogeneity was significantly reduced.
• Transverse coupling was enhanced, further improving spectral homogeneity across the array.
• A 49-emitter laser array achieved a spectral linewidth of 0.1 nm at 12.5 W output power.

Conclusions:

• The compound external cavity effectively achieves homogeneous spectrum distribution in laser diode arrays.
• This design successfully narrows the spectral linewidth of the entire array.
• The implemented system demonstrates a significant advancement in laser diode array performance.