Blue GaN-based DFB laser diode with sub-MHz linewidth.

Area of Science:

• Optoelectronics
• Semiconductor Lasers
• Photonics

Background:

• Distributed feedback (DFB) laser diodes are crucial narrow-band light sources for photonics.
• Short-wavelength Gallium Nitride (GaN)-based DFBs typically exhibit poor or unreported linewidths compared to infrared counterparts.
• Achieving narrow linewidths in GaN DFBs is essential for advancing short-wavelength photonic applications.

Purpose of the Study:

• To present a free-running Indium Gallium Nitride (InGaN) DFB laser operating at 443 nm.
• To characterize the intrinsic linewidth and output power of the developed DFB laser.
• To investigate the performance of an embedded hydrogen silsesquioxane (HSQ) surface grating for linewidth reduction.

Main Methods:

• Fabrication of a first-order embedded HSQ surface grating for the InGaN DFB laser.
• Continuous wave (CW) operation of the DFB laser at 443 nm.
• Frequency noise measurement using a cross-correlated self-heterodyne frequency discriminator.
• Linewidth estimation using 1/π integration and β-separation line integration methods.

Main Results:

• A free-running InGaN DFB laser operating at 443 nm was successfully demonstrated.
• An intrinsic linewidth of 685 kHz was achieved at a continuous wave output power of 40 mW.
• The performance was attributed to the use of a first-order embedded HSQ surface grating.

Conclusions:

• The developed InGaN DFB laser offers a significant improvement in linewidth for short-wavelength applications.
• Embedded HSQ gratings are effective for achieving narrow intrinsic linewidths in GaN-based DFBs.
• This work paves the way for high-performance short-wavelength photonic devices.