Suppressing mode partition noise in multimode VCSELs via lateral geometry control.

Area of Science:

• Photonics and Optical Engineering
• Semiconductor Device Physics

Background:

• Mode partition noise (MPN) is a significant challenge in high-speed short-reach optical links utilizing vertical-cavity surface-emitting lasers (VCSELs).
• MPN arises from the complex interplay of different transverse mode groups within the VCSEL cavity.
• Existing methods for MPN suppression often impact the intrinsic performance of VCSELs.

Purpose of the Study:

• To investigate a geometry-driven approach for suppressing MPN in VCSELs.
• To correlate lateral aperture geometry with transverse modal distribution and MPN characteristics.
• To demonstrate improved performance metrics for optical interconnects through optimized VCSEL design.

Main Methods:

• Fabrication and characterization of three VCSELs with distinct lateral aperture geometries.
• Analysis of static and small-signal performance characteristics.
• Measurement of root-mean-square (RMS) spectral width and low-frequency relative intensity noise (RIN).
• Evaluation of transmitter dispersion eye closure quaternary (TDECQ) and timing jitter in back-to-back and fiber transmission scenarios.

Main Results:

• Lateral aperture geometry was found to be the primary determinant of the transverse modal distribution and MPN.
• An asymmetric aperture design concentrated modal energy into a dominant mode group, significantly reducing MPN.
• The optimized VCSEL achieved an RMS spectral width of 0.387 nm and the lowest observed RIN.
• Excellent TDECQ (0.86 dB back-to-back, 1.24 dB after 100m OM4 fiber) and low timing jitter (6.65 ps, 8.03 ps) were recorded.

Conclusions:

• Lateral-geometry optimization is an effective strategy for suppressing MPN in VCSELs.
• This approach enhances optical interconnect performance without compromising intrinsic laser characteristics.
• The findings enable higher-margin optical interconnects for demanding high-speed applications.