Large-area Vertical-cavity Surface-emitting Laser Research Articles

Computational metrics and parameters of an injection-locked large area semiconductor laser for neural network computing [Invited

Artificial neural networks have become a staple computing technique in many fields. Yet, they present fundamental differences with classical computing hardware in the way they process information. Photonic implementations of neural network architectures potentially offer fundamental advantages over their electronic counterparts in terms of speed, processing parallelism, scalability and energy efficiency. Scalable and high performance photonic neural networks (PNNs) have been demonstrated, yet they remain scarce. In this work, we study the performance of such a scalable, fully parallel and autonomous PNN based on large area vertical-cavity surface-emitting lasers (LA-VCSEL). We show how the performance varies with different physical parameters, namely, injection wavelength, injection power, and bias current. Furthermore, we link these physical parameters to the general computational measures of consistency and dimensionality. We present a general method of gauging dimensionality in high dimensional nonlinear systems subject to noise, which could be applied to many systems in the context of neuromorphic computing. Our work will inform future implementations of spatially multiplexed VCSEL PNNs.

Thermal properties of GaN-based semiconductor-metal subwavelength grating VCSELs and novel current injection scheme

This paper provides a thermal and electrical analysis of semiconductor-metal subwavelength-grating (SMSG) vertical-cavity surface-emitting lasers (VCSELs). In the proposed design, the top distributed Bragg reflector (DBR) of a GaN-based VCSEL is replaced with a GaN–Ag SMSG, which serves as both an optical reflector and an electrical contact. Using a numerical 3D self-consistent thermo-electric model combined with a 3D optical model, we show that GaN-based SMSG VCSELs with aperture sizes of over 50 µm are capable of laser operation. We also propose spatial tuning of the injected current density to eliminate the current crowding effect in large area VCSELs. The use of GaN–Ag SMSGs in GaN-based VCSELs eliminates the need for a top dielectric DBR and intracavity injection scheme, making the fabrication of monolithic VCSELs possible. It also eliminates the need to use a tunnel junction with optical confinement built into the cavity. Although the GaN–Ag SMSG introduces higher optical losses than a DBR, its advantage is that it permits vertical current injection into the active region, enabling laser emission from broader-area active regions in comparison to conventional VCSELs.

Numerical investigation of side emission from large-area vertical-cavity surface-emitting lasers.

For large-area ion-implanted vertical-cavity surface-emitting lasers (VCSELs), side emission from the edges of a chip disturbs the laser emission of a VCSEL mode, and suppression of it is fundamental. In this paper, we present results of a numerical investigation of the side emission from large-area VCSELs. We have modeled a VCSEL structure by an infinitely broad layer structure with mirror loss at the edge surfaces. Estimated threshold gains indicate that laser emission occurs either in a VCSEL mode or in an edge-emitting Fabry-Perot (EEFP) mode. Calculated emitter length dependence of the threshold gain of these modes shows good agreement with experimental results, and the side emission is verified to be the laser emission of the EEFP mode. We have also discussed the way to suppress the side emission and confirmed that our recent achievement of over 200 W quasi-continuous-wave output from an ion-implanted VCSEL array is due to antireflection coatings of the edges and introduction of optical losses in ex-emitter regions.

Self-consistent eigenmode analysis of the dielectrically apertured Fabry–Perot microcavity

Analysis is presented to calculate the eigenmode of a Fabry–Perot microcavity containing an optically thin dielectric aperture. The treatment yields the eigenmode field distribution, frequency, and threshold susceptibility. It is also suggested that self-focusing phenomena in large area vertical-cavity surface-emitting lasers can arise due to aperture formation by the complex susceptibility of a quantum well active region.