Fig. 1. Cross view of the VCSEL structure.

Fig. 2. Schematic view of (a) an HCG VCSEL and (b) a VCSEL with dielectric top DBRs.

Fig. 3. Field distributions of different transverse modes inside VCSEL cavity.

Fig. 4. Schematic of the VCSELs with (a) zinc-diffusion on top mirrors and (b) the multijunction VCSEL with surface relief. BCB, benzocyclonbute.

Fig. 5. Schematic of the single-mode VCSEL utilizing P-contact metal as a spatial mode filter.

Fig. 6. (a) Schematic of the metal-aperture (MA) VCSEL; (b) photo of the fabricated devices; (c) principle of the optical feedback. Reprinted with permission from Ref. [91]. 2021, IEEE.

Fig. 7. (a) Schematic of an InP-based 1.5 µm VCSEL with BTJ and dielectric DBRs; (b) refractive index profile and field intensity distribution of the device. Reprinted with permission from Ref. [97]. 2017, IEEE.

Fig. 8. (a) Schematic of the 1300 nm wafer-fused VCSEL; (b) field distribution and refractive index profile in the center; (c) field distribution and refractive index profile of the entire structure; (d) reflection spectra and PL spectrum of the device. Reprinted with permission from Ref. [103]. 2022, SPIE.

Fig. 9. (a) 3D Schematic of the 1060 nm surface relief VCSEL; (b) cross view of the device showing optical coupling; (c) top view of a fabricated device.

Fig. 10. (a) Schematic of the CPO CWDM optical module; (b) CPO module on a PCB. Reprinted with permission from Ref. [134]. 2020, IEEE.

Fig. 11. (a) Top view of the flip-chip bonded VCSEL matrix; (b) bottom view of the VCSEL matrix; (c) micro-photo showing 250-µm spaced VCSEL apertures; (d) photo of the CPO module. Reprinted with permission from Ref. [135]. 2022, IEEE.

Fig. 12. (a) Schematic of the bottom-emitting VCSEL; (b) schematic of the VCSEL CPO transceiver. Reprinted with permission from Ref. [137]. 2023, OSA.