Vertical-cavity surface-emitting lasers with post-supported high-contrast gratings towards 100 Gbps data rate

Abstract

Vertical-Cavity Surface-Emitting Lasers (VCSELs) are widely used for optical interconnects, 3D sensing like face recognition, or automotive applications. Conventional VCSELs with top/bottom distributed Bragg reflectors (DBRs) for any wavelength range are costly and bulky, needing precise growth control. High-contrast subwavelength gratings (HCGs) show a near 100% reflectivity across a wide wavelength range, and have a typical thickness of a few hundred nanometers, much thinner than epitaxial DBRs. In addition, HCGs were reported to have the ability to tightly confine the field in the HCG-based vertical cavities, very promising for high-speed devices. Thus HCGs are ideal candidates for mirror replacements, at least at the top, to construct vertical cavities. Currently HCGs are often based on an oxide layer, being monolithically integrated, or air-suspended, and the fabrication of these HCGs is still challenging. VCSELs at 940 nm have been attracting particular attention for short-wave wavelength division multiplexing and sensing. Here we report for the first time electrically injected 940-nm HCG-VCSELs using post-supported air-suspended HCGs. The HCG-VCSELs are fabricated without critical point drying, and the HCGs can be released with a 100% yield in water or isopropanol. Our first generation HCG-VCSELs achieve already a low threshold current of 0.65 mA, and a large side-mode suppression ratio of 43.6 dB at 25 ℃ under continuous-wave operation. Theoretically, these HCG-VCSELs have a smaller effective mode length of 1.38*(λ/n), than that of conventional VCSELs with λ/2 cavities. The relaxation resonance frequency will increase by 16%. A data rate of 100 Gbps for these HCG-VCSELs is expected for the on-off keying modulation format. Our present design and fabrication methods of the HCG-VCSELs can be extended to other wavelength ranges.