New wavelength tuning strategy for realizing VCSEL wafers with highly uniform wavelength

Precise lasing wavelength control of VCSELs is attractive for several applications: 3D sensing, atomic clock, laser pumping, and the like. The wavelength of commercially available VCSELs is typically varied for each chip. This is because the thickness of epitaxial layers inevitably varies on a wafer due to the distribution of temperature and gas flow. VCSEL users on the module side have tolerated the problem. Here, we propose the novel strategy for precise wavelength control of VCSELs with simple fabrication by applying multi-wavelength (MW) VCSEL. We proposed two ways to achieve that. One is uniform wavelength method on wafer, and another is wavelength selection method. In both concepts, MW-VCSELs with wavelength-tuning-layer (WTL) inside DBR are suitable. Uniform wavelength method is followed by three steps: 1) A lower DBR, a cavity consisting of active layers, a first top DBR, and a WTL are grown. 2) The dip wavelength of the Fabry-Perot cavity is measured over the wafer. The WTL thickness is processed as to cancel out the wavelength variation in the two-dimensional data, which is performed by photolithography and etching techniques. 3) A remaining second top DBR is formed by regrowth technique to achieve more uniform wavelength than epitaxial growth alone. In our experiment, the reduction of wavelength variation from 6.6 nm (epitaxy only) to 2.0 nm was demonstrated. The concept can provide large scale array with uniform wavelength. Therefore, it is advantageous on high power applications as well as applications in which VCSELs with precise lasing wavelength are required. In wavelength selection method, precise wavelength is obtained by selecting emitters that met wavelength specification from emitters that are formed with different wavelengths by applying MW-VCSEL technology.