Resonant-antiresonant coupled cavity VCSELs.

The wavelength tuning range of a tunable vertical-cavity surface-emitting laser (VCSEL) is strongly influenced by the design of the interface between the semiconductor cavity and the air cavity. A simplified model is used to investigate the origin of the dramatic differences in free spectral range (FSR) and tuning slope observed in semiconductor cavity dominant, extended cavity, and air cavity dominant VCSELs. The differences arise from the positioning of the resonant and antiresonant wavelengths of the semiconductor cavity with respect to the center wavelength. The air cavity dominant design is realized by designing an antiresonant semiconductor cavity, resulting in a larger tuning slope near the center of the tuning range and a wider FSR toward the edges of the tuning range. The findings from the simplified model are confirmed with the simulation of a full VCSEL structure. Using an air cavity dominant design, an electrically pumped laser with a tuning range of 68.38 nm centered at 1056.7 nm at a 550 kHz sweep rate is demonstrated with continuous wave emission at room temperature. This epitaxial design rule can be used to increase the tuning range of tunable VCSELs, making them more applicable in swept-source optical coherence tomography and frequency-modulated continuous-wave LIDAR systems.

MEMS-tunable VCSELs using 2D high-contrast gratings.

We demonstrate the room-temperature operation of a two-dimensional (2D) high-contrast grating (HCG) vertical-cavity surface-emitting laser (VCSEL) at 1080 nm. To the best of our knowledge, this is the first tunable electrically pumped surface-emitting laser using a 2D HCG. Our theory successfully explains the mechanism of broadband ultrahigh reflection of 2D HCGs. Our monolithic integrated laser exhibits single-mode output power above 0.68 mW under continuous-wave operation. Wavelength tunability is demonstrated via microelectromechanical system-controlled voltage.

One-step index-tunable antireflection coatings from aggregated silica nanoparticles.

We demonstrate a method for producing thickness- and refractive index-tunable antireflection coatings utilizing a one-step spin coating procedure with silica nanoparticle solutions. Aging nanoparticle solutions under controlled pH and temperature induces aggregation, allowing precise control of the porosity and refractive index of the spin-processed coating. Coating thickness measurements as a function of solution aging time and temperature allow for determination of the activation energy of the reaction-limited aggregation process. We demonstrate optimization of the antireflection effect for a single-layer silica nanoparticle coating on glass, and suggest that the aggregation method may be generalized to various other nanoparticle-based assemblies.