Microelectromechanical Wavelength-Tunable Vertical - Light-Emitters and Lasers
Vertical-cavity surface-emitting lasers and resonant -cavity light-emitting diodes have seen a great deal of interest because of their single longitudinal mode nature, low-cost high-yield fabrication, and ease of integration into two-dimensional arrays. In these devices the operating wavelength is determined by fixed vertical layer thicknesses and refractive indices. However, there are a number of potential applications in which wavelength tunability is a desirable feature, such as wavelength division multiplexing in fiber telecommunications, free-space optical interconnects, and spectroscopic remote sensing. Previous attempts at wavelength tuning in vertical cavities have relied on refractive index modulation, limiting the practical tuning range to a few nanometers in the near IR. This work focuses on achieving broad tunability from vertical cavity structures by using a micromechanically movable top mirror suspended by an air gap above the semiconductor optical cavity and bottom mirror. Electrostatic force from an applied bias on the top mirror controls the air gap thickness, enabling large changes in the effective cavity length and therefore a much wider tuning range. Both optically- and electrically-pumped structures have been fabricated using surface micromachining techniques in the GaAs material system. We have demonstrated a record continuous tuning range as large as 18 nm for vertical-cavity lasers operating near 970 nm, and nearly 40 nm for resonant-cavity light -emitters. Maximum tuning voltages were typically 15 to 25 V, and microsecond wavelength switching has been observed. Furthermore, optimized devices have the potential for even larger wavelength ranges. This dissertation describes in detail the theory, design, fabrication, and characterization of these novel tunable optical sources.
- Pub Date:
- Engineering: Electronics and Electrical; Physics: Optics