25 nm wavelength range tunable vertical cavity lasers

Wavelength tunable lasers are attractive for Wavelength Division Multiplexing (WDM) applications. Conventional WDM relies on fixed wavelength laser arrays, which have temperature-control, system reliability, and manufacturability problems. Because of these shortcomings, wavelength tunable lasers are indispensable elements of such an array since the lasing wavelength of each laser can be set, maintained, or changed to any wavelength within its tuning range. Tunable vertical cavity lasers are optimum for such an array because their short cavity length translates into a single longitudinal mode inside the laser's gain spectrum. This allows continuous tuning without mode hopping. Our approach to tunable VCSEL uses a micromachined suspended deformable membrane that also functions as the top mirror above the semiconductor cavity. Modulating the air gap thickness by applying a bias between the membrane and the semiconductor cavity results in an additional phase shift that effectively modulates the resonance frequency of the VCSEL.