Micromachined tunable vertical-cavity surface-emitting lasers with narrow linewidth for near infrared gas detection

摘要

The design, technology and characteristics as well as sensing applications of micromachined long-wavelength (～1.55/μm) tunable vertical-cavity surface-emitting lasers are reported. The laser combines an active optical component (so-called half-VCSEL) and an agile mechanical component (MEMS) in a hybrid assembly. Electrothermal actuation expands the enclosed air-gap and continuously shifts the cavity resonance towards longer wavelengths. A curved mirror membrane is deployed to solely excite the desired fundamental mode with high output power and high sidemode suppression. The comparatively high stiffness of the MEMS lifts its mechanical resonance frequency to values around 150 kHz as measured by laser Doppler vibrometry under electrostatic actuation and - at the same time - reduces its susceptibility to Brownian motion. Laser linewidths as narrow as 32 MHz are demonstrated by using the self-heterodyning technique and the wavelength dependent linewidth variation is presented for the first time. After successful absorption spectroscopy experiments under steady laboratory conditions the tunable VCSEL is used for trace gas detection in a combustion process. Preliminary experimental results are shown and practically encountered problems are discussed.