Benjamin Koegel

Experimental comparison of piezoresistive MEMS and fiber bragg grating strain sensors

We report on the experimental comparison of piezoresistive MEMS sensors and optical fiber BRAGG grating sensors (FBGS) for strain measurements in force sensors. To our knowledge, this is the first direct comparison of piezoresistive and FBG transducers as force sensors. Cantilevers are used as deformation elements. The sensors are bonded on top and bottom side of the cantilever using a heat-curing epoxy adhesive. The piezoresistive ones are micro machined silicon chips with decoupled adhesive areas, and four ion implanted piezoresistive areas (R<inf>sq</inf> = 125 Ωcm, (1 × 2)mm²×350 µm). The FBGS are draw-tower-gratings (0.78mm² × 9 mm). The measured values are compared by analyzing nominal strain, sensitivity, resolution, measurement uncertainty and thermal behavior. The MEMS sensor is more sensitive than the FBGS (0.28%, /N ≫ 0.004%/ N), its measurement uncertainty is lower (2% ≪ 5%) and the resolution Δ∈ = 10⁻³ µm /m is 100 times higher than in case of FBGS Δ∈ = 1.38 µm / m.

Bulk- micromachined dielectric tunable optical filter realized with inductively coupled plasma chemical vapour deposition

We present the characterization of silicon oxide (SiOx) and silicon nitride (SiNx) films deposited by inductively coupled plasma chemical vapour deposition (ICP-CVD) at low temperature (< 100°C). A tunable optical Fabry- Perot (FP) -filter operating at a wavelength around 1.5μm is realized. It is hybridly assembled with two dielectric distributed Bragg reflectors (DBR). One of the DBR- mirrors is intentionally curved using the intrinsic stress inside the films. Our aim is the development of a tunable surface micromachined VCSEL with a curved dielectric mirror. Therefore ICP-CVD with a low deposition temperature is used for SiOx and SiNx films. As a first step the realization of a tunable bulk- mircomachined optical FP- filter is presented. The refractive index, deposition rate, stress and etching rate in buffered hydrofluoric acid (BHF) of thin dielectric films (<500 nm) in dependence on deposition temperature and on gas flow ratio are investigated. The knowledge of the deposition characteristics of the dielectric films is used to realize DBRs with a given curvature that are applied to electrothermally actuated, optical tunable FP- filters. The presented filter has a free spectral range of 29 nm, an insertion loss of 10 dB and a full width half maximum of 0.16 nm.

Coupled cavity phenomena within MEMS-tunable long-wavelength VCSELs

We present a tunable VCSEL emitting around 1.55 /spl mu/m with a maximum tuning range of 43 nm. To investigate the effects of coupled cavities within such a structure, simulations have been performed and compared to experimental results.

Ultra wide mode-hop free tuning around 1550-NM telecom wavelength using high-speed MEMS-VCSELS

We report ultra-wide tuning of a 1550 nm BCB based high-speed MEMS-VCSEL. The MEMS is electrothermally actuated for a continuous tuning of 101 nm. Maximum output power and minimum threshold current is 3.2 mW and 2.6 mA, respectively.