Abstract
A micromechanically wavelength-tunable optical filter with an integrated pin-photodetector for the wavelength band around 1.55 micrometer is demonstrated. The micromechanical modification of the resonator length realized by either thermal or electrostatic actuation of micromachined Bragg reflectors is used as tuning principle. The maximum tuning of the filter can be determined by its free spectral range (FSR) in the order of 40 nm, according to a resonator length around 30 micrometer. The required micromechanical displacement of the movable Bragg mirror of 800 nm is observed for an actuation voltage of 32 V utilizing capacitive actuators, while a heating power of 1.3 mW is required for electrothermally actuated membranes. Epitaxial (InAlGaAs/InAlAs) as well as dielectric (SiO<SUB>2</SUB>/Si<SUB>3</SUB>N<SUB>4</SUB>) material compositions are used for the Bragg reflectors to meet the mechanical and optical demands of the filter. The experimental full width at half maximum (FWHM) of the tunable wavelength division multiplexing (WDM) filter is 0.24 nm corresponding to a finesse of F equals 180. The insertion loss at resonance wavelength is 2.8 dB, whereas the contrast between maximum and minimum transmission exceeds 40 dB. The integration of an InGaAs/InP photodiode and a bulk- micromachined Bragg mirror allows the realization of a wavelength-selective pin photodetector. We report on bulk- micromachined thermally actuated highly selective photodetectors with a maximum tuning range of 35 nm, a FWHM around 0.4 nm and a tuning sensitivity of 20 nm mW<SUP>-1</SUP>. The technology discussed in this paper will be compatible to opto-electronic integrated circuit (OEIC) fabrication processing based on the InP-material system and therefore will enable the realization of receiver front ends with higher functionality for future dynamic WDM systems.
Published Version
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