Nonsilicon micro-machined variable optical attenuator

Abstract

Optical power equalization between wavelength-path slots in wavelength division multiplexing (WDM) networks is an increasingly concerning issue in all-optical networks, and this made variable optical attenuators (VOAs) play an increasingly important role in fiber optic transmission systems. Various types of optical attenuators have been realized, but conventional available mechanical VOAs are bulky, costly, and slow. MOEMS technology provides new approaches to improve the characteristic mentioned above. Previous attempts to realize MEMS variable optical attenuators include the use of a micro-driven shutter, a mechanical antireflection switch (MARS) modulator, a micro-machined tilted mirror, and a micro-machined membrane-type waveguide. In this paper, we report the design and fabrication of two types of electromagnetically actuated variable optical attenuator (VOA). They are both driven by a similar construction containing of a plane coil and a FeNi armature. The first one adjusts the attenuation by moving a shutter between the two fibers, the second one by moving one of the fibers directly. The first one is fabricated by nonsilicon surface micromachining technology. In which a copper layer was used as the sacrificial layer, and the electroplated FeNi as the structure layer. This scheme provides another way to fabricate the optical microstructure. According to the experiment results, it has insertion loss less than 3 dB at 1550-nm wavelength, dynamic range greater than 40 dB, 0.2-dB repeatability, and return loss better than 40 dB, driving voltage less than 20 V. For the second one, it included the silicon platform for adjustment of optical coupling between two optical fibers. The main fabrication process of the silicon platform is was the KOH antistrophic wet chemical etching of silicon wafers. The silicon wafer is further selectively etched from the bottom side to subtract the thickness of the silicon elastic platform. In addition, two V grooves were fabricated for alignment of the input and output optical fibers. One of the V grooves is on the mobile elastic platform; the other is on the fixed framework. When the platform is attracted downward by the electromagnetic force, the central axes of the two fibers are mismatched to adjust the attenuation. The insertion loss is less than 1 dB, the polarization dependent loss is less than 0.1 dB, dynamic range is larger than 50 dB, and the driving voltage is less than 5 V. The design, fabrication, and test of the two devices are all introduced detailedly below. The first device is suitable for fast adjustment. The second one may be adopted in applications where, the fabrication cost and polarization-dependent loss is of more concern.