Abstract
Applications in broadband optical fiber communication system need variable optical attenuators (VOAs) with low wavelength-dependent loss (WDL). Based on analysis on the dispersion of the optical system of a MEMS-based VOA, we provide a method to reduce the WDL significantly with minor revision on the end-face angle of the collimating lens. Two samples are assembled, and the measured WDL is <0.4 dB over the C-band (1.53–1.57 μm) at a 0–20 dB attenuation range. Meanwhile, the new structure helps to reduce the polarization-dependent loss (PDL) to <0.15 dB, which is only half that of conventional devices.
Highlights
A variable optical attenuator (VOA) is an important optical device for optical fiber communication and optical instrumentation [1,2]
The main approaches for a VOA include: thermo-optically adjusted Mach–Zehnder interferometer (MZI) based on a planar lightwave circuit (PLC) [3], optical fluid driven by a pump [4,5], liquid-core fiber driven by thermo-optical effect [6], and mechanical systems (MEMS) technology
Chengkuo Lee’s group did much work to develop different mechanisms for MEMS VOAs, such as retro-reflective mirrors driven by electro-thermal actuators [7], and reflective mirrors driven by rotary comb drive actuators [8]
Summary
A variable optical attenuator (VOA) is an important optical device for optical fiber communication and optical instrumentation [1,2]. One application of VOAs is in erbium-doped fiber amplifier (EDFA) modules for optical fiber communication. A VOA is employed in the EDFA module to control the optical power dynamically, which requires it to generate nearly the same attenuation for different wavelengths over the bandwidth of 40 nm. VOAs based on a MEMS torsion mirror are widely employed in optical fiber communication. They are confounded by high WDLs, especially when operating at a high attenuation level. The optical attenuation is tunable by adjusting the tilt angle of the mirror, which results in a lateral offset X of the refocused beam spot on the facet of the output fiber.
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