Fiber optic attenuators are devices that reduce signal power in fiber optic links by inducing a fixed or variable loss. They are used to control the power level of optical signals at the outputs of light sources and electrical-to-optical (E/O) converters. They are also used to test the linearity and dynamic range of photo sensors and photo detectors. Fiber optic attenuators use several methods of attenuation. Examples include air gaps, microbends, acousto-optic modulators, and electro-optic modulators. Air gaps between optical fibers cause light to be reflected because of the change in refractive index. Microbends are sharp curvatures with local axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Microbending can cause significant radiative loss and mode coupling. Acousto-optic modulators use sound waves to modify the amplitude, frequency, or phase of light passing through an acousto-optic material. Similarly, electro-optic modulators use an electric field to alter the characteristics of light passing through an electro-optic material.