Enhancement of Low Spatial Frequency Signals with Optical Aperture Tapering

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Abstract
Detection of weak signals in an optical spectrum analyzer is impaired by sidelobes from nearby large signal components in the output spectrum. Strong sidelobes about the zero frequency component particularly inhibit detection of low frequency signals. Sidelobe response can be attenuated by suitable illumination tapering over the input data aperture. Changes of first and second sidelobe levels and main lobe width have been investigated for gaussian, lorentzian, and exponential tapers. Improved capability to distinguish weak low frequency signals in the presence of distortions introduced by component flaws is demonstrated for the exponential form.