Rainbow_heterodyne_detection
The objective of synthetic array heterodyne detection is to isolate regions of a large area detector surface into virtual pixels. This provides the benefits of having multiple pixels (for example, to make an image) without having to have physical pixels (i.e. isolated detector elements). The detector can be a simple single wire output over which all the virtual pixels can be read out continuously and in parallel. The pixels are multiplexed in the frequency domain.
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This solves two common problems encountered in optical heterodyne detection. First, heterodyne signals are beat frequencies between the signal source and a reference source (dubbed local oscillator). They are not DC light levels[clarification needed] but oscillating signals and thus unlike conventional detectors the light flux from the signal cannot be integrated on a capacitor. Therefore, to have an array of pixels, each pixel must be backed by AC amplifier and detection circuit which is complex. With synthetic array detection, all the signals can be amplified and detected by the same circuit. The second problem synthetic array detection solves arrises, not in pixel imaging but when the signal is not spatially coherent across the surface of the detector. In this case, the beat frequencies arising are differently phased across the detector surface and these destructively interfere producing a low signal output. In synthetic array detection, each region of the detector has a different fundamental for its beat frequency and thus there is no stationary interference even if the signal's phase varies across the surface of the detector.