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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.
Of special interest, this solves two common and vexing problems encountered in optical heterodyne detection. First, Heterodyned signals are beat frequencies between the signal source and a reference source (dubbed local oscillator LO). They are not DC light levels 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 it solves arrises not is 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.
== Illustration of the concept ==
Figure 1 shows a particular implementation format of the Synthetic Array method. This implementation is called "Rainbow Heterodyne Detection" because the Local Oscilator has its frequencies spread out like a rainbow across the surface of the detector.
The output from the detector is a multifrequency signal. If this output signal is spectrally resolved then each different electrical frequency corresponds to a different location on the detector.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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