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What is coh?
(Coherent Detection)
Coherent Detection (COH) is an advanced optical signal processing technique used in optical communications and sensing to extract the full vector profile of an incoming light wave. Unlike standard direct detection (which only measures the presence or absence of raw optical power), coherent detection mixes the weak incoming signal with a known, stable reference laser called a Local Oscillator (LO).
Its primary purpose is to completely reconstruct the phase, amplitude, and polarization state of the arriving light wave, drastically boosting receiver sensitivity and enabling massive data transmission over long distances.
HOW coherent detection (coh) Works
Coherent detection translates high-frequency optical information down to lower electrical frequencies where electronic digital signal processors (DSPs) can decode the data, operating in three main phases:
Optical Wave Mixing
The weak, incoming laser signal enters the receiver and is combined with a stable, local reference laser (the Local Oscillator) inside an optical waveguide structure. The two light beams overlap, creating an optical interference pattern.
Signal Amplification
Because the local reference laser is kept at a high power level, it naturally boosts the weak incoming signal during the mixing process. When this combined light hits the photodetectors, it generates an electrical current that is significantly stronger than the noise floor, allowing the system to detect faint signals that would otherwise be lost.
Full Wave Decoding
By analyzing the interference patterns, the receiver simultaneously separates the light's layout into two distinct tracks: the parts that are in phase and the parts that are out of phase. This gives the system the exact data needed to completely reconstruct the original signal and correct any distortions caused during transmission.
