Coherent detection

Coherent detection is an optical-signal reception method in which the received signal is mixed with the wave of a local laser oscillator, letting you recover the full amplitude, phase, and polarization information of the signal — not just its intensity.

How does coherent detection work?

Unlike simpler direct detection (which registers only light intensity), coherent detection uses interference between the signal and the local oscillator in a 90-degree optical hybrid, followed by digital signal processing (DSP) to recover the data and compensate for distortions such as chromatic dispersion and PMD in the electronic domain.

Applications

Coherent detection is the standard in modern long-haul 100G and faster transmission systems, enabling advanced modulation formats (DP-QPSK, DP-16QAM) and electronic distortion compensation, dramatically increasing the capacity of existing fiber-optic infrastructure.

Related terms

PMD

Mach-Zehnder modulator

BER