Lightcarriers

Lightcarriers are the optical signals that carry information in optical communications and photonics. In this usage, a carrier is the steady-state light field produced by a laser or light-emitting diode that is modulated to encode data. Photons acting as carriers transmit both energy and information through a medium such as an optical fiber or free space.

In modern fiber networks the optical carrier is typically a narrow-linewidth laser at a characteristic wavelength, often in the near-infrared (for example around 1550 nm in the C-band). Data is encoded by altering the carrier's properties: amplitude (on-off keying, ASK), phase (PSK, QPSK), polarization, or combinations thereof (QAM). Coherent detection, which measures both amplitude and phase, enables higher spectral efficiency. When multiple carriers share a fiber, wavelength-division multiplexing (WDM) is used to pack many channels.

The carrier's properties determine performance. The frequency and spectral width affect channel spacing and distance, while coherence and phase stability influence demodulation accuracy. The medium's dispersion and nonlinearities shape signal integrity. Detectors convert photons back into electrical signals; typical receivers use photodiodes, with coherent receivers offering sensitivity advantages for advanced formats.

Lightcarriers differ from radio-frequency carriers in frequency, energy per photon, and propagation characteristics. They enable high-bandwidth communication and compact multiplexing, but require precise wavelength control, amplification, and dispersion management. In other applications such as LiDAR and spectroscopy, individual photons or narrowband carriers are used to probe or measure physical properties.

See also: optical carrier, photon, laser, modulation, wavelength-division multiplexing.