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Explanation 1: Wavelength division multiplexing

Wavelength Division Multiplexing (WDM) is a type of communication technology using optical fiber. By transmitting multiple optical signals (i.e. light with various wavelengths) simultaneously, it is possible to put more data on a single fiber. Optical signals processed by a multiplexer are transmitted on an optical fiber and are re-separated into the original multiple optical signals by a demultiplexer on the receiving side. While arrayed waveguide grating (AWG) is mainly used for multiplexing/demultiplexing light at present, the device size becomes larger with an increased number of multiplexed wavelengths. Since a photonic crystal optical circuit can transmit light along a path without loss, even if bent at a right angle, it is attracting attention as a new technology that can withstand increased wavelengths.


Explanation 2: Photonic crystal

A photonic crystal has a periodic structure based on the wavelength level of light. There are one-, two- and three-dimensional structures. Similar to the occurrence of a band gap in the energy levels of electrons due to the periodic potential of the nucleus, a photonic band gap of electromagnetic waves occurs in a photonic crystal, and light can be confined, bent sharply or branched easily by creating point, line and other arbitrary defects. With the advance of nanotechnology, it has become possible to create nanometer-size periodic structures artificially. Photonic crystal fibers with several dozen to more than one hundred holes in a section approximately 125 millimeters in diameter have also been realized.

Photonic crystal


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