Introduction of PLC Technology I—PLC Devices

PLC is more known in the field of electronic technology. It is the acronym of the terminology ‘programmable logic controller’. However, in the field of optical communication, PLC is the acronym of another terminology, i.e. ‘planar lightwave circuit’, which is variable optical waveguide structures fabricated with integrated optics technologies. PLC technologies can implement functional devices as directional coupler (DC), Y-branch splitter, multimode interferometer (MMI), arrayed waveguide grating (AWG), optical interleaver (ITL), Mach-Zehnder (MZ) electro-optical modulator, thermo-optical variable optical attenuator (TO-VOA), thermo-optical switch (TO-SW), etc.

In the optical communication industry, the widely deployed PLC devices include optical power splitter, AWG, MZ electro-optical modulator and TO-VOA, etc. optical power splitter is a device consisting of Y-branch splitters in cascade and parallel connection. For example, a 1×16 power needs 15 Y-branch splitters. AWG is a device with 1×N ports, which separates tens of wavelengths from the input to each output. MZ modulator based on lithium niobate optical waveguide is the main approach for optical modulators. Meanwhile, modulators based on silicon optics are commercialized and become the first choice for high-speed modulators >50G. TO-VOA based on PLC technology is deployed in combination with AWG, which compose a VMUX module with functions of multiplexing/demultiplexing and dynamic channel equalization.

Optical communication devices based on PLC technology and widely deployed are variable. However, PLC is usually specified as optical power splitters in the industry, which is a most widely deployed passive optical device in the FTTH network. After the internet bubble in 2000, optical communication industry entered a period of depression. Then in 2004, Japan first invested on FTTH construction as a new infrastructure, although the application scenario of FTTH had not emerged yet. In 2008, China added in the construction of FTTH and reached the peak in 2012. FTTH network usually adopts PON structure. The key device is optical power splitter, which is widely deployed in the business and residential buildings. In our lives, the most approach to an optical power splitter is the modem for internet access. The pigtail of the modem was upgraded from twist-pair electrical wires to an optical fiber jumper, which is led to one of the ports of an optical power splitter. The optical fiber access can support transmission speed of 100-200M, which is much higher than 4M through electrical wires.

written by Zhujun Wan, Jianwei Feng

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