Why use POF for Media Oriented Systems Transport (MOST)-Automotive Multi-media Network?
Nowadays, the number of electronic devices in a car increases year by year, mainly due to an increase in the entertainment equipment desired for modern passenger cars—from simple radios in the 1970s to radios, DVD players, TVs, and even GPS consoles. To realize ubiquitous access to multiple digital equipment sites in a car, each equipment site or node must be connected, leading to an exponential increase in the number of communication cables within the vehicle (see Fig. 1).

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FIGURE 1. The simple radios found in automobiles from the 1970s have progressed into complex infotainment systems in modern cars, requiring an exponential increase in communication connections between radios, TVs, DVD tuners, and even GPS consoles.
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This ubiquitous connection need is a huge problem in networking system designs for automotive fiber from the viewpoint of both physical space and system load. Consequently, POF is specified in the MOST standard to achieve the lowest overall system weight and easiest connectivity. Common POFs in use today typically have a 980-μm-diameter polymethylmethacrylate (PMMA) core and a 1000-μm-diameter fluorinated polymer cladding (see Fig. 2). The fiber is jacketed with polyamide (PA) material to enhance its robustness in vehicle use.

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FIGURE 2. The MOST cable jacket comprises two layers of nylon (upper). The POF fiber adheres to the inner jacket with polyamide12 (PA12), giving enough tensile strength that tension members are not needed outside the cable. The POF (lower) is composed of two layers: a PMMA core and fluorinated polymer cladding. For a 1.492 PMMA refractive index and 1.402 fluorinated polymer index, the numerical aperture here is defined as 0.50.
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The high numerical aperture (typically 0.50 to 0.58), easy connection ability, and mechanical strength and flexibility of POF have cemented its use in automotive infotainment (information and entertainment) networking systems in passenger cars since the late 1990s. A typical automotive POF network uses 660 nm light-emitting diode (LED) sources and photodiode receivers. Transceivers for POF have been mass-produced for more than 30 years, making them a cost-effective networking component.
The POF cable and connectors in the MOST standard have a simple structure, making them as easy to produce and connect as copper cables. In an automated production line, end termination is completed in two seconds using a laser welding method (see Fig. 3). An inline POF coupler is used for fiber-to-fiber connection between equipment nodes.

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FIGURE 3. The inner jacket of a plastic optical fiber (POF) cable is easily incorporated in a POF connector using laser welding; the termination is completed in two seconds in an automated assembly process.
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