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Current systems are typically hybrid assemblies of packaged photonic devices where printed circuit boards often serve to route electrical signals and power , and in some cases , have runs of optical fibers .
 printed circuit boards, electrical, power, optical, fibers
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: manufacturing standard, machanical property, manufacturing process, material, engineering feature, process parameter, machine or equipment, application, process characterization, enabling technology, biomedical, concept or principle 
Text: {0} 
Answer:
 printed circuit boards, electrical, power, optical, fibers