Fig.3 Configuration of a high-speed digital optical repeater

Configuration of a high-speed digital optical repeater

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This figure shows the configuration of a regenerative type of optical repeater. The transmission medium is single-mode fiber, optical wavelength is 1.3 μm, and transmission speed is 400 Mbps. The input and output sections have optical-electrical and electrical-optical converters; main processes like amplification, waveform shaping, decision, and timing extraction are performed with electrical signals.

The optical-electrical converter features a Ge-APD with an optical-detector diameter of 100 μm and the electrical-optical converter uses an InGaAsP laser. The use of a confocal compound lens system improves the coupling efficiency with single-mode fiber. The laser is driven at 400 Mbps by a high-speed optical modulation circuit.

In addition to the signal-regeneration function, a fault-detection function is important from a practical point of view. The fault-detection circuit here consists of SVA and SVB circuits. The former circuit detects breaks in the input signal through the absence of timing-extraction output, and the latter circuit enables the bit error rate of a repeater to be remotely measured offline at the time of a system fault so that fault location can be identified.

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