New patent promises inexpensive power monitoring

Genoa Corporation has recently been issued a US patent for the world’s first integrated chip-based optical amplifier and signal power monitor.

The patent, #6,347,104, represents a novel use for Genoa’s linear optical amplifier semiconductor technology, and promises a significant reduction in the cost and complexity of managing optical communications networks from the standpoint of power management and fault isolation.

‘This is an important step towards integrating key optical functions on a single chip,’ said Gerlas van den Hoven, Genoa’s vice president of product management.

‘A challenge with optical networks is the monitoring and management of the network itself. It’s vital to have insight into the power at any network node so that signal strengths can be maintained at required levels and faults can be immediately identified and isolated. Integrating the monitor function with amplification on a single chip will make such insight possible at low costs.’

Today, optical power is monitored at key locations in the network, typically at the location of the optical amplifier. Today’s conventional technology – the erbium doped fibre amplifier (EDFA) – requires diverting a portion of the signal to a separate monitoring device. In addition to the complexity and cost of adding these ‘T’-like taps, there is a loss of power associated with each tap. With the recent Genoa invention, power monitoring can be added virtually ‘for free,’ with no loss of power.

The linear optical amplifier, also invented by Genoa, is the first chip-based optical amplifier that is immune to crosstalk distortion from multiple wavelengths, and the first optical amplifier of any configuration that is inherently immune to power transients from optical switching. It achieves these novel results by incorporating a ‘ballast’ laser right into the amplifier chip itself. The ballast laser provides a vast and continuous source of light photons to ‘smooth’ out or ‘linearise’ any signal passing through the amplifier chip.

When power monitoring is needed, the light from the ballast laser is put to use. The intensity of ballast laser light reacts to the input signal power. When a low input signal is present, the ballast light output is high; as the input power increases, the ballast light output decreases proportionally. In other words, variations in the optical signal are directly and instantaneously mirrored in the ballast light, enabling monitoring of the signal through the ballast light.

For optical network engineers, this breakthrough means that wherever amplification is needed in the network, a monitoring port can essentially be added at that point ‘for free,’ simply by using Genoa’s LOA for the amplification stage.

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