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OMS as a Modulator
In fiber-optic communications, information can be carried by a light wave of varying amplitude (changing brightness). The amplitude is varied by modulating the single-wavelength light coming from a laser source. The OMS varies the brightness of a low-level laser light source by switching it on and off at nanosecond rates. Then its built-in amplifier boosts the varying signal to levels suitable for transmission over long optical communication links.
As Wieskamp explains it, commercially available modulators do not amplify the signal. This means that a separate amplifier-which can cost thousands of dollars-must be added to the communication chain after the modulating device.
The OMS device, contained on a chip as big as a medium-size integrated circuit, derives its built-in amplification from the interaction of input signals with semiconductor material. Inside the device, photons from the input signal travel through a waveguide with an applied electric field. This electric field has been exciting atoms in the device's semiconductor material and increasing their energy. When the photons pass through the semiconductor, they cause the semiconductor atoms to give up energy and become photons just like them-of exactly the same wavelength, traveling in the same direction. This increase in the number of photons thus amplifies the signal.
OMS as a Switch
When used as a switch, the OMS can receive signals in different configurations and switch them out in any combination of outputs. The figure above shows its use in both cross-bar and tree switching of optical signals. In switching the optical signals-again, an on-and-off action-the OMS is a thousand times faster than current optical switches.
With many signal outputs, amplification becomes particularly critical. An optical signal can lose half of its input power every time it is sent through a switch or any type of connector; it loses an equal amount traveling through 4 kilometers of fiber. For a signal going across the country, from, say, San Francisco to Washington, DC, this adds up to significant power losses. To counteract these losses, such signals must be amplified or boosted as they are switched and relayed over complex routes or long distances. |