Working in the Dark

Many optical switch systems require light on a fiber in order to maintain a connection.  The optical power is required to provide the feedback for position control.  There are several operational disadvantages in using this method.  For example:

• Fiber connections cannot be pre-provisioned.  The need for optical power monitoring means that unlit fibers cannot be connected.  This is a severe limitation in protection switching and planned maintenance operations where fiber paths may need to be set up in advance of carrying traffic.
• Transient signals are not readily handled.  In remote fiber test applications, OTDRs (Optical Time-Domain Reflectometers) are vital characterization tools.  For successful operation, the ability to hold a connection while - i) optical power radily varies and ii) the fiber path is unlit; is essential for any optical switch used to enable fiber test access.
• Bidirectional signals are not fully supported.  Optical power monitoring is direction sensitive and consequently so is signal transmission through the switch.  Bidirectional operation is a prerequisite for many applications - including break location using OTDRs.

In contrast, the Polatis Direct BeamSteering (TM) method uses collimator position sensing to maintain fiber to fiber connections.  There is no requirement for optical power to be monitored or indeed for light to be present at all.  Consequently, this technology produces a true dark fiber switch, capable of handling bidirectional and transient signals.  Polatis optical switches are therefore ideal for protection switching planned maintenance and remote fiber test access applications.