A bandwidth variable transmitter (BVT) that converts electronic signals to optical signals has been shown to work without service interruptions, an advantage known as being "hitless." The transmitter’s bandwidth can also be adjust for varying bandwidths, allowing for optimized performance without constant and costly infrastructure upgrades. Arnaud Dupas of Nokia Bell Labs will describe the device at The Optical Fiber Communication and Exhibition Conference (OFC) in Anaheim, Calif., in March. Most BVTs work by changing the format of the optical signal, converting between digital and analog formats, Dupas said. Bell Labs’ system instead changes the symbol rate, also known as Baud rate, which is the number of signal events transmitted per second; a single signal event can encode one or several bits of information. The advantage of focusing on the symbol rate is that it's easier to implement with electronics and is cost-effective, Dupas said. This approach incorporates smart processing and makes the transmitter hitless, working without interruption and data loss. Normally transmitters have to reconfigure themselves when interrupted, which can take several seconds or minutes and requires the traffic to be stopped. But the new transmitter can configure itself in less than 450 μs. The device connects to a commercially available optical transport network switch, which aggregates all kinds of signals, such as video and audio, and puts it through the transmitter. It works at a bit rate between 10 and 107 Gbps. The BVT is still a prototype, and would be only one piece of a large flexible optical network. The next step is be to test it in the field with network operators, integrating it with the management software and systems that control a network from end-to-end, Dupas said. The ongoing work is supported by grant funding under the FP7 European Union project IDEALIST.