High-Speed Measurements

Today's economy relies on high-speed communications that ride fiber-optic networks, and EEEL physicists play a crucial role in providing the means to test the equipment on which these communications depend. The High-Speed Measurements Project calibrates photodiodes that turn light into electrical signals. Electronics manufacturers use the EEEL photodiodes to help tune oscilloscopes and other high-speed test equipment, which in turn tune commercial communications hardware. Project scientists are also working to measure the quality of light signals pulsing through optical fiber, which will be vital to for future networks with all-optical switching equipment. The end result is better, faster, more robust hardware for current and next-generation fiber-optic networks.

E-mails, Web searches, text messages, bank transfers, landline phone calls, even wireless calls (which are wireless only from handset to antenna tower) all spend time as pulses of infrared light flashing through fiber-optic lines spanning tens, hundreds, or thousands of miles. Optoelectronic communications hardware translates electric currents into light waves and back again at a pace that can move data as fast as 40 gigabits per second — a speed great enough to transmit full-length digital movies across the country in something over a second. Such hardware, a key engine of the modern networked economy, has gotten so fast that the devices used to test it have had trouble keeping pace. Without accurate testing, engineers have had to either overbuild equipment or else slow transmissions down to ensure that signals remain clear.

EEEL researchers have pioneered high-speed measurement standards that underpin the functioning of high-speed communication equipment as well as other vital radar, remote sensing, wireless communications, and computer-networking hardware.

The project works to define fundamental standards for commercial telecommunication hardware and to provide the means to implement them. EEEL calibrates and provides photodiodes for use as standard reference receivers. Telecommunication equipment manufacturers use the reference receivers to test oscilloscopes and lightwave component analyzers, high-speed test equipment that industry uses to assess how cleanly its communication hardware transmits information.

EEEL researchers are looking past today’s networks, which convert a transcontinental phone conversation from electrical to optical signals and back several times and spruce up the degrading signal along the way. With much faster all-optical switching equipment (such commercial hardware does not yet exist), telecom engineers will need a way of measuring light-signal quality, understanding its inevitable degradation, and dynamically compensating for such impairments in the equipment sending the original signal. To this end, EEEL scientists are measuring light signal quality as well as deducing the causes of various forms of signal degradation in work indispensable to making the leap to next-generation all-optical networking.

• Unique electro-optic sampling system, traceable to fundamental SI units, to calibrate photodiodes up to 110 GHz.
• First calibration of complex frequency response and time-domain impulse response of an oscilloscope with mismatch corrections and full point-by-point uncertainty analysis in both the time and frequency domains that is traceable to fundamental SI units.
• Developed software to correct for both random and systematic timebase errors in high-speed sampling oscilloscopes.