Are We On Exactly The Same Wavelength?

Stephanie Weiss, Executive Editor

If you have been using lasers for more than a few years, you can recall the days when the wavelength specified on a commercial diode laser was a rough estimate rather than a precise figure. As recently as the early 1990s, it was not unusual to buy "1550-nm" diode lasers that really emitted light at 1552 or 1555 nm. That's changed, partly because of the influence of telecommunications companies that want to save capital costs by pouring many wavelengths of light into a single optical fiber. To do this, each laser must emit at a precise wavelength, exactly 0.8 nm from its neighbor. And the optical components that select those signals (in splitters or add-drop switches, for example) must be able to pick out one wavelength and no others. Gas spectroscopists know that measuring wavelengths with such high accuracy is no simple task, and precision wavemeters are expensive. But the telecommunications market demands for not only lasers but other optical fiber components has driven some significant improvements in photonics instrumentation and calibration techniques.