IEEE J. Quant. Electron. http://dx.doi.org/10.1109/jqe.2011.2165317 (2011)

Optical coherence tomography (OCT) is a medical imaging technique that provides information about an object by analysing the coherence of reflected light. OCT devices containing fixed reference mirrors are simpler and require less power than those exploiting moving reference mirrors, albeit with the need for a tunable laser. Bauke Tilma and colleagues have now designed and characterized a monolithically integrated tunable laser containing quantum-dot amplifiers, phase modulators and passive components for use in medical OCT. The device operates at a central wavelength of 1,700 nm, which reduces absorption due to water in human tissue and minimizes Rayleigh scattering. The tuning bandwidth of more than 100 nm is the largest hitherto demonstrated for an arrayed waveguide-grating-controlled tunable laser, and the device's linewidth of less than 0.07 nm provides the 6 mm coherence length necessary for medical imaging. In addition, this device demonstrates that the active–passive integration technology designed for the 1,550 nm telecommunications wavelength region can also be used in the 1,600–1,800 nm range.