06 Sep 2002
A Dutch collaboration has unveiled what it claims is the first integrated, multiwavelength ring laser.
A research team from the Eindhoven and Delft universities of technology, JDS Uniphase and the COBRA/DIMES research institutes have fabricated a digitally tunable laser with seven output wavelengths and a total size of just 1 x 1.5 mm.
The device contains four semiconductor optical amplifiers (SOAs) monolithically integrated with a 4 x 4 phased-array (PHASAR) multiplexer. Operating each of the SOAs individually produces lasing at four separate wavelengths, spaced by 3.2 nm. When two amplifiers are operated simultaneously, additional channels are created, giving a total of seven emission wavelengths from 1538 to 1547 nm.
Ring lasers function by using a loop of fiber or a circular waveguide as the laser cavity. "Previously, multiwavelength ring lasers were made from discrete components connected by fibers," explained researcher Jan Hendrik den Besten. "Their performance was sensitive to fiber vibrations."
The integrated device, on the other hand, offers high wavelength stability. "When a PHASAR is integrated, it is possible for the device to lase at well defined wavelengths, determined by the passbands of the PHASAR," den Besten explained.
The laser operates with a threshold current of 70 mA, a sidemode suppression ratio of 40 dB (when pumped at 100 mA) and a fiber-coupled output of -20 dBm. The low output power is attributed to high intracavity loss and low output coupling efficiency.
Future designs will incorporate an extra SOA in the output waveguides to boost power. The team also plans to increase the number of available channels by rearranging the amplifiers within the device.
Tami Freeman is technology editor with the FiberSystems magazine group.