ADC drives tunable laser production forward
US telecom equipment maker ADC has completed the commissioning of a new high-volume facility dedicated to the production of tunable lasers for dense wavelength-division multiplexing (DWDM) applications.
Located in Jarfalla, Sweden, the plant, which currently employs around 160 staff, supports all stages of the manufacturing process - from wafer fabrication through to final packaging, qualification and reliability testing.
Progress has been swift. At the recent Optical Fiber Communication show in California, the Jarfalla group unveiled the latest addition to ADC s Anywave family of tunable sources.
The NYW-60-B features a wavelength locker integrated into the butterfly package, as well as drive and control electronics in a board-mountable footprint. The module supports up to 160 factory-calibrated wavelengths in the 1529-1561 nm spectral band, with a tuning speed of 2 ms channel-to-channel.
According to Björn Broberg, director of technology management at ADC Photonics, Sweden, the laser addresses the two big concerns that have traditionally dogged tunable technology: production capacity and reliability.
"We have a new family of products with improved control electronics," he explained. "By building the wavelength locker into the laser package itself, we can save a lot of space and a lot of cost to the customer."
Equally significant, he says, are the proprietary control algorithm and active mode-stabilization scheme that ensure long-term stability (i.e. no mode jumps) across all of the laser s channels.
The NYW-60-B is a four-section, monolithic InGaAsP/InP semiconductor laser based on ADC s patented GCSR chip. (GCSR stands for grating-assisted codirectional coupler with rear sampled reflector).
The design uses coupled semiconductor waveguides (adjacent to the gain section) to act as a widely tunable filter, though the filter function alone is not narrow enough to select laser modes. The answer is to add a suitable rear reflector with a modulated grating behind the coupler section. A phase-control section completes the tuning region.
"It [the laser] is a monolithic semiconductor chip, so there are no moving parts, temperature tuning or mechanical tuning," said Broberg. "It works through current injection in the three tuning sections [coupler, phase and reflector].
One effect of this is that the switching speed is very fast compared with other technologies. The gain section works the same way as a distributed-feedback laser. The more current you put into it, the more power you get out - so that s the power control."
But what about applications? DWDM "sparing" is one opportunity that ADC and others like it are hoping to address. By opting for tunable technology, equipment makers can not only reduce the cost of their DWDM gear; they can also simplify inventory headaches in high-channel-count backbone systems.
"You can have a tunable laser as a back-up for any fixed-wavelength lasers that might go down," said Broberg.
In the medium term, it seems inevitable that tunable lasers will also enable the routing of an optical signal to be determined by the wavelength it is transmitted on.
"That [wavelength routing] is probably the area that has grown the most in the last year or so," said Broberg. "The wavelength is used as a so-to-speak address within the system."
Applications like this are likely to prove especially suitable for the metro market. "The dynamic capabilities of this laser simplify the networks considerably, as you can do a lot of the routing and switching within the wavelength domain," Broberg added. "The network becomes cheaper to begin with, and also much more flexible."
