Beam Express demos tunable 1550 nm VCSEL
The device is also notable for its tuning voltage of only 4 V. Beam Express says this figure is around one-tenth of existing tunable MEMS devices, and makes it compatible with standard low-voltage drive electronics. In addition, the 980 nm optically-pumped design leads to a CW single-mode power output of 1 mW from an aperture diameter of 5 µm. Other features include 40 dB of side mode suppression.
Beam Express is led by Jean-Claude Charlier, an ex-Agilent executive who joined the company as CEO this April. According to Charlier, Beam Express has a unique wafer-fusion technique that allows it to integrate high-performance VCSELs with high-bandwidth MEMS tuning structures.
"The MEMS mirror can be electrostatically activated at very low tuning voltages and uses standard, low cost electronics," says Charlier. "This approach is key to producing long-wavelength VCSELs with high yield and higher functionality, resulting in significant cost savings during component manufacturing."
Charlier adds that tunable lasers are key elements for reconfigurable Metro networks, but will be commercially viable components only if their cost matches fixed-wavelength telecommunication lasers. "Our tunable VCSEL meets this requirement due to the inherently inexpensive manufacturing process involved," he says.
The company is also currently developing 1550 nm multi-channel VCSEL transmitters for CWDM Metro applications. Preliminary specifications include 1 mW output power for a 2.5 Gbit/s-per-channel transmitter with a reach of 50 km. The transmitters can emit anywhere from 1470 to 1610 nm with 20 nm channel spacing, in accordance with the CWDM grid.
VCSELs are fabricated using wafer fusion to integrate the AlGaAs/GaAs DBRs with the InGaAlAs/InP active region. The air gap for the MEMS tuning structure is produced by etching away part of the isolation spacer layer in the top DBR, which is suspended by one or several narrow blocks.
Beam Express says that by structuring one or both of the wafers before they are fused together, it is able to fabricate built-in lateral electric and optical confinement. The company calls this "localized wafer fusion", a proprietary process it says provides high performance devices with high yield. So far, 1550 nm VCSELs with 3 mW output power have been demonstrated at room temperature using a pump power of 70 mW.
Other companies that have developed long-wavelength VCSELs with tunable MEMS mirrors are Bandwidth9 and CoreTek, the now defunct Nortel subsidiary.
