Four-channel EA array operates at 10 Gbit/s

Paula Noaker Powell

Based on their high-speed modulation, polarization independence, low power consumption, and a high extinction ratio, electroabsorption (EA) modulators show promise as both wavelength-conversion and optical-switching systems. A response time below 100 ps makes them especially attractive for high-speed gate applications. While semiconductor optical amplifiers have been used as optical gates, response time is as high as 1 ns. Researchers at NTT Photonics Laboratories and NTT Electronics Technology Corp. (both in Atsugi, Japan) believe that an EA modulator will improve on this time.

One problem so far with arrayed EA modulators involves the electrical signal feed. To resolve the issue, the NTT scientists developed a four-channel EA modulator array that uses an impedance-matched film (IPF) carrier to feed the electrical driving signal. The carrier is made of an insulating polyimide film on which a coplanar waveguide is formed. With this system, the researchers achieve 10-Gbit/s operation for all channels with clear eye opening and negligible crosstalk. The array also exhibits polarization independence, a high extinction ratio, and a 50-ps switching time.

For ultrahigh-speed modulation with EA modulator arrays, the device must be less than 100 µm long to limit its capacitance-making it extremely hard to cleave and handle. In addition, the IPF carrier forming the four-channel coplanar waveguide lines is more than 1000 µm wide-the EA modulator array should thus be wider than this dimension for optical coupling between input/output fibers. The NTT researchers overcame these pitfalls by integrating the EA modulator with a low-loss passive waveguide and fabricating a 1400-µm-wide device.

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