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GC-DFB features high optical reflection tolerance

Posted: 30 Mar 2007 ?? ?Print Version ?Bookmark and Share

Keywords:gain-coupled DFB laser? FTTH? optical transmitter? DFB lasers?

Oki Electric Industry Co. Ltd has announced a gain-coupled DFB (GC-DFB) laser that is tolerant of optical reflection.

By employing the GC-DFB laser, Oki claims it is the first company to develop optical isolator-free optical transmitter modules for practical applications, enabling lower-cost, smaller-size optical modules for use in long-distance networks, such as fiber-to-the-home (FTTH).

Optical reflection noise
For a normal FTTH light source, Fabry-Perot that emit multiple modes are used for short-distance transmission (up to 10km), while index-coupled DFB (IC-DFB) lasers that emit a single mode are used for long-distance transmission (up to 20km). In long distance transmission, IC-DFB lasers contribute to increased degradation in receiver sensitivity after sending data as the noise from unwanted optical reflection increases. Because of this, an optical isolator is necessary to shut out reflection. Optical isolators, however, are costly components and require space on the order of several millimeters.

Oki claims to have achieved optical isolator-free capability through a GC-DFB laser with improved tolerance of optical reflection and reduced degradation from relative intensity noise when impacted by reflected light. The company conducted 25km transmission experiments over the temperature range where optical modules normally operate (0 to 70?C) and found that in a state where reflected light (-14dB) was forcefully applied, there was almost no degradation of reception sensitivity. This marked improvement in tolerance to reflected light, compared to conventional IC DFB lasers.

Lower-cost optical subassembly
"The results we obtained from this technology confirm that it will contribute to achieving lower-cost, isolator-free optical subassembly modules," said Harushige Sugimoto, senior VP and chief technology officer at Oki. "Because the manufacturing process of the GC-DFB laser is approximately equivalent to that of conventional IC-DFB lasers, chip manufacturing costs are expected to be the same as well."

The company is developing samples for evaluation and plans to market the product by June this year.

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