News | April 3, 2007

OKI Develops First Gain-Coupled DFB Lasers For Practical Use

Anaheim, CA - OKI Electric Industry Co., Ltd. recently announced it has developed a gain-coupled (1) (GC-) DFB laser (2) that is tolerant of optical reflection. By employing the GC-DFB laser, OKI succeeded in becoming the world's first 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 FTTH.

"The results we obtained from this technology confirm that it will contribute to achieving lower cost, isolator free optical subassembly modules. Because the manufacturing process of the GC-DFB laser is approximately equivalent to that of conventional index-coupled (IC-) DFB lasers, chip manufacturing costs are expected to be the same as well. We are developing samples for evaluation, planning to provide them to the market by June this year," said Harushige Sugimoto, Senior Vice President and Chief Technology Officer at Oki Electric Industry. "In our long term plan, we are aiming to commercialize small and low cost components for optical communication using OKI's original silicon lens technology (3)."

For a normal FTTH light source, Fabry-Perot (4) lasers that emit multiple modes are used for short distance transmission (up to 10km), while 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. However, optical isolators are costly components and require space on the order of several millimeters. Thus, for optical sources, the market has been requesting semiconductor lasers which do not require optical isolators.

OKI 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. With this advance, OKI conducted 25km transmission experiments over the temperature range where optical modules normally operate (0 ~ 70ยบ C) and found that in a state where reflected light (-14dB) was forcefully applied, there was almost no degradation of reception sensitivity. This confirmed a marked improvement in tolerance to reflected light, compared to conventional IC DFB lasers.

[Glossary]

  1. Gain-coupled: To oscillate in a single mode by periodically gain (or loss) in the waveguide layer in the laser.
  2. DFB (Distributed Feedback) laser: The whole cavity contains active layers and thus creates a periodic structure which acts as a distributed reflector in the wavelength range of laser operation. Therefore, single-frequency operation is easily achieved.
  3. Silicon Lens: OKI's ultra small lens for optical communication developed in 2002. This lens can be manufactured in volume with LSI manufacturing technology.
  4. Fabry-Perot lasers: Fabry-Perot Diode Lasers are the most common type of diode lasers. Laser oscillation is demonstrated in multiple modes as the light in the active layer is amplified when it goes back and forth in the resonator.

SOURCE: Oki Electric Industry Co., Ltd.