A linear optical amplifier that fits on a single chip was demonstrated in a switched high-speed WDM environment. Dan A. Francis and others at Genoa Corp. (Fremont, CA) integrated a semiconductor optical amplifier with a vertical-cavity surface-emitting laser (VCSEL) on an indium phosphide (InP) chip.1
Because optical networks are changing from static point-to-point systems to dynamic reconfigurable architectures, the requirements on optical amplifiers are also changing. Amplifiers need to operate at any data rate, operate in multiple wavelength environments, and not create undesired gain transients as a result of adding or dropping wavelengths or optical packet switching. In addition, smaller would be better, since space in the central office is at a premium.
Erbium-doped fiber amplifiers (EDFAs) have slow gain dynamics, which create unwanted gain transients when operated in a switched environment. They also contain a number of components and are relatively large.
Semiconductor optical amplifiers are compact but inherently nonlinear. Francis and his coworkers modified an SOA by integrating it with a VCSEL on an InP substrate. The VCSEL and the amplifier share the same active region. The VCSEL operates along the entire length of the amplifier (see Fig. 1). The circulating optical power in the VCSEL acts as a ballast to maintain the gain in the amplifier, despite power changes in the signals.
The chip measures 1 x 0.5 x 0.15 mm, and was made using standard MOCVD processes. The VCSEL threshold current was about 100 mA and typical operating currents were 200 to 300 mA. The amplifier worked across the C-band.
The LOA showed no power penalty in a 10-Gbit/s WDM transmission, no crosstalk due to either WDM or TDM, and almost no switching transients (see Fig. 2).
For more information contact Dan Francis at firstname.lastname@example.org.
- D. A. Francis, S. P. DiJaili, J. D. Walker, OFC 2001 Postdeadline paper 13.
Yvonne Carts-Powell is a science and technology writer based in Belmont, MA.