Roger Helkey, Peter Davis
Optical Switching Applications of Delayed
Feedback Nonlinear Systems
Abstract:The goal of this project was to develop an optical switching system based on an optical nonlinear delayed-feedback system
previously developed at ATR by T. Aida and P. Davis.
A secondary task was optimizing the feedback system for the switching application.
Nonlinear delayed- feedback systems are useful because for a relatively simple implementation they exhibit a wide
range of complex functions, such as data storage, random data generation, and adaptive data generation.
The primary project was to set up an optical switching system using the output of the nonlinear fiber-delayed-feedback system.
The switching technique that was chosen is direct injection of an optical pump signal into a lasing device.
Optical switching has previously been demonstrated in traveling-wave or Fabry-Perot optical amplifiers using a separate
CW laser as the probe source. However, direct injection is a simpler technique combining the optical source and wavelength
conversion mechanism into a single device.
The lasers used in this experiment are conventional single-stripe long-wavelength lasers which are available commercially.
Lower switching thresholds have been demonstrated using a multisegment laser with a saturable absorber to quench lasing in
the absence of a pump signal.
The saturable absorber also induced bistability, which is an interesting subject for further investigation.
Bistable devices were not readily available for use here. Distributed feedback (DFB) lasers were used to provide single-frequency
output.
The price of pigtailed lasers is about an order of magnitude higher than for chip-mounted or can-mounted devices.
The cost of building a general-purpose fiber pigtailing setup is comparable to buying a pigtailed laser.
However, a general-purpose setup can be used to compare switching in many different kinds of lasers at relatively low cost.
For example, Fabry-Perot lasers vs DFB lasers, and gain-depletion pumping vs gain-enhancement pumping.
A major component of the project was construction of a 1.3 μm semiconductor optical amplifier.
A commercially available Erbium-doped fiber amplifier was used to get high-power signals for switching at 1.55 μm.
A semiconductor amplifier can be used to directly do optical switching in the amplifier itself due to gain saturation or four-wave
mixing. A semiconductor amplifier was constructed for backup as a 1.3 μm amplication source as well as a frequency-conversion
component.