Quantum dots enhance amplifier bandwidth
Optical amplifiers based on quantum dots (QDs) offer a number of sought-after features, including broadband gain and a high saturation output power.
Properties like these could well make them ideal for use in low-cost CWDM systems, in which the aim is to cover a wide range of transmission bands with the least number of amplifiers.
Now, a Japanese collaboration (from the University of Tokyo, the Optoelectronic Industry and Technology Development Association, and Fujitsu) has developed a QD-based semiconductor optical amplifier (QD SOA) that is said to offer a wider bandwidth than that achieved by bulk or quantum-well SOAs, or any other existing optical amplifier.
The researchers fabricated the QD SOA using InAs QDs in InGaAsP on an InP substrate. The device achieved a gain of more than 25(20)dB, a noise figure of less than 5(7)dB, and a 3dB saturation output power of more than 19dBm, between approximately 1410nm and 1500 (1530)nm.
QDs are also ideal for high-power applications, due to their ultrafast gain response (a few picoseconds), which suppresses signal distortion in the gain-saturated regime. The QD SOAs achieved distortion-free outputs at powers of up to 22.8dBm.
This high-quality waveform results in a penalty-free output power of 23.1dBm, which is a figure of merit claimed to be 8dBm higher than that achieved by conventional SOAs.
While QD SOAs have progressed rapidly, the researchers note that there is still much room for improving the quality of the crystal, which could increase the bandwidth further.
To commercialize such devices for telecoms applications, the next step is the elimination of polarization sensitivity and gain inequality.
Author
Tami Freeman is deputy editor of fibers.org and Fibre Systems Europe magazine in association with LIGHTWAVE Europe magazine.
