Jm Pozo

QDot and GaInNAs/GaAs Broadband Semiconductor Optical Amplifiers for Simultaneous Multiwavelength Amplification

The need for simultaneous multi-channel transmission in optical communication systems has led to a requirement of semiconductor optical amplifiers (SOAs) with flat gain over a broad range of wavelengths and minimum channel interspacing for the independent and simultaneous amplification of several different laser sources. In addition for ultra-high speed communication with femto-second pulses, composed of a spectrum of wavelengths, simultaneous multi-wavelength amplification is required. The goal of this paper is the modelling, fabrication and characterization of SOAs made from GaInNAs/GaAs quantum-well edge emitting lasers and InAs/GaAs QDot edge-emitting lasers. Both QDots and GaInNAs/GaAs quantum wells (QWs) exhibit broad gain for a range of temperatures and current as measured experimentally.

GaInNAs/GaAs quantum wells: Advantages for SOAs

GaInNAs/GaAs quantum wells are a relatively new material system for telecom/data com application. Generally it has been thought that the material offers an improved temperature performance and lattice matching to GaAs both significant advances. However studies of the material show that it has more parameters to control: in particular controlling the N distribution within the QW and the nature of the N states- single, pair states or cluster states allows tunability of the band gap, conduction band effective mass and quantum-dot-like localised states. These features offer a number of new device applications which will be discussed in this talk

Improvements in GaInNAs/GaAs quantum-well lasers using focused ion beam post-processing

At the present time, there is a considerable demand for long wavelength (1.3μm-1.5μm) laser diodes for low cost data-communication applications capable of operating at high speed and at high ambient temperatures without the need for thermoelectric coolers. First proposed in 1995 by M. Kondow, the GaInNAs/GaAs material system has attracted a great deal of interest as it promises good temperature performance. The broad gain observed in GaInNAs/GaAs QW samples suggests that wavelength tuning should be possible by the application of gratings to select an optical mode. In addition, splitting the contact has been shown to improve modulation speed in other materials. These two methods should be able to be used jointly and processed together. The use of split-contact lasers has the advantage of that no change is made in the processing steps, since there is only need for a new metal mask to define a new top p-contact. Despite the bandwidth enhancement of two-contact lasers compared to the single contact case is well known, to the authors knowledge, so far it has not being applied to GaInNAs/GaAs lasers. The use of Bragg-gratings on the ridge waveguide of the laser will generate a periodic modulation inducing an interaction between the forward and backward travelling modes. The effect of this interaction is the one of a band pass filter on the gain shape of the laser, allowing filtering out the actual lasing wavelength, and tuning the lasing wavelength in the range of wavelengths with substantial optical gain. Therefore, this method can be used optimally in lasers with broad gain, as is the case of GaInNAs/GaAs. In this paper, we reveal experimental investigations in how to apply these two post-processing methods to 600m-long 1.25μm-Ga0.66In0.34N0.01As0.0.99/GaAs 6nm single quantum-well ridge waveguide lasers.

Quantum dot vs. GaInNAs/GaAs quantum wells for broad band amplification

Summary form only given. There has been a lot of interest in broad band amplifiers required for ultra-fast communications systems where a fast pulse with a wide spectral range is put through fibre. Quantum dot SOAs with inhomogeneous broadening provide broad gain. Different sizes of dots can amplify different wavelengths but their interaction is governed by their homogeneous linewidth. We examine the limitation that this puts on multi-wavelength amplification and examine the effect of barrier height. We consider the quantum well system GaInNAs/GaAs and consider whether local fluctuations within this system can act as localised centres for amplification as in the quantum dots. We examine the controlling parameters for this system and compare and contrast these two systems for use as broad band SOAs.