Sources For Optical Communication Systems Research Articles

Vertical Cavity Surface Emitting Lasers as Sources for Optical Communication Systems: A Review

Next generation integrated photonic circuits will be dominated by small footprint devices with lower power consumption, low threshold currentsand high efficiencies. Vertical Cavity Surface Emitting Lasers (VCSELs) having those attractive qualities has shown results to meet the next generation demands for optical communication sources. VCSELs applications are sensors, data com, optical communication, spectroscopy, printers, optical storage, laser displays, atomic optical clocks, laser radar, optical signal processing to name a few. This review centres around on the basic operation of semiconductor lasers, structure analysis of the devices and parameter optimisation for optical communication systems. This paper will provide comparisons on growth techniques and material selection and intends to give the best material realisation for nano optical sources that are up to date as used in optical communication systems. It also provides summarised improvements by other research groups in realisation of VCSELs looking at speeds, efficiency, temperature dependence and the device physical dimensions. Different semiconductor device growth methods, light emitting materials and VCSELs state of art are reviewed. Discussions and a comparisons on different methods used for realising VCSELs are also looked into in this paper.

Numerical approach to field fluctuations and spectral lineshape in InGaAsP laser diodes

AbstractThis paper reports on a numerical approach to model the field fluctuations, spectral lineshape and linewidth in semiconductor lasers. The approach is based on numerical solution of the laser rate equations augmented by Langevin noise sources that account for fluctuations in the lasing field. The paper newly examines contributions of intensity and frequency noises to the spectral characteristics of the lineshape and its linewidth over a wide range of injection current. The model is applied to InGaAsP lasers emitting in a wavelength of 1.5 μm as the most representative light sources in optical communication systems. Accuracy of approximated models of calculating linewidth from low‐frequency components of the frequency noise is checked. Effect of non‐linear gain suppression on the lineshape is also explored. The spectral lineshape promotes and the linewidth decreases as the laser is injected far from the near‐threshold region. The lineshape changes mainly with changes in the frequency noise spectrum while the linewidth is sensitive to variation in the low‐frequency levels of both intensity and frequency noises. Copyright © 2004 John Wiley & Sons, Ltd.

Semiconductor lasers with a thin active layer (>01 μm) for optical communications

Double heterostructure lasers with a thin active layer have been investigated. Device parameters have been optimized for using laser diodes as light sources in optical communication systems. Threshold current density takes a minimum value for an active layer thickness of around 800 A in the case of undoped active layers. Full width of beam divergence for active layer thicknesses smaller than 0.1 microm is smaller than 30 degrees , and the resultant coupling efficiency into an optical fiber of a numeric aperture as small as 0.05 is 50% on the average and is 80% at maximum in conjunction with a focusing lens. Other features of the thin active layer discussed are polarization and available output powers.

Fluorescence and oscillation characteristics of LiNdP<inf>4</inf>O<inf>12</inf>lasers at 1.317 µm

Spectroscopic data and laser oscillation characteristics of the 1.317 μ line in lithium neodymium tetraphosphate (LNP) are reported. A stimulated emission cross section of this transition was spectroscopically determined as <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.1 \times 10^{-20}</tex> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which corresponds to 1/4.5 of that at the 1.047-μm transition. Cross-section temperature dependence, laser cavity loss, threshold versus crystal length, and threshold temperature dependence were measured experimentally. Since resonant loss was negligible at the 1.317 μm line, room temperature threshold is lower than that at 1.047-μm in the case of long crystal, and threshold temperature dependence is weaker than that at 1.047 μm. A miniaturized LNP laser, using a graded index fiber as a focusing medium, is also shown. LED pump intensity required to obtain a constant output is compared for 1.047- and 1.317-μm wavelengths. The 1.317-μm line seems to be useful as miniaturized optical sources in optical communication systems, since required intensity is around several W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for the side pump, and the wavelength corresponds to the most transparent band of ultra low-loss optical fibers.

Semiconductor sources for optical communication systems

Following the first practical demonstration of laser action in 1960, engineers and scientists began to consider seriously the possibility of developing long-distance, high-capacity optical communication systems. The first practical systems for the civil telecommunication network are expected to be demonstrated under field conditions in Britain and elsewhere by 1977. Throughout the intervening 16 years, the development of system expertise has been closely linked with the growing capability of the optical source, and the future progress will undoubtedly depend on the advances in source performance that show promise of achievement in the next five years