Relative Intensity Noise (RIN) in High-Speed VCSELs for Short Reach Communication

Abstract

Lasers in the steady state condition do not provide constant carrier and photon densities even without any current modulation. These optical power variations provide an intensity noise. Since optical transmission systems have a critical impairment due to this noise source, it is quite important to know how it can be defined and measured. Relative intensity noise (RIN) is a measure in order to quantify and determine how noisy the laser, as the transmitter of transmission line, is. The work of this Master degree project has been both experimental and analytical. In the first experimental part of the project, relative intensity noise (RIN) was measured on state-of-art high-speed multi-mode 850-nm vertical-cavity surface-emitting lasers (VCSELs) intended for next generation short reach data communication standards. Measurements have been performed on devices with different current aperture diameters, at different bias currents, and at both room temperature (RT) and 85°C. The RIN values obtained are shown to be in most cases below the requirements, for example, in the future 32 Gb/s Fibre Channel (32GFC) standard. The second analysis part of the project dealt with extracting values of intrinsic dynamic laser parameters from RIN measurements and comparing to those extracted from corresponding S21 measurements, which is the conventional method. Good agreement was found, and the pros and cons for the two extraction techniques are discussed.