Wideband Modulation and Tuning of Semiconductor Lasers Using Novel Quantum WellStructures

摘要

Angle modulation techniques enable analogue optical transmission systems to berealised which have dynamic ranges in excess of those possible with conventional intensity modulation direct detection (lMDD) links. Tunable semiconductor lasers are essential components for links employing optical frequency modulation (OFM) for enhanced dynamic range or dense wavelength division multiplex (DWDM) for multichannel capability. They are also key components in many advanced sensor systems. Existing lasers use the forward bias injection effect (CIE) to obtain tuning. whilst this is a convenient technique for wavelength setting it suffers from severe limitations when fast tuning or modulation. Of the laser frequency is required. At low modulation frequencies the response is dominated by thermal effects, leading to a decrease in emission frequency with increasing current, whereas at high frequencies the response is dominated by plasma and band filling effects giving an increase in frequency with increasing current. The resulting overall frequency response typically varies by more than an order of magnitude 0-1 Ghz accompanies by phase variations of up to pi radians. Equalising such a response even over a restricted frequency range, requires complex networks that have to be optimised for the particular laser and its operating conditions. Improved uniformity of response has been obtained in multielectrode distributed feedback (DFB) lasers by critical adjustment of the distribution of current between sections, but the settings needed are highly sample dependent, and may drift with laser ageing, making this an unreliable approach.