New Branches on the Tunable Laser Family Tree: Recent Technical Progress

摘要

Tunable lasers offer significant advantages in (D)WDM systems like inventory reduction and reduced product count, as well as the possibility of building wavelength routed networks. Tunable and wavelength selectable laser structures have been subject to intense research for about 20 years, but it was the emergence of WDM which brought the interest in these lasers to the fore. There is now a long list of proposed and demonstrated laser structures, and in this presentation we will make an attempt on classifying the large number of technical options. Lasers will be classified according to operational principles and the technologies used for making lasers with adjustable wavelength. The emphasis will be on tunable semiconductor based structures, including: external cavity lasers, multi wavelength sources, monolithic vertical lasers (VCSELs) and monolithic horizontal lasers (mainly DFB and DBR types). For the monolithic horizontal structures we will show the different schemes used to achieve wavelength selection/tuning. Many of the widely tunable lasers rely on a combination of wavelength selection mechanisms. In the last couple of years new or modified laser structures have been demonstrated, partly by established companies, but also, in spite of the downturn, by some new companies. In the same period other companies have pulled out of this area, been taken over, or even closed down. Several examples of new lasers will be described, in some cases using material which has not yet appeared in print. The examples include new types of external cavity lasers, laser arrays and DBR type lasers. In addition to the laser structures, there has also been technical progress on important practical issues such as long-term spectral stability and control of tunable lasers. Examples of this work will also be shown and discussed.