Integrated passive wavelength athermalisation for vertical-cavity semiconductor laser diodes

The ITU G.694.2 CWDM wavelength grid spacing is largely determined by an allowance for source wavelength drift. A method of reducing this is introduced by stabilising the optical length of a short semiconductor laser cavity, using the phase contribution of DBR reflectors to compensate the increase in its optical length with temperature. It is shown that it is necessary to adopt a VCSEL design incorporating optical polymers in air-gap DBRs. Giving consideration to the technical problems of such an approach, a design procedure is developed based on a TMM survey of the available DBR design space. An example design for a 1λ InP cavity is shown to reduce temperature drift of the design wavelength of 1320nm to -4.3pm/°C over the range 0-80°C.