The Effect of Die Bonding Distributed Feedback Lasers

The effect of die-bonding-induced strain on the output spectra of gain-coupled distributed feedback (DFB) diode lasers was investigated. Bonding strain affects the in situ diffraction grating in DFB lasers and manifests itself as changes in the output spectrum. It is shown in this paper that such changes are observed in DFB lasers by comparing the spectra before and after die bonding. In addition, it was also observed that upon die bonding the lasing mode can, in some cases, flip from one side of the stopband to the other. This flip was modeled using a probability-amplitude transfer-matrix DFB laser model that included a bonding-induced perturbation of the pitch of the Bragg grating along the length of the cavity. The nonuniform strain perturbation of the pitch of the grating was determined from a finite element method simulation of a die bonded laser chip and correlated well with the strain that was deduced from measurements of the degree of polarization of photoluminescence from bonded chips.