Recently, Coarse Wavelength Division Multiplexing (CWDM) systems expand in local access and metropolitan area optical networks. In CWDM systems, uncooled and directly modulated DFB lasers are used, and the eight wavelengths spaced by 20nm from 1470 nm to 1610 nm are multiplexed. Then, in the eight wavelengths, each laser has been demanded to have similar characteristics such as threshold currents and slope efficiencies.
However, among the eight wavelengths, L-band (1590 nm and 1610 nm) DFB lasers are inferior to S, C-band DFB lasers in performances such as threshold currents and slope efficiencies, so that the improvement of L-band laser performances have been demanded. The inferior of performances of L-band lasers is said to be mainly caused by increases of Auger recombination and Intervalence band absorption (IVBA).
We designed the S-band, C-band and L-band lasers to improve the internal loss values and minimize the difference of laser performance among these bands. In L-band, we achieved the successful wide temperature range (-40 °C to 95 °C) operation of 300 μm long DFB lasers. They showed the threshold current of as low as 40 mA and the slope efficiency of as high as 0.27 W/A at 95 °C.
As a result, regardless of the peak-wavelength difference, the CWDM DFB lasers show the similar performances and the excellent high temperature L-I characteristics. These results show that these lasers are suitable for using as the uncooled light source in CWDM applications.