In this paper we characterize the switching dynamics of a novel three section slotted Fabry-Perot laser for phase modulated transmission systems. The static characterization shows that an average linewidth of 538 kHz is achieved for all 25 ITU 100 G channels of the laser, which is able to support differential quadrature phase-shift-keying (DQPSK) transmission at 10 Gbd symbol rate. An average wavelength switching time of 5 ns is also demonstrated using two measurement techniques. The performance during switching is examined by measuring the time resolved bit error rate (BER) of a 10.7 Gbd DQPSK packet transmission system. The time taken to go from no measured errors on one channel to no measured errors on the other channel is found to be less than 16 ns for the switching combination studied. © 2006 IEEE.