TUNING CHARACTERISTICS OF MONOLITHIC PASSIVELY MODE-LOCKED DISTRIBUTED-BRAGG-REFLECTOR SEMICONDUCTOR-LASERS

Tuning characteristics of multicontact passively mode-locked distribut ed Bragg reflector (DBR) semiconductor lasers are investigated in term s of center wavelengths and pulse repetition frequencies. It is shown that the center wavelength of the pulses can be tuned over a wide rang e by changing the refractive index of the Bragg reflector section eith er by means of carrier injection or by thermal effects while maintaini ng the pulses to be nearly transform-limited. Tuning of the pulse repe tition rates is realized by using four different approaches, i.e., cur rent injection to a passive phase-control section, varying of the reve rse bias to the absorber, varying of the injection current to the gain region, and thermal effects. Injecting current into the phase-control region results in a tuning range of more than 400 MHz while maintaini ng the pulses at transform-limited condition. Varying the reverse bias voltage to the absorber is shown to be an alternative to achieve larg e repetition rate tuning, by which a tuning range of 600 MHz is obtain ed. By combining these tuning schemes, a total tuning range of more th an 1 GHz is realized.