Research On The Dynamic Tuning Characteristics Of DFB Lasers And Its Measurement Methods

Distributed-Feedback Diode Laser (DFB) is a kind of high quality narrowlinewidth, dynamic single mode and wavelength tunable laser, which is widelyutilized in optical communications，sensing and measurement. To be the corecomponent in the system, the dynamic characteristics of the tuning of DFB laser,including dynamic SMSR，transient wavelength，and dynamic linewidth，effect theentire properties of the system. So the real-time online measurement is very necessary.However, the quickly change of the dynamic characteristics requires the highresolution and fast response of the measure equipments, which cannot be achieved byconventional methods. In addition, due to the nonlinear phenomena in the currenttuning process and difficulty in the measurement of dynamic properties, there are fewmathematical models for the depicting of laser’s wavelength in tuning.This paper represents a novel delayed self-heterodyne interferometer measuremethod for dynamic tuning characteristic of lasers, then analyses the feasibility of themeasurement of dynamic wavelength and linewidth, and forms a measure system. Inaddition, based on the tunable mechanism of DFB laser, this paper comes up ananalytical model of static wavelength in tuning. Using the spectrometer to measurefour different manufacturers’ DFB laser’s static mode spectral, it obtains the6parameters of the analytical model. Working under the temperature tuning, by usingthe TDLAS to measure the8absorption lines of CO2near1582nm, and comparingwith HITRAN database, the reliability of this model was confirmed. The main contentof the work and innovation, include the following three aspects:1．Measurement methods of DFB laser’s dynamic tuning characteristic: In thispaper, the dynamic tuning characteristics of diode lasers are studied. Based on theMach-Zehnder interferometer, a measurement method of fiber delayedself-heterodyne interferometer (FDSHI) is proposed. We measured the dynamicwavelength and linewidth characteristics of DFB lasers in the saw-tooth currenttuning. Comparing the2absorption lines of CO2around1600nm with the ones inHITRAN database, the dynamic wavelength is identified and also reliable. The errorbetween database true value and dynamic wavelength calculated by the beat signal is only0.001nm, which verified the reliability of the dynamic tuning characteristics ofFDSHI measurement methods.2．The best range of dynamic tuning linewidth of DFB lasers: Using the FDSHIof experimental systems, the dynamic linewidth of DFB lasers was measured.Experimental results show that the dynamic linewidth with the injection current isnarrowed initially and then widened. When the injection current is about0.6times ofthe maximum current in the entire tuning range, the dynamic linewidth gets thenarrowest. The best operating current is around0.5to0.8times of the maximum.3．The analytical model of the static wavelength characteristic: According to thetuning mechanism of the diode lasers, an analytical model of the wavelengthcharacteristics is established. The parameters of the model were identified byexperimental results. The model was applied to analyze four DFB diode lasers. Weobtained the transient characteristics of the lasers. We also received the staticcharacteristic of these lasers from the spectrometer. The correlation coefficients aremore than0.9999. At the same time, based on the absorption spectrum of CO2gas, wealso measured the emission wavelength of lasers. We compared it with the HITRANdatabase, the difference is within3pm. The analytical model can accurately predictthe transient output wavelength of lasers in tuning; the accuracy can meet thespectrum, optical coherence measurements and other practical requirements.The experimental results, obtained in the paper provide a theoretical andexperimental basis for the real-time monitoring and control optimization tuningcharacteristics of the diode lasers.