Research On The Novel Bragg Gratings And Their Applications In Tunable Semiconductor Lasers

Bragg gratings and tunable semiconductor lasers are some of essential devices inoptical networks,and provide important guarantee for the reconfigurable AutomaticallySwitched Optical Network (ASON).They also are the key components for optical fibersensors and measurements.Due to these wide applications,many scientists and expertshave been attracted to research on the Bragg gratings and tunable semiconductor lasers.Inthis dissertation,Bragg gratings and their applications on tunable semiconductor lasers havebeen explored and investigated.The main contents are as follows:(1)Due to the Fourier transform theory on the fiber Bragg grating,the analyticalexpressions on the sampled fiber grating,Gauss-apodized sampled fiber grating,sampledGauss-apodized fiber grating,and interleaved sampled fiber grating withψphase shift havebeen presented.Accuracy of those expressions has been verified by a good agreement withtheir reflection spectrum obtained by the transfer matrix method.Impacts of parameters inthe sampled fiber grating on the reflection spectrum envelope and sidelobes have beenstudied.The impacts of temperature and stress on reflection spectrum of the sampled fibergrating have also been discussed in detail.(2)Based on the analytical expression of interleaved sampled fiber grating,impacts ofshift phases of the inserted sub-grating,grating length,as well as interleaved length on itsreflection spectrum envelope have been analyzed.It provides theoretical reference to designthe interleaved sampled fiber grating in detail.(3)According to the linear invariability and reversibility of Fourier transform theory,anovel multiple reflection spectrum envelope concatenated technology has been proposed.The proposed technology can densify spectral channels of sampled gratings with fixed peakspace,as well as spatially physical corrugation of structure.Using such technology,twomulti-peak Bragg gratings have been designed:one is the digital concatenated grating;theother is the consecutive interleaved sampled grating.These proposed gratings can provide afiat reflection spectrum envelope and high peak reflectivity.(4)The theoretical simulation model of the tunable sampled fiber grating externalcavity semiconductor laser has been built by combining the equivalent reflection cavitytheory with the transmission line laser theory.Due to this model,the steady-state propertiesof sampled fiber grating external cavity semiconductor lasers,such as thresholdcharacteristics,P-I curves,line-width,output spectra,static wavelength tuning curve,as wellas SMSR,have been simulated and analyzed.It is useful for designing tunable external cavity semiconductor lasers with Vernier tuning principle.(5)The nonlinear phenomena such as asymmetric side mode suppression ratio orpower characteristics and tuning hysteresis phenomena are the ubiquitous phenomena intunable semiconductor lasers,which have been observed in the sampled fiber gratingexternal cavity semiconductor lasers by studying its static characteristic curves,such as thewavelength tuning curves,side mode suppression ratio curves,output power curves and soon.In order to analyze the origin of these nonlinear phenomena,the nonlinear effects insemiconductor (e.g.cross-gain modulation effect,cross-phase modulation effect,and fourwave mixing effect)have been considered in the theoretical model of the sampled fibergrating external cavity semiconductor laser.Influence of its internal physical parameters andthe four wave mixing effect on nonlinear phenomena of such laser are analyzed anddiscussed.It is helpful for exploring the internal nonlinear mechanism of tunablesemiconductor lasers.(6)In order to suppress the nonlinear effect in such sampled fiber grating extemalcavity semiconductor laser,apodization and interleaved technology have been introducedinto the external sampled fiber grating of such laser.The suppression of side-lobes cansuppress the nonlinear phenomena in the sampled fiber grating external cavitysemiconductor laser and increase its tuning range.An interleaved technology can make suchlaser obtain 18.4 nm tuning range.In its whole tuning range,side mode suppression ratio of40 dB and output power around 10dBm have been obtained.(7)The theoretical model of the SG-DBR laser has been established based on thetransmission line laser theory.The steady-state characteristics of the SG-DBR laser havebeen discussed.It is found that the invisible F-P cavity between anti-reflection coating andsampled grating has existed in the SG-DBR laser.Such invisible F-P cavity has taken largeinfluences on the steady-state characteristics of the SG-DBR laser,especially on its tuningcurves.(8)Two designs of the digital concatenated grating on the semiconductor materialhave been proposed for providing the top flat reflection spectrum envelope.One is forchanging the grating period of the conctenaed sub-grating;the other is for changing theeffective material index of the sub-grating.Three manufacture methods of these digitalconcatenated gratings have been proposed,which are holography method,electron beamlithography,and nanoimprint lithography.(9)A novel digital concatenated grating DBR laser has been proposed,for obtainingwidely tuning range (＞50 nm),high side mode suppression ratio (＞35 dB),and high output power (～10 dBm)with low power varation (0.6 dB).Such proposed laser has high outputpowers with small power variation,and high toleration on facet reflectivity.