| The output power of conventional distributed feedback(DFB)semiconductor lasers is generally limited by catastrophic optical damage(COD)and thermal effects.To overcome these limitations and further improve the output power of semiconductor lasers and their reliability,this thesis mainly studies 1550 nm DFB single-mode high-power semiconductor lasers with the design,fabrication and characterization.The main research contents are as follows:A novel single mode high-power semiconductor DFB laser based on offset quantum wells has been proposed.By introducing a relatively thick passive waveguide layer just below the active layer,the loss of the laser is reduced,while the slope efficiency of the laser is improved,and the coupling coefficient of the grating is reduced to avoid longitudinal space hole burning.Along the laser cavity,a three-section structure,consisting of reflective section,active section and passive section,is adopted.The reflective section is used to replace the high reflection coated facet,therefore,the random phase caused by the facet cleaving is eliminated and the single mode yield is improved.Both the reflective and passive regions do not contain materials that can absorb 1550 nm light,so the threshold of COD will be further increased and the saturated output power will be improved.The design,fabrication and characterization of the proposed high-power DFB laser has been carried out.The material composition and thickness of each layer of the laser are optimized,and the quantum well has an appropriate optical confinement factor and coupling coefficient.The influence of doping on resistance and free carrier absorption loss is also investigated.A laser simulation model based on time-domain traveling-wave method is established,and the performance of high-power semiconductor DFB laser is simulated by this model.The effects on the device performance have been analyzed for coupling coefficient,length and loss.On this basis,the structural parameters of the highpower semiconductor DFB laser are designed.The processing procedures for the highpower semiconductor DFB lasers have been studied.The gratings are etched at different depths in the active and reflective regions.A three-section high-power semiconductor DFB laser is fabricated for the first time,and the results show that the proposed DFB laser scheme is feasible.After optimizing the structure and fabrication process of three-section high-power semiconductor DFB laser based on offset quantum well,a wide-waveguide high-power semiconductor DFB laser is designed and demonstrated.Because the mode field is further away from the ridge waveguide,the confining ability of the ridge waveguide to the modes is weakened,and the overlap of the higher-order mode with the active region having current injection becomes worse,which increases the threshold gain of the higher-order mode,thus ensuring that the laser still maintains good single-mode characteristics with wide waveguide.At the same time,the wide waveguide increases the COD threshold of the laser and reduces the thermal effect,thus further improves the output power of the laser.The test results show that,for a laser with ridge waveguide width of 8 μm and cavity length of 800 μm,its threshold current is only 50 m A,and the output power reaches to 180 m W.The laser yields good single-mode characteristics,and the side mode suppression ratio(SMSR)of the laser is more than 55 dB with variations of temperature and current.The relative intensity noise(RIN)of the laser is less than-157 dB/Hz,and the linewidth is less than 250 kHz. |
