Lasing Properties of Microcavity Semiconductor Lasers and Spatial Coherence in Gain Profiled Semicnductor Lasers with Optical Feedback

Download or read book Lasing Properties of Microcavity Semiconductor Lasers and Spatial Coherence in Gain Profiled Semicnductor Lasers with Optical Feedback written by Guan Hong Wu and published by . This book was released on 2004 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: Investigated in this thesis are some methods to control the optical modes of semiconductor lasers with different cavity geometries such as microdisks, microrings, and broad-area lasers with external cavities. The characteristics of lasing spectra from microdisk and microring semiconductor lasers are examined in detail. Microcavity devices are mounted on either glass substrate or the end facet of a multi-mode optical fiber, which is first realised in the mounting technology area of microcavity lasers. Under optical pumping in pulsed or continuous wave condition at room temperature, all sample devices achieved lasing. Lasing modes have been identified to be consistent with Whispering-Gallery modes. Quality factors are estimated to be of the order of 2500. We also observed for the first time that the mode spectral broadening with microring devices under high pulsed pump powers is attributed to the transient red shift of the lasting mode. These work show that optical pumping is an easy and flexible way to study lasing characteristics of semiconductor microcavity lasers. We can control the wavelength and intensity of optical modes in these devices through changing their diameters and varying their geometries. Two mounting configurations expand the optical pumping schemes and application areas with microcavity lasers. Mounting microcavities on the end facet of fiber will find possible applications in the integrated optical circuit, in which microcavity devices can be coupled with optical fiber as filters, add-drop filters, etc. Further work needs to be done on mounting microcavity devices at the end facet of a single-mode fiber due to the wide adoption of this fiber in telecommunication systems. How the optical feedback from an external cavity affects the spatial coherence of optical modes in gain profiled broad area semiconductor lasers consists of another part of the research work in this thesis. This device shows good spatial coherence with increasing output optical field under pulsed operation but has limited operation range with good spatial coherence under CW condition. The optical feedback reduces the threshold current of the gain profiled device by up to 8%. This is a trivial improvement that could lead to higher reflective coatings on the facets of laser diode. Feedback also restores the symmetry of beam profiles and increases the total intensity of the output beam without degrading its spatial coherence. It reduces the effect of any local perturbations in the thermal lens profile. The appearance of interference fringes between the near field profile segments when the feedback mode matches the output mode perfectly is another evidence of the food spatial coherence with this device. Simulations based on the modified Maxwell-Bloch equation verify the above experimental results.