Study On DFB Semiconductor Laser Based On Reconstruction-equivalent-chirp Technique And Photonic Integrated Device

With the rapid development of internet and wireless communication, all kinds of data services increase explosively. As a result, the demand of network bandwidth capacity has been increasing dramatically. As one of three pillars of modern communication network, optical fiber communication is heading to the way of high-speed, large capacity and integration. Semiconductor laser, which is considered as the dominating light source in optical fiber communication, has experienced almost fifty years of development. With the increasment of network capacity, the present optical fiber communication systems which are built up by discrete devices face great pressure in the respects of quantity, volume and energy consumption. The monolithic integration of different photonic devices onto a single chip which is called as Photonic Integrated Circuit (PIC) is considered as the most likely solution to this problem. The PICs have entered in a rapid development stage since2004. Nowdays, the commercial large-scale photonic-integrated chips are available in the market. However, for various reasons, the development of optoelectronic core chip has been slow in China. The mid-to-high-end laser chips mainly depend on import. Hence, it is an exigent problem to develop and manufacture laser chip product of low cost and high end. In this thesis, my research is mainly based on reconstruction-equivalent-chirp (REC) technique. A detailed introduction on the principle of REC technique and the relevant design, simulation and fabrication of DFB semiconductor laser based on REC technique is given. The complex grating structure can be equivalently realized by specially designed sampled Bragg gratings (SBGs) with uniform seed grating. It provides a simple and mature approach to fabricate the high end DFB semiconductor lasers and laser array, which is promising for massive production. The high end DFB semiconductor lasers based on REC technique are experimentally demonstrated. In addition, a preliminary research on PIC chips is carried out.The meaningful results in this work are in the following:1. The equivalent corrugation-pitch-modulated (CPM), distributed-coupling-coefficient (DCC) and DCC-CPM DFB semiconductor lasers based on REC technique are developed. In CPM structure, the phase-arranging-region (PAR) is introduced to flat the photon density distribution along the laser cavity, hence the spatial hole burning (SHB) can be reduced. In DCC structure, the grating coupling coefficient in the center section of the laser cavity is larger than the ones in the side sections, hence the gain margin is enlarged and the single-longitude-mode (SLM) operation is improved. DCC-CPM structure combines the advantages of both structures. Although these DFB structures are with complex varying longitudinal parameters, the fabrication process and cost based on REC technique are the same as the equivalent phase shift DFB semiconductor laser. Simulation results show that the negative and positive effects of different parameters should be weighed up for structure design. Experimental results show that the lasers operate in good SLM with large side mode suppression ratio (SMSR) even under high injection current.8-wavelength100GHz equivalent CPM DFB semiconductor laser arrays with precise wavelength spacing control and high yield are obtained as well.2. The dual wavelength DFB semiconductor lasers based on REC technique are developed. Stable dual wavelength lasing is established by the grating structure consisting of two asymmetric phase-shifts±θ to spatially separate power distributions. The abrupt phase shifts are replaced by PARs for the advantages of separating power distributions in large θ, overcoming the small sampling linewidth on photo mask in small0and reducing the SHB. Stable dual wavelength lasing with about0.5nm wavelength spacing is experimentally demonstrated. A microwave signal at about64GHz can be generated by beating the two wavelengths. The dual wavelength semiconductor laser array with varying wavelength spacing by different phase shift is obtained as well.3. The study on quantum well intermixing (QWI) and the relevant PIC chip are carried out. An improved technique for QWI by generating point defects during the deposition of a thin layer of sputtered SiO2can massively increase the ratio of intermixing. Experimental results show that the sample with sputtered SiO2has a blue band shift of170nm by a temperature annealing at650℃, while a blue band shift of the sample with PECVD SiO2is only6nm at the same annealing temperature. It provides a simple and reliable method to obtain different band gaps for active and passive devices on the same wafer. The suitable length of multimode interference area of multimode interference (MMI) coupler is obtained by simulation. A monolithic integrated four channel DFB laser array and a MMI coupler chip is designed and the fabrication process is studied.