| With the development of the communication services, the demand for the capacity increases rapidly. At present, the key devices of the optical communication system, such as lasers, modulators and detectors, are usually separately fabricated, packaged and utilized. But as the optical network capacity will grow fast in the near future, if the devices keep discretely, the traditional optical communication systems will become very huge and complex, thus the cost of the energy consumption and management will be very high. So it would be hard to maintain the system. In contrast, dozens or hundreds of photonic elements are monolithically integrated on a single substrate to form the photonic integrated circuits (PICs). The main elements of PICs such as size, energy consumption and management are all superior to these with discrete devices. Therefore, PICs are widely considered as the only way to solve the problem and the main developing trend.Wavelength division multiplexing (WDM) technology is widely used to increase the information capacity at present. The key device is the WDM photonic integrated circuits. It includes multi-wavelength DFB semiconductor laser array (MLA) and other various passive filters. The fabrication process of MLA is the most difficult among these elements. In the introduction of this thesis, we briefly review the development of the PICs and discuss some techniques to fabricate MLA presented up to now. Finally, we introduce the advantages of Reconstruction-equivalent-chirp (REC) technology for fabricating MLA. The equivalent phase shift and equivalent chirp are used to improve the yield of lasers working under single longitudinal mode condition. Only an additional μm level photo-lithography should be added comparing with the processes to fabricate the ordinary DFB lasers, so it would reduce the costs. In this thesis, one of the important works is the research of REC based DFB semiconductor laser with special grating structures and corresponding laser arrays. Another is the proposal and study of the Microstructure quasi-phase matching technology (MS-QPM). We found that the REC technology is a special case in one-dimensional. We also reveal its physical nature, and discuss the potential applications.In the first chapter, the brief introduction of the development of the PICs is given. Then, the difficulty for fabricating the the waveguide grating and multi-wavelength DFB semiconductor laser array is described. The corresponding fabrication technologys are also given. At last, the main work and the arrangement of this thesis are given.In the second chapter, the basic principle of the waveguide grating is introduced. In the following, the basic principle of the REC technology is also given. It shows that the change of the initial phase of the sampling structure changes the initial phase of the Fourier sub-gratings, and the change of the sampling period changes the period of the Fourier sub-grating. So the arbitrary grating profile can be equivalently formed if we carefully design the sampling structure. Finally, the whole design process is given.In the third chapter, some special types of DFB semiconductor lasers and DFB laser arrays based on REC technology are studied. The following are some special types of DFB lasers studied and experimentally realized.1. The equivalent A/8phase shifted DFB semiconductor laser was experimentally realized for the first time. Its performances such as small signal frequency response,1dB compression point and input3rd intercept point were tested. The directly modulated back to back error free transmissions in radio over fiber (RoF) system with operation temperatures of25"C and60"C, baseband signal frequencies of1.0-Gb/s and1.4-Gb/s and local oscillator signal frequency of7.64GHz are experimentally realized respectively.2. The equivalent3PS DFB semiconductor laser was experimentally realized for the first time. The spectral characteristics were tested when the bias currents varied from20mA to100mA. It is found that the laser has good single longitudinal mode (SLM) performance. The side mode suppress ratio (SMSR) is56dB under the bias current of100mA.3. Initialing with the a firstly proposed high performance Y branch waveguide based on the transverse apodized grating, the equivalent apodized DFB semiconductor lasers based on the sampled grating were proposed and theoretically analyzed. This type of lasers can be grouped into two kinds. The one is the apodization with two sides; the other is the apodization with middle. It is found that the sidelobes can be suppressed so that the side modes of the lasers can be suppressed accordingly when the first kind of apodization is applied. The second kind of apodization can suppress the spatial hole burning (SHB). Therefore the SLM operation can be maintained under high bias current. The experiment results show good SLM performance with SMSR of50dB when the bias current is100mA. If the apodiztion with two sides is designed reasonablely, it also can be used to suppress the potential lasing of the0th order Fourier sub-grating.In addition, another novel DFB laser structure which is called SHB compensation (SHBC) DFB semiconductor laser is proposed. That is to say, use the predesigned chirped grating to compensate the index change caused by the SHB. Theoretical analysis shows that it has better SLM performance, narrower linewidth and better dynamic properties compared with the3PS DFB laser. This kind of lasers can also be realized by REC technology.Some kinds of DFB laser arrays based on REC technology were also experimentally realized:1.3.2nm×11wavelengths and6.4nm×7wavelengths A/4equivalent phase shifted DFB laser arrays;2.0.4nm×50wavelengths and1.6nm×30wavelengths equivalent3PS DFB laser arrays.The experimental results show that the measured wavelength spaces are smaller than that of designed to the extent of90%. According to the linear fitting line, the wavelength residuals are within+1nm～-1nm. These results are accurate enough to control the wavelength grid in the future. If the heart fine tune or the current fine tune is used, it is promising to meet the ITU-T standard precisely. For the3PS laser array, up to48lasers can work with SMSR larger than35dB except that two of them fail. According to the reports about the DFB laser arrays, the results exhibit the maximum lasing number.In the fourth chapter, the further study for the DFB laser arrays based on REC technology is given. The influence of the sample mask error on the lasing wavelength is analyzed. Some conclusions can be drawn that the lasing wavelength error is related to the laser cavity length and the sampling period. However, even though this error is considered, the precision can only be controlled within1nm. Fortunately, this value is accurate enough for the laser arrays. The effluence on the effective index cansed by the lateral etch of the samping structure during the fabrication of the sampled grating is also analyzed. The results show this effluence is very small. On the other hand, the measured lasing wavelength space shrinked error is caused by the dispersion of the laser waveguide. The value of the dispersion was measured and the actual wavelength space considering dispersion is calculated. It matches well with the measured results.In the fifth chapter, the crossed sampled grating is proposed for the first time. The±1st order reflective wavelengths are blue shifted of this grating. So the performance of this grating can be improved if the+1st order Fourier sub-grating is used. It is because that the0th order of this grating is farther away from the+1st sub-grating than that of traditional gratings so the unwanted resonance of the0th order can be avoided. Then based on the theoretical analysis for the crossed sampled grating, the MS-QPM is firstly proposed and theoretical analyzed and simulated. The REC technology becomes a one dimensional case of the MS-QPM. In the following, the physical nature of MS-QPM/REC is also revealed. That is to say, an additional grating vector produced by the sampling structure is applied to compensate the difference between the vectors of the working light and the seed grating. This principle is very similar with that of QPM in nonlinear optics. MS-QPM is expected to equivalently fabricate various complex multi-dimensional gratings with low cost. Its potential applications are discussed and some photonic devices are also proposed. Finally, the reconstruction algorithm of the MS-QPM is studied. Because the sampling pattern is usually very complex and hard to give an analytical expression, the reconstruction algorithm appears more important. |
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