Theoretical Analysis And Experimental Research On Widely Tunable SGDBR Laser Diode

Widely tunable laser diodes, which can set output wavelength according to the requirements, are one of the most important semiconductor optoelectronic devices. They are now playing an important role in the dense wavelength division multiplexing (DWDM) systems for reducing the required number of inventory lasers, and also expected to have wide applications in the further intelligent optical network. Furthermore, they also have widespread application prospects in the measurement and sensing field. Sampled-grating distributed Bragg reflector (SGDBR) lasers are the most promising candidates since they have wide tuning range, high side-mode suppression ratio (SMSR), small linewidth, fast switching speed and strong expanding characteristic of function.In this dissertation, the research work focus on the theoretical analysis and experimental research on widely tunable SGDBR laser diode. Specifically, the main work contains the followings:1. Design and optimize the sampled-grating structure for the tunable laser diode. The impact of the sampled grating in a distributed Bragg reflector laser on the tuning range, output power, and side-mode suppression ratio were investigated in detail. The optimization parameters consisted of the sampled length, the number of the sampled period, duty cycle and facet reflectivity.2. Numerically simulated the semiconductor materials of the active and passive regions of the laser diode. The band structure and gain spectrum of the multi-quantum wells were provided. The tuning range and the corresponding absorbing losses of semiconductor materials with different band-gap were calculated. Furthermore, by utilizing OlympIOs simulator software, optical field distribution in the active and passive regions, the refractive index mismatch and optical overlap were also studied.3. A new dynamical theoretical model for simulating widely tunable SGDBR lasers has been developed. The model integrates both time-domain traveling-wave method and frequency-domain transfer-matrix method into a single procedure. The active region of the device is still operated in the conventional time domain, while the passive parts are firstly performed by the transfer-matrix method and then transformed to the time domain via digital filters approach. Both the static and dynamic characteristics of SGDBR lasers, such as L-I curve, output spectrum, tuning characteristics, large-signal modulation, and dynamic wavelength switching, can be clearly visible in our model and in qualitative agreement with the published experimental results. Furthermore, this new model is also applied in the investigation of the dynamical properties of the complex Photonic Integrated Circuits (PICs).4. Using C12/H2 as etching etchants, the surface damage of the InP/InGaAsP material in ICP etching system was investigated. By measuring the changes of photoluminescence (PL) intensity from a specially designed InP/InGaAsP multi-quantum well (MQW) in both exposed and protected regions, and utilizing a Gaussian Depth Distribution model, the extent of damage was quantitatively analyzed. The influences of pressure, ICP power, RF power and Cl2/H2 mixing ratio of ICP system on the surface damage extent were revealed. Based on these results, a set of optimized low damage etching parameters with a less than 16 nm damage-depth was finally obtained. This technique has been successfully applied into the fabrication of DFB laser and the sampled grating. Both laser performance and accelerated aging test verified the reliability of our ICP etching processing in Bragg grating fabrication.5. The systematic study has been made to investigate the Butt-Joint techniques. The total wet-etching process for butt coupling was replaced by dry-etching followed by a small amount of selective wet etching to improve the reproducibility and the uniformity of the process. Meanwhile, the growth procedure of MOCVD was also adjusted to obtain a more reliable butt coupling.6. Based on the optimized parameters and related processing technology, the widely tunable SGDBR laser diode has been made. The residual reflection at the butt-joint interface is as low as 10-4 tested by precision reflectmeter. Furthermore, in order to overcome many defects existing in the nature structure of SGDBR laser diode, the SGDBR laser diode integrated with SOA is also fabricated.7. An automatic wavelength measurement and control system for SGDBR laser diode was developed by using LabVIEW virtual instrument software. The fabricated device features that quasi-continuous wavelength tuning range is more than 35 nm and the side mode suppression ratio (SMSR) is higher than 30 dB within the whole tuning range. The uniformity of different channel can be improved by integrating SOA in the SGDBR device. The wavelength-switching test indicated that the time delay can be less than 6.2 ns when the output wavelength switched from 1542.92 nm to 1546.76 nm.The main innovations of this dissertation are as follows:â… . The relationship between the structure parameters of sampling grating and the reflection spectrum has been analyzed systematically. The impacts of the sampling grating in a distributed Bragg reflector laser on the tuning range, output power, and side-mode suppression ratio (SMSR) were analyzed. Finally, optimized grating parameters were obtained.â…¡. A new dynamical model was established. This model integrates both time-domain method and frequency-domain method into a single procedure. The active region of the device is still operated in the conventional time domain, while the passive parts are firstly performed by the frequency method and then transformed to the time domain via digital filters. Both the static and dynamic characteristics of SGDBR lasers, especially the wavelength switching performance, can be clearly visible in our model. And it indicates that this new model can be furthre extended to the dynamical simulation of the complex Photonic Integrated Circuits (PICs).â…¢. The dry-etch damage of high-density plasma was studied. The effects of various etching parameters of Inductively Coupled Plasma (ICP) system on the etching damage using Cl2 and H2 mixing gases were investigated systematically, and the law of low-damage etching conditions were summed up. These conclusions have been applied to the fabrication of DFB lasers. The performance and aging experiment of lasers confirmed the validity of our conclusions and techniques. And it was used for improving the fabrication of sampling grating.â…£. The Butt-Joint techniques were studied. The total wet-etching process for butt coupling was replaced by dry-etching followed by a small amount of selective wet etching to improve the reproducibility and the uniformity of the process. Meanwhile, the growth procedure of MOCVD was also adjusted to obtain a more reliable result. Based on the optimized parameters and related processing technology, the widely tunable SGDBR laser diode has been made. Furthermore, in order to overcome many defects existing in the nature structure of SGDBR laser diode, the SGDBR laser diode integrated with SOA is also fabricated.