The Research On The Novel Distributed Feedback Semiconductor Laser And Laser Array

The transmission capacity of optical fiber communication network being demanded sharp increasingly, more and more channels are utilized in a WDM system, while a lot of lasers with different lasing wavelengths are needed for light sources. If a WDM system is consisted of discrete devices, it will be very complex and bulky. For such a system, being proportional to its transmission capacity, the maintenance costs and the energy consumption grow surprisingly.To slove these problems, the best way is to use photonic integrated circuit (PIC) to replace discrete functional devices. However, to fabricate multi-wavelength laser array, the key component for PIC, is much more difficult than single laser. At present, in commercially available PIC, DFB semiconductor multi-wavelength laser array is processed by0.1nm precision, which only can be fabricated by special E-beam equipment with low yield slowly and costly. This situation prevents PIC from being large-scale commercial production.In this dissertation, the reconstruction-equivalent chirp (REC) technology is proposed to design and fabricate semiconductor laser and laser array. The main contents of this dissertation are as follows:1. The principles and methods of REC technology. To fabricate true chirp or true phase-shift grating, high-precision E-beam equipment should be used. The required procession precision for equivalent chirp or equivalent phase-shift grating based on REC technology is lower than that for true chirp or true phase-shift grating by one to two orders of magnitude. Therefore, REC-based DFB semiconductor laser can be fabricated with ordinary procession platform. Furthermore, equivalent apodization can also be achieved by varying the sampling duty cycle.2. Coupled-mode theory and transfer matrix theory. For a normal DFB semiconductor laser, the waveguide structure can be seen as a linear waveguide. According to coupled-mode theory, in such a waveguide structure only the forward mode and the backward mode are considerable. In transfer matrix theory, a waveguide grating can be thought as a cascade of many of uniform grating segments. Thus the optical matrix of the waveguide grating can be represented by multiplying the optical matrices of the uniform grating segments orderly. When the parameters, such as optical gain, detuning factor and coupling coefficient keep constants along the laser cavity, the characteristcs of a laser can be solved only relied on the coupled-mode theory. Or else, for sloving them correctly, coupled-mode theory has to be combined with transfer matrix theory.3. A SBG semiconductor laser is with asymmetric refractive index distribution and the other one with asymmetric sampling duty cycle. An equivalent π phase shift was introduced into the center of the former that had two sections with the same lengths, but different effective refractive indices. In such a structure, the lasing wavelengths in the-1st channel of its left and right sections are equivalent while that different in their0th channels, therefore the0th channel lasing can be suppressed greatly. For the latter, both lengths and sampling periods in the left and right sections are uniform, while sampling duty cycles being unequal and their summation being1. Mathematical investigation shows that arbitrary equivalent phase shift can also be introduced into this structure. Compared with normal SBG laser, the asymmetric sampling duty cycle structure has an improved effection for suppressing lasing in its0th channel.4. The fabrication and expriments of REC-based semiconductor laser. The fabrication approach of REC-based semiconductor laser and laser array is introduced firstly. The optical spectrum of an equivalent π phase shift laser and two kinds of dual-wavelength lasers with double of equivalent phase shift are shown. Experimental results have shown REC-based semiconductor lasers have good performance, meanwhile the impact on the lasing wavelength caused from the production error of the the duty cycle can be negligible. Furthermore, asymmetric sampling duty cycle laser has better suppression for the0th channel lasing than conventional one do.