Study Of Wavelength Control Of The Multi-wavelength Laser Array

In recent years,with the emergence of new internet applications,such as cloud computing and virtual reality(VR),the speed,capacity,and bandwidth of signal transmission in communication systems are increasingly demanded.In addition,the massive data exchange driven by emerging applications also requires a much-higher-rate and much-higher-bandwidth in the data center network to sustain the increase of network traffic.The wavelength division multiplexing(WDM)technology applied to the optical communication system has made a significant contribution to the demand for explosive growth of the internet business.As a key component of the WDM system,the multi-wavelength laser source has been extensively investigated and developed.The preferred choice of multi-wavelength source is the multi-wavelength laser array,for the reason that they are compact,robust and suitable for monolithic integration.Many works have been done in the past few years.Currently,several issues still exist,such as the complicated manufacturing process,high cost and lower yield led by the insufficient accurate control of channel wavelengths.Therefore,it is of great significance to study and develop a low-cost and high-performance scheme of laser array with well controlled channel wavelengths.In this thesis,a scheme of varying-ridge-width and tilted ridge waveguide DFB laser array with complex coupling grating and curved connecting waveguide has been proposed.A high single-longitudinal-mold yield could be obtained and the reflection loss could be reduced via curved waveguide.By changing the ridge widths and tilt angles of each ridge waveguide of the laser array,the effective refractive index and the grating pitch of each channel are effectively controlled simultaneously,targeting at achieving a multi-wavelength array with an equally spaced and specified channel distance.The main contents of this thesis include:(1)The theoretical principles of laser operation and the numerical model of DFB laser have been firstly studied.Based on Maxwell's equations,the time-domain coupled wave equations,the carrier rate equation and the spontaneous random noise model of the DFB laser are combined and constitute the traveling wave model for DFB laser simulation.And then,the numerical solution schemes of the traveling wave mode have been reviewed and implemented.(2)The varying-ridge-width and tilted ridge waveguide DFB laser array has been studied in detail.The capability of the proposed scheme in controlling lasing wavelengths of the DFB laser array has been investigated and its possible potential impact on high-order transverse mode lasing and coupling coefficient variations has been studied as well.Based on these findings,an array of 4-channel DFB lasers has been designed and optimized by utilizing the aforementioned numerical simulation model,according to the specified requirement of the project,i.e.to achieve an accurate frequency spacing of 400 G Hz among channels.Simulation results show that the proposed array scheme can effectively control the lasing wavelength of each channel,leading to an equally spaced lasing array.(3)According to the preceding theoretical analysis and numerical simulations,we have fabricated the 4-wavelength DFB laser array.The experimental results prove that the wavelength control scheme proposed and studied in this thesis is an effective and feasible solution to the DFB laser array.Meanwhile,some related potential issues have been discussed and their solution schemes have been suggested.More concretely,the experiment indicates: 1)varying-ridge-width tilted ridge waveguide is a low-cost and effective way of controlling lasing wavelength in an array;2)An accurate wavelength spacing of 2.8nm for the channel wavelength spacing and an error of less than 0.4dB for the channel lasing power have been measured.Further performance improvement will be ensured by re-optimizing array waveguides in the next-round.3)The proposed compact array scheme only requires a replacement of the ridge mask,with other processing techniques compatible with those in conventional DFB laser fabrication.