Tunable Laser Control System Based On DFB Laser Array

Due to the advantages of small size,light weight,and high efficiency,semiconductor lasers are widely used in communications,scientific research,military,medical and other fields.According to the different lasing modes,semiconductor lasers can be divided into continuous and pulsed lasers.Different application fields have different requirements for the performance of semiconductor lasers.In dense wavelength division multiplexing passive optical network(DWDM-PON)systems for optical access networks,low-cost broadband tunable lasers are required;in high-speed optical switching networks,tunable lasers are required to be capable of high-speed switching at the source to achieve fast routing;and in applications such as optical phased array(OPA)lidar based on pulsed laser ranging,wide wavelength tuning range helps to expand the spatial angle range of radar scanning,while the laser output pulse width and repetition frequency adjustable range are also critical to the resolution and flexibility of detection.Most semiconductor lasers use current injection as the excitation source to achieve light emission,so their working mode and light-emitting characteristics largely depend on the current output form and stability of the driving power supply.In order to realize that semiconductor lasers can be used in many fields with different working characteristics and output modes,this paper develops a tunable laser control system that can output in continuous and pulsed modes.The control system developed in this thesis is based on a series-parallel distributed feedback(DFB)semiconductor laser array.The laser integrates 16 lasers based on the reconstruction equivalent chirp(REC)technology in a 4×4 matrix arrangement,and uses a two-level cascaded Y-shaped branch acts as a beam combiner to combine and output the four waveguides.The thesis first investigated the research status of semiconductor lasers at home and abroad,and then introduced the principle and advantages of REC technology.On the basis of analyzing the characteristics and design requirements of the laser,we designed the control system.The continuous tunable laser control system consists of three parts: a main control module,a drive module and a temperature control module.The main control module is controlled by a combination of a single-chip microcomputer and a field programmable gate array(FPGA)to ensure that it can flexibly realize multi-channel high-speed switching.In order to achieved independent control of 16 lasers arranged in series and parallel,we propose a solution using 4 drive current sources combined with 4 multiplexer switches to provide current for lasers.Besides,we also used a combination of semiconductor thermoelectric cooler(TEC)drive circuit and proportional integral differential(PID)circuit to complete the system operating temperature.The control of the pulsed tunable laser is based on the continuous tunable laser control system,and a pulse drive current source is made independently to drive the semiconductor optical amplifier(SOA),using a combination of FPGA and high-speed comparator to realize the output of narrow pulse signal with adjustable repetition frequency.After experimentally testing,the 16-channel laser based on the two design schemes can achieve continuous wavelength coverage in the range of 39.2 nm by means of temperature tuning and current tuning.Lasers can achieve high switching speed under 100 ns among multiple channels in any order.Each laser can output a narrow pulse light signal with a pulse width of 5ns.The continuous and pulsed tunable laser module designed based on the control system of this paper has the characteristics of wide wavelength tuning range,adjustable output mode,fast channel switching speed,simple and flexible control method,narrow pulse width,low cost,miniaturization and etc.Besides,it can further expand the number of channels.Therefore,if the solution can be further improved and optimized,it is expected to be applied to many fields such as optical communications,optical switching networks,OPA lidars and so on.