Research On Speckle Suppression Using Chaotic Laser In Laser Display System

Laser display technology has become the most promising new display technology after CRT,plasma,and LCD/LED display technologies.Because the technology has the advantages of larger display color gamut,higher color saturation,and higher display brightness.Due to the high coherence of laser light sources,speckle noise exists in the laser projection display,which seriously affects the imaging quality and hinders the further development of laser display technology.Therefore,the suppression of speckle noise is a key problem that laser display technology urgently needs to solve.In this thesis,we use the chaotic laser with low coherence property to achieve speckle suppression.In particular,we use high-power multimode laser diodes commonly used in laser display to generate chaotic laser by two methods: diodes with optical feedback perturbation and diodes with electrical chaotic signal modulation.These methods don't increase mechanical motion and relatively maintain the stability of the optical path.The effects of bias current and feedback strength in the optical feedback system,and the bias current and modulation amplitude in the modulation system on speckle suppression are studied respectively.Moreover,the speckle suppression effects of two systems are compared.The experimental results show that the chaotic laser generated by the two methods can effectively suppress speckle noise,and the speckle contrast can be reduced by more than 0.9.The main work of this thesis is as follows:1.The development of laser display technology and the problems encountered are introduced;the origins and classification of optical speckle are elaborated;the statistical characteristics of laser speckle and the principle of superposition are summarized;And the existing methods for suppressing speckle are briefly introduced.2.The method of chaotic laser generation by applying the laser diode with optical feedback perturbation to suppress speckle is proposed.The influence of bias current and feedback strength on speckle suppression in optical feedback system,as well as the optical spectrum and the variation of coherence length are studied.Eventually,it is found that under a certain feedback intensity,the spectrum of the chaotic laser generated by the laser diode is broadened to a certain extent.At this time,the speckle contrast of the diode output patterns is reduced,which realizes the suppression of the speckle noise in the laser display.3.The method of chaotic laser generation by using electrical chaotic signal modulation to suppress speckle is proposed.In this experiment,an autonomous Boolean network structure is used to generate electrical chaotic signal.And the influence of bias current and modulation amplitude on speckle suppression in the electrical chaotic signal modulation system is investigated.In order to ensure that the electrical chaotic signal can effectively modulate the laser diode,the peak-to-peak value of the electrical chaotic signal is gradually increased,the influence of the electric chaotic signal modulation on the spectrum and coherence length of the diode output is studied.The research results in this thesis have important theoretical significance and practical value for the use of chaotic laser to suppress speckle noise in the laser display technology.