Fast Phase Modulation Scheme With Thermal Light For Correlation Imaging

With the development of imaging technology,correlation imaging is attracting more and more attention.Correlation imaging obtains image by correlating the outputs from two photodetectors: a high spatial-resolved detector that records a speckle field which does not interact with the object to be imaged and a bucket(single-pixel)detector which collects light that did interact with the object.To reconstruct image of the object,many frames of different speckles are required.For computational correlation imaging there is only a bucket detector with a high sampling frequency.Therefore the speed of correlation imaging is strongly limited by the speed of modulation of the light field.Usually,we use spatial light modulator(SLM)to load different random phase at different positions of a plane-wave light field.Then speckle fields of random spatial-temporal intensity fluctuations will be generated at far field,by the interference(of many sub-source)after propagation of light.The refresh rate of the speckle fields is thus limited by the refresh rate of SLM.Usually SLM performs better when modulated with sinusoidal signals which are also easier to be created,than that of random modulation signal.And we can insert multiple light pulses in a sinusoidal cycle.Based on this fact,we propose to modulate each pixel independently with different sinusoidal signals,in order to improve the refresh rate of speckle field.By laser pulse onto the SLM,the refresh rate of the speckle fields is determined by the repetitive frequency of the laser pulse.The speckle field will be changed after the pulse light modulated by SLM because of the modulation phase is changed differently over time.Through the theoretical analysis and numerical simulation,we show that the speckle fields generated with this method can be used for correlation imaging to speed up the sampling frequency and increase the number of effective speckle field with optimizing the modulated amplitude and the selection of the frequency combination.