激光光谱展宽散斑抑制效果分析

Analysis of Speckle Suppression by Laser Spectral Broadening

针对激光显示技术中的散斑干扰,提出了一种利用外腔半导体激光器来展宽光谱的散斑抑制方法。利用外腔半导体激光器中光反馈引起的自混合干涉效应,适当调节反馈强度使激光器进入相干坍塌态,以获得具有宽带发射特性的激光。然后将该宽带激光光源用于散斑测量系统,由于光谱展宽降低了激光的时间相干性,从而散斑现象能够得到有效抑制。实验结果表明,在自由空间反射光路中,当激光器处于相干坍塌态时,光谱展宽至6 nm且为多纵模振荡,散斑对比度降低至0.049。

For the speckle noise in laser display, a speckle reduction method by the spectral broadening is proposed, which is based on the external cavity semiconductor laser system. Firstly, by appropriately tuning the feedback ratio, the state of coherence collapse is obtained using the optical-feedback-induced self-mixing interference and can be harnessed for the realization of the spectrally broadband emission. Then the optimized broadband laser source is utilized in the speckle measurement system. Significant speckle reduction can be achieved by the spectral broadening due to the low temporal coherence properties of lights. Experimental results show the performance of the proposed approach. The extraordinarily high spectral bandwidth of about 6 nm with multimode emission is achieved in the coherence collapsed state. In free-space reflection geometry, the speckle contrast has been successfully reduced down to 0.049 with this broadband laser source.