Multi Spectral Laser Speckle Reduction using Liquid Lightguide

 Advanced applications such as including multispectral microscopy, endoscopy, display applications, structured illumination, and precision optical sensing, require high color accuracy, a narrow-band light source, and low-noise imaging. To produce high-quality white light with enhanced color rendering, laser of multiple wavelengths are combined directly. Traditional laser-based white light generation is expensive and inefficient, as it requires beam splitters, dichroic mirrors, diffusers, and complex alignment. Therefore, a cost-effective method for creating white light by mixing multiple lasers using pulse-width modulation (PWM) in 255 levels at a chosen bias through direct current modulation. While this approach generates white light without a sluggish phosphor color convertor, it adds speckle noise. The superposition of lasers yields mixed speckles (MS) using a 7x1 fiber coupler, which exhibits a speckle contrast of 14%. By directing the fiber-coupled combined output through a liquid light guide (LL) and employing PWM, the speckle contrast was reduced to 3.8%, without the need for mechanical vibration or moving parts. Red speckled images had the worst autocorrelation with diffused white light. The correlations among these lasers and white light were analysed. The red laser shows the highest reconstruction error (mean square error (MSE) = 0.51) after compression and rescaling. We created novel neuromorphic implementations using Poisson spike encoding to convert pixel intensities into spike trains that represent neuronal currents. Cumulative speckle contrast estimation via neuron model responses yielded values of 54% for multispectral (MS) fiber-coupled output and 27% for liquid lightguide (LL) illumination. By blending six laser wavelengths, we created a high-CRI (93) multispectral light source with a 72% reduction in speckle contrast as compared to MS.