Micro-refractive optical elements fabricated by multi-exposure lithography for laser speckle reduction.

Area of Science:

• Optics
• Photonics
• Materials Science

Background:

• Laser speckle is a common interference pattern that degrades image quality.
• Existing macro refractive optical elements (mROEs) for speckle reduction have limitations due to their entrance facet size.
• Developing scalable micro-optical solutions is crucial for advanced imaging systems.

Purpose of the Study:

• To fabricate and evaluate a micro-refractive optical element (μROE) for enhanced laser speckle reduction.
• To overcome the size limitations of traditional mROEs.
• To improve the performance of speckle reduction techniques using low-coherence laser sources.

Main Methods:

• Fabrication of a micro-ROE using SU-8 photoresist and multi-exposure lithography.
• Integration of the μROE with a macro-ROE.
• Characterization of speckle contrast reduction using a low-coherence multimode laser diode.

Main Results:

• A μROE with 2 × 2 duplicated multi-level cells was successfully fabricated.
• The combined μROE and mROE system reduced objective speckle contrast to 0.2.
• The study demonstrates the potential for further speckle reduction by optimizing μROE design.

Conclusions:

• The developed μROE offers a promising solution for effective laser speckle reduction.
• Micro-optical elements can overcome limitations of macro-scale optical components.
• Further design iterations of μROEs can lead to even greater speckle contrast reduction.