Fabrication of multilevel phase computer-generated hologram elements based on effective medium theory

Area of Science:

• Optics and Photonics
• Holography
• Nanofabrication

Background:

• Conventional fabrication of diffractive optical elements and computer-generated holograms (CGHs) with high diffraction efficiency typically requires multiple lithography steps or complex electron-beam lithography techniques.
• These multi-step processes are often time-consuming and can lead to cumulative errors, impacting the final device performance.

Purpose of the Study:

• To develop a simplified, one-step fabrication method for multilevel phase CGHs.
• To leverage effective medium theory for precise control over phase modulation in CGH fabrication.
• To demonstrate a viable alternative to conventional multi-step fabrication processes for CGHs.

Main Methods:

• The proposed method utilizes effective medium theory to design subwavelength structures within each cell of the CGH.
• Phase modulation is achieved by dividing CGH cells into fine structures whose surface features dictate their effective optical indices.
• A binary structure is patterned onto a dielectric material using direct electron-beam lithography or one-step photolithography followed by ion etching.

Main Results:

• The fabricated CGHs successfully synthesized multilevel phases by controlling subwavelength structures.
• Experimental reconstruction of the wave field closely matched computer simulations.
• The results validate the effectiveness of the one-step fabrication approach based on effective medium theory.

Conclusions:

• The developed one-step method offers an efficient and effective way to fabricate multilevel phase CGHs.
• Effective medium theory provides a powerful tool for designing CGHs with desired phase modulations.
• This technique simplifies the fabrication process, paving the way for more accessible high-performance diffractive optical elements.