Applied Digital Optics: From Micro-optics to Nanophotonics

5

Digital Diffractive Optics: Analytic Type

Chapter 2 proposed a classification of free-space digital optics into the following five types, which are differentiated by either their structural aspects or their optical functionalities:

• Type 1 – Holographic Optical Elements (HOEs);
• Type 2 – Diffractive Optical Elements (DOEs);
• Type 3 – Computer-Generated Holograms (CGHs);
• Type 4 – Sub-Wavelength digital Elements (SWEs); and
• Type 5 – Dynamic digital optics.

This classification is also chronological, with Type 1 (HOEs) being the first elements developed, and with Type 4 (especially photonic crystals and metamaterials) and Type 5 (dynamic diffractives) being the most recently developed (see Figure 5.1).

By the term ‘digital diffractive optics’, we actually mean diffractive optical elements calculated by computer and fabricated by lithographic techniques (using binary masks, as done for digital electronics) as planar elements.

Chapters 5 and 6 focus mainly on Types 2 and 3, which make up the vast majority of diffractive optics used in industry today. This chapter is longer than many of the others because of the importance of these elements today.

Holographic Optical Elements (HOEs, Type 1), dynamic digital optics (Type 5) and sub-wavelength digital elements (Type 4) will be covered in Chapters 8–10. Although HOEs and dynamic diffractives can be calculated by a computer and recorded from a digital CGH master, neither are directly fabricated by means of a binary lithographic. Photonic ...