Diffractive optical element

Figure 2.8. Scanning electron microscopy (SEM) photomicrographs of (a) a micro-diffractive optical element mold fabricated by a focused ion beam (FIB) and (b) the transferred optical element on a sol-gel film. [Reprinted with permission from Ref. 98.]... 

Another important optical phenomena that relies on light interference and diffraction is holography, the process by which holograms (interference patterns) are produced. Whilst holograms are best known for the reproduction of near perfect 3D images of an object in the graphic arts, they also find apphcations in newer areas such as laser eye protection, LCDs, diffractive optical elements, optical processing... 

The optical scheme of holographic lithography is schematically illustrated in Fig. 4. The beam of the same laser system as used for DLW recording passes through a diffractive optical element (DOE), where it is spht into a set of diverging multiple beamlets by diffraction. The set of beamlets is subsequently colhmated by a lens, and passed through the transmission mask, which selects... 

The inscription of SRGs on polymer films also allows for fabricating diffractive optical elements that require intricate surface structxires. For a review of unconventional methods to fabricate and pattern nanostructures, see Xia et Viswanathan et illustrated several such possibilities, such as the honeycomb pattern shown in Figure 14.28, the e -crate-like structure of Figure 14,29, or the beat structure shown in Figure 14.30. These widely... 

Xripathy, S. K., Viswanathan, N. K., Balasubramanian, S., and Kumar, J. Holographic fabrication of polarization selective diffractive optical elements on azopolymer film. Polym. Adv. Technol. 2000,11, pp. 1-5. 

T. Hessler, M. Rossi, R.E. Kunz, M.T. Gale, Analysis and optimization of fabrication of continuous-relief diffractive optical elements. Appl. Opt. 37, 4069-4079 (1998)... 

For the matrix of this holographic diffractive optical element, created in this case, we will have (Jones, 1941 Kakichashvili, 1974) ... 

The possibility of creation of the holographic diffractive optical elements with anisotropic structure with advanced features. 

Golub MA, Hutter T, Ruschin S (2010) Diffractive optical elements with porous silicon layers. Appl Optics 49(8) 1341-1349... 

Gargas DJ, Muresan O, Sirbuly DJ, Buratto SK (2006) Micropattemed porous-silicon Bragg mirrors by dry-removal soft lithography. Adv Mater 18(23) 3164 Golub MA, Hutter T, Ruschin S (2010) Diffractive optical elements with porous silicon layers. Appl Opt 49(8) 1341-1349... 

Gale MT (1997) Replication techniques for diffractive optical elements. Microelectron Eng 34 321-339... 

Different strategies can be used to concentrate the incident optical power. There are three main groups of optical concentrators. One of them is based on refractive optics (conventional lenses). The second one is reflective concentrators (mirrors), while the third group is diffractive optical elements. Obviously, a system may simultaneously incorporate two or even aU three of the mentioned structures. 

Conventional injection molding (the most often used technique for low-end diffractive elements, for instance for the best-known diffractive optical elements, CD, DVD, and BluRay disks) and epoxy molding (the latter being more expensive because of longer curing cycles). 

We start this section with some definitions. First, we define a diffractive optical element (DOE) as a passive optical element, its properties being either stationary or switchable, with operation based on diffraction or interference of light beams passing through it or being reflected from it. This is a very broad definition and includes a large number of specific subclasses. 

Any diffractive optical element may be computer-generated (CGH, computergenerated hologram) or designed directly using a physical interference pattern, either from some object or generated in an interferometer. 

The family of diffractive optical elements is schematically shown in Fig. 2.13. 

A diffractive optical element can be either transmissive or reflecting. It may be polarization sensitive or it can be insensitive to it. 

Practically, it may be said that several different diffractive optical elements can coexist on the same substrate without interfering with one another. They can perform the same function, either selectively, as described above, or implement completely different functions. For example, a single DOE can be simultaneously used as a lens, beam splitter and spectral filter. 

F. Wyrowski, Diffractive optical elements iterative calculation of quantized, blazed phase structures. JOSA A 7(6), 961-969 (1990)... 

Cheong, W.C., Yuan, X.-C., Koudriachov, V., and Yu, WJC (2002) High sensitive Si02/Xi02 hybrid sol-gel material for fabrication of 3 dimensional continuous surfece relief diffractive optical elements by electron-beam lithography. Opt. Express, 10 (14), 586-590. 

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