Diffractive optics has traditionally been used to transform a parallel beam of light into a pattern with a desired phase and intensity distribution. One of the advantages of using diffractive optics is the fact that multiple functions can be integrated into one element. Although, in theory several functions can be combined, the efficiency reduces with each added function. Also, depending on the nature of each function, feature sizes could get finer. Optical lithography with its 1 ?m limit becomes inadequate for fabrication and sophisticated tools such as e-beam lithography and focused ion beam milling are required. In this paper, two different techniques of fabrication of composite elements are studied. A comparison of the beams generated in both cases is presented. © 2014 SPIE.

Shanti Bhattacharya

Department of Electrical Engineering

Anand Vijayakumar

DIFFRACTIVE OPTICS

Electron beam lithography

Ion beams

lithography

Multiplexing

Photolithography

COMPOSITE ELEMENT

e-Beam lithography

FOCUSED ION BEAM MILLING

INTENSITY DISTRIBUTION

Multi-functional

Multifunctionality

Multiple function

PARALLEL BEAMS

Laser beams

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Multi-functional diffractive optical elements

Proceedings of SPIE - The International Society for Optical Engineering

Focused ring patterns are used for many applications like corneal surgery, micro drilling, optical trapping, etc. The generation of focused ring patterns in the earlier reported cases employed many refractive optical components with different functions. As a result the optics configurations of the ring pattern generation systems are bulkier. In diffractive optics, it is possible to alter a function of an element and also integrate multiple functions in a single element. In this paper, we present the design, fabrication and evaluation of single and composite diffractive optical elements for the generation of focused ring patterns. A diffractive toric Fresnel zone lens was designed for parallel beam illumination. This element is compared with other composite diffractive elements capable of generating focused ring patterns. The toric Fresnel zone lens and composite elements were fabricated using electron beam direct writing. The fabricated elements were found to exhibit interesting properties, with the toric lens out-performing the other elements in several areas such as efficiency, focal depth, and ring thickness.. © 2015 SPIE.

Design, fabrication, and evaluation of diffractive optical elements for generation of focused ring patterns

Higher Order Bessel Beams (HOBBs) have many useful applications in optical trapping experiments. The generation of HOBBs is achieved by illuminating an axicon by a Laguerre-Gaussian beam generated by a spiral phase plate. It can also be generated by a Holographic Optical Element (HOE) containing the functions of the Spiral Phase Plate (SPP) and an axicon. However the HOBB's large focal depth reduces the intensity at each plane. In this paper, we propose a multifunctional Diffractive Optical Element (DOE) containing the functions of a SPP, axicon and a Fresnel Zone Lens (FZL) to generate higher efficiency higher order Bessel-like-beams with a reduced focal depth. The functions of a SPP and a FZL were combined by shifting the location of zones of FZL in a spiral fashion. The resulting element is combined with an axicon by modulo-2π phase addition technique. The final composite element contains the functions of SPP, FZL and axicon. The elements were designed with different topological charges and fabricated using electron beam direct writing. The elements were tested and the generation of a higher order Bessel-like-beams is confirmed. Besides, the elements also generated high quality donut beams at two planes equidistant from the focal plane of the FZL. © 2015 SPIE.

Multifunctional diffractive optical elements for the generation of higher order Bessel-like-beams

The phase of a standard Fresnel zone lens (FZL) is periodically modulated in the radial direction using the phase of a binary fraxicon. The resulting element (rf -FZL) focuses light into a ring. The ring is found to be quasi-achromatic, in that the diameter is wavelength independent but its location is not. The binary rf -FZL is fabricated using electron beam direct writing. Experimental results confirm the generation of a wavelength-independent ring pattern at the focus of the rf-FZL. An efficiency of 24% was obtained. The variation in radius of ring pattern was reduced from 61 μm to less than 10 nm for a corresponding wavelength variation from 532 to 633 nm. © 2014 Optical Society of America.

Applied Optics

Quasi-achromatic Fresnel zone lens with ring focus

As with a conventional lens, a Fresnel zone lens (FZL) can be used to image objects at infinity or nearby. In the latter case, the FZL converts a diverging spherical wavefront into a converging spherical wavefront. The glass substrate on which the FZL is fabricated introduces spherical aberration resulting in a shift of the image plane and blurring of the image. Two novel schemes for correction of this spherical aberration are proposed and studied in this paper. To demonstrate them, FZLs are designed with and without aberration correction. They are fabricated using electron beam direct writing. The devices are evaluated and the accuracy of the proposed aberration correction schemes is validated. © 2013 Optical Society of America.

Characterization and correction of spherical aberration due to glass substrate in the design and fabrication of Fresnel zone lens

Applied Digital Optics

Journal of Cataract & Refractive Surgery

Clinical outcomes and intraocular optical quality of a diffractive multifocal intraocular lens with asymmetrical light distribution

Optics Letters

Multifunctional double-layered diffractive optical element

Journal	Data powered by TypesetProceedings of SPIE - The International Society for Optical Engineering
Publisher	Data powered by TypesetSPIE
ISSN	0277786X
Open Access	No