Characterization Of Diffractive Optical Elements Research Articles

Research & Technology: Optik & Photonik 2/2018

AbstractThe use of diffractive optical elements (DOE) leads to new applications in all optical fields. The accurate measurement of the micro structures is an important part of production. Mahr offers manufacturers of these optics convenient and highly accurate solutions for the measurement and characterization of DOEs.

Compact sorting of optical vortices by means of diffractive transformation optics.

The orbital angular momentum (OAM) of light has recently attracted a growing interest as a new degree of freedom in order to increase the information capacity of today's optical networks, both for free-space and optical fiber transmission. Here we present our work of design, fabrication, and optical characterization of diffractive optical elements for compact OAM mode division demultiplexing based on optical transformations. Samples have been fabricated with 3D high-resolution electron beam lithography on a polymethylmethacrylate resist layer spun over a glass substrate. Their high compactness and efficiency make these optical devices promising for integration into next-generation platforms for OAM modes processing in telecom applications.

Scatterometer for characterization of diffractive optical elements

Diffractive optical elements can control light beyond the capabilities of traditional optical components, which offers great opportunities for numerous applications. However, modern functionalities are related to even smaller feature sizes, which causes remarkable challenges for the structure measurements in the nanoscale. The current methods are not optimal for the characterization of diffractive structures. Optical scatterometry, however, would be a good tool for non-destructive characterization, and in particular, for inline process control of the fabrication. In this paper, detailed information about a goniometric scatterometer built at MIKES (Centre for Metrology and Accreditation), basics of the inverse problem approach for solving the parameters of the structure and first measurements for confirming the functionality of the scatterometer as well as the capabilities of it are discussed.

Optical characterization of diffractive optical elements replicated in polymers

We present an optical laser-based method to visualize repli- cation of microperiodic profile structures in polymers. Diffraction effi- ciency of diffraction gratings originally produced in silicon, quartz glass, and in replicated polymer substrates is measured experimentally and simulated using linear dimensions of gratings, or their replica defined by atomic force microscopy AFM. Diffraction efficiency of the periodic structure is used to test the surface relief formation during the combined ion etching of crystalline Si 100 and replication of this structure using UV light hardening and hot embossing. The main experimental results are compared with computer simulations where the standard program PCGrate-SX6.0 is employed. Angular dependence of relative efficiency RE appears a versatile tool to analyze the process of origination and replication of diffraction grating in a micrometer range. Both the shape of the grating and linear dimensions can be reconstructed by comparing experimental values of relative efficiency with the simulation results. Ex- amples of hot embossing of different periods of diffraction gratings to the Al/polymethyl methacrylate PMMA on polyethylene terephthalate PET illustrate vitality of such approach.

Ideal collimation, concentration, and imaging with curved diffractive optical elements

In this article the design, optimization and characterization of diffractive optical elements formed on a curved surface are reviewed. For such curved diffractive optical elements not only the phase function, but also the surface shape are free parameters that can be used for optimization, yielding much better performances than both flat diffractive optical elements and reflective/refractive optical elements when operating with quasimonochromatic light. We present a new analytic design approach for the surface shape that ensures uniform collimation of a light source with any angular distribution. We demonstrate the usefulness of this design also for ideal (brightness conserving) collimation and concentration of diffuse light, aberration-free imaging, and optical Fourier transform. We present experimental results that confirm our theoretical analysis.

Fabrication and characterization of diffractive optical elements in InP for monolithic integration with surface-emitting components

We report on the fabrication and subsequent characterization of binary diffractive optical elements (DOE's) in InP for operation at 1.3 microm. Fresnel lenses of different focal lengths and a DOE that splits and focuses an incident beam into a 1 x 4 array of spots (optical fan-out) were fabricated. We realized the surface reliefs by patterning resist, using electron-beam lithography and etching with a chemically assisted ion beam, which produced well-defined patterns with smooth sidewalls and little if no surface roughness. The measured efficiency for the lenses was 36%. For the fan-out element the efficiency and the uniformity error were 26% and 30%, respectively. Spot sizes as small as 16 microm were measured.