Zone-boundary optimization for direct laser writing of continuous-relief diffractive optical elements

Abstract

Enhancing the diffraction efficiency of continuous-relief diffractive optical elements fabricated by direct laser writing is discussed. A new method of zone-boundary optimization is proposed to correct exposure data only in narrow areas along the boundaries of diffractive zones. The optimization decreases the loss of diffraction efficiency related to convolution of a desired phase profile with a writing-beam intensity distribution. A simplified stepped transition function that describes optimized exposure data near zone boundaries can be made universal for a wide range of zone periods. The approach permits a similar increase in the diffraction efficiency as an individual-pixel optimization but with fewer computation efforts. Computer simulations demonstrated that the zone-boundary optimization for a 6 microm period grating increases the efficiency by 7% and 14.5% for 0.6 microm and 1.65 microm writing-spot diameters, respectively. The diffraction efficiency of as much as 65%-90% for 4-10 microm zone periods was obtained experimentally with this method.

Diffractive optical elements: fabrication and application

“…The following parameters were used in the simulation: Δx=0.4µm, 1.65 µm writing-spot diameter (FWHM) or 1.4 µm at level e -2 . The same parameters were used for simulation and optimization of direct laser writing in papers 16,21 . It simplifies comparing different methods.…”

“…It is interesting to compare OCMM with laser direct writing methods based on exposure optimization 16,17,21 which are simpler from technological point of view. Figure 12 allows one to estimate considerable improvement in the diffraction efficiency in 1 st order for grating formed by OCMM (curve CM1) in comparison with values for the linear gratings simulated in papers 16,17 by different methods of exposure distribution optimization: Diff -differential algorithm 16,17 , SQP -sequential quadratic programming 16 , ZBO6 -zone boundary optimization with 6-steps stepped transfer function 21 .…”

“…Figure 12 allows one to estimate considerable improvement in the diffraction efficiency in 1 st order for grating formed by OCMM (curve CM1) in comparison with values for the linear gratings simulated in papers 16,17 by different methods of exposure distribution optimization: Diff -differential algorithm 16,17 , SQP -sequential quadratic programming 16 , ZBO6 -zone boundary optimization with 6-steps stepped transfer function 21 . Curves M1-M3 depict calculated diffraction efficiency for the convoluted profiles of the gratings working in 1 st , 2 nd , and 3 rd orders 16 .…”

Development of functional sub-100 nm structures with 3D two-photon polymerization technique and optical methods for characterization

“…8 Due to the two-photon absorption and the threshold behavior 9 of the used material, it is possible to reach higher resolution than with the often used laser direct writing process. 10,11 Also the precise control of the processing parameters such as the number of pulses, pulse duration, or pulse energy, for example, allow increasing the resolution. Such small structures produced by TPP suffer from destruction and deformation caused by surface tension during the development process in the posttreatment.…”

Analysis of microstructure heights error of multilayer diffractive optical elements for far infrared optical system

“…There are many fabrication techniques, such as single-point diamond turning (SPDT) [6] , laser direct writing [7] , electron beam direct writing [8] , photolithography and different replication methods [9,10] et al are used to fabricate DOEs. For DOEs used in imaging optical elements, SPDT is the major fabrication technique.…”