Continuous-relief diffractive optical elements for two-dimensional array generation

Abstract

Continuous surface-relief diffractive optical elements for two-dimensional array generation (fan-out) are designed and fabricated. Separable and nonseparable solutions for the two-dimensional element design are compared. The phase-grating microstructures are generated by laser-beam writing lithography in a single exposure step and converted to nickel shims by electroplating, enabling low-cost replicas to be produced by using laboratory and commercial replication processes. Results are presented for a 9 x 9 fan-out diffractive optical element with a measured efficiency of 94% and an overall uniformity within ±8%; replicas in epoxy have the same efficiency and a uniformity of ± 15%.

<title>Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresist</title>

“…Arrays of up to 80x80 lenslets were fabricated, electroformed into nickel shims and replicated into thin optical epoxy films on glass substrates to produce high quality elements of good mechanical stability. [2]. The performance was excellent -measured efficiency for resist recordings (after correction for reflection losses) was better than 94% and overall uniformity better than of the average spot intensity; replicas in epoxy had the same efficiency and a uniformity of (the lower uniformity being due to a known error in the recording of the corresponding relief structure).…”

“…Fresnel microlenses). They can be realised as continuous surface-relief microstructures [1,2] or as binary or multilevel reliefs the latter often being referred to as 'binary' optics (from the binary mask lithography steps used to fabricate the multilevel structures).…”

“…Simple microstructures can be fabricated by diamond milling [5], but limited resolution restricts applications to relatively smooth, slowly-varying relief structures. Direct writing in photoresist by a focused laser beam, in which accurate control of the process parameters enables a complex continuous-relief microstructure to be fabricated in a single exposure scan and development step, has been shown to produce excellent results [2,6]. A similar approach using e-beam writing has also been investigated [7,8] but requires significantly more complex (expensive) equipment and, with the exception of high-resolution microstructures with submicron feature sizes, has not shown any significant advantage over laser writing for the fabrication of microoptical elements.…”

High-power operation of coherently coupled tapered laser diodes in an external cavity

“…This optical element is made with a silica plate in which a continuous phase profile was engraved and an additional AR coating added on both sides at the end of the process. The phase profile of the DOE used in this experiment has been designed numerically through an optimization procedure 20 to provide a diffraction efficiency in the 5 main orders theoretically better than 98% while maintaining a diffraction uniformity along the same orders better than 30% RMS (Fig. 8, bottom).…”

Polarization device employing the combination effect of double refraction and diffraction

“…On its surface, a series of grooves of a sawtooth profile, which constitute a blazed grating, are fabricated by the technique of mechanical ruling 2 or stamping replication. 3 The groove spacing is denoted by d. For each sawtooth, its facet ͑which corresponds to diffraction slit͒ normal is NЈ, its facet angle is b , and its facet width is b(bϭd/cos b ). N is the grating normal.…”