Alois M. Herkommer

Sub-micrometre accurate free-form optics by three-dimensional printing on single-mode fibres

Micro-optics are widely used in numerous applications, such as beam shaping, collimation, focusing and imaging. We use femtosecond 3D printing to manufacture free-form micro-optical elements. Our method gives sub-micrometre accuracy so that direct manufacturing even on single-mode fibres is possible. We demonstrate the potential of our method by writing different collimation optics, toric lenses, free-form surfaces with polynomials of up to 10th order for intensity beam shaping, as well as chiral photonic crystals for circular polarization filtering, all aligned onto the core of the single-mode fibres. We determine the accuracy of our optics by analysing the output patterns as well as interferometrically characterizing the surfaces. We find excellent agreement with numerical calculations. 3D printing of microoptics can achieve sufficient performance that will allow for rapid prototyping and production of beam-shaping and imaging devices.

3D-printed eagle eye: Compound microlens system for foveated imaging

A highly miniaturized vision system is realized by directly 3D-printing different multilens objectives onto a CMOS image sensor. We present a highly miniaturized camera, mimicking the natural vision of predators, by 3D-printing different multilens objectives directly onto a complementary metal-oxide semiconductor (CMOS) image sensor. Our system combines four printed doublet lenses with different focal lengths (equivalent to f = 31 to 123 mm for a 35-mm film) in a 2 × 2 arrangement to achieve a full field of view of 70° with an increasing angular resolution of up to 2 cycles/deg field of view in the center of the image. The footprint of the optics on the chip is below 300 μm × 300 μm, whereas their height is <200 μm. Because the four lenses are printed in one single step without the necessity for any further assembling or alignment, this approach allows for fast design iterations and can lead to a plethora of different miniaturized multiaperture imaging systems with applications in fields such as endoscopy, optical metrology, optical sensing, surveillance drones, or security.

Ultra-compact on-chip LED collimation optics by 3D femtosecond direct laser writing.

By using two-photon lithographic 3D printing, we demonstrate additive manufacturing of a dielectric concentrator directly on a LED chip. With a size of below 200 μm in diameter and length, light output is increased by a factor of 6.2 in collimation direction, while the emission half-angle is reduced by 50%. We measure excellent form fidelity and irradiance patterns close to simulation. Additionally, a more complex shape design is presented, which exhibits a nonconventional triangular illumination pattern. The introduced method features exceptional design freedoms which can be used to tailor high-quality miniature illumination optics for specific lighting tasks, for example, endoscopy.

Phase space optics: an alternate approach to freeform optical systems

Abstract. Freeform optical surfaces are of increasing interest in the design of modern imaging and illumination systems. However for the optical designer there are still methods missing in order to illustrate and quantify the effect of freeform surfaces in terms of aberrations or their impact on illumination performance. Phase space optics might offer an alternative way to understand freeform optics and their impact within optical systems. To prove this, phase space in geometrical optics is generally introduced, and some example systems are presented which allow us to relate phase space transformations to geometrical aberrations. In this way, we show that aberrations can be understood as nonlinear deformations of phase space, which need to be minimized in imaging designs or to be employed for homogenizing radiation in illumination designs.

Single Quantum Dot with Microlens and 3D-Printed Micro-objective as Integrated Bright Single-Photon Source

Integrated single-photon sources with high photon-extraction efficiency are key building blocks for applications in the field of quantum communications. We report on a bright single-photon source realized by on-chip integration of a deterministic quantum dot microlens with a 3D-printed multilens micro-objective. The device concept benefits from a sophisticated combination of in situ 3D electron-beam lithography to realize the quantum dot microlens and 3D femtosecond direct laser writing for creation of the micro-objective. In this way, we obtain a high-quality quantum device with broadband photon-extraction efficiency of (40 ± 4)% and high suppression of multiphoton emission events with g(2)(τ = 0) < 0.02. Our results highlight the opportunities that arise from tailoring the optical properties of quantum emitters using integrated optics with high potential for the further development of plug-and-play fiber-coupled single-photon sources.

High order surface aberration contributions from phase space analysis of differential rays.

Phase space methods are very popular for illumination systems or paraxial system analysis. In this paper it will be shown that it is also a promising tool to visualize and quantify surface aberration contributions, including all orders. The method is based on the calculation and propagation of a differential ray pair. In order to validate the method we compare to Aldis calculus, an exact method to determine high order aberrations in rotational symmetric systems. A triplet lens is used as an example to visualize the results. The analysis indicates that the phase space method is a very good approximation to Aldis calculus and moreover it is not limited to any symmetry assumptions.

Phase space approach to the use of integrator rods and optical arrays in illumination systems

Abstract Integrator rods and optical arrays are the most frequently used components in illumination design for homogenizing radiation fields. However, these two standard components are very different in their performance and characteristics. This tutorial is aimed to illustrate the operation principle, basic design rules and the performance of those components. It should guide the optical designer towards the optimum choice for the individual illumination application. To illustrate the functionality of integrator rods and optical arrays simultaneously in angle and position, the concept of phase space is introduced. Here the effect of the homogenizing components can nicely be illustrated in the form of phase space transformations. This offers new insight and a different perspective onto the employment and characteristics of those elements.

Generalized Aldis theorem for calculating aberration contributions in freeform systems

Compact folded imaging systems often require freeform surfaces to correct astigmatic and other off-axis aberrations. However, aberration theory for non-rotational symmetric systems is quite complex and it is especially hard to quantify individual surface aberration contributions. In this paper we develop a matrix method based on the propagation of a differential ray pair, which allows determining the aberration contribution of each individual surface for any ray. We can mathematically prove that the sum of the aberrations is identical to the exact ray-tracing result at the image plane. A head-mounted display lens is employed for testing and verification of this method. As will be shown, the method proves to be a universal tool for aberration calculations within freeform system.

Wave-optical design of a combined refractive-diffractive varifocal lens

A novel type of integrated refractive-diffractive varifocal membrane lens is designed and analyzed by wave-optical methods. In contrast to other hybrid devices, the diffractive microstructure is directly imprinted onto the soft deflecting membrane, allowing for a high level of integration. Elastic deformation is taken into account by mechanical simulations with the finite element method (FEM). We show, that the superimposed structure can considerably suppress chromatic and spherical aberration. Furthermore, our algorithm is successfully applied to design a confocal hyperspectral lens.

In situ microscopy using adjustment-free optics

Abstract. In the past years, in situ microscopy has been demonstrated as a technique for monitoring the concentration and morphology of moving microparticles in agitated suspensions. However, up until now, this technique can only achieve a high resolution if a certain manual or automated effort is established for continuous precise focusing. Therefore, the application of in situ microscopes (ISMs) as sensors is inhibited in the cases where unattended operation is required. Here, we demonstrate a high-resolution ISM which, unlike others, is built as an entirely rigid construction, requiring no adjustments at all. This ISM is based on a specially designed water immersion objective with numerical aperture=0.75 and a working distance of 15  μm. The objective can be built exclusively from off-the-shelf parts and the front surface directly interfaces with the moving suspension. We show various applications of the system and demonstrate the imaging performance with submicron resolution within moving suspensions of microorganisms.