We present the design and fabrication of a multicomponent optical system for LiDAR applications. The system comprises four stages: a commercial cylindrical lens, a custom freeform trilobe lens, a set of three custom reflective diffraction gratings, and a custom monolithic array of nine freeform mirrors. This optical set-up is coupled to an on-chip linear Optical Phase Array (OPA): the combination of linear beam steering provided by the OPA, and orthogonal linear steering achieved by the diffraction gratings results in a beam scan over nine directions in 3D. All the custom components have been designed and fabricated at VUB B-PHOT’s Photonics Innovation Center.
We present an example of design, tolerancing and fabrication of freeform plastic lightguides for optical sensing applications. The design of the lightguides relies on Nonimaging Optics principles and uses raytracing simulations for analysis and optimization. We examine the influence of fabrication parameters on the simulated performance and show ways to minimize their impact. The presented lightguides have been fabricated at the Photonics Innovation Center of VUB – B-PHOT.
Earth observation and greenhouse gas sensing from space provides vital information for climate and climate change monitoring, indicating the importance of novel spaceborne telescopes and spectrometers. We present a novel freeform pushbroom imaging spectrometer enabling the sensing of water vapor, carbon dioxide and methane in the atmosphere, while fitting within 2 CubeSats Units. The design comprises a 2-mirror freeform telescope, combined with a near-infrared (1100 – 1700 nm) spectrometer featuring 3 freeform mirrors and a reflective grating, providing both spatial and spectral information using a 2D detector. All mirrors are described and optimized using XY polynomials, enabling a nearly diffraction-limited performance. The novel design is exceeding the state-of-the-art, by showing a full FOV of 120°, a spatial resolution of 2.6 km, and a spectral resolution of 13 nm. According to our knowledge, our novel design shows the widest field-of-view that has ever been realized for space-based telescopes, nearly reaching Earth observation from limb to limb from an altitude of about 700 km. The freeform telescope mirrors were manufactured in-house using high-precision 5-axis milling and 5-axis ultraprecision diamond tooling. Finally, a laboratory proof-of-concept demonstrator was realized validating the field-of-view and focusing spot sizes, paving the way for future space missions that target wide field-ofview imaging and/or an enhanced climate monitoring.
Illumination optical design using non-coherent sources is of major interest for sensing applications requiring a uniform illumination. We present the development of a custom biconic lens array, enabling beam shaping of a halogen source array to a rectangular uniform illumination. First, the tungsten halogen sources were accurately modelled considering the nearfield emission pattern and broadband spectrum. Following, the illumination lens array is optimized, including a study on the optimal arrangement and pitch of the array, and ensuring a manufacturable design by taking the optical and mechanical tolerances into account. The optimized lens array comprises of custom lenses (Ø 20 mm) featuring a first spherical surface and a second biconic surface with different radii of curvature and aspherical coefficients (up to the 8th order) in the X and Y direction. A spatial uniformity, defined as the standard deviation of the flux distribution, of 0.0002 was achieved within the envisioned illumination area of 50 x 20 mm², being close to a perfect uniformity considering a targeted value of 0. Finally, the aspheric biconic lens is manufactured using ultraprecision diamond tooling (Nanotech 350FG), and its performance is successfully validated in a laboratory demonstrator setup, giving rise to an optimized and uniform halogen source illumination.
Wide field-of-view imaging optics offers a huge potential for space-based Earth observation and climate change monitoring by capturing global data. We present the design and proof-of-concept demonstration of a freeform 2-mirror space-based telescope featuring a full field-of-view of 120°, nearly reaching Earth observation from limb to limb from a nominal altitude of 700 km, while showing a spatial resolution of 2.6 km, and fitting within 1 CubeSat unit. Our design benefits from freeform optics to maximize the field-of-view, while maintaining a diffraction-limited image quality and minimizing the system dimensions. Particularly, both mirror surfaces were accurately modelled and optimized using an XY polynomial description. Subsequently, the mirrors are manufactured using high-precision 5-axis milling and ultraprecision diamond tooling, after which a laboratory demonstrator setup of the telescope was realized. We believe this design paves the way towards future space missions enabling an improved Earth observation, leading to an enhanced monitoring of climate and climate change.
Optimization of road lighting towards more sustainable and efficient sources is of major importance. We therefore pursue developing a LED roadway lighting design methodology, from luminance optimization towards the design of the freeform optics, enabling to optimize the illumination power distribution on the street to minimize the required optical output power and power consumption while still fulfilling the CIE 140 – 2000 standard. First, an artificial source is designed featuring an optimized illumination pattern towards the CIE standards while minimizing the required optical output power. Following, the design and optimization of the freeform optic is tackled, enabling the beam shaping of the LED emission pattern towards the optimized illumination pattern. Successful optimization of the freeform optic was achieved, starting from sequential mode calculations using an ideal point source, followed by an iterative optimization using backward raytracing of the requested illumination pattern and extended source simulations. The optimized freeform illumination lens comprises 2 biconic Zernike surfaces, and outperforms the state-of-the-art with respect to the average luminance, and the overall and longitudinal uniformity of the luminance. As a result, we believe our design methodology offers a promising procedure for efficient road lighting design, while having the potential to contribute to more eco-friendly lighting.
We present a miniature freeform lightguide for sensing applications, designed according to the principles of the flow-line method from Nonimaging Optics. The optic is obtained by combining two 2D flow-line concentrators in a curved monolithic piece, achieving 45° half-acceptance angle and 40° beam steering in a very compact volume (about 1.3 x 2.0 x 20 mm3). We show how the initial design has been adjusted after a thorough tolerance analysis and describe its fabrication through plastic injection molding. The design of the mold involves a non-standard 3D-puzzle approach, which allows uniform high optical quality and minimizes the fillet radius on the optic.
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