News › Fraun­ho­fer IOF · New opti­cal coa­ting sys­tem pre­vents fog­ging and unwan­ted reflections

Tech­no­logy impro­ves per­for­mance of LiDAR and other sen­sor and camera systems

Optics that do not fog up and hardly reflect at all – this will be pos­si­ble in the future thanks to a new opti­cal coa­ting sys­tem. The tech­no­logy deve­lo­ped by rese­ar­chers at the Fraun­ho­fer Insti­tute for Applied Optics and Pre­cis­ion Engi­nee­ring IOF is expec­ted to help improve the per­for­mance of LiDAR sys­tems and came­ras in auto­no­mous dri­ving cars, for exam­ple. The rese­arch team is now pre­sen­ting the new method with a paper in the jour­nal »Applied Optics«.

»When you go from cold to a warm room, your glas­ses can fog up, sever­ely limi­ting the vision of the per­son wea­ring them,« says Anne Gärt­ner. »The same can hap­pen with sen­sors like the LiDAR sys­tems in auto­no­mous dri­ving cars. Here, it is important that the sur­faces remain highly trans­pa­rent even when fog­ged, so that func­tion­a­lity is maintained.«

Gärt­ner and her team have the­r­e­fore deve­lo­ped a novel opti­cal coa­ting sys­tem desi­gned to pre­vent just that. In the jour­nal Applied Optics, published by Optica Publi­shing Group, the rese­ar­chers describe how they com­bi­ned a poly­mer coa­ting with porous silica nanos­truc­tures. In the pro­cess, the poly­mer coa­ting pre­vents fog­ging while the nanos­truc­tures reduce reflec­tions. Alt­hough the coa­tings descri­bed in the paper were deve­lo­ped spe­ci­fi­cally for LiDAR sys­tems, the tech­no­logy can be tail­o­red for many dif­fe­rent appli­ca­ti­ons. LiDAR (light detec­tion and ran­ging) refers to laser sys­tems used for opti­cal distance and speed measurement.
Fog-redu­cing and anti-reflec­tive coa­ting sys­tem to improve lidar sys­tems, for example.

Opti­cal coa­ting sys­tem ensu­res clear vision

The novel coa­ting sys­tem is based on the AR-plas2 tech­no­logy deve­lo­ped at Fraun­ho­fer IOF and was adapted to their requi­re­ments as part of the col­la­bo­ra­tion with Leica Geo­sys­tems AG from Heer­brugg, Switz­er­land. Leica Geo­sys­tems deve­lops air­borne LiDAR mea­su­re­ment sys­tems used for ter­rain and urban map­ping. Extreme tem­pe­ra­ture dif­fe­ren­ces bet­ween the envi­ron­ment and the mea­su­re­ment sys­tem can cause fog­ging of the opti­cal sur­faces, which would impair func­tion­a­lity. To pre­vent this, Gärtner’s team then worked with Leica Geo­sys­tems to deve­lop a solu­tion that addres­sed both fog­ging and unwan­ted light reflections.

»We used a poly­mer that pre­vents fog­ging of an opti­cal sur­face by acting as a water reser­voir,« Gärt­ner explains. »Howe­ver, dif­fe­ren­ces in the refrac­tive indi­ces of the poly­mer mate­rial and the sur­roun­ding air lead to unwan­ted reflec­tions and ghost light in the opti­cal sys­tem. To pre­vent these reflec­tions, we com­bi­ned the anti-fog­ging layer with very small struc­tures – up to 320 nm high – to achieve an anti-reflec­tive effect with simul­ta­neous water permeability.«

Mul­ti­ple nanos­truc­tures on top of each other pre­vent reflections

AR-plas2 tech­no­logy allows seve­ral nanos­truc­tures to be pro­du­ced on top of each other. In this pro­cess, one nanos­truc­ture is etched into the anti-fog layer and then a second nanos­truc­ture is pro­du­ced on top of it. With this tech­no­logy, it is pos­si­ble to adjust the refrac­tive indi­ces of the nanos­truc­tures and design the dual nanos­truc­ture to achieve very low reflec­tion over a wide spec­tral range.

The rese­ar­chers tes­ted the anti­re­flec­tion and anti­fog­ging per­for­mance of their coa­ting sys­tem using reflec­tance mea­su­re­ments with a spec­tro­pho­to­me­ter and fog­ging mea­su­re­ments. These were per­for­med after hol­ding the anti-reflec­tive and anti-fog side of the optics over hea­ted water. The labo­ra­tory tests showed that the mul­ti­layer sys­tem exhi­bits very low reflec­tance over a wide spec­tral range. This would not be pos­si­ble with a sin­gle nanos­truc­ture. In addi­tion, the nanos­truc­tures did not impair the effect of the under­ly­ing anti-fog layer. Due to the touch-sen­si­tive nature of the sur­face, this form of layer sys­tem is par­ti­cu­larly sui­ta­ble for inte­rior surfaces.

Appli­ca­tion in quan­tum com­pu­ters conceivable

AR-plas2 tech­no­logy can be applied to almost all types of mate­ri­als: poly­mers, but also glass or fluo­ride crys­tals. It is the­r­e­fore widely appli­ca­ble, for exam­ple for optics in light­ing, auto­mo­tive and con­su­mer goods, but also for future tech­no­lo­gies such as quan­tum com­pu­ting. Here, rese­ar­chers at Fraun­ho­fer IOF are alre­ady deve­lo­ping sys­tems made of opti­cal lay­ers and nanos­truc­tures for expe­ri­ments to deve­lop a quan­tum com­pu­ter as part of the »Qzell« project.

»Opti­cal sys­tems are beco­ming incre­asingly com­plex, and with them the demands on image qua­lity are also incre­asing,« says Gärt­ner. »Nanos­truc­tures can be used to achieve anti­re­flec­tion pro­per­ties with impres­sive results that are often not fea­si­ble with con­ven­tio­nal coa­tings. With the fun­da­men­tal under­stan­ding we’ve gai­ned in recent years, we’re con­fi­dent that we can bring nanos­truc­tu­red coa­tings into many real-world applications.«

Ori­gi­nal publi­ca­tion: A Gärt­ner, A. Sab­bagh, U Schulz, F. Rickelt, A. Bin­gel, S. Wol­leb, S. Schrö­der, A. Tün­ner­mann: »Com­bi­ned anti­fog­ging and anti­re­flec­tive dou­ble nanos­truc­tu­red coa­tings for LiDAR appli­ca­ti­ons,« Applied Optics, 62, 7, pp. 112–116 (2023), DOI: 10.1364/AO.476974, URL:
https://opg.optica.org/ao/fulltext.cfm?uri=ao-62–7‑B112&id=525109

CONTACT

Anne Gärt­ner
Fraun­ho­fer IOF
Albert-Ein­stein-Str. 7
07745 Jena
Phone +49 3641 807–522
Send e‑mail: ed.refohnuarf.foi@rentreaG.ennA