Ultra-High Refractive Index Polymers in theVisible Wavelength for Nanoimprint
Lithography
Carlos Pina-Hernandez,1 Khai Lee,1 Arian Gashi,1 Stefano Cabrini,2 KeikoMunechika1
1HighRI Optics, Inc, 5401 Broadway Terr #304 Oakland, CA 95618
The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA94720

2E-mail: cpina@highrioptics.com, km@highrioptics.com

The development of advanced photonic devices working in the visible light promises arevolution in a broad range of areas from biochemical sensing to quantum computing. Over thelast years, novel nanophotonic devices were demonstrated but are still limited to researchlaboratories due to the lack of suitable materials with high refractive index and opticaltransparency. Polymers with high index of refraction can find a broad range of applications
including light emitting diodes (LEDs), CMOS sensors, large area displays, eyeglasses andoptical elements for augmented reality. Polymers, in general, are easy to process, arelightweight and can be cost-effective. The majority of polymers present low refractive index
values ranging from 1.50 to 1.60 and the design and synthesis of purely organic polymers withhigher refractive index (n > 1.70) and high transparency has proven extremely challenging.
Here, we demonstrate the development of organic polymers with ultra-high refractive index (n= 1.90) for thin-film applications. The synthesized polymers show high transparency in thevisible wavelength, are easy to process and soluble in common non-polar solvents. They areamong the organic polymers with the highest refractive index ever reported (figure 1a). The
developed polymers can be nanopatterned via nanoimprint lithography (figure 1b), a powerfultool to fabricate nanostructures following a simple and scalable high-throughput process. UVand thermal nanoimprint processes were employed to pattern different structures on thepolymer films. The patterned films represent the directly nanoimprinted polymers with thehighest refractive index found in the literature.
As a proof-of-demonstration, applications including nanoimprinted photonic crystals,
microlenses and antireflective structures (figure 2) patterned on ionizing scintillators, fiber
endfaces and curved optical elements have been performed. This work shows that the designand synthesis of organic polymers with high refractive index and optical transparency arefeasible and opens a promising route to the realization of novel photonic devices andapplications.
Reference:[1] C. Pina Hernandez, et al. “A Route for Fabricating Printable Photonic Devices with Sub-10
nm Resolution”, Nanotechnology 24 (2013) 065301.
[2] C. Pina Hernandez, et al. “Printable planar lightwave circuits with a high refractive Index”,
Nanotechnology 25 325302 (2014).
[3] G. Calafiore, Q. Fillot, S. Dhuey, S. Sassolini, F. Salvadori, C. A. Mejia, K. Munechika,
C. Peroz, S. Cabrini and C. Piña-Hernandez, "Printable Photonic Crystals with high refractiveindex" Nanotechnology 27 (2016) 115303 (7pp).

2.05

Refractive index, n2a)

CP5A1A2A4A51.95b)

1.9
1.85
1.8

1 µm

1.75
1.7400 450 500 550 600 650 700 750 800

Wavelength (nm)Figure 1. a) Refractive index of infrared polymers developed by HighRI Optics; b) SEM image of ananoimprinted infrared transparent polymer with a refractive index of 1.90.

Figure 2. (a) A photograph of a silica substrate with imprinted RAR, replicated from black silicon. Bothsides of the silica substrate are coated with RAR, indicated in a red dotted square. This image showsthat imprinted regions successfully minimize the reflection from the room backlight. (b) Cross-sectional
image of the imprinted RAR using a commercial imprint material (n = 1.51). (c) A photograph of thecontact angle measurement revealing that the imprinted structure is hydrophobic (contact angle = 109
deg) (c)-(d) Polarization- dependent reflection as a function of the angle of incidence @ 520 nm
measured from the imprinted region (c) and a bare glass (d) for comparison.