This technology can be used to develop broad wavelength range tunable photonic crystals. Tunable photonic crystals are optical filters whose stop-band position can be modulated by external control signals, giving them diverse applications including colorimetric sensors, display device components, and photonic switches.
Photonic crystals with lamellar internal structure can be tuned by altering the refractive index of individual layers and/or the inter-lamellar spacing. In photonic crystals constructed with block copolymers (BCPs), it has been demonstrated that refractive index and inter-lamellar spacing can be modulated by the selective sequestration of nanoparticles and addition of homopolymers respectively. However, these methods are limited to tunability over limited wavelength ranges. The technology described in this invention extends the capabilities of tunable BCP photonic crystals to enable reversible real-time stop-band tunability over exceptionally large wavelength ranges.
The photonic crystal described in this invention is constructed via self-assembly of high molecular weight block copolymers, which form a 1D periodic lamellar stack with alternating hydrophobic glassy block layers and hydrophilic polyelectrolyte block gel layers. By modifying the ionic strength of the aqueous solvent in which the photonic crystal is immersed, the polyelectrolyte block layers can be made to undergo reversible swelling, thereby simultaneously increasing the interlamellar spacing and refractive index contrast, shifting the stop-band position to longer wavelengths. At the laboratory scale, the Inventors have demonstrated reversible shifts of the stop-band position by over 1250 nm, or 450% of the wavelength, compared to shifts of 100-200 nm (<50%) achievable using existing technology.
10x increase in maximum achievable stop-band position shift compared to existing methods of swelling
- Rapid, sub-second response time with full reversibility of stop-band position