All Optical Signal Processing Materials
If the molecular third-order nonlinearities of molecular materials can be translated into macroscopic third-order nonlinearities χ (3) in concentrated chromophoric materials, such materials could enable high-speed all-optical signal processing (AOSP) devices possible. We focus on rational control of aggregations and spatial arrangements of active molecules in solid-state supramolecular assembly to efficiently translate the microscopic nonlinearities of molecules into macroscopic nonlinearities as followings; 1) development of strongly delocalizing and potentially J-aggregating end groups that lead to new polymethines with significantly larger Re (g) than conventional polymethines with comparable chain lengths, 2) rational engineering of molecular structures of polymethines with controlled aggregation properties based on complementary salt complexes between cationic and anionic polymethines, 3) development of covalently linked pre-organized chromophore building blocks, 4) development of organized counter ions that template spatial arrangement of polymethines, 5) development of polyelectrolytes as host polymers, 6) development of fully conjugated polycyanines, and 7) optimization of auxiliary molecular structures of chromphoresto improve material processability and stabilities for the fabrication of optical quality films for device applications.
Current Projects
- Development of TPA and Raman materials for optical Zeno switches (ZOE: DARPA-DSO).
- Development of polymethines for all-optical signal processing (COMAS: MURI-AFOSR).
Research Highlight
Complementary Cyanine Salts: Since a typical polymethine consists of a charged chromophores with a counter ion, understanding the role of counter ion in affecting the properties of polymethines can provide an effective way to improve processibility and mitigate intermolecular interactions between chromophores in solid-state. We have developed device quality optical materials with excellent nonlinearity as demonstrated in organic-silicon hybrid waveguide devices using the approach. Moreover, we have systematically studied effects of counter ionic polymethines that can template counter polymethines using J-aggregating quinolinium cyanines, pseudoisocyanine (PIC), and have prepared materials that can be applied as an active clad in SOH devices.
The complimentary cyanine salt complex AJCC13701 showed excellent solubility and processability, and 50%(wt) doped composite of the cyanine in APC form thick (~2 mm) optical quality film. The salt of complementary polymethine AJCC13703 crystalizes into a P-1 space group from chloroform with two solvates in a unit cell (the single crystal x-ray structure is shown left), and the structure clearly shows that the oppositely charged polymethines form extended molecular packing with alternating complementary charges, which is consistent with our initial design of using complementary salts to control spatial arrangements and interactions of polymethines in solid-state. Both the cationic and anionic polymethines in the complementary salt maintain generally symmetric geometries without significant twisting of the polymethine cores. The phenyl substituents at the center of the molecules are nearly perpendicular (~ 70°) to the polymethine backbone because of large steric hindrance between the ortho-hydrogen atoms of the phenyl ring and the polymethine backbone.
The macroscopic NLO properties of the complementary polymethines were investigated on a strip SOH waveguide platform as clad. Wavelength conversion was performed through a non-degenerate Four Wave Mixing (ND-FWM) experiment. Simulation of the FWM conversion generated in the SOH device allows the determination of the χ(3) of the organic clad. Additionally, the strong nonlinear absorption of these blends enables observation of optical power modulation in an SOH device using a pump-probe geometry, thus, simulation of this loss modulation permit an extraction of Imχ(3). The cyanine salt AJCC13701 showed excellent off-resonant Kerr coefficient at 1550 nm (n2 = -54.1±9.9×10-18 m2w-1) with loss of 1.8 dB/cm. The AJCC13703 showed the highest n2 value (~71.9×10-18 m2 w-1) reported for organic c3 materials with FOM of 1.1. This value is ~16 times that of Silicon, and is 4 times higher than the best organic clad previously reported for a SOH waveguide that demonstrated ultrafast signal processing (above 100 Gbit/s).
Related Publication
- Z. Li, Y. Liu, H. Kim, J. M. Hales, S.-H. Jang, J. D. Luo, T. Baehr-Jones, M. Hochberg, S. R. Marder, J. W. Perry, and A. K.-Y. Jen, “High-Optical-Quality Blends of Anionic Polymethine Salts and Polycarbonate with Enhanced Third-Order Non-linearities for Silicon-Organic Hybrid Devices”, Adv. Mater. (Adv. Opt. Mater.): 2012, (Early View: DOI: 10.1002/adma.201202325).
Current Team Members: Dr. Sei-Hum Jang, Dr. Joshua Davies, Dr. Zhong’an Li, Jeffrey Yang, and Chuck Wang
Research Collaborators
J. W. Perry (Georgia Institute of Technology)
S. R. Marder (Georgia Institute of Technology)
J.-L Brédas (Georgia Institute of Technology)
N. Peyghambarian (The University of Arizona)
R. A. Norwood (The University of Arizona)
E. W. Van Stryland (University of Central Florida)
M. Lipson (Cornell University)
M. Hochberg (University of Delaware)
Related Interests and Keywords: all-optical signal processing, polymethines (cyanines), two-photon absorption, inverse-Raman scattering, silicon-organic hybrid nanophotonics, photonic bandgap materials, and plasmonics.