Mechanically robust amino acid crystals as fiber-optic transducers and wide bandpass filters for optical communication in the near-infrared

Durga Prasad Karothu,Mahmoud Rasras,Luca Catalano,Ghada Dushaq,Panče Naumov,Sharmarke Mohamed,Srujana Polavaram,Liang Li,Ejaz Ahmed,Rodrigo Ferreira

doi:10.1038/s41467-021-21324-y

Abstract

Organic crystals are emerging as mechanically compliant, light-weight and chemically versatile alternatives to the commonly used silica and polymer waveguides. However, the previously reported organic crystals were shown to be able to transmit visible light, whereas actual implementation in telecommunication devices requires transparency in the near-infrared spectral range. Here we demonstrate that single crystals of the amino acid L-threonine could be used as optical waveguides and filters with high mechanical and thermal robustness for transduction of signals in the telecommunications range. On their (00bar 1) face, crystals of this material have an extraordinarily high Young’s modulus (40.95 ± 1.03 GPa) and hardness (1.98 ± 0.11 GPa) for an organic crystal. First-principles density functional theory calculations, used in conjunction with analysis of the energy frameworks to correlate the structure with the anisotropy in the Young’s modulus, showed that the high stiffness arises as a consequence of the strong charge-assisted hydrogen bonds between the zwitterions. The crystals have low optical loss in the O, E, S and C bands of the spectrum (1250−1600 nm), while they effectively block infrared light below 1200 nm. This property favors these and possibly other related organic crystals as all-organic fiber-optic waveguides and filters for transduction of information.

Highlights

Organic crystals are emerging as mechanically compliant, light-weight and chemically versatile alternatives to the commonly used silica and polymer waveguides
The studies have focused on the demonstration of passive and active transduction of visible light, which has been already demonstrated for a number of organic crystalline materials[2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]
We report that single crystals of the amino acid Lthreonine (2-amino-3-hydroxybutanoic acid; Fig. 1a), which are endowed with exceptional mechanical robustness, can be used as a prototypic organic waveguide and a filter in the near-infrared region of the spectrum

Summary

Introduction

Organic crystals are emerging as mechanically compliant, light-weight and chemically versatile alternatives to the commonly used silica and polymer waveguides. We report that single crystals of the amino acid Lthreonine (2-amino-3-hydroxybutanoic acid; Fig. 1a), which are endowed with exceptional mechanical robustness, can be used as a prototypic organic waveguide and a filter in the near-infrared region of the spectrum In addition to these crystals being advantageous for being lighter (ρ = 1.3 ± 0.1 g cm−3) than silica (ρ = 2.65 g cm−3), unlike silica they come with the possibility for chemical modifications that would alter the optical and other physical properties of the ensuing organic waveguides. This novel result of using stiff and hard organic crystals as optical waveguides in the infrared range opens up prospects for application of small-molecule organic crystals with high stiffness and hardness as durable signal-transducing media

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Methods

Results