A single multimode fiber has been considered an ideal optical element for endoscopic imaging due to the possibility of the direct image transmission via multiple spatial modes. However, the wave distortion induced by the mode dispersion has been a fundamental limitation. In this Letter, we proposed a method for eliminating the effect of the mode dispersion and therefore realized wide-field endoscopic imaging by using only a single multimode fiber with no scanner attached to the fiber. Our method will potentially revolutionize endoscopy in various fields encompassing medicine and industry.

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The strengths of hydrogen bonding interaction between formamide (FA) and thioformamide (TFA) were investigated at the B3LYP level with the 6-311G(d,p), 6-31+G(d,p), and 6-311++G(2d,2p) basis sets. The 18 minimum energy structures of FA-FA, TFA-TFA, and TFA-FA dimers were examined. The average strength of the OCN-H---OdC, SCN-H---SdC, OCN-H---SdC, and SCN-H---OdC hydrogen bonds at the B3LYP/6-311++G(2d,2p) level was -6.1 ( 0.3, -5.0 ( 0.1, -4.8 ( 0.3, and -7.3 ( 0.4 kcal/mol, respectively, when the basis set superposition error (BSSE) was corrected. The results show that TFA is a good hydrogen bond donor but a poor hydrogen bond acceptor as compared to FA. For the OC-H---OdC, SC-H---SdC, OC-H---SdC, and SC-H---OdC hydrogen bonds, the average strength has been predicted to be -2.2 ( 0.3, -2.2 ( 0.2, -1.0 ( 0.3, and -3.1 ( 0.3 kcal/mol, respectively. It is remarkable that the thioformyl hydrogen atom of TFA has a strong hydrogen bonding ability as compared to that of FA. The abilities of the hydrogen bond donor have a good correlation with the proton affinities of the deprotonated anion.