[1] C. Gómez-Reino, M. V. Pérez, C. Bao. Gradient-Index Optics: Fundamentals and Applications(2002).
[2] R. K. Luneburg. Mathematical Theory of Optics(1964).
[3] A. S. Gutman. Modified Luneberg lens. J. Appl. Phys., 25, 855(1954).
[8] A. A. Maradudin, J. R. Sambles, W. L. Barnes. Modern Plasmonics(2014).
[9] N. Yu, F. Capasso. Flat optics with designer metasurfaces. Nat. Mater., 13, 139(2014).
[14] A. Sihvola. Electromagnetic Mixing Formulas and Applications(1999).
[15] S. P. Morgan. General solution of the Luneberg lens problem. J. Appl. Phys., 29, 1358(1958).