[16] S. Longhi. PT-symmetric mode-locking. Opt. Lett., 41, 4518-4521(2016).
[17] S. Longhi. PT-symmetric laser absorber. Phys. Rev. A, 82, 031801(2010).
[19] A. K. Jahromi, A. U. Hassan, D. Christodoulides, A. Abouraddy. Statistical parity-time-symmetric lasing in an optical fiber network. Nat. Commun., 8, 1359(2017).