# Research Progress on Carrier-Free Phase-Retrieval Receivers  
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Key Laboratory of Photonic Technology for Integrated Sensing and Communication, Ministry of Education of China, Guangdong University of Technology, Guangzhou 510006, China; [EMAIL_ADDRESS] (Y.M. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); [EMAIL_ADDRESS] (N.G. ); 211210303@mail2. In order to adapt to the receiver requirements of short-reach optical communication with low cost, low power consumption, and high receiver sensitivity characteristics, reconstructing the optical signal field from the intensity measurement of the optical signal has attracted intensive attention. In recent years, self-coherence detection schemes have been proposed to reconstruct complex-valued signals in single-polarization systems by using direct detection, including the Kramers-Kronig (KK) [14; 15; 16; 17] receiver, asymmetric self-coherence detection (ASCD) receiver [18], carrier-assisted differential detection receiver (CADD) [19], and the Stokes vector receiver (SVR) [20]. These self-coherent schemes need to insert a continuous-wave (CW) optical carrier along with the modulated optical signal. Consequently, the optical field of the modulated signal at the Rx can be reconstructed using the beat term between the signal and the CW carrier based on direct detection. However, direct detection introduces signal-to-signal beat interference (SSBI) [21; 22; 23], which results in the poor performance of these self-coherent receivers. The KK receiver can suppress SSBI using the KK relationship, but in order to meet the minimum phase condition of the KK algorithm, only single sideband (SSB)-modulated optical signals can be used, thus reducing the electrical spectral efficiency (ESE) by half. In addition, the KK operation adds a non-negligible computational complexity, especially considering the high oversampling rate required. SVR and CADD receivers are proposed to enhance the ESE of the system, which can reconstruct the field of double-sided band (DSB) signals, but both schemes require at least three single-ended PDs and one optical hybrid, which results in complex hardware configurations.