Fig. 1. Scheme of self-homodyne coherent system^[22], where CW represents continue wave, LO represents local oscillator, DP-IQM represents dual-polarization IQ modulator, PC represents polarization controller, SDM represents space division multiplexing, and PDM represents polarization division multiplexing. (a) PDM based self-homodyne coherent system; (b) SDM based self-homodyne system; (c) bidirectional SDM based self-homodyne coherent system

Fig. 2. Needed ADC sampling rate of classic intradyne coherent and self-homodyne coherent systems^[5]. (a) Received electrical spectra of Nyquist pulse shaping signal for classical coherent system with LOFO; (b) received electrical spectra of Nyquist pulse shaping signal for self-homodyne coherent system without LOFO; (c) received optical power (ROP) penalty of 86 GBaud DP-16QAM Nyquist signal versus LOFO

Fig. 3. A silicon photonic adaptive polarization controller^[5,25]. (a) Structure schematic; (b) schematic polarization manipulation principle; (c) microphotograph of silicon photonic adaptive polarization controller; (d) polarization state of output light of silicon photonic adaptive polarization controller; (e) waveforms of diving signal and feedback optical signal after detection

Fig. 4. MZI-based adaptive polarization controller^[25]. (a) Flow of the state of polarization (SOP) rotation and control, where the left and right images are the description of SOP in Jones and Stokes domains, respectively; (b) microphotograph of silicon-based adaptive polarization controller; (c) polarization stabilization result under a polarization rotation speed of about 300 rad/s; (d) scrambled SOP trace; (e) SOP trace locked by MZI-based adaptive polarization controller

Fig. 5. Bit error rate (BER) versus laser linewidth and mismatch length for self-homodyne system under different modulation formats and baudrates^[22]. (a) 400 Gbit/s 16QAM; (b) 800 Gbit/s 16QAM; (c) 400 Gbit/s 64QAM; (d) 800 Gbit/s 64QAM

Fig. 6. Principle, flow, and performance of relative delay estimation algorithm^[27]. (a) Formation of colored frequency modulation noise and extraction process of its effective part, as well as estimation flow of relative time delay (RTD); (b) experimental results of RTD estimation precision under different fast Fourier transformation (FFT) sizes and received optical powers for two-fiber based SDM self-homodyne scheme

Fig. 7. Schematic of PDM self-homodyne transmission system^[29]

Fig. 8. Experimental setup and result of bidirectional PDM self-homodyne transmission^[29].(a) Experimental setup and DSP flows at transmitter side and receiver side; (b) photo of APC; (c) received constellation with 10 MHz DFB laser after RD-CMA (radius-directed constant modulus algorithm); (d) received constellation with 10 MHz DFB laser after pilot-aided rotation; (e) BER versus upstream laser power with and without a notch filter; (f) performance comparison of ECL and DFB laser for downstream transmission; (g) BER versus polarization rotation rate when wavelength difference between upstream and downstream (Δλ) is 0; (h) BER versus Δλ

Fig. 9. MIMO-free bidirectional transmission of SDM self-homodyne system^[30]. (a) Architecture diagram, where C1-C4 present polarization maintaining circulator, APC presents adaptive polarization controller, PMC presents polarization maintaining coupler, and SMF presents single mode fiber; (b) schematic of proposed APC, where PSR presents polarization splitter and rotator, PS presents phase shifter, and DC presents directional coupler; (c) polarization crosstalk ratio (PCR) versus RSOP speed; (d) MIMO weight versus tap; (e) experimental result of SOP trace of locked LO at different RSOP speeds; (f) average PCR versus wavelength separation (Δλ＝λ₂－λ₁); (g) pre-FEC BER versus launch power